Note: Descriptions are shown in the official language in which they were submitted.
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A RESIDUE CONDITIONING SYSTEM
FIELD OF THE INVENTION
The present invention relates to systems for converting waste residue
materials to an inert
slag, and in particular to systems for the plasma assisted conversion of
residual materials
to an inert slag and a gas having a heating value.
BACKGROUND OF THE INVENTION
Gasification is a process that enables the conversion of carbonaceous
feedstock, such as
municipal solid waste (MSW) or coal, into a combustible gas. The gas can be
used to
generate electricity, steam or as a basic raw material to produce chemicals
and liquid
fuels.
Possible uses for the gas 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
fertilizers; the
extraction of both hydrogen and carbon monoxide as discrete industrial fuel
gases; and
other industrial applications.
Generally, the gasification process consists of feeding carbonaceous feedstock
into a
heated chamber (the gasifier) along with a controlled and/or limited amount of
oxygen
and optionally steam. In contrast to incineration or combustion, which operate
with
excess oxygen to produce CO?, H2O, SOX, and NOx, gasification processes
produce a raw
gas composition comprising CO, H2, H2S, and NH3. After clean-up, the primary
gasification products of interest are H2 and CO.
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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 H2O, H2, N2, 02, CO,, CO, CH4, H2S, NH3, C2H6,
unsaturated
hydrocarbons such as acetylenes, olefins, aromatics, tars, hydrocarbon liquids
(oils) and
char (carbon black and ash).
As the feedstock is heated, water is the first constituent to evolve. As the
temperature of
the dry feedstock increases, pyrolysis takes place. During pyrolysis the
feedstock is
thermally decomposed to release tars, phenols, and light volatile hydrocarbon
gases while
the feedstock is converted to char.
Char comprises the residual solids consisting of organic and inorganic
materials. After
pyrolysis, the char has a higher concentration of carbon than the dry
feedstock and may
serve as a source of activated carbon. In gasifiers operating at a high
temperature ( >
1,200 C) or in systems with a high temperature zone, inorganic mineral matter
is fused
or vitrified to form a molten glass-like substance called slag.
Since the slag is in a fused, vitrified state, it 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. It is becoming less desirable to dispose of
waste material
by incineration because of the extreme waste of fuel in the heating process
and the further
waste of disposing, as a residual waste, material that can be converted into a
useful
syngas and solid material.
The means of accomplishing a gasification process 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 design 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;
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residence time; the plant configuration including whether it employs a dry or
slurry feed
system, the feedstock-reactant flow geometry, the design of the dry ash or
slag mineral
removal system; whether it uses a direct or indirect heat generation and
transfer 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.
There are a number of systems that have been proposed for capturing heat
produced by
the gasification process and utilizing such heat to generate electricity,
generally known as
combined cycle systems.
The energy in the product gas coupled with substantial amounts of recoverable
sensible
heat produced by the process and throughout the gasification system can
generally
produce sufficient electricity to drive the process, thereby alleviating the
expense of local
electricity consumption. The amount of electrical power that is required to
gasify a ton of
a carbonaceous feedstock depends directly upon the chemical composition of the
feedstock.
If the gas generated in the gasification process 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. Some
gasification facilities employ technologies to convert the raw off-gas or the
raw syngas to
a more refined gas composition prior to cooling and cleaning through a gas
quality
conditioning system.
Utilizing plasma heating technology to gasify a material is a technology that
has been
used commercially for many years. Plasma is a high temperature luminous gas
that is at
least partially ionized, 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
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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, a plasma is
electrically neutral.
Some gasification systems employ plasma heat to drive the gasification process
at a high
temperature and/or to refine 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 will disassociate into their constituent atoms. Many of these atoms will
react with
other input molecules to form new molecules, while others may recombine with
themselves. 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.
The very high temperatures (3000 to 7000 C) achievable with plasma heating
enable a
high temperature gasification process where virtually any input feedstock
including waste
in as-received condition, including liquids, gases, and solids in any form or
combination
can be accommodated. The plasma technology can be positioned within a primary
gasification chamber to make all the reactions happen simultaneously (high
temperature
gasification), can be positioned within the system to make them happen
sequentially (low
temperature gasification with high temperature refinement), or some
combination thereof.
The gas produced during the gasification of carbonaceous feedstock is usually
very hot
but may contain small amounts of unwanted compounds and requires further
treatment to
convert it into a useable product. Once a carbonaceous material is converted
to a gaseous
state, undesirable substances such as metals, sulfur compounds and ash may be
removed
from the gas. For example, dry filtration systems and wet scrubbers are often
used to
remove particulate matter and acid gases from the gas produced during
gasification. A
number of gasification systems have been developed which include systems to
treat the
gas produced during the gasification process.
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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.
Prior systems and processes have not adequately addressed the problems that
must be
dealt with on a continuously changing basis. Some of these types of
gasification systems
describe means for adjusting the process of generating a useful gas from the
gasification
reaction. 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.
The disposal of solid waste has become a major issue due to space limitations
for
landfills and the environmental issues that arise. Attempts have been made to
reduce the
volume and recover the energy content of municipal solid waste (MSW) and other
waste
through various methods. These methods include incineration in which excess 02
is
added to the input waste so that at low temperature it burns. The result is
heat and an
exhaust of C02, H2O and other products of combustion or partial combustion. In
incineration, as much as 30% of the processed solid waste remains as a solid
hazardous
waste, ash.
Waste materials such as ash and slag are typically discarded in landfills,
however, there is
increasing public concern about gaseous emissions from landfills and the
possibility of
contamination of groundwater. Alternatively, these waste by-products may be
processed
into cost effective commercial materials and used in many downstream
applications, such
as sandpaper, glass wool, asphalt, cinder or building blocks, and glass tiles.
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U.S. Patent No. 5,280,757 describes the use of a plasma arc torch in a reactor
vessel to
gasify municipal solid waste. A product having a medium quality gas and a slag
with a
lower toxic element leachability is thereby produced.
United States Patent No 5,666,891 describes an are plasma-melter electro
conversion
system for waste treatment and resource recovery. The gas may be utilized in a
combustion process to generate electricity and the solid product can be
suitable for
various commercial applications. The apparatus may additionally be employed
without
further use of the gases generated by the conversion process.
Accordingly, there remains a need in the art for a system for converting the
by-products
of carbonaceous feedstock gasification or incineration processes, into a safe,
stable form
for commercial use or which does not require special hazardous waste
considerations for
disposal, while also maximizing the recovery of gases having heating value.
SUMMARY OF THE INVENTION
This invention provides a system for the conversion of residual matter of a
carbonaceous
feedstock gasification or incineration process into an inert slag product and
a gas having a
heating value. In particular, the system comprises a refractory-lined residue
conditioning
chamber comprising a residue inlet, a gas outlet, a slag outlet, a plasma heat
source port,
and a control system for monitoring operating parameters and adjusting
operating
conditions within the conversion system to optimize the conversion reaction.
The plasma
heat causes the residue to melt, and converts carbon present in the residue to
a residue
gas, which exits the chamber through the gas outlet, and optionally into a gas
conditioning subsystem for cooling and conditioning as required for downstream
considerations.
