Note: Descriptions are shown in the official language in which they were submitted.
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
A GASIFIER COMPRISING VERTICALLY SUCCESSIVE
PROCESSING REGIONS
FIELD OF THE INVENTION
[0001] The invention pertains to the field of gasification, and, in
particular, to a
vertically oriented gasifier for conversion of carbonaceous feedstock into a
gas.
BACKGROUND
[0002] Gasification is a process that enables the conversion of carbonaceous
feedstock,
such as municipal solid waste (MSW), biomass or coal, into a combustible
product gas.
The product gas can be used to generate electricity or as a basic raw material
to produce
chemicals and liquid fuels.
[0003] Generally, the gasification reaction consists of feeding carbonaceous
feedstock
into a heated gasifier along with a controlled and/or limited amount of
oxygen/air and
optionally steam. In contrast to incineration or combustion, which operates
with excess
oxygen to produce C02, H20, SOx, and NOx, gasification reactions produce a raw
gas
composition comprising CO, H2, H2S, and NH3. After clean-up and appropriate
processing, the primary gasification products of interest are H2 and CO.
[0004] Possible uses for the product gas from the gasification reaction
include: the
combustion in a boiler for the production of steam for internal processing
and/or other
external purposes, or for the generation of electricity through a steam
turbine; the
combustion directly in a gas turbine or a gas engine for the production of
electricity;
fuel cells; the production of methanol and other liquid fuels; as a further
feedstock for
the production of chemicals such as plastics and fertilisers; the extraction
of both
hydrogen and carbon monoxide as discrete industrial fuel gases; and other
industrial
applications.
[0005] A number of systems have been proposed for capturing heat produced by
the
gasification reaction and utilising such heat to generate electricity,
generally known as
1
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
combined cycle systems. The energy in the product gas coupled with substantial
amounts of recoverable sensible heat produced by the process throughout the
gasification system can generally produce sufficient electricity to drive the
process,
thereby alleviating the expense of local electricity consumption.
[0006] Useful feedstock can include any municipal waste, waste produced by
industrial
activity and biomedical waste, sewage sludge, coal, heavy oils, petroleum
coke, heavy
refinery residuals, refinery wastes, hydrocarbon contaminated soils, biomass,
and
agricultural wastes, tires, and other hazardous waste. Depending on the origin
of the
feedstock, the volatiles may include H20, H2, N2, 02, C02, CO, CH4, H2S, NH3,
C2H6,
unsaturated hydrocarbons such as acetylenes, olefins, aromatics, tars,
hydrocarbon
liquids (oils) and char (carbon black and ash).
[0007] The means of accomplishing a gasification reaction vary in many ways,
but rely
on four key engineering factors: the atmosphere (level of oxygen or air or
steam
content) in the gasifier; the configuration and dimensions of the gasifier;
the internal and
external heating means; and the operating temperature for the process. Factors
that
affect the quality of the product gas include: feedstock composition,
preparation and
particle size; gasifier heating rate; residence time; material feeding method
(dry or slurry
feed system), the feedstock-reactant flow arrangement, the design of the dry
ash or slag
removal system; whether it uses a direct or indirect heat generation and
displacement
method; and the syngas cleanup system. Gasification is usually carried out at
a
temperature in the range of about 650 C to 1200 C, either under vacuum, at
atmospheric
pressure or at pressures up to about 100 atmospheres.
[0008] As the feedstock is heated, water is the first constituent to evolve.
As the
temperature of the dry feedstock increases, volatilization takes place. During
volatilization, the feedstock is thermally decomposed to release tars and
light volatile
hydrocarbon gases, with the formation of char, a residual solid consisting of
both
organic and inorganic materials. At high temperatures (such as above 1200 C),
inorganic mineral matter is fused or vitrified to form a molten glass-like
substance
called slag. The slag is usually found to be non-hazardous and may be disposed
of in a
landfill as a non-hazardous material, or sold as an ore, road-bed, or other
construction
material.
2
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0009] If the gas generated in the gasification reaction comprises a wide
variety of
volatiles, such as the kind of gas that tends to be generated in a low
temperature gasifier
with a "low quality" carbonaceous feedstock, it is generally referred to as
off-gas. If the
characteristics of the feedstock and the conditions in the gasifier generate a
gas in which
CO and H2 are the predominant chemical species, the gas is referred to as
syngas.
Optionally, the raw off-gas or the raw syngas is converted to a more refined
gas
composition in a gas reformulating system (GRS) prior to cooling and cleaning
through
a gas conditioning system (GCS).
[0010] The GRS can employ plasma heat to reformulate the offgas/syngas by
converting, reconstituting, or reforming longer chain volatiles and tars into
smaller
molecules with or without the addition of other inputs or reactants. When
gaseous
molecules come into contact with the plasma heat, they disassociate into their
constituent atoms. Many of these atoms will react with other input molecules
to form
new molecules, while others may recombine with like atoms (e.g. one hydrogen
atom
combines with another hydrogen atom). As the temperature of the molecules in
contact
with the plasma heat decreases, all atoms fully recombine. As input gases can
be
controlled stoichiometrically, output gases can be controlled to, for example,
produce
substantial levels of carbon monoxide and insubstantial levels of carbon
dioxide.
Alternatively, plasma heating can be used within the gasification reaction
itself.
[0011] Plasma is a high temperature luminous gas that is at least partially
ionised, and is
made up of gas atoms, gas ions, and electrons. Plasma can be produced with any
gas in
this manner. This gives excellent control over chemical reactions in the
plasma as the
gas might be neutral (for example, argon, helium, neon), reductive (for
example,
hydrogen, methane, ammonia, carbon monoxide), or oxidative (for example,
oxygen,
carbon dioxide). In the bulk phase, plasma is electrically neutral.
[0012] The reformulated gas from the GRS may contain small amounts of unwanted
compounds and requires further treatment to convert it into a useable product.
Undesirable substances such as metals, sulphur compounds and ash may need to
be
removed from the gas. This is usually done in the gas conditioning system
(GCS). For
example, dry filtration systems and wet scrubbers are often used in a GCS to
remove
particulate matter and acid gases from the gas.
3
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0013] These factors have been taken into account in the design of various
different
systems which are described, for example, in U.S. Patent Nos. 6,686,556,
6,630,113,
6,380,507; 6,215,678, 5,666,891, 5,798,497, 5,756,957, and U.S. Patent
Application
Nos. 2004/0251241, 2002/0144981. There are also a number of patents relating
to
different technologies for the gasification of coal for the production of
synthesis gases
for use in various applications, including U.S. patent Nos. 4,141,694;
4,181,504;
4,208,191; 4,410,336; 4,472,172; 4,606,799; 5,331,906; 5,486,269, and
6,200,430.
[0014] Numerous converters are known in the art, however, a practical
efficient system
has not yet achieved significant commercial use. Most of them have been
affected in the
volatilization stage by heat transfer problems attendant to the large variance
in
composition and moisture content of the feedstock. To achieve relatively
steady state
operation, volatilization temperatures must be used that approach the
temperature at
which slagging of inorganic material occurs within the gasifier. However, in
practise,
the temperature in the gasifier often rises above the slagging temperature due
to
variances in content and moisture of the feedstock. This results in formation
of a
tenaciously adhering slag coating comprising of the inorganic components of
the waste
melt, on all surfaces of the gasifier exposed to the waste.
[0015] Known vertically oriented gasifiers have utilized fixed-bed processing
chambers
and moving bed processing chambers, the latter being superior due to their
ability to
handle the residue without vitrification, and include gravity-induced vertical
processing
chambers, mechanically-assisted flow processing chambers, entrained flow
processing
chambers, fluidised bed processing chambers and any combination thereof. All
known
designs have the direction of flow of input air counter-current to the
direction of flow of
the reactant material.
[0016] Prior systems and processes in vertically oriented gasifiers have not
adequately
addressed the problems that must be dealt with on a continuously changing
basis.
Accordingly, it would be a significant advancement in the art to provide a
system that
can efficiently gasify carbonaceous feedstock in a manner that maximizes the
overall
efficiency of the process, and/or the steps comprising the overall process.
[0017] This background information is provided for the purpose of making known
information believed by the applicant to be of possible relevance to the
invention. No
4
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
admission is necessarily intended, nor should be construed, that any of the
preceding
information constitutes prior art against the invention.
SUMMARY OF THE INVENTION
[0018] The object of the invention is to provide a vertically oriented
gasifier for
conversion of carbonaceous feedstock into a gas.
[0019] In accordance with one aspect of the invention, there is provided a
gasifier for
conversion of carbonaceous feedstock into gas and residue, the gasifier
comprising: one
or more processing chambers, two or more vertically successive processing
regions
being distributed within said one or more processing chambers, within each one
of
which a respective process selected from the group consisting of drying,
volatilization
and carbon conversion is at least partially favoured, said processing regions
being
identified by temperature ranges respectively enabling each said respective
process; one
or more additive input elements associated with said processing regions for
inputting
additives to promote each said at least partially favoured process therein;
one or more
material displacement control modules adapted to control a vertical movement
of the
feedstock through said processing regions to enhance each said at least
partially
favoured process; one or more feedstock inputs located near a first of said
processing
regions; one or more gas outputs; and one or more residue outputs.
[0020] In accordance with another aspect of the invention, there is a provided
a
vertically oriented gasifier for conversion of carbonaceous feedstock into gas
and
residue, the gasifier comprising: one or more processing chambers, each one of
which
comprising one or more additive input elements for input of additives therein,
wherein
combination of said one or more processing chambers and a positioning of said
one or
more additive input elements thereof promoting creation of two or more
vertically
successive processing regions within the gasifier within each one of which a
respective
process is at least partially favoured, said processing regions being
identified by
temperature ranges respectively enabling each said respective process; one or
more
feedstock inputs proximal to a first of said processing regions; one or more
material
displacement control modules adapted to control a vertical movement of the
feedstock
5
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
through said processing regions to enhance each said at least partially
favoured process;
one or more gas outputs; and one or more residue outputs.
[0021] In accordance with another aspect of the invention, there is a provided
a method
for converting a carbonaceous feedstock into gas and residue comprising the
steps of:
providing a gasifier; creating two or more vertically successive processing
regions
within said gasifier, within each one of which a respective process selected
from the
group consisting of drying, volatilization and carbon conversion is at least
partially
favoured, said processing regions being identified by temperature ranges
respectively
enabling each said respective process; inputting additives within the gasifier
to promote
each said at least partially favoured process; controlling a downward movement
of the
feedstock through said processing regions thereby optimizing each said at
least partially
favoured process; and outputting the gas and residue from the gasifier.
BRIEF DESCRIPTION OF THE FIGURES
[0022] Figure 1 shows a general schematic of a vertically oriented gasifier,
in
accordance with one embodiment of the present invention.
[0023] Figure 2 shows a general schematic of a vertically oriented gasifier,
in
accordance with another embodiment of the present invention.
[0024] Figure 3 shows a general schematic of a vertically oriented gasifier
comprising
multiple processing chambers with vertically successive movement of the
reactant
material from one chamber to the next, each with its own set of one or more
additives
and off-gas extraction points, in accordance with one embodiment of the
present
invention.
[0025] Figure 4 is a representation of the processing regions in a gasifier
comprising a
single processing chamber with symmetric placement of the additive input
elements, in
accordance with one embodiment of the present invention.
[0026] Figure 5 is a representation of the processing regions in a gasifier
comprising a
single processing chamber with asymmetric placement of the additive input
elements, in
accordance with one embodiment of the present invention.
6
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0027] Figure 6 is a representation of the processing regions in an ideal
gasifier
comprising three processing chambers, each with symmetric placement of the
additive
input elements to enable the formation of individual processing regions for
drying,
volatilization and carbon conversion, in accordance with one embodiment of the
present
invention.
[0028] Figure 7 is a representation of the processing regions in a gasifier
comprising
three processing chambers, each with symmetric placement of the additive input
elements enabling the formation of processing regions with different
proportion of the
drying, volatilization and carbon conversion processes occurring in them, in
accordance
with one embodiment of the present invention.
