Down-draft fixed bed gasifier system

A gasifier system for obtaining relatively clean combustible gaseous products from solid fuel materials, such as processed sewage sludge, comprises a gasifier reactor which communicates a raw, combustible gas to a cyclone separator, a gas scrubbing device and a gas cooling and drying device. Gas which exits the system is relatively clean and may be used in a prime mover for the production of energy. The gasifier reactor of the present invention is a down-draft fixed bed gasifier. The gasifier is constructed of several interconnected modular units. Moreover, the gasifier is constructed so as to efficiently gasify fuel materials while maintaining excellent horizontal temperature control.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to down-draft fixed bed gasifiers for 
converting biomass material such as wood and processed sewage sludge to a 
low BTU combustible gas. More particularly the invention is directed to 
such a gasifier having a cleaning system for processing the gas produced 
from the gasifier. 
2. Background of the Invention 
The expense and potential shortage of petroleum-based fuels makes the use 
of biomass fuel an attractive alternative. At the same time, biomass 
materials such as wood waste and other wastes such as sewage and/or 
industrial sludge are in abundant supply in most parts of the world. 
Indeed, supplies of such materials are so extensive that disposal of wood 
waste and sludge has become a problem. It would be advantageous to 
efficiently dispose of such materials and, at the same time, obtain useful 
fuel products from them. 
Gasifiers which convert wood products, garbage and biomass materials to 
combustible gases are disclosed, for example, in U.S. Pat. Nos. 4,659,340; 
4,583,992; and 4,348,211. However, many currently known gasifiers lack 
efficiency because it is difficult to achieve acceptable horizontal 
temperature control (i.e., stratified horizontal zones of constant 
temperature) within the gasifiers. Moreover, many known gasifiers may 
product combustion by-products which have a high ash and particulate 
matter content. Accordingly, there is a need for an apparatus which will 
efficiently convert biomass materials (i.e., wood scrap and sewage sludge) 
to useful fuel products. 
SUMMARY OF THE INVENTION 
A primary objective of the present invention is to provide a gasification 
apparatus which efficiently converts biomass materials such as wood waste, 
sewage sludge and other such organic compositions, having up to 25 percent 
inorganics, to a useful, combustible gas. Another objective of the 
invention is to provide a gasifier apparatus in which horizontal 
temperature control within the gasifier is easily obtained and maintained. 
A further objective of the invention is to provide a gasification 
apparatus in which the various components which constitute the apparatus 
are modular and exchangeable with other such components having different 
features and characteristics. It is also an objective of the invention to 
provide a gasification apparatus and a cleaning system for such an 
apparatus which yields a relatively dry and clean combustible gas. Other 
objectives of the invention will be apparent to those having ordinary 
skill in the art upon reading this disclosure. 
The above objects are accomplished by providing a gasification system, 
including a gasifier reactor, a scrubber apparatus and a dryer apparatus, 
which efficiently converts biomass materials such as sewage sludge, other 
organic wastes and wood waste to a low BTU combustible gas. 
The gasifier apparatus is of the type known as a down-draft fixed bed 
gasifier. Generally, the gasifier is a vertically-oriented apparatus, 
having an uppermost portio which comprises a hopper for receiving solid 
fuel. The fuel may be communicated through the hopper and selectively 
operable seals, to vertical, adjacent chambers in which the fuel is first 
dried and preheated, and then gasified. The seal assembly preferably is an 
air-tight, electric, hydraulic or pneumatic sliding gate valve which is 
positioned below the hopper. Optionally, a second hopper, followed by a 
second seal assembly, may be disposed below the first seal assembly for 
more efficient and safe operation of the gasifier. 
The vertical chambers of the gasifier comprise a first, drying chamber, and 
intermediate and lower gasification chambers. The chambers are modular 
units which are vertically aligned and in direct communication with each 
other. The inner walls of each chamber are generally constructed so as to 
be slightly diverging. However, some portions of the intermediate and 
lower chambers may have inwardly diverging walls as disclosed hereinafter. 
The intermediate chamber, which hosts the highest temperature during the 
gasification reaction, features air inlets which extend through the outer 
skin of the gasifier to enable air to be drawn into the gasifier during 
the gasification process in order to promote and maintain the gasification 
reaction. 
An annular flange extends downwardly from the intermediate chamber into the 
lower chamber. Within the lower chamber a gas discharge passageway is 
formed between the outer walls of the flange and the inner walls of the 
lower chamber. The gas produced as a result of the gasification reaction 
is drawn downwardly within the gasifier from the intermediate and lower 
chambers where the gas is generated, then upwardly into the gas discharge 
pathway. At the top of the gas discharge pathway the gas is withdrawn from 
the gasifier through two gas discharge conduits which extend through the 
gasifier wall on opposite sides of the gasifier. 
