US2657501A - Method for gasifying coal - Google Patents

Description

Nov. 3, 1953 B. J. MAYLAND 2,657,501

METHOD FOR GASIFYING COAL Filed Sept. 12, 1949 i 5 I ll I2 I J I Y INVEN TOR.

B. J. MAYLAN D A TTORNEYS Patented Nov. 3, 1953 METHOD FOR GASI FYING COAL Bertrand J. Mayland, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application September 12, 1949, Serial No. 115,210 3 Claims. (01. 48-202) This invention relatesto pebble heater'apparatus. In onesof its more specific aspects it relates to-a method for the gasification of coking and low ash-iusion-temperature coals. In another of its more specific aspects itrelates to an apparatus for thegasification of coking and low ash-fusionetemperaturecoals. In another of its more specific-aspects it relates to a method and apparatus for removing sulfur impurities from water gas producedby the gasification of coal.

Thermal conversion processes which are carried out in so-called pebble heater apparatus utilize a flowing'mass of solid heat exchange ma terial, which mass is heated to a high temperature bypassing hot gas therethrough in a first direct heat exchangestep, and is then caused to contact a second fluid heat exchange material, furnishing heat thereto in a second direct heat exchange. The conventional pebble heater apparatus generallycomprises two chambers which may be disposed insubstantially vertical alignment. The solidheat exchange material is introduced into the upper portion of the first or upper chamber. "Ilhat material forms a moving bedof solid heat exchange material which flows downwardly throughthechamber in direct heat, exchange with hotgaseous heat exchange .ma terial. The solid;heat.,exchange material is heated to a high temperaturein the heat exchange and is then passed to a second chamber in which the hot solid heat exchange material is caused to contact a second fluid heat exchange material in a second directheat exchange relation, furnishing heat to thesecond fluid heat exchange material.

' temperature coals to form water gas.

Conventional pebble heater chambers of pebble heater apparatus are generally formed as cylinders and a solidheat exchange material is passed thereinto in the form of a moving bed. Hot heat exchange gases are sometimes intro-v duced into theupper cylindrical bed at its lower end and at the periphery of its enclosing chamber. A liquid fuel is sometimes used in placeof thehot gas, the fuel being injected onto the surface of the downfiowing solid heat exchange ma-. terial and being burned thereon, heating the solid heat exchange material during the. decomposition of the fuel and providing combustion gases which flow upwardly through the bed, providing additionalheat to the downfiowing pebbles; The solid heat exchange material is generally drawn from a substantially central point in the bottom of the bed and is passed downwardly into a gas heating chamberwhere a second moving bed of solid heat exchange material is formed.

Such pebble heater apparatus is readily adaptable to the :gasification of coals. Conventional pebble heater apparatus, however, provides one rather serious difilculty when used for the purpose of converting coking and low ash-fusion- The gasification of coal can be represented by the reaction between steam and carbon, i. e.,

This reaction takes place at temperatures in the neighborhood of approximately 1200" E, but in commercial operation it is ordinarily desirable to use higher temperatures so as to obtain a more rapid rate of reaction. Other reactions also occur in the gasific ation of coal, e. g.,

The resulting gas therefore is a mixture of hydrogen, carbon monoxide, steam, carbon dioxide, and hydrocarbons. A-t temperatures in the neighborhood of between 460 F. and 500 F., coal starts to lose its volatile material, the first released material being mainly loosely bound water. As the temperature is increased, more violent thermal decomposition of some coals occurs and hydrocarbon fragments are given ofi as volatile matter. Larger hydrocarbon fragments resulting either from cracking. or polymerization of small hydrocarbon fragments remain in the coal and exert a solvent action thereon. When this occurs, the coals go through a plastic or semi-fluid state. The temperature at which the coals are converted to a plastic or semi-fluid state depends upon the particular coal which is being reacted. With a bituminous coal, a plastic or semi-fluid: state is encountered at temperatures in the neighborhood of between 800 F. ahdl000 F. Certain types of coals, such as lignitic and high rankanthracite "coal, do not go through the plastic state.

Commercial gasification processes utilizing pebble heaters have heretofore used as feeds coke and coals which do not pass through a plastic or semi-fluid state. Since these materials do not go through a plasticstage, no difiiculty is encountered in supplying the feed to the reaction chamber of'the pebble heater apparatus. A good deal offthe coal which is available for gasification in the United States is of a coking variety, such as bituminous and subbituminous coals. When these coals are supplied to pebble heater apparatus, considerable plugging of the feed inlet is encountered because of caking of coke in the.

inlet conduit. Ithas therefore been necessary,

heretofore, to convert such coal to colre before supplying the material to a gasification System or, if the coal has a low ash-iusion-temperature, to use a flux in combination with the coal or coke, which flux will liquely the ash at reaction temperature so that it will drain or? in a liquid state.

