US2622059A - Low-temperature carbonization of coal - Google Patents

Description

Dec. 16, 1952 c. E. LESHER 2,622,059

LOW-TEMPERATURE CARBONIZATION OF COAL Filed Feb. 2a, 1948 2 SHEETS-SHEET 1 a/x A INVENTOR CARL E. LESHER ATTORNEY Dec. 15, 1952 c. E. LESHER 2,622,059

LOW-TEMPERATURE CARBONIZATION OF COAL Filed Feb. 28, 1948 2 SHEETS-SHEET 2 3 I00 98 I 94 M, 9 84 o we 6 l5 2,6 /'o8' l6 8 l8 a7 I9 mg L Hgurz 3 INVENTOR CARL E. LE SH/ER J). I F e ZTTQRNEY Patented Dec. 16, 1952 LOW-TEMPERATURE CARBONIZATION OF COAL Carl E. Lesher, Ben Avon Heights, Pa., assignor to Pittsburgh Consolidation Goal 1 Company, Pittsburgh, Pa., a corporation of'Pe'nnsylvania Application February 28, 1948, Serial No. 11,964

4 Claims.

This invention relates to the distillation of carbonaceous materials and, more particularly, to the distillation of distillable carbonaceous solids such as bituminous coal, lignite and oil. shale.

The primary object of the present invention is to provide a process and an apparatus for continuously distilling carbonaceous solids.

Another object of the present invention is to provide a process and an apparatus for the distillation of carbonaceous solids to continuously produce a solid product and a maximum yield of volatile products at a high throughput rate of carbonaceous solids.

A further object of the present invention is to provide a process and apparatus for continuously producing from distillable bituminous coals or lignites a granular carbonaceous product within the approximate size range of the coal or lignite charge and substantially free of lumps of coke.

- In accordance with my invention, the above objects are attained by the use of a two vessel system. One vessel serves as a preheating zone for raising the temperature of finely divided previously distilled carbonaceous material to a temperature sufficiently high to distill the material being treated. The second vessel is the distillation zone and comprises a substantially cylindrical horizontal retort which is mounted for rotation aboutits central longitudinal axis.

In operation, hot distillation residue from the I heatin zone and finely divided undistilled carbonaceous solids areseparately chargedinto one end of the rotating retort in such proportions that the average temperature of the solids in the retort .'is' within the. distillation range of the car- P."

bonaceous solids. The rotation of the retort produces intimate mixing of the hot distillation residue and distillable solids whereby distillation of the latter takes place. Solid distillation residue is continuously removed from the opposite and outlet end of the retort, thereby causing progressive and continuous movement of solids through'the retort. The volatile products are also continuously removed through the same outlet end of the retort. To complete the cycle a In the preferred embodiment of this invention, thepreheating zone, as distinguished from: the distillation. zone, comprises a-fluid iz ed, bed of granular distillation residue with the fluid condition being maintained by oxygen or an oxygen bearing gas. The entire bed of granular car.- bonaceous solids is thereby uniformly raised to the desired'temperature by combustion of a part thereof. I have found that the granular distillation residue produced in the rotating retort is eminently adapted to being fluidized. The'us e of the fluidized bed to effect heating'of the distillation residue-in combination with distillation of the distillable carbonaceous solids by direct contact with the hot dlstillationvresidue results in the maximumutilization of heat in the system.

The operation of the above two vessel system on bituminous solids such as high volatile Pittsburgh seam coal which is acoking coaLproduces continuously a high yield of liquid tarrich in tar acids, a substantial quantity of high B. t. u. gas, and. a granular loose char which is suitable for a number of usesincluding that as solid boiler fuel. Furthermore, the production capacity of the system has been found to considerably exceed expectations and to be greatly superior to any heretofore proposed to the best or my knowledge.

Other details, objects and advantages of the invention will become apparent upon reference to the following description of a preferred embodiment thereof.