An eccentrically rotatable grate is disposed at a bottom portion of the 
lower chamber. The grate serves as a base upon which fuel may rest, and 
also provides a means for breaking clinkers and ash particles into smaller 
units. In addition, the grate has a number of openings through which ash 
particles may pass to a collection chamber disposed below the lower 
gasification chamber of the gasifier. The collection chamber may be 
emptied of its contents by an auger or a discharge screw. 
The gasification system also includes several elements to clean, dry and 
cool the gas generated by the gasification process. One or more cyclone 
separators for removing larger particulate wastes entrained with the gas 
communicate with the gas discharbe conduits of the gasifier. After the gas 
is passed through the gas discharge pathway it proceeds downstream to a 
gas scrubbing and cooling unit and finally to a gas drying unit. Upon 
exiting the gas drying unit the gas may be transported to a prime mover 
for the production of energy. Alternatively, the gas may be fed into a 
prime mover, boiler or incinerator immediately after exiting the cyclone 
separator if purity of the gas is not essential. 
The gas scrubbing and cooling apparatus of the present invention comprises 
a circuitous passageway through which the gas passes. This passageway is 
interrupted by several baffle regions which alter the flow rate of the gas 
and provide an increased surface area to facilitate the removal of solids 
from the gas. In addition, gas flowing through the scrubber is contacted 
by a fluid spray which further facilitates the removal of solids. 
The gas drying apparatus generally comprises a vertically oriented 
structure which houses filters and baffle regions to facilitate the 
removal of moisture and solids from the gas. 
The gasifier system of the present invention is designed to be useful for 
the gasification and subsequent treatment of a variety of fuels. For 
example, the fuels which may be utilized with the present system include 
organic and biomass materials such as wood scrap, processed sewage sludge, 
and processed manures, as well as conventional fuel materials such as 
coal. The fuels which may be burned in the present gasifier apparatus may 
also include those which have relatively low BTU values (i.e., less than 
11,000 BTU) as well as those possessing higher BTU values. Moreover, the 
size of the gasifier apparatus may be modified to accommodate specific 
applications. Thus, the following disclosure refers to embodiments which 
are desirable for smaller gasifier units (60-110 kwe) as well as for 
larger units (greater than 110 kwe) and very large units (about 180 kwe).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, gasification system 10 generally includes a gasifier 
12, a gas scrubbing and cooling apparatus 14 and a gas drying apparatus 
16. The gasifier 12 converts a solid fuel to a useful, combustible gas 
which is cleaned, cooled, and dried by scrubbing apparatus 14 and drying 
apparatus 16. Following the cleaning and drying operation, the gas may be 
delivered to a prime mover 18 or similar apparatus to produce energy 
either before the gas cleaning and drying operations (if a clean fuel is 
not essential), or after the cleaning and drying operations (if a clean 
fuel is desirable). 
The gasifier of the present invention is advantageous as it provides 
excellent horizontal temperature control within the portions of the 
gasifier where gasification occurs. That is, within the gasification 
chambers of gasifier 12, the temperature at a given point is substantially 
constant across a horizontal cross section of the gasifier at that point. 
Such horizontal temperature control facilitates efficient gasification. 
The gasifier apparatus 12 of the present invention may be used to convert a 
variety of solid fuel materials, having either high or low BTU values, to 
a useful, combustible gas. The gasifier apparatus may range in size from 
small (i.e. 60-110 kwe output) to large (i.e. over 110 kwe output). 
Gasifier 12 may be a vertically-oriented device with a generally 
cylindrical shape. Referring to FIGS. 2 through 5, the gasifier 12 
comprises a hopper 20 which is disposed above a seal assembly 22 which may 
take the form of a sliding gate valve. Disposed directly below the sealing 
apparatus 22 is a drying chamber 24 which represents a first chamber of 
the gasifier reactor. An intermediate chamber 26 which forms a 
gasification chamber is disposed directly below and in communication with 
the drying chamber 24. A lower chamber 28, which forms a second 
gasification chamber, is disposed directly below and in communication with 
intermediate chamber 26. An end cap 9 forms the bottom-most portion of the 
gasifier, providing a collection chamber for ash waste while also sealing 
the bottom of the gasifier to the outside environment. Preferably, the end 
cap 29 does not rest on the ground, but is instead supported by legs 30. 
Each of the components of gasifier 12 is a modular unit which is 
independent of other components of the gasifier. The modular design 
enables the various modules to be interchangeable and useable with the 
other modular components having different sizes or characteristics. It 
should also be appreciated that chambers 24, 26 and 28 are each bottomless 
modules which are in direct communication with each other. 
As best shown in FIG. 2, gasifier 12 may also include a rate 66 disposed at 
a bottom portion of chamber 28. Grate 66 preferably is eccentrically 
rotatable, having a high point offset from its center. Moreover, grate 66 
includes elongate openings 68 which facilitate the removal of ash waste 
from the interior of gasifications chambers 26 and 28 to a collecton 
chamber within end cap 29. Grate 66 is rotated by shaft 70 which may be 
driven by a suitable motor (not shown). 
