Note: Descriptions are shown in the official language in which they were submitted.
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PYROLYSIS SYSTEM USING COOLED FLUE GAS FOR DRYING
FIELD OF THE INVENTION
[0001] The present invention relates to the pyrolysis of organic material and
combustion of
coke, and more particularly to use of the resulting combustion gases to dry
additional organic
material. Still more particularly, the present invention relates to the
cooling of combustion gas
left over from a pyrolysis process to make the gas suitable for transfer to a
heat exchange dryer.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] Pyrolysis is a process of thermochemical decomposition of an organic
material, such as
biomass, at high temperatures and usually in the absence of substantial
amounts of oxygen.
Pyrolysis systems are useful because they are capable of taking a feed stream
of raw organic
material, and converting that material to, for example, coke, oil, and/or
other byproducts.
[0003] The feed stream of organic material that is input to a pyrolysis system
usually should be
properly prepared. This preparation may include drying of the organic material
if the organic
material comprises too much moisture, i.e., an amount that may interfere or
inhibit processing.
This varies, of course, with the specific organic material but in some
instances raw organic
material may contains more than about 10% moisture, and often as high as 50%
moisture
depending upon its source. In many instances the moisture content of the
material should be
lowered to about 10% or less before subjugation to a pyrolysis reaction. This
often assists in
reducing or substantially eliminating the formation of a tar-like substance
that may inhibit and/or
interfere with further processing.
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[0004] There are multiple ways of drying organic material. One way is through
the use of drum
dryers. Another is using heat exchangers. One advantage to using heat
exchangers, rather than
drum dryers, is that heat exchangers may assist in reducing volatile organic
compound (VOC)
emissions that ultimately enter the environment. In some instances a dryer
arrangement may
include a conveyor belt that conveys the organic material past one, two, or
even a series of heat
exchangers that dry the organic material. Such an arrangement requires a
constant supply of
heated gas to the heat exchangers.
[0005] After the organic material has been dried, it may be subjected to
pyrolysis which
typically produces compositions comprising, for example, one or more of coke,
gaseous
products, and/or oil. The coke is typically introduced to a regenerator, where
it is combusted, to
form a flue gas. Due to the high heat required for the pyrolysis reaction, and
the additional heat
added during combustion, the flue gas may leave the regenerator at a very high
temperature,
often as high as 1200 F or more.
[0006] Accordingly, many pyrolysis systems share two common features. First,
they require
that the raw organic material be dried prior to the pyrolysis reaction, and
second, one byproduct
of the process is hot regenerator flue gas. Efficiency may be gained,
therefore, by drying the
raw organic material using the hot regenerator flue gas. This may be achieved
by using heat
exchangers, as discussed above, where the gas supplied to the heat exchangers
is the regenerator
flue gas.
[0007] One problem with this arrangement, however, is that in some cases
safety considerations
prevent the transfer of the very high temperature regenerator flue gas to the
heat exchangers in
common gas lines, such as carbon steel gas lines. Instead, the pipework
interconnecting the
pyrolysis regenerator and the heat exchanger must be constructed of more
expensive materials
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that are rated to more safely carry very high temperature gas, such as, for
example, stainless
steel. This requirement adds additional cost since often the regenerator may
be separated from
the heat exchangers by up to several hundred feet or more.
[0008] In one embodiment, the present invention provides a system that
includes a pyrolysis
unit for pyrolyzing organic material to produce a composition comprising at
least pyrolysis oil
and coke, a regenerator unit to combust at least a portion of the coke and
produce a regenerator
flue gas, and a mixer connected to the regenerator unit to mix the regenerator
flue gas with air to
produce a cooled flue gas. The system may further include at least one heat
exchanger
connected to the mixer to extract heat from the cooled flue gas, and a
conveyer belt in thermal
communication with the at least one heat exchanger and operably connected to
the pyrolysis
unit. The conveyer belt can convey organic material in need of drying past the
at least one heat
exchanger to dry the organic material.
[0009] A variant of or addition to this system may include a pyrolysis unit
employing a heat
transfer medium such as a particulate source of heat like sand, wherein the
pyrolyzing unit
pyrolyzes biomass to form a mixture comprising at least pyrolysis oil, coke,
and heated
particulate source like sand, and wherein the unit has an outlet to transfer
the coke and heated
particulate source like sand. The system also may include a regenerator
operably connected to
the outlet of the pyrolysis unit to receive the coke and heated particulate
source like sand,
wherein the regenerator combusts the coke to a regenerator flue gas and
transfers at least a
portion of the particulate source like sand back into the pyrolysis unit, and
a mixer operably
connected to the regenerator to receive the regenerator flue gas and mix the
regenerator flue gas
with ambient air to produce a cooled flue gas. In addition, the system
includes at least one heat
exchanger operably connected to the mixer to use the cooled flue gas to dry
biomass in need of
drying.