[0029] Figure 8 is a representation of the processing regions in a gasifier
with two
processing chambers, with the first processing chamber containing the drying
and
volatilization regions and the second processing chamber predominantly
containing the
carbon conversion region, in accordance with one embodiment of the present
invention.
[0030] Figure 9 is a representation of the processing regions in a gasifier
with two
processing chambers, with the first processing chamber containing the drying
region
predominantly and the second processing chamber containing the volatilization
and
carbon conversion region, in accordance with one embodiment of the present
invention.
[0031] Figure 10 shows the schematic of a gasification system with a gasifier
with a
lateral material displacement control module followed by a gasifier with
vertical
material displacement control module, in accordance with one embodiment of the
present invention.
[0032] Figure 11 shows the schematic of a gasification system with a gasifier
with a
vertical material displacement control module followed by a gasifier with
lateral
material displacement control module, in accordance with one embodiment of the
present invention.
[0033] Figure 12 is a cross-sectional schematic diagram of a processing
chamber with a
rotating arm-based material displacement control module, in accordance with
one
embodiment of the invention. Figure 12B is the top-view of the rotating arm-
based
material displacement control module.
7
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0034] Figure 13A is a perspective, cut away view of a processing chamber
using an
extractor screw-based material displacement control module, in accordance with
an
embodiment of the invention. Figure 13B shows a cross-sectional view of a
slight
variation where the residue outlet is moved away from the main processing
chamber to
avoid direct drop, in accordance with one embodiment of the present invention.
[0035] Figure 14A is a perspective, cut away view of a processing chamber
using a
pusher ram-based material displacement control module, in accordance with one
embodiment of the invention. Figures 14B and 14C show cross-sectional views of
two
different processing chambers using pusher ram-based material displacement
control
modules, in accordance with one embodiment of the present invention.
[0036] Figures 15A and 15B show embodiments of rotating grates that can be
used in a
material displacement control module, in accordance with different embodiments
of the
present invention.
[0037] Figure 16 shows various embodiments for movement of reactant material
from
one processing chamber to another in a two-processing chamber gasifier. The
material
displacement control modules employed include (a) gravity; (b) gravity with
sideways
top valve; (c) gravity with hopper; (d) gravity with screw; (e) vertical
screw; (f)
horizontal extractor screw; (g) vertical screw with hopper; (h) gravity with
screw and
hopper; and (i) horizontal extractor screw and hopper.
[0038] Figure 17 is a schematic diagram of an entrained flow processing
chamber, in
accordance with one embodiment of the invention, in accordance with one
embodiment
of the present invention.
[0039] Figure 18 is a schematic diagram of a fluidized bed processing chamber,
in
accordance with one embodiment of the invention, in accordance with one
embodiment
of the present invention.
[0040] Figure 19 is a schematic diagram of a moving bed processing chamber, in
accordance with one embodiment of the invention, in accordance with one
embodiment
of the present invention.
8
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0041] Figures 20A to 20D show different embodiments for the placement of
additive
input elements around the processing chamber with the depiction of the
processing
regions in each case, in accordance with one embodiment of the present
invention.
[0042] Figures 21A and 21B show different shapes of processing chambers
according to
different embodiments of the invention, in accordance with one embodiment of
the
present invention.
[0043] Figure 22 shows different embodiments of feedstock input means to the
gasifier:
(a) secondary feed fed to the primary feed screw; (b) primary and secondary
feed fed
into a mixed hopper and conveyed via screw to the gasifier; and (c) for two or
more feed
streams.
[0044] Figure 23 shows the connection of a single-chamber or multi-chamber
vertically
oriented gasifier to a gas conditioning system (GCS) either through or without
a gas
reformulating system (GRS) , in accordance with one embodiment of the present
invention.
[0045] Figure 24 shows a system similar to that of Figure 23, further
connected to a
residue conditioning system, in accordance with one embodiment of the present
invention.
[0046] Figure 25 shows a system similar to that of Figures 23 and 24, with
further
transfer of product gas from the residue conditioning system either to the GRS
or to the
GCS.
[0047] Figure 26A shows the use of a GCS for the product gas generated in a
residue
conditioning system, in accordance with one embodiment of the present
invention.
[0048] Figure 26B shows the use of a mini-GCS for the product gas generated in
a
residue conditioning system before it is fed to a primary GCS, in accordance
with one
embodiment of the present invention.
[0049] Figure 27 shows a modular approach for building a gasification facility
comprising of two parallel streams with independent GRS and GCS.
9
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0050] Figure 28 is a cross-sectional schematic of a cascade of a gasifier
with a single
processing chamber with a plasma-based residue conditioning system.
[0051] Figure 29 is a cross-sectional schematic of a cascade of a gasifier
with two
processing chambers with a plasma-based residue conditioning system.
[0052] Figure 30 shows one embodiment of a distributed control system for a
gasification facility using a gasifier, GRS, GCS, GHS and a downstream
application for
the output syngas generated upstream.
[0053] Figures 31 to 34 depict various combinations of how the different
function
blocks processes of a gasification facility can be constructed, wherein "1"
depicts
function block 1 (a gasifier), "2" depicts a function block 2 (a residue
conditioning
system) and "3" depicts function block 3 (a gas reformulating system).
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0054] As used herein, the term `about' refers to a+/-10 Io variation from the
nominal
value. It is to be understood that such a variation is always included in any
given value
provided herein, whether or not it is specifically referred to.
[0055] The terms `carbonaceous feedstock' and `feedstock', as used
interchangeably
herein, are defined to refer to carbonaceous material that can be used in the
gasification
process. Examples of suitable feedstock include, but are not limited to,
hazardous and
non-hazardous waste materials, including municipal wastes; wastes produced by
industrial activity; biomedical wastes; carbonaceous material inappropriate
for
recycling, including non-recyclable plastics; sewage sludge; coal; heavy oils;
petroleum
coke; heavy refinery residuals; refinery wastes; hydrocarbon contaminated
solids;
biomass; agricultural wastes; municipal solid waste; hazardous waste and
industrial
waste. Examples of biomass useful for gasification include, but are not
limited to, waste
wood; fresh wood; remains from fruit, vegetable and grain processing; paper
mill
residues; straw; grass, and manure.
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0056] The term `reactant material' is defined to refer to any feedstock,
including but
not limited to partially or fully processed feedstock.
[0057] As used herein, the term, `input' denotes that which is about to enter
or be
communicated to any system or component thereof, is currently entering or
being
communicated to any system or component thereof, or has previously entered or
been
communicated to any system or component thereof. An input includes, but is not
limited
to, compositions of matter, information, data, and signals, or any combination
thereof.
In respect of a composition of matter, an input may include, but is not
limited to,
influent(s), reactant(s), reagent(s), fuel(s), object(s) or any combinations
thereof. In
respect of information, an input may include, but is not limited to,
specifications and
operating parameters of a system. In respect of data, an input may include,
but is not
limited to, result(s), measurement(s), observation(s), description(s),
statistic(s), or any
combination thereof generated or collected from a system. In respect of a
signal, an
input may include, but is not limited to, pneumatic, electrical, audio, light
(visual and
non-visual), mechanical or any combination thereof. An input may be defined in
terms
of the system, or component thereof, to which it is about to enter or be
communicated
to, is currently entering or being communicated to, or has previously entered
or been
communicated to, such that an input for a given system or component of a
system may
also be an output in respect of another system or component of a system. Input
can also
denote the action or process of entering or communicating with a system.
[0058] As used herein, the term `output' denotes that which is about to exit
or be
communicated from any system or component thereof, is currently exiting or
being
communicated from any system or component thereof, or has previously exited or
been
communicated from any system or component thereof. An output includes, but is
not
limited to, compositions of matter, information, data, and signals, or any
combination
thereof. In respect of a composition of matter, an output may include, but is
not limited
to, effluent(s), reaction product(s), process waste(s), fuel(s), object(s) or
any
combinations thereof. In respect of information, an output may include, but is
not
limited to, specifications and operating parameters of a system. In respect of
data, an
output may include, but is not limited to, result(s), measurement(s),
observation(s),
description(s), statistic(s), or any combination thereof generated or
collected from a
system. In respect of a signal, an output may include, but is not limited to,
pneumatic,
11
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
electrical, audio, light (visual and non-visual), mechanical or any
combination thereof.
An output may be defined in terms of the system, or component thereof, to
which it is
about to exit or be communicated from, currently exiting or being communicated
from,
or has previously exited or been communicated from, such that an output for a
given
system or component of a system may also be an input in respect of another
system or
component of a system. Output can also denote the action or process of exiting
or
communicating with a system.
[0059] The term `residue' generally refers to the residual material produced
during
processes for the gasification or incineration of carbonaceous feedstocks.
These include
the solid and semi-solid by-products of the process. Such a residue generally
consists of
the inorganic, incombustible materials present in carbonaceous materials, such
as
silicon, aluminium, iron and calcium oxides, as well as a proportion of un-
reacted or
incompletely converted carbon. As such, the residue may include char, ash,
and/or any
incompletely converted feedstock passed from the gasification chamber. The
residue
may also include materials recovered from downstream gas conditioning
processes, for
example, solids collected in a gas filtering step, such as that collected in a
baghouse
filter. The residue may also include solid products of carbonaceous feedstock
incineration processes, which may come in the form of incinerator bottom ash
and
flyash collected in an incinerator's pollution abatement suite.
[0060] The term `sensing element' is defined to describe any element of the
system
configured to sense a characteristic of a process, a process device, a process
input or
process output, wherein such characteristic may be represented by a
characteristic value
useable in monitoring, regulating and/or controlling one or more local,
regional and/or
global processes of the system. Sensing elements considered within the context
of a
gasification system may include, but are not limited to, sensors, detectors,
monitors,
analyzers or any combination thereof for the sensing of process, fluid and/or
material
temperature, pressure, flow, composition and/or other such characteristics, as
well as
material position and/or disposition at any given point within the system and
any
operating characteristic of any process device used within the system. It will
be
appreciated by the person of ordinary skill in the art that the above examples
of sensing
elements, though each relevant within the context of a gasification system,
may not be
specifically relevant within the context of the present disclosure, and as
such, elements
12
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
identified herein as sensing elements should not be limited and/or
inappropriately
construed in light of these examples.
[0061] The term `response element' is defined to describe any element of the
system
configured to respond to a sensed characteristic in order to operate a process
device
operatively associated therewith in accordance with one or more pre-
determined,
computed, fixed and/or adjustable control parameters, wherein the one or more
control
parameters are defined to provide a desired process result. Response elements
considered within the context of a gasification system may include, but are
not limited
to static, pre-set and/or dynamically variable drivers, power sources, and any
other
element configurable to impart an action, which may be mechanical, electrical,
magnetic, pneumatic, hydraulic or a combination thereof, to a device based on
one or
more control parameters. Process devices considered within the context of a
gasification
system, and to which one or more response elements may be operatively coupled,
may
include, but are not limited to, material and/or feedstock input means, heat
sources such
as plasma heat sources, additive input means, various gas blowers and/or other
such gas
circulation devices, various gas flow and/or pressure regulators, and other
process
devices operable to affect any local, regional and/or global process within a
gasification
system. It will be appreciated by the person of ordinary skill in the art that
the above
examples of response elements, though each relevant within the context of a
gasification
system, may not be specifically relevant within the context of the present
disclosure, and
as such, elements identified herein as response elements should not be limited
and/or
inappropriately construed in light of these examples.
[0062] As used herein, the term `real-time' is used to define any action that
is
substantially reflective of the present or current status of the system or
process, or a
characteristic thereof, to which the action relates. A real-time action may
include, but is
not limited to, a process, an iteration, a measurement, a computation, a
response, a
reaction, an acquisition of data, an operation of a device in response to
acquired data,
and other such actions implemented within the system or a given process
implemented
therein. It will be appreciated that a real-time action related to a
relatively slow varying
process or characteristic may be implemented within a time frame or period
(e.g.
second, minute, hour, etc.) that is much longer than another equally real-time
action
related to a relatively fast varying process or characteristic (e.g. lms,
lOms, lOOms, ls).
