US2772954A - Gasification method - Google Patents

Description

Dec. 4, l956- JEQUIER GASIFICATION METHOD 3 'Sheets-Sheet 1 Filed Jan. 24, 1952 Dec. 4, 1956 l. JQ'uu-:R 2,772,954

GAsIFIcATIoN mamon Filed Jan. 24. 1952 s sheets-snm s IMGWMR.-

UnitedStates Patent GASIFICATION IVIETHOD Lon Jqnier, Basel, Switzerland, assignor of one-half to IAmonia Casale Societa Anonima, Massagno,'Te`ssin,

l ly 1 Application January 24, 1952, Serial No. 267,948 Claims priority, application Switzerland January `29, 1951 1 claim. (cl. 48-202) The present invention relates to a gasification method -and more particularly to a method for gasifying fine particles of solid fuels such as slack of coke, anthracite, pit coal, lignite, etc.

The gasification of such slack presents substantial difficulties due to the fact that the slack must be treated in sufliciently permeable layers and a good contact must be obtained between the gasification medium and the particles. For a long time, it has been endeavoured to treat such slack, either in its normally occurring condition or after preliminary crushing, which maintaining its particles in suspension in a stream of 'air for the production of generator gas or in a stream of water steam and oxygen for the production `of water gas. Considerably elaborate installations have been built on this principle, but theyl have not given the expected results because the useful gas output was insufficient and the gas carried too large quantities of incompletely burned dust for which there was no use. When producing water gas, the method proved to be uneconomical becauseof its very high oxygen consumption. lIt has also been attempted to produce water gas from pulverized solid fuels while violently agitating them in a high velocity gas stream. The tests have shown that this principle will result ingood gasification but that much dust is carried with the gas, that oxygen consumption is rather high, that the gasification media, steam and oxygen, have to be preheated considerably, and that comparatively complicated apparatus involving high purchase, maintenance and operation costs must be used.

It is one of the objects of the invention to provide a method of gasifying slack maintained in suspension which avoids the above-mentioned disadvantages and which can be carried out by means of an apparatus of comparatively simple and durable construction.

A further object of the invention is to provide a` method which for a given quantity of gas will -require less fuel, oxygen and steam than the methods hitherto emv ployed.

Still another object of the invention is to provide a method whereby the dust carried by the gas can be eliminated almost entirely.

The formation of dust in lthe course of the gasification of solid fuel slack is due chiefiy to two factors:

First, the fuel grains introduced into the gas generator are of all sizes from the finest dust particles up to grains which may be, in some instances, several millimeters in diameter. Under `these conditions, while the largest grains will drop to the bottom of the apparatus,the finest ones may be `carried off by the gaseous stream before having been completely gasified.

On" the other hand, even if grains of quite uniform size are used, these become gradually lighter, in the gasification process and finally are carried out ofthe burst due to a too rapid evolution of the water steam which they contain. f

To overcome this disadvantage it has been attempted ICC to provide above the gasification zone proper, a widened Zone where the finest dust particles would remain. Experience has shown that this is not sufficient, but outstanding-.results have been obtained by using a generator preferably in theshape of a cone or pyramid resting on its apex land by giving this cone or pyramid such dimensions that the gas stream entering its lower part has'a velocity sufiiciently high to maintain suspended the coarsest fuel grains while in its uppermost part the gas velocity is suticiently low so as not to carry off any particles, even very fine ones, before they are entirely gasified. The cone or pyramid, i. e., the zone of upwardly increasing cross-section, may be surmounted by `a vertical-walled zone serving asa decantation zone for the dust carried by the gas, and may be closed by a cover which preventsthe developed heat from vradiating tofthe outside. Under these conditions, it is easy to obtain so high a temperature in the whole gasification zone that the ashes of the treated fuel begin to melt, i. `e'. `a temperature of about 1100 to 1500 deg. C. As the movement of the particles within the apparatus is very vigorous, many particles hit each other. If they have reached a sufficiently highdegree of gasification to carry at their external portions enough ashes which have already been initially subjected to fusion, they will stick to eachother, and as more of such particles agglomerate to them, they finally will drop to the bottom of the apparatus from which they can be withdrawn easily by any suitable means. Experience shows that the fall of 'the gradually growing particles is slow and leaves enough timefor .the carbon which they still may contain to be gasified. This gradual agglomeration of the first ash grains permits comparatively high gas velocities (between 0.5 and 5 meters per second) to be used without abduction of fuel particles.

It is to be noted that as the walls of the apparatus are cooler than the central part of the latter, due to radiation to the outside, which radiation exists even if the apparatus is duly and carefully lagged, the ashes will not tend to stick to the wall lining, because they will already have solidified when the particles reach the said lining. On the other hand, the abrasive action of the particles not yet substantially gasified willtend to remove whatever material may be sticking to the lining. It is advisable to use a very refractory and compact lining of such chemical composition that the ashes have no tendency to adhere to it. Bricks preferably comprising chromite, carborundum, mullite or any other product suitable for the ashes of the coal to be used may be conveniently employed. Also, the temperature within the apparatus will have to be controlled by changing more or less the relative quantities of steam and oxygen introduced, according to the point of initial or incipient fusion of the ashes, in order to avoid any Arisk of particles agglomerating on the walls.

