CA1114612A - Process for gasifying organic fibrous material and the product thereof - Google Patents

Abstract

Abstract of the Disclosure A method is provided for producing a combustible gas from an organic fibrous material in which a mass of free flowing pellets containing compressed organic fibrous material is supported in a substantially enclosed space. The fuel pellets are burned while supported and while air is dispersed substantially uniformly through the burning fuel. An insula-ting layer of fuel pellets is maintained above the fuel which provides a temperature in the burning mass at which the fuel is substantially completely consumed without ash formation and nitrogen from the air is chemically combined with products of the combustion of the fuel to produce combustible gases containing nitrogen in admixture with combustible gaseous carbon compounds. The combustible gas burns with a BTU pro-duction of as much as four times the BTU produced when the solid organic fuel from which it was produced is burned.

Description

1~ 14~;12 . ~, . . .

- This invention relates'generally ~o a fuel and .

more particularly to a method and apparatus for producing .. . . . .................... . . . . , ~- - -- a combustible gas from organic fibrous-materials w*ich burns . .

to .proauce more BTU'than the hereto~ore available ga'ses'pro~ .
. ~
duced from wood and agricultural waste products. : ............. .. ~. ' It has been proposed'heretofore~to burn wood and -other organic waste materials under conditions which proauce '. .~ ~
a combustlble gas which can be burned later as a-fuel. .The : 1, .wood-is burned in a vessel commonl~ called a gasifier.or.~ - ~-gester which is usually cylinarica1 wi~h a diameter o~ about our feet and a height of about twelve feet or similarly pro- ~ ' .
'. .. ~., portioned vessels. Various types.of,wood waste'suc~ as hog- .
., fuel or other wood wa~te,material is bur~Led in ,the bottom of :'' this high slender tank with air added slowly from the bo-ttom.
,The wood contains a high percentage of.water and is. burned ~ ' .

j under conditions which produce a temperature of about 12-00 F.. :
and produces a gas which contains some relatively low molecular ~
weight hydrocarbons and oxides such as methane, carbon monoxide ...
; and'carbon dioxide. These processes are designed to convert .'. only the carbon of the wood into comb~stibl~ gases so ~he ;
BTU,output of the gas is low. Consequently, the gas has not .
been usea extensively industrially. '' ' ' ' ' ''' ' '' _..
A gasifier unit somewhat similar to the ones just des- .~
cribed was used in Germany and other European countries during .. .
the period of ~he 1940-195~'s to produce a gas substitute. for .~' .. . ........... . . . .
diesel fuel and.gasoline for motor vehicle,s,but there was a ~ , substantial loss of power in the vehicle. , ... .... .. . . ...... . . ............. , ,. .. ..
It is an object of this invention to provide an im-., proved process for making a combustib~e gas from fibrous .

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or~anic mateLial. Anothex object of the invention is to -provide a method for making a combustible gas for use as a fuel industrialiy which can be practiced in a comm~rciall~
- practical apparatus. Still another object of the invention is to provide a method for conver~ing organic fi~rous _ , ..... .. .. . . . ,,.. ; .
materials such as wood waste into a gas which burns to pro-duce a substantially highër BTU ~British Thermal Units) than -the heretofore available fuels produced from hogfuel and -- --similar wood waste materials. A still further object of the invention is to provide an improved fuel gas produced by burning organic waste materials which not only contains com-bustible products obtained by conversion of carbon to com~us-, tible gases but also contains combustible nitrogen contain;~g ., , . , , , . . , gases or dispersed minute particles. Another object of the invention is to provide an apparatus for practicing the process of the invention and for producing the product of the invention.
Other objects will become apparent from the following description with reference to the accompanying drawing wherein one embodiment of the invention is illustrated diagrammatically.
The foregoing objects and others are accomplished in acco~dance with this invention, generally speaking, by pro-viding a process for burning pelletized organic fibrous c material in air ur.der conditions whereby nitrogen from the ~;~
air combines chemically with products of the combustion of !;1 the fuel to produce combustible gaseous pro~ucts mixed with l :
the carbon compounds obtained from the combustion of the j ;
.. ..... ........ . . ~............... .. .. ., fuel. It has been found that a gas which burns to produce as much as four times or more the BTU obtained when an .. . . .. . , . .. .

