Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: METHOD AND SYSTEM FOR ACCOMPLISHING FLASH OR FAST
PYROLYSIS WITH CARBONACEOUS MATERIALS
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system for processing various carbonaceous
feedstocks
into useful energy, such as, gaseous, liquid, and char products. In
particular, the
invention relates to a system for optimizing the decomposition of carbonaceous
feedstocks using heat in an oxygen depleted atmosphere in a manner that
results in the
production of useful products. Usable feedstocks may indude carbonaceous waste
materials or residues.
2. Descripdon of the Prior Art
Current worldwide demands for energy sources necessitate that additional
energy
sources be developed for efficiently and cost effectively providing energy.
Researchers
have attempted to develop renewable oil sources by converting carbonaceous
feedstock,
for example, biomass materials, into useful energy sources. Many of these
processes rely
upon the thermal decomposition, for example, pyrolysis, of the feedstock for
converting
the feedstock into readily usable energy sources.
While some success has been found through the utilization of prior systems, a
need still exists for an improved and more efficient process for the
conversion of
carbonaceous feedstock to useful energy sources. The present invention
provides such a
process.
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SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a system for
the
conversion of carbonaceous feedstocks into useful sources for energy,
chemicals, or
other materials. The system indudes a reactor chamber for receiving
carbonaceous
feedstock and heat carrier for processing of the feedstock in the generation
of useful
sources for energy, chemicals, or other materials. The system also includes a
char
separation and recovery mechanism linked to the reactor chamber for separating
char
produced as a result of processing of feedstock within the reactor chamber
from heat
carrier and a condenser in communication with the reactor chamber for
receiving gas and
vapor from the reactor chamber. A furnace is linked to the char separation
mechanism
providing energy for operation of the system. The system also includes a heat
exchanger
through which heat carrier from the char separation and recovery mechanism is
reheated
and recirculated to the reactor chamber.
It is a further object of the present invention to provide a system wherein
the
heat exchanger is a jacketed auger through which heat from the furnace passes
for
heating the heat carrier as it is carried back to the reactor chamber.
It is another object of the present invention to provide a system wherein the
char
separation and recovery mechanism includes a screen separating system based
upon
relative particle size.
It is also an object of the present invention to provide a system wherein the
char
separation and recovery mechanism includes an air classifier system.
It is stiIl another object of the present invention to provide a system
wherein the
char separation and recovery mechanism includes a magnetic separation system.
It is a further object of the present invention to provide a system wherein
the
condenser includes a fractional condensation column.
It is still a further object of the present invention to provide a system
including a
char trap or tar trap positioned between the reactor chamber and the
condenser.
It is also an object of the present invention to provide a system wherein the
reactor chamber is a stirred tank reactor or a rotating cylinder reactor.
It is a further object of the present invention to provide a system including
a drier
in communication with the reaction chamber, wherein a feed mechanism transfers
the
feedstock from the dryer to the reactor chamber.
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It is also another object of the present invention to provide a system wherein
the
feed mechanism includes a central air lock between first and second feed
sections.
Other objects, advantages and salient features of the invention will become
apparent from the following detailed description, which taken in conjunction
with the
annexed drawings, discloses a preferred, but non-limiting, embodiment of the
subject
invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an overview of the present system.
Figure 2 is a schematic of the present system in accordance with a preferred
embodiment.
Figure 3 is a schematic showing a feeding mechanism in accordance with the
present invention.
Figures 4, 5, 6 and 7 show various char separation systems for use in
accordance
with the present invention.
Figure 8 is a schematic showing a heat exchanger for use in conjunction with
the
return heat carrier to the reactor.
Figure 9 is a side view of the char/syngas burner in accordance with a
preferred
embodiment of the present invention.
Figures 10 and 11 show potential reactor chamber designs for use in accordance
with the present invention.
Figure 12 shows a schematic view of a condenser for use in accordance with the
present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
The detailed embodiments of the present invention are disclosed herein. It
should be understood, however, that the disdosed embodiments are merely
exemplary of
the invention, which may be embodied in various forms. Therefore, the details
disdosed
herein are not to be interpreted as limiting, but merely as the basis for the
claims and as a
basis for teaching one skilled in the art how to make and/or use the
invention.