13
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0063] As used herein the term `continuous' is used to define any action
implemented
on a regular basis or at a given rate or frequency. A continuous action may
include, but
is not limited to, a process, an iteration, a measurement, a computation, a
response, a
reaction, an acquisition of data via a sensing element, an operation of a
device in
response to acquired data, and other such actions implemented within the
system or in
conjunction with a given process implemented therein. It will be appreciated
that a
continuous action related to a relatively slow varying process or
characteristic may be
implemented at a rate or frequency (e.g. once/second, once/minute, once/hour,
etc.) that
is much slower than another equally continuous action related to a relatively
fast varying
process or characteristic (e.g. 1KHz, 100Hz, 10Hz, 1Hz).
[0064] Unless defined otherwise, all technical and scientific terms used
herein have the
same meaning as commonly understood by one of ordinary skill in the art to
which this
invention belongs.
[0065] The invention provides a gasifier comprising two or more vertically
successive
processing regions, within which a certain process such as drying,
volatilization or
carbon conversion is at least partially favoured. The processing regions are
identified by
their different temperature ranges that enable the different processes
therein. The
gasifier comprises one or more processing chambers; the vertically successive
processing regions are distributed throughout the one or more processing
chambers.
Additive input elements are associated with the processing regions to promote
the at
least partially favoured process therein. Thus, the processing regions can be
considered
to be promoted by a combination of the one or more processing chambers and/or
by a
positioning of the one or more additive input elements in each of the
processing
chambers. The gasifier comprises one or more feedstock inputs located near the
first
processing region, one or more gas outputs, one or more residue outputs, one
or more
material displacement control modules and optionally, a global control system.
[0066] In the following discussion, the overall gasification process will be
considered to
consist of three processes in sequence: drying, volatilization and carbon
conversion. It
will be appreciated that these processes are meant to be exemplary only and
should not
be considered to be limited to this example as a gasification process can be
defined to
consist of any two or more processes, as can any such process can be defined
to consist
14
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
of one or more sub-processes as appropriate. For the purpose of clarity and
consistency,
the following will focus on describing various embodiments of the present
invention
wherein the gasification process consists of three exemplary processes
described below.
(a) Drying of the Material
[0067] The feedstock delivered into the gasifier undergoes a drying process
under a
temperature range between 25 C and 200 C. In this temperature range, drying
may also
be accompanied by minor amounts of volatilization.
(b) Volatilization of the Material
[0068] This process occurs mainly between 350 C and 800 C and may also be
accompanied by a small remainder of the drying operation as well as a
substantial
amount of carbon conversion. The composition of air supplied in this region is
typically
varied depending on the feedstock supplied (e.g. oxygen enriched or depleted
air).
(c) Carbon Conversion
[0069] At temperatures between 900 C and 1000 C, the main process reaction
occurring is that of carbon conversion with the remainder of volatilization.
By this time
most of the moisture has been removed from the material. The flow rate of air
supplied
can be varied depending on the reactant material supplied. Steam is also
optionally
added in this region.
[0070] A worker skilled in the art would readily appreciate that in a given
temperature
range, all of the three processes are occurring somewhat simultaneously and
continuously, though, depending on the temperature range, one of the processes
is at
least partially favoured.
[0071] In one embodiment of the invention, the gasifier comprises three
vertically
successive processing regions with the first processing region at least
partially favouring
drying, the second processing region at least partially favouring
volatilization and the
third processing region at least partially favouring carbon conversion. A
worker skilled
in the art will understand that the gasifier can in general comprise of a
large number of
processing regions with a different proportion of drying, volatilization or
carbon
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
conversion occurring in each processing region. Thus, the number of processing
regions
can be as many or as few as desired, without loss of generality.
[0072] The present invention provides a vertically oriented gasifier for
conversion of
carbonaceous feedstock into a fuel gas. In general, the gasifier comprises one
or more
processing chambers, each one of which comprises one or more additive input
elements
for input of additives therein, wherein combination of the one or more
processing
chambers and a positioning of the one or more additive input elements, or
group thereof,
enable two or more vertically successive processing regions within the
gasifier, within
each one of which a respective process is at least partially favoured. The
gasifier further
comprises one or more feedstock inputs for input of the feedstock into a first
of the
processing regions, one or more material displacement control modules for
controlling a
downward displacement of the feedstock through the processing regions for
enhancing
each respective process, one or more gas outputs for output of gas from the
gasifier, and
one or more residue outputs for output of residue from the gasifier.
[0073] For example, with reference to the embodiment of Figure 1, a gasifier
10 having
a single processing chamber 20 may comprise two or more distinct additive
input
elements 30, or groups thereof, positioned so to respectively promote or
favour
processes within respective vertically successive processing regions 40 within
the single
processing chamber 20. A feedstock input 50 provides feedstock to the first of
the
processing regions 40, a gas output 60 for output of gas from the gasifier 10,
and a
residue output 70 for output of residue from the gasifier 10. The orientations
and
positions of the input and output elements for feedstock, additives, residue
and gas, in
Figure 1 are merely exemplary and any variations in their orientations and
positions are
considered to be within the scope and nature of the invention disclosed
herein.
[0074] A material displacement control module operatively controlling one or
more
process devices and/or mechanisms (not shown) configured to control a vertical
displacement or a rate of vertical displacement of the material through the
vertically
successive processing regions, is also provided thereby promoting the
efficient
processing of the material within each of these processing regions wherein a
particular
process is at least partially favoured. For example, as will be described in
greater detail
below, various devices and/or mechanisms may be controlled by the material
16
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
displacement control module to implement a downward displacement of the
material,
either by direct control of material displacement between each processing
region, by
controlled extraction of material from a lowermost processing region thereby
indirectly
controlling a downward displacement of material from an uppermost processing
region
toward the lowermost processing region under gravity, or using any combination
thereof.
[0075] As depicted by the additives input and off-gas output phantom lines of
Figure 1,
it will be appreciated that additives may be input in each processing region,
for instance
via appropriate positioning of additive input elements adapted therefor, or
provided to a
select number of these processing regions as appropriate for a given design
and
embodiment of the gasifier 10. It will also be appreciated that the additive
input
elements may be actively controlled by a common response element configured to
provide a pre-selected quantity or input rate of additives (e.g. set absolute
or relative
input) for a given sensed process characteristic (e.g. process temperature,
pressure,
throughput, etc.; product gas quality, quantity, composition, pressure, flow,
heating
value etc.; feedstock input rate, quality, composition, etc; and the like), or
again
controlled by distinct response elements, possibly operatively linked via a
same local,
regional and/or global control system.
[0076] Similarly, gas outputs may be provided for each processing region
independently, or provided by one or more cooperative gas outputs allowing for
the
output of off-gases from the processing chamber 20 from more than one
processing
region simultaneously.
[0077] In the embodiment of Figure 2, a gasifier 110 may comprise two or more
processing chambers 120 vertically and operatively coupled, each comprising
one or
more additive input elements 130, or groups thereof, positioned so to
respectively
promote or favour processes within respective processing regions 140 of each
processing chamber 120, thereby providing a vertical succession of two or more
processing regions 140 when the processing chambers 120 are combined. A
feedstock
input 150 provides feedstock to the first of the processing regions 140, a gas
output 160
provides for output of gas from the gasifier 110, and a residue output 170
provides for
output of residue from the gasifier 110. The orientations and positions of the
input and
17
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
output elements for feedstock, additives, residue and gas, in Figure 2 are
merely
exemplary and any variations in their orientations and positions are
considered to be
within the scope and nature of the invention disclosed herein.
[0078] A material displacement control module operatively controlling one or
more
process devices and/or mechanisms (not shown) configured to control a vertical
displacement of the material through the vertically successive processing
regions (i.e.
between chambers and/or through the processing regions of a same chamber), is
also
provided thereby promoting the efficient processing of the material within
each of these
processing regions wherein a particular process is at least partially
favoured. For
example, as will be described in greater detail below, various devices and/or
mechanisms may be controlled by the material displacement control module to
implement a downward displacement of the material, either by direct control of
material
displacement between each processing region, by controlled extraction of
material from
a lowermost processing region thereby indirectly controlling a downward
displacement
of material from an uppermost processing region toward the lowermost
processing
region under gravity, or using any combination thereof.
[0079] As depicted by the additives input solid and phantom lines of Figure 2,
it will be
appreciated that additives will generally be input in each processing chamber,
though
not exclusively, and may also optionally be input at multiple locations within
a given
processing chamber to promote definition of two or more processing regions
therein. It
will also be appreciated that the additive input elements may be actively
controlled by a
common response element configured to provide a pre-selected quantity or input
rate of
additives (e.g. set absolute or relative input) for a given sensed process
characteristic
(e.g. process temperature, pressure, throughput, etc.; product gas quality,
quantity,
composition, pressure, flow, heating value etc. ; feedstock input rate,
quality,
composition, etc; and the like), or again controlled by distinct response
elements,
possibly operatively linked via a same local, regional and/or global control
system.
[0080] Similarly, off-gas outputs may be provided for each processing chamber
independently, or provided by one or more cooperative off-gas outputs allowing
for the
output of gas form more than one processing chamber 120 at a time.
18
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0081] As will be described in greater detail with reference to a number of
illustrative
embodiments of the present invention, various combinations of processing
chambers
and additive input elements therefor can be adapted to provide two or more
vertically
successive processing regions as contemplated herein, wherein an appropriate
material
displacement control module can be adapted for a given embodiment to enable
the
controlled displacement of material through these processing regions to
enhance a
processing thereof. Such control may be imparted uniquely for each of the one
or more
processing chambers of the gasifier, optionally imparting indirect
displacement of
material through successive processing regions of the same processing chamber
within
which more than one processing region is defined and/or imparting a
displacement of
material from a first processing chamber to a subsequent vertically successive
processing chamber of a gasifier comprising more than one processing chamber.
Alternatively, control may be imparted to various cooperative control devices
and/or
mechanisms configured to directly control displacement of material from one
processing
region to another, possibly within a same processing chamber.
[0082] In one embodiment 310, and referring to Figure 4, the symmetrical
placement of
three sets of additive input elements, or groups thereof 330, around one
processing
chamber 320 promotes the substantially horizontally planar nature of the
interfaces
between the resulting three processing regions 340.
[0083] In one embodiment 410, and referring to Figure 5, three additive input
elements,
or groups thereof 430, are placed asymmetrically around the processing chamber
420
resulting in non-horizontally planar interfaces between the resulting three
processing
regions 440.
[0084] It will generally be appreciated that symmetric processing regions may
promote
optimal gasification and can generally be enhanced using mixing/agitation
means (e.g.
as seen in Figure 19). Such agitation means may comprise, for example, a
rotating shaft
controlled using a motorized drive. These agitator shafts can also be
operated, in one
embodiment, as a sensing element of an integrated global control system
wherein torque
measurements on these shafts can serve as an indicator of the pile height,
especially if
the agitator has multi-level flights. To reduce false reports due to the
formation of
agglomeration on the flights, two agitator shafts may be used which clean each
other as
19
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
they rotate, thus knocking off agglomeration. Other such agitators may be
considered
herein without departing from the general scope and nature of the present
disclosure, as
will be apparent to the person of skill in the art.
[0085] In one embodiment of the invention, the gasifier comprises two or more
processing chambers each one of which comprising one or more additive input
elements. Each of the two or more processing chambers provides a different
processing
region and the different processing chambers are arranged in a vertically
successive
fashion.
[0086] In one embodiment and referring to Figure 6, the gasifier 510 comprises
three
processing chambers 520 each with its own additive input elements, or groups
thereof
530, positioned as to promote definition of one processing region 540 in each
processing
chamber 520, wherein each of the three processes of gasification (drying,
volatilization
and carbon conversion) is respectively favoured. A worker skilled in the art
will readily
understand that the scenario in Figure 6 is ideal and in practice, each
processing region
however will have different proportion of each of the gasification processes
taking
place, as shown in Figure 7, for example.
