Apparatus for producing combustible gases from carbonaceous materials

A reactor for generating combustible fuel gases comprising a chamber, an inclined grate extending from adjacent the top of the chamber to near the bottom and sloping forwardly within the chamber from the top to the bottom, said grate dividing the chamber into a primary chamber at the forward side of the grate and an antechamber at the rear side, a conveyor for delivering a solid fuel such as wood chips and other chopped-up woody material to the upper end of the grate at a rate to maintain a continuous bed of fuel from top to bottom, a blower for delivering primary air to a plenum chamber at the downwardly facing side of the grate to sustain combustion of the fuel at the lower end of the bed and to generate sufficient heat above the place of combustion to effect destructive distillation of a portion of the fuel in the bed above the place of combustion said primary air at said place of combustion converting the charcoal remaining after distillates have passed off descending from the place of distillation to CO and ash, an ash pit at the lower end of the grate for receiving the ash, a conveyor situated in the ash pit for removal of the ash to make room for descent of the fuel from above and a port in the forward wall of the mixing chamber at the downwardly facing side of the grate thru which the mixed distillate and CO are removed.

BACKGROUND OF INVENTION 
Recently because of the high cost of oil, gas and electricity the use of 
bio-mass materials such as wood chips, bark, sawdust and the like for 
heating and generation of power is being seriously considered as a 
supplement to and even a replacement for oil, gas and electricity. Such 
apparatus as is available generates so much air borne ash that it is 
objectionable from the standpoint of pollution and is rapidly rendered 
ineffective by deposits of tar and resin on the grates and in the flues. 
The apparatus of this invention is designed to convert bio-mass materials 
such as wood, wood chips, sawdust, bark and the like to a combustible gas 
without generation of pollutants either in the form of solid particles 
such as ash or condensates such as tars and resins and to obtain a maximum 
BTU value per unit of wood consumed. 
SUMMARY OF INVENTION 
As herein illustrated the apparatus for generating combustible gas from 
bio-mass materials comprises a closed retort within which there is 
supported a downwardly and forwardly extending grate which divides the 
retort into a plenum chamber at the downwardly facing side of the grate 
and a mixing chamber at the upwardly facing side of the grate. There is a 
conductor in communication with the interior of the retort at the top for 
supplying the wood in the form of chips to the grate, a port at the bottom 
of the retort in communication with the interior thru which primary air 
can be induced to the downwardly facing side of the grate and a discharge 
port at the forward side of the mixing chamber thru which the gaseous 
products can be delivered to the fire box of a furnace or other heating 
unit in the form of a gaseous combustible fuel for combustion therein. A 
conveyor such as a screw is arranged to deliver wood chips to the 
conductor at the top at a rate to maintain a continuous supply to the 
grate and a blower is provided for introducing primary air to the port at 
the bottom of the plenum chamber at a rate to produce maximum efficiency 
in the conversion without carrying solid particles forwardly from the 
grate into the mixing chamber and at a controlled rate which determines 
the rate of distillation and C .fwdarw. CO conversion. A pit at the lower 
end of the grate is arranged to gravitationally receive the ash below the 
path of flow of the primary air and convection currents so as to isolate 
the ash and there is a conveyor such as a screw in the pit for removing 
the ash, operation of the latter being controlled so as to remove ash only 
when the temperature in the pit is below that of the burning coals at the 
lower end of the grate. A conductor may be employed to connect the stack 
of the furnace or heating unit to which the mixed gases are supplied as a 
fuel to the conveyor by means of which the wood chips are delivered to the 
grate to dry the chips and preheat the same and when such a conductor is 
employed an induction fan is also employed to maintain the necessary draft 
in the furnace or heating unit and to deliver the hot gases of combustion 
from the furnace or heating unit to the conveyor. The retort comprises a 
base from which rises a cupola and the grate which may be in the form of 
horizontally arranged louver-like bars or spaced grids comprising 
transversely spaced parallel bars divides the retort from the top to 
bottom into said plenum and mixing chamber which are narrower at the top 
than at the bottom. A vibrator may be employed to effect vibration of the 
grate and a refractory lining may be applied to a part or all of the 
interior of the retort. 