Referring to Figure 1, a flow chart of the present system and method for the
conversion of carbonaceous feedstocks into char, useful liquids, gases, and
other useful
byproducts is shown. The resulting char and byproducts may then be used in
various
applications for the creation of heat and energy, or for other applications.
As those
skilled in the art will appreciate, the term "char" is meant to refer to
carbon-rich matter
that has been partially, but incompletely, combusted when subjected to heat in
a
controlled manner for a predetermined period of time. The application of heat
to the
feedstock in an oxygen depleted atmosphere results in the removal of some
hydrogen,
oxygen and carbon from the feedstock, leaving a char material primarily
composed of
carbon.
The present system 10 employs a dryer 12 into which carbonaceous feedstock,
such as biomass, for example, wood at 30% moisture content and having
approximately
12.6 MBtu of available energy, is placed. In order for the present system 10
to work
properly, the feedstock must be ground to a fine consistency and dried. As
those skilled
in the art will certainly appreciate, the equipment used in grinding and
drying of the
feedstock is readily available, and various known devices may be employed for
this
purpose.
From the dryer 12, which may be heated from waste heat from an associated
reactor chamber 16 or from another source, the dried feedstock is forwarded to
the
reactor chamber 16 with the emissions from the dryer 12 forwarded to a cyclone
and/or
bag house 14 (or other suitable device which removes particulates from the
emission
stream). It is contemplated that where the drying of carbonaceous materials
may
generate other emissions, for example, volatile organic compounds (VOCs), the
cyclone
and/or bag house 14 may be replaced with a wet scrubber or other suitable
device
known to those skilled in the art for the control of emissions. The dried
biomass, for
example, the dried wood, is transferred to the reactor chamber 16 which
operates at
approximately 350 C to approximately 560 C. While drying of the feedstock is
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disclosed in accordance with a preferred embodiment of the present invention,
those
skilled in the art will appreciate that drying is not always necessary as some
feedstock
arrives dry enough for processing and the drying step may be skipped.
Gas and vapor from the reactor chamber 16 is passed through a condenser
system 72 as discussed below in greater detail and the vapor is condensed to
recover the
liquid product. This liquid product is known by several names including bio
oil, pyrolysis
oil, wood distillate, and other names, and is composed of water and numerous
chemicals.
Useful gas, for example, syngas, is collected as it exits the condenser system
72. The bio
oil is collected for later use and the syngas is forwarded to a furnace 18,
where it is
combusted to provide at least part of the energy for the system 10.
Alternatively, the
syngas could be used to fuel an engine to generate heat and electricity for
the system. As
those skilled in the art will appreciate, syngas (or synthesis gas) is the non-
condensable
gas portion of the gas and vapor stream from the reactor chamber 16 and has
energy
value. The bio oil may be used as an energy source or a source of chemicals,
or for other
applications, in much the same manner as petroleum products.
The char, ash and heat carrier are transferred from the pyrolytic reactor 16
to the
char separation and recovery system 20. The char separation and recovery
system 20
separates the heat carrier (HC) 21, which is transferred to a heat exchanger
22 to be
reheated and recirculated to the reactor chamber 16, and the char, which is
collected and,
to the extent necessary needed for process heat, burned in the furnace 18. Any
char not
needed for process heat becomes a byproduct. The hot heat carrier 21, when
mixed with
the feedstock in the reactor chamber 16, provides the thermal energy for
pyrolysis to
occur in the reactor chamber 16 without the introduction of oxygen into the
reactor
chamber 16.
With this in mind, and in accordance with a preferred embodiment of the
present
invention, the method is achieved by drying carbonaceous feedstock (if
necessary),
processing the dried carbonaceous feedstock and heat carrier 21 in a reactor
chamber 16,
separating char produced as a result of processing of feedstock within the
reactor
chamber 16 from heat carrier 21, separating and recovering liquid product and
non-
condensable gases from gas and vapor emitted by the reactor chamber 16, and
burning
the non-condensable gases and char as needed to provide energy for operation
of the
method.