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[0010] In one embodiment the present invention also provides a process for
pyrolysis and
drying of organic material, including the steps of pyrolyzing organic material
to generate at least
pyrolysis oil and coke, combusting the coke in a regenerator to produce flue
gas, cooling flue
gas from the regenerator by mixing the flue gas with air, and channeling the
cooled flue gas to a
heat exchanger to assist in drying wet organic material.
BRIEF DESCRIPTION OF THE DRAWING
[0011] A more complete appreciation of the subject matter of the present
invention and the
various advantages thereof can be realized by reference to the following
detailed description in
which reference is made to the accompanying drawing in which:
[0012] FIG. 1 is a diagram of an integrated pyrolysis regenerator and biomass
dryer according to
one specific embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] In general teims one embodiment of the present invention pertains to a
process for
pyrolysis and drying of organic material. The organic material may be any
suitable material that
is capable of being pyrolyzed. The type of material selected may, of course,
vary depending
upon, for example, the desired products and/or their desired use. Since in one
embodiment the
present invention also assists in drying the starting organic materials, the
present invention may
be most advantageous when pyrolyzing materials that may need to be at least
partially dried
before undergoing pyrolysis. Such materials may include, for example, coal,
biomass, and/or
mixtures thereof.
[0014] Typically, useful biomass includes any cellulosic or lignocellulosic
material and includes
materials comprising cellulose, and optionally further comprising
hemicellulose, lignin, starch,
oligosaccharides and/or monosaccharides. Biomass may also comprise additional
components,
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such as protein and/or lipid. Biomass may be derived from a single source, or
biomass can
comprise a mixture derived from more than one source; for example, biomass
could comprise a
mixture of corn cobs and corn stover, or a mixture of grass and leaves.
Biomass includes, but is
not limited to, bioenergy crops, agricultural residues, municipal solid waste,
industrial solid
waste, sludge from paper manufacture, yard waste, wood and forestry waste.
Examples of
biomass include, but are not limited to, corn grain, corn cobs, crop residues
such as corn husks,
corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice
straw, switchgrass, waste
paper, sugar cane bagasse, sorghum, soy, components obtained from milling of
grains, trees,
branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables,
fruits, flowers
and/or animal manure.
[0015] The organic material is pyrolyzed under any convenient conditions to
form coke and/or
byproducts such as oils. The pyrolysis conditions such as time and pressure
may vary
depending upon the specific organic material and desired products. Typically,
the material is
heated in a pyrolysis unit at atmospheric pressure or under pressure at a
temperature and time
suitable to form coke. Such pyrolysis temperatures vary depending upon the
material but often
are above about 800F. Typically, the pyrolysis is conducted in the substantial
absence of
oxygen and/or water.
[0016] While any suitable pyrolysis unit may be employed, in one embodiment a
pyrolysis unit
is employed wherein a solid particulate may be used as a heat transfer media
is used when
pyrolyzing the organic material. Any convenient particulate source of heat may
be employed so
long as it does not substantially inhibit or interfere with the process. In
some instances, such
particulate sources of heat are employed in, for example, the manner of a
fluidized bed. The
precise type of particulate source of heat is not critical. However, it may be
advantageous in
some situations to employ a particulate source of heat which can be recycled,
e.g. by transferring
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it to a regenerator with the coke and then returning at least a portion of the
particulate source to
the pyrolysis unit for reuse in pyrolyzing additional organic material. Such
particulate sources
of heat are widely available and include, for example, silicas, aluminas, and
the like. In one
embodiment, at least a portion of the particulate sources of heat comprises,
for example, sand.
Additionally or alternatively, the particulate source or a portion of it may
be separated from the
coke within the pyrolysis unit.
[0017] At least a portion of the coke may be combusted in any convenient
manner to produce
flue gas. Typically, the coke is combusted in a regenerator unit. The specific
composition of
the resulting regenerator flue gas will vary depending upon the starting
material, pyrolysis
conditions, and combustion conditions. That is, the flue gas will vary in
amount of nitrogen,
carbon dioxide, water, and/or other components. Advantageously, the flue gas
will have very
little to substantially no volatile organic compounds when, for example,
conveyer drying as
opposed to drum drying is employed.
[0018] The flue gas will usually be very hot, e.g. above 900F or above 1000F,
due to the
pyrolysis and combustion conditions. If it is desired to transport the flue
gas through, for
example, carbon steel lines then it may be advantageous to quench or cool it.
The temperature
to which it should be cooled and the method used to do it will necessarily
vary depending upon
its initial composition, temperature, and/or equipment employed. In one
embodiment, the flue
gas is cooled by mixing the flue gas with a fluid such as air, e.g., ambient
or even cooled air.
This may usually be accomplished in a mixer connected to or even within the
regenerator unit to
generate a cooled flue gas which may then be transported via, for example, the
carbon steel
lines.