The chamber may also optionally comprise one or more inlets for introducing
air (or
other oxygen containing additives) into the residue conditioning chamber to
control the
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conditioning process. The chamber may also optionally comprise one or more
additive
inlets for introducing additives to control the composition of the resulting
slag product.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only, by
reference to the attached Figures, wherein:
Figure 1 is a block flow diagram showing the inputs and outputs of a residue
conditioning
system of the present invention;
Figure 2 is a block flow diagram showing the inputs, optional inputs and
outputs of a
residue conditioning system of the present invention;
Figure 3 is a schematic representation of a typical residue conditioning
chamber in
accordance with the present invention;
Figure 4A illustrates a perspective view of one embodiment of a residue
conditioning
chamber;
Figure 4B is a cross-sectional view of the embodiment of Figure 4A;
Figure 5A is a schematic depiction of a residue conditioning chamber in
indirect
communication with two residue sources, in accordance with one embodiment of
the
present invention;
Figure 5B is a schematic depiction of a residue conditioning chamber in
indirect
communication with one residue source, in accordance with one embodiment of
the
present invention;
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Figure 6 illustrates a cross-sectional view of one embodiment of a residue
conditioning
chamber integrated with a residue conditioning chamber;
Figure 7 is a partial cross-sectional view of an S-spout type slag outlet, in
accordance
with one embodiment of the present invention;
Figure 8 is a partial cross-sectional view of a tiltable slag crucible in a
residue
conditioning chamber in accordance with one embodiment of the present
invention;
Figure 9 is a partial cross-sectional view of one embodiment of a slag outlet,
in
accordance with the present invention;
Figure 10 is a partial cross-sectional view of one embodiment of a slag
outlet, in
accordance with the present invention;
Figure 11 is a partial cross-sectional view of one embodiment of a slag
outlet, in
accordance with the present invention;
Figure 12 is a partial cross-sectional view of one embodiment of a slag
outlet, in
accordance with the present invention;
Figure 13 illustrates one embodiment of a residue conditioning chamber in
relation to a
gasifier and baghouse, in accordance with one embodiment of the present
invention;
Figure 14 is a cross-sectional view of one embodiment of a residue
conditioning
chamber, in accordance with one embodiment of the present invention;
Figure 15 is a perspective view of one embodiment of a residue conditioning
chamber, in
accordance with one embodiment of the present invention;
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Figure 16 is a cross-sectional view of one embodiment of a residue
conditioning chamber
in relation to a slag cooling subsystem, in accordance with one embodiment of
the
present invention;
Figure 17 is a perspective view of one embodiment of a residue conditioning
chamber in
relation to a residue gas conditioning subsystem, in accordance with one
embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
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.
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,
aluminum,
iron and calcium oxides, as well as a proportion of unreacted 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 quality 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.
As used herein, the term (carbonaceous) feedstock can be any carbonaceous
material
appropriate for gasifying in the present gasification process, and can
include, but is not
limited to, any waste materials, coal (including low grade, high sulfur coal
not suitable
for use in coal-fired power generators), petroleum coke, heavy oils, biomass,
sewage
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sludge, sludge from pulp and paper mills and agricultural wastes. Waste
materials
suitable for gasification include both hazardous and non-hazardous wastes,
such as
municipal waste, wastes produced by industrial activity (paint sludges, off-
spec paint
products, spent sorbents), automobile fluff, used tires and biomedical wastes,
any
carbonaceous material inappropriate for recycling, including non-recyclable
plastics,
sewage sludge, coal, heavy oils, petroleum coke, heavy refinery residuals,
refinery
wastes, hydrocarbon contaminated solid waste and biomass, agricultural wastes,
tires,
hazardous waste, industrial waste and biomass. Examples of biomass useful for
gasification include, but are not limited to, waste or fresh wood, remains
from fruit,
vegetable and grain processing, paper mill residues, straw, grass, and manure
"Residue conditioning" means the conversion of a residue to a vitrified,
homogenous slag
exhibiting low leachability and a gas having a heating value, wherein the
residue is a
residual material produced during processes related to the gasification or
incineration of
carbonaceous feedstocks, as defined above.
"Residue gas" refers to the gases produced during the residue conditioning
process.
As used herein, 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
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identified herein as sensing elements should not be limited and/or
inappropriately
construed in light of these examples.
As used herein, 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 feedstrock 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.
Overview of the Residue Conditioning System
This invention provides a system for the conversion of a residue into a
vitrified substance
and a residue gas having a heating value, wherein the residue is obtained from
one or
more sources generated from a gasification system or an incineration system.
The system
comprises a refractory-lined residue conditioning chamber comprising: a
residue inlet, a
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residue gas outlet, a slag outlet, and one or more ports for heating devices
such as a
plasma torch; and a control subsystem for monitoring operating parameters and
adjusting
operating conditions within the system to optimize the conversion reaction.
Sensing
elements and response elements are integrated within the system, and the
response
elements adjust the operating conditions within the system according to the
data obtained
from the sensing elements.
Figure 1 is a schematic depiction of the representative residue conditioning
system, in
accordance with one embodiment of the present invention. The residue
conditioning
system 4000 comprises residue inputs 4010 into a residue conditioning chamber
4020,
where plasma heat inputs 4030 convert the residue into a molten slag material
4041 and a
residue gas product 4051. The molten slag material 4041 is output from the
residue
conditioning chamber 4020 and passed into an optional slag cooling subsystem
4040 for
cooling. The residue gas 4051 is output from the chamber 4020 and is
optionally passed
into a gas conditioning subsystem 4050 for cooling and cleaning.
Figure 2 is a schematic depiction of the representative inputs and outputs of
a typical
residue conditioning system, including optional inputs, in accordance with one
embodiment of the present invention. The residue conditioning system comprises
residue
inputs that include a residue product 4013 of a carbonaceous feedstock
gasifier 2000 or a
residue product 4913 of a carbonaceous feedstock incinerator 4900 and an
optional
secondary residue product 4019 obtained from a particulate matter separation
apparatus
(e.g., a baghouse filter or cyclone) of a gas conditioning subsystem. These
two residues
are passed, along with an optional solid process additive 4035 into a residue
conditioning
chamber 4020, where plasma heat inputs 4030 with optional air additives 4031
and/or
steam additives 4033 convert the residue into a molten slag material 4041 and
a residue
gas 4051. The molten slag material 4051 is output from the residue
conditioning
chamber 4020 and passed into a slag cooling subsystem 4040 for cooling. The
residue
gas 4051 is output from the chamber 4020 and passed through residue gas
conditioning
subsystem 4050.
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The present system is suitable for conditioning residue that is, for example,
the residual
by-products of a carbonaceous feedstock gasification process, or the solids
collected in
gas conditioning and/or cleanup systems. The residue may also come in the form
of
incinerator bottom ash and fly ash collected in an incinerator's pollution
abatement suite.
The residue conditioning process is accomplished by raising the temperature of
the
residue to the level required to melt the residue to form a vitreous material
that cools to a
dense solid. The high temperature also converts carbon in the residue to a
residue gas
having a heating value. The residue gas produced in the conditioning process
exits the
chamber via a gas outlet. The gaseous product at this stage typically
comprises heavy
metal and particulate contaminants. Accordingly, the system optionally
comprises a gas
conditioning subsystem for cooling and conditioning the residue gas as
required for
downstream applications.
According to the present invention, the heat required to condition the residue
is provided
by one or more plasma heat sources. Additional or supplemental heating as may
be
required can be provided by one or more heating means known in the art
including
induction heating, joule heating, or a gas burner. Additional heat may also be
provided
by injecting oxygen or air into the conditioning chamber where the oxygen will
react
exothermically with carbon and volatiles present in the residue.