The method of generating gas from bio-mass material according to the 
invention as carried out by the apparatus described above gravitationally 
moving a layer of wood chips downwardly and forwardly on the upwardly 
facing side of an inclined grate within a confining retort such as to form 
a bed of chips of more or less uniform thickness, establishing a zone of 
combustion near the lower end of the grate, supplying primary air to the 
rear side of the bed in the zone of combustion to effect reduction of the 
chips in such zone to CO and ash, heating of the chips above the zone of 
combustion to a temperature to effect destructive distillation of the 
chips and the evolution of the gaseous medium, collecting the ash at the 
lower end of said zone of combustion below the path of flow of the primary 
air and convection currents, removing the collected ash so as to promote 
progressive gravitational descent of the distilled chips above the zone of 
combustion into the zone of combustion and combining the mixture of 
evolved gaseous medium and CO at the forward side of the bed. Removal of 
the ash at the lower end of the combustion zone is effective only when the 
temperature at the lower end is lower than the burning charcoal. The chips 
are supplied to the upper end of the bed at a rate to maintain a 
continuous layer of chips and the primary air is supplied at a rate to 
maintain combustion without causing the solid particles and ash to become 
air borne. The chips may be dried and preheated prior to delivery to the 
zone of distillation.

The apparatus of this invention is designed to convert bio-mass materials 
such as wood, wood chips, sawdust and other woody materials to a 
combustible gas and deliver it to the fire box of a domestic heating unit 
or commercial boiler and in one form as shown in FIGS. 1, 2 and 3, 
comprises a sheet metal box 10 having top and bottom walls 12 and 14, 
front and back walls 16 and 18 and side walls 20-20 which define an 
interior retort. Intermediate the front and back walls extending 
transversely throughout the entire width of the box from side wall to side 
wall there is a grate comprising downwardly and forwardly inclined grids 
24 and 26 which in conjunction with a fire wall 28 perpendicular to the 
bottom wall 14 divide the interior of the retort into a plenum chamber 30 
and a mixing chamber 32. 
The grids 24 and 26 are of identical construction each comprising, as shown 
in FIG. 3, a rectangular frame having spaced parallel top and bottom frame 
members 34-34, spaced parallel side frame members 36-36 and intermediate 
the latter spaced parallel bars 38 which are parallel to the side frame 
members 36-36. The grids are made of steel with a spacing of 1/8 to 1/2 
inch between the bars depending upon the size of the chips or other 
particulate material to be processed. A typical grid would be made of 1/4 
inch by 11/4 inch bars spaced on 3/4 inch centers with the bars as 
uniformly parallel as possible and finished so as to be free of any 
obstructions on their surfaces. As illustrated the grids diverge slightly 
from top to bottom to facilitate downward flow of the fuel in the space 
between them as it is consumed, however, if the fuel flows readily without 
such divergence the grids may be parallel. The grate is inclined with 
respect to the vertical at an angle of approximately 30.degree., however, 
the inclination may be varied to increase the angle of inclination or 
decrease it according to the flowability of the material being processed. 
If the fuel is sufficiently resistant to free flow the forward grid 24 may 
be omitted. 
At the top of the combustion chamber there is an opening 40 in the top wall 
12 which provides communication with the interior of the retort at the 
upper end of the grate for receiving the lower end of a conductor 42 by 
means of which the material to be burned is delivered to the space between 
the grids. The conductor 42 is connected at its upper end to a conveyor 44 
which is herein shown as a screw 46 rotatably supported within a manifold 
48. The conveyor is driven by a suitable motor so as to transfer the chips 
from a hopper, not shown, to the upper end of the conductor 42. 
There is a port 50 in the rear wall of the retort near the bottom through 
which primary air is delivered to the plenum chamber 30 at the downwardly 
facing side of the grate. A blower F of conventional construction is 
coupled to a flange pipe 52 surrounding the port 50 for supplying the 
primary air to the plenum chamber 30. There is also a port 52 in the 
forward wall of the retort near the bottom designed to be connected to an 
opening 56 in communication with the fire box of a domestic heater or 
boiler so as to transmit the gases generated in the retort directly to the 
fire box. Secondary air is introduced to the mixed combustible gases as 
they enter the heater thru openings 55 provided at the junction of the 
port 54 with the opening 56 as indicated diagrammatically by the arrows. 
