US2729598A

US2729598A - Fluidized bed coating of coal with nonagglomerative material

Info

Publication number: US2729598A
Application number: US93158A
Authority: US
Inventors: Paul W Garbo
Original assignee: Hydrocarbon Research Inc
Current assignee: Hydrocarbon Research Inc
Priority date: 1949-05-13
Filing date: 1949-05-13
Publication date: 1956-01-03
Anticipated expiration: 1973-01-03

Description

Jan. 3, 1956 P. w. ,GARBO 2,729,598

FLUIDIZED BED COATING OF COAL WITH NON-AGGLOMERATIVE MATERIAL Filed May 13. 1949 I an Y s TOPA as #01 1 5 e INVENTOR. PA 1

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ATT'QENEYQ United States Patent i FLUIDIZED ear) COATING or Conn wrrn NON- AGGLOMERATIVE MATERIAL Paul W. Garbo, Freeport, N. Y., a ss'ignor to Hydrocarbon Research, Inc., New York, N. Y., a corporation of New Jersey Application May 13, 1949 SerialNo; 93,158 4 Claims. (Cl. 202 -45) This invention relates toe; process for treatment of a solid carbonaceous material. In one of its more specific aspects it relates to a process for thecarbonization of coal. The process of the invention is particularly applicable to the treatment of those carbonaceous materials which tend to agglomerate on heating, for example, caking coals.

The fluidized solids technique has been applied to processes for the distillation and gasification of solid carbonaceous materials. It is known, for example,- that coal in finely divided form may be treated in a fluidized bed with hot gases to effect removal of volatiz'able constituents by distillation therefrom. Various solid carbonaceous materials have been reacted with reactant gas in a fluidized bed of particles of said material for partial or complete gasification of the material. Oxygen, hydrogen, carbon dioxide, and steam are useful gaseous reactants for the conversion of solid carbonaceous materials to valuable gases. Fluidized bed gasificatioii is particularly adapted to the treatment of coke or hard coal, such as anthracite, which does not tend to agglomerate on heating. G'asification of coal in moving beds in processes such as the Lur'gi process is generally dependent for success upon a nori-ctikirig fuel. Frequently, however, those coals which are most readily available and most economical for gasification are bituminous coals of the caking type. p

The present invention provides an improved process by which caking coals and like agglomeratingsolid fuels may be pretreated to eliminate their caring tendency and thus eliminate difiiculties due to taking in subsequent carboni zation and/or gasification reactions. V

Coal may be treated to prevent agglomeration by subjecting the coal to distillation to drive on at least a portion of the volatilizable constituents or by partial pioxidation of the coal with an oxygen-containing gas. An expedient which has been proposed to prevent agglomeration of caking coals involves admixing the raw coal with clay, ash, sand, or other inert material. A disadvantage of this procedure is the necessity of using relatively large proportions of the inert material, which is circulated through the gasification equipment. Such inert materials reduce the capacity of the apparatus to be a considerable extent because of the volume of inert material required for effective results. From about 3 to about 10 parts. of inert material must be used per part of fresh coal, depending. upon the character of the raw coal, to prevent agglomeration. A further disadvantage of using such large proportions df in'ert material in subsequent processing steps is the increased loss pt heat resulting from the heating up of the inert material to the desired processing temperature.

The process of the present invention avoids the dithculties attendant upon these various methods of handling coal and provides a method whereby the coal may be 'efiec tively pretreated to avoid agglomeration and the resulting pretreated material charged directly to a subsequent pro cessing zone like carboniiation and/or gasifica'tioh apparatus.

The process of this invehtibn may be carried out Si multaneously with the carbonization of coal by distillation and/ or the partial oxidation of the coal to eliminate its (taking tendencies.

In accordance with this invention, particles of a solid carbonaceous material. which has the property of caking or agglomerating, when exposed to an elevated temperature are contacted at such an elevated temperature with a gaseous stream carrying in suspension finely divided non-agglomerating material,- such as fine sand, clay, diatomaceous earth, bentonite, fly ash, slate dust or powdered talc, to destroy the agglomerating property of. the carbonaceous particles by modifying the surfaces of these particles through coating thereof with a non-agglomerating material and/or chemical change effected in the carbonaceous particles. The contacting of the particles of solid carbonaceous material with the gaseous stream containing suspended non-agglomerating material may be achieved by any of several conventional procedures. For instance, the solid particles may be passed through a rotary kiln while flowing a hot gaseous stream containing suspended non-agglomerating material countercurrently through the kiln. Alternatively, the solid. particles may be dropped through a tower against an ascending gaseous stream carrying finely divided non-agglomeratirig material.