A stirring rod 31 may, optionally, be mounted upon grate 66 and extend 
upwardly therefrom into gasification chambers 26 and 28. Stirring rod 31 
aids in dispersing the fuel so as to avoid the formation of "hot spots" 
within chambers 26 and 28 during the gasification process. Stirring rod 31 
can have radial paddle elements 33 which assist in dispersing the fuel. 
FIG. 2 illustrates one embodiment of the invention generally suitable for 
both smaller and larger gasifier units. This embodiment features a single 
hopper 20 and seal 22. The hopper 20 features a generally circular or 
rectangular opening 32 having inwardly diverging walls. The opening 32 
leads to a hopper chamber 34, where fuel is temporarily stored. Hopper 
chamber 34 has a generally cylindrical shape with outwardly diverging 
walls. Fuel which is input to the hopper chamber 34 is prevented from 
entering the drying chamber 24 by sealing assembly 22. Once seal 22 is 
opened, the fuel will flow directly into chambers 24, 26 and 28 and will 
rest on grate 66. 
FIG. 8 illustrates another embodiment of the invention, generally 
well-suited for very large gasifier units (e.g., 180 kwe). In this 
embodiment, the gasifier 12 features a secondary hopper 21, disposed below 
seal assembly 22, and a secondary seal assembly 23, disposed below 
secondary hopper 21. One advantage of this embodiment is that, with the 
use of a secondary hopper 21 and a secondary seal 23, the gasifier is 
rendered essentially free of air drafts entering the reactor from the 
hopper 20. The seals 22, 23 are designed such that at least one of the two 
seals will be closed at all times. Thus, when fuel is added to the 
reactor, the first seal 22 is opened while the secondary seal 23 remains 
closed. Seal 22 will close only after the secondary hopper 21 has been 
charged with fuel. Secondary seal 23 is not opened until after first seal 
22 is closed. 
The dimensions of hoppers 20, 21 are not critical to the operation and 
efficiency of the gasification apparatus, as long as they are of a size 
sufficient to accommodate a suitable amount of fuel to efficiently 
practice the gasification process. Those having ordinary skill in the art 
may easily design a hopper module useful with the present gasification 
apparatus. 
The hoppers 20, 21 and seals 22, 23 are each modular components which may 
be removed and replaced with other components independent of each other, 
having different features, dimensions or characteristics. 
Referring again to FIGS. 2 and 8, in a preferred embodiment of the 
invention drying chamber 24 is a substantially cylindrically shaped module 
having side walls which taper outwardly. The drying chamber 24 preferably 
is constructed of a single inner wall. The inner wall of the drying 
chamber may be constructed of a steel or stainless steel compound. In 
another embodiment of the invention (not shown), useful with fuels having 
high moisture contents, drying chamber 24 may have a double inner wall 
construction in which the innermost wall is constructed of a stainless 
steel material which has a multitude of perforations. Moisture is removed 
through the perforations in the innermost wall and collected and withdrawn 
through a drain element incorporated between the two walls. The modular 
feature of the present gasifier apparatus facilitates efficient 
modification of the gasifier by simply exchanging a module for chamber 24, 
(e.g., one similar to that described with respect to a preferred 
embodiment) with another having different features or characteristics 
(e.g., a double wall construction). 
The intermediate chamber 26 is also a modular unit which may be bolted or 
similarly joined to the bottom portion of drying chamber 24. Chamber 26 
has inner walls which diverge outwardly to a slight degree until reaching 
a lower, keel portion 36, which has inwardly diverging walls as best shown 
in FIG. 2. The intermediate chamber 26 preferably has a single inner wall 
38 made of a refractory ceramic material or refractory cement. In a 
preferred embodiment, a refractory cement is poured into a mold of a 
desired shape to form chamber 26. 
In an embodiment desirable for use with larger gasifier units (e.g., 
approximately 110 kwe), illustrated in FIG. 2, chamber 26 has dual radial 
air inlet conduits 40 and axial air inlet conduit 42 which supply to the 
gasifier air necessary for the pyrolysis reaction. Radial inlet conduits 
40 are disposed exterior of and adjacent to opposite sides of chamber 26. 
The conduits 40 communicate with an annular manifold 45 which surrounds 
the gasifier and extends through outer shell 46 and refractory wall 38 of 
chamber 26. The annular manifold 45 disperses incoming air into nozzles 41 
disposed within the walls of chamber 26, in both upper and lower rows, 
about the circumference of chamber 26. The manifold 45 includes a diverter 
valve (not shown) which directs air flowing from manifold 45 into chamber 
26 by way of the upper and/or lower row of nozzles. Both the upper and 
lower row of nozzles direct air into the chamber 26 at a slight downward 
angle. Chamber 26 typically preferably has approximately 20 to 30 nozzles 
in each row. 