The present invention also provides for the addition of air and/or steam as
optional
gaseous process additives to facilitate the conversion of the carbon to
residue gas having
a heating value.
The source of the residue may be, but is not limited to, a low temperature or
high
temperature gasifier, an incinerator, a hopper in which the residue is stored,
or particulate
matter separators within a gas conditioning system, for example, a baghouse
filter or
cyclone. The residue conditioning chamber may be directly or indirectly
connected to the
source of the residue to be conditioned. The residue is conveyed, continuously
or
intermittently, from the source of the residue through appropriately adapted
outlets and/or
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conveyance means to the residue inlet of the chamber, as would be known to the
skilled
worker, according to the requirements of the system and the type of by-product
to be
removed.
The molten slag, at a temperature of, for example, about 1200 C to about 1800
C, may
periodically or continuously be output from the residue chamber and thereafter
cooled to
fonn a solid slag material. Such slag material may be intended for landfill
disposal or
may further be broken into aggregates for conventional uses. Alternatively,
the molten
slag can be poured into containers to form ingots, bricks tiles or similar
construction
material. The resulting slag material may also be used as a supplementary
cementing
material in concrete, in the production of a lightweight aggregate or mineral
wool, in the
manufacture of foam glass, or in the development of packaging materials. The
composition of the resulting slag material may be controlled through the
addition of
process additives to change melting point and/or other properties of the slag.
Such solid
process additives may include, but are not limited to silica, alumina, lime or
iron.
Accordingly, the present invention also includes a subsystem for cooling the
molten slag
to its solid form. The slag cooling subsystem is provided as appropriate to
afford the
cooled slag product in the desired format.
The present invention also provides a control system for managing the residue
conditioning process. In particular, the residue conditioning system comprises
a control
subsystem comprising sensing elements for monitoring operating parameters of
the
residue conditioning system, and response elements for adjusting operating
conditions
within the residue conditioning system to manage the conversion process,
wherein the
response elements adjust the operating conditions within the system according
to the data
obtained from the sensing elements, thereby promoting efficient and complete
melting.
The adjustable operating parameters include, for example, plasma heat rate
(power) and
position, residue feed rate, air and/or steam inputs and system pressure.
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Residue Conditioning Chamber
The residue conditioning system of the present invention comprises a residue
conditioning chamber which is adapted to i) input the residue to be
conditioned, ii) input
heat and condition the residue to form a molten slag material and a gaseous
product
having a heating value, and iii) output the molten slag and gaseous product.
Accordingly,
the residue conditioning chamber is a refractory-lined chamber comprising a
residue
inlet, a gas outlet, a slag outlet, and a plasma heat source port. The residue
conditioning
chamber further optionally includes one or more air and/or steam inlets.
The residue conditioning chamber is designed to ensure that the residue
conditioning
process is carried out efficiently and completely, in order to use a minimum
amount of
energy to effect complete conditioning of the residue. Accordingly, factors
such as
efficient heat transfer, adequate heat temperatures, residence time, molten
slag flow,
input residue volume and composition, and size and insulation of the chamber
are taken
into account when designing the residue conditioning chamber. The chamber is
also
designed to ensure that the residue conditioning process is carried out in a
safe manner.
Accordingly, the system is designed to isolate the residue conditioning
environment from
the external environment.
The residue conditioning chamber is provided with a plasma heat source that
meets the
required temperature for heating the residue to levels required to convert any
remaining
volatiles and carbon to a gaseous product having a heating value and to melt
and
homogenize the residue to provide a molten slag at a temperature sufficient to
flow out of
the chamber. The chamber is also designed to ensure highly efficient heat
transfer
between the plasma gases and the residue, to minimize the amount of sensible
heat that is
lost via the product gas. Therefore, the type of plasma heat source used, as
well as the
position and orientation, of the plasma heating means are additional factors
to be
considered in the design of the residue conditioning chamber.
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The residue conditioning chamber is also designed to ensure that the residue
residence
time is sufficient to bring the residue up to an adequate temperature for
melting and
homogenization, and to fully convert the carbon to the gaseous product.
Accordingly, the
chamber is provided with a reservoir in which the residue accumulates while
being
heated by the plasma heat source. The reservoir also allows mixing of the
solid and
molten materials during the conditioning process. Sufficient residence time
and adequate
mixing ensures that the conditioning process is completely carried out, and
that the
resulting slag and gaseous products have the desired composition.
The chamber is designed for continuous or intermittent output of the molten
slag
material. Continuous slag removal allows the conditioning process to be
carried out on a
continual basis, wherein the residue to be conditioned may be continuously
input and
processed by the plasma heat, without interruption for periodic slag removal.
In one embodiment, continuous slag exhaust is achieved by using a reservoir
bounded on
one side by a weir that allows the slag pool to accumulate until it exceeds a
certain level,
at which point the molten slag runs over the weir and out of the chamber. In
the
embodiment depicted in Figure 3, the residue 4010 drops through a residue
inlet 4012
located at the top of the conditioning chamber 4020 into a reservoir 4060,
where it is
conditioned by a plasma torch plume 4036. The molten materials are held in the
reservoir 4060 by a weir 4162 until the pool 4044 reaches the top of the weir.
Thereafter,
as additional residue enters the system and is conditioned, a corresponding
amount of
molten material overflows the weir and out of the chamber through a slag
outlet 4042. A
residue gas product 4954 exits the chamber via a gas outlet 4052.
Where the residue being conditioned contains a significant amount of metal,
and the
residue conditioning chamber comprises a reservoir bounded by a weir, the
metals, due to
their higher melting temperature and density, typically accumulate in the
reservoir until
such time as they are removed. Accordingly, in one embodiment of the present
invention, the reservoir is optionally provided with a metal tap port, whereby
the tap port
is plugged with a soft refractory paste, through which a hole may be
periodically opened
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using the heat from an oxygen lance. Once the tap port has been opened and the
chamber
temperature has been raised sufficiently to melt the accumulated metals, the
molten
metals are tapped off from the bottom of the reservoir. The outlet is resealed
by placing
refractory or other suitable material into the hole.
In one embodiment, the reservoir itself may also be provided with a slag
outlet adapted
for continuous exhaust of the molten slag. In one embodiment, the reservoir
may also
provide for intermittent slag removal, wherein the reservoir is designed to
allow the
accumulation of molten materials until the conditioning process is complete,
at which
point the molten slag is exhausted. Such slag outlet design options will be
described in
more detail later.
Due to the very high temperatures needed to melt the residue, and particularly
to melt any
metals that may be present, the residue conditioning chamber wall is lined
with a
refractory material that will be subjected to very severe operational demands.
The
selection of appropriate materials for the design of a residue conditioning
chamber is
made according to a number of criteria, such as the operating temperature that
will be
achieved during typical residue conditioning processes, resistance to thermal
shock, and
resistance to abrasion and erosion/corrosion due to the molten slag and/or hot
gases that
are generated during the conditioning process.
The inner refractory is selected to provide an inner lining having very high
resistance to
corrosion and erosion, particularly at the slag waterline, in addition to
resistance to the
high operating temperatures. The porosity and slag wetability of the inner
refractory
material must be considered to ensure that the refractory material selected
will be
resistant to penetration of the molten slag into the hot face. The materials
are also
selected such that secondary reactions of the refractory material with
hydrogen are
minimized, thereby avoiding a possible loss of integrity in the refractory and
contamination of the product gas.