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[0019] The cooled or quenched flue gas advantageously still has a substantial
amount of useful
heat. Accordingly, the heat may still be used advantageously in any convenient
manner to assist
in drying organic material in need of such drying. In one embodiment, the gas
is channeled to a
heat exchanger of a dryer to assist in drying, for example, wet biomass. The
wet biomass may
be conveyed along a conveyer belt in thermal communication with the at least
one heat
exchanger and operably connected to the pyrolysis unit. In this manner, the
wet biomass in need
of drying is conveyed past the at least one heat exchanger may be made useful
as a feed to the
pyrolysis unit.
[0020] Referring now to the drawing, wherein like reference numerals indicate
similar features,
there is shown in FIG. 1 a diagrammatic overview of one possible system.
According to the
system, an organic material may be fed into a pyrolysis unit 10. Preferably,
the organic material
introduced to the pyrolysis unit 10 has a moisture content of about 10% by
weight or less.
Although it is possible to pyrolyze organic material having a moisture content
of greater than
about 10% by weight, and the present invention contemplates pyrolyzing such
material, this can
lead to problems due to evaporation of moisture from the organic material
within the pyrolysis
unit 10. Such evaporation within the pyrolysis unit may lead to lower
temperatures and partially
impair the pyrolysis reaction. The organic material may be any carbon-based
organic material,
such as, for example, biomass, coal, etc.
[0021] The pyrolysis unit 10 contains a heat transfer medium which may be a
solid particulate,
such as, for example, sand. Any solid heat transfer medium may be used within
the pyrolysis
unit 10, as long as it has the necessary properties to avoid breaking down
under the high
temperature conditions that exist within the pyrolysis unit 10 during the
pyrolysis reaction.
Upon entering the pyrolysis unit 10, the organic material is converted through
a pyrolysis
reaction into a plurality of components, including, for example, volatile
compounds, such as
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CH4, pyrolysis oil, and a typically solid residue called coke. Coke is
typically composed mostly
of carbon, but may also include hydrogen and other components. Typically,
substantially all of
the components except the coke and the heat transfer medium vaporize within
the pyrolysis unit
and are separated from the coke and the heat transfer medium after the
pyrolysis reaction.
The coke may mix with the heat transfer medium in the pyrolysis unit 10 and
exit the unit as a
coke/heat transfer medium mixture. After exiting the pyrolysis unit 10, the
volatile compounds
and the pyrolysis oil, as well as any other byproducts of the pyrolysis
reaction, may be collected
or disposed of using conventional methods. The coke/heat transfer medium
mixture may be fed
into a regenerator unit 12.
[0022] The regenerator unit 12 is typically a cylinder or other suitable
container that is
configured to accept the coke/heat transfer medium mixture. In the regenerator
unit 12, the
coke/heat transfer medium mixture is mixed with air, which causes combustion
of the coke,
thereby producing a regenerator flue gas. Typically, the regenerator flue gas
is composed
mostly of nitrogen, but may also contain oxygen, carbon dioxide, and/or water
vapor. The
composition of the flue gas may vary depending on the organic material that
has been pyrolyzed
and other factors. After combustion, the heat transfer medium is preferably
fed back into the
pyrolysis unit 10 for reuse. The regenerator flue gas is transferred from the
regenerator unit 12
to a mixer 14. Typically, the regenerator flue gas leaves the regenerator unit
12 at a high
temperature, such as a temperature of up to about 1200 F or higher. The
regenerator flue gas is
preferably transferred to the mixer 14 through transfer lines made of a
material suitable for
safely carrying high temperature gas, such as, for example, stainless steel.
[0023] In the mixer 14, the regenerator flue gas is mixed with air. The air
may be provided to
the mixer 14 by an air blower 16 and is preferably ambient air. As the air
mixes with the
regenerator flue gas in the mixer 14, the regenerator flue gas is cooled. In
one preferred
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embodiment, the flue gas is cooled to a temperature of about 700 F or less.
The cooled flue gas
is then transferred to at least one heat exchanger 20. One advantage of
cooling the regenerator
flue gas in the mixer 14 is that the cooled flue gas may be safely transported
in gas lines 18
made of a material suitable for carrying lower temperature gases, such as
carbon steel.
[0024] In one preferred embodiment, the heat exchangers 20 are positioned near
a conveyer belt
22 so that the conveyor belt 22 is in thermal communication with the heat
exchangers 20. Wet
organic material is fed onto the conveyor belt 22 and then carried past the
heat exchangers 20.
As the wet organic material passes the heat exchangers 20, the moisture in the
biomass
evaporates into the air surrounding the organic material, thereby moistening
the air and drying
the organic material. At least one fan 24 may be positioned near the organic
material on the
conveyor belt and arranged to direct the moist air away from the organic
material and out a vent
(not shown). The dried organic material may then be fed into the pyrolysis
unit 10.
[00251 Although the invention herein has been described with reference to
particular
embodiments, it is to be understood that these embodiments are merely
illustrative of the
principles and applications of the present invention. It is therefore to be
understood that
numerous modifications may be made to the illustrative embodiments and that
other
arrangements may be devised without departing from the spirit and scope of the
present
invention.
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