In a preferred embodiment of this invention, a bed of particles of solid non-agglomerating material of fine particle size and having a lower settling rate than the relatively coarse particles of caking coal or other agglomerating solid fuel, is maintained in a fluidized state in a treating zone by the action of a stream of a suitable gas passing upwardly therethrough. Particles of coal are fed into the upper portion of the fluidized bed of non-agglomerating material and settle downwardly therethrough. During their passage through the fluidized bed, the particles of coal are subjected to sufiicient heating to at least soften or taokify the surface of the particles. If desired, the heating may be conducted at an elevated temperature adapted to distill at least a portion of the volatilizable constituents of the coal, particularly the moisture in the coal. in such case, the treated coal particles may be made non-agglomerating by coating or by carbonization or by both. If the fluidizing, gas contains a reactive component, e. g., oxygen, the coal particles may also be at least superficially reacted to destroy their agglomerating property. Thus, coating, carbonization, or reaction with the gas, either singly or in combination, accounts for the elimination of the agglomerating tendency in the treated coal particles which collect at the bottom of the fluidized bed and are withdrawn therefrom. The velocity of the fluidizing gas may be such that the non-agglomerating, material is maintained within the treater as a fluidized fixed bed With only a relatively small proportion of particles entrained in the gas leaving the treater. Alternatively, although less desirably, the particles of non-agglomerating material may be suspended in the gas stream and carried upwardly through the treating zone; entrained particles discharged from the treating zone with the gas stream may be returned to the treating zone.

Some of the fine non aggiornerating material may be bound to the surface of the coal particles by reason of the softening tendencies of the coal. Thus coated, the coal particles are substantially free of the caking characteristics of the original coal. At the same time, when desired, more or less of the volitilizable constituents, particularly undesirable moisture in the coal, are distilled from the coal. Additional non-agglomerating material is added to the treating zone as required to make up for that which adheres to the surface of the treated coal particles. Clay or fly ash is particularly suited as the non-agglomerating material for the present process.

The non-agglomerating material has a relatively smaller particle size than the coal ted to the apparatus. The solid non-agglomerating material is of a particle size, generally Patented Jan. 3,, 1956 less than about 100 mesh and preferably less than about 200 mesh while the solid fuel particles are generally coarser than about mesh and preferably coarser than about /8 inch diameter. As a rule, the coal particles do not exceed 2 inches in diameter. It is advisable to maintain the ratio of the diameter of the coal particles to that of the non-agglomerating material at a value in excess of about 10. As an example, a fluidized bed of clay composed of particles all of which pass through a 100 mesh screen and having about a 25 percent fraction retained on a 200 mesh screen is effective for treating coal of a particle size ranging from about /s to about 1 inch in diameter The non-agglomerating solid particles maintain the dispersion of coal particles in the treating zone, while at the same time providing all of the advantages, from the heat transfer standpoint, of a fluidized bed. By the process of this invention, it is possible to pretreat agglomerating coal in a fluidized state and to eliminate the agglomerating tendency without substantial dilution of the solid carbonaceous product with the non-agglomerating material. The non-agglomerating material may be chosen to have a high thermal conductivity and high specific heat. Because of the fluidized bed of non-agglomerating material, the distribution and transfer of heat in the treating zone may be greatly facilitated. The danger of forming hot spots is substantially eliminated. Also the thermal condition of the treating zone is rendered more stable inasmuch as it possesses an increased overall heat capacity for withstanding changes in thermal load.

The composition of the treating gas depends largely on the type of treatment to be effected. For simple coating and/or dry distillation of coal, an inert gas is preferably used as the gaseous medium. For treatment under reaction conditions, a gaseous reactant such as oxygen, steam, carbon dioxide, or hydrogen may be included in the gas eous medium. Hot gases from a subsequent gasification step are frequently suitable as the treating gas stream, serving to supply heat for the treatment of the coal. The resulting gas discharged from the treating zone may contain products of reaction and/or volatilized constituents from the coal. Distillates may be recovered from the gaseous effluent of the treating zone.

An object of this invention is to provide an improved process for the treatment of solid carbonaceous material having an agglomerating propensity.

Another object is to provide a process for the treatment of caking coals to render them substantially non-caking in character.