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The residue conditioning chamber is typically manufactured with multiple
layers of
materials as are appropriate. For example, the outer layer, or shell, of the
chamber is
typically steel. Moreover, it may be beneficial to provide one or more
insulating layers
between the inner refractory layer and the outer steel shell to reduce the
temperature of
the steel casing. Where a second layer (for example, an insulating firebrick
layer) is
provided, it may also be necessary to select a material that does not react
with hydrogen.
An insulating board around the outer surface of the slag reservoir may also be
provided to
reduce the temperature of the steel casing. When room for expansion of the
refractory
without cracking is required, a compressible material, such as a ceramic
blanket, can be
used against the steel shell. The insulating materials are selected to provide
a shell
temperature high enough to avoid acid gas condensation if such an issue is
relevant, but
not so high as to compromise the integrity of the outer shell.
The refractory material can therefore be one, or a combination of,
conventional refractory
materials known in the art which are suitable for use in a chamber for
extremely high
temperature (e.g., a temperature of about 1100 C to 1800 C) non-pressurized
reaction.
Examples of such refractory materials include, but are not limited to, high
temperature
fired ceramics (such as aluminum oxide, aluminum nitride, aluminum silicate,
boron
nitride, chromium oxide, zirconium phosphate), glass ceramics and high alumina
brick
containing principally, silica, alumina and titania.
Due to the severe operating conditions, it is anticipated that the reservoir
refractory will
require periodic maintenance. Accordingly, in one embodiment, the residue
conditioning
chamber is provided in separable upper and lower portions, wherein the chamber
lower
portion (where the reservoir is located) is removable from the chamber upper
portion. In
one embodiment, the chamber is suspended from a support structure such that
the lower
portion can be dropped away from the upper portion to facilitate maintenance.
This
embodiment provides for removing the lower portion without disturbing any
connections
between the chamber upper portion and upstream or downstream components of the
system.
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The residue conditioning chamber may also include one or more ports to
accommodate
additional structural elements or instruments that may optionally be required.
In one
embodiment, the port may be a viewport that optionally includes a closed
circuit
television to maintain operator full visibility of aspects of the residue
processing,
including monitoring of the slag outlet for formation of blockages. The
chamber may
also include service ports to allow for entry or access into the chamber for
maintenance
and repair. Such ports are known in the art and can include sealable port
holes of various
sizes.
In one embodiment, the residue conditioning chamber may be tubular in shape,
as
depicted in Figures 4A and 4B. This embodiment comprises a torch mounting port
4871,
a residue inlet 4812, a reservoir 4860 bounded on one side by a weir 4862, a
gas outlet
4852, a slag outlet 4842, a metal tap port 4849 and view ports 4878.
Residue Input
The system of the present invention comprises a residue input means in
association with
the residue inlet of the conditioning chamber. The residue inlet is adapted to
receive the
residue into the residue conditioning chamber. The residue input means conveys
the
residue from a source of the residue material to the inlet of the conditioning
chamber.
Residue material entering the chamber may come from one or multiple sources.
Sources
of the residue may include, but are not limited to, a low temperature or high
temperature
gasifier, an incinerator, a hopper in which the residue is stored, or upstream
gas
conditioning systems, for example, a baghouse filter.
Where the residue to be conditioned is provided in more than one input stream,
or from
more than one source, the different streams may each be passed into the
conditioning
chamber through a dedicated residue inlet, or they may be combined prior to
introduction
into the residue conditioning chamber. In the latter embodiment, there is
provided one
residue inlet through which all residues are provided. Accordingly, the
chamber may
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comprise a common inlet or multiple inlets to cater to any physical
characteristics of the
input residue material.
The source of the residue may be provided in direct communication with the
conditioning
chamber, i.e., each residue input is fed directly from the source into the
residue
conditioning chamber. Alternatively, the source may be provided in indirect
communication with the residue conditioning chamber, wherein the residue
inputs are
conveyed from the source into the residue conditioning chamber via a system of
conveyor means.
Where the residue conditioning chamber is indirectly connected to the source
of the
residue, the residue input means comprises one or more means for conveying the
residue
from the source into the residue conditioning chamber. For example, the
residue input
means may include a single screw conveyor or a series of screw conveyors.
In one embodiment, the residue conditioning chamber is provided to condition
the by-
products of a carbonaceous feedstock gasification process. In such an
embodiment, the
residue sources may include the gasifier, as well as the baghouse filter of
any gas
conditioning system(s) associated with the gasification process. Figure 5A is
a
schematic depiction of one embodiment of a residue conditioning chamber 4520
indirectly connected to two sources of residue to be conditioned, where one
source is a
carbonaceous feedstock gasifier 2000, and the other source is baghouse filter
6030 of a
gas conditioning subsystem. Figure 5B is a schematic depiction of one
embodiment of a
residue conditioning chamber 4620 indirectly connected to one source of
residue to be
conditioned, where the source is a carbonaceous feedstock gasifier 2000.
In embodiments wherein the residue conditioning chamber is directly connected
to the
source of the residue, the residue source and residue conditioning chamber
employed
may be the same as those of the indirectly connected embodiment, with the
exception that
the source of residue communicates directly with conditioning chamber, without
the need
for an intermediate conveying means. In this arrangement the residue passes
directly
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from the source of residue into the adjoining (and integral) residue
conditioning chamber.
In such a "contiguous" embodiment, the residue may be conveyed actively or
passively
(i.e., by gravity) from the residue source into the chamber.
In directly connected (or contiguous) embodiments where the residue is
actively
conveyed into the residue conditioning chamber, the residue input means is
typically
located within the residue source. Such conveyance means may include screw
conveyors, rotating arms, rotating chains, traveling grates and pusher rams.
Figure 6 depicts one embodiment of the present invention in which a gasifier
2800 is
provided in direct communication with a residue conditioning chamber 4820. In
this
embodiment, the residue input means comprises a series of pusher rams 2826.
The residue input means optionally include a control mechanism such that the
input rate
of the residue can be controlled to ensure optimal melting and homogenization
of the
residue material.
In one embodiment of the invention, solid process additives are added to the
residue to be
conditioned in order to adjust the composition of the slag product. These
solid process
additives may be added to the residue prior to introduction into the residue
conditioning
chamber, or they may be added directly to the residue conditioning chamber
through a
dedicated additive inlet. In one embodiment, the solid process additive is
added directly
to the conditioning chamber via a dedicated additive feed inlet. In one
embodiment, the
additive is introduced to the residue prior to introduction to the
conditioning chamber.
Where the residue conditioning system is associated with a carbonaceous
feedstock
gasification process, it is also possible to add the solid process additive to
the feedstock
prior to gasification.
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Plasma Heat
The system of the present invention employs one or more plasma heating sources
to
convert the residue material produced by the upstream processes. The plasma
heat
sources may be movable, fixed or a combination thereof.
The plasma heat sources may comprise a variety of commercially available
plasma
torches that provide suitably high flame temperatures for sustained periods at
the point of
application. In general, such plasma torches are available in sizes from about
100 kW to
over 6 MW in output power. The plasma torch can employ one or a combination of
suitable working gases. Examples of suitable working gases include, but are
not limited
to, air, argon, helium, neon, hydrogen, methane, ammonia, carbon monoxide,
oxygen,
nitrogen, and carbon dioxide. In one embodiment of the present invention, the
plasma
heating means is continuously operating so as to produce a temperature in
excess of about
900 C to about 1800 C as required for converting the residue material to the
inert slag
product.
