Note: Descriptions are shown in the official language in which they were submitted.
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GASIFIER SYSTEM
This invention relates to a gasifier unit for
generating combustible gases from organic biomass
material. The combustible gases generated are burned to
generate heat which is captured by a heat exchange system
or used to produce electrical power or for other
purposes.
Gasifiers for converting organic biomass materials
such as wood chips are well known. For example, United
States Patent 5,138,957 issued August 18, 1992 to Morey
et al. discloses a typical gasifier system. The biomass
fuel is fed into a primary chamber from below to form a
fuel bed. The atmosphere in the primary chamber is
maintained at a high temperature in the range of 1200-
1300 ~F by limited combustion of the gases generated from
the fuel bed. Air to support the limited combustion is
admitted through a system of manifolds. The fuel bed
smoulders in the primary chamber and the incomplete
combustion that occurs in the body of the fuel bed is
responsible for the generation of combustible gases that
are collected and oxidized in a secondary chamber that is
maintained at temperature range of 2200 to 2500 ~F.
Sufficient air is supplied to the secondary chamber to
fully combust the combustion gases in order to generate
heat.
The fuel bed is gradually converted into ash and an
ash disposal system is provided to periodically remove
ash, dirt and clinkers from the primary chamber for
disposal.
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The present invention is directed to a gasification
unit that offers a number of improved features over
conventional gasifiers.
The auger conveyor feeding biomass material to the
bed is formed with a upstanding member that projects into
the bed to assist in distributing new material outwardly
away from the central auger site. This ensures that
foreign materials in the biomass material such as rocks,
dirt and sand are continually moved to the outer edges of
the biomass bed and the bed maintains its preferred
generally frustoconical shape for efficient gasification.
In another feature, the unit of the present
invention has a unique table and air manifold structure
for delivering air through the bed of biomass material.
A zone of no air supply is provided at the edge of the
table where clinkers (accumulations of dirt, rocks and
sand) normally tend to form. Not providing air at the
edge of the table prevents the flow of air under the
biomass bed to the outer edge of the table. In
conventional gasifiers, airflow in the relatively thin
edge layers of the biomass combined with ash as fuel
tends to create a blow torch effect that rapidly
deteriorates the table edge and the ash removal system.
As a further improvement according to the present
invention, a cooling unit can be added to further lower
temperatures at the edge of the biomass bed. Scraping
members are provided to extend inwardly over the edge of
the table to break off and break up clinkers that do form
at the table edge and deposit them into the waste removal
system. Without a zone of no air supply in which to
work, the scraping members would be rapidly destroyed by
the blow torch effect described above. In addition, the
manifolds of the present gasifier system are formed with
sealable clean out passages to allow dirt and small rocks
to be removed from the air chambers without shutting down
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the entire gasifier. Such dirt and small rocks are
present in the biomass and tend to fall into the manifold
chambers where they can plug the air chambers.
In a further improvement, the gasifier unit of the
present invention includes a waste handling system to
receive ash and foreign material from the primary
chamber. The handling system includes a sealed waste
passage with an auger. The passage acts as an ash dump
bin and includes an air supply system for further
gasification of the waste ash. The waste handling system
is sealed so that the entire gasifier unit including
primary and secondary chambers and the waste handling
auger can be maintained at sub-atmospheric pressure to
induce a draft through the unit that improves
gasification efficiency and gas flows through the
gasifier unit. Conventional gasifiers tend to rely on a
natural draft system. A fan unit is provided in the
gasifier unit of the present invention at the secondary
chamber to create the negative internal pressure.
As a still further improvement, the gasifier unit of
the present invention includes a removable collection
chamber for particulates that is associated with the
secondary chamber. The collection chamber communicates
with the secondary chamber via a passage formed with a
lip that protrudes into the secondary chamber to direct a
portion of high velocity cyclonic flow created in the
secondary chamber into the collection chamber where lower
flow velocity causes deposition and collection of
particulates and slag.
