Processing carbonaceous solids

May 6, 1952

W. W. ODELL ET AL

2,595,366

PROCESSING CARBONACEOUS SOLIDS

Filed June 14, 1947

SHEETS—SHEET 1

<img file="US2595366A_D0001.tif" />

<img file="US2595366A_D0002.tif" />

May 6, 1952

W. W. ODELL ET AL

PROCESSING CARBONACEOUS SOLIDS

2,595,366

Filed June 14, 1947

SHEETS—SHEET 2

<img file="US2595366A_D0003.tif" />

Inventors

<img file="US2595366A_D0004.tif" />

. AttoT-ne-Y

Patented May 6, 1952

2,595,366

UNITED STATES PATENT OFFICE

2,595,366

PROCESSING CARBONACEOUS SOLIDS

William W. Odell, Washington·, D. C;, and George L. Matheson, Union, N. J., assignors to Standard Oil Development Company,, a corporation of Delaware

Application June 14,1947, Serial No. 754,624

Claims. (C 1

This invention relates to a process of producing coke or char of low sulfur content, from coal, lignite and other carbonaceous solids of relatively high sulfur content. In particular it has to do with the treatment of coal initially in a finely ₅divided state whereby the ash content is materially reduced, the carbonization of the coal at an elevated temperature, and elimination of the remaining sulfur compounds by subjecting the hot freshly carbonized coal in a fine state of sub- jq division to the reducing action of a reducing gas such as hydrogen.

When coal is carbonized in a fine state of subdivision, such as occurs when powdered coal is continuously introduced into a fluidized mass of 15 incandescent carbonaceous solids which solids may be previously carbonized coal, the resulting product can be treated, as defined hereinafter, by treatment with a reducing gaseous fluid at a temperature of the order of 400° to 600° C., and 20 the sulfur content of the carbonized product decreased by virtue of contact of the reducing gases with the freshly carbonized finely divided product. It has long been known that reducing gases when passed over hot coke will tend to reduce the 25 sulfur content of the coke but no practical application of this has been possible, so far as we are aware, for a number of reasons. First coking processes have not' been developed whereby coking coal could be carbonized in a fine state of 30 division without forming, lump coke. Again lump cokes does not readily lend itself to the desulfurizing process by treatment with hydrogen.

Another difficulty in the practical application of known procedures, so far as we are aware, is 35 that of eliminating sulfur present initially in the coal as gypsum. The gypsum at high, temperatures of the order of 1300° to 1500° C. is dissociated but at the temperatures common to carbonation dissociation does not occur but rather 40 a partial reduction occurs whereby a calcium sulphide, chiefly the monosulphide, forms and the elimination of this sulfur is a lengthy procedure unless the char or coke under process is very finely divided. 45

The present invention deals with improvements and combinations whereby the sulfur initially present in various forms in coal can be very largely eliminated in a relatively short period of time yielding a carbonized· product in. a finely 50 divided state with a very low sulfur content.

One of the objects of this invention is to produce a solid highly carbonaceous finely divided· fuel which has so low a sulfur content that it, is a preferred fuel for use in metallurgical and gas- 55 · (Cl. 202—31) making processes. Another object is to produce a carbonized solid fuel of low sulfur content which can be utilized in the manufacture of briquettes for domestic or other uses. Still an₅ other object is to produce an active carbon of low sulfur· content which may be used with or combined with catalysts usable in promoting chemical reactions. Other objects will appear from the disclosures made hereinafter.

We have- described in Serial No. 726,530 filed in the' U. Si Patent Office February 5, 1947, a process by which coal can be largely de-ashed and appreciable portions of the gypsum and pyrite When they are present with the coal can be eliminated therefrom by fluidizing the coal in a finely' divided state under definitely prescribed conditions. We have also described in Serial No. 754,623 filed in the U. S. Patent Office June 14, 1947, and now abandoned a process in which 20 the treated (partly de-ashed) coal is carbonized rapidly' at high temperature by introducing it in a fine state of division into a hot fluidized mass of finely divided coke to produce a char which has a very large surf ace area per Unit of weight.