In this respect, a number of alternative plasma technologies are suitable for
use in the
present system. For example, it is understood that transferred arc and non-
transferred arc
torches (both AC and DC), using appropriately selected electrode materials,
may be
employed. It is also understood that inductively coupled plasma torches (ICP)
may also
be employed. Selection of an appropriate plasma heat source is within the
ordinary skills
of a worker in the art.
The use of transferred arc torches instead of non-transferred arc torches may
improve the
efficiency of the residue conditioning process due to their higher electrical
to thermal
efficiency, as well as the higher heat transfer efficiency between the hot
plasma gases and
the material being melted because the arc passes directly through the melt.
Where
transferred arc torches are used, it is necessary to ensure that the
conditioning chamber is
electrically isolated since the chamber outer shell will be electrically
connected to the
power supply.
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In one embodiment, the plasma heat source is a DC non-transferred arc torch.
In one embodiment of the present invention, the one or more plasma heat
sources are
positioned to optimize the conversion of the residue material to inert slag.
The position
of the plasma heat source(s) is selected according to the design of the
residue
conditioning chamber. For example, where a single plasma heat source is
employed, the
plasma heat source may be mounted in the top of the chamber and disposed in a
position
relative to the slag pool collecting at the bottom of the chamber to ensure
sufficient heat
exposure to melt the residue material and force the slag to flow. In one
embodiment, the
plasma heat source is a plasma torch vertically mounted in the top of the
chamber.
All plasma heat sources are controllable for power and optionally (where
movable heat
sources are used) position. In one embodiment, the plasma heat rate is varied
to
accommodate varying residue input rate. The plasma heat rate can also be
varied to
accommodate varying residue melting temperature properties.
The plasma heat sources may be operated on a continuous or non-continuous
basis at the
discretion of the operator to accommodate varying residue input rate and
melting
temperature properties.
Air and Steam Inputs
The residue being conditioned will typically contain a proportion of unreacted
or
unconverted carbon. Accordingly, air and/or steam may optionally be added to
the
residue conditioning chamber to ensure complete conversion of the carbon, as
required
by the varying carbon content of the residue material being conditioned. Since
the
carbon reacts with oxygen in an exothermic reaction, air inputs may also be
used and
adjusted to maintain optimum processing temperatures while minimizing the cost
of
plasma heat required in the conditioning process. As such, the amount of air
injection is
maintained to ensure the maximum conversion of carbon to carbon monoxide with
the
minimum plasma heat requirement to carry out the process.
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If the temperature within the conditioning chamber is too high and/or the
gaseous product
of the conditioning process has a high carbon particle (soot) content, steam
can be
injected to control the temperature and/or convert the solid carbon to carbon
monoxide
and hydrogen.
The chamber, therefore, can include one or more air input ports for air
injection, and
optionally one or more steam input ports for steam injection. The air and
steam input
ports are strategically located in and around the residue conditioning chamber
to ensure
full coverage of the air and steam inputs into the chamber.
Slag Output
The system of the present invention comprises a slag output means in
association with the
conditioning chamber. The slag output means includes an outlet on the residue
conditioning chamber through which molten slag is exhausted. The outlet is
typically
located at or near the bottom of the chamber to facilitate the gravity flow of
the molten
slag pool out of the chamber. The slag output means also includes a slag
cooling
subsystem to facilitate the cooling of the molten slag to it solid form.
The molten slag can be extracted in a continuous manner throughout the full
duration of
processing. The molten slag can also be extracted from the chamber
intermittently, e.g.,
through a batch pour or periodic exhausting at the end of a processing period.
The
molten slag from either method can be cooled and collected in a variety of
ways that will
be apparent to a person skilled in the art, to form a dense, non-leachable,
solid slag. The
slag output means may further be adapted to minimize heating requirements and
to avoid
contact of the product gas with external air by keeping the residue
conditioning chamber
sealed.
According to the present invention, as the residue is conditioned by the
plasma heat, the
resulting molten slag accumulates in a reservoir.
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As discussed previously, in the embodiments of the invention depicted in
Figures 3, 4A
and 4B, the molten slag is extracted in a continuous manner, i.e., as the
volume of molten
slag in the reservoir increases, it passes over a weir and exits the
conditioning chamber
through an outlet.
In one embodiment of the residue conditioning chamber, as depicted in Figure
7, the
molten slag is exhausted through an S-trap outlet 4142. In this embodiment,
the slag
output means may optionally comprise a burner 4138 or other heating means
located at or
near the outlet 4142 in order to maintain the temperature of the molten slag
at the outlet
4142 high enough to ensure that the outlet 4142 remains open through the
complete slag
extraction period. This embodiment also ensures that the level of the slag
pool 4144 does
not go below a predetermined level, thereby keeping the melt environment
sealed to
avoid gaseous contact with the external environment.
Continuous pour embodiments are particularly suitable for systems that are
designed to
operate on a continuous basis, for example, where the residue conditioning
system is
provided in association with a continuous feedstock gasification facility.
In one embodiment, the molten slag accumulates in a reservoir until the
reservoir is
periodically emptied. In such an embodiment, the reservoir may be emptied by a
tipping
mechanism, or through an outlet in the reservoir as may be provided to
controllably
exhaust the molten slag.
Figure 8 illustrates one embodiment that may be provided to controllably
exhaust the
molten slag from a reservoir by a tipping mechanism. In this embodiment, the
residue
conditioning chamber 4320 has a tiltable crucible 4362 comprising reservoir
4360, a
spout 4342, a counterweight 4368 and a lever arm 4364 provided as a mechanism
for
tilting the crucible 4362.
Figures 9 to 12 schematically illustrate portions of different design options
that may be
provided for controlled exhaust of the molten slag through an appropriately
adapted
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outlet in the reservoir or chamber. The molten slag exhaust may be controlled
to ensure
that the level of the molten slag is not allowed to reach below the top of the
outlet, so that
gases from the external atmosphere do not enter the interior melt region.
Figure 9 depicts a reservoir or chamber having an outlet 4542 in a side wall
near the
bottom of the reservoir/chamber. The outlet 4542 is surrounded by an induction
heater
4538 enclosed in the refractory that can control the temperature of the
refractory in the
region surrounding the outlet 4542. Increasing the temperature sufficiently to
maintain
the slag in the molten state allows the slag to flow though the outlet 4542.
When the level
of the slag pool 4544 reaches the desired level, the induction heater 4538 is
turned off,
and the slag is allowed to solidify in the outlet 4542.
Figure 10 depicts one embodiment wherein the outlet 4442 is "plugged" with a
soft
refractory paste 4444. An oxygen lance 4438 is provided in a position suitable
to "burn"
a hole into the soft refractory paste 4444 allowing molten slag to pour out.
The flow is
stopped by placing refractory or other suitable material back into the outlet
4442.
Figure 11 depicts one embodiment wherein the outlet 4742 is covered by a
movable
water cooled plug 4744. The plug 4744 is movable from a closed position to an
open
position, thereby exposing the outlet 4742 to allow the molten slag to exhaust
through the
outlet 4742. The molten material should not adhere to the smooth surface of
the plug
4744 because of the water cooling effect.