While the inventionthus makes it possible to prevent the formation of abundant dust quantities which would be carried away by the gases before complete gasification,

which is one of the major drawbacks in the gasification' the second drawback which lies in excessive consumption,Y

as will be understood by the following: In a gas generator, as in any other device in which powders suspended in` a gas stream are treated, temperature varies by a few degrees at most throughout the enclosed space of -the apparatus, because the particles are stirred very violently. Under these conditions, the gas discharged at high temperature removes a large quantity of heat which thus is lost for the operation. In gas generators infwhich coal is treated in big lumps, in a stationary bed, this heat is, however, used in major part for heating the incoming coal to the desired temperature. According to the inven- 4 tion, this heat may be used to heat the gasification medium E such as air, or oxygen and steam, oroxygen and carbonio gas, etc., rather than to heat the coal. For this purpose, it is easiest to use a heat exchanger mounted directly at the outlet of the gas generator, but any other type ofiheat exchanger or regenerator may be used without departing from the scopeof the present invention.

The fact that the temperature-is equaland highthroughout the gasification space has other advantages whichin certain cases may beimportant. Thus, as the fuel grains are suddenly subjected to a high'temperature, they cannot agglomerate even if they have a strong tendency to coking, because they do not pass through the pasty stageof fusion. On the other hand, all gases Vwhich might .bedistilledin the course of heating are subjected to -very highternperatures, so that the Vtars and other complex organic bodies are immediately dissociated into simpler compounds, namely, hydrogen, carbon monoxide, carbon dioxide, and possibly some methane. Thus it is possible, Vwithout :inconvenience, touse very young fuels providedpof course, that they are not introduced into the apparatus .with such an excessively high water content thatit' will beV difficult or impossible to reach the necessary temperatureand provided further that the grains'will not be .broken up into very ne dust by too violent'elimination of this water. This maximum water contentdepends on the kind 'ofv fuel used and may be determined by simple laboratory tests 'or by calculation.

In order that the invention may be Vfully understood, several preferred'modes of effectuating the method according to the invention will ynow be described, yby'way of example, with reference to the attached drawings, in which: v

Fig. 1 is a schematic representation of a gas generating apparatus for carrying out the method according to the invention;

Fig. 2 shows an apparatus of the vsame kind as that of Figure 1 but provided with a modified heat transfer device,

Fig. 3 schematically represents another gas generating apparatus comprising means for gasifyinga pulverized fuel such as coke,'semicoke or anthracite, havingonly a small content-of volatile substances, and'in which the said puli verized fuel is'preheated before it enters the gasification zone;

Fig. 4 schematically represents a further gas generating apparatus, which also involves preheating of the pulverized fuel, but adapted for gasification of a'young, not'yetncarbonised fuel such as pit coal, lignite or other.

Fig. 5 shows, also inschematic representation, a combined apparatus for producing hydrogen from water steam, and for producing generator gasto-be used as a reduction means in the process of hydrogen production.

With the apparatus -shown in Fig. '1, the fuel, if-used in the conditionof slack in the sizes of 0 to 5 or even 0 to '10 mm., vneed not be crushed'or pulverized; -it is suicient to dry it partly in certain cases. l Y

The rkgenerator vproper 2 is `a hollow body forming'a chamber inthe shape of a cone or pyramid the'ap'ex of whichis Adirected downwardly, which chamber is further provided with a cylindrical or prismatic zone. The 'fuel is introduced-into the. generator at 1 through a convenient feeding device,`hereshown as a worm feeder. Simultaneously, a gas herein referred toas the gasification medium, is introduced into the generator near its bottom-,i e. near the pointof the cone or pyramid, through apipe 13. This gas will consist of air for the production'of generator gas, or oxygen and'water steam-for the production-of water gas, or oxygen and 'carbon dioxide for that f of carbon monoxide. As this gasification medium ascends through the generator chamber, its velocity decreases accordmg to the larger cross-sectional area available. The

gas current maintains in suspension, i. e., `as a dense, Y ebullient, fluldized mass,the fuel particles introduced at 1; the coarser ones will remain :in the lowergpart'of the generator chamber, while the finer onesvwill .be carried to a higher level. vAs the weightof thenindividualgpar- 1;"

ticles .decreases in the Acourse of their gasification, .they will move upwardly in the generator. In the process, the ash contained in the particle undergoes initial fusion and in part forms a tacky layer at the surface of the particle. Thus, when two or more particles hit each other, they agglomerate to form a larger grain which again gradually sink to the bottom .of `the generator. Thence, the ash is extracted `by a device 3 whichV may be of any convenient type `but which must :be gas-tight to preventtheescape 'of gas with its attendant drawbacks.