The interior surface of the walls 12, 14, 16 and 20 defining the mixing 
chamber 32 are refractory lined. The corresponding portions of the walls 
defining the plenum chamber 30 may or may not be so lined. 
At the lower end of the grate and behind the fire wall 28 there is an ash 
pit in the form of a trough 58 which is spaced from the bottom and extends 
transversely of the plenum chamber from side wall to side wall into which 
the ash gravitates and within the pit there is mounted a conveyor in the 
form of a screw 60 which is rotated periodically as will be described 
hereinafter to remove the ash. 
A chip level switch S1 which controls the operation of the conveyor 44 is 
located in the conductor 42 to maintain the bed of chips between the 
grids, a switch S2 is located in the bin from which the chips are supplied 
to maintain an adequate supply to the conveyor and a switch S3 is provided 
for controlling the rate of discharge of the conveyor 60, operation of the 
latter being controlled by a thermostat T mounted in the pit 58 adjacent 
the lower end of the grate. 
The operation is started by feeding chips thru the manifold 48 to the upper 
end of the conductor 42 wherein they gravitationally descend into the open 
space between the grids forming a relatively thick layer or bed of 
predetermined uniform thickness. When the space between the grids becomes 
filled the chips are ignited at the downwardly facing side of the grate at 
approximately the region C while primary air is supplied to support 
combustion thru the port 50. The primary combustion will proceed upwardly 
toward the region B. As the chips descend from the region A in the 
conductor 42 toward the region B they will be progressively heated to a 
point where distillation will begin at a temperature slightly in excess of 
450.degree. F. so that in the region between zones A and B a gaseous 
distillate is evolved which enters the upper part of the mixing chamber 
32. The conductor 42 above the grates is solid imperforate and since there 
is no draft at this point distillation at the zone A will not occur. As 
the distillation progresses the size of the wood chips shrink until at the 
region C only charcoal remains. In the region C the only reaction will be 
the conversion of the carbon charcoal to carbon monoxide which will be 
drawn into the mixing chamber and become mixed with the gaseous products 
of distillation. As this conversion takes place only a small amount of ash 
will remain and this will drop down into the pit 58 where it will be 
removed by means of the screw 60. The pit as illustrated is located at the 
very lower end of the grate behind the fire wall 28 so that ash that drops 
into it becomes substantially isolated and out of the path of flow of the 
primary air so that it does not become air borne and carried over into the 
mixing chamber. In order to insure that the screw 60 removes only ash a 
thermostat T is provided to control the switch S3 for driving the screw 
only when the temperature over the screw is less than that of the burning 
charcoal. 
As long as the fuel bed is maintained between the grids the rate of 
distillation and thus the ultimate heat output of the system can be 
controlled by regulation of the flow of primary air. This air flow will 
determine the rate in which the incoming fuel can be elevated to 
distillation temperature and also the rate of conversion of charcoal to 
carbon monoxide. The mixed gaseous products of distillation and CO combine 
in the mixing chamber and are delivered to the fire box and the boiler 
together with secondary air, if required. 
It may be desirable to dry the chips to remove excessive moisture and 
preheat them to a temperature somewhat near the temperature of 
distillation as they enter the space between the upper ends of the grids 
and so there is provided means for heating the chips in the hopper or on 
their way from the storage hopper thru the manifold 48 to the grate. The 
means employed may, for example, be the hot gases of combustion emitted 
from the heating unit or boiler delivered to the hopper or manifold thru a 
suitable conductor 62 including an induction draft fan 64. The hot gases 
from the unit or boiler would normally be lost to the atmosphere but by 
conducting them to the hopper the chips may be heated to a temperature of 
approximately 120.degree. F. to 125.degree. F. By following this procedure 
green chips just as they are received from the wood chipper may be used 
with an efficient evolution of wood gas. 