Figure 12 depicts one embodiment wherein the outlet 4642 is plugged by a wedge-
type
device 4644. The "wedge" is pushed in and out of outlet 4642 as required to
control the
exhaust of the molten slag.
In one embodiment, the slag output means also comprises a slag cooling
subsystem for
cooling the molten slag to provide a solid slag product. In one embodiment,
schematically depicted in Figure 7, the molten slag is poured into a quench
water bath
4141. The water bath 4141 provides an efficient system for cooling the slag
and causing
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it to shatter into granules suitable for commercial uses, such as for the
manufacture of
concrete or for road building. The water bath 4141 may also provide a seal to
the
environment in the form of a shroud 4148 that extends from the base of the
slag chamber
down into the water bath, thereby providing a barrier preventing outside gases
from
entering the residue conditioning chamber. The solid slag product may be
removed from
the water bath 4141 by a conveyor system 4149.
In one embodiment of the slag cooling subsystem, the molten slag is dropped
into a thick
walled steel catch container for cooling. In one embodiment, the molten slag
is received
in an environmentally sealed bed of silica sand or into moulds to provide
solid slag
suitable for small scale processing or for testing certain parameters whenever
such testing
is performed. The small moulds can be control cooled in a preheated oven.
In one embodiment of the slag cooling subsystem, the molten slag is converted
to a
commercial product such as glass wool.
Where the residue conditioning system is provided to condition the residue
remaining
after the gasification of a material that contains a significant amount of
metals, such as
municipal solid waste, it is likely that a proportion of the metal will be
passed through the
gasification system and into the residue conditioning chamber. These metals
will not
necessarily melt at the normal slag vitrification temperature, therefore, the
slag reservoir
could become clogged with metal over time as it is of higher density than the
molten slag.
In order to remove accumulated metals, the chamber temperature may be
periodically
raised to melt any metals and the molten metals may be tapped off from the
bottom of the
reservoir through a metal tap port as required. Figure 4B depict one
embodiment of a
conditioning chamber comprising such a metal tap port 4849.
Residue Gas Outlet
Where the residue being conditioned contains a proportion of unreacted carbon,
a product
of the residue conditioning process will be a gas having a potentially useful
heating
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value, and may be appropriate for uses in downstream applications. This gas is
referred
to herein as "residue gas".
Gases that are produced in the residue conditioning chamber during conversion
of the
residue material to inert slag exit the chamber via a gas outlet. The residue
gas may then
be further treated in gas cooling and/or pollution abatement systems known in
the art.
Accordingly, in one embodiment of the invention, the residue gas is directed
to a system
provided for cooling and cleaning the gas, which is referred to as a "residue
gas
conditioning system". The residue gas conditioning subsystem typically
comprises
means for cooling the gas, as well as means for removing particulate matter
and heavy
metal contaminants. After the residue gas has been treated, it is ready for
use in
downstream applications.
Where the residue conditioning chamber is a component of a gasification system
having a
gas conditioning system for cooling and cleaning the gaseous product of the
gasification
process, the treated residue gas may be combined with the main gasification
gas product
stream for use in downstream applications. In one embodiment, the cleaned and
conditioned residue gas stream is diverted back to the main gas conditioning
system,
where it joins the main gas stream.
The use of a dedicated residue gas conditioning system to treat the residue
gas prior to its
introduction to the main product gas stream provides for the removal of any
heavy metals
or particulate matter that may be present, thereby minimizing the amount of
heavy metals
or particulate matter that will be passed through the main gas conditioning
system.
In one embodiment, any material accumulating in the residue gas conditioning
subsystem
may be directed back to the residue conditioning chamber of the present
invention for
further conditioning. Material from the residue gas conditioning subsystem may
also be
disposed of in a hazardous waste disposal. The quantity of residue removed
from the
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baghouse of the residue gas conditioner is typically less than that removed
from the
baghouse in the main gas conditioner.
In one embodiment of the residue gas conditioning subsystem, the residue gas
is passed
through a residue gas conditioner baghouse filter to remove particulates and a
proportion
of the heavy metal contaminants. The residue gas is then cooled using a heat
exchanger
before it is passed through an activated carbon bed for the further removal of
heavy
metals and particulate matter. In one embodiment, the residue gas undergoes a
pre-
cooling step in an indirect air-to-gas heat exchanger prior to being passed
through the
baghouse filter.
The Control System
The system of the present invention comprises a control system for use with
the residue
conditioning system to regulate the efficient and complete conversion of the
residue into
an inert slag product and a residue gas having a heating value.
In one embodiment of the present invention, a control system may be provided
to control
one or more processes implemented in, and/or by, the various systems and/or
subsystems
disclosed herein, 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 local and/or regional processes related to a given system,
subsystem or
component thereof, and/or related to one or more global processes implemented
within a
system, such as a gasification system, within or in cooperation with which the
various
embodiments of the present invention may be operated, 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
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desired result, and respond by implementing changes in one or more of the
ongoing
processes via one or more controllable process devices.
The control system generally comprises, for example, one or more sensing
elements for
sensing one or more characteristics related to the system(s), process(es)
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 with this predetermined range. A 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.
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.),
and the like, can be executed in a manner whereby one or more process-related
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characteristics are assessed and optimized according to design and/or
downstream
specifications.
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.
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
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.
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.
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.
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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 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.
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.
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
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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.
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 present 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 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.
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
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communicating data and information with external sources (e.g. modem, network
connection, printer, etc.).
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 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.
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
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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.
Control Elements
Sensing elements contemplated within the present context, as defined and
described
above, can include, but are not limited to, means for monitoring operational
parameters
such as gas flow, pressure within the residue conditioning chamber, and
temperature at
various locations within the system. The sensing elements optionally include
means for
analyzing the chemical composition of the residue gas.
The data obtained from the sensing elements is used to determine if, for
example, there
needs to be more air injected into the system, or if the residue material
input rate needs to
be adjusted. Accordingly, ongoing adjustments to operating parameters, as
determined
by the control system, enable the residue conditioning process to be carried
efficiently
and completely, ensuring that the residue is fully converted to a slag
material and gaseous
products having desired chemical compositions.
Where continuous operation of the residue conditioning chamber is desired, the
control
subsystem provides for such sustained operation by ensuring, for example, that
the torch
has an adequate melting capacity to process a steady-state addition of the
residue to the
conditioner.
The following operational parameters may be intermittently or continuously
monitored
by the sensing elements, and the data obtained are used to determine whether
the system
is operating within the optimal set point, and whether, for example, there
needs to be
more power delivered by the torches, more air injected into the system, or if
the residue
material input rate needs to be adjusted.
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Temperature
In one embodiment of the invention, the control system comprises means to
monitor the
temperature at sites located throughout the system. Means for monitoring the
temperature may be located on the outside wall of the chamber, at locations
throughout
the interior of the chamber, or in the gas handling subsystems as may be
required. The
means for monitoring the temperature may be thermocouples or optical
thermometers
installed at locations in the system as required.
In one embodiment of the invention, the temperature monitoring means are
provided as
one or more optical thermometers for measuring the surface temperature of the
surface
upon which they are aimed. In one embodiment, the residue conditioning chamber
is
provided with one or more vapour space thermocouples mounted in ceramic
thermowells
above the molten slag reservoir. In one embodiment, the residue conditioning
chamber is
provided with external skin mounted thermocouples mounted on the outer metal
shell.