Axial air inlet conduit 42 extends angularly through the wall of drying 
chamber 24 and downwardly into the center of chamber 24 as shown in FIGS. 
2, 3 and 4. Referring to FIG. 2, conduit 42 bends within chamber 24 to 
extend downwardly into preliminary gasification chamber 26, becoming 
coaxial with the longitudinal axis 52 of gasifier apparatus 12. Conduit 42 
terminates in a nozzle (not shown). The nozzle of conduit 42 may be of a 
variety of designs. For example, it may be capped at the bottom and open 
at the sides to allow air to exit in a substantially horizontal manner. 
Alternatively, the nozzle of conduit 42 may have a baffle which causes air 
to flair upon exiting the nozzle. In yet another embodiment, the nozzle 
may include extension pipes (not shown) which direct the air further into 
chamber 26. 
For smaller gasifier units (e.g., 60-80 kwe), chamber 26 may be slightly 
modified by eliminating axial inlet conduit 42. The nozzles 41 supply an 
amount of air sufficient for such units. 
For very large gasifier units (e.g., 180 kwe), chamber 26 may feature an 
air inlet system as shown in FIGS. 8 and 9. Referring to FIG. 8, radial 
air inlet conduits 40 communicate with manifold 45 which, in turn, 
communicates with internal air supply pipes 57, connected between manifold 
45 and an internal air manifold 59. Internal air supply pipes 57 each 
include a multitude of outlet nozzles 53 for distributing air into chamber 
26. Internal air manifold 59 also includes similar nozzles 55 for 
releasing air into chamber 26. Preferably, nozzles 53 and internal air 
supply pipes 57 are disposed in a side of pipes 57 facing away from the 
direction in which strirring rod 31 turns the fuel. 
In each of the above embodiments, the air inlet conduits communicate with a 
fan 50 which, when desired, may force air into the gasifier. Fan 50 draws 
outside air from a vent stack 51 for disposal within the gasifier. 
Generally, fan 50 is necessary to force air into chamber 26 only at the 
initiation of the gasification reaction. After the initiation of the 
reaction, a vacuum force is created by a blower unit 90 located downstream 
of gasifier 12. The vacuum force draws air into the gasifier 12 through 
vent stack 51. 
Also shown in FIG. 8 is stirring rod 31 which includes stirring flanges 35 
(instead of radial paddles 33) to disperse the fuel. Flanges 35 are 
disposed within chamber 26 extending throughout the length of chamber 26 
from a location just below internal pipes 57 to the keel 36 of chamber 26. 
Moreover, each flange is of a width sufficient to allow it to extend 
substantially from the stirring rod 31 to the inner wall of chamber 26. 
Flange 35 is adapted to rotate in a chosen direction so as to completely 
turn the fuel within chamber 26. 
Moreover, in order to protect stirring rod 31 from damage due to melting, 
where extremely high temperatures will be encountered within the gasifier, 
water may be passed upwardly though rod 31. As the water ascends through 
rod 31, it is converted to steam as it exits through nozzles 55 in 
internal manifold 59. This feature also aids in controlling temperatures 
within the gasifier. 
Referring to FIGS. 3 and 4, apparatus 12 may also include a water spray 
assembly 112. Water spray assembly 112 comprises a water storage tank 114 
having attached thereto water conduit 116. Water conduit 116 delivers 
water to conduit 118 which, in turn, leads to conduits 120. Conduits 120 
extend through the wall of drying chamber 24 and deliver a water spray 
into the bottom portion of chamber 24 and intermediate chamber 26. The 
water spray assembly is selectively operable and is useful in providing 
additional temperature control within the gasifier apparatus 12. 
Lower gasification chamber 28, like chambers 24 and 26, also forms a 
modular unit which may be joined with the other components of apparatus 
12. Chamber 28 is bolted or similarly secured to the bottom of the module 
which forms chamber 26. The top portion of this chamber is substantially 
cylindrical in shape, having inner walls 47 which diverge outwardly 
throughout most of its length. At a lower portion of chamber 28 the inner 
walls 47 diverge inwardly, but never meet, to form a bottom portion 49 of 
chamber 28. The inner walls 47 of chamber 28 are also constructed of the 
type of refractory material described with respect to chamber 26. 
Additional temperature control within chambers 26 and 28 may be provided by 
internal cooling lines (not shown) disposed within the walls of chambers 
26 and 28. In this embodiment chambers 26 and 28 both feature a double 
interior wall wherein each interior wall is constructed of stainless 
steel. Cooling lines may be disposed between the two walls. 
