CA1211286A

CA1211286A - Fixed bed gasifier with gas cleaning means and method for producing combustible gases

Info

Publication number: CA1211286A
Application number: CA000453042A
Authority: CA
Inventors: Hugh L. Campbell, Iii
Original assignee: Dravo Corp
Current assignee: Dravo Corp
Priority date: 1983-05-16
Filing date: 1984-04-27
Publication date: 1986-09-16
Also published as: GB2140026A; ZA843271B; GB8410904D0; JPS59219389A

Abstract

Abstract of the Disclosure A fixed bed gasifier and method of gasification of solid carbonaceous fuel wherein there is provided a fuel supply and inlet means to the gasifier and at least one vertical feed tube in the form of an inverted truncated cone. The feed tube is enclosed in a gaseous exhaust gas conduit and the bulk of gases from the gasifier passes upwardly through descending coal in the feed tube and through apertures in the wall of the feed tube into a chamber formed between the feed tube and exhaust gas conduit while a portion of hot gases from the gasifier passes directly into the chamber to maintain the temperature of the gases when combined in the chamber above their dew point. The combined gases are tangentially discharged from the chamber and, when a plurality of feed tubes are provided, the discharged gases combined and removed through a common offtake conduit.

Description

lZ~L~Z136 HUG~ L. CAMPBEII
FIX~D BE~ GASIFIER WITH GAS CLEA~ING MEANS
AND M~THOD FOR PRODUCING COMBUSTIBLE GASES
. ~

The present invention relates to an improved fixed bed9 single sta~e Raslfier. Fixed bed, sin~le stage gas,.fiers are used to combust coal or other solid carbonaceous fuel. to produce combustible gases. Generally, the gases produced are collected at the top of the gasifier vessel, abov~ the fuel bed, and are exhausted from the vessel through an offtake pipe. The ~ases are at an elevated temperature and contain particulate matter. If the carbonaceous fuel being gasified ls a bit.uminous coal or any coat of lower rank, the offtake gases also contai.n 1~ vaporized tars and oils.
In conventional practice, the offtake gases from a fixed bed gasifi.er are passed ehrou~h a refractory-lined cyclone which removes a portion of the particulates. In conventional bituminous coal gasiflcation, the gases are then delivered to 15 ~ the burner in an insulated pipe so as to prevent the deposit:ion of tars and oils on the internal surface of the delivery pipe, which woulcl require subsequent removal. If the ~ases are to be transported or any ~significant distance, it is customary practlce to cool the gases in a scrubber, whlch causes condensa-~n t~ on of the tAr~ ~nd o~ls And remov~l. from the tr~n.s~nrted~aseous stream.

~llZ~6 In situations where the hot gases containing tars and oils are Le(i d.Lrectly to a burner, ~he constructlorl of refractory-lined distribution piping is expensive~ and inter-mittent operation of the gasifier will still resul~ in the need for frequent cleaning of the gas distribution pipe.
In sltuatiorls where cooled gas is required, the problem of rer.loving the tars and oils from the scrubbing water requires the use of separation tanks and pumps which are both costly and cumbersome. Also, cooling of the product ~ases, to remove tars and oils, reduces the efficiency of the gasification process.
In additiong in conventional fixed bed gasifiers the space within the gas-ifier vessel, at the top of ~he vessel, which must be pro-~.lded so as to allow the ~ases to flow to the offtake pipe~ lowers the fuel reac~ion potenti~l at full losd by imposing a limit on ~he contact time between the gas being produced and the coal entering the ~asifier. .
A~tempts have been made to use the coal in the gasifier for the purpose of removing some of the particulates ~0 ¦ from the gases~ In U.S. 4,165,970, there is dlsclosed a gasifier for the high pressure gasification of coal, of a particle size of 2-60 mm. A shielding wall is provided within the gasif.ier through which coal is fed and the coarser particles are said to accumulate near the shielding wall, while finer particles tend to enrich the central portion of the bed. The shLelding wall is eparate from the reactor wall and an Annular space is formed.