Means for monitoring the temperature of the residue gas may also be located at
the
residue gas outlet, as well as at various locations throughout the residue gas
conditioning
system.
If a subsystem for recovering the sensible heat in the residue gas produced by
the residue
conditioning process is employed (such as a heat exchanger or similar
technology), a
means for monitoring the temperature at points in the heat recovery subsystem
may be
incorporated. For example, the temperature may be monitored at the coolant
fluid inlet
and outlet, as well as at the residue gas inlet and outlet.
System Pressure
In one embodiment of the invention, the control system comprises means to
monitor the
pressure within the residue conditioning chamber, as well as throughout the
entire residue
conditioning system. These pressure monitoring means may include pressure
sensors
such as pressure transducers, pressure transmitters or pressure taps located
anywhere
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system, for example on a vertical wall of the conditioning chamber. Data
relating to the
pressure of the system is used by the control system to determine whether
adjustments to
parameters such as blower speed or valve settings are required.
In one embodiment, the pressure in the different components in the system is
monitored.
In this manner, a pressure drop or differential from one component to another
can be
monitored to rapidly pinpoint developing problems during processing.
In one embodiment, the pressure in the residue conditioning chamber is
monitored by a
pressure transmitter tapped into the vapour space of the chamber.
Gas Flow Rate
In one embodiment of the invention, the control system comprises means to
monitor the
rate of residue gas flow at sites located throughout the system. Fluctuations
in the gas
flow may occur as the result of non-homogeneous conditions in the conditioning
process
(e.g. malfunctions in the torch or interruptions in the residue feed). If
fluctuations in gas
flow persist, the system may be shut down until the problem is solved.
Gas Composition
In one embodiment of the invention, the control system comprises means to
monitor the
composition of the residue gas. The residue gas produced during the residue
conditioning
process can be sampled and analyzed using methods well known to the skilled
technician.
As discussed previously, air inputs may be provided to ensure that the carbon
content of
the residue is completely converted to a useful gas product. In order to
ensure that the
conditioning process is carried out efficiently and safely, the composition of
the residue
gas may be monitored to determine whether there is an excess of oxygen in the
residue
gas exiting the chamber. In one embodiment, the composition of the residue gas
is
monitored at the chamber's gas outlet.
One method that can be used to determine the chemical composition of the
product gas is
through gas chromatography (GC) analysis. Sample points for these analyses can
be
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located throughout the system. In one embodiment, the gas composition is
measured
using a Fourier Transform Infrared (FTIR) Analyser, which measures the
infrared
spectrum of the gas.
Although high temperature gas analysis means exist, one skilled in the art can
appreciate
that it may be required to cool the gas prior to analyzing its composition,
depending upon
the type of system used for gas analysis.
In one embodiment, sampling ports are installed at locations throughout the
residue gas
handling subsystem.
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,
means for adjusting various operational parameters such as the rate of
addition of the
residue, air and/or steam, as well as operating conditions, such as power to
the torch,
torch position and system pressure.
Plasma Heat Source
In one embodiment of the invention, the control system comprises means to
adjust the
power, and optionally the position, of the plasma heat source. For example,
when the
temperature of the melt is too low, the control system may command an increase
in the
power rating of the plasma heat source; conversely, when the temperature of
the chamber
is too high, the control system may command a drop in the power rating of the
plasma
heat source.
In one embodiment, the power of the torch is maintained at a level that is
proportional to
the rate of the residue addition, i.e., an increase in the residue feed rate
results in an
increase in the torch power. The torch power can also be adjusted to react to
changes in
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the characteristics and composition of the residue, for example, with respect
to its melting
properties such as temperature, specific heat capacity, and heat of fusion.
In one embodiment, the position of the plasma heat source is adjustable to
ensure
complete coverage of the melt pool, and the elimination of areas of
incompletely reacted
materials.
Residue Feed Rate
In one embodiment of the invention, the control system comprises means to
adjust the
rate of addition of the residue. The material is added to the residue
conditioning chamber
using a number of possible input means that are selected and adapted as
required for the
form of the material added. The residue may be added in a continuous manner,
for
example, by using a rotating screw or auger mechanism. Alternatively, the
residue can
be added in a discontinuous fashion, for example, by using a pusher ram to add
material
in portions as required.
Where the residue input means comprises a series of pusher rams, the control
system may
employ limit switches or other means of travel control such as computer
controlled
variable speed motor drives to control the length, speed and/or frequency of
the ram
stroke so that the amount of residue fed into the conditioning chamber with
each stroke
can be controlled. Where the residue input means comprises one or more screw
conveyors, the rate of addition of the residue to the conditioning chamber may
be
controlled by adjusting the conveyor speed via drive motor variable frequency
drives.
The feed rate is adjusted as required to ensure acceptable temperature
control, according
to the melting capability of the plasma torches, and to prevent the
accumulation of
unconditioned materials in the residue conditioning chamber. The residue input
rate can
also be varied to accommodate varying residue melting temperature properties.
Addition of Air and/or Steam
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In one embodiment of the invention, the control system comprises means to
adjust the
rate and/or amounts of air inputs into the residue conditioning chamber. In
one
embodiment of the invention, the control system comprises means to adjust the
rate
and/or amounts of steam inputs into the conditioning chamber.
As discussed previously, air and/or steam may be added to the conditioning
chamber to
ensure complete conversion of unreacted carbon, as required by the varying
carbon
content of the residue being conditioned.
Air inputs may also be provided as required to maintain optimum processing
temperatures while minimizing the cost of plasma heat required in the
conditioning
process. As such, the amount of air injection is maintained to ensure the
maximum
conversion of carbon to carbon monoxide with the minimum plasma heat
requirement to
carry out the process.
The amount of air inputs are also controlled to ensure that an excess of
oxygen is not
introduced into the conditioning chamber, to avoid producing a residue gas
product
having unsafe (i.e., ignitable) levels of oxygen.
Pressure
In one embodiment of the invention, the control system comprises means to
adjust the
pressure within the residue conditioning system, thereby maintaining a desired
pressure
in the system within certain defined tolerances. Any pressure variations
caused for
example, when the plasma torch power or residue feed rate is adjusted, are
corrected by
making adjustments to certain operational parameters as determined by the
control
system.
In one embodiment, the system is maintained at an operating pressure that does
not
exceed the pressure of upstream elements such as the source of the residue
material (e.g.,
a gasification chamber or feed hopper). Maintaining the pressure at or below
that of
upstream components ensures that there is a minimal driving force urging the
flow of the
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residue gas back toward the upstream component through, for example, the screw
conveyors.
In one embodiment, the system is maintained under slight negative pressure
relative to
atmospheric pressure to prevent gases being expelled into the environment.
In one embodiment, the means for adjusting the internal pressure is provided
by a valve
at a location downstream from the residue conditioning chamber, for example,
at the
outlet of the residue gas conditioning subsystem. Adjustments to the pressure
are made
by opening or closing the valve in response to measured changes in the system
pressure.
A controller calculates the valve position needed to achieve the desired
operating
pressure.
In one embodiment, the means for adjusting the internal pressure is provided
by an
induction blower located downstream of the residue conditioning chamber that
operates
by pulling the residue gas out of the conditioning chamber. The induction
blower thus
employed maintains the system at atmospheric or negative pressure. In one
embodiment,
a control valve is provided in the gas outlet line to increase or restrict the
flow of gas that
is being removed by the downstream residue gas blower.