According to our present invention coal, thus treated (de-ashed) and quickly carbonized, is subsequently treated with a stream of hot reducing- gas such as one comprising hydrogen or hydrogen- in admixture with carbon monoxide at 35 a temperature of the order of 400° to 600° C., whereby the sulfur content of the quickly carbonized product is not only materially reduced but it is reduced so rapidly that the process is commercially feasible. Although we do not limit 35 ourselves to the treatment of a freshly carbonized product nor to one that has been quickly carbonized, nevertheless such a fuel is preferable in the rapid production of a product low in sulfur. Whereas our previous inventions, starting 40 with-coal, include the carbonization of coal in a fine state of subdivision, preferably by quickly heating it in a continuous process in a hot fluidized- bed of coke at a temperature preferably above 900° F. and below about 2000° F., and pref45 erably conducting carbonization in the presence of some steam and/or subsequently steaming' the carbonized product for a brief period, the basic or specific feature with which this invention is particularly concerned is the treatment of the carbonized product thus prepared while still hot and while at a temperature of the order of 400’ to 600° C. with a reducing gas such as or including hydrogen for a period sufficient to materially reduce the sulfur content of the car55., bonized product; Best results are obtained when

2,595,366 the carbonized product treated with a reducing gas has been freshly prepared as described.

The operation will be better understood with reference to the accompanying drawing, in which; £

Figure 1 shows diagrammatically in elevation but largely as a flow diagram one type of apparatus in which the process of this invention may be practiced, adapted for the treatment of previously carbonized finely divided solid fuel li at the aforementioned temperatures with a reducing gas; and

Figure 2 shows in a similar diagrammatic manner another embodiment of the invention particularly suited for operation at temperatures 1 above about 1650° F., depicting especially a reactor with a double packed portion.

Referring to Figure 1, reservoir I is adapted to receive hot, freshly carbonized, highly carbonaceous finely divided solids from a carbonizer 2 through valve 2. It functions as a stripper for gases associated with the solids, the gases passing out through valve 3. The hot carbonized solids pass down under control through valve 4 into reactor 5 wherein they are fluidized by means of 2 gas which may pass chiefly through valves 6 and 7 into the reactor through grid 8. Gasiform fluid also may pass into 5 through valve 28 and conduit 9, and also through valve 14. The reactor has a packed zone (2 located in a middle zone 3 thereof. This packed zone contains large size bodies as shown in similar packed zones in Figure 2. The bed of fluidized solids extends above and below Ϊ 2 into zones B and A respectively, the top level of the bed being at L. The gas stream from 2 the reactor passes out hot through offtake 15, valve 16, heat exchanger 17, sulfur removal apparatus 18 and offtake 19 from which a portion is bled through valve 25 and a portion passes on through 20, valve 21, pump 22, exchanger 17 &lt; and conduit 23 back to the reactor. For cooling purposes gas may be returned to the reactor through bypass conduit 27 and valve 28. The sulfur removal may be effected in any known manner as by contacting the sulfur containing gas _iwith a sulf-reactive metal or the like.

Fresh reducing gas may be supplied to the system through valve 7. Combustion supporting gas may be introduced into the reactor through valve 29, and bustle pipe 30. Thermocouples _tare shown at 32 and 33.

In Figure 2 the same system of numbering is employed except that the packed portions of the reactor 5 are numbered 12A and 12B, and the free zone wherein finely divided solids may be in , free fluidized motion are lettered A, B, and C. * Irrespective of the packed zones, 12 of Figure 1 and 12-A and ί 2-B of Figure 2, it will be understood that the fluidized bed of solids is continuous from top level L to the bottom zone A, the bed density in the packed zone being less than in the non-packed zones. The packing is supported on supporting grids which are pervious to the flow of gas therethrough and in which the finely divided solids are substantially in a fluidized state.