l Gn leaving the generator, the' gases are dected Yby a screen 4 mainly provid'edto-preventheat radiation to theoutsideand to maintainas much heat as possible within the'generator proper 2. After they have left the latter, the gases flow through a heat exchanger' 5 .builtof refractory material, traversed by one or more tubes 6 through which the gasification medium to be heated circulates, These tubes, made from heat-resistant material such as steel with high chromium content, follow the convolutions formed `by the battles 7 so as to circulate the gasification medium in counterow to the gases. The gas velocity being much higher'in'this heat exchanger than in the upperpart of the gas generator 2, there should be no dust deposit in the heat exchanger 5, but nevertheless doors should be provided 'forinspectiom assembly and dismantling of the heat'exchange tubes 6. The cooled gas leaving the heat exchanger'then passes -into a waste-heat recovery boiler 9 andthence proceeds to the point of use throughipipe v10. 4The steam required for gasification when producing water gas is in part generated by the boiler 9 and enters the apparatus through pipe 11; oxygen is supplied through pipe 12. Preferably, the gasification medium is mixed before it enters the heat exchanger, in order to have as-thorough a mixture as possible at the inlet of the generator 2. Obviously, without departing from the scope of the invention, one might replace the water steam by carbon dioxide in order to obtain a gas of high carbon monoxide content instead of water gas. On the other hand, air may be used instead of oxygen to produce ordinary generator gas. 4

The Vheat exchanger of the type lshown in Fig. 1 of course requires the use of specially heat-resisting metals for the tubing. Such metals have been made available by the industry and it must be remembered that in this particularv case they are used under comparatively easy conditions because they are only subjectedtovery slightmechanical stress. Moreover, as the gasification medium is only ata slightly higher pressure than the water gas, there is no danger of hydrogen diffusion even at high temperatures. VThough the gas generator 2 must be maintained at temperatures between 1100 and 1500 deg.'C.,

the gasification medium generally may leave the heat exchanger at'temperatures in the order of 900 to 1200 deg. C. Under these conditions, oxygen consumption will be extremely low. Thus, when using coke slack and a generator-of adequate dimensions, the consumptions would amount to`less 'than 0.4 kg. of pure carbon; less than 0.2v

Obviously, and again without departing from the scopeVv ofthe invention, one could introduce, together with the gasification medium, a gas mainly formedby hydrocar-4 bons which vwould be cracked at the considered tem peratures and would increase the water gas production. Such a method would be particularly advantageous for usingfthe residual gases in such processes as the synthetic production of carbon monoxide and hydrogen, which yield considerable quantities of gaseous by-products rich in light` hydrocarbons. .Introduction Vof 'suc-h by-products after p their reheating in a separate heat exchanger, by means' OJJart-of .the .waste heat pf the gas produced 'might take the gasification zone.

. et. the. @PGK of the" con@ r pyram must, 1.1.,.hef09 largeZO, i640 (legi Will be Convenient. The treatment t0 which the coarse; grinsare to. be degli-the Smaller Should, the said an'gf be# T0 free en rely the agglomerated ashes from their carbon conf means may be` provided to introduceY 'at'fthe very bottom end of the generator `aV small quantity of air, or tigen; or Oxygen and Steam, or Oxygen and Carbon 9X. dioxide- W hout departing from the scope of the invention, the heat exchanger provided according to Fig'l might be replaced by lany other type of heat exchanger- A tubular heat exchanger may begsuitableand in Fig. 2 provision i s made for transmitting the heat of the outgoing gas to `the incoming gasification by means of circulating heat-resistant balls. In this figure, reference numbers 1, and 3 have the same meaning as in `Fig. 1. The gases leave the generator 2 lthrough a pipe 20, andenter a column 2.1 filled'with balls made from refractory materia'lmsn'c'zh as alumina, aluminium silicate,` heat-resisting metals, etc. These ballshave a diameter of about l c m. and'V proceed in cold condition from a filling tunnel 22 through a pipe 23. After having been at "least `partly cooled Vyby `these balls, ythe gas is delivered through the pipef24, a heat-recovery boiler 34 and a blower 2 6. manometer 25 connected between pipes 23 and 24 permits manual or automatic control of the'pres'sure of the gas before it enters the boiler 34 so as `to prevent both the escape of gas and the entrance o f airthrough the lballintroduction means 422, 23.V The Vhea-tedl balls drop through a tube 27, which may be provided with addi# tional heating means (not shown) into another column 28 where they are cooled by the gasiflca'tionrnedim; the latter is supplied to the column 2 8 through-a pipe 30 andV after heating by the balls is transferredto the generator 2 through tube 2.9. The tube 27 should be 'long enough lto prevent any escape, `through this tube, of gasification medium intot'thc gas produced. After having yielded part of'their heat to the gasification means,`the balls are discharged from column 258 through a suitable device 31 andthen -conveyed back to the funnel 22 by a suitable conveying devi-ce, here 4shown as a worm conveyor and ascending tube 32, 4but which preferablymight be a bucket conveyor. For starting operations, the generator 2 is provided with a valve-controlled outlet funnel 33.

As the temperature in the gasification zone of the generator'Z-ha's to Abe rather high, about 1100 'to 1500 deg. C. according to the `kind of fuel, the heat exchanger 'o would have to be constructed from special metals which in the presen-t `state of `the art are very expensive and which WG111@ not permit to reach the desired temperatures without complica-tions. This difficulty might .be overcome by using a `ball heat exchanger of the kind described, but the invention also compri-ses means for transmitting heat recovered from the gas, not only to the gasification mel dium but to the fuel slack as well before the latter enters rThus, a larger quantity'of heat will .be transmitted into the gasification zone than if the gasification medium alone (or the coal `alone as in conventional gas generators) were heated, although 4the ternperature yoftne gasification medium and ofthe coal when entering the gas generator will be definitely lower than otherwise; this makes it easier-to find suitable materials for .constructing the apparatus.