Referring to FIGS. 2 and 8, within the top portion of chamber 28 is an 
annular flange 56 which is integral with and extends downwardly from the 
innermost wall 38 of chamber 26. The flange 56 is spaced apart from the 
inner wall of chamber 28 by a slight distance, for example, by 
approximately 3-4 inches. The gap between the outer wall of flange 56 and 
the inner wall 47 of chamber 28 forms a gas discharge pathway 60. Gas 
discharge pathway 60 leads to radial gas discharge conduits 62 which 
remove the combustible gas produced by the gasification process from 
apparatus 12 and transport it to downstream processing stations. Discharge 
conduits 62 are offset by an angle of approximately 45.degree. to 
90.degree. from radial air inlets 40, thereby allowing advantageous 
circulation of air and gas before the gas exits the gasifier through 
discharge conduits 62. (For the purposes of illustration the bottom 
portions of the gasifiers shown in FIGS. 2 and 8 have been rotated 
90.degree..) In addition, the bottom edges 64 of flange 56 are rounded in 
order to reduce eddies and currents in the vicinity of discharge conduit 
62. 
The bottom portion 49 of chamber 28, which begins slightly below flange 56, 
is characterized by inwardly diverging walls. The bottom-most portion of 
chamber 28 is occupied by an eccentrically rotatable grate 66 (best shown 
in FIGS. 2 and 8) which has slot-like openings 68. As noted above, grate 
66 is mounted upon a rotatable support shaft 70. The grate serves as a 
base upon which any fuel added to the system may rest during gasification. 
Additionally, ash particles and any "clinkers" which may form during the 
gasification process are broken up by the eccentric rotation of grate 66 
and fall beneath grate 66 through holes 68. Ash particles and clinkers are 
collected in a chamber formed within end cap 29 which lies beneath the 
grate 66. These accumulated wastes may be removed through conventional 
methods using, for example, an auger (not shown) or a discharge screw (not 
shown). 
Slots 68 of grate 66 may have serrated edges (not shown) which may 
cooperate with a stationary bar (not shown) to assist in the breaking up 
of clinkers. The stationary bar may be disposed a predetermined distance 
above grate 66 such that clinkers lodged between the bar and the serrated 
edges of the slots are broken up so as to easily pass through slots 68. 
As shown in FIGS. 3, 4 and 5, gas discharge conduits 62 each lead to 
cyclone particle separator units 74. For larger capacity gasifiers, 
conduits 62 preferably lead to a single, larger cyclone separator unit 
which may replace separator units 74. The single separator unit (not 
shown) may be disposed between the gasifier apparatus 12 and scrubber 
apparatus 14. The gas discharge conduits enter the cyclone particle 
separators 74 (or alternatively a single separator unit) at top portions 
thereof. The gas exiting cyclone separator(s) proceeds through conduits 76 
to connector 78 and then to downstream processing stations. 
The cyclone separator units 74, or a single separator unit, can be of 
virtually any type generally known in the art, and are designed to remove 
larger particulate wastes which are entrained with the exiting gas. The 
dimensions of the cyclone separator units may be easily determined by 
those having ordinary skill in the art to accommodate a given gasifier 
unit. 
Conduit 80 communicates with connector 78 and thus conduits 76 and directs 
the gas to scrubbing and cooling apparatus 14 through scrubber inlet port 
81 which preferably is mounted at the top portion of the scrubbing/cooling 
vessel. Scrubber 14, as best shown in FIG. 6, is a vertically oriented 
vessel having a plurality of concentric chambers 82 which form a 
circuitous pathway. Each chamber 82 contains one or more contact points 84 
which impede flow through a portion of the passageway. Contact points 84 
comprise a plurality of ceramic or steel elements which act as baffles and 
provide a tortuous path with a relatively large surface area through which 
the gas must flow. A spray nozzle (not shown) is preferably disposed 
slightly above each contact point 84. The spray nozzles are oriented to 
downwardly project a spray of an aqueous cleaning solution into the gas 
stream and onto contact points 84 to remove particulate impurities. 
Moreover, larger particulate impurities adhere to the ceramic or steel 
elements which comprise the contact points 84. 
Referring to FIG. 6, the gas stream enters the top portion of the outermost 
chamber 82A of scrubber 14. The gas flows downwardly through chamber 82A 
as it is drawn through the scrubber 14 by a vacuum force created by blower 
unit 90. Upon reaching the bottom of chamber 82A the gas is drawn upwardly 
through chamber 82B after which it proceeds through chamber 82C. The gas 
is then drawn out of the scrubber unit 14 and through blower unit 90, then 
forced into dryer 16. Additional aqueous solution may be added to the gas 
as it passes through blower 90. 