Accordingly, in a gasifier unit incorporating all of
the above features, the present invention provides a
system for gasifying organic biomass material to produce
combustible gases comprising:
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an enclosed primary heating chamber having a top
wall, side walls and a floor with a raised table for
supporting a bed of biomass material and a generally
central opening in the table;
a conveyor system for delivering biomass material
through the central opening to create and maintain the
biomass material in a generally frustoconically shaped
mass on the table, the conveyor system including a
portion that extends upwardly into the base of the
frustoconically shaped mass to push new biomass material
outwardly from the central opening;
an air supply manifold below the table for
delivering air upwardly through the bed from adjacent the
central opening to the edges of the table, the manifold
being dimensioned to define an annular zone of no air
supply adjacent the edge of the table;
a waste removal system adjacent the perimeter of the
table to remove ash and waste from the primary chamber
including inwardly extending scraping members positioned
over the edges of the table to scrape material from the
annular zone of no air supply into the ash removal
system;
a waste handling system to receive waste from the
removal system including a sealed waste auger with an air
supply system for further gasification of the waste and
ash;
a discharge passage in the chamber for release of
gases produced by the bed;
a secondary chamber in communication with the
discharge passage for heating the gases from the
discharge passage and establishing a cyclonic flow of
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gases to remove suspended particulates from the flow to
produce a flow of hot combustible gases, the secondary
chamber including a collection chamber for particulates;
and
means for maintaining the primary and secondary
chamber at a negative pressure.
Aspects of the present invention are illustrated,
merely by way of example, in the accompanying drawings in
which:
Figure 1 is a schematic, partially sectioned side
elevation view of a gasifier system incorporating the
improved feature of the present invention;
Figure 2 is a section view taken along line 2-2 of
Figure 1 showing the fuel bed table and the waste removal
system of the present invention;
Figure 3 is a detailed view of the auger used in the
waste handling system of the present invention; and
Figure 4 is a detail cross-sectional view of the
auger of Figure 3.
Referring to Figure 1, there is shown a gasifier
unit 2 according to a preferred embodiment of the present
invention for gasifying organic biomass material to
produce combustible gases.
The gasifier unit includes an enclosed primary
heating chamber 4. The chamber has a top wall 6, side
walls 7 and a floor 8 with a raised table 10 for
supporting a bed of biomass material 12 to be gasified.
As is conventional, the primary chamber is constructed of
a steel shell lined with refractory material that acts as
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a heat sink to maintain the primary chamber at high
temperature during operation of the gasifier unit.
Floor 8 comprises a steel plate and the entire
primary chamber 4 is supported above ground level 14 by
legs 15 to permit access for cleaning and maintenance to
the manifold system 16, the waste removal system 17 and
the waste handling system 18 of the gasifier which are
located at or adjacent the floor of the primary chamber.
Floor 8 supports raised table 10 having a generally
central opening 20 to permit vertical conveyor 21 to
deliver organic biomass to the table. Conveyor 21 is fed
by generally horizontal conveyor 22 which transports
material from storage hopper 24. Storage hopper 24 is,
in turn, fed from a main supply (not shown) of biomass
material such as wood chips or the like by conveyor 25.
Hopper 24 is fed by conveyor 25 to ensure a constant and
steady supply of biomass material to gasifier unit 2.
Vertical conveyor 21 includes an auger 26 that lifts
biomass material into primary chamber 4 to create and
maintain biomass bed 12 in a generally frustoconically
shaped mass on table 10. As shown in Figures 1 and 2,
auger 26 includes an additional portion comprising plate
30 welded to the end of the auger to protrude through
central opening 20 into the base of the biomass bed. As
auger 26 rotates plate 30 acts to push biomass material
way from the central opening to maintain the
frustoconical shaped of the bed. Plate 30 also tends to
move denser non-organic foreign material such as rocks,
dirt and stone to the outer edges of the biomass bed
where it can be removed by the waste removal system of
the present invention. Without plate 30, foreign
material tends to remain mixed in with the biomass
material and as the biomass is gasified, clinkers or
lumps of melted foreign material form at the surface of
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the biomass bed and prevent efficient removal of waste
ash from table 20. The result is the biomass bed tends
to build upwardly on the table and clinkers accumulate
requiring frequent shutdown of the system to clean out
foreign material.
An air supply manifold 16 is positioned below table
10 to provide air to biomass bed 10 from below to travel
upwardly through the bed. Referring to Figure 1, air
supply manifold comprises a plurality of concentric
annular chambers 32 in communication with a source of
pressurized air (not shown). Each annular chamber 32 is
formed with a series of air feed openings 33 to deliver
air through the bed of biomass material at a velocity
that does not disturb the bed and prevents biomass
material from falling into chambers 32. In the event
that material such as dirt and small rocks does get into
chambers 32, the manifold of the present system is
provided with sealable access passages 34 that can be
opened from below via hinged doors to remove the dirt and
rocks before they adversely affect air flow through
openings 33. In prior art gasifier designs, it is
generally necessary to shut down the entire system and
remove the table to access and clean out the manifold
chambers.