[0087] The different processing chambers can also be separately optimized for
maximal
efficiencies. In one embodiment of the invention, and referring to Figure 8,
the gasifier
710 comprises two processing chambers 720, the first one of which is used
predominantly for drying and volatilization while the second processing
chamber is used
predominantly for carbon conversion. In this embodiment, each processing
chamber 720
in the gasifier 710 exits its off-gas stream through an outlet 760 which may
be kept
separated or merged. These off-gas streams may either be sent to a storage
tank or for
further processing in a gas reformulating system (GRS). In an alternate
embodiment,
and referring to Figure 9, the first processing chamber is used predominantly
for drying
and the second processing chamber is used predominantly for volatilization and
carbon
conversion.
[0088] Multiple processing chambers are also useful if the feedstock has a
high content
of plastics. In this situation, the use of the second processing chamber can
be used to
recover additional valuable compounds such as paraffins and waxes. This can be
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
accomplished by operating the first processing chamber at a lower temperature
than the
second processing chamber.
[0089] A worker skilled in the art will understand that while we have
described a
vertically oriented gasifier as taking in carbonaceous feedstock and
outputting a residue,
it can also take in partially processed carbonaceous reactant material from
another
gasifier and/or output its residue to another gasifier. In one embodiment of
the
invention, and referring to Figure 10, a horizontally (laterally) oriented
gasifier is
followed by a vertically oriented gasifier. In an alternate embodiment of the
invention,
and referring to Figure 11, a vertically oriented gasifier is followed by a
horizontally
(laterally) oriented gasifier. A worker skilled in the art will readily
understand that the
orientations and positions of the inputs and outputs to the gasifiers shown in
Figures 10
& 11 are merely exemplary and are not intended to limit the orientations and
positions
of the inputs in an actual implementation of these systems.
Material Displacement Control Module
[0090] In contrast to standard descending bed gasifiers that rely on the
gradual
consumption of the reactant material in the gasifier to move the material
downwards,
the vertically oriented gasifier of the present invention actively controls
the movement
of the reactant material through the gasifier via a material displacement
control module,
thus allowing the overall gasification process to be enhanced, if not
optimized for a
given set of process conditions.
[0091] As will be described in greater detail below, the material displacement
control
module may further be associated with, or integrated within a local, regional
and/or
global control system adapted to actively control various elements of the
gasifier in
response to sensing one or more process characteristics, either within the
gasifier, or
external thereto, for example, in a downstream process or application of the
product gas.
In such an embodiment where the material displacement control module is
actively
operated in conjunction with a local, regional and/or global process control
system,
further refinement of the material processing may be achieved to meet
downstream
needs, for example, when the product gas, or a further processed derivative
thereof, is
used for a selected downstream application. Alternatively, or in combination
therewith,
the combined control of the gasification process may be implemented so to
maximise
21
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
gasification of the material, for example, to meet environmental regulations
where such
regulations exist, and/or to minimise an energetic impact of the process.
[0092] In general, the material displacement control module may be configured
to
operate under pre-set operational parameters, for example, allowing for a
substantially
constant residence time of the material in each processing region, or again,
may be
configured to operate under dynamically updated or generated operational
parameters
adapted to optimise processing of the material to achieve a given result. In
either
scenario, the material displacement control module, and any control system
operatively
coupled thereto, may comprise one or more sensing elements for sensing one or
more
process characteristics, such as process temperature(s), pressure(s), reactant
composition, product gas composition, and adjust one or more process devices,
such as
mechanisms and/or devices operatively controlled by the material displacement
control
module for enabling a controlled displacement of the material through the
processing
regions within the gasifier, in response to these characteristics.
[0093] In general, the primary function of the material displacement control
module is
to promote the downward movement of the reactant material through the
different
processing regions of the gasifier in an actively controlled fashion in order
to facilitate
efficient overall gasification. It may also optionally incorporate means to
break up
residue agglomerates that can cause jamming at the residue outlet of the
gasifier. The
material displacement control module can be configured to operate one of a
variety of
mechanisms or devices known in the art for enabling displacement of material
from one
region to another. Examples include, but are not limited to rotating arms,
rotating
wheels, rotating paddles, moving shelves, pusher rams, screws, conveyors, and
combinations thereof.
[0094] In addition to controlling the displacement of material through the
gasifier, the
material displacement control module can also be specifically optimized to
also
minimize the carbon content in the residue. In one embodiment of the
invention, this is
achieved using a plug flow pattern for the movement of the reactant material
and a total
control over the residue removal rate.
[0095] The factors involved in the choice of a particular type of device or
mechanism
operated by the material displacement control module include but are not
limited to: (a)
22
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
controllability & speed: how well can the flow of the reactant material
through the
gasifier be controlled accurately; (b) variance in reactor flow: if additives
are added
below the material displacement control module, is there a disruption to the
flow and is
the disruption manageable; and/or (c) power requirements and durability: how
much
energy and maintenance is required for proper operation of the device or
mechanism,
e.g. rotating grates require more maintenance than screws and pusher rams when
properly designed.
[0096] Figure 12 depicts one embodiment of the invention in which the material
displacement control module comprises a rotating paddle 81 at the bottom of
each
processing chamber 20 which moves the reactant material out of the processing
chamber
through a small residue outlet 70. To avoid the waste of partially/unprocessed
reactant material through the residue outlet 70 by a direct drop, a hat
covering 82 is
placed over the residue outlet 70. Limit switches may be optionally used to
control the
speed of the bar rotation and thus the rate of removal of residue. A worker
skilled in the
15 art will readily understand that in embodiments where the multiple
processing chambers
are operatively coupled, a rotating paddle may be used at the bottom of only
the
lowermost processing chamber and the reactant material passes from the
uppermost
processing chamber to the lowermost processing chamber by the action of
gravity.
[0097] Figure 13A depicts one embodiment of the invention in which the
material
20 displacement control module comprises a set of extractor screws 83 at the
bottom of
each processing chamber 20 which moves the residue out of the processing
chamber 20.
Serration on the edge of the extractor screw flight helps in the breaking up
of the residue
agglomerations that could otherwise result in jamming at the residue outlet 70
of the
gasifier 10. A hat covering 82 is not required if the residue outlet 70 is
moved away
from the processing chamber 20, as for the embodiment shown in Figure 13B.
Limit
switches may be optionally used to control the speed of the screws and thus
the rate of
removal of residue. A worker skilled in the art will readily understand that
in
embodiments where the multiple processing chambers are operatively coupled, a
set of
extractor screws may be used at the bottom of only the lowermost processing
chamber
and the reactant material passes from the uppermost processing chamber to the
lowermost processing chamber by the action of gravity.
23
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0098] Figure 14 depicts one embodiment of the invention in which the material
displacement control module comprises a single thin pusher ram 85 for each
processing
chamber 20 which moves the residue out of the processing chamber 20 through a
small
residue outlet 70. Depending on the position of the residue outlet 70, a hat
covering 82
may or may not be required as shown in figure 14. Limit switches may be
optionally
used to control the length of the pusher ram stroke and thus the amount of
residue
moved with each stroke. The use of thin, pusher rams 85 is unlike lateral
transfer
gasifiers where the rams used are typically carrier-rams that carry large
amounts of
reactant material from one processing region to another. As the pusher rams 85
used are
thin, only a small amount of residue is moved out of the processing chamber
20. A
worker skilled in the art will readily understand that in embodiments where
the multiple
processing chambers are operatively coupled, a pusher ram may be used at the
bottom
of only the lowermost processing chamber and the reactant material passes from
the
uppermost processing chamber to the lowermost processing chamber by the action
of
gravity.
[0099] In one embodiment of the invention with one or more processing regions
being
promoted by one or more additive input elements within each processing
chamber, the
material displacement control module may comprise an array of one or more
pusher
rams within each processing chamber, each of which is used to actively control
the
movement of the reactant material from one processing region to the next until
the final
pusher ram pushes the residue out of the processing chamber. Thus, the
reactant
material is actively controlled through the entire height of a single
processing chamber.
A worker skilled in the art will understand that such a material displacement
control
module can enable setting up of different `residence times' in the different
processing
regions even within the same processing chamber.
[00100] In embodiments where the material displacement control module
comprises a moving element and a guiding element, suitable moving elements
include,
but are not limited to, a shelf / platform, pusher ram, plow, screw element or
a belt. The
guide element can include one or more guide channels located in the bottom
wall of the
processing chambers, guide tracks or rails, guide trough or guide chains.
Alternatively,
the guide element can include one or more wheels or rollers sized to movably
engage
the guide element. In one embodiment of the invention, the guide engagement
member
24
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
is a sliding member comprising a shoe adapted to slide along the length of the
guide
track. Optionally, the shoe further comprises at least one replaceable wear
pad.
[0100] The material displacement control module may be powered using a motor
and
drive system, or other such means as readily known in the art. In one
embodiment the
motor means is an electric variable speed motor which drives a motor output
shaft
selectably in the forward or reverse directions. Optionally, a slip clutch
could be
provided between the motor and the motor output shaft. The motor may further
comprise a gear box.
[0101] Alternatively, operation of the material displacement control module
can be
implemented by a hydraulic or pneumatic system, chain and sprocket drive, or a
rack
and pinion drive. These methods of translating the motor rotary motion into
linear
motion have the advantage that they can be applied in a synchronized manner at
each
side of the material displacement control module (e.g. a pusher ram) to assist
in keeping
the mechanism aligned and thus minimize the possibility of jamming. In one
embodiment, the use of two chains provides a means of maintaining angular
alignment
without the need for precision guides.
[0102] For the embodiments using two processing chambers, Figure 16 shows a
variety
of different devices and/or mechanisms that can be used by the material
displacement
control module for displacement of reactant material from one processing
chamber to
another. A worker skilled in the art will understand that the options in this
figure are
merely exemplary and other appropriate designs for such devices/mechanisms can
be
considered to be within the scope and nature of the invention disclosed
herein.
Processing Chambers
[0103] The vertically oriented gasifier comprises one or more processing
chambers. The
processing chamber can be chosen from a group consisting of fixed-bed
processing
chambers, gravity-induced vertical processing chambers, mechanically-assisted
flow
processing chambers, entrained flow processing chambers, and fluidised bed
processing
chambers, to name a few.
[0104] In fixed-bed processing chambers known to a worker skilled in the art,
the
feedstock enters the system from the top and rests on a surface through which
input gas,
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
such as heated air or steam (or other additives), may be communicated. The
input gas
passes through the feedstock bed in a counter-current fashion, from the bottom
and all
output gases, including off-gas, syngas, cooled air and steam, or volatiles,
leaves the
processing chamber through vents or other outlets at the top of the processing
chamber.
Any residue such as ash or char passes through the communicable surface and
exits the
processing chamber through the bottom portion.
[0105] In entrained flow processing chambers 22, with reference to Figure 17,
the input
gas travels in a counter-current flow relative to the feedstock. Here, the
feedstock is at
least partially suspended by the movement of the additives, thereby promoting
a more
distributed contact between the input and the feedstock. The reaction occurs
as the
reactant material moves downward, driven by gravity, in opposition to the
direction of
travel of additives, the flow of which has sufficient force to partially
suspend the
descending feedstock. Output gases, including off-gas, syngas, cooled air,
steam and
other volatiles, exit at the top of the processing chamber, and the resulting
residue exit
at the bottom.
[0106] In fluidized bed processing chambers 24, with reference to Figure 18,
the
feedstock is suspended in the upward moving additives similar to entrained
flow
processing chambers. The distinction however lies in the behaviour of the
feedstock in
the bed. In fluidized beds, the additives enter the processing chamber at
velocities that
greatly overcome any gravitational force, and the feedstock bed moves in a
much more
turbulent manner thereby causing a more homogeneous reaction region and
behaving in
a fashion similar to that of a turbulent fluid even though the feedstock may
in fact be
solid. The additives enter the processing chamber from the bottom, passes
counter-
current to the feedstock and output gases, including off-gas, syngas, cooled
air and
steams, or volatiles, leave the processing chambers at the top.
[0107] In one embodiment of the invention using a moving-bed processing
chamber 26,
the processing chamber 26 comprises a feedstock input proximal to the top of
the
processing chamber, two or more additive input elements for injection of pre-
heated air
and positioned such that each promotes determination of a different processing
region, a
product gas outlet, a residue outlet and an actively controlled material
displacement
control module at the base of the processing chamber. In one embodiment and
referring
26
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
to figure 19, separate additive input elements are also reserved for addition
of steam into
the processing chamber. Also, mixing mechanisms 27 may be used to promote
enhanced
interaction between the additives and the reactant material within the
processing
chamber.
