US2516974A - Method and apparatus for gasifying carbonaceous material - Google Patents

Description

A. D. GARRlsoN 2,516,974 mman ma APPARATUS FOR GASIFYING cmoNAcEous uATERIAL Fnednec. 4. 194e Aug. 1; 195o I.; 10:4 s acida-al. ninfa..

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IN VEN TOR.

ALLEN D. GARR/50N ATTH EY 'Plantea Aeg.' 1,1950

METHOD AND APPARATUS FOB GASIFYING CABBONACEOUS MATERIAL Allen D. Garrison, Houston, I'1 ex., lassigner to Texaco Development Corporation, New York, Y N. Y., a corporation of Delaware Application December 4, 194s, semi No. 113,895

4 calms. (01.. 413-2061 The present invention relates to gasification of solid fuels and is more particularly concerned with the conversion of carbonaceous materials into a gaseous'product of high heating value composed primarily of carbon monoxide and hydrogen, this application being a continuationin-part of my copending application Serial No. 682,908, filed July 11. 1943- In accordance with the present invention a stream of combustible gases, predominantly hydrogen and carbon monoxide, is produced by the reaction of water vapor with carbon or carbonaceous materials.

More specifically, the solid carbonaceous fuel is caused to react with the water vapor within the usual temperature range for this reaction, but in the presence of, at most, only a limited quantity of oxygen or other reactant conventionally supplied to furnish the requisite heat energy of the main reaction. In fact, the present invention may be carried out in the total absence of an oxygen feed to the reaction zone, or with a material reduction in the amount of oxygen hitherto considered necessary for feed to the reaction zone, a highly satisfactory fuel gas, low in incrts, being produced in either case. The thermal requirements of the process or a substantial portion thereof, at least, are met by means of the exothermic combustion of a stream of hydrogen diffused out of the reaction mass-.at a predetermined rate and caused to burn with oxygen, or an oxygen-containing gas such as air, adjacent a diffusion barrier disposed within the reaction mass in direct heat exchange relationship with the solid fuel. Accordingly. the diffusion barrier, raised to an elevated temperature by the combustion of the diffused product, supplies heat energy directly to the adjacent gasification zone.

Preferably the diffusion surfaces are disposed throughout the gasification zone in such area and arrangement as to present heat transfer surfaces adequate to maintain optimum fuel temperature. The opposite or effusion surfaces of the diffusion members are preferably physically separated from the fuel gasifyingzone whereby the products of combustion of the diffused hydrogen may be withdrawn separately from the products of coal gasification and without dilution thereof.

As above indicated, the reaction of water vapor and carbon, being endothermic, requires the exthis objective by alternately blasting an incandescent fuel bed with air to a high degree. oi incandescence and passing water vapor in the form of superheated steam through the hot incandescent bed. Obviously, this involves consumption of fuel during the air blast stages and has given way in many instances to the more recent proposal involving the continuous introduction of water vapor and oxygen to the fuel` bed at a relative rate appropriate to maintain the required temperature of operation and support the reaction between the -water vapor and incandescent carbon.

However, in the production of a gas of high heating value it is necessary to use high purity oxygen to avoid dilution of the product gases with nitrogen. The equipment for meeting the pure oxygen requirements, as, for example, a

plant for the rectification and fractionation of uct of the water vapor-carbon reaction to supply heat energy requirements of the operation.'

More specifically, the invention contemplates, for example, subjecting a carbonaceous solid fuel at elevated temperature to the action of water vapor with the production of hydrogen and carbon monoxide, diffusing product hydrogen preferentially through a permeable wall of the fuel 'gasification zone, subjecting the diffused hydrogen to combustion in the vicinity of the exterior or eusion surface so as to heat the wall or barrier to an elevated temperature, and the transmission of heat` from the diifusion wall to the mass of reactants in the gasificationzone so as to supply aportion, at least, of the heat required for the endothermic reaction'.

The .invention is of particular advantage, as indicated above, in reducing or -obviating the requirement for high purity Oxygen since the combustion of the .hydrogen on the effusion surface of the diffusion member may be carried out with air or any similarV oxygen-containinggas. This is particularly true where heat exchange betweenthe incoming stream of oxygen-containing gas and the reaction products of the hydrogen combustioi are exchangedefciently as to heat c ontent so that there is no material loss of exothermic heat energy from theA diffusion zone except that transmitted tion zone.