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The breakdown of biomass during the present process is shown in Figure 1. In
particular, beginning with 2,000 lbs (907.2 kg) of wood at 30% moisture
content results
in approximately 6001bs (approximately 272.2 kg) water, stack gas and heat,
350 lbs of
(158.8 kg) char, 6 lbs (2.7 kg) of ash, 8401bs (381.0 kg) of bio oil, and 210
lbs (95.3 kg) of
syngas. The available energy is also shown in Figure 1, and includes 1.2 MBtu
of energy
released through the cyclone and/or bag house 14, 2.9 MBtu of energy in excess
char
gathered from the char recovery system 20, 5.04 MBtu of energy in char passed
to the
furnace 18, 2.84 MBtu of energy release from the furnace 18 and transferred
back to the
reactor 16, 6.93 MBtu of energy in bio oil generated by the condenser 72 and
0.63 MBtu
of energy in syngas transferted from the condenser to the furnace 18.
Referring to Figure 2, a preferred embodiment for the present system 100 for
the
pyrolytic conversion of carbonaceous feedstock (such as waste carbonaceous
materials
including biomass) into useful sources for energy, chemicals, and other
materials, for
example liquids, char and gases used in the production of energy is disclosed.
In
accordance with a preferred embodiment of the present invention, the feedstock
may
include many types of carbonaceous materials, including, but not limited to,
various types
of wood and wood residues such as sawdust, wood chips, wood shavings, bark,
construction and demolition debris, and post consumer wood waste; paper,
cardboard,
straw, hay, grasses, manure, chicken litter, bagasse, tires, tire crumb,
plastic, automobile
fluff, treated wood, sewage and other types of sludge, herbaceous crops and
residues
including processing residues, food processing residues, peat, municipal solid
waste,
certain industrial wastes, heavy hydrocarbons such as from the petroleum
industry, and
coal fines.
In accordance with this embodiment, and after drying as discussed above, the
carbonaceous feedstock is fed into a storage hopper 112. The carbonaceous
feedstock is
directed from the storage hopper 112 by virtue of a feed mechanism, for
example, and in
accordance with a preferred embodiment, a rotating feed auger 126. In
accordance with
a preferred embodiment, the feedstock is fed to the reactor chamber 116 via a
rotating
feed auger 126 such as a conventional centerless auger (i.e., shaftless auger)
in a tube or
one or more side-by-side augers in a common trough. The use of the centerless
or one
or more side-by-side augers may facilitate feeding of particles that are
irregular in shape
or rod-shaped, such as short pieces of straw or grass. The distance is
increased between
the feed point and the reactor chamber 116 so as to reduce bum back and to
form a
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better air seal, since it is necessary to maintain oxygen deleted conditions
inside the
reactor chamber 116. Where a single auger is used, a relief, such as, a raised
ridge may be
added to the inside of the end of the auger tube where the auger enters the
reactor
chamber 116 to increase the degree of fecdstock compression and better
facilitate the
formation of an air seal. Although various auger systems are discussed above
for feeding
feedstock in accordance with a preferred embodiment of the present invention,
other
feed mechanisms may be employed without departing from the spirit of the
present
invention. -
As shown Figures 2 and 3, the auger 126 is composed of first and second auger
sections 128, 130 with a motorized star wheel airlock 132 positioned
therebetween. The
motorized star wheel airlock 132 drops material through an air gap 134 between
the first
and second feed auger sections 128, 130 to improve the air seal and reduce the
chances
for burn back. The air lock 132 is more important for granular, or other,
materials that
do not naturally compact when conveyed by an auger.
As mentioned above, and in accordance with a preferred embodiment, the feed
auger 126 is split into first and second auger sections 128, 130 with an
airlock 132
positioned there between. After passing through the first auger section 128,
airlock 132
and second auger section 130, the carbonaceous feedstock enters the pyrolytic
reactor
chamber 116, which houses a rotating auger 134 or some other mixing device.
The
carbonaceous feedstock is formed into plugs as the feedstock is conveyed by
the first and
second auger sections 128, 130. The formation of plugs within the first and
second auger
sections 128, 130 in combination with the airlock 132 excludes air from the
reactor
chamber 116. Where bum-back is not a concern, the feeding system may consist
simply
of a single feed auger or multiple augers feeding into the reactor chamber or
other
feeding devices. In accordance with a preferred embodiment of the present
invention,
the heat carrier 121 is hot steel shot, although a variety of heat carriers
may be utilized
widiout departing from the spirit of the present invention.