1~

lZl~ZlY6 IThe shiPlding wall has apertures through which gases will pass ¦ after flowing through the coal fed to the reactor. The passage of gas through the coal bed havir~g a distribution of the different particle siæes is said to tend to decrease the rate at which dust is entrained by the produst gas leaving the reactor.
This is due to the gas entering the annular chamber at its lower end as well as entering through ~he openings in the shielding wall~ While some tangentlal flow of gases toward the discharge from the vessel may result, no specific such tangential fJow is discussed. While such an approach may remove some parEic~lates from the gases to be exhausted from the gasifier since the coal acts in the nature of a filter, it does not significantly reduce the amount of vaporlzed tars and oils present in the gases that are exhausted from the gasifier.
According to the present invention3 an appara~u and process are provided which clean th~ gases produced ln a fixed hed gasifier to remove particulate matter, tars, and oils from the gases which may then be either immediately conlbusted or transported to distinct locations for combustion.
It is an object of the present invention to increase the contact surface and duration of an incoming coal charge to a gasifier without increaslng the depth of the gasifier vessel.
This will result in the ability to operate the gasification unit at high loads with less possibility of formation o~ blowholes or other we~ nesses in the fire bed.

nother object of the present invention is to coo] the hot gases leaving the gasifier with the f]ow oE incomin~ coal to the gasifier. .~uch coo]ing wi]l resul~- in ~he de~osition of some tar and oil leaving the gasifier on the surEace of the incomin~
¦ coal, and reinlection of these tars and oils into ~he gasifier vessel.
It is yet another object of the present invention to provide a fue] feed configuration wn-ich will allow for the use I of swelling and cak-Lng coals in the gasifier.
1~ ¦ It is a further obJect of the present invention to impart a ro~atiorlal motion to the gases exhausted from the gasifier at a poin'~ where particula~e matter separatecl by the change in flow of the gases and the rotational motion will return by gravity to the gasifier and be entrained in the t5 incoming fuel stream.
I~ is yet a f,urther object of the presen~ invention to cause a gradual blending of gases exhausted from the gasifier in a manner which will -result in an exit gas from which ~.ar and oil have been re~oved, but which will be heated to a temperature

2~ above the dew point o~ the exit gas so that deposition of remainin~ tar and oil in the distribution pipes is minimized.
Brief_Summary of the Invention A fixed bed, single stage gasifier for producing combustible gases from a solid carbonaceous fuel, having a f~lel ~5 ¦ supply means and inlet means for supplyinR fuel to the upper region of the gasifier vessel~ has at least one verticallY

.

lZl~Z86 ex~ending coal feed tube of an inverted truncated cone design which feeds coal from a fuel supply bin into the inlet of the gasifier vessel. Preferably, a plurality of such tubes are provided. The feed tubes have a smaller interior diameter at the upper region thereof than at the lower region, and the tubes have apertures therein for passage of gases therethrough. A
gaseous exhaust gas conduit surrounds each of the feed tubes.
¦Gases from the gasifier pass upwardly through countercurrently descending c031 in .he feed pipes and out of the slots into a chamber formed between the tubes and the gas conduit,, while a minor amount of hot ~ases passes upwardly from the vessel directly into the chamber. The gases are exhausted from the chamber tangentially into an exit conduit with gases from the exit conduits of ~ plurality of such conduits combined in a common offtake conduit.
Upon passage of the ~ases through the descending coal in the feed tubes, the tars and oils are condensed and returned to the gasifier vessel, while the descending coal bed also ~ filters out particulates.
Brief Description of the Drawin~s Figure 1 is a vertical sectional view of the upper section of a fixed bed gasifier of the present invention; and Figure 2 is a view taken along lines II-II o Figure 1.
De~ailed Description Reerring now to the drawings, there is illustrated a fixed bed carbonaceous fuel gas producer ~essel 1, hav~g a _5_ combustion chamber~ the vessel having a jacket 3, and a shaft 5 for an agitator which passes through the roof 7 of the vessel.
The roof 7 also has therein a plurality of openin~s g Eor the introduction ~o the vessel of coal.
An elevated fuel bin 11 is providecl, above the vessel 1 from which coa] is to be charged, by gravity, to the vessel, the bin having a valve 13 to effect flow of coal through an opening 15 in the bin.
A feed tubeg in the form of an inverted, truncated conical member 17~ ;s connected to the opening 15 of the coal bin and con~rols tke flow of coal from the bin 11 into the vessel 1, through openings 9, the terminus 19 of the conica]
member situated within the vessel 1. The term "conicaL member,"
as used hereln, is meant to include, in additiona' to a cone of clrcular cross-section, a conlcal member of elliptical or rectangular cross-sectional shape. A baffle 21 is provided, depending from the roof 7 of the vessel 1 and spaced from the terminus 1~ of the conical member 17. The conical member 17 is constructed such that the terminus 19 has a ]~;ger interior ~ di~meter d th~n the interlor diameter d' of the upper region of the conical member at the opening 15 of the fuel bin.
A conduit 23, which forms a gaseous exhaust sleeve, is provided which is coaxial with, surrounds, and encloses the conical member 17 while being spaced therefrom. The cond~ t 23 extends from the roof 7 of the gasifier vessel 1 to the elevated feed bin 11.