For this purpose, the fuel slack may be ground to the desired fineness such as, for instance, 2 to '3 millimeters, althoughthemo-st desirable .fneness may vary Isomewhat aecording tothe kind of fuel). The possibility of reducing the sizeof the grain-s to Vthat extent ,permitsthe useof a ,soicalled .fluidization column which -is based on th ollowing principle: `lf a gas streamof appropriate isA `directed `upwards through ra layer of pulverized material? the latterkwill be .suspended in the gas and stream.

Thus, they will remain Iin a comparatively dense disc tribution within the space occupied by the layer of powf' dered material, so that .the latterrnay be said to be :in Va dense fluidized state. The said advantages of `'this `state are'excellenlt mixing of the particles with the gas, high uniformity` of temperature evenfwithin large spaces, arid easy transportabili-ty of the fluidized lpowder. When using a fluidization column for the purposes now to be consid-ered, the pulverize'd -coal or other solid fuel maybe maintained in dense `ui`dized state in "se'veral' superpo'sed lay-ers,` by means' o f` a gas stream ascending,E Ithrough the several layers, and the fluidized -materialrn'ay be made to flow 'from' one layer to a lower one"b`y"mere gravity, as would a liquid; meanwhile, the gasprocee'ds'r4 from each layer to that immediately above it.

` In an apparatus of the kind herein Vreferred to, part of the gasV produced may be 'carried through a liuidization column of the type -outlined for pre-heating the coal' or other fuel to be gasied, and the remainder of the gas' may be used yto heat the gasification medium in a separate yhea-t exchanger provid'edfor this purpose and which may be an ordinary tubular heat exchanger. As Ithe transfer of heat from a dense fluidized layer to a heat exchange surface placed `in this la'yer is excellent, it ispreferable, however, 'to provide for heating the gasication medium in series of heat exchangers having comparatively small surfaces and arranged within `the fluidized' layers. Calcu lation shows that in this way the gasification medium may 'be heated to Va temperature which is -only slightly lower than that of the fuel, and that the latter temperature, which is not very high, does not require the use of special and costly materials. Moreover, the total quantity' of heat `whichthus can be recovered from the produced gas, is vdefinitely `higher than that which could be recovered by pre-heating only the gasification medium.

This pre-heating of the fuel in a series of dense iluidized `layers further has various other advantages when young or not yet carbonized fuels must be treated, because the pre-heating may be effected by groups of layers and the various phases of such pre-heating, such as drying, carbonizing at low temperature, and final pre-heating, 'maybe separated, so that the gases produced in these various phases can be separated in order not to contaminate the gasification medium with too large quantities of undesirable products such as carbon dioxide, sulphurated hydrogen, etc. Fig. 3 schematically represents an apparatus vaccording to the invention, working 0n this principle and particularly adapted to the gasification of a fuel such fas coke, semi-coke or anthracite, which has only a small content in volatile substances and contains practically no tar. Fig.r4 on the other hand, relates to the gasification of pit coal, lignite or other'young fuel which has not yet been carbonized.

According to Fig. 3, the coal ground to the desired fneness, at 41 enters the uppermost stage 42 of the iluidization column 43. IOn this stage, the coal isninaintained in dense fluidized condition by gas which arrives from the nextlower stage'44, through a grid 45 and which leaves the column through a pipe v'46. 47 designates@ separating device for retaining the dust which the "gas might carry away on leaving theicolumn. Obviously'fi separator of any kind, including a Vseparator -mountedl 7 powder transfer tube 48; this is a conventional overflow tube, 'the open upper end of which is slightly beneath the surface of the uidized powdered coal layer in the stage 42 and the lower end of which extends into the corresponding layer on the next lower stage 44. Being in dense liuidized condition, the powdered coal will overflow from the upper layer to the lower one, through the transfer tube 48, in the same way as would a liquid. Means such as an adjustable telescopic extension tube (not shown) mounted on the top end of tube 48 may be provided for adjustment of the surface level of the fluidized layer.

The grid 45 may be constructed in various ways. According to one preferred construction, it may comprise a series of steel channels disposed parallel to each other with their flanges turned upwards, and leaving between them elongated interstices for the passage of the ascending gas. A second series of steel channels would be disposed on the first-mentioned ones with their anges turned downwardly, so as to cover the said interstices for preventing the pulverized coal from falling through the latter; passages for the gas from the interstices to the upper side of the` grid may be provided by suitable indentations in the flange edgesV of the channels.