The invention is `furthermore advantageous t where it is desired to produce a heating gas relatively low in hydrogen, since the proportion of hydrogenwhich diffuses may be controlled within rather wide limits, the resulting product of gasication being largely carbon monoxide, if desired. On the other hand, it is to be noted' that the invention is equally suitable for the production of a fuel gas containing relative proportions of carbon monoxide and hydrogen typical of those above mentioned processes wherein oxygen and water vapor are continuously supplied to an incandescent fuel bed. That is to say, where given amounts of oxygen, water-vapor and carbon are involved, the net thermal requirements are substantially the same whether the stream of oxygen is supplied to the incandescent fuel bed or reacted with diffused hydrogen and the resulting thermal energy supplied directly to thefuel bed. So also,

where the net production of carbon monoxide and hydrogen approximates that of the aforementioned, earlier proposed process, the overall heat energy supplied, is substantially the same.

Preferably, the extent to which diifuslon of hydrogen ls carried out is such that its combustion with oxygen or air will just furnish the thermal to the reactants vin the gasicatory such," for example, as `magnesia or zirconia.

closed at its bottom extremity and lined with a thin layer of palladium permeable to hydrogen.

' The upper extremity of each tube is provided with a flange I 9 which seats in a suitable recess in the header Il, as shown. The header is provided with an upper, preferably removable, closure 2l. In plan, the header is preferably shaped as shown in Figure 2 or in some similar manner so that the solid fuel may fall freely thereby and the resultant gases rise without interference. Additionally, closure 2l maybe sloped in section as shown in Figure 3 so that solid yfuel will not collect thereon.- Tubes II are provided in each branch of the header to contact all portions of the ebullient fuel;

l Internally, header Il is provided, as indicated, with a manifold 2i, supporting a plurality of dependent tubes 22. The tubes 22, preferably formed of any suitable heat resisting material,

requirements of the' process. The extent of the'Y diuslonmay be controlled in any suitable manner, such as by selection of an-appropriate diffusion barrier, by predetermining the thickness, area, disposition, size and surface area of the diffusion walls, by controlling contact time so that the reaction products are in the vicinity of the diiusion wall for only that time period required to diffuse the desired portion of hydrogen, and by other factors.

'I'he present invention is particularly advantageous in connection with the use of iiuidized fuel beds wherein the incandescent solids, usually in the form of fine particles or grains, are maintained in a turbulentcondition by the upiiowing gases. More specifically, under such conditions the solid fuel appears to form a mass similar to a boiling liquid, the particles of which continuously vibrate into and out of contact with the heated surfaces of the diffusion barrier with a resultant high eiciency of heat transfer.

Other objects and advantages of the invention will be apparent from the following description and claims wherein:

Figure l is a vertical section, diagrammatic in character, of a generator suitable for practicing the invention.

Figure 2 is a section taken on the line 2-'2 of Figure l.

Figure 3 is a section taken on the line of Figure 2. v Referring to Figure 1, the numeral III repre-- sents a chamber lined with a suitable refractory I I and continuously supplied with finely powdered coal, coke, or like carbonaceous material, from an upper feed hopper I2.

The particle size of the solid fuel is inthe range of small particles and finer, capable of being iiuidized by the upflow of reactant gas. In the embodiment disclosed, the reactant gas; namely, steam, is introduced at the bottom of the vessel Ill through inlet pipe 2B, passing upwardly through a lower chamber I3 and a grate or screen I4 carrying a layer I5 of heavier refractory particles such as tire clay. The water vapor thus moves upextend coaxially into each of the diffusion tubes l1 to a point just short of the bottom thereof and are open at their lower extremities whereby gaseous reactants introduced therethrough reach each diffusion tube adjacent its base and pass upwardly along the interior o r eusion walls thereof in close contact with the difused gas, thereby acting to wipe, strip, purge, or sweep the dinused gas from the interior walls of the tubes. The combustion products are ultimately withdrawn from the header Il through outlet pipe 23 which is oonnected to a heat exchanger 2l in heat exchange relation with manifold 2 I.

Alternatively, the direction of iiow may be reversed with the gas introduced through pipe 23 and the products withdrawn through manifold 2 I However, with manifold 2| asthe inlet supplied with an oxygen-containing gas such as air from any suitable source, not shown, heat exchanger 2l serves to provide good countercurrent, indirect exchange with the hot gases in outlet pipe 23 so that the outlet gases are discharged at substantially the temperature of the fresh inlet gases, while the latter reach the interior of the dtfusion unit at a temperature approximating normal operating temperature therein.

