Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE CONVERSION OF CARBONACEOUS FEEDSTOCK INTO
LIQUID, CHAR, AND GAS
Field of the Invention
This invention relates to a process for the pyrolytic conversion of
carbonaceous materials
into liquid, char, and gas. The process improves upon current practices by
eliminating the
need for a blower and cyclone to circulate gas, thus significantly reducing
energy
requirements. In addition, the process results in a relatively high yield of
good quality
pyrolytic liquids at temperatures lower than those reported by others.
Background to the Invention
Pyrolysis is the decomposition of compounds caused by rapid heating in an
oxygen-
depleted environment. The process may be used to derive fuel oils from a
number of
carbonaceous materials. The wood or forest products industry produces sawdust,
wood
chips, bark, construction debris, and post consumer wood waste. The
agricultural sector
has abundant supplies of straw, hay, wood crop grown specifically for energy,
and manure.
Miscellaneous wastes consisting of tires, plastic, and treated wood may also
be converted
into value-added fuels and chemicals. Greater yields of pyrolytic oils are
produced where
the time between thermal decomposition and condensation is minimized, the
ideal time
being in the order of a few seconds. U.S. Patent No. 5,853,548 to Piskorz et
al. shows that
the requirement for short residence time decreases as the temperature
decreases.
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Most pyrolysis reactors are of the fluidized bed, circulating fluidized bed or
transport bed
type (see, for example, Canadian Patent No. 2,150,231 to Scott et al. and
Canadian Patent
No. 982,073 to Garrett and Mallan). In each of these reactor types, termed
circulating gas
pyrolysis systems, heating of the carbonaceous material is accomplished, at
least in part, by
mixing the carbonaceous material with a hot, inert substance. The inert
substance always
consists of gaseous materials, but solids may also be present. The inert gas,
along with any
products of the pyrolysis reaction, is directed out of the reactor by a
recycle gas stream
produced by a blower. The recycle gas stream flows into a cyclone, where the
char is
separated out. Next, the pyrolytic oils are isolated by condensation. The
inert gas is then
reheated and cycled back to the reactor. The presence of this recycle gas
stream not only
increases the size and complexity of the pyrolysis system, but it increases
the size of the
condensing system and, due to continual heating and cooling of the recycle
gas, greatly
increases the energy requirements of the system. Additionally, the amount of
recycle gas
becomes so great that a larger cyclone is required, thus increasing the time
between
thermal decomposition and condensation.
A further difficulty with circulating gas pyrolysis systems is the
condensation of vapours.
Despite the presence of condensers, filters and demisters are normally
required, and the
latter may trap as much as half of the pyrolytic oils. This necessitates
frequent draining and
servicing of filters and demisters.
Optimum pyrolysis temperatures in the prior art are in the range of 500 C for
a circulating
bed transport reactor (U.S. Patent No. 5,961,786 to Freel and Graham), and
Piskorz et al.
have reported a preferred temperature of 430 C in a fluidized bed reactor
(U.S. Patent No.
5,853,548).
There have been attempts to use auger systems as pyrolysis reactors (U.S.
Patent No.
4,983,278 to Cha et al., and U.S. Patent No. 5,720,232 to Meador). These
reactors were
designed primarily for the recovery of oil from tar sands and tires, and are
slow pyrolysis
systems with limited product throughput. In H.W. Campbell "Converting Sludge
to Fuel - A
Status Report" in Hogan et al eds., Biomass Thermal Processing, (Berkshire,
UK: CPL
Press Newbury, 1992) at 78-84, Campbell describes a heated auger and gas flow
process
for the conversion of sludge to fuel. This system produced lower liquid yield
and higher char
yield than the present invention as claimed.
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Object and Summary of the Invention
An object of the invention is to provide a process with improved energy
efficiency and
reduced financial cost for the pyrolytic liquidation of carbonaceous
feedstock.
A further object of the invention is to provide a flexible process for the
pyrolytic liquidation or
gasification of carbonaceous feedstock to produce better quality pyrolytic
oils and/or
combustible gas.
Broadly, this invention relates to a process for the conversion of hydrocarbon
feedstock into
pyrolytic liquid, char and gas, comprising the following: introducing
carbonaceous
feedstock, through an inlet means, into a pyrolytic reactor tube wherein said
carbonaceous
feedstock is moved through said pyrolytic reactor tube by a rotating auger;
heating said
feedstock in said reactor tube by mixing said feedstock with a heated inert
particulate
material, causing the pyrolysis of said carbonaceous feedstock, and resulting
in solid
product and gaseous product; discharging said solid product through an outlet
means;
discharging said gaseous product through a second outlet means; and cooling
and
condensing said gaseous product in a series of condensers, said series of
condensers
comprising at least one venturi scrubber.