From stage 44 the coal, while being gradually heated, successively proceeds to the stages 49, then 50, then 51, and finally into the gas generator 52 from which the ashes are removed through tube 53. The thus used gas produced in the generator 52 ascends through the said stages, in opposite sequence while its temperature diminishes, The unused gasification media arrive through the pipe 54 and are carried through a heat exchange pipe 55 located in the uppermost stage 42. Thence they proceed through pipe 56 to a similar heat exchanger pipe 57 in stage 44, and so on through the other stages. Finally, the unused gasification medium is introduced through pipe 58 into the bottom part of the generator 52. In the embodiment shown in Fig. 3, five preheating stages are provided both for the powdered coal and the gasification medium. This number may be varied according to the desired conditions of operation and to the quality of fuel to be treated. In certain cases, it may be desirable to place the first heat exchanger in the second stage 44, or even in a lower stage, rather than in the uppermost stage 42. Similarly, if a hydrocarbon is to be cracked in the generator 52 simultaneously with the gasification of coal, it will be possible to preheat this hydrocarbon in a series of heat exchangers mounted in the various stages in the same way as the heat exchangers provided for heating the gasification medium. Of course, the latter will not be mixed with the hydrocarbons before they enter the gasid ication zone in the generator.

As a variant, if it is desired for some reason to preheat separately the coal and the gasification medium, e. g., for simplifying the construction or for reducing the size of the column, one may replace the heat exchangers 55, 57, etc. by a heat exchanger 59 mounted externally of the fiuidization column; part of the gas leaving the gasification zoneV would then pass through the column, in counterfiow to the coal as above described, and the remainder would be branched off through a conduit 60 to the separate heat exchanger 59 which it leaves through another conduit 62 provided with a control valve 61, to join theV gas outlet pipe 46 at the top of the column 43. The gasification medium in this case enters the heat exchanger 59 through a conduit 63 and leaves it through conduit 64 to join the aforementioned pipe 58 entering the gasification zone of the generator. Obviously, a second separate heat exchanger might be provided for preheating a hydrocarbon to be cracked, or any combination between heat exchangers mounted in the column 43 and separate heat exchangers may be provided without departing from the scopeA of the present invention.

In Fig. 4`which schematically represents an apparatus for the treatment and final gasification of a young fue1,

the coal, having been ground to the desired fineiiess, enters Ythe upper zone 72 of a' drying and pre-carbonization device 73. In this device, which Vcomprises two or more such zones 72, 74, the coal, while being maintained in dense fluidzed condition by lan ascending gas, is preheated, dried and Vsubjected to a beginning of distillation. For in most cases, before the coal is properly distillated at' low temperature, it is advantageous to extract from it the gas which is freed by heating to 200 to 300 deg. C. This' gas nearly exclusively contains carbonV dioxide and sulphuratcd hydrogen, which thus are easily eliminated while it always is costly to extract them from the carbonization gas. permits the accomplishment of this separation without difficulty. Also, if small quantities of combustible gases are freed with these undesirable gases, it is possible to burn the latter as will be explained below, and thus to use their latent heat. dense Y iiuidized condition, a circuit of gases is used which enter v'the lowermost part 78 of the device 73 through pipe 77. These gases are heated by burning, in a combustor 79, a fuel which may be the combustible fraction of the gas in this fiuidization circuit, or la gas p roduced inone of the other devices of the apparatus, or any other solid (pulverized), liquid or gaseous fuel, which will be introduced through pipe and burned with air introduced through another pipe 81. Valves 82 and 83 are provided for regulating the combustion and the heat consumption.

After having passed through the stages 72 and 74 containing the uidized coal, the gas leaves the column through conduit 84, after having been freed from dust in a separator 85, shown here as a cyclone, but which could be of any other type, or placed outside the column, without departing from the scope of the present invention. The gas which has left the column passesl through a cooler 86 in which its water content is condensed and discharged through a pipe 87. Upon leaving the cooler 86, the gas is ldrawn in by a blower 88 which sends it back into the fluidization circuit. Part of the gas is discharged to the chimney through conduit 89, two regulating valves 90V permitting simple control of the quantity of gas thus discharged and gas sent back into the circuit. Finally, the gas is preheated in va heat exchanger 91 by means of the gas which leaves the next device of the apparatus, whereby part of the heat of the gas circulating in that device is recovered, and returns to the inlet pipe 77 of device 73.

The coal thus precarbonized leaves the device 73 through an overflow tube 92 and reaches the upper zone 93 of the carbonizing device 94 in which it passes, in succession, through one or more stages in which it is maintained in dense fluidized condition by an ascending gas stream. The coal passes from one zone or stage to that next below, through overow tubes 96. The zones are separated from each other by grids 95. In this device, the coal is heated to a temperature in the order of 600 to 700 deg. C. so that it leaves the device perfectly free of tar and unable to yield anything else than hydrogen, carbon monoxide, some methane and a few traces of higher hydrocarbons. Besides, these traces will be very small if the coal stays a sufficient time in the carbonization zone. It will be easy to find out, by laboratory tests, how long and at what temperature the coal' should stay in this zone, depending on the coal used and on the purpose to be served by the water gas which will be produced in the gasification device, and to select accordingly the dimensions of the apparatus.