Manifold chambers 32 extend from adjacent central
opening 20 to a region short of the table edge to define
an annular zone 35 of no air supply adjacent the edge of
table 10. Preferably zone 35 includes means for cooling
the zone in the form of a sealed outer annular chamber 38
fillable with a cooling fluid such as air or water that
can be continuously recirculated to maintain a lowered
temperature.
Zone 35 with no air supply is provided at the edge
of the table where clinkers (accumulations of dirt, rocks
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and sand) often tend to form. Not providing air at the
edge of table 10 prevents the flow of air under the
biomass bed 12 to the outer edge of the table. In
conventional gasifiers, airflow in the relatively thin
edge layers of the biomass combined with ash as fuel
tends to create a blow torch effect that rapidly
deteriorates the table edge and the ash removal system of
the gasifier. Cooling of zone 35 acts to cause breakup
of clinkers that do form for quick and efficient removal
of the clinkers by the improved waste removal system of
the present invention which will be described. In
prototype testing, it has been determined that a cooled
no air zone 35 that is approximately 8 inches wide works
well.
When the gasifier unit is working under steady state
conditions, biomass bed 12 smoulders and gasifies. The
incomplete gasification that occurs in bed 12 is
responsible for giving off incomplete products of
combustion comprising gases with entrained fly ash.
These gases exit primary chamber 4 through discharge
passage 42 as indicated by arrows 40 in Figure 1 for
further processing in secondary chamber 46. Air supplied
through manifold 16 is sufficient to provide enough
oxygen to create gas production in the smouldering bed
which ideally is flaming evenly only over its outermost
layer. The interior of bed 12 is only incompletely
gasified and gives off combustible gases in great volume.
The gases are mixed with only sufficient air provided
through a plurality of ports 48 in side walls 7 to
combust only that small portion of the gases that will
maintain the temperature of the atmosphere in the primary
chamber at a level sufficient to sustain the gasification
process.
As biomass bed 12 is continually replenished by new
biomass material, older material moves upwardly and
21 88736
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outwardly to the outer surface of the bed in a continuous
manner and chars as gases are released to create ash.
Foreign material in the biomass bed tends to form
clinkers. The ashes and clinkers are waste material that
must be removed from the primary chamber. The gasifier
unit of the present invention includes a waste removal
system to accomplish this task.
Figure 2 iS a section view taken along line 2-2 of
Figure 1 showing the waste removal system 17 of the
present invention comprising a ring member 49 in primary
chamber 4 mounted for rotatable movement in the annular
channel 50 defined by the side walls and the floor of the
chamber and raised table 10. As is conventional, ring
member 49 is formed with internal teeth 52 adapted to
15 engage with drive gear 54 of motor 56 which is activated
to rotate ring member 49 about an axis defined by central
opening 20. A plurality of spaced plough members 55 are
mounted on ring member 49 and, when ring member 49 is
periodically rotated, ash and clinkers that accumulate in
20 channel 50 are pushed to a waste aperture 56 in the floor
of the primary chamber and removed from the chamber.
With reference to Figures 1 and 2, it can be seen
that two of the plough members 55 are formed with
scraping member 60 that extend inwardly over the edge of
25 table 10. Scraping members 60 sweep ash from the edge of
table 10 into channel 50 for disposal. As well, the
scraping members tend to break off and break up clinkers
that form at the table edge. Note that scraping members
60 operate in cooled zone 35 having no air supply.
Without a zone of no air supply in which to work, the
scraping members would be rapidly destroyed by the blow
torch effect previously described.
In the apparatus of the present invention, waste
material that is pushed through waste aperture 56 enters
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a waste handling system 18 for further processing.
Figures 1, 3 and 4 illustrate the component parts of
waste handling system 18 which includes an enclosed waste
passage 70 that extends from a dump bin 71 that receives
5 waste and ash by gravity from waste aperture 56. Within
passage 70, there is an auger 72 that collects and moves
waste clinkers and ash from dump bin 71 to a sealed gate
73. Waste material is held in dump bin 71 and passage 70
for further treatment and periodically dumped from
passage 70 at gate 73 for collection and disposal at a
waste site.
