US3272720A

US3272720A - Coking process

Info

Publication number: US3272720A
Application number: US267674A
Authority: US
Inventors: Nick P Peet
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1963-03-25
Filing date: 1963-03-25
Publication date: 1966-09-13
Anticipated expiration: 1983-09-13

Description

Sept. 13, 1966 N. P. PEE-r COKING PROCESS Filed March 25. 1963 United States Patent O 3,272,720 CKING PROCESS Nick P. Peet, Houston, Tex., assigner, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, NJ., a corporation of Delaware Filed Mar. 25, 1963, Ser. No. 267,674 4 Claims. (Cl. 201-5) The present invention is directed to a method of manufacturing high quality coke from a slurry of small particles of coal in water. More specifically, it is directed to the preparation of coke briquettes of high quality from a water slurry of coal wherein the slurry is coked and dewatered in a Iirst stage, and a portion burned in a second stage to provide heat for the coking step.

Recent developments in the transportation of particulate coal in a water slurry make it possible to transport coal long distances at much lower costs than possible by rail or truck transportation. However, by grinding the coal into a line powder as required to produce a transportable slurry, the coal is rendered less suitable for ultimate uses such as processing in conventional steel industry coke ovens. The process of the present invention is directed to the production of coke briquettes from the slurries of iinely ground coal, which briquettes are suitable for use in the steel industry blast furnaces, as well as for other purposes.

The coal which is placed in the slurry may be of any type, from the lowest grade of lignite through high-grade bituminous coal to the highest grade of anthracite. Either a single type of coal may be used in the slurry, or mixtures of the various types may be employed. The paricle size distribution within the slurry should be kept within the range of 325 mesh to 8 mesh (U.S. Standard), it being understood that the smaller sizes should be favored. The slurry suitably may contain coal in amounts from 50% to 70% by weight.

In the present process, the slurry may suitably be preheated to about 350 F. to 600 F. in order to vaporize the slurry water before introduction into the coking zone, or the slurry may be utilized with no preheating at all or with only minor preheating. The slurry is introduced into a coking zone which may comprise a transfer line type of contacting zone or into a coking zone wherein a fluidized bed of hot coke and coal particles is maintained. If a transfer line type of contacting zone is utilized, the slurry is contacted with a hot coke stream and is entrained through the `transfer line contacting zone into a steam stripping zone wherein the solids are maintained for a time sufficient to accomplish coking. Similarly, if a fluidized bed is to be utilized, the residence time of the coke particles would be controlled to accomplish the desired degree of coking.

The first-stage coking zone is maintained at a temperature from 900 F. 1l00 F. The lower limit is chosen to insure good coking, while the upper limit is restricted to prevent thermal cracking of the carbonaceous materials which are driven from the coal during coking and which are to be used as a briquette binder. The coal is maintained in the coking zone for a time sufficient to accomplish coking, the total time depending on particle size, slurry concentration, temperature, type of coal, etc. Generally, the time will fall within the range of 0.5 minute to l minutes.

The vapor phase is withdrawn overhead from the coking zone and fractionated to recover carbonaceous materials 'to be used as a binder, the fractionator bottoms stream being preferred for this purpose. The binder may suitably boil above 750 F. The coke lines which pass overhead from the coking zone will ultimately be discharged in the fractionator bottoms stream and will thus be recovered as coke.

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The solids stream withdrawn from the coking zone is introduced into a burning zone with a stoichiometric deficiency of oxygen. About 3 to l0 weight percent of the coke is consumed in the burning zone to raise the temperature of the coke to 1200 F. to 1600 F. The combustion in the burning zone provides the heat which will be used to maintain the coking zone temperature (by means of a hot coke recycle, hereinafter described).

The hot coke stream which is discharged from the burning zone is separated into two portions. The rst portion is recycled into contact with the coal slurry to provide the heat that is necessary to raise the slurry to the coking temperature. From 5 to 20 pounds of hot coke per pound of slurry will be required, depending upon the temperature of the hot coke and lthe slurry, the slurry density, and the coking zone temperature.

The second portion of the hot coke stream is cooled (preferably to no lower than 250 F., suitably 250 F. to 350 F., in order to maintain a moisture-free environment) to obtain a product coke stream which amounts to about 40% to 70% of the coal originally charged. The coke product stream is admixed with the carbonaceous distillate binder to form a briquetting machine feed containing from 10 to 30 weight percent of the binder. This mixing may suitably be obtained by spraying the heavy tar distillate on `the coke while it is being transported upon a moving grate conveyor, and then passing the admixture through kneading rolls in order to obtain a satisfactory admixture; a plurality of such combination sprays and kneading rolls may be required.

