US3251751A

US3251751A - Process for carbonizing coal

Info

Publication number: US3251751A
Authority: US
Publication date: 1966-05-17
Anticipated expiration: 1983-05-17

Description

May 17, 1966 D. R. LINDAHL ET AL 3,251,751

PROCESS FOR CARBONIZING COAL Filed July 21, 1960 0 5 U5 g In r N LJ g 8 w 9 5 J F 5 m N 8 o m I m .2

INVENTOR. BY JOHN A. PHINNEY ERIC H. REICHL DONALD R. LINDAHL 3,251,751 PROCESS FOR CARBONIZING COAL Donald R. Lindahl, Bethel Park, and John A. Phinney and Eric H. Reich], Pittsburgh, Pa., assignors to Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 21, 1960, Ser. No. 44,511 3 Claims. (Cl. 201-12) This invention relates to a process for carbonizing coal and more particularly to a process for treating the carbonized coal and for removing the volatile constituents of coal from a distillation vessel.

This invention in certain aspects is concerned primarily with the removal of tar vapors from a distillation vessel that employs twin mixing screws to rapidly transfer heat from an inert heat carrier to the raw coal and autogenously evolve tar from the coal. This invention is also concerned with treating the solid residue discharged from the distillation vessel. A carbonization process of the type that employs a twin screw mixer in the distillation.

vessel is described in British Patent 793,518, entitled Method of Degasifying or Degasifying and Gasifying Pulverulent or Finely Granular Fuels.

Briefly, the above referred to British patent describes a carbonization process wherein raw coal and an inert heat carrier are intimately mixed in a distillation vessel in the absence of oxidizing gases. The intimate mixing of the inert heat carrier and the raw coal rapidly increases the temperature of the coal above the lower distillation temperature and the tar vapors are rapidly evolved from the coal. Throughout this specification the terms tar and tar vapors are intended to include any of the constituents of the coal that are autogenously evolved as a vapor during the carbonization process. The term distillation temperature is intended to mean any temperature at which tar vapors are evolved from raw coal. The tar vapors evolved in the distillation vessel are highly concentrated and form a vapor phase in the distillation vessel.

The distillation vessel includes a pair of conveying worms which both intimately mix the inert heat carrier and the raw coal and convey the same to an after-devolatilizer vessel. Tar in vapor form is withdrawn separately from the distillation vessel by means of a conduit extending upwardly therefrom. In the above referred to process the treated coal discharged from the distillation vessel into the after-devolatilizer is partially carbonized and further carbonization takes place in the after-devolatilizer. .The tar vapors evolved in the after-devolatilizer are separately withdrawn therefrom and transported to a condensing vessel.

Considerable operating difficulty has been encountered with the above described process due to plugging of the tar vapor withdrawal conduit in the distillation vessel. It is believed that substantial polymerization of the volatile constituents takes place in the withdrawal conduit to form solid coke particles of certain fractions of the vaporized volatile constituents. Also, substantial amounts of solid heat carrier and partially devolatilized coal are entrained with the tar vapors and deposited in the withdrawal conduit. The tar vapors, being at their dew point, alsoare United States Patent The gas introduced adjacent the bottom portion of the heat carrier at this elevated temperature, rapid heat transfer occurs and the tar vapors literally flash off the coal. The tar vapors so evolved havedifierent physicaLand chemical properties than the tar vapors evolved by either fluidized low temperature carbonization processes or high temperature carboniz-ation processes. The liquid viscosity of the tars obtained by the previously described processes is higher than the liquid viscosity of the tars obtained by fluidized low temperature carbonization. Further, it has been found there is a substantially larger fraction of tar having a boiling point above 400 C. in the tar evolved by means of the previously described process. The difference in the physical and chemical properties of the tar vapors evolved is believed to contribute substantially to the operating difliculties encountered in this process.