In the accompanying drawings I have shown apparatus by the use of which the invention may be practiced and have illustrated a. present preferred method of practicing the invention, in which:

,Figure 1 is a diagrammatic showing of the apparatus in which the invention may be practiced; I

Figure 2 is a centrallongitudinal cross-seetional view of'a portion of the apparatus illustrated in Figure l;

Figure 3 is a vertical transverse cross-sectional view taken on the line 33 of Figure 2.

Referring to Figure 1 of the drawings, a flow sheet of a preferred embodiment of the invention is shown. Numeral l0 designates a substantially cylindrical horizontal retort which is mounted for rotation about its central longitudinal axis. This retort is provided with a layer of insulating material ii. A. hopper 14 serves to hold distillable carbonaceous solids which are conveyed to the interiorof the retort Ill through a conduit l5 by means of a variable screw feeder l 6. Another variable screw feeder I8 located adjacent to feeder i6 is adapted to introduce hot carbonaceous distillation residue in granular form through a conduit IS into the retort wherein a bed 28 of solids of substantially constant level is maintained by means of lifters 22 and 24. The latter upon rotation of the retort l0 pick up solids from the bed 20 and drop them into a hopper 26 from which the solids are. conveyed out of the retort through a conduit 21 by means of a screw feeder 28. A more detailed description of the retort 10 will be given later in connection with Figures 2 and 3.

The volatile products produced within the retort l0 leave the retort through the conduit 21 and are conducted to a dust chamber 30 which is provided with water 32 for the collection of dust. From this chamber the gas is carriedthrough conduit 34 to a spray scrubber 36 where condensa tion of any condensable vapors takes place. Liquid condensate is removed through the bottom 38 of the scrubber while the non-condensable gas product leaves the scrubber at the top through conduit 40.

The solid products from the rotating retort ID are prevented from entering the dust chamber 30 by means of a guard 42 and are forced to pass through discharge conduit 44. This discharge conduit is divided into two conduits 46 and 48.

The latter leads to product storage while the former serves to recirculate a portion of the distillation residuein the system. In order to insure that the size of the solid distillation residue is kept below a certain size it is passed through a screen 50, the oversize particles being conducted by conduit 52 to product storage. The remaining portion of the distillation residue which passes through the screen 59 is carried by conduit 54 to 'a hopper 56 from which it is fed by means of a variable screw feeder 58 into a preheating vessel B0. 7

Vessel 69 comprises two sections 62 and 3. The former and lower section serves to hold a bed of granular solids 66 upon a grid element 68 while the latter section serves as a disengaging space.

'To maintain bed 85 in fluidized condition, gas

containing oxygen such as air, is introduced through tube 70 at the bottom of the gas vessel 60. A cyclone 12 is provided for returning the solid fines to the bed while the gaseous product escapes from the vessel through conduit M to 4 another cyclone EB where the separation of gas from solids is substantially completed. The gas is then led to purifying apparatus through conduit 78.

Referring to Figures 2 and 3 of the drawings for detailed views of the rotary retort H), numbers 80 and 82 designate cone-shaped end sections provided with cylindrical flanges 84 and 86, respectively. The retort is rotatably supported at each end by rollers 88 and 90- which are mounted upon pedestals 92 and 93, respectively. Heavy flanges 94 and 95 are connected l6 and i8 extend. A sealing device 185 is provided to seal off the end of the retort. At the opposite end of the rotary retort a cylindrical flange encloses an opening I08 through which the screw feeder 28 disposed in conduit 21 extends. A sealing device H0 serves to seal this end of the retort from the atmosphere.

Within the retort in line with hopper 26 and directly opposed to one another are two lifters H2 and H4 (Figure 3). Each of these comprises a rigid supporting member H6 which is sealed at one end to the inner wall of the cylindrical portion of the retort. This supporting member extends toward the central longitudinal axis of the retort and is attached at its interior end to one edge of a scoop-like member H8, the other edge of the member H8 being attached to the cone-shaped section 82. The lifters are arranged so that their scoop portions are in line with the hopper 2B and are shaped in such a manner as to release their contents into the hopper as they traverse their paths above'the hopper.