The mixture of tar distillate and coke products is then charged into a briquetting machine wherein it is formed into r-aw briquettes. Compressive briquetting machines are preferred in order to avoid disintegration of the briquettes in the oven. The raw briquettes are then transported through a kiln or oven `at 2200 F. to 2800 F. for about 10 minutes to 2 hours in order to completely cure the coke briquettes. The briquette products of the present invention are of extremely high quality and are suitable for use either in blast furnaces in the steel industry or generally as electrode-grade coke for the manufacture of electrodes for use in the electric furnace process industry.

All this will be made more clear by reference to the drawing wherein is set forth a preferred rnode of the present invention.

Referring now to the drawing, the slurry is suitably introduced at a temperature of about 350 F. by way of line 101 into the riser 102. It is contacted with from 5 to 20 pounds of hot coke per pound of slurry, the hot coke being introduced by way of line 104 at a temperature of about l200 F. to l600 F. The admixture of coke, coal particles, and steam is introduced by way of riser 102 into the coker 106, wherein is maintained .a fluidized bed 108. The solid particles are maintained in that iluidized bed at a temperature of 900 F. to 1l00 F. for a period of about 0.5 to l0 minutes, and are then discharged over the dam through steam stripping section 112 to be discharged from the first-stage Coker by way of line 114.

While in the coker 106, the volatile carbonaceous materials and steam are generally separated from the solid particles and pass overhead from the coker by way of line 116, and `are passed into a distillation fractionator 118 for further separation. In the fractionator 118, the water and light volatile material are passed overhead by way of line 120, while the heavy tar clistillates are discharged from the bottoni of the tower by way of line 122. Suitable side streams of intermediate boiling range tar distillates may be withdrawn from the tower, as indicated by line 124.

The heavy tar distillate withdrawn from the bottom of the fractionating tower contains the coke fines which passed overhead from the coker. The bottom stream is passed by way of pump 126 and

coolers

128 and 130 into a spray system generally indicated by 132. The spray system comprises nozzles 134 which direct the heavy tar distillate into contact with the coke to be made into briquettes. Thus, it is seen that the heavy tar distillate comprises the sole source of binder for the coke.

The bottoms stream is also provided with a recycle line 136 which returns a portion of the heavy tar distillate into the desuperheating section of the distillation tower, which is shown to comprise disc and doughnut plates in the lower section thereof.

Returningy to the solids product of the Coker, the product which is discharged by way of line 114 is admixed with a stoichiometric deficiency of air introduced by way of line 140, and this admixture of coke and air is passed by way of riser 142 into the burner 144. Within the burner 144 a dense phase fiuidized bed 146 is maintained, wherein 3% to 10% of the coke is consumed, which raises the temperature to about 1200 F. to about 1600 F. The flue gas is Withdrawn from the burner by way of line 148 and may be contacted with air and burned to recover heat. The CO and coke fines in the flue gas will be consumed, .and the recovered heat used to preheat the slurry or the combustion air, or for other uses such as steam generation.

The hot coke stream is withdrawn through a steam stripping section 150 and is discharged by way of line 152. The hot coke stream is separated into two portions, the first portion being passed through line 104 into admixture with the fresh slurry introduced by way of line 101, while the second portion of the hot coke stream is passed by way of line 154 suitably provided with fluidizing steam inlet 156 and is cooled in the exchanger 158-. From the cooler 158 t-he coke product is passed through a system for ad-mixing the coke with the tar distillate binder in order to produce a briquetting machine feed. This is suitably accomplished by passing the coke particles across a plurality of moving grate conveyers 160, wherein the tar distillate is sprayed upon the surface of the coke particles by Way of nozzles 134. The coke and distillate are discharged from the moving grate conveyer into rollers 162 which adrnix the distillate with the coke in order to provide a suitable briquett-ing machine feed. Although only two sprayer-conveyor combinations have been shown, in some cases fewer or more stages may be required.

The final admixture of coke and binder is introduced into a briquetting machine 164, wherein it is formed into raw briquettes. These raw briquettes are then transported, for example, by a moving grate or a moving chain conveyer (not shown) through an oven 166, wherein the briquettes are baked at a temperature of about 2500 F. for about 10 minutes to 2 hours in order to completely cure the briquettes.

Having disclosed the invention in detail and having set forth the preferred mode of practicing that invention, what is desired to be protected by Letters Patent should be limited not by the specific examples herein given, but only by the scope of the appended claims.