:1211Z1~6 A plurality of slots or apertures 25 are provided in ¦¦~he conical. member 17 which provide access between the ;nterior of the con;cal member 17 and the chamber 2i formed by the conical member and the spaced condui L 2~. The apertures 25 are sized and spaced such that gas from the gasifier l wi.ll flow through the Euel feed and be gradually admitted ~hrough aper-tures 25 into the chamber 27. The apertures are further design~d such that most of th~ gas will flow through most of the Euel flowing into the gasifier l, that is, most of the gas will exit near the top of the conical member 17.
: A ~angetltial exi~ conduit 29 is connected tG and communicates with the conduit 23 (Figure 2) and this conduit is l in turn connected to a simi]ar exlt conduit 29' on an adjacent:
: conduit 23, both of which exit conduits discharge in~o a gas offtake conduit 31.
In the operation of a fixed bed solid carbonaceous fuel gasifier of the present lnvention, coal. from a fuel bin ll flows through valve 13, through opening 15, into the upper region of the conical member 17 and at substantially atmospheric 2n ~ pressures down~ardly by gravity through the opening 9 ln the roof 7 of the vessel l. The larger interior diameter d at the terminus l9 of the conical member 17~ relative to the upper region interior diameter d', allows continued flo~ of coal c , despite swelling or caking which may occur when high swelling bituminous coals are gasified. The baffle 21, extending down-¦wardly into the gasifier vessel l, allows for a slight space lZ11;:86 between the underside of the roof 7 and ~he top of the fuel bed.
Gases generated in the combustion chamber flow upwardly through the terminus 21 countercurrent to the flow of coat and di~fuses into the chamber 27 formed between the conical member 17 and the conduit 23, throu&h apertures 25 in the conical member 17. As the gas flows upwardly through the descending coal, it is cooled by the coal, and tar~ and oils contained in the hot gas condense and are deposited on the surface of the descending coal. While most o the gases flow throu~h the coal, a .mal] fraction of the hot ~as stream flows through the annulus formed by the openin~at the bottom o~ ~he conical member 17 and ~he conduit 23. This hotter gas blends in the chamber 27 with the ~ases flowing through apertures 25 so as to keep the temperature of the exil:
gas stream above the dew point of the gas.
lS The amount of hot gases that is passed throu~h the flnnulus directly into the bottom of the chamher 23 ls determined by the temperatures required to keep the exit gas stream above the dew point. The amount may vary dependent upon the type of coal being gasified. Preferably, however, about 90 percen~, and 2~ up to about 95 percent, of the volume of the gases should be passed upwardl~ through the descending coal in the ccnical member and out ~hrough the apertures 25 into ~he chamber 27, while the remaining volume of the ~as will pass throu~h the annulus directly into the chamber from the gasifier vessel. I
Normally, tars and oils wlll condense from the ~ases when the gases are ooled to temperstures oE below sbo~t 400F.

lZllZ~16 Gases flo~ing to the top of the conduit 23 exi~ j tangentially to the conduit through exit condu~ 29 which merges with a similar conduit 29' connected to the ~op of a second conduit 23 on the other side of the gasifior. The tangential exit gas conduits 29 and 29' combine to form a gas offtake conduit 31 which may be, in turn, connected to the conventional cyclone for secon~ary removal of fines. I
The change in di.rection of fiow of the gases at the top o the conduit 23 and the circular motion imparted to the gases by the tangential exit gas condui~s 29 and 29' will ca~se a primary separation of particulate matter from the ~as stream, and such particulate matter will drop hy gravity through the annulus back into the gasiier vessel 1 and be recombined with the incoming coal~
The operation of the gasifier of the present i.nvention will produce ~ gas that will be cleaner and have less ta-, oil, and particulate matter than gases produced in conventi.onal fixed bed gasifiers. Cooling of the gases with the incoming coal wil]
~ also reduce or eliminate heavy tars and pi~ch caused by 2~ "cracking" volati.les with hot offtake gas. The use of t:he present invention will enable the use of fixed bed, single stage gasifiers operating in a "hot raw gas" mode in more applications than has hereto:fore been possible using conventi.onal technolog~y.
The present i.nven~ion provides the benefits claimed for two stage gasifiers wlthout the capital expense or coal selecti.on ¦
restrictions inherent in such two stage gasifiers.