Withcoals showing a tendency to agglomerate in the course of their heating, the temperature of the first stage' in this carbonization device should be definitely higher than the temperature at which fusion of the coal begins, i. e. in the order of 500 deg. C. A temperature in this order has the additional advantage that all risk of condensation of tar in the apparatus with its attendant in` The method according to the invention In order to maintain the coal in 9 conveniences `is avoided. The gas enters the lower part 9 8 of the carbonizing device 94 through a pipe `97 and is heated by means of the combustion gases produced by a combustor 99 which is supplied with gas through pipe 100 and with air through pipe 101, control of the gas and air supply being effected by means of valves 102 and 103. In Fig. 4, it has been assumed that the gas obtained in lthe circuit is itsel-f used ras fuel but it would be possible, without departing from the scope of the invention, to use any other type of solid (pulverized), liquid or gaseous fuel, or to effect this heating indirectly. After having passed through the carbonization device and after the primary tar and gas developed by the coal as it is heated has been fadrnixed to it, the gas is freed in a separator 105 from the dust which it contains and is carried off through a pipe 104. Then it passes through the aforementioned heat exchanger 91 in which it yields part of its sensible heat to the gas entering the drying device 73. If the temperature at which the gas crculates through the carbonization device 94 is adequate (between 100 and 200 deg. C.), nearly all the tar will be condensed in this heat exchanger and flow out through a pipe 106; this eliminates the problems and difficulties which often are encountered in the separation of water and primary tar. Then the gas is cooled in a condensation device 107 in which the constitutive water of the coal and the light tar, which easily splits therefrom, is extracted through pipe 108. From the condenser 107, the gas is drawn in by -a blower 109 which sends it into a disessenciation device 110 land thence through the inlet pipe 97 of the carbonization device 94. Excess gas, if thereis any, may be used as it is, if tapped through conduit 111, or cracked in the gasification device, if carried away through conduit 112. Control of the gas redistribution between the conduits 97, 111 and 112 is eifected by means of the three valves 113.

The carbonized hot fuel proceeds from the carbonization device 94 to a preheating zone 114 comprising one or `more stages, through an overflow tube 115. This preheating zone immediately precedes the gasification zone 116, and what has been said in respect of Fig. 3 also applies to zone 116. The number of stages, however, is smaller in Fig. 4 because the coal is already warm on entering the preheating zone 114. Consequently, the gas leaves the latter in hot condition as well, and its sensible heat must be recovered by means of a heat ex changer 117 into which the gasification medium to be preheated enters from conduit 118 while the cooled water gas is carried to the point of use through conduit 119. In `the same heat exchanger 117, one also can preheat the gas adducted from the carbonization device through pipe 112 and which is to be cracked. Both the gasification medium from conduit 118 and the gas to be cracked are further pre-heated by circulating them through heat exchanger tubes 120 in the preheating zone 114. These heat exchanger tubes might be replaced by an external heat exchanger like that shown in Fig. 3.

If it were necessary to obtain an absolutely pure water gas, there would be no diiiiculty in providing the preheating zone in the circuit of the carbonization device and in modifying accordingly the heat recovering system. If it is desired to produce generator gas by gasification and therefore to use as rich a carbonization gas as possible, part of the generator gas might be used for indirect preheating of the gasification medium outside the gasiication zone, in a heater provided forV this purpose; by this method, introduction of nitrogen into the rich gas would be avoided.

With coals having a particularly high ash content, it

may be useful to recover the sensible heat of the ashes by cooling them, in the condition of agglomerated balls, in an apparatus of known construction mounted below the gasification zone traversed by an ascending current formed by part of the gasification medium.

With the above-described arrangements, it is possible toV produce generator gas byv using, s the gasicatior medium, air with more or less water steam, or to pro'- duce water gas with steam and oxygen, or carbon monoxide with carbon dioxide and oxygen. It is not possible, however, to obtain directly hydrogen with these means. Nevertheless, hydrogen can be` manufactured from solid fuel slack, according to the following con# s iderations It has been known for a long time that hydrogen may be produced by subjecting iron or ferrous oxide to water steam, according to either of the following reactions:

and thereafter reducing the `higher oxide thus obtained by means of a suitable reducing gas such as generator gas. This sequence of reactions may be elected either by means of stationary beds of iron oxide with alternating reduction andhydrogen production periods, or by means of fluid beds of powdered ironV oxide, which is transferred, in a closed circuit, from a reduction apparatus to a hydrogen production apparatus and from the latter back to the reduction apparatus. Unfortunately in both cases a large heat quantity is con sumed for heating the 'gas and the steam up to the reaction temperatures which are in the order of 500 to 800l deg. C., so that the efficiency of the process is not satisfactory when operating at industrial scale. Moreover, impure hydrogen is produced, because it is contaminated by the reducing gases which adhere to the iron or oxide granules in spite of scavenging generally provided between two phases of the operation. Careful crubbing of the hydrogen is .absolutely necessaryif this gas is to be used either for chemical syntheses or for hydrogena tion. rI'his method of producing hydrogen is rarely ernployed nowadays, excepting for the production of hydrogen in countries where cheap electric energy and suitable fuel for the manufacture of water gas are not readily available. If the generatorgas is produced according to the present invention, however, this gas leaves the generator at high temperature, and as it is not necessary..

to preheat the gasification air, as a brief calculation will show, a good part of the freely available or sensible heat of the generator gas leaving the generator can be employed for the iron-steam process which thus becomes economical.