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organic fibrous fuel is burned can be prepared by burning - fuel pellets prepared by compressing organic fibr~us materials .
.
such as sawdust or other wood,waste material, peat moss., or ' the like, in a vessel while simultaneously maintaining a heat -' insulating layer of pellets over'the burnin~ mass and dis~
persing ,air substantia.lly uniforml~ through the ~urning mass . 'LS
at a rate whereby the burning mass is at a temperature of at .
- least about 2700 ~. It is believed that a-t such te.mperatures,, . ~ _ the gas that is produced contains combus~ible gaseous carbon ' .:, compounds and gaseous nitrogen compounds produced by the - . .
chemical reaction of nitrogen with elements of the fuel such .:
as alkali metals'(primarily sodium a~d potassium~, calcium .
and possibly ~ther materials contained in the-fuel. It is . ...
,the burning of these nitrogen containing combustion pro~ucts .
along with'those produced from the carbon Of the fuel.which.
~.
is helieved to ~e responsible for the surprisingly'large BTU . ..
produced when the combustible gas is burned. .
It is preferred to coordinate the thickness of the ' fuel mass abo~e the burning uel with.the air flow introauced into the burning fuel so that'the temperature is about 3000 F, to 3500 F. in the center of the burning mass. The fuel burns .
under these conditions somewhat like the fuel in a blacksmith's forge and the fuel pellets in the insulating layer which is immediately above the burning fuel becomes charred and the pellets are co.nver,,ed to a large extent into a charcoal layer.,,, The fuel pellets which are prelerably prepared in accordance with m~ earlier i,nvention to be descri~ed hereina~ter should be free flowing and may be introduced continuously to the ;
fuel bed ~rom above at a controlled rate. Alternately, the . . ... ,. . .. . . , . .

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"`..'.'' vessel in which the fuel is burned may be eauiped with a -device which monitors the height of the fuel and triggers -, ,:. .
a fuel feed mechanism when the height of the fuel bed reaches the point where additional fuel is required to maintain the insulating blanket of pellets which malntains the burning -~
temperature at about 2700F. or higher. A commercially available device sold under the trademark "Bindicator" may .~
be used for this purpose.
The invention contemplates burning any suitable organic fibrous material such as, for example, agricultural products such as straw, corn husks or the like, sawdust, shavings, hogfuel, wood chips, peat moss, paper or the like.
Embodiments of the preferred fuel pellets which are burned in accordance with this invention are described in my copending Canadian Application Serial No. 269,091 filed January 4, 1977 and my corresponding U.S. Patent No. 4,015,951.
In accordance with the disclosed process, an organic fibrous material is pelletized into a form which adapts it to be burned substantially uniformly in a furnace by a process which involves adjusting the particle size of the fibrous material to not more than about 85% of the minimum dimension of the pellet to be formed, adjusting the moisture of the fibrous material to a substantially uniform content of from about 16% to about 28% by weight, and shaping and compressing the fibrous material while at the adjusted moisture content into substantially symmetrical pellets having a maximum di-mension of 1/2 inch or less.