In a preferred embodiment scrubbing and cooling unit 14 also features a 
collection vessel 86 disposed below the scrubber 14 and in communication 
with pathways 82. Waste liquid and solid debris from scrubber 14 is drawn 
by gravity to the bottom portion of scrubber 14 and into collection vessel 
86 through waste conduit 87. Waste liquid and debris collects within 
holding chamber 89 of vessel 86. Generally, solid debris will fall to the 
bottom of vessel 86 where it is allowed to collect. When sufficient liquid 
is added to vessel 86 it overflows holding chamber 89 and is collected in 
separation channel 91. Generally, the liquid collected in channel 91 is 
relatively free of impurities and may be withdrawn from the system by way 
of conduit 88 and reused. 
Water is the preferred aqueous solution for use in scrubber 14 and dryer 
16. However, one skilled in the art may deem it advantageous to include 
detergents or other surfactants in the solution. In some instances, such 
as when burning a fuel having a high soot content, it may be desirable to 
use certain oils as a cleaning solution in order to remove soot from the 
gas. 
Upon exiting blower 90, the gas enters dryer apparatus 16 through conduit 
92 and an inlet port 94, preferably disposed in the bottom portion of 
dryer 16. Dryer 16 is a vertically-oriented vessel, designed to remove 
moisture from the gas and to further cool the gas. Gas entering dryer 16 
initially passes through a first separator plate 98 and then flows 
upwardly through a screen-like perforated plate 100. Next, the gas flows 
through a second separator plate 102, followed by a baffle system 104. 
Finally the gas passes through a mist-eliminating screen filter 106 and 
exits the drying chamber through outlet 108 disposed at a top portion of 
dryer 16. The gas may then be directed to a prime mover 18 for generating 
energy. 
Separator plates 98 and 102 comprise a plurality of angularly-oriented 
plates 110 mounted adjacent each other. The plates 110 are adapted to 
enable gas to flow through channels formed between the plates. The first 
separator plates 98 alter the flow of gas to direct it downwardly at an 
angle of about 20.degree. to 30.degree. while the second separator plate 
102 similarly alters the direction of gas flow to direct it upwardly at an 
angle of about 20.degree. to 30.degree.. The downstream end of each plate 
features an inwardly hooked portion adapted to further interrupt the flow 
of gas and to remove moisture from the gas. 
Perforated plate 100 is a filter-like screen which is horizontally disposed 
across the entire cross-section of dryer 16. A spray nozzle 109 is 
disposed above the plate 100 to direct a fine spray of water on top of 
plate 100 to form a thin layer of water on top of plate 100. This layer of 
water aids in removing solid impurities from the gas as the gas traverses 
plate 100. 
Baffle system 104 represents a plurality of ceramic or steel elements which 
are disposed across the entire cross-section of dryer 16 and for a 
vertical distance of about 1 to 4 feet. Ceramic or steel elements 111 
provide a tortuous path with an increased surface area through which the 
gas flows. Elements 111 aid in the removal of remaining moisture and 
impurities which may be present in the gas. 
Screen filter 106 is horizontally disposed across the entire cross-section 
of dryer 16 and comprises a relatively fine steel mesh screen which 
facilitates the removal of any remaining water droplets and moisture from 
the gas. 
Dryer 16 also has a collection vessel 92 disposed adjacent its bottom 
portion. The vessel 92 communicates with the main portions of dryer 16, 
and is of a design similar to that described above for collection chamber 
86 of scrubber 14. 
As noted above, the gasifier unit design described herein may apply to 
gasifiers having various output capacities. Accordingly, the size of the 
gasifier itself and its various chambers and components will vary 
depending upon the output capacity of the gasifier. The desired dimensions 
may be easily determined by one having ordinary skill in the art. 
Generally, however, a gasifier unit having an output capacity of 
approximately 180 kwe has dimensions as follows. 
A gasifier apparatus according to the present invention measures 
approximately 5-7 meters in height from the top of hopper 20 to the base 
of gasifier 12. Referring to FIG. 7, the drying chamber 24 has a length 
(L.sub.1) of about 1450 mm while the intermediate and lower chambers 26, 
28 each have a length (L.sub.2) which measures approximately 1000 mm. 
Additionally, the drying chamber 24 measures approximately 900 mm in 
diameter (D.sub.1) at its uppermost portion and approximately 950 mm in 
diameter (D.sub.2) at its bottom portion. The intermediate chamber 26 has 
a diameter (D.sub.3) at its upper portion of about 950 mm, a diameter 
(D.sub.4) at its widest portion (just above keel region 36) of about 970 
mm and a lower diameter (D.sub.5) of about 770 mm. The upper diameter 
(D.sub.6) of lower chamber 28, measured inside of the inner walls of 
flange 56, is also approximately 770 mm. At the base of flange 56 the 
diameter (D.sub.7) increases to approximately 840 mm. At the widest 
portion of chamber 28, measured between the inner walls 47 of chamber 28 
below flanges 56, the diameter (D.sub.8) is approximately 1200 mm. 