In accordance with a preferred embodiment, the feedstock is injected into the
bed of downwardly flowing heat carrier 121 or, alternatively, above the bed of
downward
flowing heat carrier 121. Char, ash and the heat carrier 121 exit the
pyrolytic reactor
chamber 116 via a separation and recovery mechanism 120 in which the heat
carrier 121
is recovered for further use and separated from the char. Once the char and
heat carrier
121 are separated, the char (which contains the feedstock ash) is passed to a
char storage
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hopper 136 via an auger 137 (or some other conveying mechanism). From there,
char
product is removed and, as needed for process heat, a portion of the char is
sent to a
char/syngas burner (or furnace) 118. In particular, char is separated out from
the heat
carrier 121 by the separation and recovery mechanism 120, and conveyed via an
auger
137 to a lock hopper 136 for storage.
As briefly mentioned above, the char and heat carrier mixture exiting the
pyrolytic reactor chamber 116 are immediately separated. As those skilled in
the art will
appreciate, separation is impacted by the physical and chemical properties of
the char and
heat carrier 121. In accordance with a preferred embodiment, a stationary
screen or
moving screen (for example, including trommel or shaker screens) is used to
separate the
char and heat carrier 121 based upon relative particle size. With reference to
Figure 4, a
trommel screen 138 is employed in accordance with a preferred embodiment. The
trommel screen 138 includes an open ended, slightly inclined rotating
horizontal cylinder
140 whose outer surface is covered with a screen 144. The opening size of the
screen
144 is changed over the length of the cylinder 140 with hoppers 146 placed
beneath the
different screen sections 144a, 144b in order to recover and keep separate the
various
particle sizes. More particularly, the cylinder 140 in accordance with the
present
invention includes a first section 144a with a fine screen shaped and
dimensioned for the
passage of char therethrough and a second section 144b with a more coarse
screen
shaped and dimensioned for the passage of heat carrier 121 therethrough.
Oversize particles may pass the entire length of the cylinder 140 and drop off
the
exit end 148, where they are recovered separately. Screen opening size, speed
of screen
rotation, size of screen surface area, screen diameter, angle of screen
inclination and
other factors are some of the control parameters that may be adjusted to
control
screening effectiveness for separation of the char and heat carrier 121.
In accordance with an alternate embodiment, and with reference to Figure 5, an
air classifier system 150 may be employed for the separation of char and heat
carrier 121.
The air classifier system 150 uses heat carrier 121 and char particle weight
differences to
facilitate the separation thereof. In accordance with a preferred embodiment,
the air
classifier system 150 is implemented by conveying the heat carrier 121 and
char mixture
with a conveying mechanism 152 and letting the mixture drop off the end of the
conveying mechanism 152 where it would be subjected to rapidly moving air
streams.
The heavier heat carrier 121 particles fall immediately to a bin 154
substantially directly
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below the end of the conveyor 152, while the lighter char particles are
conveyed by the
air stream to a settling chamber 156 where they slow down and settle out.
In accordance with yet a further separation technique, and with reference to
Figure 6, a magnetic separation system 158 may also be employed for the
separation of
char and heat carrier 121. In accordance with a preferred embodiment, the
magnetic
separation system 158 utilizes a heat carrier 121 that can be attracted to a
magnet and
thus separate=the heat carrier 121 from the char. More particularly, the
separation system
158 includes an inlet 160 and a rotating magnetically active drum 162. The
heat carrier
121 is attracted to the magnetically active drum 162 (which includes magnets
163
mounted along the outer surface of the drum) and binds thereto, while the char
passes
through the drum 162 and out of the separation system 158 where it is
collected for use
or further processing. The bound heat carrier 121 is removed from the drum 162
as it
rotates via a scraper 164 which forces the heat carrier 121 off the drum 162
and into a
collection system 166 for recycling of the heat carrier 121.
In accordance with an alternate embodiment, it is contemplated the magnets may
be mounted stationary just beyond the surface of the rotating drum causing the
heat
carrier to be held against the rotating drum as it tums. Stationary magnets
would only be
positioned along a portion of the rotating drum's surface (reducing the number
of
magnets needed) and ending at the top of the drum, causing the heat carrier
121 to be
released as the rotation of the drum carries the heat carrier 121 away from
the influence
of the magnets.