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In a preferred embodiment of the process, an organic , fibrous material such as agricultural or woo~ waste materials :
is transported by a conveyor adapted to separate rocks, metal and other non combustible contaminants of the fuel therefrom .
to'a hammer mill or the li~e where the organic fibrous materiaI
~ - .
is ground to a substantially uniform partic~e size of.not more - , . than about 85% of.the.minimum,aimension of the pellets to be ... ' j~ .
formed therefrom, the ground material is then,conveyed.to a, ~, .
hot air dryer where the moisture content i-s ad~usted to from ~ ' . ' ~., _ about 16~ to about 28% by weight water, and t~e product havin~ ~ ~ ..
the adjusted size and water.content is then conveyed to a ' . . . pelletizing machine equipped with its o~n measuring .s.crew ~evice.
for feedin~ the mass through the die of the pellet:mill and-the ~. , .resulting pellet,,is then dried until its moisture content.is , sub,stantially in equilibrium with the atmosphere. The 'fibrous material lS pressed at'''a'pressure whereby the.temperature o~ ' :' -the pellet in the die is from about 325~ F~ to ,abou~ 35:0.F.. .. . . ' '.
While the moisture con.ent of most organic fibrous ..
,, . , ................ ,....................... . .
material will be above 28% by weight and will require dryins; .
it is to be understood that, if material having a moisture con-tent below 16% is available for pelletizing, ~ts moisture con- .
tent'should be adjusted by humidification or the.like to a ., moisture content between about 16% and about 28% before .
pelletizing. As broadly contemplated by the invention, the.
moisture content may ~e within the broad range of about 16% , ;l to 28% by weight ~u. it' has been found that the best results ;
. . . , ~ , ,~", are obtained when Lhe'moisture content of.the organic fibrous i, _ , material at the time of pelletizing is between about 20~ and ~ :
24~ by weight 50 it is preferred that the moisture content be within this more limited range. The pellets may be freed .

1~1461 '~.

from surface moisture by blowing air over them immediately .
after they emerge from the' pellet mill. ' . ~.
It was found that by adjusting the organic fibrous .
material particle size to about 85% or less of the minimu~
dimension of the pellet to be formed and adjusting the mvis- . ~, ture content prior to compression to from about 16% to about 28% by weight free water content, preferably about ~ to ~
about 24%, a pellet having a protective wax-like surface ~ . ~.
formed by exudation from the fibrous material which will burn ,.~ ' substantially uniformly without the ~ormation of an undesir- . -able quantity of,ash is produced provided that the shaping and pressing is'conducted at a temperature of. from about 325 ' . , to about 3.50 F. In c~der that the ~urning rate of a mass . ,. . . , of pellets will be substantially uniform, the pellets are dried ater they have been formed to a substant,ially uniform .
moisture content which is in close-equilibrium to the sur- '' ..
rounding at sphere. These pellets can be used to advantage ' ' for making a combustible gas in accordance with this invention. .
The.pellets can be easily conveyed on.commercially availa.ble.,. :,.
inclined belt conveyors or with conventional,stoking equipment., "
The pellets are of substantially uniform shape and dimensions .
and may,be conveyed pneumatically if desirea. _ ,, It is preferred that the pellet be substantlally cylin-drical, parallelepioed or the like having a maximum,cross- ~
section within the range of from about 1/8 inch to about 1/2 :~' inch. The actual pellet size is determined by the exterior - _ sur~ace area versus the composition of the material wi~hin .. :
the pellet. The maximum thlckness of the pellet in any one :' . , . . . ,~

.. .. , , . . . . . ... , .

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direction will seldom be more than about 1 inch and will seldom be below about 1/8 inch. The absolute density of -the pellet produced in accordance with the invention is -about 50 pounds per cubic foot and often is from 65 to 90 pounds per cubic foot or higher at 13% moisture content.
The density of the particles used to make the pellets is about 10 to 30 pounds per cubic foot at the same moisture content. The absolute density of a commercial "Pres-to-log", Trade Mark, on the other hand, is less than 65 pounds per cubic foot and thus lighter than water.
The apparatus used to practice the process of the invention may be varied. It is not necessary to use the tall slender vessel of the prior art for producing carbon containing gases from wood waste materials. In fact, it is preferred to use a vessel which is somewhat larger in cross-section than it is high. For example, a cold rolled steel vessel having an upper cylindrical chamber and a substantially conically shaped bottom portion may be used. This vessel has a closed top provided with a manhole for access to its interior and a centrally disposed opening for the introduction of fuel to the fuel bed. A pipe may be welded to the top with its end about the fuel feed opening and a conventional air-lock installed in the pipe to avoid loss of gases. A small conically shaped bin for storage o fuel may be installed above the air-lock or any other reliable source of fuel pellets may be connected to the pipe. A monitoring device such as a Bindicator may be installed on the tank with its responsive element at the de-sired level and connected to a solenoid actuated valve in the pipe between the bin and air-lock for automatic control of the ... .. . . .