Some coals, especially the lower rank coals, have a fairly high sulfur content. As the coal is heated up to gasirlcation temperature, much of this sulfur is released as organic sulfur com pounds by thermal decomposition. These compounds are undesirable in synthesis operation because they poison Fischer-Tropsch catalysts and are equally undesirable in fuel gas applica tion because they have unpleasant odors and are corrosive. Organic sulfur impurities are dime cult to remove from gas by ordinary methods such as scrubbing.

The present invention is designed to overcome the obstacles and difficulties described above which beset conventional gasification processes when utilizing coking and low ashiusioi1- temperature coals and coals which have a relatively high sulfur content. Broadly speaking, this invention comprises supplying powdered coal to a coking zone of a pebble heater apparatus as a suspension in a gas, such as steam. The coal is rapidly converted to coke and the coke so formed mixes with the pebbles and is converted to water gas by contact with steam which introduced into the bottom portion of a reaction chamber. The resulting product gas is passed upwardly through the coking zone into a treating zone in the upper portion of the reaction chamber and is contacted with the hot solid heat exchange material in the absence of oxygen, during which time the organic Sulfur impurities are converted to hydrogen sulfide. The resulting product gases are then removed from the reaction chamber, after which condensible materials are separated from the gas and the gas is subsequently scrubbed to remove the hydrogen sulfide therefrom.

An object of this invention is to provide im proved means for gasifying coal. Another ob ject of the invention is to provide an improved method for gasifying coal. Another object. of the invention is to. provide an improved method for gasifying low ash-fusion-temperature coals. An-v other object of the invention is to provide an improved method for removing organic sulfur im-- purities from product gases resulting in the gasification of coal. Other and further objects and advantages of this invention will be apparent to those skilled in the art upon study of the acoompanying disclosure.

Solid heat exchange material which is conventionally used in pebble heater apparatus is generally called pebbles. The term pebbles as usedherein denotes any solid refractory material of flowable size and form which has considerable strength and which is suitable to carry large amounts of heat from the pebble heating chamber to the gas heating chamber without rapid deterioration or substantial breaking. Pebbles which may be satisfactorily used in this gasification system may be substantially spherical in shape and range from about /8 inch to about 1 inch in diameter. When gasifying coal which is in a finely powdered state, I prefer to use pebbles which range within a size of from /8 inch to inch in diameter. Silicon carbide, alumina, periclase, beryllia, stellite, zirconia, and mullite are a few of the materials which may be satisfactorily used to form such pebbles or may be used in admixture with each other or with other materials.

More complete understanding or" the invention will be obtained upon reference to Figure 1 of the drawing which is a schematic representation of the device of this invention. Figure 2 is a sectional view of a portion of the reaction chamber of this invention.

Referring particularly to the drawing, heater chamber ll comprises an upright shell l2 which is closed at its upper and lower ends by closure members it and is, respectively. Pebble inlet conduit iii and gaseous effluent outlet conduit it are provided in closure member :3 and fluid heat exchange material inlet conduit ll extends into the lower portion of shell [2. Although inlet conduit ll is shown schematically a entering shell l2 at a single point, it is within the scope of this invention that the fluid heat exchange material inlet conduit may extend into shell [2 at a plurality of points distributed about the lower portion of that chamber. Reaction chamber la; comprises upright shell l8 disposed below chamber H and pebble conduit ill extends between the lower portion of chamber ii and clo sure member 22 which closes the upper end of shell 59. Gaseous effluent outlet conduit 23 is provided in closure member 22. Pebble support member 24. is provided within shell it at a point intermediate its ends and is spaced downwardly from the upper end of shell l9 and upwardly from the bottom end thereof so as to divide chamber ill into two sections. lebble support member 2% is formed as a doughnut baille Which forms a pebble conduit in its central portion, which conduit extends between and provides communication between the upper and lower sections of chamber ill. The upper surface of support member 2% is preferably formed as an inverted cone, the included angle within said cone being between 65 and A support member which has such a slope on its upper surface will direct pebbles through its central inlet and substantially prevent the accumulation of stagnant pebbles on its upper surface. Coal inlet conduits 25 extend into chamber ill to a point below pebble support member ti l as radii of an extended axis passing through the conduit formed in the center of a support member The lower end of shell is is closed by closure member 26 and gasification medium inlet conduit 2i is provided in the lower portion of shell it and, like conduit ll in chamber l2, may communicate with shell ill at a plurality of points. Pebble outlet conduit 28 is provided in closure member 26 and provides outlet for pebbles from the lower portion of shell ill. Outlet conduit 28 is connected at its lower end to the lower portion of elevator Elevator Z9 is connected at its upper end portion with pebble inlet conduit l5. Separation means SE is provided adjacent the bottom of a portion of pebble outlet conduit and has a screen section 32 which forms a portion of the lower side of conduit it; within the confines of a chamber also forming a part of .ration means Gil. Conduit provides an outlet from separation means ill. It is preferred that conduit 2 l, which communicates between the lower end of chamber l2 and the upper end of shell it, have a larger horizontal cross section than the conduit which is formed in the center of pebble support member 2a. A conduit i is connected to pebble conduit 25 for transmitting an inert gas to conduit 2 5.