In the preferred operation of my two vessel system as applied, for example, to high volatile Pittsburgh seam coal which as previously stated,

is a coking coal, the raw materials are finely divided coal and air with possibly a small amount of steam. The retort Hl'is first charged with finely divided previously distilled coal (preferably 0 to +4 mesh) which has been uniformly raised by suitable means to a distillation temperature for starting purposes only. The temperature is preferably in the range 800 to 1000 F. Finely divided previously distilled coal is also charged to the preheating vessel 8i! and is raised to a temperature substantially above that to be maintained in the retort and in general is in the range 1000 to 1400 F. but may be less depending upon the temperature to be maintained in-the retort. The heat required in the vessel 60 is preferably created by passing air or oxygen up through the bed of granular carbonaceous solids 68 whereby partial combustion takes place and heat is evolved. This heat is immediately and uniformly conducted throughout the entire bed.

The operation of the fluidization vessel to produce a fluidized condition is well known in the art. The velocity of the air, the depth of the bed, etc. are factors which can be readily determined. Because of the fluid condition of the bed, the granular solids therein contained are maintained at a uniform temperature. The gaseous products of combustion are separated from fines in the disengaging chamber 64 by means of a cyclone 12. Further separation is obtained by means of cyclone 16. The gas so produced is a low E. t. u. gas useful for certain limited purposes. If so desired. steam may be used in conjunction with the air to produce a fluidized condition in the vessel 50. The composition of the resulting gas is accordingly changed to some extent. While the use of a fluidized heating zone is preferred in practicing the present invention, other heating devices which are adapted to heat granular solids uniformly throughout may be employed, for example, rabbled hearths or rotating kilns.

Hot distillation residue from vessel 60 is conducted to the retort, Iii through conduits l8 and i9 by means of the variable speed screw l8. Concurrently with the introduction of this residue a stream of finely divided coal is introduced from hopper IQ. Both the coal and the distillation residue are substantially within the same size range i. e. 0 to +4 mesh. The two streams of solids are intimately mixed in the retort by in temperature with the" result' that distillation ofthecoal is rapid-and effective and the transition of the coal through the -plasti'c stage'to-a drystateis rapid. Little or no agglomeration of the-'coaltakes place;

The vaporous products are immediately withdrawn'from the upper-half of theretort through.

the hopper 26 and out through conduitzl. Concurrently-with the removal of the vaporous prod ucts theabed of solidsin the rotating retort is maintained at a substantially constant level by meansof lif-ters22- and 24 which-pickup dry granular solids-from the opposite end of theretort-a-ndidrop it into the hopper 26 This-continuous withdrawal of granularsolids results in: a continuous and progressive movement of the solids from the inlet to the outlet end. The time within the retort'is adjusted by varying the'total input of solids into the retort as can Ice-readily understood. For instance, ithas been found that with the preheater at 1200F. and a distillation temperature of 90'0" F. in the retort, the time requiredto distill Pittsburgh seam coil, less than A- -inch size, within the retort by the present process is from fifteen to twentyminutes.

The temperature maintained 'inthe retort is controlled by adjustingthe relative proportions of coal and granular distillation residue introduced by the variable screw feeders l6 and It as well as by adjusting the temperature of the heated distillation residue before its introduction into the retort. If'desired; the coal charge canbe preheated up to a point just below that at which it begins'to give off hydrocarbon vaporsbeforebeing-ch'arged' to the retort. The temperature differential between the distillation residue being fe d to the retort and the average distillation temperature within-the retort may be'asl'ow as'50 F. In adjustingthe ratio of the proportion-of the Pittsburghseamcoal to that 'of-"itsdistillation residue beingcharged to the retort, to avoid agglomeration I havefound it neecssary to keep the ratio: lessthan -l to 3 by weight.