' To minimize the operating difliculties encountered in this type of process we have found by introducing an inert gas into the distillation vessel to serve as a diluent for the tar vapors that polymerization is minimized and coking or plugging of the transport conduits is substantially eliminated. The dilution of the tar vapors with the heated inert gas lowers the ratio and partial pressure of the tar vapors in the combined stream and minimizes condensation within the transport conduit.

Further, by diluting the tar vapors with an inert gas the vapor velocity of the vapor mixture is increased to thereby reduce tar vapor residence time at the high temperatures present in the distillation vessel. The inert gas further serves as a sweep gas to strip tar vapors from the char particles being discharged from the distillation vessel.

Further, by eliminating the after-devolatilizer vessel as taught in the heretofore described process and providing a vertical receiving portion adjacent one end of the distillation vessel, the gas supplied as an inert diluent for the tar vapors may also be employed as a reducing gas to desulfurize the solid residue being discharged from the distillation vessel at the elevated distillation temperature.

receiver flows upwardly and countercurrently to the solids discharged from the distillation vessel and removes as a stripping gas any tar vapors entrapped in the solids and may also remove at least a portion ofthe sulfur present in the solids withdrawn from the distillation vessel.

In the hereinafter described carbonization process substantially all the tar vapors are evolved from the raw coal in the distillation vessel and the solid residue is product char. The product char may then be subjected to a desulfurization process within the receiving portion of the distillation vessel and then transported to a heater. An inventory of the product char is maintained under fluidizing conditions as a dense phase fluidized bed in the heater and combustion supporting gas is provided to elevate the temperature of the char in the heater to between 1000 and 1400 F. A portion of the char is withdrawn from the heater and introduced into the distillation vessel as the inert heat carrier. A predetermined amount of product char is withdrawn from the heater vessel as product char.

It is, therefore, a primary object of this invention to provide an improved means of carbonizing coal wherein polymerization of the volatile constituents evolved is minimized.

'It is anotherobject of this invention to provide a gas to remove tar vapors entrapped in the char particles, and employing the same gas to dilute the tar vapors evolved in the distillation vessel.

It is another object of this invention to subject the product char withdrawn from the distillation vessel to a desulfurization process by means of countercurrent mixing with a reducing, sulfur removing, gas and further employing the same gas to dilute the tar vapors evolved in the distillation vessel.

Another object of this invention is to provide a carbonization process including a distillation vessel wherein inert heat carrier and raw coal are intimately mixed to autogenously evolve tar vapors from the-coal, and a heating vessel having a fluidized bed of inert charwhich is heated by means of controlled combustion and supplied to the distillation vessel as the inert heat carrier.

These and other objects and advantages of this inven: tion will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

The figure is a schematic representation of our improved process.

There is shown schematically apparatus for carbonizing finely divided coal which includes a distillation vessel having a vertical receiver portion 12, a char heater 14 and a condensing vessel 16. The distillation vessel 10 has a pair of

mixing worms

18 and 20 driven by a motor 22. The

mixing worms

18 and 20 rotate in the same direction and intimately mix material fed into the distilllation vessel 10 and convey the material through the distillation vessel 10 into the vertical receiver portion 12. The worms .18 and 20 are self-cleaning and remove any material adhering to the blades as they rotate during the distilling or carbonizing operation.

The char heater 14, as will later be described, provides inert heat carrier comprising char at a temperature of between 1000 and 1400" F. to the distillation vessel 10 through conduit 24. A regulating means such as slide valve 26 is provided in conduit 24 to regulate the rate of char or inert material fed into the distillation vessel 10. A raw coal storage chamber 28 is provided to maintain an inventory of raw coal that is to be subjected to carbonization or devolatilization in distillation vessel 10. The storage chamber 28 has a conduit 30 through which the char is introduced into distillation vessel 10. A regulating means 32 is provided in conduit 30 to regulate the amount of raw coal fed into the distillation vessel 10.

Predetermined amounts of coal and heated inert material are fed through

respective conduits

30 and 24 into the distillation vessel 10. Where substantially complete earbonization in the distillation vessel 10 is desired, the ratio of inert heat carrier to coal and the temperature of the inert heat carrier is regulated so that substantially all the tar is evolved in the distillation vessel 10 before the solids mixture is conveyed by mixing

worms

18 and 20 to the receiver 12.