[0108] In one embodiment of the invention using moving-bed processing
chambers, the
gasifier comprises two or more moving-bed processing chambers, each with an
additive
input element, or group thereof, for injection of pre-heated air at the bottom
of the
processing chamber. The injection of pre-heated air from the bottom enables
the
oxidation of char formed near the bottom of the processing chamber. The
counter-
current flow of the pre-heated air with respect to the feedstock also enhances
the energy
utilization. As the pre-heated air passing through the moving feedstock bed
loses its
temperature, a temperature gradient is formed within the processing chamber
that is
consistent with the higher temperatures needed for the latter processes of
gasification.
[0109] In one embodiment of the invention using moving-bed processing
chambers, the
one or more additive input elements for each processing chamber are
distributed all
around the processing chamber. This distribution of a plurality of input
elements allows
finer control of the processes of gasification. Figures 20A to 20D show other
embodiments of the invention with differences in the placement and type of
additive
input elements. The general shapes of the processing regions for each case are
also
shown.
[0110] The processing chambers used can be of any shape so long as the
internal
volume is sufficient to accommodate the appropriate amount of reactant
material for the
designed residence time, and sufficient for a reasonable gas superficial
velocity to be
attained. In one embodiment of the invention, the processing chamber is a
refractory-
lined cylinder and its length is between about 1 and 3 times its diameter. In
one
embodiment, its length is between about 1 and 2 times its diameter. In one
embodiment,
its length is about 1.5 times its diameter.
[0111] In one embodiment of the invention, the processing chamber has a
cylindrical
outer wall and a refractory-lined, downward sloping, inner walls. Figures 21A
and 21B
show a few more possible shapes for the processing chamber. Other appropriate
shapes
will be apparent to a worker skilled in the art.
27
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0112] The refractory lining protects the processing chamber from the effects
of high
temperatures and corrosive gases and minimizes unnecessary loss of heat from
the
process. The refractory material is a conventional refractory material, which
is well-
known to those skilled in the art and which is suitable for use for a high
temperature e.g.
up to about 1800 C, un-pressurized reaction. Examples of such refractory
material
include, but are not limited to, high temperature fired ceramics, i.e.,
aluminum oxide,
aluminum nitride, aluminum silicate, boron nitride, zirconium phosphate, glass
ceramics
and high alumina brick containing principally, silica, alumina, chromia and
titania. To
further protect the processing chamber from the impact of corrosive gases, it
may be
lined with a membrane. Such membranes are known in the art and as such a
worker
skilled in the art would readily be able to identify appropriate membranes
based on the
gasifier requirements.
[0113] The roof or upper portion of the processing chamber should also be
designed for
the optimal flow and residence time of gas. The roof portion can be flat,
domed or other
practical configurations that promote the flow of gas through the processing
chamber,
and thus the avoidance of dead (a.k.a `cold') spots.
[0114] The physical design characteristics of a processing chamber are
determined by a
number of factors that can be readily determined by one skilled in the art.
For example,
the internal configuration and size of the processing chamber are dictated by
the
operational characteristics through analyses of the chemical composition of
the input
feedstock to be processed. Other design factors include the type of heating
means used
and the position and orientation of the heating means used. These heating
means are
generally positioned within the processing chamber at the desired depth in
order to
concentrate the high temperature processing region where it will be most
effective,
while at the same time minimizing heat losses. Sometimes, other additives such
as
steam are added into the gasifier in addition to the pre-heated air, to
improve the quality
of the product syngas. The position, orientation and number of the injection
ports for
these additional additives also have to be considered in the design of the
processing
chamber to ensure that they are injected where they will promote efficient
reaction to
achieve the desired conversion result.
28
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0115] A worker skilled in the art will readily understand that the one or
more
processing chambers used in the vertically oriented gasifier can each use
different
refractory materials, different shapes, different sizes and different material
displacement
control modules as suitable for the processing done within that chamber.
[0116] Various computer-based simulation and modeling tools can facilitate the
physical design of the processing chamber by taking into account factors such
as
efficient heat transfer, gas flow, mixing of additives, etc. Computer-based
tools virtually
eliminate the need for experimentation prior to preliminary system design and
provide
rapid confirmation of process characteristics and efficiency with any input
waste stream.
They also permit interactive iteration to optimize operational
characterization for any
particular system prior to system commissioning and facilitate real-time
optimization of
processes for non-homogeneous materials based on product gas characterization
as
input.
[0117] One such simulator is the Chemical Process Simulator, as detailed in
U.S. Patent
6,817,388 (incorporated by reference). It uses the principle of minimization
of Gibb's
free energy to allow prediction of the product gas components at a specific
temperature
and specific set of input parameters. In general, the simulator consists of
three main
computational blocks:
a. An Ideal Reaction Model: This calculates the ideal, steady state
equilibrium composition of the product gas, by minimizing the Gibbs free
energy of the product chemical species in adiabatic, isobaric equilibrium.
A generalized Gibbs minimization approach is used here to find the
equilibrium composition of arbitrary large systems without the need to
write equilibrium reactions.
b. A Carbon Deposition Model: This calculates the amount of soot (solid
Carbon C(s)) formed, or the amount of steam needed to eliminate soot
formation by comparing the input composition vs. equilibrium curves.
This model can also be used to recursively solve for the amount of water
that must be added in order to reduce the amount of solid carbon formed.
29
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
c. A Non-Ideal Reaction Model: This determines the amount of methane,
acetylene and ethylene that is formed in excess of the ideal as calculated
by multiplying the amount of Carbon in the system by experimentally
derived ratios. This approximates the result of non-total decomposition of
long-chain hydrocarbons or polymers.
[0118] In addition to using the Chemical Process Simulator, flow modeling of
the
processing chamber may also be used in the design process to ensure proper
mixing of
the process inputs, to analyze impact of the kinetic effects, and to adjust
the reaction
temperature profile within the simulator. Flow modeling results also assist
refractory
design since all operating characteristics at the refractory surface can
readily be
identified.
[0119] Optionally, and as mentioned earlier, one or more of the one or more
processing
chambers of the gasifier may comprise a mixing means for ensuring efficient
exposure
of the reactant material to the pre-heated air thus allowing efficient
gasification. The
mixing means prevents gas channelling, a condition where the additive inputs
such as
pre-heated air burns a path through the bed, resulting in more pre-heated air
travelling
down that `channel' avoiding the reactant material completely. The passage of
pre-
heated air into the gas phase, also called breakthrough, can cause rapid
combustion with
gas phase combustibles, agglomeration of the reactant material and channel
burning.
Good mixing also stabilizes the gas composition and reduces the risk of
downstream gas
explosion.
[0120] Gasification requires heat and an oxidant such as oxygen or steam.
Heating can
occur either directly by the heat released due to partial oxidation of the
feedstock or
indirectly by use of a heat source known in the art.
[0121] In one embodiment of the invention, the heat source is pre-heated air
added into
the processing chambers through the additive input elements. The air is either
obtained
from air heaters or heat exchangers, both of which are known to a worker
skilled in the
art and fed through to each processing region using an independent air feed
and
distribution system such as an air box. Alternatively, the indirect heat
source could
either be circulating hot sand or an electrical heating element.
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0122] In order to facilitate initial start up of the gasifier, the processing
chambers can
include access ports sized to accommodate various conventional burners, for
example
natural gas or propane burners, to pre-heat the gasifier.
[0123] In addition, the processing chambers can further comprise one or more
service
ports to allow for entry for maintenance and repair. Such ports are known in
the art and
can include sealable port holes of various sizes. In one embodiment, access to
the
processing chamber is provided by a manhole at one end which can be closed by
a
sealable refractory lined cover during operation. In one embodiment of the
invention, a
manhole is placed on both ends of the processing chamber for maintenance.
Additive input elements
[0124] As mentioned earlier, additives may be added to each of the one or more
processing chambers of the vertically oriented gasifier to facilitate
efficient conversion
of feedstock into product gas. The type and quantity of the additives is
selected to
optimize the process reactions while maintaining adherence to regulatory
authority
emission limits and minimizing operating costs. The different types of
additive input
elements include but are not limited to air, oxygen-enriched air, oxygen,
steam and
ozone. The additive input elements play a key role in determining the
temperatures
within the processing chambers and thus the extents of the processing regions
wherein
different processes are at least partially favoured.
[0125] Air or oxygen input can be used to maximize carbon conversion (i.e.,
minimize
free carbon) and to maintain the optimum processing temperatures while
minimizing the
cost of input heat. The quantity of both additives can be established and
rigidly
controlled as identified by the outputs for the feedstock being processed. The
amount of
air injection is established to minimize the cost of heating while ensuring
the overall
process does not approach any of the undesirable traits associated with
incineration
(such as unwanted dioxins, furans, NOx, SOx in product gas, metals in ash and
lower
carbon conversion), and satisfies the emission standards requirements of the
local area.
[0126] Steam inputs promote sufficient free oxygen and hydrogen to maximize
the
conversion of decomposed elements of the feedstock into product gas and/or non-
hazardous compounds. As the conversion of the reactant material to gas via
reaction
31
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
with steam is an endothermic one, it can serve to balance out the endothermic
nature of
the reaction via air. In addition, steam provides additional hydrogen for the
proper
balancing of C, H, 0 reactions.
[0127] In some embodiments of the invention, a secondary feedstock stream is
also
introduced as a process additive. This feedstock stream can be dynamically
manipulated
by the global control system depending on the downstream parameters of the
gasifier
such as the quality of the product gas, pressure etc as sensed by the sensing
elements. A
typical secondary feedstock is high carbon feedstock such as plastics.
[0128] Each of the processing chambers therefore, may include a plurality of
additive
input elements that include inlets for steam injection and/or air injection.
The steam
inlets can be strategically located to direct steam into high temperature
regions and into
the product gas mass just prior to its exit from the processing chamber.
[0129] The additive input elements can be strategically located to ensure full
coverage
into the processing regions. In one embodiment, they are located proximal to
the floor
of the processing chamber. Alternatively, they are located either in the floor
of the
processing chamber or are distributed all around the walls of the processing
chamber. In
embodiments in which pre-heated air is used as the gasifier heating means,
additional
air/oxygen injection input elements may optionally be included.
[0130] The actual location of the additive input elements may determined based
on any
number of the following factors: (a) maximize heat transfer; (b) maximize
contact with
carbon; (c) minimize pressure loss; (d) avoid pluggage; (e) minimize potential
for gas
channelling.
[0131] For embodiments of the invention where additives are added from the top
of the
processing chamber, the gases added at the top may help dry the wet
carbonaceous
feedstock at the top of the bed or help in the distribution of the material by
the use of
jets (by spraying the material around the top of the pile, rather than the use
of
mechanical agitation means). If air or hot steam is added at the top, the
temperature of
the product gas increases resulting in the breakdown of tars in the gas phase.
Alternatively, the addition of low temperature steam or nitrogen (or other
liquid fluids)
lowers the gas temperatures and protects the downstream equipment. The major
32
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
drawback of having the additive input elements on the top of the chamber is
however
the risk of dilution of the product gas.
[0132] For embodiments of the invention where additives are added from the
bottom of
the processing chamber, the residence time of the additives in the processing
chamber is
maximised, which can be beneficial in low-temperature systems with slower
reactions.
While poor designs run a high risk of producing slag, agglomerations, etc.
that interfere
with operations, proper design can reduce the likelihood of these problems.
The
injection of additives at the bottom promotes that the entire processing
chamber is
affected and that the carbon is removed from the ash before it exits the
processing
chamber.
[0133] For embodiments of the invention where additives are added from the
sides of
the processing chamber, even distribution of additives and hence more stable
reactions
are promoted. This design also evens out the processing regions and reduces
the
concentration of some additives (such as oxygen or ozone) to avoid localized
combustion or agglomeration. However, the main drawback is that the additives
injected
along the sides do not reach the middle of the processing chamber unless high
flow rates
are used which tend to fluidize the bed or create hot spots near the walls.