1~14Ç;1Z
- height of the fuel bed in the vessel. For safety purposes, -a safe-ty valve responsive to say about five pounds pressure , may also be installed in the top of the vessel. ' A perforatea stainless steel plate ~or supporting the fire bed is disposed across the tank at a point spaced from the apex o~ the conical.bottom of the vesseI. This plate has ~'' substantially evenly spaced holes of substantla~1y equal ~- -' ' cross-section,so that air entering from below is dispersed -~ ~ :
substantially uniformly through the flrè bed. An openi g is ' ~ ~ _ 10, provided in the wall of the vess~l adjacent to the fire bed - ' for the insertion of an acetylene torch or other dev1ce for~ , initially igniting the fuel supported-on the plate. Pre-ferably, an imperforate margin is left around the periphery of,the plate so that air does not enter the fuel bed along ' the sides of the vessel. In this way a protective layer o~
non-burning fuel is provided around the fuel bed against the ' inner wall of the vessel and it is nOt necessary to apply insulation to the vessel wall. However, in some-instances it may be advantageous to provide a'shroud or jacket about the bottom of the vessel and to circulate the air to be in-troduced into the vessel through the shroud to preheat the air. In other embodiments, it may be desirable to line at least that part of the vessel wall about the fire bed with , a ceramic such as fire brick. , , An opening is provided in the apex of the bottom por-tion of the vess~l for introducing air'below the perfo~ated' ' ' fuel bed supporting plate. A pipe or other conduit is attached to the vessel around the opening ana to a source of air. The fitting Nsed to connec-t the,pipç to the vessel may ;

.... . ........ .. . ....... . ..... .. . . . . . . . . -- -8- . .

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be T-shaped with one leg of the T disposed verti.cally for collecting a material in the fuel such as rocksl metal scrap .
or the like which does not burn and falls through the per- .
... .... ... . .
orations in the plate. A cap ~an be provided on the leg ' ~
to be removed for periodically dumping the non-com~ustible .,-; .
... material. , ~ . . ~:, The gas produced by burning the fueI is removed-f~om . - r~ .
the vessel at a point above the fuel bed. An opening may be '' ' provided in the sidewall of the vessel for this purpose. , 10 . The opening may be attached by a pipe directly to a burner . ::~
which.will burn the fuel or it may be.attached to a su~table:
tank or other storage vessel for the gas. ..

, , The fuel produced in accordance,lwith.this,invention ,: ,, .
. . . ..
may be,used for producing energy in any suitabIe apparatus ., . . which.burns a combus.tible gas. .For example, it may be usea . . ' ;~
1 to prod~e steam for heating or for-indus.trial purposes or,. - ---it may be used in the generation of.electricity. It is be- :' lieved that at the temperatures at which'the fuel is burned, ' ' ' .
pyrolysis of the fuel o~curs to form the c~hemical compounds -i 20 of the gas. As pointed out above, the pyrolysis products , ' include compounds produced by a combination of nitrogen . .
from the air with constituents of the fuel. When this mixture ..
burns a much higher B~U is produced than would ~e produced if ~-' .
only carbon pro~ucts from the fuel were present in the gas. .. , I In one gas genera'o- of the type described above, it was found I that a fuel prepared in accordance with the disclosures in my , earlier applications, when burned in an,apparatus of the type ~_ ¦ ., , de,scribed .above, at an air-pressure of about one psi burned ,;
I to produce about four times the BTU obtainea when the fuel - .
. .. . . . . .. . .. .. .... .. . .