The receiver 12 positioned adjacent the discharge end of distillation vessel 10 is arranged to receive the solids discharged from the distillation vessel 10 by means of

worms

18 and 20. The solids discharged from distillation vessel 10 descend by gravity through the receiver 12 and into conduit 34, and are conveyed therethrough to conduit 36. An inert gas under pressure is introduced into conduit 36 and flows in the direction of arrow 37. The inert gas entrains the solids introduced through conduit 34 and conveys the solids to the char heater 14. If desired a portion of the solids may be withdrawn from the system at conduit 36 by any suitable means (not shown) instead of the char heater 14 as later set forth.

A gas which serves as a sweep gas and may also serve as a reducing gas to combine with the sulfur in the solids discharged from distillation vessel 10 is introduced into the lower portion of receiver 12 throughconduit 3 5 at the desired pressure. The gas is intimately mixed with the descending char particles and removes therefrom any tar vapors entrapped in the porous char particles. The gas may be a reducing gas and combine with at least a portion of the sulfur in hot solids discharged from dist-illation vessel 10 to form a sulfur containing gas. In this manner at least a portion of the sulfur contained in the solids is removed as a gas. For example, a gas comprising hydrogen and being substantially free of hydrogen sulfide is introduced through conduit into the lower portion of receiver 12 at a suitable temperature and pressure. The gas is intimately mixed with the solids being discharged from the distillation vessel 10. The solids are at a temperature of about 1100" F. Atleast a portion of the sulfur in the solids at this elevated temperature combines with the hydrogen in the reactant gas to form hydrogen sulfide gas. In this manner the sulfur content of the solids discharged from distillation vessel 10 is reduced and the solids may be employed as a premium material in briquetting, coking or the like.

The gas after passing upwardly through the receiver 12 is intimately mixed with the tar vapors in the distillation vessel 10 to reduce the partial pressure of the tar vapors .and minimize condensation in the transport conduits. The gas, although a rectant gas with the solids, is substantially inert relative to the tar vapors.

The mixture of tar vapor and gas is discharged from distillation vessel 10 through conduit 38 and is conveyed to a cyclone separator 40. Solids entrained with the tar vapors and gas are separated therefrom in the cyclone separator 40 and are conveyed through conduit 42 to conduit 36. A regulating means 44 controls the solids in the conduit 42. The tar vapors and diluent gas are conveyed from the cyclone separator 40 through a conduit 46 into the condensing vessel 16. The condensing vessel 16 separates the volatile constituents from the diluent gas.

An inventory of char is maintained in char heater 14. The solids withdrawn from distillation vessel 10 are transported through conduit 36 and enter char heater 14 through inlet port 48. The' char heater 14 has a gas inlet port 50 adjacent its bottom portion. A conduit 52 is connected to the gas inlet port 50 and a combustion supporting and fluidizing gas is transported through conduit 52 and enters char heater 14 through gas inlet port 50. The gas entering through inlet port 50 is at a sufiicient velocity to maintain the inventory of char within the char heater 14 under dense phase fluidized conditions. Controlled combustion of the char within char heater 14 elevates the temperature of the char to between 1000 F and 1400 F. A predetermined amount of char at this elevated temperature is withdrawn'from char heater 14 1 through conduit 24 and fed into distillation vessel 10. The combustion supporting gas which also serves as the fiuidizing gas enters cyclone 54 where entrained solids are separated therefrom. The gas leaves the char heater 14 through conduit 56 and enters heat exchanger 58. The

combustion supporting gas enters the heat exchanger 58 through conduit 60. The temperature of the combustion supporting gas is elevated to about 750 F. and is fed at this elevated temperature through conduit 52 intothe lower portion of char heater 14. The gas which enters heat exchanger 58 through conduit 56 is discharged through conduit 62 for further treatment. The product char is withdrawn from the char heater 14 through char outlet 64 and enters conduit 66. A regulating means such as slide valve 68 is provided in conduit 66 to control the rate of withdrawal of product char from char heater 14. The char is transported through conduit 66 to storage means orthe like.