Agitators can
be used to promote mixing of the reactant material from the middle with that
of the
sides.
Feedstock Input Means
[0134] The vertically oriented gasifier includes a material feeder system
comprising one
or more input feed ports catered to any physical characteristics of the input
feedstock,
each of which feed directly into the gasifier. In one embodiment of the
invention, the
material feeding subsystem consists of a feed hopper and a screw conveyor used
to
transport feedstock to the gasifier. In some embodiments of the invention, the
material
fed into the vertically oriented gasifier can be partially processed reactant
material from
an upstream gasifier. The feed hopper acts as a buffer for the material ready
to be fed
into the gasifier. The hopper can optionally have high and low level
indicators that
control the flow into the hopper and are optionally under the control of the
process
controller to match the feed rate to process demands.
33
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0135] Optionally, referring to Figure 22A, the material feeding subsystem can
further
comprise an additional entry to accept a secondary feed (usually high carbon
feedstock
such as shredded plastic), thereby enabling quick response to process demands
for
higher or lower carbon input to meet the required gas quality for the
downstream
applications.
[0136] Referring to Figure 22, various embodiments of the invention can be
envisioned,
whereby the different feed streams are either mixed together in a common
hopper before
insertion into the gasifier or not. Optionally, the gasifier has a separate
feeding
subsystem for feeding the high carbon feedstock into the gasifier. Also, a
more general
case can be considered where there are more than two feed streams as well.
[0137] In one embodiment of the invention, the material feeding system
consists of a
rectangular feedhopper and a hydraulic assisted ram. A gate may be installed
in the
middle of the feed chute to act as a heat barrier between the processing
chamber and the
feedhopper. Limit switches on the feeder control the length of the ram stroke
so that the
amount of material fed into the processing chamber with each stroke can be
controlled.
[0138] In one embodiment of the invention, the primary material feeding system
may
also be modified to accommodate the feeding of boxes, the form in which
hospital
biomedical type waste is provided for processing. A rectangular double door
port will
permit the boxes to be fed into the primary feed hopper where the hydraulic
ram can
input them into the processing chamber.
[0139] In one embodiment of the invention, an auger can be inserted
hydraulically into
the processing chamber to provide a granular waste material feed. In addition,
ram,
rotary valve, top gravity feed, are examples of other feeders that can be used
in the
present context to facilitate the introduction of desired feedstocks. In
addition, liquids
and gases can be fed into the processing chamber simultaneously through their
own
dedicated ports.
[0140] Optionally, the feedstock will pass through a pre-processing system
before being
fed into the feedstock input means. The pre-processing subsystem may comprise
a
shredder to reduce the as-received feedstock to a size more suitable for
processing. As,
components of the feedstock may include materials large enough to jam the
shredder,
34
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
the shedder is optionally equipped to stop when a jam is sensed, automatically
reverse to
clear the jam and then restart. If a jam is still detected the shredder will
shut-down and
send a warning signal to the controller. Appropriate shedder and shedder
designs are
known in the art.
[0141] The pre-processing subsystem may also include a magnetic pick-up
located
above the conveyor to avoid the undesirable feeding of excessive amounts of
metal
through the gasifier. Appropriate magnetic pick-ups are known in the art and
consist of
a powerful magnet over a pick conveyor belt to attract any ferrous metal that
may be
present in the shredded waste. Optionally, a non-magnetic belt can run across
the
direction of the pick conveyor, between the magnet and the feedstock so that
any metal
attracted to the magnet gets moved laterally away from the feedstock stream.
When the
metal has been moved away from the magnet it can be dropped onto a pile that
is either
disposed or sold.
Gas Outlet
[0142] In one embodiment of the invention, the off-gas generated in each
processing
chamber 20 is taken out using a gas outlet 60 that is at the top of the
processing chamber
20. The off-gas streams from the different processing chambers 20 may be kept
separate
or merged before being sent either to a storage tank for future use or for
further
processing in a gas reformulating system (GRS) 92, as shown in Figure 23C.
Alternatively, the gas outlet is placed at the bottom of the processing
chamber and the
product gas is drawn out using a blower kept downstream or other suction means
as
known in the art. A worker skilled in the art will readily understand that the
placement
of the gas outlet at other positions within the processing chambers are all
considered to
be within the scope of the invention, even if not explicitly mentioned herein.
[0143] In one embodiment of the invention, the gasifier is connected to a gas
reformulating system (GRS) 92 either directly or via piping for the
reformulating of
input gas derived from gasification of carbonaceous feedstock into
reformulated gas of a
defined chemical composition. In particular, the gas reformulating system uses
torch
heat from one or more plasma torches to dissociate the gaseous molecules
thereby
allowing their recombination into smaller molecules useful for downstream
application,
such as energy generation. At the high temperatures, typically 900 C-1200 C,
provided
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
by the plasma torches, `tar cracking' usually occurs to eliminate the tar as
well. The
system may also comprise gas mixing means, process additive means, and a
control
system with one or more sensors, one or more process effectors and computing
means to
monitor and/or regulate the reformulating reaction. Referring to Figure 23,
the syngas
produced in the GRS may be sent to a gas conditioning system (GCS) 90 and/or a
gas
homogenization system (GHS) and/or a storage tank.
[0144] In other embodiments of the invention, low temperature gas
reformulating
systems can be used which do not result in tar cracking but result in the
conversion of
the gas to a different composition tailored for a particular downstream
application.
[0145] The GCS 90 serves to remove particulate matter and other impurities
from the
syngas while the GHS serves to smooth out any time variations in the
composition and
pressure of the syngas by providing adequate mixing means and residence time
within a
homogenization chamber. A storage tank is optionally used if the conditioned,
homogenized syngas needs to be stored for future use. Otherwise, the
conditioned,
homogenized syngas can be used for downstream applications such as gas
engines,
boilers etc. Excess syngas can also be disposed of safely using a flare stack.
Residue Outlet
[0146] The residue outlet 70 is used to remove the residue out of the final
processing
region 40 of the gasifier 10. The configurations in which the residue exit the
processing
chamber are dependent on the design and function of the subsequent process and
can be
readily determined by one skilled in the art.
[0147] As mentioned earlier, the residue is removed from the gasifier by the
material
displacement control module. In different embodiments of the invention, the
residue can
be removed into, for example, an ash collection gasifier or to a water tank
for cooling as
is known in the art, from where it is transmitted through a conduit under
control of a
valve, to a point of discharge. In one embodiment of the invention, the
residue from the
vertically oriented gasifier is sent to another gasifier for further
gasification. This is
useful if the vertically oriented gasifier is not able to achieve thorough
volatilization and
carbon conversion.
36
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0148] In one embodiment of the invention and referring to Figure 24, the
residue is
moved to a residue conditioning system 94 which is either directly connected
to the
gasifier 10 or connected via a conveyor. In the residue conditioning system
94, plasma
arc heating is used to convert the residue (char, ash) to slag by raising the
temperature of
the residue to the level required for complete melting and homogenization to
guarantee
trouble free, continuous and automatic (i.e. unattended) slag removal. Other
heating
mechanisms can also be used in other embodiments of the residue conditioning
system.
The molten slag is quenched in a water tank to form a vitreous, solid slag
that can either
be used in the construction industry or disposed off in a non-hazardous manner
in
landfills. Referring to Figure 25, any product gases generated in the residue
conditioning
system 94 is sent to the GCS 90 either after passing through the GRS 92 or
otherwise.
[0149] Additionally, referring to Figure 26, the residual particles collected
in the GCS
90, can be sent back to the residue conditioning system 94 for conversion to
molten slag
and quenching. For the case of the transfer of the product gas from the
residue
conditioning system 94 to the GCS 90 without passing through the GRS 92, the
gas can
reach the GCS 90 either directly or through a secondary GCS 96, as shown in
Figure 26.
[0150] In one embodiment of the invention and referring to Figure 27, the
overall
system is constructed using a modular approach where the product gas output
from the
plurality of processing chambers 20 of the gasifier are not combined to pass
through a
single GRS and GCS but is split up into two parallel streams, each with its
own GRS 92
and GCS 90. A worker skilled in the art will understand that Figure 27 is
merely
exemplary and that other designs of the overall systems using interconnections
of the
different components of the multiple parallel processing streams can be
considered to be
within the scope and nature of the invention disclosed herein.
[0151] Figure 28 and 29 shows the particular implementation of the gasifier
where a
residue conditioning system 94 based on a plasma-torch 95 is interfaced in a
vertically
successive fashion to a gasifier comprising either one or two vertically
successive
processing chambers 20.
[0152] As mentioned earlier, the gasifier 10 of the invention can be combined
with
various other systems, such as a residue conditioning system 94, gas
reformulating
system 92, gas conditioning system 90, gas homogenization system, to form a
complete
37
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
gasification facility. This facility will take in carbonaceous feedstock and
convert it into
a refined, conditioned and homogenized syngas that can be used for various
downstream
applications. The overall gasification facility can be controlled using a
global control
system 98 as described above to ensure that the overall process meets the
requirements
set by the particular downstream application and by the relevant regulatory
standards.
One embodiment of a control system for an overall gasification facility is
shown in
Figure 30.
Control system
[0153] A control system 98 is generally provided to control one or more
processes
implemented in, and/or by, the vertically oriented gasifier, or affecting any
downstream
process or application of the gas produced thereby, and/or provide control of
one or
more process devices contemplated herein for affecting such processes. In
general, the
control system may operatively control various processes related to the
vertically
oriented gasifier and/or related to one or more global, upstream and/or
downstream
processes implemented within a gasification system comprising such a gasifier,
and
thereby adjusts various control parameters thereof adapted to affect these
processes for a
defined result. Various sensing elements and response elements may therefore
be
distributed throughout the controlled system(s), or in relation to one or more
components thereof, and used to acquire various process, reactant and/or
product
characteristics, compare these characteristics to suitable ranges of such
characteristics
conducive to achieving the desired result, and respond by implementing changes
in one
or more of the ongoing processes via one or more controllable process devices.
[0154] The control system generally comprises, for example, one or more
sensing
elements for sensing one or more characteristics related to the system(s),
processe(s)
implemented therein, input(s) provided therefor, and/or output(s) generated
thereby. One
or more computing platforms are communicatively linked to these sensing
elements for
accessing a characteristic value representative of the sensed
characteristic(s), and
configured to compare the characteristic value(s) with a predetermined range
of such
values defined to characterise these characteristics as suitable for selected
operational
and/or downstream results, and compute one or more process control parameters
conducive to maintaining the characteristic value within this predetermined
range. A
38
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
plurality of response elements may thus be operatively linked to one or more
process
devices operable to affect the system, process, input and/or output and
thereby adjust
the sensed characteristic, and communicatively linked to the computing
platform(s) for
accessing the computed process control parameter(s) and operating the process
device(s)
in accordance therewith.
[0155] In one embodiment, the control system provides a feedback, feedforward
and/or
predictive control of various systems, processes, inputs and/or outputs
related to the
conversion of carbonaceous feedstock into a gas, so to promote an efficiency
of one or
more processes implemented in relation thereto. For instance, various process
characteristics may be evaluated and controllably adjusted to influence these
processes,
which may include, but are not limited to, the heating value and/or
composition of the
feedstock, the characteristics of the product gas (e.g. heating value,
temperature,
pressure, flow, composition, carbon content, etc.), the degree of variation
allowed for
such characteristics, and the cost of the inputs versus the value of the
outputs.
Continuous and/or real-time adjustments to various control parameters, which
may
include, but are not limited to, heat source power, additive feed rate(s)
(e.g. oxygen,
oxidants, steam, etc.), feedstock feed rate(s) (e.g. one or more distinct
and/or mixed
feeds), gas and/or system pressure/flow regulators (e.g. blowers, relief
and/or control
valves, flares, etc.), material displacement within the gasifier (e.g. between
vertically
successive processing regions), and the like, can be executed in a manner
whereby one
or more process-related characteristics are assessed and optimized according
to design
and/or downstream specifications.