Example 1

Referring to Figure 1 and considering the treatment of a carbonized de-ashed coal made by ;

quickly heat treating finely divided coal in a fluidized bed of finely divided coke at a temperature above 900° F. and below 2200° F. preferably at 1050° to 1650° F. the operation may be conducted as follows: Pass the hot, freshly carbonized ;

coal, which may be called char, from a carbonizer down through valve 2 into stripping reservoir I at a controlled rate which is sufficient to maintain a level therein as at LA with valve 4 open and > allow the hot char to pass downwardly into reactor 5 at a rate adapted to maintain the bed level therein at L, meanwhile allowing stripped gas from i to pass out through valve 3. Fluidizing gas is introduced through valve 6 and as needed 0 through valve 7 also, the combined volume of fluidizing gas being sufficient, at least, to maintain the char in 5 in a fluidized state. The gas from 6 and 7 passes up as a stream through porous member 8 into the bed of char. The gas intro5 duced through 6 is a reducing gas preferably substantially free of H2S and at a temperature above 100° F. and preferably above 600° F. but below that temperature at which damage to equipment might occur. The treated char is re0 moved from the reactor through conduit 9 and valve 10, preferably continuously at a rate adjusted to suit the desired reduction in the sulfur content of the char; the rate being synchronized with the feed rates so that the levels L and LA :5 are maintained.

The gas stream passing up through grid 8 and flaring member 11 passes serially through a free zone A, the packed portion 12 and free zone B and then through dust separator 13, offtake i 5, Ό valve ί 6, heat exchanger 17 wherein its temperature is reduced, sulfur removal vessel 18, conduits 19 and 20, valve 21, pump 22 and back through exchanger 17 wherein its temperature is raised, through conduit 23 and valve 6 and is ip again circulated through reactor 5. Excess gas is bled from the system through valve 25; additional fresh reducing gas as may be required is introduced through valve 7. The by-pass conduit 27 with valve 28 is used to reduce the temperature 10 of the outgoing treated char by allowing cooled gas to pass up through conduit 9 and through the char in flaring member ί I.

Sulfur exists in lignite, coal, coke, char and certain other carbonaceous solids in a number of _lg different forms which should be considered in treating them at elevated temperatures. For example the sulfur present as free sulfur, held in solid solution, upon reacting with hydrogen generates a small amount of heat; that is, the reaction is exothermic substantially as follows:

(1) H2J-S—H2S4-3.9 calories

This reaction is not favored by extremely high temperatures; a temperature approximately or somewhat above the boiling point of sulfur is preferred. Similarly ferrous sulfide is reduced by reaction with hydrogen with the evolution of heat as in Equation 2.

(2) FeS+H2=H2S+Fe-|-14.3 calories

At higher temperatures the endothermic reaction expressed by Equation 3 occurs (3) FeS+H₂O=FeO+H₂S-17.6 calories

Although water vapor is not usually considered a reducing gas, it may advantageously be employed with reducing gas as a fluid for treating hot carbonaceous solids in a fine state of subdivision at high temperatures, namely above about 1500° F. Under these conditions the reaction for the removal of sulfur is more complex than indicated by Equation 3. For example carbon reacts with steam at high temperatures forming carbon monoxide and hydrogen, also by endothermic reactions; the carbon monoxide, hy2,595,3.66 drogen and carbon are reducing agents tending to reduce iron sulfide and oxides to iron simultaneously forming volatile sulfur compounds.

The heat recovered in the heat exchanger 17 of Figure 1 is usually sufficient to. carry on the operation, when the char supplied through valve 2 is. at a high temperature. However, when considerable sulfur is: to be removed or when the temperature of the char thus, fed to the reactor 5 is not at a sufficiently high temperature, to. maintain the desired temperature in the bed of char in process the extra, heat, may be supplied, by introducing a relatively small amount of air or other combustion supporting gas. as. through valve 29, bustle-pipe 30 and inlets 31.