Figure 2 shows a portion of a reaction cham-v ber which is similar to that shown in Figure l but is modified by;the'iextension ofthe coal-inlet conduitst 5=tangentiallyinto-shell l 9-.

3.;In .the operation ofathe.idevice; showneasEigure 1 of. the drawingg -pebbles are; supplied to the I upper portionvofchamber --l l through pebble inlet conduit l 5. and-form a flowing,contiguous-bed therein. A hot gas, such as the products of combustion, or a liquid or gaseous fuel is supplied to the lower portion of chamber II. The hot gas I is passed upwardly through chamber 11 countercurrent tokthe-"flow of thesolid heat. exchange material. If-a liquid or gaseous fuel is supplied to the lower portion ofchamber H,- the fuelis through'pebble conduit 2 l into the upper portion "of chamber I 8. The pebblesform a second flowing'contiguous pebblemass inthe upper portion of chamber is andflow downwardly through the conduit formed-in the center of pebblesupport member 2 -A third flowing contiguous pebble bed is formed in the lower portion of chamber is, but-thepeb-bles areremoved-from the lower end of that chamber at a sufficient rate tomaintain a substantial void -spacebetween the lower side of pebble support-member 24 and theupper surface of the-pebble-bedformed in the lower-section of chamber 53.

Powdered coal is suspended in a gaseous medium, such as steam, and is injected into the void space formed between pebble support member 24 and the upper surface of the pebble bed formed in the lower portion of chamber l8. The powdered coal is rapidly diffused in the void space and is raised to its coking temperature, forming .coke particles which settle on the surface of the pebble bed and flow downwardly through the lower portion of chamber is with the pebbles therein. Steam is injected into the lower portion of chamber l8 through inlet conduit 2? and flows upwardly countercurrent to the flow of hot pebbles and the coke. The pebbles preheat the steam as it passes upwardly therethrough and the preheated steam reacts with the coke to form water gas as described above. The product gases pass upwardly through the void space, through the conduit formed by pebble support member 24 and into the upper portion of chamber 18 where a bed of hot pebbles is maintained. An inert gas, such as steam, is supplied to conduit 2| through conduit 34 so as to prevent product gas from passing into chamber H.

The product gases are heat treated in the upper portion of chamber [8 in the heat exchange with the hot pebbles therein and a major portion of any organic sulfur impurities in the gases is converted to hydrogen sulfide. The heat treated product gases are removed from the upper portion of chamber l8 through gaseous effluent outlet conduit 23 and are passed to a condensation chamber, not shown, wherein the product gases are quenched and a portion of the condensible materials are removed therefrom. The cooled pebbles and solid ash are removed from the lower portion of chamber l8 through outlet conduit 28 and pass over screen 32 whereby the solid ash is separated from the pebbles. The solid ash is collected in separation means 3! and is removed therefrom through outlet conduit 33. The cooled pebbles are elevated by means of .6 elevator-29. to. pebbleiinletzconduitj 5.,.ahd. thus.j;d i the 'upper. portionof chamber, l I.

The pebbleiheaterapparatus shownin Eigure 1 is if desired modified by changing the -.c,oal,inlet conduits 35 so as to project tangentially into shell '19,- as shoWn- -in--Ffigure; 2 rot-the. drawing, 'when the coal to: beegasified is of.,a type.. which passes less readilytthrough. the; plastic onsemifluid state. The ash-fusion=temperature.is. ,an important property. of. the coal .which must..be considered -in coal gasification. -.Ash-.f.usi,ontemperatures vary from about 1200" F..to,a.tem-

perature above 30-00%1. The present invention is particularly adapted for gasifying coals attemperatures within the rangeof- -from..12002 F.-.to 2500 F. It :ispreferredto utilize reactorltemperatures -within.;.the; range of from l 500. F.,.to

.2200": F; for -.the;best commercial results.