In systems in which positive pressure is maintained, the blower is operated
such that the
rate of removal of the residue gas is decreased, or even shut off, so that the
gases are
forced to "push" their way through the system resulting in a higher (positive)
pressure.
In response to data acquired by pressure sensors located throughout the
system, the speed
of the downstream induction blower is adjusted according to whether the
pressure in the
system is increasing (whereby the fan will increase in speed) or decreasing
(whereby the
fan will decrease in speed). In one embodiment, data relating to the pressure
at points
throughout the system are obtained on a continuous basis, thereby allowing the
control
system to make frequent adjustments to the fan speed to maintain the system
pressure
within a predetermined set point.
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The invention will now be described with reference to a specific example. It
will be
understood that the following example is intended to describe an embodiment of
the
invention and is not intended to limit the invention in any way.
EXAMPLES
The present example is to provide an exemplary embodiment of the residue
conditioning
system of the present invention. Accordingly, the present example, as depicted
in
Figures 13 to 17, is provided to condition the residual matter produced in a
typical
gasification system during the gasification of carbonaceous feedstock. The
sources of the
residue to be conditioned are therefore the gasifier 2200 and the baghouse
filter 6230 of a
downstream gas conditioning subsystem of the gasification system. According to
this
example, the gasifier residue is removed from the gasifier 2200 by a first
screw conveyor
2209 mounted at the end of the gasifier 2200. The first screw conveyor 2209 is
provided
as a toothed or serrated screw to break up agglomerated material. The residue
is then
conveyed via a gasifier residue screw conveyor 4218 to a main residue screw
conveyor
4217. The baghouse residue is conveyed from the baghouse 6230 via a baghouse
residue
screw conveyor 4618 into the main residue screw conveyor 4217. The main screw
conveyor 4217 passes the combined residues into the top of the residue
conditioning
chamber 4220. A cross-sectional view of an exemplary conditioning chamber is
depicted
in Figure 14.
The residue drops through the residue inlet 4212 located at the top of the
conditioning
chamber 4220 into a reservoir 4260 whose depth is determined by the height of
a weir
4262, where it accumulates while undergoing heating by the plasma torch 4236.
The
level of the molten slag pool rises as more residue is added to the chamber
4220, until the
level of the pool reaches the top of the weir 4262. Thereafter, as additional
residue enters
the reservoir 4260 and is conditioned, a corresponding amount of molten
material
overflows the weir 4262 and out of the chamber 4220 through a slag outlet
4242.
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In order to remove metals that may have accumulated in the reservoir, the
reservoir 4260
is provided with a metal tap port 4249 plugged with a soft refractory paste
4244 which
may be periodically removed using the heat from an oxygen lance. Once the tap
port
4249 has been opened and the chamber temperature has been raised sufficiently
to melt
the accumulated metals, the molten metals are tapped off from the bottom of
the reservoir
4260.
The exemplary chamber depicted in Figure 15, shown disconnected from upstream
and
downstream components of the system, comprises a lower chamber portion 4222,
where
the reservoir is located, and an upper chamber portion 4224, comprising
connections to
the upstream residue source and the downstream gas conditioning subsystem. The
chamber lower portion 4222 can therefore be removed from the chamber upper
portion
4224 without disturbing any connections between the chamber and upstream or
downstream components of the system. To facilitate the lowering of the lower
chamber
portion 4222 away from the upper portion 4224, the chamber 4220 is suspended
from a
support structure by supporting means 4229 attached to the upper portion 4224.
Thus the
lower portion 4222 can be dropped away from the upper portion 4224 to
facilitate
maintenance.
The exemplary chamber depicted in Figures 14 and 15, includes a port 4271 for
receiving the plasma torch 4236, a residue inlet 4212 through which the
residue is
received, and a gas outlet 4252 through which the residue gas passes into a
downstream
gas conditioning subsystem 4250. This exemplary chamber also includes two
ports 4272
and 4273 for mounting optical thermometers 4282 and 4283, a port 4274 for
mounting a
burner for preheating the conditioning chamber, and a port 4275 for mounting
an oxygen
lance.
The cross sectional view of the exemplary chamber depicted in Figure 16 shows
the slag
outlet 4242 and the water seal duct 4248 through which the molten slag falls
into the
water tank 4241 below. The water seal duct 4248 is provided to ensure that the
residue
conditioning environment is sealed to the atmosphere. The cooled and
solidified slag is
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removed from the water bath using a wet conveyer system 4249 and is collected
for
disposal or later use.
As shown in Figure 17, the residue gas exits the residue conditioning chamber
4220
through the gas outlet 4252 and is passed into a residue gas conditioning
subsystem 4250.
In the residue gas conditioning subsystem, the residue gas undergoes a pre-
cooling step in
an indirect air-to-gas heat exchanger 4252 prior to being passed through a
baghouse filter
4254 to remove particulates and a proportion of the heavy metal contaminants.
The
residue gas is then cooled using a second heat exchanger 4256 before it is
passed through
an activated carbon bed 4258 for the further removal of heavy metals and
particulate
matter.
Control Strategy
The following describes typical control strategies according to the present
example. In
the present example, the sensing elements include at least two optical
thermometers for
measuring the surface temperature of the molten slag pool, a plurality of
vapour space
thermocouples mounted in ceramic thermowells above the melt pool, and a
plurality of
external skin mounted thermocouples mounted on the outer metal shell. The
sensing
elements of this example also include a pressure transmitter for measuring the
process
pressure inside the residue conditioning chamber. In the present example, the
operational
parameters to be adjusted include the power of the plasma heat source, the
residue feed
rate, and the pressure within the system.
According to one control strategy suitable for this example, the temperature
differential
as measured by the at least two optical thermometers is determined. One
optical
thermometer is aimed at the melt pool below the torch, the other at the melt
pool near the
weir. If the temperature measured near the weir is cooling off relative to the
temperature
measured below the torch, then more torch power is applied to ensure that the
slag is
maintained in a molten state until exhausted from the chamber.
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According to a second control strategy suitable for this example, the
temperature as
measured by the optical thermometers is determined, and compared to a
predetermined
set point. For example, a set point of between about 1400 - 1800 C, known to
be above
the melting temperature of most components of the residue to be conditioned,
is selected
and entered into the controller. The control system will then adjust the torch
power as
required to meet this set point.
In the present example, the state of material in the molten slag pool is not
measured
directly, but is inferred by measurements obtained using both optical
thermometers
directed at the surface of the pool and vapour space thermocouples. For
example, if the
temperature measured by these devices falls below the predetermined
temperature set
point, this may be an indication of the presence of unmelted material.
Accordingly, the
control system will adjust operating parameters as required, for example, by
momentarily
slowing the residue feed rate, or increasing the plasma torch power.
In the present example, the residue feed rate is adjusted as required to
ensure acceptable
temperature control, according to the melting capability of the plasma
torches, and to
prevent the accumulation of unconditioned materials in the residue
conditioning chamber.
In the present example, the pressure in the slag chamber is monitored by a
pressure
transmitter tapped into the vapour space of the vessel, and a control valve in
the gas
outlet line is adjusted to increase or restrict the flow of gas being removed
by a
downstream syngas gas blower. The controller calculates the valve position
needed to
achieve the desired operating pressure.