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was burnea in an open furnace under normal conditions.............. .
- During one hour in which about 104 pounds of the iuel was burned in about 250 cubic feet of air per minute at a pres- .`
- - sure of about 5 1/2- inches of waterr a gas~was produced whichJ . ff when burned, developed 4,000,000 BTU. The same fuel pellets ~yhen bu-rnea under normal conditions to produce reaction pro- i-.. .. . . . . . .~
ducts only from carbon produced about 9,000 .BTU. per pound . . . 7J. .
or 936,000 BTU for 104 pounds. These tests were made in a Heil Drum Dryer at 14 miliion BTU per.hour capacity while -.. .. ..
burning natural gas as normal fuel. After operating the gas :
generator or 72 to 96 hours continuously, 8 tests of one .
hour duration each were made.with the same production~of BTU.
Referring now to the drawing, a preferred embodimen~ ..
of the apparatus has digester 10 which may be convenientiy ...
about ive feet in diameter and about Eour feet deep. Digester .
10 has a substantially flat top.ll and a subs-tantially coni- :
oally shaped bottom 12. The waIl of the cone is preferably sloped at about 30-45 with respect to the horizontal axis . :
. . . of the tank. An opening 13 (pre~erably about 3 ox.4.inches . .... .. ..
in diameter) is provided at the apex of.the conically shaped :~.
bottom and a pipe 14 connected to a source of air under a .
positive pressure is secured to the tank about the opening. __.
A perforated stainless steel plate 15 is disposed above khe air intake openirg across the tank to provide a base for ::
supporting the fuel bed 16. An acetylene.torch 17 is inse~ted in an opening in the wall of the digester to ignite the fuel. _ As shown in the drawing, the fuel is fed-from.a bin 18 through . .
airlock 19 and pipe 20 to provide a conically shaped fuel bed -. . .
.16.above the fire bed 21 on plate 15. At an air flow of up .
.. ,. ........... . . ......................... ...... , -10- ' ' ' ' to about 250 (CFM at 5 1/2 inches water) and a fuel con-sumption of about 100 pounds per hour the temperature ~f' -f'ire bed 21 is about 3000 F. to about 350bo F. - .
' In an apparatus o.' the dimensions described, plate 15 may be'provided with one-fourth inch holes drilled on one- ~ .
hal~ inch centers to insure substantially uniform air disper- r~`' .
sion through the ~uel bed. An imperforate margin of about 2 ' inches~or more in larser tanks and narrowe in smaller tanXs ~ ~'-is left around the edge of plate 15 so fuel can accumulate around the fire bed and insulate the digester wall from the heat oE the fire bed. The pressure in the-tank may be main-tained at about 1 to 2 psi or less.' . ' ~-As illustrated in the drawing, the.fuel mass immPdiately above the flre bed is converted into charcoal before it'falls into the fire bed and is consumed. A safety valve 20 respon- ' , , . .
sive to a pressure of about 5 psi is disposed on top 11 A .
manhole 23 for access to the inside of the digester 10 is pro- .
vided in the flat top. . .
' In'the embodiment illustrated in the drawing., the fuel is ed from above and assumes a substantially conical shape above the fire bed. The gas produced by the burning of the ~ ' fuel passes through the fuel bed into the area about the con- _ ~:
ically shaped bed and through a pipe 24 to a burner 25.
Burner 25 may be any suitable device used to generate heat ' r-by the burning o' the gaseious combustion product obtained !f 1.' when the fuel'is burned. In one embodiment of a burner '' `suitable ~or use with the apparatus described above, a shroud about 24 inches long and about 1~ inches in diame-ter is pro- .
vided about the burner. The flame developed when.the gas is .
... . . . . . .. . . ......
.