Referring to Figure 7, a hybrid separation and recovery system is disclosed
combining the features of the air classifier system disclosed with reference
to Figure 5
and the magnetic separation system disclosed with reference to Figure 6. In
accordance
with this embodiment, separation is achieved using a magnetic head pulley 162'
on the
conveying mechanism 152'. If magnetized heat carrier 121 is used, the heat
carrier 121
will follow the belt 153' of the conveying mechanism around the head pulley
162' before
dropping off into a bin (not shown). The lighter char is then thrown forward
into a
settling chamber 156'.
Separation of the char and heat carrier may also be accomplished by using
electrostatic charges to attract the char and thereby separate it from the
heat carrier. The
characteristics of the char particles, particularly size, versus the heat
carrier, allow for
separation of the char particles from the heat carrier. The collected char
particles can
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then be periodically removed from the plates or surfaces by a number of means,
such as
rapping the plates, reversing the charges, and other means.
It is also contemplated, separation of the char and heat carrier may be
accomplished by using a cyclone, typically oriented vertically, whereby the
heat carrier
and char are conveyed into the cyclone by a rapidly moving gas stream, or
other means,
and separated by density differences of the respective particles. Those
skiIled in the art
will appreciate that these methods may be used separately or in combination
with other
methods.
By implementing the separation and recovery of the char as outlined above, the
following improvements are noted. The excess char may be sold as a co-product.
Char
can have values of over $100 per ton and, for wood, can be in the range of 25%
of the
incoming dry weight of the wood. For poultry litter, it can be in the range of
45% of the
incoming dry weight of poultry litter and can have values over $180 per ton.
Thus, the
separated and recovered char can represent a substantial revenue stream.
In addition, removal of the char allows for better process temperature control
as
the amount of char fuel can be precisely metered into a burner based upon
process heat
requirements. The removal of char also allows the char/syngas burner 118 to be
placed
outside the process loop and does not require the introduction of air into the
process
material flows or process loop. Therefore, the char/syngas burner 118 is not
impacted
by other process conditions and allows better control of combustion air since
primary
and secondary air can be introduced and controlled separately. Since the
char/syngas
burner 118 is separate from the process, it simplifies recovery of ash after
combustion of
the char. For example, one method is the use of a cyclone and/or a bag house
in the
burner stack emission stream. In fact, one design uses a burner that is also a
cyclone so
as the char is burned, the ash is automatically separated from the stack gases
and
recovered.
For various reasons, clinkers may sometimes be formed in the process or
foreign
objects may be introduced into the system. The use of a char/heat carrier
separation
system allows the removal of these oversize or foreign particles before they
cause a
problem. More particularly, and with reference to the trommel screen
separation and
recovery mechanism 138 discussed above, the screen 144 of the separation and
recovery
mechanism 138 is constructed with a fine mesh screen along the first section
144a at the
initial length of the screen 144 to remove fine char particles. The fine mesh
screen is
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followed by a coarser screen along the second section 144b at the final length
of the
screen 144 with openings just large enough for the heat carrier to pass
therethrough.
The clinkers (as well as stones, tramp metal, and other large particles) drop
off the exit
end 148 of the screen 144 where they may be recovered and removed by various
means.
As discussed above, the char and heat carrier 121 are separated. Once the char
has been separated from the heat carrier 121, the separated heat carrier 121
is transferred
to and readily reheated in a heat exchanger 122 associated with the pyrolytic
reactor
chamber 116 and the char/syngas burner 118. Char acts as an insulator and,
since it
typically has particle sizes smaller than the heat carrier 121, it tends to
fill the voids
between the heat carrier 121 partides thus effectively insulating the heat
carrier 121
particles. Char can also tend to act as a "flowable filP' when mixed with the
heat carrier
121, which may then cause the char/heat carrier mixture to set up when a
conveying
auger is stopped. By separating the heat carrier 121 and char, especially if
performed as
soon as possible after the reactor chamber 116, this inefficiency is
eliminated and the
heat carrier 121 may be reheated in a much more efficient manner.
As such, the heat carrier 121 is coupled with a heat exchanger 122 that is
heated
by the separately controlled char/syngas burner 118 as previously described.