Summarily the operation comprises passing a stream initially comprising essentially a reducing gas at an elevated temperature upwardly through a bed of finely divided solid char, preferably fluidized, while said char is at an elevated temperature suitable, for the chemical reaction of sulfur contained therein, continuously feeding fresh hot char to an upper portion of the bed and continuously withdrawing the treated, char from a zone of said bed adjacent the bottom thereof, meanwhile, introducing a relatively small amount of steam and/or air into a zone of said bed adjacent the bottom thereof, as required; the total amounts, of air and steam used preferably should be kept to such low limits that the gas stream as discharged through offtake (5 of Figure 1 is still a reducing gas.

Under some conditions the gas discharged from stripper 1 through 3 of Figure 1 is a. reducing gas and this, under these conditions, may be circulated. as a reducing gas using valve 7 as a control. However, it. will be noted that in applying the foregoing disclosure the reducing gas circulated through the system, may be generated in amounts required by the use. of. the small amounts of. steam and combustion supporting gas. described when the temperature in the. fluidized bed. of char in reactor 5 is maintained at a temperature above about 1600° F. and preferably in the range 1650° to 1750° F. Higher temperatures may be employed but commonly employed alloy steels are. not so satisfactory as: materials: of construction of certain exposed equipment at these temperatures.

Referring to Figure 2 the operation is substantially as described, but additional economies are obtainable. By introducing a combustion supporting fluid in zone C separated from zones A and B by packed zones I2A and I2B respectively it is possible to maintain a high temperature in zone C and a lower temperature in zones A and B. Zone B is cooler because of the endothermic water gas reaction in. the bed and also because fresh feed is or may be supplied at a lower temperature through feed: valve 4. Zone. A may be appreciably cooler by virtue of cooling fluid introduced therein through valve 28,. and/or valve 14. Similarly a cooling gasiform medium may be introduced through valve 7. In this manner the treated char not only contacts the reducing gas after passing, through the hottest zone or combustion zone C but some of the sensible heat initially in the char as it leaves zone C is returned thereto in the upwardly moving stream of reducing gases from zone A. This not only permits a heat economy to be made but it minimizes the amount of combustion supporting fluid which may be required in zone C.

In carrying out the desulfurization operation as described there, is a. relationship between the initial size of particles of char treated, the. duration of the treating period, the amount of sulfur reduction and the velocity of the gas stream passing up through the char in process. Tire finer the size of the char the lower the stream velocity should be. For. any particular char the optimum superficial velocity can be determined by experiment but-it has been found that with mean, particle size of 200 mesh and of 6 mesh the approximate velocities of the gas stream leaving the bed, for satisfactory conditions, should be about 0.35. and 2.5 feet per second respectively; velocity calculated as for a gas stream in an empty reactor at standard conditions of temperature and pressure. The finer the size of char particles treated the more readily or more quickly is the sulfur content reduced. Whereas the. size of char used depends, upon the ultimate use to which the treated product is put, it is preferable, other factors remaining the same, to treat char having a mean particle size less than one-eighth (¹½) inch. The sulfur content of the treated product, without using excessive or uneconomical amounts of reducing gas, may be as low as 0.1 percent or even lower according to size of char treated, the initial sulfur content of the feed char, and the duration of the treating period.

In the foregoing consideration has been given primarily to the removal of sulfur and its compounds from carbonized carbonaceous solids (char). It is not always desirable to precarbonize before treating. In other words finely divided carbonaceous solids such as oxidized coal, animal bones, and certain other materials may be treated: as described by feeding them into the reactor without precarbonization. Bone is treated to make a carbonaceous absorbent rather than to desulfurize.