burned is a deep blue and will be as much as 2 feet in dia~
meter and from 8 to 12 feet in length depending upon the amount of air which is induced into the shroud to achieve a swirl in the flame pattern. Any commercial burner designed to burn gas may be used. In operating the illustrated vessel under the conditions outlined above, it was possible to produce up to about 5,000,000 BTU per hour for as many hours as air -was injected into the fuel bed. The amount of ash produced is negligible. The fuel is consumed completely and converted into gaseous products by oxidation of the carbon in the fuel ~;~
and also by converting other elements of the fuel into nitro-gen containing compounds. In some tests it has been found that the gas produced by burning a fuel of the type described in my aforesaid Canadian Application Serial No. 269,091 con-tained about 6% carbon dioxide, about 25% carbon monoxide, about 5% hydrogen probably in the form of water and about 50%
by weight of volatile compounds containing nitrogen.
The process of this invention can be practiced with already available boilers for producing steam and for use with turbines designed to produce electricity by merely connecting the gas outlet from the vessel of the invention to a suitable burner. It is also contemplated that the gas provided by the invention can be used to drive internal combustion engines or other prime movers.
Wood ash usually contains about 50~ calcium, 5-10~ by weight potassium and the remainder of inorganic salts. This ash is consumed in the process of the invention to produce combustible gases by reaction with nitrogen from the air and lS~46~
these ~ases are mixed with the carbon compounds of the com-bustion products. . . . . .
Although the invention is described in detail for the purpose of illustration it is to be understood that such .
dc-~tail is solely for tha-t purpose and that variations can be '. .
made therein by those skilled in the art without departing . . i.
from the spirit and scope of the in~ention except as it may be ,: .
limited by the claims. ~ .
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Claims (9)

I CLAIM:

1. A process for producing a combustible gas which comprises supporting a mass of free flowing fuel pellets comprising compressed organic fibrous waste material in a furnace on a perforated grate, flowing air upwardly through the grate and through the resulting mass of supported fuel pellets, maintaining a heat insulating layer of pellets in the mass over the burning pellets, igniting the fuel pellets near the grate and burning the heat insulated pellets while the air flows therethrough at a rate whereby the temperature where the fuel pellets are burning is from 2700°F. to 3500°F.
and pellets immediately above the burning pellets are car-bonized to form charcoal pellets, and any alkali metals and other non-combustible materials in the fuel pellets which ordinarily are removed from the bottom of the furnace as ash are instead reacted with elements in the air to form a com-bustible gas which is mixed with other combustible gases formed by oxidation of carbon in the fuel and are removed with said other combustible gases from the top of the furnace to contribute to heat, formed when the said combustible gases are burned and increase the BTU above that produced when the said other gases are burned alone.

2. The method of claim 1 wherein the fuel is substantially completely digested into gaseous products.

3. The method of claim 2 wherein the gaseous products of combustion include chemical reaction products of nitrogen with an alkali metal, reaction products of nitrogen and calcium, or mixtures thereof.

4. The method of claim 3 wherein the alkali metal is potassium.

5. A method of producing a combustible gas which comprises supporting a mass of free flowing fuel pellets containing compressed organic fibrous material in a substantially enclosed space, burning the fuel pellets while thus supported and while simultaneously dispersing air substantially uniformly through the burning fuel and maintaining an insulating layer of pellets above the fuel to provide a temperature in the burning mass of at least about 2700°F. at which temperature the fuel is substantially completely burned and nitrogen from the air combines chemically with products of the combustion to produce combustible gaseous products containing nitrogen mixed with combustible gaseous carbon compounds substantially without ash formation, and collecting the resulting mixture of gases.

6. The method of Claim 5 wherein the insulating layer of fuel pellets above the burning fuel comprises a layer of charred pellets adjacent the burning fuel.

7. The method of Claim 5 wherein the fuel pellets are added from above at a rate substantially equal to the loss in volume of the burning fuel to maintain a substantially coni-cally shaped mass of unburned fuel over the burning fuel.

8. The combustible gas produced by the method of Claim 1.

9. The gaseous pyrolysis product of the method of Claim 5.