The heating
of the heat carrier 121 can, therefore, be better controlled. For example, and
with
reference to Figures 2 and 8, one or more augers 168 may be used to move the
heat
carrier 121 through the heat exchanger 122 and back to the reactor chamber 116
for
reuse thereof. The auger diameter, length, rotational speed, and other factors
(all of
which effect heat carrier 121 residence time and heat exchanger effic.iency)
may be varied
to suit specific applications. In addition, the heat exchanger 122 shell
temperature and
the heating of the sheli in the counter current or co-current mode may also be
adjusted
to control the efficiency of the heat transfer process. In addition, so long
as the heat
exchanger 122 throughput is sized to match the process loop heat carrier mass
flow
recirculation requirements, the exchange process can be controlled
independently of the
rest of the process.
As those skilled in the art will certainly appreciate, the heat exchanger 122
may be
formed as part of the heat carrier recirculation loop, thus combining the
function of the
heat exchanger 122 so that it can be both a heat exchanger and a conveyor (see
Figures 2
and 8). This simplifies construction and reduces capital and O&M costs for the
system.
More particularly, the heat carrier 121 is returned to the reactor chamber 116
via a heat
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exchanger 122 composed of a jacketed auger 168. The jacketed auger 168
provides a
flow path for the heat generated by the char/syngas burner 118. In this way,
the heat
carrier return (or heat exchanger) 122 functions as both a heat carrier return
mechanism
and a heat exchanger designed to heat the heat carrier 121 prior to being
reintroduced
into the reactor chamber 116. Heat exiting the heat exchanger 122 may be
directed to a
jacket 169 surrounding the reactor chamber 116 to provide additional heat
transfer to the
reactor chamber 116 and then directed to the dryer 12 (see Figure 1) to
provide heat for
drying. Alternatively, the heat from the heat exchanger may be ducted directly
from the
heat exchanger to the dryer or recovered for other uses.
Gas and vapor depart the pyrolytic reactor chamber 116 via a tube 114 and may
be directed to a condenser system 172 or, alternatively, the gas and vapor-
comprising a
syngas-may be used for energy directly without a condensing system. Condensed
liquids, for example, bio oil, are collected by virtue of a liquid transfer
pump or pumps.
The gas and vapor is directed out of the pyrolytic reactor chamber 116 via an
exit
tube 114. Prior to entering the condenser system 172, the gas and vapor may be
cleansed
by passing it through a char trap 178 and a tar trap 180, as well as other
suitable cleansing
devices. Vapor and gaseous material depart the pyrolytic reactor chamber 116
via the
gas exit chamber 114 and are ultimately directed to a condenser system 172.
Condensed
liquids (for example, including bio oil) from the condenser system 172 are
transferred to
storage tanks 182 by gravity or by virtue of one or more liquid transfer
pumps.
The uncondensed gases, which can contain considerable energy value (for
example in the form of syngas), are also collected and used for energy by
directing them
to the char/syngas burner 118 or for applications independent of the pyrolysis
process.
The uncondensed gases may be used for energy by using the uncondensed gases to
fuel
an engine (for example, reciprocating internal combustion engine, combustion
turbine, or
Stirling engine) to provide mechanical and/or electrical power and heat for
the process.
Depending upon the type of feedstock and the feedstock moisture content, there
can be
enough energy in the uncondensed gas to supply all the electrical and/or heat
requirements of the present system 100. The use of the uncondensed gas can
thus
minimize or eliminate the need for extemal fuel sources which reduces
operating expense
and may allow the units to be operated in remote areas (for example, military
camps
and/or logging camps).
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Conventional condenser designs subject vapors exiting the reactor chamber to
either a cold surface or a cold liquid stream (which may be bio oil, water, or
another
suitable liquid stream) to cause the vapors to condense to create a single
liquid product
that is a mixture of many chemicals. Due to the physical and chemical
characteristics of
the liquid product generated, the resulting liquid pyrolysis oil product using
these
methods may have limited uses and thereby limitations in value.
In accordance with a preferred embodiment, and with reference to Figure 12,
one
or more fractional condensation columns 300 may, therefore, be employed in
accordance
with a preferred embodiment of the present invention. The fractional
condensation
column(s) 300 include a series of plates 302a-i which are connected directly
to the reactor
chamber(s) 116 (typically above the reactor chamber 116 to take advantage of
the
tendency of the warm, low-density vapor to rise) to create an integral unit so
that the gas
and vapor generated by the process in the reactor chamber 116 is continuously
and
immediately passed through the condensation columns 300.