On the other hand, the present invention makes it possible to `obtain directly hydrogen in a form which is pure enough to be used for the principal applications of this gas, such as hydrogenation or chemical syntheses.

The principle of this method will be explained with reference -to Fig. 5 of the drawings. It is possible, however, to provide other general arrangements without departing from the scope of the invention, if for some reason or another the conditions appear to make such change desirable.

In Fig. 5, the reference numbers 1, 2, 3, 4, 12 and 13 app'ly to elements corresponding to those bearing the same numbers on Figs. l and 2. The coal slack is introduced at 1 into the gas generator `2, from which `the ashes are drained through the device 3. The screen 4 prevents radiation heat losses from the generator 2. Air containing such quantity of steam as is necessary to maintain the convenient temperature (see above) in the gas generator is admitted from a conduit 12 through a heat exchanger 133 which is heated by the gases leaving the reduction device which will be referred to later on. v From the heat exchanger 133, 'the said air is introduced into the generator 2 through the pipe 13. The generator gas produced in the generator leaves the latter through a throat 127 and thence ascends through a grid 128 into a zone 129 in which the reduction of the iron oxide takes place. The ,gases carry their freely available or sensible heat into zone 12.9, s0 that no heat has to be 1 1 supplied from outside to this zone to maintain it at the desired temperature. In this zone, the gas maintains in dense tluidized condition an iron oxide powder; temperature is in the order of 500 to 800 deg. C. and the gas speed just above the fluidization zone is in the order of 0.1 to 2 metres per second, according to the size and properties of the oxide particles. After having been partly oxidised by reduction of the oxide, the gas leaves through a separator 130, which is shown in the drawing as a centrifugal type separator but which could be, withf out departure from the scope of the invention, of any other type of separator capable of reintroducing, e. g. through a tube 131, such dust as has been separated from the gas. Of course, this separator could as Vwell be mounted outside the reduction zone. The gases, which still have Vthe temperature they acquired in the reduction zone and which also contain a proportion of combustible gases corresponding to the reaction equilibrum at the reduction temperature, proceed through a pipe 132 to'the aforementioned heat exchanger 133 which they leave through a conduit 134 to be used, for instance, in the production of the water steam necessary for the production of hydrogen as will be explained below, or for any other heating purpose. The iron oxide powder of the desired particle size, which usually is less than 0.5 mm. but does not Vcontain more than a small proportion of grains smaller than 0.01 mm., comes from the hydrogen production device and enters the reduction zone 129 by gravity through an overow tube 158 in which a control valve 159 is provided. It is noteworthy that to intensify the reduction of the oxide and'thus to diminish the quantity'of powder in circulation, and also to improve the utilisation of the gas as a reduction means, the reduction could be carried out in two or more stages, instead of one only as shown in Fig. 5. To that end, a multi-stage uidization column such as that shown Vin Fig. 3 might be used. As this reduction device consumes large quantities of heat to heat up the iron oxide powder which enters it and to supply the heat necessary for the reaction, a little air may be introduced for burning the whole generator gas or part of it. For this purpose, it is preferable to have several iluidization stages as mentioned above, and to feed the combustion air to the upper stages only in order not to disturb the reduction in the lower stages; these also have the benefit of the sensible heat of the generator gas leaving the generator 2. The powder leaves the reduction zone 129 through an overiiow tube 136 provided with a control valve 137, and falls through a degasication device 138. drops from one bafe 139 to another, across and in counter-flow of a cleaning gas stream which will be referred to below. In this degascation device, the gas speed is sufficient to remove the line ash or fuel particles which might have passed from the gas generator 2 into the reduction zone 129 and which might have escaped reaction in the latter. In fact, it is preferable not to provide a dust separator at the very outlet of the generator, because this separator would be exposed to high temperatures and might cause too considerable heat' losses. On the other hand, the gas Velocity in the degasitication device here described can be controlled in such a way that no iron oxide particles, the vspecific weight of which is definitely higher than that of the fuel or of the ashes, are carried away by the gas; also, the sizeof the iron oxide particles is chosen large enough that a very high gas velocityvis required to carry these particles away. A particle size between 0.05 mm. and` In the latter, the powderV by it through a conduit 147. Before reaching the de-l gasilication device, this gas is heatedin a heat exchanger 149 and if necessary, especially duringthe starting period, in a heater 150 which may be put into circuit or cut off by a set of cocks 151.

The hot neutral gas enters the degasitication device through a pipe 152 and leaves it through another pipe 153 leading it into the heat exchanger 149, where it yields its sensible heat and then is carried olf to the chimney stack through a conduit 154. The degasitied powder leaving the degasitication device 138 through a tube 140 is taken up ina distribution box 170 by hot neutral gas coming from the blower 142, at the outlet which two valves 148 are providedfor adjusting the rates at which theneutral gas is fed to the degasication device lthrough conduit 147, and to the distribution box 170 for removing the degasitied hot powder. The mixture of n'eutralgas andpowde'r is sent, through a conduit 143, to a separator 1,44 from which the Vseparated powder drops into a supply bunker 145. The neutral gas which hasgbeen separated from the powder returns to the blower 142, through a conduit 146. Before entering the blower, it is carried through a heat exchanger 172 provided With a by-pass 173, to yield its heat to the neutral gas entering the distribution box 170.