In the case where the throughput is five (5) tonnes per day or less, the
requirement for a
heated inert particulate material can be eliminated. The hot pyrolytic reactor
tube provides
sufficient heat transfer to rapidly convert the carbonaceous material to
liquid, solid and gas.
Detailed Description of the Invention
The applicant's invention is designed to overcome the drawbacks listed above.
Briefly, the
invention relates to a process whereby carbonaceous feedstock is directed from
a storage
hopper, by virtue of a rotating feed auger, into a pyrolytic reactor tube,
which houses a
rotating auger. An external heat source heats the pyrolytic reactor tube, and
a heated solid
inert particulate material, such as steel shot, may be mixed with the
carbonaceous
feedstock. Pyrolysis occurs at a temperature of approximately 400 C. Solid
materials (char
and inert particulate material when required) exit the pyrolytic reactor tube
and are
separated. The inert particulate material may be reheated and reused, while
the char may
be combusted. The heat provided by combustion of the char is used to heat the
pyrolytic
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reactor tube and the inert particulate material (if present). Gaseous material
exits the
pyrolytic reactor tube and is cooled and condensed in a primary condenser,
consisting of a
cooled tubular shell or a venturi scrubber followed by a polishing venturi
scrubber.
Uncondensed gaseous material may be passed through a demister and filter.
This invention eliminates the need for a blower and cyclone, thereby
decreasing the size of
the system and increasing energy efficiency. Because char is mechanically
conveyed
directly from the reactor, separately from gaseous materials, a large cyclone
is unnecessary.
Furthermore, gas produced from the pyrolysis reaction is swept from the
reactor within less
than approximately one or two seconds. This is accomplished without the need
for a blower,
as the downstream venturi scrubber(s) and the increasing gas pressure within
the reactor
create a pressure differential which forces the pyrolysis gas out of the
reactor. A further
advantage is that because the system acts with virtually zero pressure, it is
not subject to
strict ASME fabrication codes regulating pressure vessels, meaning that the
system is less
expensive to manufacture.
Condensation difficulties in circulating gas pyrolysis systems are believed to
be caused by
the atomization of pyrolysis gases by the high circulating gas flow. The
atomization
prevents condensation from occurring. The elimination of a recycle gas flow in
this invention
has led to better condensation. In a full-sized reactor, the need for a filter
and demister may
be entirely eliminated, due to virtually 100% condensation in the primary and
venturi
condensers. Tests to date have shown that only 1.5% of the condensable liquids
are
recovered in the demister and filter.
It was discovered that with the heated auger reactor, maximum liquid yields
were obtained
at a temperature slightly under 400 C, and excellent yields were obtained over
the range of
380 C to 420 C. These temperatures are quite low, meaning that the system may
be
operated at a lower cost due to lower energy requirements. Furthermore, a
lower operating
temperature reduces the need for expensive process parts m,made from stainless
steel.
It was also discovered that with the heated auger reactor, maximum gas yields
were
obtained at a temperature above 500 C. At this temperature there is a need for
more
expensive process parts from stainless steel.
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An additional advantage of the low operating temperature is an improved
quality of pyrolytic
oils. At temperatures above 360 C, pyrolytic oils are relatively unstable, and
will undergo
secondary reactions which decrease the quality of the pyrolytic oils. It is
therefore crucial to
minimize the time at which the pyrolytic oils are at a temperature above 360
C. An optimum
temperature of 400 C will decrease the likelihood of secondary reactions and
decrease the
importance of a short time between thermal decomposition and cooling below 360
C.
In fact, the pyrolytic oils obtained were in a single phase, and with a
moisture content of
nearly 40% . These are both positive qualities, as a single phase oil may be
pumped
directly into an engine without preheating, while water content helps to
reduce NOX
emissions, and to atomize the oil, thus allowing for better combustion. Lower
pyrolysis
temperature is thought to allow for the preservation of bridging compounds
which allow the
oil and water to maintain a single phase, even where water content is
relatively high.
Description of the Drawings
In drawings that illustrate the present invention by way of example:
Figure 1 is a schematic drawing of one embodiment of the process of the
invention.
Figure 2 is a schematic drawing a second embodiment of the process of the
invention.
Figure 1 illustrates a preferred embodiment of the process of the invention.
In this
embodiment, the carbonaceous feedstock is fed into a storage hopper (1). The
carbonaceous feedstock is directed from the storage hopper (1) by virtue of a
rotating feed
auger (2). The carbonaceous feedstock enters an open chamber in a hydraulic
ram (3) and
is compressed by the ram. From the hydraulic ram the feedstock enters a second
rotating
feed auger (4). From the second rotating feed auger (4), the carbonaceous
feedstock
enters the pyrolytic reactor tube (5), which houses a rotating auger (6).