More particularly, the condensation column 300 has intemal packing, or, more
typically, horizontal plates 302a-i (for example, sieve trays) similar to a
distillation tower
to create points for condensation of the vapors to occur as the vapors pass
through the
previously condensed liquids with some reflux liquid returned to the highest
plate. The
temperature inside the condensation column 300 will decrease as the vapors
flow upward
and the composition of the liquids on the plates 302a-i will reflect the
boiling point of
the liquid as in a similar fractional distillation column. Additionally, if
needed, the
internal temperature of the condensation column 300 can be controlled by
heating or
cooling systems placed around the condensation column 300 at different
heights. Thus,
the liquid on each plate 302a-i will have a different chemical composition as
reflected by
the boiling point of the liquid. Liquids from the different plates 302a-i may
be extracted
continuously as the reactor 116 is fed feedstock continuously and gas and
vapor is
produced and fed continuously to the condensation column. The upward flow of
gas
and vapor from the reactor 116 may be aided by a recycling stream consisting
of the non-
condensable gas from the process or by another suitable gas.
By coupling the reactor chamber with a fractional condensation system as
described above, a simpli$ed, continuous method of recovering various
chemicals from
condensed liquid is achieved. This minimizes or eliminates the need for
additional
processing of the liquid (which requires additional equipment, energy and
cost) in order
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to recover chemicals from the liquid product. It also reduces cost since an
additional
extraction, upgrading, separation, and/or other system is not necessary to
recover the
chemicals and multiple, individual condensers are not required.
As discussed above, a char/syngas burner 118 is utilized in burning the
separated
and gathered char for use in heating the heat carrier 121 and thereby the
pyrolytic reactor
116. The char is combusted in a combustion device that is outside the process
loop.
Referring to Figure 9, the device may be, for example, a fluidized bed burner
or a
suspension burner that could be in the form of a horizontal or vertical
cylinder, or air
spreader stoker or other device. In accordance with a preferred embodiment of
the
present invention, the char/syngas bumer 118 includes a refractory lined
combustion
chamber 184 through which char is blown along a tangent with the combustion
air. The
char is combusted while suspended by centrifugal force against the cylinder
walls 186.
Although a horizontally oriented combustion chamber 184 is disclosed in
accordance
with a preferred embodiment of the present invention, those skilled in the art
will
appreciate that a vertical combustion chamber could be employed without
departing
from the spirit of the present invention.
By utilizing a better designed char/syngas burner 118, better efficiency in
using
the char is provided and process heat for the plant is provided. Both types of
systems
provide for very rapid burning response because only a very small amount of
fuel is in
the burner 118 at any one time. The fluidized bed system also has the
distinction of
infiaite tumdown since one can stop feeding fuel to it for a period of time
and, so long
as enough heat is retained in the refractory insulation and bed material to
ignite incoming
fuel, can start up automatically when fuel is again fed into the bu.rner. As
those skilled in
the art will certainly appreciate, a variety of burcrner configurations are
commercially
available. However, in accordance with a preferred embodiment some or all of
the char
is burned outside the process loop to provide some or all of the process heat.
As discussed above, a pyrolytic reactor chamber 116 is utilized in accordance
with the present invention. In accordance with the present reactor design, the
biomass is
conveyed into the reactor chamber 116 with an auger or some other feed
mechanism
126. The heat carrier 121 enters the reactor chamber 116 above the biomass so
as to
sweep the lighter biomass particles into the vapor/gas stream downward with
it.
Alternatively, the biomass may be fed directly into a bed in the reactor
chamber 116
consisting of the heated heat carrier 121. The reactor chamber 116 throat
cross sectional
CA 02656684 2008-12-30
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area may be increased in size to decrease the velocity of the vapor/gas so as
to minimize
the particulate carryover. The inside of the reactor chamber 116 may be lined
with
refractory material to increase its efficiency and the inside of the reactor
chamber 116 is
designed to be free of protrusions which may impede flow of materials or form
a basis
for buildup of slag.