The residence time of the carbonaceous solids within the reactor in counter contact with hot gases is usually more than one minute and the total depth of the fluidized bed is preferably more than 10 feet and may advantageously be more than 20 feet particularly as the diameter increases from about 5 feet. With the fluidized solids descending through the reactor at a mean velocity of 5 feet per minute, the duration of residence time of the carbonaceous solids in the reactor, when the bed is 20 feet deep, is 4 minutes. Employing the latter residence time and using a gas velocity of say 1 foot per second the approximate volume of gas passed per square foot of mean sectional area of the reactor during the 4 minutes is 240 cubic feet. The approximate quantity of carbonaceous solids treated with this 240 cubic feet of gas in 4 minutes is say 300 pounds. In order to increase the volume of gas used per unit weight of carbonaceous solids treated one can decrease the rate of discharging the treated char which increases residence time in the reactor, or within certain limits, increase the gas velocity, or both. It will be noted that the bed density in the reactor as shown in the Figures at 5 is less in the packed portion (or portions) than in the remainder of the bed.

Organic sulfur reacts with steam yielding hydrogen sulfide and carbon dioxide commonly by reactions which are endothermic and these reactions are favored by high temperatures; the overall reactions wherein the carbon dioxide formed reacts with incandescent carbon to form carbon monoxide absorb a greater amount of heat than the straight sulfur reactions. Sulfur combines, with carbon monoxide to form carbonyl

2,595,366 sulfide and this reaction is exothermic but occurs at an elevated temperature. The total amount of heat energy due to the oxidation or removal of sulfur from the char is very small, but elevated temperatures are required for promoting the desulfurizing reactions. It will become evident that, with good heat exchange in exchanger 17 of the figures, only a small amount of heat energy need be supplied to the system and this can. be accomplished by introducing the combustion supporting fluid as through 29 and 30 as described. By removing the treated char from the reaction chamber at a lower temperature than that at which it is fed into the reactor makes possible the further economy of heat.

Before defining my claims attention is called to the fact that the operation described can be conducted at reduced pressure, normal, or at superatmospheric pressure. It is usually economical to operate at pressures not appreciably greater than atmospheric. The duration of time the solids in process are resident in the reactor is determined by the result sought. Samples of the treated material as discharged through 9 and 10 of the figures are analyzed and if they signify undertreatment the residence time is increased by decreasing the rate of discharge of solid through 9 and 10 and, when desired, the rate of circulation of reducing gas is increased. The circulation rate can only be varied within limits determined by the quantity of blown over solids and by the desirability to maintain the solids in a fluidized state in the reactor.

Oxidation, conducted at a temperature below 600° C. or about 500° to 550° C. with oxygen is conducive to the removal of sulfur from such products as high temperature coke and this is particularly true of cokes containing only small amounts of sulfate sulfur and a larger amount of other forms of sulfur. This preferential oxidation of sulfur instead of the carbon of the coke is possible because the ignition temperature of the coke is above 550° C. We find that many carbonaceous solid fuels that contain sulfur compounds, such as low temperature coke, ignite at temperatures below 550° C. and hence preferential oxidation of sulfur is not possible at the latter temperature. Frequently its oxidation with combustion of some carbon is not economical.

It is economical to promote some oxidation reactions, as described above, wherein the heat generated is utilized in maintaining the system at the chosen temperature, wherein the overall result of reaction is the production of a reducing gas, and wherein the carbonaceous solids thus treated are finally subjected to a strongly reducing atmosphere before they are finally discharged from the reactor in which they are treated. We find that oxidation of sulfur in solid fuels by blasting with air occurs with most fuels, simultaneous with oxidation of carbon and the difficulty heretofore experienced has been that the accompanying oxidation of carbon generates so much heat that difficulties are experienced. It is necessary, to obtain optimum results, to maintain a quite uniform temperature throughout the mass of solids being treated, in the oxidation zone, or rather in the zone in which combustion supporting gas is introduced. This cannot be accomplished in a fixed bed but is readily accomplished in the manner described above.

The foregoing description and examples of operations have been presented to show specific applications of this invention and some of the results attainable by its use. Other modifications will be obvious to those skilled in the art hence only such limitations should be imposed on the invention as are indicated in the following claims.