[0156] Alternatively, or in addition thereto, the control system may be
configured to
monitor operation of the various components of a given system for assuring
proper
operation, and optionally, for ensuring that the process(es) implemented
thereby are
within regulatory standards, when such standards apply.
[0157] In accordance with one embodiment, the control system may further be
used in
monitoring and controlling the total energetic impact of a given system. For
instance, a
given system may be operated such that an energetic impact thereof is reduced,
or again
minimized, for example, by optimising one or more of the processes implemented
thereby, or again by increasing the recuperation of energy (e.g. waste heat)
generated by
39
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
these processes. Alternatively, or in addition thereto, the control system may
be
configured to adjust a composition and/or other characteristics (e.g.
temperature,
pressure, flow, etc.) of a product gas generated via the controlled
process(es) such that
such characteristics are not only suitable for downstream use, but also
substantially
optimised for efficient and/or optimal use. For example, in an embodiment
where the
product gas is used for driving a gas engine of a given type for the
production of
electricity, the characteristics of the product gas may be adjusted such that
these
characteristics are best matched to optimal input characteristics for such
engines.
[0158] In one embodiment, the control system may be configured to adjust a
given
process such that limitations or performance guidelines with regards to
reactant and/or
product residence times in various components, or with respect to various
processes of
the overall process are met and/or optimised for. For example, an upstream
process rate
may be controlled so to substantially match one or more subsequent downstream
processes. Namely, the residence time of the material within the gasifier,
and/or
processing regions thereof, may be set and/or dynamically adjusted by a
material
displacement control module, which may operate independently, cooperatively
and/or as
a submodule of an overall or global control system, to meet certain
preferences and/or
requirements of downstream processes and/or applications.
[0159] The control system can be adapted for maintaining conditions suitable
for local
and/or downstream needs, e.g., temperature, feedstock input rate, displacement
of
material, etc. can be controlled to meet local needs, such as fast processing
of waste,
and/or to meet downstream needs such as suitable gas composition.
[0160] In addition, the control system may, in various embodiments, be adapted
for the
sequential and/or simultaneous control of various aspects of a given process
in a
continuous and/or real time manner.
[0161] In general, the control system may comprise any type of control system
architecture suitable for the application at hand. For example, the control
system may
comprise a substantially centralized control system, a distributed control
system, or a
combination thereof. A centralized control system will generally comprise a
central
controller configured to communicate with various local and/or remote sensing
devices
and response elements configured to respectively sense various characteristics
relevant
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
to the controlled process, and respond thereto via one or more controllable
process
devices adapted to directly or indirectly affect the controlled process. Using
a
centralized architecture, most computations are implemented centrally via a
centralized
processor or processors, such that most of the necessary hardware and/or
software for
implementing control of the process is located in a same location.
[0162] A distributed control system will generally comprise two or more
distributed
controllers which may each communicate with respective sensing and response
elements
for monitoring local and/or regional characteristics, and respond thereto via
local and/or
regional process devices configured to affect a local process or sub-process.
Communication may also take place between distributed controllers via various
network
configurations, wherein a characteristics sensed via a first controller may be
communicated to a second controller for response thereat, wherein such distal
response
may have an impact on the characteristic sensed at the first location. For
example, a
characteristic of a downstream product gas may be sensed by a downstream
monitoring
device, and adjusted by adjusting a control parameter associated with the
converter that
is controlled by an upstream controller. In a distributed architecture,
control hardware
and/or software is also distributed between controllers, wherein a same but
modularly
configured control scheme may be implemented on each controller, or various
cooperative modular control schemes may be implemented on respective
controllers.
[0163] Alternatively, the control system may be subdivided into separate yet
communicatively linked local, regional and/or global control subsystems. Such
an
architecture could allow a given process, or series of interrelated processes
to take place
and be controlled locally with minimal interaction with other local control
subsystems.
A global master control system could then communicate with each respective
local
control subsystems to direct necessary adjustments to local processes for a
global result.
[0164] The control system of the present invention may use any of the above
architectures, or any other architecture commonly known in the art, which are
considered to be within the general scope and nature of the present
disclosure. For
instance, processes controlled and implemented within the context of the
invention may
be controlled in a dedicated local environment, with optional external
communication to
any central and/or remote control system used for related upstream or
downstream
41
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
processes, when applicable. Alternatively, the control system may comprise a
sub-
component of a regional and/or global control system designed to cooperatively
control
a regional and/or global process. For instance, a modular control system may
be
designed such that control modules interactively control various sub-
components of a
system, while providing for inter-modular communications as needed for
regional
and/or global control.
[0165] The control system generally comprises one or more central, networked
and/or
distributed processors, one or more inputs for receiving current sensed
characteristics
from the various sensing elements, and one or more outputs for communicating
new or
updated control parameters to the various response elements. The one or more
computing platforms of the control system may also comprise one or more local
and/or
remote computer readable media (e.g. ROM, RAM, removable media, local and/or
network access media, etc.) for storing therein various predetermined and/or
readjusted
control parameters, set or preferred system and process characteristic
operating ranges,
system monitoring and control software, operational data, and the like.
Optionally, the
computing platforms may also have access, either directly or via various data
storage
devices, to process simulation data and/or system parameter optimization and
modeling
means. Also, the computing platforms may be equipped with one or more optional
graphical user interfaces and input peripherals for providing managerial
access to the
control system (system upgrades, maintenance, modification, adaptation to new
system
modules and/or equipment, etc.), as well as various optional output
peripherals for
communicating data and information with external sources (e.g. modem, network
connection, printer, etc.).
[0166] The processing system and any one of the sub-processing systems can
comprise
exclusively hardware or any combination of hardware and software. Any of the
sub-
processing systems can comprise any combination of none or more proportional
(P),
integral (I) or differential (D) controllers, for example, a P-controller, an
I-controller, a
PI-controller, a PD controller, a PID controller etc. It will be apparent to a
person skilled
in the art that the ideal choice of combinations of P, I, and D controllers
depends on the
dynamics and delay time of the part of the reaction process of the
gasification system
and the range of operating conditions that the combination is intended to
control, and
the dynamics and delay time of the combination controller. It will be apparent
to a
42
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
person skilled in the art that these combinations can be implemented in an
analog
hardwired form which can continuously monitor, via sensing elements, the value
of a
characteristic and compare it with a specified value to influence a respective
control
element to make an adequate adjustment, via response elements, to reduce the
difference between the observed and the specified value. It will further be
apparent to a
person skilled in the art that the combinations can be implemented in a mixed
digital
hardware software environment. Relevant effects of the additionally
discretionary
sampling, data acquisition, and digital processing are well known to a person
skilled in
the art. P, I, D combination control can be implemented in feed forward and
feedback
control schemes.
[0167] In corrective, or feedback, control the value of a control parameter or
control
variable, monitored via an appropriate sensing element, is compared to a
specified value
or range. A control signal is determined based on the deviation between the
two values
and provided to a control element in order to reduce the deviation. It will be
appreciated
that a conventional feedback or responsive control system may further be
adapted to
comprise an adaptive and/or predictive component, wherein response to a given
condition may be tailored in accordance with modeled and/or previously
monitored
reactions to provide a reactive response to a sensed characteristic while
limiting
potential overshoots in compensatory action. For instance, acquired and/or
historical
data provided for a given system configuration may be used cooperatively to
adjust a
response to a system and/or process characteristic being sensed to be within a
given
range from an optimal value for which previous responses have been monitored
and
adjusted to provide a desired result. Such adaptive and/or predictive control
schemes are
well known in the art, and as such, are not considered to depart from the
general scope
and nature of the present disclosure.
[0168] Sensing elements contemplated within the present context, as defined
and
described above, can include, but are not limited to, temperature sensing
elements,
position sensors, proximity sensors, pile height sensors and means for
monitoring gas.
[0169] In one embodiment, the gasifier comprises a temperature sensor array of
one or
more removable thermocouples. The thermocouples can be strategically placed to
monitor temperature at various points within each processing region of the
gasifier.
43
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
[0170] Appropriate thermocouples are known in the art and include bare wire
thermocouples, surface probes, thermocouple probes including grounded
thermocouples,
ungrounded thermocouples and exposed thermocouples or combinations thereof.
[0171] In one embodiment of the invention, individual thermocouples are
inserted into
the chamber via a sealed end tube (thermowell) which is then sealed to the
vessel shell,
allowing for the use of flexible wire thermocouples which are procured to be
longer than
the sealing tube so that the junction (the temperature sensing point) of the
thermocouple
is pressed against the end of the sealed tube to assure accurate and quick
response to
temperature change. Optionally, to prevent material from getting blocked by
the
thermocouple tube the end of the sealed tube cap can be fitted with a
deflector. In one
embodiment, the deflector is a square flat plate, with bent corners that
contact the
refractory and are in-line with reactant material flow to slip-stream
particles over the
thermowell.
[0172] In addition, the invention may comprise devices for monitoring the exit
of
product gas. These may include but are not limited to gas composition monitors
and gas
flow meters. For example, as depicted in Figure 30, a gas analyser is provided
downstream from the gasifier enabling analysis of the product gas, in this
embodiment
before homogenization for downstream use, in order to regulate various aspects
of the
gasification process. For example, when it is determined that the carbon
content of the
product gas is insufficient, an increase in the high carbon fee rate (e.g.
plastics in
feedstock input), when available, is increased accordingly. In another
example, when
the heating value of the product gas (e.g. high heating value, low heating
value) is
determined to be too low, the feed rate and additive input ratio may be
adjusted, or
again, the high carbon feed rate to MSW feed rate adjusted.
[0173] Similarly, a gas flow or pressure monitor may be used in an embodiment
where a
selected downstream application is adversely affected by variations and/or
absolute
fluctuations in gas flow/pressure. In response to a sensed variation in
product gas
pressure, for example, additive input feed rates may be adjusted, thereby
adjusting the
gas output of the gasifier. In response to such adjustment, other process
characteristics,
such as feedstock input rate, HCF input rate, process temperature, etc. may
also be
44
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
adjusted to rebalance the process and substantially maintain desired output
characteristics.
[0174] Furthermore, by measuring process temperatures throughout the material
pile,
gas phase temperatures above the pile, and by measuring resultant off-gas
flowrate and
analyzing off-gas composition, the amount of air injected can be optimized to
maximize
efficiency and minimize undesirable process characteristics and products
including
slagging of ash, combustion, poor off-gas heating value, excessive particulate
matter
and dioxin/furan formation thereby meeting or bettering local emission
standards. Such
measurements can be taken during initial start-up or initial testing of the
gasifier,
periodically or continually during operation of the gasifier and may
optionally be taken
in real time.
[0175] In one embodiment of the invention, the gasifier can optionally
comprise a
pressure sensor or monitor within the gasifier.
[0176] The gasifier can further comprise level switches or monitors to assess
pile
height. Appropriate level switches, sensors and monitors are known in the art.
In one
embodiment of the invention, the level instrumentation comprises point-source
level
switches. In one embodiment of the invention, the level switches are microwave
devices
with an emitter on one side of the processing chamber and a receiver on the
other side,
which detects either presence or absence of solid material at that point
inside the
processing chamber.
[0177] A worker skilled in the art would readily be able to determine the
appropriate
placement of level switches, sensors and monitors such that the desired
reactant material
pile profile can be obtained. In one embodiment, the gasifier further
comprises
proximity or position sensors.
[0178] Response elements contemplated within the present context, as defined
and
described above, can include, but are not limited to, various control elements
operatively coupled to process-related devices configured to affect a given
process by
adjustment of a given control parameter related thereto. For instance, process
devices
operable within the present context via one or more response elements, may
include, but
are not limited to elements controlling chamber heating, elements controlling
the input
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
of additives, feedstocks and other process constituents, and elements of the
material
displacement control module, to name a few.
[0179] The material displacement control module may be used in such
embodiments to
regulate the pile height inside a given chamber of the gasifier. Low levels of
the
feedstock pile can result in fluidization of the reactant material from
injection of pre-
heated air while high levels of the feedstock pile can result in poor
temperature
distribution through the reactant material pile due to restricted airflow.