The nozzles 41 disposed in the walls of intermediate chamber 26 are, as 
noted above, present in upper and lower rows. The upper row of nozzles is 
preferably located a distance (L.sub.3) of about 350 mm below the top 
portion of chamber 26. The lower row of nozzles is, in turn, located a 
distance (L.sub.4) of about 550 mm below the top portion of chamber 26. 
Still referring to FIG. 7, the keel region 36 of intermediate chamber 26 
begins a distance (L.sub.5) of approximately 850 mm below the top portion 
of chamber 26. Keel region 36 extends over a distance (L.sub.6) of about 
150 mm. Flange 56 extends into lower chamber 28 for a distance (L.sub.7) 
of about 600 mm. Gas discharge pathway 60 is approximately 125 mm in width 
(W.sub.1) as measured between the outer wall of flange 56 and the outer 
wall 47 of chamber 28. Moreover, the length (L.sub.8) of gas discharge 
pathway is about 500 mm. 
It is understood that the above dimensions are intended to be exemplary, 
and should not be read to limit the scope of this invention to covering 
only those gasifiers having dimensions as disclosed above. One skilled in 
the art may easily make modifications to the dimensions set forth above 
for a gasifier having an output capacity of about 180 kwe, or may 
construct a gasifier having a smaller or larger output capacity which 
necessarily will require modifications to various dimensions of the 
gasifier. It is further understood that the dimensions set forth above all 
may vary within the range of .+-.15% of the stated values without 
adversely affecting gasifier performance. 
Additional exemplary dimensions which may be used with larger and smaller 
gasifier units are set forth in Table I. The dimensions shown in Table I 
correspond to the regions identified in FIG. 7. 
TABLE I 
______________________________________ 
Exemplary Gasifier Dimensions 
______________________________________ 
Thermal input 
(kW) 100 300 600 1500 2000 2500 
Electrical output 
(kWE) 20 60 120 300 400 500 
Input % 
4 12 24 60 80 100 
Dimensions: (mm) 
D.sub.4 
320 600 780 1250 1440 1600 
D.sub.5 
250 443 600 990 1140 1280 
D.sub.7 
280 500 650 1080 1250 1400 
D.sub.8 
460 800 950 1540 1760 1920 
L.sub.8 
325 400 450 600 750 900 
L.sub.7- L.sub.8 
80 100 100 125 150 175 
L.sub.6 
70 100 100 160 180 200 
L.sub.5 
500 600 800 900 950 1000 
L.sub.3 
200 250 350 375 400 450 
L.sub.4 
320 400 550 550 600 650 
______________________________________ 
All values .+-.15% 
The operation of the gasifier system 10 of the present invention is 
efficient and relatively simple. Fuel 11 is input through hopper 20 (and 
any secondary hopper). In another embodiment of the invention, the hoppers 
may be omitted and fuel, such as processed sewage sludge, is fed to the 
gasifier directly from the sludge processing equipment. The fuel of the 
present invention may comprise biomass material such as wood waste, wood 
scrap, manure or it may comprise processed sewage sludge which has been 
dewatered, dried and processed into a briquette-like form. Such a sewage 
sludge treatment process is described in U.S. Pat. Nos. 3,525,685 and 
3,772,188 to Edwards. It is understood that other methods of processing 
sewage sludge and other sludges for use as a gasification fuel may also be 
practiced in conjunction with the present invention. 
To initiate the fire required for the gasification process, a small amount 
of fuel may be placed within preliminary gasification chamber 26 and 
primary gasification chamber 28. This fuel is ignited, and when it begins 
to burn rather intensely, additional fuel is added until chambers 24, 26 
and 28 are filled. While the fuel is being ignited it may be necessary to 
force air into chamber 26 through conduits 40 and 42 by way of fan 50. 
Thereafter, sufficient quantities of air to satisfy the gasification 
process will be drawn into chamber 26 without the aid of fan 50 as a 
vacuum force will be created by downstream blower unit 90. 
During the gasification process, the temperature within the gasifier 
typically ranges from approximately 100.degree. C., in the drying chamber, 
to approximately 600.degree. C. in the vicinity of grate 66. The highest 
temperature (approximately 900.degree. C.-950.degree. C.) exist in the 
intermediate chamber in the vicinity of the air nozzles. The temperature 
decreases gradually and uniformly from the region of highest temperature 
to a region just above keel 36. The temperature at the keel region 
increases slightly to about 750.degree. C. and thereafter decreases 
gradually and uniformly to a temperature of about 600.degree. C. adjacent 
grate 66. Moreover, the present gasifier exhibits efficient horizontal 
temperature control. Thus, at any given vertical point of the gasifier, 
the temperature should be substantially constant throughout a cross 
section of the gasifier at that point. 