_~_ '~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1, In combination with a fixed bed, solid carbonaceous fuel gasifier having a combustion chamber, a solid fuel supply means, and an inlet means for charging solid carbonaceous fuel from the supply means to the upper portion of the gasifier, the improvement comprising:
(a) a vertically extending feed member extending from the solid fuel supply means to the inlet means, the feed member having an enlarged interior diameter in the direction of the inlet means, through which solid fuel is charged by gravity to the gasifier;
(b) a gaseous exhaust conduit, exterior of the combustion chamber, coaxial with and surrounding the feed member and spaced therefrom;
(c) the feed member having a plurality of aper-tures therethrough for the flow of gases therefrom into the exhaust conduit;
(d) the exhaust conduit having means adjacent the upper end thereof for the tangential removal of gases.

2. The fixed bed, solid carbonaceous fuel gasifier as defined in claim 1 wherein said vertically extending feed member is in the shape of an inverted truncated cone.

3. The fixed bed, solid carbonaceous fuel gasifier as defined in Claim 2 wherein said cone has an elliptical cross-sectional shape.

4. The fixed bed, solid carbonaceous fuel gasifier as defined in claim 2 wherein said cone has a rectangular cross-sectional shape.

5. The fixed bed, solid carbonaceous fuel gasifier as defined in claim 1 wherein said vertically extending feed member terminates within the gasifier vessel and a baffle means is provided in the vessel dependent from the roof thereof spaced from and surrounding the terminus of said feed member.

6, The fixed bed, solid carbonaceous fuel gasifier as defined in claim 1 wherein a plurality of inlet means are present in the gasifier and wherein a vertically extending feed member and gaseous exhaust conduit are provided for each of said inlet means.

7. The fixed bed, solid carbonaceous fuel gasifier as defined in claim 6 wherein said vertically extending feed members are in the shape of inverted truncated cones.

8. The fixed bed, solid carbonaceous gasifier as defined in claim 7 wherein said cones have an elliptical cross-sectional shape.

9. The fixed bed, solid carbonaceous gasifier as defined in claim 7 wherein said cones have a rectangular cross-sectional shape.

10. The fixed bed, solid carbonaceous fuel gasifier as defined in claim 6 wherein gases removed tangentially from the upper end of each exhaust conduit are combined and fed to a common exit gas conduit.

11. In a method for producing combustible gases in a fixed bed, single stage coal gasifier wherein coal, from a source thereof, is charged through an inlet into a combustion chamber and gasified to produce combustible gases, the improve-ment comprising:
(a) passing coal from the source thereof down-wardly through a vertically extending feed member posi-tioned above the gasifier, said feed member having apertures therein, the feed member contained within an exhaust gas conduit forming an annular chamber therewith, the exhaust gas conduit having a tangential exit gas conduit at the upper region thereof;
(b) passing a portion of the hot gases directly from the gasifier into the annular chamber;
(c) passing, the remainder of the hot gases from the gasifier upwardly through the descending coal in the feed tube to cool the same and condense tars and oils therein and discharging the cooled gases through the apertures in the feed tube into the chamber to combine with said hot gases; and (c) tangentially discharging the combined hot and cooled gases from the upper region of the chamber into an exit conduit.

12. In the method defined in claim 11, the improve-ment wherein the portion of hot gases passed directly from the gasifier into the annular chamber is sufficient to maintain the temperature of the combined gases above the dew point of the gas.

13. In the method defined in claim 12, the improve-ment wherein up to ten percent of the gases from the gasifier are passed directly from the gasifier into the annular chamber.

14. In the method defined in claim 11, the improvement wherein a plurality of said vertically extending feed members and exhaust gas conduits are provided and gases from the gasifier are passed therethrough and the gases discharged from the upper region of the chambers into exit conduits are combined in a common gas offtake conduit.

15. In the method defined in claim 11, the improvement wherein said feed member has a larger interior diameter at the terminus thereof than at the upper region thereof, sufficient to permit the passage of swelling and caking coals by gravity downwardly therethrough into the gasifier.