Therefore, a
level control system with the use of a series of level switches may be used to
maintain
stable pile height inside the gasifier. Maintaining stable level also
maintains consistent
residence time in the gasifier.
[0180] The material displacement control module may be used as necessary to
ensure
that pile height is controlled at the desired level. To accomplish this in
embodiments in
which the material displacement control module comprise pusher rams, the
pusher rams
move in a series of programmed step of which there may exist a number of
control
parameters that may include, but are not limited to: specific movement
sequence, speed,
distance, and sequence frequency.
[0181] In some embodiments, the pusher rams move out to a set point distance,
or until
a controlling level switch is tripped; either at the same time or in a pre-
determined
sequence. The level switch control action can be based on a single switch,
tripping
either empty or full, or may require multiple switches tripping, empty or
full, or any
combination thereof. Afterwards, the pusher rams move back to end the cycle,
and the
process is repeated. There is an optional delay between cycles as required by
the
process and residence time requirements of the gasifier.
[0182] In one embodiment of the invention where the material displacement
control
module comprises an array of pusher rams in each processing chamber, the
height of the
reactant material pile in the processing chamber is a function of the input
feed-rate and
the pusher ram motion. Optionally, one processing chamber has three processing
regions
and the material displacement control module has three pusher rams with one
pusher
ram dedicated to each of the three processing regions for the movement of
reactant
material/residue out of that processing region. The third pusher ram
controlling the
movement of the residue out of the third processing region of the processing
chamber
46
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
sets the throughput by moving at a fixed stroke length and frequency to
discharge the
residue out of the processing chamber. The second pusher ram follows and moves
as far
as necessary to push reactant material onto the third processing region and
change the
third processing region's start-of-stage level switch state to "full". The
first pusher ram
follows and moves as far as necessary to push reactant material onto the
second
processing region and change the second processing region's start-of-stage
level switch
state to "full". All three pusher rams are then withdrawn simultaneously, and
a
scheduled delay is executed before the entire sequence is repeated. Additional
configuration may be used to limit the change in consecutive stroke lengths to
less than
that called for by the level switches to avoid excess ram-induced
disturbances. The
pusher rams will always need to be moved fairly frequently in order to prevent
over-
temperature conditions at the bottom of the processing chamber.
[0183] A worker skilled in the art will readily understand that the same
pusher ram
sequence mentioned above is applicable also when the three processing regions
are
distributed across three processing chambers with one pusher ram per
processing region.
Appropriate pusher ram sequences can be readily developed for different
embodiments
of the gasifier and are considered to be within the scope of this invention.
[0184] As with controlled pusher ram sequences between processing regions
and/or
chambers, different material movement units (e.g. mechanisms, devices, etc.)
may also
be used in a given sequence and/or according to control parameters of the
material
movement control module at least partially influenced by pile height readings.
For
example, rotary arm configurations controlling movement of material between
distinct
chambers may be used in step to adjust pile heights within respective
processing
regions, as can others of the above examples, as will be apparent to the
person of skill in
the art. The control system may be further configured to assess optimal
processing
characteristics, taking into account optimal residence times of material
within each
region, pile height restrictions and favourable conditions, as well as other
characteristics
as described herein for a given process result.
[0185] Optionally, the control system may further provide for the control of
temperature
within the gasifier. For example, to promote optimisation of the conversion
efficiency,
the feedstock should be kept at as high a temperature as possible, for as long
as
47
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
possible. However, at very high temperatures, the material begins to melt and
agglomerate forming `clinkers' which affects the gasification performance in
multiple
ways: (1) it reduces the available surface area and hence the conversion
efficiency; (2) it
causes the airflow in the reactant material pile to divert around the chunks
of
agglomeration, aggravating the temperature issues and further accelerating the
agglomeration process; (3) it interferes with the normal operation of the
material
displacement control module; and (4) it can jam the residue removal mechanisms
thus
potentially causing a system shut down.
[0186] In order to get the best possible conversion efficiency, the
temperatures in the
gasifier and temperature distribution through the pile can be stabilized and
controlled.
Stable temperature distribution throughout the reactant material pile may also
be used to
prevent a second kind of agglomeration, in which plastic melts and acts as a
binder for
the rest of the reactant material.
[0187] In one embodiment, temperature control within the pile is achieved by
changing
the flow of process air into a given region (ie. more or less combustion). For
example,
the process air flow provided to each processing region in the gasifier may be
adjusted
by the control system to stabilize temperatures at that region. Temperature
control
utilizing displacement units may also be used to break up hot spots and to
avoid
bridging.
[0188] In one embodiment, the air flow at each processing region is pre-set to
maintain
substantially constant temperature ranges and ratios between processing
regions.
Alternatively, air input ratios may be varied dynamically to adjust
temperatures and
processes occurring within each processing region of the gasifier and/or
within the GRS.
[0189] The means for controlling the reaction conditions to manage the
chemistry and
energetics of the gasification of a feedstock comprise a main integrated
processor and a
series of sensors for monitoring the state of the system and control systems
for
controlling various operational parameters, for example, the rate of addition
of
feedstock and/or additives, as well as operating conditions, such as pressure
in the
processing chamber. The main integrated processor receives data obtained from
sensors
relating to current states of the gasification reaction, and processes these
data to
generate an appropriate set of output instructions to manage the chemistry and
48
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
energetics of the conversion reaction, whereby the optimal reaction set point
is
maintained.
[0190] In response to the information input, the conditions within the
gasifier can be
adjusted either manually or automatically. The gasifier can be regulated by a
series of
on/off switches and instruments. The computation means can optionally include
various
output means. Different types of control schemes, outlined below, can be used.
a) Fuzzy logic control and other types of control:
[0191] Fuzzy logic control as well as other types of control can equally be
used in feed
forward and feedback control schemes. These types of control can substantially
deviate
from classical P, I, D combination control in the ways the reaction dynamics
are
modeled and simulated to predict how to change input variables or input
parameters to
affect a desired outcome. Fuzzy logic control usually only requires a vague or
empirical
description of the reaction dynamics (in general the system dynamics) or the
operating
conditions of the system. Aspects and implementation considerations of fuzzy
logic and
other types of control are well known to a person skilled in the art.
b) Feed-forward control:
[0192] Feed forward control processes input parameters to influence, without
monitoring, control variables and control parameters. A gasification facility
can use feed
forward control for a number of control parameters such as the amount of power
supplied to one of the one or more plasma torches in the gas reformulating
chamber
(GRS). The power output of the arcs of plasma torches can be controlled in a
variety of
different ways, for example, by pulse modulating the electrical current which
is supplied
to the torch to maintain the arc, varying the distance between the electrodes,
limiting the
torch current, or affecting the composition, orientation or position of the
plasma.
[0193] The rate of supply of additives to the gasifiers and/or the gas
reformulator in a
gaseous or liquid form or a pulverized form which can be sprayed or otherwise
injected
via nozzles, can be controlled with certain control elements in a feed forward
way.
Effective control of an additive's temperature or pressure, however, may
require
monitoring and closed loop feed back control.
49
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
c) Feed-back control:
[0194] In feedback control the value of a control parameter or control
variable is
compared to a desired value. A control signal is determined based on the
deviation
between the two values and provided to a control element in order to reduce
the
deviation. For example, when the output gas exceeds a predetermined H2:CO
ratio, a
feedback control system can determine an appropriate adjustment to one of the
input
variables, such as increasing the amount of additive air to return the H2:CO
ratio to the
desired value. The delay time to affect a change to a control parameter or
control
variable is sometime called loop time. The loop time, for example, to adjust
the power
of the plasma arc, air or steam flow rate, can amount to 30 to 60 seconds.
[0195] Feed back control may be used for all control variables and control
parameters
which use direct monitoring or where a model prediction is satisfactory. There
are a
number of control variables and control parameters of the gasifier that lend
themselves
towards use in a feedback control scheme. Feedback schemes can be effectively
implemented in aspects of the control system for those control variables or
control
parameters which can be directly sensed and controlled and whose control does
not, for
practical purposes, depend upon other control variables or control parameters.
Modularity of the System
[0196] Modulated plants are facilities where each function block is pre-built
components. This allows for the components to be built in a factory setting
and then
sent out to the facility site. These components (or modules) include all the
equipment
and controls to be functional and are tested before leaving the factory.
Modules are
often built with a steel frame and generally incorporate a variety of possible
sections,
such as: Gasifier Block, Gas Conditioning System Block, Power Block, etc. Once
on-
site, these modules would only need to be connected to other modules and the
control
system to be ready for plant's commissioning. This design allows for shorter
construction time and economic savings due to reduced on-site construction
costs.
[0197] There are different types of modular plants set-ups. Larger modular
plants
incorporate a'backbone' piping design where most of the piping is bundled
together to
allow for smaller footprint. Modules can also be placed in series or parallel
in an
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
operation standpoint. Here similar tasked equipment can share the load or
successively
provide processing to the product stream.
[0198] One possible application of modular design in this technology is it
allows more
options in the gasification of multiple wastes. This technology can allow for
multiple
gasifiers to be used in a single high-capacity facility. This would allow the
option of
having each gasifier co-process wastes together or separately; the
configuration can be
optimized depending on the wastes.
[0199] If an expansion is required due to increasing loads, a modular design
allows this
technology to replace or add modules to the plant to increase its capacity,
rather then
building a second plant. Modules and modular plants can be relocated to other
sites
where they can be quickly integrated into a new location.
Function Block Combination
[0200] It is possible to combine the functions of different gasification
trains (series of
equipment) so that common functions can be carried out in function blocks that
take in
gases or material from more than one stream. The following diagrams
demonstrate this
concept as applied to carbonaceous feedstock gasification.
[0201] In these embodiments there are two trains shown although this set-up of
combined functions between trains can occur for any number of trains and for
any
feedstock per train (even if one train has a combined feedstock). Once a
stream has been
combined one may still choose parallel handling equipment downstream; the
parallel
streams do not need to be of the same size even if handling the same gases.
[0202] For the following description, GCS refers to the gas conditioning
system
mentioned above and the numbers represent the following systems
1. Gasifier
2. Residue Conditioning System
3. Gas Reformulating System
[0203] None Combined, Figure 31
51
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
In this embodiment there are two separate systems that can have the gas
streams
mixed for downstream system; like the homogenization tank or engines.
[0204] GCS Combined
In this embodiment the gases from function blocks 2 & 3 from each train are
fed
together into a single GCS which has been sized appropriately for the gas
flow.
[0205] Function 2 Combined, Figure 32
In this embodiment the trains differ only in function block 1, with all other
functions being handled by the same combined train of equipment.
[0206] Function 3 Combined, Figure 33
In this embodiment gases from function blocks 1 go to a combined function
block
3; which is sized appropriately.
[0207] Function 2 & 3 Combined, Figure 34
In this embodiment gases from function blocks 1 go to a combined 2 and
material
from function block 1 go to a combined function block 3; which are sized
appropriately. Gases from combined function blocks 2 & 3 then travel to a
combined GCS.
[0208] A worker skilled in the art will readily understand that while in the
above section
we have mentioned the gasification system as comprising of the function blocks
1, 2 &
3 and the GCS, it can be further subdivided into other smaller function
blocks. For
example, the function block 1, 2 & 3 could represent the drying region,
volatilization
region and the carbon conversion region respectively such that a single
gasifier can be
formed by the combination of these function blocks. A worker skilled in the
art will
readily appreciate that for each designation of function blocks, the trains
can be
combined in a larger family of schemes depending on where the combination of
the
trains is effected.
[0209] The disclosure of all patents, publications, including published patent
applications, and database entries referenced in this specification are
specifically
52
CA 02654367 2008-12-04
WO 2007/143673 PCT/US2007/070456
incorporated by reference in their entirety to the same extent as if each such
individual
patent, publication, and database entry were specifically and individually
indicated to be
incorporated by reference.
[0210] The embodiments of the invention being thus described, it will be
obvious that
the same may be varied in many ways. Such variations are not to be regarded as
a
departure from the spirit and scope of the invention, and all such
modifications as would
be obvious to one skilled in the art are intended to be included within the
scope of the
following claims.
53