Th'e vaporous products from the carbonizer are at least partially freed of'dust in the dust chamb'er -i'nthe conventional manner and from there are" passedthrough a scrubber or condensing chambertdwhere the 'tar portion of the products is condensed out. The non-condensable portion which ishigh' B. t. u. gas'is removed fromthe top "through conduit 4B,..to be further purifiedaccordingto the usual practices. 7

Theso'lid. products from the retort areforced by screw" 28 through the. discharge conduit 44 where. a portion thereof. is conducted toproduct storage through conduit. 45. 'Ihesize ,.of the distillation residue. leaving theretortis in.v general substantially the same as that of the coalintroduced which in itself is anoteworthy discovery as respects strongly coking coal. since this solid prod: uct can .be-recirculated for usewithout further treatment and consequent loss of heat. However, occasionally a small percentage of the charmay beeabove the size desired. This larger size is screened-out on screen and conducted to the product storage through conduit 52. That-part which passes through'screen '50 .is carriedby-conduitM-orby any suitable means such as an elevator; screw feeder, pneumatic means, etc. to the hopper 56 from which it is fed to the fluidized vessel 60 by variable screw feeder 58. The rate of feed of the solids will depend, of course'uponthe bed "level desired "in tl'ie lower section BZ-i'of the vessel-. Theabove cycle-isthenrepeated;

The products from the retort are carbonaceous: distillation residue, gas, tar, and water vapor. The product from the fluidized preheaterds a vent gas.

The solidproduct produced as-the result of-' the application of'myprocess and apparatus to high volatile Pittsburgh seam coal as described above; is a loose granular solid within substantially the same size range as the coal charged to the process. It .is friable, cellular and non-agglomerated'in: contrast to that produced: by other methodsfrom coking coals. If properly controlled, as has beendscrib'ed-{with respect to the ratio of 'preheated material and coking coal charged, theproduct is substantially free-of lumps of coke. Since a. large part" of this solidproduct has: passed through the preheating zone, this part has alower volatile content than that part which haspassed onl-ythrough the retort. The volatile content-or the: latter part is determined bythe averagetemperature within the retort. The difference in volatile content depends on the temperature dif'-'-' ference between the preheating zone and the;distill'ation zone and may accordingly be varied if desired. The solid product is suitable for use as solid boiler fuel as welI as for many other applications.

The-tar product is a fluid and by theabove process in the case of'the Pittsburgh seamcoal; a yield of 26'to 27 gallons per ton of coal is obtained; Its ash content is less than 1% and when distilled up to 300"-'C. 30% is found to pass over as distillate. Of this distillate approximately 40% represents tar acids.

The gas from the-retort when separated from the condensable-portion has approximatelykBOO" B. t'. u. or more per cu. ft; The-yield of such gas-is approximately 2000 cu. ft. per ton of'coal. The gaseous product from the'fluidized-preheater'hasa-B. t. u; content of 75'to and is at a temperature corresponding to that 'of-the"fluid izing vessel. About 28,000 cu. ft. of this: gas is produced per tonof coal processed.

While the above example described the application of my invention to high volatile Pittsburgh seam coal, it was for purposes of illustration1only'. The process andv apparatus hereinbeforedescribed maybe applied to any distillable carbonaceous solids including" both coking and non-cokingbituminous coal,: lignites,- oil shales, and the like: In thegapplication. to coking coals other: than: high volatile Pittsburgh seam coal and: other: than coking 'oilshales, thezpreferred proportions of coal: or shale and, distillation residue-'charged"to the: retort may be othersthan those specified in the above example-depending on: the particularcoking qualities: of the, coal but these may be-readily" deter-mined. In:.the application to non-cokingcoals, lignites; andnon-coking oil shalesgreater latitude'in theadjustment of the proportions of fresh charge and hot distillation. residue and also in the selection of the operation temperatures is permitted, since these materials donot agglomerate. IHQSllCh cases the temperature to which. the chargeis heated and. the temperature ofthe-preheating zone-may be as high as it'is practical in order to accomplish the desired distillation. 1

According to the provisions of the patent statutes, I have explained the principle} preferred construction, and mode of'operationof my invention and have illustrated and described what I now consider to represent itsbest-em- 7 bodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Iclaim:

1. In the method of distilling high volatile Pittsburgh seam coal by contacting said coal directly with hot distillation residue from previously distilled coal in a closed unobstructed substantially cylindrical horizontal retort which is mounted for rotation about its longitudinal central axis, the steps comprising maintaining a granular bed consisting of said distillation residue in said retort in direct contact with the walls of said retort to serve as a barrier between fresh coal and said retort walls, rotating said retort, whereby a rotary movement is imparted to said bed, continuously and separately feeding a stream of said coal in finely divided form and a stream of hot finely divided distillation residue into one end of said retort onto the top of said bed, the mixing of said fresh coal and said hot residue being effected solely by the aforesaid rotary movement of said bed, said hot distillation residue being at a temperature between 1000 and 14:00 F. and in such quantity that the average tem perature of the total solids in the retort is between 800 and 1000 F., the ratio by weight of coal and distillation residue fed to said retort being less than 1 to 3, distilling the coal by heat supplied from the distillation residue, removing the volatile products from the retort, withdrawing distillation residue from the retort in excess of that required to provide the aforesaid bed of distillation residue in said retort, conducting at least a portion of said withdrawn residue to a preheating zone, circulating a gas containing oxygen gas under fluidizing conditions through said portion in said preheating zone, oxidizing a portion of the solids in the fluidized preheating zone to maintain a temperature in said zone between 1000 and 1400 R, and returning said heated residue to the retort to repeat the above cycle.

2. In the method of distilling high volatile Pittsburgh seam coal by contacting said coal directly with hot distillation residue from previously distilled coal in a closed unobstructed substantially cylindrical horizontal retort which is mounted for rotation about its longitudinal central axis, the steps comprising maintaining a granular bed consisting of said distillation residue in said retort in direct contact with the walls of said retort to serve as a barrier between fresh coal and said retort walls, rotating said retort, whereby a rotary movement is imparted to said bed, continuously and separately feeding a stream of said coal in finely divided form and hot finely divided distillation residue into one end of said retort onto the top of said bed, the mixing of said fresh coal and said hot residue being effected solely by the aforesaid rotary movement of said bed, said hot distillation residue being at a temperature between 1000 and 1400 F. and in such quantity that the average temperature of the total solids in the retort is between 800 and 1000 F., the ratio by weight of coal and distillation residue fed to said retort being less than 1 to 3, distilling the coal by heat supplied by the distillation residue, removing distillation residue from the retort in excess of that required to provide the aforesaid bed of distillation residue in said retort, removing the volatile products from the retort, and returning at least a portion of the distillation residue after heating it to the aforementioned temperature range of 1000 to 1400" F. to the retort to repeat the above cycle.

3. In the method of distilling a highly coking coal by contacting said coal directly with hot distillation residue from previously distilled coal in a closed unobstructed substantially cylindrical horizontal retort which is mounted for rotation about its longitudinal central axis, the steps comprising maintaining a granular bed consisting of said distillation residue in said retort in direct contact with the walls of said retort to serve as a barrier between fresh feed and said retort walls, rotating the retort, whereby a rotary movement is imparted to said bed, continuously and separately feeding a stream of said coal in finely divided form and a stream of hot finely divided distillation residue into one end of said retort onto the top of said bed, the mixing of said fresh coal and said hot residue being effected solely by the aforesaid rotary movement of said bed, said hot distillation residue being at such a temperature and in such quantity that the average temperature of the total solids in the retort is at a distillation temperature of said coal, the ratio by weight of coal and distillation residue fed to said retort being less than 1 to 3, distilling the coal by the sensible heat supplied by the distillation residue, continuously removing solid distillation residue from the opposite end of the retort in excess of that required to maintain the aforesaid bed of distillation residue in said retort, removing the volatile products from the retort, continuously circulating at least a portion of the distillation residue to a combustion zone, circulating a gas containing oxygen gas under fiuidizing conditions through a bed of said distillation residue, oxidizing a portion of said solids in said fluidzed bed whereby the entire bed is maintained at a temperature substantialyl higher than that required to effect distillation of said fresh coal, continuously withdrawing a portion of the hot solids from the fluidized bed, and recycling it to the retort as said hot distillation residue.