The apparatus and process previously described may be employed in carbonizing agglomerative coal that exhibits plastic properties during the carbonization process. The high ratio of inert heat carrier to raw coal in the distillation vessel plus the relatively high temperature of the inert heat carrier rapidly vaporizes the tars in the coal so that agglomeration in the distillation vessel 10 is not a problem. Further, the

worms

18 and 20 are self-cleaning so. that there is no substantial deposition of agglomerated coal thereon. By providing a heat carrier at a sufiiciently. high temperature, a sufficiently high ratio of heat carrier to raw coal, and a predetermined residence time within distillation vessel-10, it is possible to substantially completely carbonize or devolatilize the raw coal introduced into the distillation vessel so that the solids discharged into receiver 12 are product char.

It will be noted from the description of the apparatu set. forth in the figure that there is little, if any, inert gas introduced into the distillation vessel 10 with the raw coal and inert heat carrier. The primary constituents entering the distillation vessel 10 are the heated char from the char heater 14 and the raw coal from storage chamber 28. The volatile constituents evolved in the distillation vessel 10 are in a highly concentrated form and are not diluted with noncondensible gases as the tar vapors are evolved from the raw coal. The gas entering the vertical receiver 12 is intimately mixed with the tar vapors adjacent the discharge portion of the distillation vessel 10 to dilute the same and to rapidly convey the tar vapors from the distillation vessel 10 to the condensing vessel 16.

The solids discharged from distillation vessel 10, which 7 may be termed char since the raw coal is substantially completely devolatilized, are at a temperature of between about 900 F. and 1200 F. The char particles as they descend by gravity in the vertical receiver 12 are intimately mixed with a countercurrent stream of gas which removes entrapped tar vapors. The gas may also be a reducing gas such as hydrogen or the like. The reducing gas removes at least a portion of the sulfur in the char as hydrogen sulfide gas to provide a product char that has a reduced amount of sulfur. The gas after passing upwardly through the receiver is the same gas that is intimately mixed with the tar vapors to dilute the same.

The char heater is of the dense phase fluidized bed type and provides an inventory of char at an elevated temperature of between 1000" F. and 1400 F. which is employed as the inert heat carrier in the distillation vessel 10.

According to the provisions of the patent statutes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiments. However, we 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.

We claim: 1. In the method of carbonizing finely divided coal to produce therefrom a liquid distillate comprising,

introducing said coal into a distillation vessel having a feed end portion, a discharge end portion and two rotatable worms, concurrently introducing an inert finely divided solid heat carrier into said distillation vessel feed end portion, said distillation vessel having a vertical receiver adjacent said discharge end portion and a separate distillate vapor withdrawal conduit adjacent said discharge end portion, said inert heat carrier being at a temperature above the distillation temperature of said coal, intimately mixing said coal and said inert heat carrier by means of said two worms in said distillation vessel to transfer heat from said inert heat carrier to said coal to thereby substantially completely carbonize said finely divided coal and evolve in said distillation 6 vessel substantially all of said distillate as a distillate vapor, the improvement comprising,

introducing a diluent gas into' said distillation vessel adjacent said discharge end portion, admixing said diluent gas with said distillate vapor and forming a gaseous admixture, withdrawing substantially all of said gaseous admixture from said distillation vessel through said distillate vapor withdrawal conduit, said inert diluent gas in said gaseous admixture reducing the partial pressure of said distillate vapor to thereby reduce the condensation of said distillate vapor in said withdrawal conduit,

conveying said gaseous admixture through said distillate vapor withdrawal conduit to a condensing zone, and

collecting liquid distillate in said condensing zone.