Solid materials exit
the pyrolytic reactor tube via the solids exit tube (7), and are directed
towards a rotating
transfer auger (8). Solids are then transferred via a bucket elevator (9) to a
rotating
separation auger (10). Char is separated out from inert particulate material,
and funnelled
off to a lock hopper (11) for storage. The inert particulate material is
heated in a heater (12)
and directed through a rotating feed auger (13) to the rotating feed auger (4)
which leads
back to the pyrolytic reactor tube (5). Gaseous material departs the pyrolytic
reactor tube
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(5) via the gas exit tube (14) and is directed to a primary condenser (15)
which is run using
a primary cooling pump (16). From the primary condenser (23), uncondensed
gaseous
material is directed to a venturi condenser (16) which is run using a
secondary cooling pump
(24). Condensed liquids are collected by virtue of a liquid transfer pump
(18). -
Figure 2 illustrates a preferred embodiment of the process of the invention
for systems with
less than 5 tonnes of throughput per day. In this embodiment, the carbonaceous
feedstock
is fed into a storage, hopper (1). The carbonaceous feedstock is directed from
the storage
hopper (1) by a rotating feed auger (2). The carbonaceous feedstock enters an
open
chamber in the reciprocating ram (3) and is compressed by the ram (3). From
the
reciprocating ram (3), the carbonaceous feedstock enters a rotating feed auger
(4) and is
conveyed to the pyrolytic reactor tube (5), which houses a rotating auger (6).
Char exits the
pyrolytic reactor tube (5) via the solids exit tube (7), and is directed
towards a lock hopper
(11). Char is then combusted in a fluid bed furnace (29). Fluidization and
combustion air
are provided by a blower (25) and the residual solid ash is separated from the
combustion
gas via a cyclonic separator (26). The ash is directed through a rotary air
lock (27) to an
ash storage bin (28). The cleansed combustion gas is directed out of the
cyclone via an exit
tube (30) and the hot combustion gas circulates around the rotating auger
shell (6) and
heats the pyrolytic reactor tube (5). Gaseous material departs the pyrolytic
reactor tube (5)
via the gas exit tube (14) and is directed to a primary venturi condenser (15)
which is run
using a primary cooling pump (16). Fluids pumped by the primary cooling pump
(16) are
cooled by a heat exchanger (17) prior to entering the primary condenser (15).
From the
primary condenser (15), uncondensed gaseous material is directed to a
secondary venturi
condenser (23) which is run using a secondary cooling pump (24) and a heat
exchanger
(20). Condensed liquids are transferred to storage tanks by a liquid transfer
pump (18).
Non-condensing gases are directed out of the secondary venturi scrubber to a
flare stack
(22).
The examples and embodiments described herein are for illustrative purposes
only, and are
not meant to limit the scope of the invention. Various modifications or
changes will be
suggested to persons skilled in the art, and are to be included within the
spirit and purview
of this applications and the scope of the appended claims.
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Example 1
Oak sawdust was subjected to pyrolysis at 431 C with a feed rate of 0.76 kg/h
and a rotating
auger speed of 2.0 rpm, resulting in the following yields:
Liquid: 46.9%
Char: 26.0%
Gas: 27.0%
Example 2
Oak sawdust was subjected to pyrolysis at 391 C with a feed rate of 0.80 kg/h
and a rotating
auger speed of 2.0 rpm, resulting in the following yields:
Liquid: 54.1%
Char: 21.6%
Gas: 24.3%
Example 3
Oak sawdust was subjected to pyrolysis at 349 C with a feed rate of 1.04 kg/h
and a rotating
auger speed of 2.0 rpm, resulting in the following yields:
Liquid: 51.7%
Char: 28.9%
Gas: 19.4%
Example 4
Pine sawdust was subjected to pyrolysis at 406 C with a feed rate of 1.4 kg/h
and a rotating
auger speed of 2.0 rpm, resulting in the following yields:
Liquid: 58.0%
Char: 33.0%
Gas: 8.7%
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Example 5
Pine sawdust was subjected to pyrolysis at 390 C with a fe d rate of 1.4 kg/h
and a rotating
auger speed of 2.0 rpm, resulting in the following yields:
Liquid: 57%
Char: 25%
Gas: 8%
Example 6
Chicken manure was subjected to pyrolysis at 399 C with a feed rate of 2.2
kg/h and a
rotating auger speed of 2.0 rpm, resulting in the following yieIds:
Light liquid: 29%
Heavy liquid: 10%
Char: 40%
Gas: 21%