It is also possible to recycle a portion of the hot gases produced within 
the unit by conducting some of these gases into and thru the manifold 48 
so that the chips can actually be delivered to the upper end of the grate 
at a temperature close to the point of incipient destructive distillation, 
for example 325.degree. F., and by so doing substantially increased 
distillation rate may be maintained. 
It is also possible to conduct a portion of the burning charcoal from the 
region C to the region A where it can be admixed with the fresh incoming 
chips so as to substantially increase the rate at which the incoming fuel 
mass is raised to the distillation temperature. The admixture of a portion 
of the hot coals with the fresh chips can increase the capacity of the 
unit by two to three times which would be a considerable factor in 
determining the size of the unit for the particular installation desired. 
Desirably, the hot coals should be removed before complete distillation so 
that it still contains a controlled residual of volatiles. 
A modification of the apparatus is shown in FIGS. 4 and 5 wherein the 
retort comprises a sheet metal box 10.sup.1 having top and bottom walls 
12.sup.1 and 14.sup.1, front and back walls 16.sup.1 and 18.sup.1 and side 
walls 20.sup.1 -20.sup.1 which define an interior combustion chamber. 
Intermediate the front and back walls extending transversely throughout 
the entire width of the box from side wall to side wall there is a grate 
comprising horizontally arranged grid bars 24.sup.1 which in conjunction 
with a riser 28.sup.1 perpendicular to the bottomwall 14.sup.1 divides the 
combustion chamber into a plenum chamber 30.sup.1 and a mixing chamber 
32.sup.1. 
The grid bars 24.sup.1 of the grate are of L-shaped cross section and are 
fastened in spaced parallel relation between spaced parallel frame members 
36.sup.1 -36.sup.1 so as to overlap in louver-like form and so that 
overlapping portions defined a downwardly and forwardly sloping fuel 
supporting surface. In this form of the apparatus the top of the grid is 
arranged so that it is adjacent to the rear wall and the bottom is 
approximately halfway to two-thirds the way between the back and front 
walls. The upwardly facing side of the grid is nearly parallel to the 
front wall. The overlapping bars permits the use of finely dried fuels, 
such as wood shaving, sawdust, etc. without the danger of unburned fuel 
falling thru the grate. Also, the inclined bars help to reduce carry over 
of particles. With this grate system, using dry hardwood chips, heat 
outputs have been developed of up to 500,000 BTU/hrs per square foot of 
grate use. 
At the top of the retort there is an opening 40.sup.1 in the top wall 
12.sup.1 which provides communication with the interior of the mixing 
chamber at the upper end of the grate for receiving the lower end of a 
conductor 42.sup.1 by means of which the material to be burned is 
delivered to the surface of the grate. The conductor 42.sup.1 is connected 
at its upper end to a conveyor, not shown, the latter being driven by a 
suitable motor so as to transfer chips from a hopper to the upper end of 
the conductor 42.sup.1. 
At the bottom of the plenum chamber 30.sup.1 there is a port 50.sup.1 thru 
which primary air is delivered to the plenum chamber 30.sup.1 at the 
downwardly facing side of the grate. A blower F.sup.1 of conventional 
construction is coupled to a flange 52.sup.1 surrounding the port 50.sup.1 
for supplying primary air to the plenum chamber. The mixing chamber 
32.sup.1 has at the bottom a port 54.sup.1 which is connected by a 
conductor 56.sup.1 and venturi 57.sup.1 to the fire box of a domestic 
heater or boiler so as to transmit the gases generated by the unit 
directly to the fire box. Secondary air is delivered to the venturi thru a 
conductor 59.sup.1. The venturi not only provides for mixing the gases but 
also to induce the mixture to flow into the fire box of the unit within 
which it is to be burnt as a fuel. The interior walls of the entire retort 
are lined with a refractory material 61.sup.1. 
At the lower end of the grate and forwardly of the riser 28.sup.1 there is 
an ash pit 58.sup.1 which is below the lower level of the grate and well 
below the port 54.sup.1 into which the ash gravitates and within the pit 
there is mounted a conveyor in the form of a screw 60.sup.1 which is 
rotated periodically to remove the ash. 