4. In the method of distilling highly coking coal by contacting said coal directly with hot distillation residue from previously distilled carbonaceous solids in a closed unobstructed substantially cylindrical horizontal retort which is mounted for rotation about its longitudinal central axis, the steps comprising maintaining a granular bed consisting of said distillation residue in said retort in direct contact With the walls of said retort to serve as a barrier between fresh feed and said retort Walls, rotating the retort, whereby a rotary movement'is imparted to said bed, continuously and separately feeding a stream of said coal in finely divided form and a stream of hot finely divided distillation residue into one end of said retort onto the top of said bed, the mixing of said fresh coal and said hot residue bein eifected solely by the aforesaid rotary movement of said bed, said hot distillation residue bein at such a temperature and in such quantity that the average temperature of the total solids in the retort is at a distillation temperature of said coal, the ratio by Weight of coal and distillation residue fed to said retort being less than 1 to 3, distilling the coal solely by the sensible heat supplied by the distillation residue, continuously removing solid distillation residue from the opposite end of the retort in excess of that required to maintain the aforesaid bed of distillation residue in said retort, removing the volatile products from the retort, and continuously returning at least a portion of the distillation residue after heating it to an elevated Number Name Date temperature to the retort to repeat the above 1,704,956 Trumble Mar. 12, 1929 cycle. 1,775,323 Runge Sept. 9, 1930 CARL E. LESHER. 1,899,887 Thiele Feb. 28 1933 5 1,983,943 Odell Dec. 11, 1934 REFERENCES CITED 2,080,946 Lesher May 18, 1937 The following references are of record in the 2,287,437 Lesher June 1942 file of this patent; 2,441,386 e g y 1948 2,455,327 Keith July 30, 1948 UNITED STATES PATENTS 10 2,462,366 Davies Feb. 22, 1949 Number Name Date 2,480,670 Peck Aug. 30, 1949.

1,432,101 Danckwardt Oct. 17, 1922 1,433,039 Rodm-an Oct. 24, 1922 OTHE R REFERENCES 1,664,723 Young Aim 3, 9 Flmdlzed Techmque, pages 261-266, Coke and 1,698,345 Puening Jan. 8, 1929 15 Gas, September 1947.

Claims (1)

1. 4. IN THE METHOD OF DISTILLING HIGHLY COKING COAL BY CONTACTING SAID COAL DIRECTLY WITH HOT DISTILLATION RESIDUE FROM PREVIOUSLY DISTILLED CARBONACEOUS SOLIDS IN A CLOSED UNOBSTRUCTED SUBSTANTIALLY CYLINDRICAL HORIZONTAL RETORT WHICH IS MOUNTED FOR ROTATION ABOUT ITS LONGITUDINAL CENTRAL AXIS, THE STEPS COMPRISING MAINTAINING A GRANULAR BED CONSISTING OF SAID DISTILLATION RESIDUE IN SAID RETORT IN DIRECT CONTACT WITH THE WALLS OF SAID RETORT TO SERVE AS A BARRIER BETWEEN FRESH FEED AND SAID RETORT WALLS, ROTATING THE RETORT, WHEREBY A ROTARY MOVEMENT IS IMPARTED TO SAID BED, CONTINUOUSLY AND SEPARATELY FEEDING A STREAM OF SAID COAL IN FINELY DIVIDED FORM AND A STREAM OF HOT FINELY DIVIDED DISTILLATION RESIDUE INTO ONE END OF SAID RETORT ONTO THE TOP OF SAID BED, THE MIXING OF SAID FRESH COAL AND SAID HOT RESIDUE BEING EFFECTED SOLELY BY THE AFORESAID ROTARY MOVEMENT OF SAID BED, SAID HOT DISTILLATION RESIDUE BEING AT SUCH A TEMPERATURE AND IN SUCH QUANTITY THAT THE AVERAGE TEMPERATURE OF THE TOTAL SOLIDS IN THE RETORT IS AT A DISTILLATION TEMPERATURE OF SAID COAL, THE RATIO BY WEIGHT OF COAL AND DISTILLATION RESIDUE FED TO SAID RETORT BEING LESS THAN 1 TO 3, DISTILLING THE COAL SOLELY BY THE

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