Through the gasification reaction which occurs within chambers 26 and 28, a 
combustible gas (comprising approximately 47% nitrogen, 21% carbon 
monoxide, 1.5% methane, 20% hydrogen, 10% carbon dioxide and 0.5% oxygen) 
is produced. This gas is continually removed from the gasification 
apparatus 12 through gas discharge pathway 60 and gas discharge conduits 
62 as a result of the vacuum created by blower unit 90. As previously 
noted, gas discharge conduits 62 are offset from 45.degree. to 90.degree., 
and preferably 90.degree., from radial air inlets 40. It is believed that 
this configuration contributes to a greater circulation of air and 
combustible gas within chambers 26 and 28 and contributes to the excellent 
horizontal temperature control achieved by the present gasifier apparatus. 
The gas exits chamber 28 through discharge conduits 62 disposed on either 
side of gasifier apparatus 12. Each conduit 62 leads to a cyclone 
separator 74 which removes any large particulate matter from the gas. The 
gas exits the cyclone separators and travels through a conduit to the 
scrubber unit 14. 
Once in the scrubber apparatus, gas flows from a top inlet port 81 and 
proceeds through concentric chambers 82. As the gas proceeds through 
chambers 82, it periodically encounters contact points 84 which comprise a 
baffle system of steel or ceramic elements to provide a large surface area 
over which the gas flows in order to remove solids such as particulate 
wastes, ash and tars. Gas flowing through chambers 82 can also be 
contacted with a spray of an aqueous solution to further facilitate the 
removal of particulates. The gas exits scrubber apparatus 14 through 
outlet port 88 and is drawn into a blower unit 90. At the blower 90, an 
aqueous solution may optionally be added to the gas in order to aid in 
removing any remaining solids. 
Blower 90 forces the gas and aqueous solution into a bottom inlet 94 of 
dryer 16. The gas proceeds through a downwardly, angularly oriented first 
separator 98 which removes solids from the gas. Thereafter the gas 
proceeds upwardly through a perforated plate 100 which removes moisture 
and solids from the gas. As the gas flows upwardly through perforated 
plate 100, it next contacts a second separator plate 102 through which the 
gas flows upwardly at a slight angle. Second separator plate 102 also aids 
in the removal of solids from the gas. Beyond second separator plate 102, 
the gas flows through a baffle region 104. The baffle region provides a 
relatively large surface area over which the gas may flow in order to 
remove moisture and solids from the gas. Finally, the gas flows upwardly 
through a relatively fine mesh screen 106 which is horizontally disposed 
across the entire cross-section of dryer apparatus 16. Screen 106 removes 
any remaining moisture from the gas. 
Upon exiting the dryer 16 through outlet port 108, the gas may be directed 
to a prime mover 18 for the production of energy. 
The gasifier apparatus may also be operated in a manner different than that 
described above in order to provide an effective increase in the capacity 
of the gasifier and the BTU value of the exiting gas. For example, the 
gasifier may be operated as a pressurized system rather than simply as a 
vacuum system. In such an embodiment, it is best to utilize a gasifier 
apparatus having a double seal structure (e.g., utilizing seal 22 and seal 
23 as shown in FIG. 8). Air may be fed into the gasifier, through an 
electric fan or a turbocharger attached to a downstream engine, to 
pressurize the gasifier up to a maximum of 30 psi. This method has been 
found to be effective to increase the capacity of the gasifier by up to 
50%. 
The gasifier apparatus may also be operated in such a way that the air fed 
into the gasifier is essentially free of nitrogen. In this embodiment, the 
exiting gas will have 85-90% less nitrogen and will thus have 
approximately double the BTU value than when the gasifier is operated in 
the conventional manner. Nitrogen may be removed from the air fed into the 
gasifier by conventional catalytic means, such as by way of a Xor-Box 
apparatus, manufactured by XorBox Corporation of Tonawanda, N.Y. Further, 
increases in gasifier capacity may be achieved when the nitrogen-free gas 
is used in a pressurized gasifier system. 
FIG. 10 is an energy balance diagram for a gasifier having an output of 
about 180 Kwe, constructed according to the present invention. The diagram 
illustrates that of the fuel input to the gasifier, approximately 83% 
yields a combustible gas. During the cooling/scrubbing process 
approximately 12% of the energy is lost as the gas remaining following 
these processes is about 71% of the total energy available from the fuel. 
This gas is fed into a generator unit which may utilize energy from the 
gas as follows: 19% to engine cooling; 24% to engine exhaust; 2% to 
process losses, 7% returned to the gasifier system; and 19% of the 
production of electricity. Of course, the above energy balance is given by 
way of example only, and the actual energy balance may differ somewhat 
from what is stated above. Generally, however, the electrical output range 
between about 19% and 20%. 
Having described preferred embodiments of the present apparatus, it is 
understood that additional modifications to this system may be made by one 
having ordinary skill in the art without departing from the scope of the 
present invention.