2. The method of carbonizing finely divided coal as set forth in claim 1 which includes discharging the admixture of solids comprising the treated coal and the inert heat carrier into the upper portion of said vertical receiver, introducing a gas into the lower portion of said vertical receiver, passing said gas upwardly through said vertical receiver in countercurrent relation With said admixture, said gas serving as a reducing gas for said admixture to remove at least a portion of the sulfur contained in said admixture, and thereafter introducing said gas from said vertical receiver into said distillation vessel to serve as said diluent gas in said distillation vessel.

3. The method of carbonizing finely divided coal as set forth in claim 1 which includes discharging the admixture of solids comprising the treated coal and the inert heat carrier into the upper portion of said vertical receiver at a temperature of 900 F. to 1200 F., introducing a gas comprising hydrogen into the lower portion of the vertical receiver, said gas being substantially free of hydrogen sulfide, passing said gas upwardly through said vertical receiver in countercurrent relation with said admixture, said gas serving as a reducing gas for said admixture to remove at least a portion of the sulfur contained in said admixture and thereafter introducing said gas from said vertical receiver into said distillation vessel to serve as said diluent gas in said distillation vessel.

References Cited by the Examiner UNITED STATES PATENTS MORRIS O. WOLK, Primary Examiner.

RICHARD D. NEVIUS, MILTON STERMAN, AL-

PHONSO D. SULLIVAN, Examiners.

R. S. CORNELL, J. H. HALL, I. SCOVRONEK,

Assistant Examiners.

10/1937 Moberly 202-3l

Claims

1. IN THEMETHOD OF CARBONIZING FINELY DIVIDED COAL TO PRODUCE THEREFROM A LIQUID DISTILLATE COMPRISING, INTRODUCING SAID COAL INTO A DISTILLATION VESSEL HAVING A FEED END PORTION, A DISCHARGE END PORTION AND TWO ROTATABLE WORMS, CONCURRENTLY INTRODUCING AN INERT FINELY DIVIDED SOLID HEAT CARRIER INTO SAID DISTILLATION VESSEL FEED END PORTION, SAID DISTILLATION VESSEL HAVING A VERTICAL RECEIVER ADJACENT SAID DISCHARGE END PORTION AND ASEPARATE DISTILLATE VAPOR WITHDRAWAL CONDUIT ADJACENT SAID DISCHARGE END PORTION, SAID INERT HEAT CARRIER BEING AT A TEMPERATURE ABOVE THE DISTILLATION TEMPERATURE OF SAID COAL, INTIMATELY MIXING SAID COAL AND SAID INERT HEAT CARRFIER BY MEANS OF SAID TWO WORMS IN SAID DISTILLATION VESSEL TO TRANSFER HEAT FROM SAID INERT HEAT CARRIER TO SAID COAL TO THEREBY SUBSTANTIALLY COMPLETELY CARBONIZE SAID FINELY DIVIDED COAL AND EVOLVE IN SAID DISTILLATION VESSEL SUBSTANTIALLY ALL OF SAID DISTILLATE AS A DISTILLATE VAPOR, THE IMPROVEMENT COMPRISING, INTRODUCING A DILUENT GAS INTO SAID DISTILLATION VESSEL ADJACENT SAID DISCHARGE END PORTION, ADMIXING SAID DILUENT GAS WITH SAID DISTILLATE VAPOR AND FORMING A GASEOUS ADMIXTURE; WITHDRAWING SUBSTANTIALLY ALL OF SAID GASEOUS ADMIXTURE FROM SAID DISTILLATION VESSEL THROUGH SAID DISTILLATE VAPOR WITHDRAWAL CONDUIT, SAID INERT DILUENT GAS IN SAID GASEOUS ADMIXTURE REDUCING THE PARTIAL PRESSURE OF SAID DISTILLATE VAPOR TO THEREBY REDUCE THE CONDENSATION OF SAID DISTILLATE VAPOR IN SAID WITHDRAWAL CONDUIT, CONVEYING SAID GASEOUS ADMIXTURE THROUGH SAID DISTILLATE VAPOR WITHDRAWAL CONDUIT TO A CONDENSING ZONE, AND COLLECTING LIQUID DISTILLATE IN SAID CONDENSING ZONE.