I claim:

1. A method of producing coke briquettes from a water slurry of finely divided coal, said slurry containing from 50 to 70 weight percent of coal having a particle size distribution within the range of 325 mesh to 8 mesh, U.S. Standard, which comprises contacting said slurry in a coking zone with a hot coke stream to form an admixture of coal particles and steam at a coking temperature Within the range of 900 F. to 1100 F., maintaining said admixture at said coking temperature for a time sufficient to drive off substantially all of the water and carbonaceous material .and reduce said coal to coke,

separating said carbonaceous material from said coke,

contacting said coke in a burning zone with a stoichiometric deficiency of oxygen at a temperature of 1200 F. to 1600 F. to consume from 3 to 10 weight percent of said coke,

withdrawing said coke from said burning zone as a hot coke stream,

recycling a first portion of said hot coke stream into contact with said slurry in said coking zone, cooling a second portion of said hot coke stream to 250 F.to 350 F. to obtain a coke product stream,

admixing said coke product stream with a portion of said carbonaceous materials to obtain a briquetting charge stream, and forming briquettes from said charge stream. 2. A method in accordance with claim 1 wherein said coal is maintained in a fluidized bed in said coking zone and said coke is maintained in a fluidized bed in said burning' zone.

3. A method in accordance with claim 1 wherein the slurry is preheated to 350 F. to 600 F. before contact with said hot coke stream.

4. A method of producing coke briquettes from a water slurry of finely divided coal, said slurry containing from 50 to 70 weight percent of coal having a particle size distribution within the range of 325 mesh to 8 mesh, U.S. Standard,

which comprises contacting said slurry in a coking zone with a hot coke stream to form an admixture of coal particles and steam at a coking temperature within the range of 900 F. to 1100 F.,

maintaining said admixture in a fludized bed in said coking zone and at said coking temperature for a period of time from 0.5 to 10 minutes, whereby carbonaceous materials are driven from said coal and said coal is reduced to coke,

separating said steam and carbonaceous materials from said coke, separating said carbonaceous materials into at least a first stream containing volatile carbonaceous materials and a second stream comprising heavy tar distillates boiling above 750 F.,

contacting said Icoke in a fluidized bed in a burning zone with a stoichiometric deficiency of oxygen at a temperature of 1200 F. to 1600 F. to consume from 3 to 10 weight percent of the coke, withdrawing said coke from said burning zone as a hot coke stream at a temperature from 1200 F. to 1600 F.,

recycling a first portion of said hot coke stream into Contact with said slurry in said coking zone,

said first portion being from 5 to 20 pounds of hot coke stream per pound of slurry,

cooling a second portion of said hot coke stream to 250 F. to 350 F. to obtain a coke product stream, admixing said coke product stream with at least a portion of said tar distillate fraction to obtain a briquetting charge stream, said tar distillate fraction comprising the sole source of binder for said coke, forming briquettes from said charge stream,

and baking said briquettes at a temperature of 2200 F. to 2800 F. for 10 minutes to 2 hours.

References Cited by the Examiner UNITED STATES PATENTS 2,761,824 9/1956 Eastman et al 201-20 X 3,051,628 8/1962 Gorin et al 201-5 3,140,242 7/1964 Work et al 201-5 FOREIGN PATENTS 532,209 10/1956 Canada.

MORRIS O. WOLK, Primary Examiner. JOSEPH SCOVRONEK, Examiner.

Claims

1. A METHOD OF PRODUCING COKE BRIQUETTES FROM A WATER SLURRY OF FINELY DIVIDED COAL, SAID SLURRY CONTAINING FROM 50 TO 70 WEIGHT PERCENT OF COAL HAVING A PARTICLE SIZE DISTRIBUTION WITHIN THE RAANGE OF 324 MESH TO 8 MESH, U.S. STANDARD, WHICH COMPRISES CONTACTING SAID SLURRY IN A COKE ZONE WITH A HOT COKE STREAM TO FORM AN ADMIXTURE OF COAL PARTICLES AND STEAM OF A COKING TEMPERATURE WITHIN THE RANGE OF 900*F. 1100*F., MAINTAINING SAID ADMIXTURE AT SAID COKING TEMPERATURE FOR A TIME SUFFICIENT TO DRIVE OFF SUBSTANTIALLY ALL OF THE WATER AND CARBONACEOUS MATERIAL AND REDUCE SAID COKE TO COKE, SEPARATING SAID CARBONACEOUS MATERIAL FROM SAID COKE CONTACTING SAID COKE IN A BURNING ZONE WITH A STOICHIOMETRIC DEFICIENCY OF OXYGEN AT A TEMPERATURE OF 1200* F. TO 1600*F. TO COMSUME FROM 3 TO 10 WEIGHT PERCENT OF SAID COKE, WITHDRAWING SAID COKE FROM SAID BURNING ZONE AS A HOT COKE STREAM, RECYCLING A FIRST PORTION OF SAID HOT COKE STREAM INTO CONTACT WITH SAID SLURRY IN SAID COKING ZONE, COOLING A SECOND PORTION OF SAID HOT COKE STREAM TO 250*F. TO 350*F. TO OBTAIN A COKE PRODUCT STREAM, ADMIXING SAID COKE PRODUCT STREAM WITH A PORTION OF SAID CARBONACEOUS MATERIALS TO OBTAIN A BRIQUETTING CHARGE STREAM, AND FORMING BRIQUETTES FROM SAID CHARGE STREAM.