The admission from the supply conduit 141 of fresh neutral gas and the circulation of the latter are controlled by means of valves 171. As the quantity of noxious gas extracted from the powder in the degasication device 138 is comparatively small, it must be possible to recirculate part of the neutral gas in closed circuit instead of discharging the whole to vthe outside. The possibility of this recirculation depends on the purity of the hydrogen to be obtained, on the quality of the fuel, on that ofthe iron oxide and on the distribution of'temperatures in the reduction zone and in the degasifcation device. Preheating of the neutral gas which leaves the blower may be provided by combustion of part or whole of the gas which leaves the reduction zone. For this purpose, an indirect heating device will be used, as the oxide must not be in contact with gases such as water, steam or carbon dioxide which would yield their oxygen to it.

The reduced iron oxide contained in the supply bunker 145 enters the hydrogen production zone 157 through a pipe 155 provided with a regulating valve 156. In the said zone, the oxide powder is maintained in dense phase uidized condition by means of a superheated steam current ascending through a grid 161. The reaction between the steam and the oxide is very quick and develops considerable heat. Thus it is possible to effect this reaction in a single stage but there would be no departure from the invention in providing two or more uidization stages.

-jacket 174 in which part or all of the steam required in the operation is raised. The reaction temperature will be in the range of 500 to 700 deg. C and the average speed of the gases as they leave the dense fluidization Zone may vary between 0.1 and 2 metres per second. The gas produced, which is a mixture of hydrogen and steam passes -through a separator 162 which is represented in Fig. 5 as a centrifugal separator but which could be replaced, without departing from the scope of the invention, by any other type of separator permitting reintroduction, for instance through a tube 163, of the dust separated from the gas. Of course this separator, as well as the separator` 130, could also be mounted outside the apparatus. The gaseous mixture of hydrogen and steam issues from the .separator through a pipe 164, then passes through a heat v exchanger 165 in which part of its sensible heat is transferred to the steam supplied to the heat exchanger 165 through a conduit 167. Then the hydrogen-steam mixture is discharged through a conduit 166 which leadsrit Y Ato final refrigeration and thence to the point `of use of the hydrogen. The steam introduced through 167 and superatc/2,954

heated in the heat exchanger 165 proceeds to the hydrogen-production zone 157 through a tube 160.

In principle, the whole apparatus should be constructed to minimize heat losses. Careful heat-insulation is necessary. Thus very pure hydrogen will be obtained under economic conditions. If a fuel is used which can be gasiied into Water gas, the process according to the inventioin will yield, for a similar quantity of fuel, a somewhat smaller quantity of hydrogen than when passing through the water'gas stage, but al1 devices for scrubbing the gas and converting the carbon monoxide then become unneccessary, whereby their considerable first cost as Well as the energy, labour, maintenance and depreciation required in their operation are saved.

Since certain modifications may be made in the method of the invention without departing from 4the scope thereof, it is intended that all matter contained in the foregoing specification and shown in the accompanying drawings be interpreted merely as illustrative and not in a limiting sense.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent, is:

The method of gasifying a powdered fuel mass which comprises the steps of feeding said mass into a iiuidization column and along a substantially vertical downward path through said column, dividing said mass during such downward feed into a plurality of discrete layers of substantially equal height spaced from one another along said downward path of feed through said iluidization column, discharging said mass from the lowermost layer into a gasification zone, introducing unused gasification medium into said gasification zone, controlling the velocity of iiow of said unused gasification medium within said gasiiication zone in an upward direction toward said 14 fluidization column, -to thereby ensure that said discharged mass when in said gasification zone is maintained in suspended condition therein for combustion purposes, directing used gasification medium and combustion gases from said gasification Zone upwardly through said uidization column to thereby transform said powdered mass into substantially liuidized condition in sai-d column, maintaining throughout said gasiiication zone a substantially constant temperature suicient to cause incipient fusion of ash of said mass, to thereby ensure complete combustion of said mass within said gasification zone, and conducting said unused gasification medium as a confined stream at least partly through and in indirect heat exchange with said layers in said uidization column and in the same direction as the direction of feed of said mass through said uidization column and simultaneously in indirect heat exchange with said used gasification medium and combustion gases passing through said discrete layers from said gasification zone and in a direction opposite to the direction of feed of said mass prior to the admission of said unused medium to said gasification zone.

References Cited in the tile of this patent UNITED STATES PATENTS 987,147 Loiseau Mar. 21, 1911 1,027,290 Smith May 2l, 1912 2,482,187 Johnson Sept. 20, 1949 2,516,974 Garrison Aug. 1, 1950 2,579,398 Roetheli Dec. 18, 1951 2,588,076 Gohr Mar. 4, 1952 2,633,417 G-oronowski et al Mar. 31, 1953 2,654,664 Reichl et al. Oct. 6, 1953 2,657,986 Barr et a1. Nov. 3, 1953

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