'I'he supply of steam previously referred to is advantageously fed to pipe 2B by way of an inlet pipe 25 and a heat exchanger 26 disposed within the upper portion of the gasincation chamber in the stneam of fuel gas product emanating from the incandescent fuel bed and constructed to superheat the steam as high as possible. The ultimate fuel gasproductis withdrawn through outlet conduit l1.

" widelyasdesiredinfurtheranceofthisideal. For

example, the steam may be at least in part` heated by exchange with the hot `eiiluenI; of the combustion of hydrogen in tubes I1 and the air preheated by the hot gaseous eIlluent of the gasiiication zone.

In operation, the chamber is provided with an ebullient bed of timely-divided t fuel l wil'uitiiisedcondition.-

l.s sjonsuinea carbon "i monoxide andhydrogen l foldll 'jpreheatetb.for'.exaltuple,to,as high a temperature as possible by the,reactionproducts overwhendisposer! adjacent the diffusion niem- Y practice, the diffusion surfaces should be spaced oi'v` theditfusion'chamber' vand .by its ethrough manifold 2|] tubes 22, passes wardly inthe vannulars'pace between Vpipes 22 and 'diffusion tubes I1, .reacting with the hydrogen'.

and transferring heat ofreaction'totubes ILf thereby bringing'f'themjto afhigh degree Offin-l brane readily supports surface combustion.

It is tofbe borne in mind that the apparatus disclosed in the drawing is bnly. diagrammatic in character and accordingly not necessarily exact as to disposition and proportioning of parts. In

uniformly throughout the fuel bed so as to presenta sumcientarea of diffusion and heat-exchange surface to maintain a temperature. as for -example '100-1000 C., proper for the reaction of water` vapor with carbon. Moreover, the spacing between such surfaces should in no event be greater .than that appropriate for maintaining good heat transfer throughout the mass of carbonaceous material. Such details, however, de-

candescence. The v.heated 4tubes thus transfer.

sensible heart tothe 'nuidized fuel mais,` maintainingthe desiredreaction temperature.

member may comprise any` ,suitable porous materialhaving coritiriuous capillary or' other pasc '-sectional 'dimensions' a s to permit the. rapid` pend on numerous variables including the degree and character of fluidization, ow rates, etc., and must be determined for each case, in accordance with good engineering practice.

. The relative rates of reactant ow can best be 1 determined, as is usual in the art, by actual trial,

sov A In fact the operation may be supplemented by such addition of oxygen as may be required when operating with only partial diffusion of the hydropermeationffbyhydfogen. while' relatively 'resist- Vgen-necessary to meet full thermal requirements.

ing'dlifusion-of carbon monoxide' or other gases.

of the reaction-gone. Such diffusion barriers may `be constructed orlunglazediporeclain or porous Carborundum, 'for example, having a thickness of vatleast v0.010 inch preferably from about `0.025to.l) .05( )il 1t.h..

It is nowk'nown, however. that superior re- `suits are achievedandrapidzand eilcient diffusion of hydrogen'maybe carried out where the diifuslonbarrier is relatively thin and has apertures or pores of the-order `of. 1 micron,for.example.

' More specifically, the dimensions for. the pores should tend to approximate the mean free path ofhydrogen under' the conditions existing in the gasification zone.

E1n view.'however,1or thediiilculties of designing anefficient andv serviceable refractory `diffusion jbar'rier and the superior efficiency of metallic diffusion barriers, I prefer to employ diffusion walls incorporating a suitable metal, such as palladium, iron, cobalt or nickel. vWhile such barriers'may be used'without additional support,1 prefer to employ them in thin.' layers mounted upon a suitable refractoryl support.

n Best illustrative of such an arrangement is, for example, a tube ofi porous Alundum, magnesio., zirconia, thoria, or other.

suitable refractory. having an inner or outer layer of palladiumof, for example, 1 to 10 one-thousandths inch 'in thickness. Such a tube is satisrefractory provides mechanical support and moreuntil the fuel bed is properly iluidized while the oxygen supply is just sufllcient to consume the dlused hydrogen with liberation of the desired thermal energy.

' 'lhe invention is not limited, in its broadest aspect, to complete elimination of free oxygen from the fuel bed, but contemplates conservation of at least a portion. of the feed normally required.

This not only limits the oxygen purification capacity required, but eliminates from the nal fuel gas such amount of nitrogen as would otherwise find its way into the product by way of even high purity oxygen feed. In short, within commercially practical ranges of oxygen purification, ni-

trogen usually remains in the 'product and dilutes y the fuel gas to some extent.