Various methods of mixing the biomass and the heat carrier 121 in the reactor
chamber 116 can be used as a replacement for a traditional horizontal auger
configuration. For example, a stirred tank reactor 116' may be utilized or a
rotating
cylinder 116" may be utilized (see Figures 10 and 11, respectively). More
particularly, the
stirred tank reactor 116' includes a tank 188 into which the biomass is
dumped. Within
the tank may be positioned a series of agitators 190 mounted upon a rotating
shaft 192.
The agitators 190 rotate within the tank 116' to mix the biomass such that
vapor and gas
exit the top 194 of the tank 116' and heat carrier 121 and char exit the
bottom 196 of the
tank 116'. With regard to a rotating cylinder reactor 116", the reactor
includes a cylinder
or drum 198 oriented substantially horizontally. Material flow through the
drum 198 may
be assisted with a slight downward tilt in the direction of the desired
biomass flow or by
the positioning of flighting internal to the drucn's surface. As those skilled
in the art will
certainly appreciate, flighting is essentially a series of internal paddles,
which may be
continuous or discontinuous, fastened to the inside wall of the drum. The
flighting lifts
the material as the drum rotates and allows better mixing of the biomass
particles and
heat carrier as the mixture falls back to the bottom of the drum. The drum 198
includes
a series of internal flights 200 for mixing of the biomass as it is passed
therethrough. As
the drum 198 rotates and the biomass is rotated, for example, vapor and gas
exit the
drum at the proximal end 202 thereof while the char and heat carrier 121 exit
at the distal
end 204 thereof along the line of flow for the biomass. Although various
reactor designs
are contemplated in accordance with a preferred embodiment of the present
invention,
other reactor designs including variations of these examples could certainly
be
implemented without departing from the spirit of the present invention.
In addition, the char/heat carrier/oversized particle screening system can be
incorporated into the reactor design in several ways. This eliminates the need
to have a
separate screening system and thus simplifies construction. For example, if
the reactor
consists of a single auger in a trough or tube, the later part of the trough
or tube can be a
screen that can be of different size openings to accommodate the separation of
fine char
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partides, heat carrier particles and oversized particles. Alternatively, the
screen could be
a trommel screen on a common shaft with the horizontal niixing auger in the
reactor.
The present reactor design allows for quick vaporization of very small sized
feedstock particles upon their entry into the reactor. The resulting very
small char
particles may be swept upward by the flow of gas and vapor and may form
deposits on
the ducting and condenser surfaces that cause plugging of passages. They may
also
contaminate the bio oil. By injecting the biomass beneath the heat carrier or
into a heat
carrier bed within the reactor chamber, these particles are swept downward by
flow of
the heat carrier. The reactor throat cross sectional area may also be
increased in size to
decrease gas and vapor flow rates from the reactor and thereby decrease the
amount of
particulate carryover in the gas and vapor stream. The inside of the reactor
may be lined
with refractory to provide better insulation and a hotter, more even
temperature
environment for the reactor. The inside of the reactor throat is smooth so
that falling
biomass does not become hung up on it in any manner. If, the screen and
reactor are a
common system, the need for separate screening system is eliminated and
construction
of the plant is simplified.
With regard to the condenser, a settling chamber or cyclone may be added
between the reactor and the condenser to remove particulates out of the
gas/vapor
stream before they reach the condenser system. A heat transfer fluid may be
used for
controIling the condenser temperature. This heat transfer fluid may be used as
a direct
contact condenser or in an indirect contact condenser such as a shell and tube
condenser.
Finally, the condenser may utilize non-stick surfaces to minimize or prevent
tar/char
build up.
The settling chamber of the condenser minimizes the amount of char the gets
into the bio oil. The use of the heat transfer fluid simplifies the control of
the condenser
system since one can obtain heat transfer control fluids that go up to several
hundred
degrees Fahrenheit without boiling or cracking. By using proportional
controls, one can
control the oil temperature, and hence condenser temperature, very precisely.
Finally, by
using non-stick materials or coatings, the formation of tar build up and
subsequent
plugging can be minimized or eliminated.
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While various preferred embodiments have been shown and described, it will be
understood that there is no intent to limit the invention by such disdosure,
but rather, is
intended to cover all modifications and alternate constructions falling within
the spirit
and scope of the invention as defined in the appended claims.
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