Although. the inventionis describedaboye. as if the totalv amount of. gasification was-carried onwithin the pebble-shed: in the lowerportion of chamber l8, it shouldbe pointed out that aportion .of the gasification takes place within the void space formed betweenthe pebble support member 24 and the upper surfaceof the pebblebedrin-the lower portion-of chamberi l8. That void-space, for.v all practical; purposes, forms 3 :'C0ki1 Zone .and the pebblexibedqforms a.;.gasification; zone. It is. obvious, however;.it-hat: no; definite.- line may be drawn. between the .two..:: Byforming the..con-

duit through. pebble-support; member ,rz l witha smaller horizontal cross, section :than. .pebbleconduit 2%, a bed of pebbles is maintained in the upper portion of chamber I 8 while allowing a void space to be formed between the lower side of pebble support member 24 and the upper surface of the pebble bed in the lower portion of chamber I8. The pebble stream which flows downwardly through pebble support member 24 forms the only portion of the pebble bed within the void space, Impingement of the coal particles upon the stream of pebbles flowing through the VOid space will result in temporary cakes of coke on the pebble surface, which cakes are removed in the lower portion of the reactor. In order to prevent a buildup of coke on the lower surface of the pebble support member or on the walls of shell l9 adjacent the void space, steam may be jetted against those surfaces at one or more points.

The description of the method of this invention has been restricted to substantially the operation of the apparatus which is shown in the drawings. The scope of the method of gasifying the coking variety of coal and of removing sulfur impurities from the product gases which is disclosed herein is broader than the specific apparatus herein disclosed. The device of this invention could be modified by providing a different type of pebble support member in chamber i9 which would allow the gases to filter therethrough at numerous points rather than causing all of the gases to pass through the central pebble conduit. It should be pointed out that such a device would not be as efficient as the device which I have disclosed, but nonetheless such a device would be adaptable for carrying on the method of this invention. By passing all of the reaction products upwardly through a single conduit countercurrent to the flow of pebbles any powdered coal which is entrained in the gases is removed from the gas stream by the pebbles.

Various other modifications of the invention will be apparent to those skilled in the art upon study of the above disclosure. It is believed that such modifications are within the spirit and the scope of the disclosure.

I claim:

1. A method for gasifying coal which comprises in combination the steps of gravitating pebbles through a pebble heating zone as a contiguous mass; heating said pebbles in said heating zone to a temperature above the desired pebble inlet temperature to a gas treating zone; gravitating said hot pebbles through said gas treating zone as a contiguous mass; gravitating said hot pebbles from said gas treating zone through a substantially void coking zone as a restricted. free-falling stream; introducing powdered coal into said coking zone in gaseous suspension; subjecting said powdered coal to radiant heat from said free-falling pebbles in said coking zone, whereby said coal is converted to coke; gravitating said pebbles and said coke particles from said coking zone through a gasification zone as a collected mass; passing steam into the lower portion of said gasification zone and upwardly therethrough in direct heat exchange with the gravitating mass of hot pebbles and coke; reacting said steam with said coke; passing resulting product gases from said gasification zone through said coking zone and said gas treating zone; subjecting said product gases to high temperatures in direct heat exchange with said hot pebbles in said gas treating zone, whereby a large portion of any organic sulphur in said product gases is converted to hydrogen sulfide; removing said heat-treated product gases from said gas treating zone; removing said pebbles from the lower end of said gasification zone; and elevating said pebbles to the upper end of said heating zone.

2. The method of claim 1, wherein said solid heat exchange material is introduced into said gas treating zone at a temperature of between 1200 F. and 2500 F.

3. The method of claim 1, wherein said solid heat exchange material is introduced into said gas treating zone at a temperature of between 1500 F. and 2200 F.

BERTRAND J. MAYLAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 911,494 Hall Feb. 2, 1909 1,654,942 Nielsen et a1. Jan. 3, 1928 1,977,684 Luckc Oct. 23, 1934 2,443,337 Weber June 15, 1948 2,445,092 Utterback July 13, 1948 2,447,306 Bailey Aug. 17, 1948 ,469,332 Evans May 3, 1949 2,482,138 Schutte Sept. 20, 1949 2,486,627 Arnold Nov. 1, 1949 2,493,036 Savage et a1 Jan. 3, 1950 2,520,096 Harter Aug. 22, 1950 2,530,274 Weber Nov. 14, 1950

Images