On the other hand,` with no oxygen addition to the fuel bed, there is no appreciable dilution from this source. irrespectiveof the composition of the oxygen stream supplied to b urn the dif- `fused hydrogen. Moreover, even where high purity oxygen up to, for example, 95 per cent purity is used to burn the hydrogen, there is the advantage of a higher fuel value gaseous product free from such dilution.

In accordance with one illustrative example, a

Y mass of coke havinga particle size of one millimeter and finer is disposed about a tube of highly porous zirconia having a layer of palladium on its interior surface. The coke is heated to about 800 C. and a stream of superheated steam at a temperature of about 7.00 C. is passed upwardly therethrough at a rate sumcient to Ahold the particles in a good state of dense phase fluidization, ixnmersing the tube to a depthof about two feet.- Air is introduced into the interior of the tube at diierent trial rates until the tube ultimately reaches a temperature 0f about 900 C. and the combustion product withdrawn from the tube is essentially water vapor and nitrogen. Underthese conditions, the fuel bed maintains its temperature continuously and its eiiluent products are essentially carbon at high temperatures without agglomerai tion and capable oi ready reaction with water vapor. O n the other `hand, the invention is also applicable to coals, either hard or soft, and particularly so-called brown coal and lignite.

The invention may take advantage of any of the conventional expedients for ash or slag removal or other operating reilnements, which per se, form no part thereof and are available to those skilled .in the art.

The invention, moreover. is not necessarily limited to use of a iluidized fuel bed and may be operative Vin the absence of such a reilne- `ment where'th'e diffusion elements are arranged to provide adequate transfer/of sensible heat energy to the reactants.

2. In the method of gasifyinga solid carbonaceous fuel which comprises passing gaseous reactants comprising water vapor into contact with said fuel in a fuel gasiiication zonefat an elevated temperature at which the water vapor ls reduced with the formation of hydrogen and carbon monoxide, preferentially separating hydrogen from the reaction products by diffusion through a diffusion barrier within the reaction Obviously. many other modifications andl Vvariations of the invention as set forth above may be made without departing from the spirit and scope thereof and therefore only such limitations should'be imposed as are indicated in the following claims interpreted in accordance with a fair and reasonable range of equivalents.

I claim:

1. In the method lof gasifying solid carbonaceous fuel wherein water vapor is passed in contact with a. mass of said solid fuel in a gasification zone at an elevated temperature at which reduction of the water vapor by the carbon proceeds with Vthe formation of hydrogen and carbon monoxide, the improvement which comprises, separating hydrogen from the gaseous rezone, burning the diffused hydrogen with an oxygen-containing gas on the opposite side of said diil'usion barrier whereby heat resulting from the combustion of hydrogen is transferred to the gasiiication-zone through said barrier. and separately recovering the'products of gasication and the products of combustion of hydrogen.

3. The method as defined inclxsiim 2 wherein the solid carbonaceous fuel in the gasication zone comprises particles of fuel maintained in a. state of dense phase iluidization by the incoming reactants. i

, 4. The method as defined in claim 2 wherein a stream of oxygen is supplied to said gasification zone, in a proportion substantiallyY less than required per se for themaintenance of the thermal requirements of the gasificationv zone.

' ALLEN D. oanmsoN.

REFERENCES CITED' The-following references are' of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,083,683 y Hirt Jan. 6, 1914 1,114,355 Hirt Oct. Y20, 1914 1,213,470'- Finlay Jan. 23, 1917 1,592,474 Szarvasy July 13, 1926 FOREIGN PATENTS Number y,Country Date I 214,544 Great Britain Apr.' 24, 1924 310,686

Great Britain May 2, 1929

Claims (1)

1. IN THE METHOD OF GASIFYING SOLID CARBONACEOUS FUEL WHEREIN WATER VAPOR IS PASSED IN CONTACT WITH A MASS OF SAID SOLID FUEL IN A GASIFICATION ZONE AT AN ELEVATED TEMPERATURE AT WHICH REDUCTION OF THE WATER VAPOR BY THE CARBON PROCEEDS WITH THE FORMATION OF HYDROGEN AND CARBON MONOXIDE, THE IMPROVEMENT WHICH COMPRISES, SEPARATING HYDROGEN FROM THE GASIOUS REACTION PRODUCTS BY DIFFUSION THROUGH A DIFFUSION MEMBER IN THE GASIFICATION ZONE, HEATING THE DIFFUSION MEMBER BY BURNING THE DIFFUSED HY-

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