As described with reference to the apparatus shown in FIGS. 1 to 3 a chip 
level switch S1 controlling the feed screw is provided in the conductor 
42.sup.1 to maintain a uniform bed of chips on the grate, a switch S2 is 
located in the supply bin from which the chips are supplied to maintain an 
adequate supply of chips, and a switch S3 is provided to control the rate 
of discharge of the conveyor 60.sup.1, operation of the latter being 
controlled by a thermostat T mounted in the pit 58.sup.1 adjacent the 
lower end of the grate. 
The operation of the apparatus shown in this form of the invention is the 
same as that described with reference to the form illustrated in FIGS. 1 
to 3 and hence need not be repeated herein. 
The specific configuration of the apparatus shown in FIGS. 4 and 5 appears 
to be the more satisfactory for adoption as a standard commercial product 
and seems to be especially effective in the handling of a wide variety of 
fuel types. Units of this configuration have been built and tested and 
have developed up to 1.7 million BTU/hour. 
In this form of the invention a vibrator 63.sup.1 may be employed which, as 
shown, is connected to the rear side of the grate thru suitable openings 
in the rear wall for the purpose of vibrating the grate to assist in the 
smooth downward movement of the fuel over the surface of the grate bars. 
Such vibration is used principally for light fuels. 
FIG. 6 is a flow chart diagrammatically illustrating the progress of the 
chips from the storage hopper 66 in the form of green chips to a drier 68 
which may be the manifold 48 and from thence to the wood gas generator 10 
where the chips are converted to gas, the delivery of the gas to the 
furnace 70 for which it is the fuel and finally the delivery of the 
products of combustion produced in the furnace to the stack 72. The stack 
gases, as shown, may be conducted back thru a conduit 62 to the drier 68 
together with a quantity of fresh air by means of the fan 64 and from the 
drier to the atmosphere. Primary air is introduced to the unit, hot gases 
are recirculated and secondary air is delivered to the furnace, all as 
diagrammatically illustrated in the flow chart. 
EXAMPLE 1 
Starting with dry approximately 5% moisture content chips of mixed origin 
of approximately 1/2 inch, produced for example in a conventional wood 
chipping machine, and supplying them to the grate to form a bed of 
approximately 2 inches in thickness from back to front, a mixture of 
gaseous products of distillation and CO were evolved at the rate of 40 
cubic feet per minute having a heat value of 8000 BTU per pound of chips 
delivered to the grates. 
EXAMPLE 2 
Starting with the same mixed chips but in the green condition and 
pre-drying with the waste heat from the stack the green chips may be 
brought to a dry condition to give the same heat value as those in Example 
1. 
Throughout the performance of the apparatus tests were made of the stack 
gases produced and it was found that the solid matter carried over was too 
low to be measurable by conventional equipment used for stack gas 
particulates. Furthermore, daily use for a period of three months of the 
unit for seasoning lumber in dry kilns resulted in no noticeable deposit 
of tar or resins on the interior surface of the unit, the grates and/or 
the ducts leading to and from the unit. 
Conventional boiler controls may be employed to control the primary air and 
thru such control effect modulation of the output. Modulation of the heat 
load can be had by controlling both the primary and secondary air. By 
regulating the feed of fuel and use of primary air to control heating of 
the fuel to above a temperature necessary to effect destructive 
distillation and controlling the rate of conversion of C to CO the rate of 
fuel feed may be established. 
The apparatus is capable of reducing bulk material, for example, municipal 
waste, bark or sawdust and agriculture waste such as beet pulp, straw, 
rice hulks, etc. 
While the grates shown in both forms of the apparatus are stationary it is 
within the scope of the invention to employ movable grates, that is, 
grates which constitute in effect conveyors for moving the fuel thru the 
second zone. 
The terminology "bio-mass" material used herein is to generically include 
materials derived from vegetable matter essentially cellulosic in 
composition which would include not only woody material but coal as 
distinct from liquid or gaseous materials. 
It should be understood that the present disclosure is for the purpose of 
illustration only and includes all modifications or improvements which 
fall within the scope of the appended claims.