Figure 3 and 4 are detail views of auger 72 which
includes an air supply system to supply air to the waste
material retained by auger 72 for further gasification of
the waste and ash. Auger 72 has a hollow shaft 75
defining a passage 76 that is supplied with air under
pressure. The walls of passage 76 are formed with a
plurality of air feed holes 78 to deliver air to the
waste and ash held by auger 72. Providing air to the
20 waste ash permits further gasification of the material
during the hold period. Carbon combustion of the ash
occurs to convert the ash from a substantially carbon ash
to a mineral ash.
As best shown in Figure 3, auger 72 is designed with
25 a flight pattern that varies along the length of shaft
75. Auger blades 80 are formed at a first smaller pitch
in zone 82 at the end of the auger adjacent waste
aperture 56. Preferably, air feed holes 78 are formed
only in zone 82. A second larger pitch zone 84 is formed
30 at the end of auger 72 adjacent gate 73. The smaller
pitch blades 80 tend to compact the loose waste and ash
that falls into dump bin 71 from waste aperture 56
thereby acting to create a plug seal of material in auger
72. The waste handling system is in open communication
35 with primary chamber 4 via waste aperture 56 so that
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waste ash and clinkers can be scraped and delivered to
dump bin 71 as required. Therefore, a plug seal of waste
passage 70 is necessary to permit maintenance of the
entire gasifier system at a negative pressure as will be
described in more detail. Gate 73 also serves to seal
waste passage 70 to permit the entire gasifier system to
be maintained at a negative pressure.
As is conventional, the gasifier unit of the present
invention includes a secondary chamber 46 in
communication with primary chamber 4 through discharge
passage 42 as best shown in Figure 1. Secondary chamber
46 is generally cylindrical and discharge passage 42
enters chamber 46 at a tangent in order to promote the
cyclonic flow of gases within the secondary chamber.
Secondary chamber 46 is lined with refractory material in
a similar manner to the primary chamber. Additional air
is added to the gases from primary chamber 4 through vent
90 to support total combustion and oxidation of the gases
to maintain the temperature of the atmosphere in the
secondary chamber into the range of 2200 to 2500 ~F. In
secondary chamber 46, the gases from primary chamber 4
are also cleaned of entrained particulate matter to
produce heated gases that support efficient final
combustion and oxidation. The cleaning action of the
gases is achieved due to the cyclonic flow of gases in
the secondary chamber which causes entrained ash to move
outwardly to the hot internal wall of the secondary
chamber where the ash is combusted and oxidized or tends
builds up as slag. In conventional gasifier units, build
up of slag over time significantly reduces the volume of
the secondary chamber and the gasifier unit has to be
shut down periodically for cleaning.
The secondary chamber of the gasifier unit of the
present invention is provided with a collection chamber
100 for particulates and slag to avoid the foregoing
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problem of slag build up in the secondary chamber.
Collection chamber 100 is a generally vertically aligned
cylinder that is removably attachable below the secondary
chamber by coupling 102. Collection chamber 100
communicates with secondary chamber 46 via a passage 104
formed with a lip 106 that protrudes into the secondary
chamber to direct a portion of the high velocity cyclonic
flow 108 from the secondary chamber into the collection
chamber where lower flow velocity causes deposition and
collection of particulates in the collection chamber.
Any molten slag that develops in the secondary chamber
also tends to drain into collection chamber 100. The
result is that secondary chamber 46 does not clog with
slag material so that efficient gas flow through the
chamber is maintained.
To further improve gas flow through the gasifier
unit of the present invention, means for maintaining the
primary and secondary chamber at a negative pressure are
provided in the form of a fan unit 110 positioned
downstream of the secondary chamber in exhaust stack 113
to maintain a negative pressure of at least .05
atmospheric pressure in the primary and secondary
chambers in order to induce gas flow through the
chambers. The sealed condition of the waste handling
system 18 permits dumping of collected waste and ash
while maintaining negative pressure throughout the
gasifier chambers.
Although the present invention has been described in
some detail by way of example for purposes of clarity and
understanding, it will be apparent that certain changes
and modifications may be practised within the scope of
the appended claims.