Still another object is to provide an improved process for the distillation or carbonization of solid carbonaceous materials containing volatilizable constituents, such as coals and oil shale which tend to agglomerate when subjected to heating.

Other objects and advantages will be apparent from the following detailed description and the accompanying illustrative drawing.

The drawing is a diagrammatic elevational view illustrating a preferred embodiment of the process of the present invention.

The'process of the invention, as illustrated by the drawing, will be described in detail with reference to coal as the carbonaceous material and to clay as the non-agglomerating material. It will be understood that coal and clay are used as specific examples and that other carbonaceous and non-agglomerating materials may be employed.

With reference to the drawing, caking coal particles, say 2 to 10 mesh size, are fed through line 1 into a feed hopper 2. An inert gas may be supplied through line 3 to build up pressure in the hopper. The gas also forms an inert blanket in the feed hopper, avoiding explosion hazards. The particles of coal from the feed hopper are fed through line 4 into a treating zone 6 at a rate controlled by valve 5 onto the top of a fluidized bed of clay particles, say finer than 100 mesh, within the treating zone.

The clay particles are fluidized by gas passing upward- 1y therethrough. The fluidizing gas is admitted to the lower portion of the treating zone through line 7. The coal particles are dispersed in the fluidized bed of clay and brought rapidly to the treating temperature. The particles of coal have a higher settling rate than the particles of clay, as a result of which they settle downwardly through the fluidized bed. As the particles of coal pass downwardly through the fluidized bed of clay particles they are heated to a temperature suflicient to at least render the surface of the coal particles tacky so that a thin coating of clay adheres to the coal particles and makes the coal particles substantially non-caking.

Heat may be supplied to the treating zone by any conventional means; desirably it is supplied by the gas stream entering through line 7. Alternatively, the heat may be supplied by indirect heat transfer through the walls of the treating zone or by heating elements or coils disposed in the fluidized bed. As pointed out hereinabove, the gas stream admitted through line 7 may contain a gaseous reactant for partial reaction of the coal, e. g., partial oxidation.

The relative proportions of coal and clay particles in the treating zone may vary considerably but preferably the clay is present in excess. For example, from 2 to 10 parts by volume of clay particles may be present per part of coal, 5 parts or more of clay per part of coal being preferred.

The particles of treated coal are withdrawn through line 9 from the bottom of the treating zone 6 at the point of introduction of fluidizing gas. A section 10 of reduced cross-sectional area is provided at the lower portion of the treating zone 6 whereby the velocity of the fluidizing gas is maintained higher in this section than in the main body of the treating zone. This permits concentration of the particles of'treated coal in section 10 and stripping of loose clay particles therefrom so that the treated coal withdrawn through line 9 is substantially free from loose particles of clay. The resulting particles of treated coal may be discharged into a conveyer 12 through which they are passed to storage or to subsequent operations.

The fluidizing gas, after passing through the bed of solid particles within the treating zone, is discharged from the treating zone through line 13. This gas may be proc-- essed for separation of various constituents, when present, and may be recycled to the treating zone or utilized as a fuel gas or the like, depending upon its composition.

The clay is supplied through line 16 into a clay storage hopper 17. Gas may be admitted to the storage hopper through line 18 to build up a pressure therein equivalent to the pressure within the treating zone 6. The particles of clay aredischarged from the storage hopper through valve 19 into line 20 through which they are conveyed to the treating zone. Gas may be supplied to line 20 through valve 21 as required. This gas transports the particles of clay into the treating zone. The gas may be supplied to line 20 continuously or intermittently, as desired.

Under preferred operatingconditions, the bed of clay within the treating zone 6 is a fixed fluidized bed. By the term fixed fluidized bed I mean that while the bed of solid particles is fluidized to the extent that it resembles a boiling liquid due to the action of the fluidizing gas, the bulk of the clay particles is retained within the treating zone. The stripping action of the gas entering through line 7 prevents any substantial loss of loose clay with the treated coal withdrawn from the bottom of the treater and the velocity, generally of the order of 1 foot per second, of the gas in the treating zone is such that the particles of clay are not entrained to any appreciable extent in'the effluent gas stream. Clay required to make up incidental losses is supplied from the storage hopper 17 as described hereinabove. v

The temperature in the treating zone should be at least high enough for the particular solid fuel undergoing treatment to ensure that the fine particles of nonagglomerating material will stick to the surfaces of the coarse particles of the solid fuel. Generally, a satisfactory temperature will be at least about 600 F. and preferably at least about 750 F. With most solid fuels like coal, temperatures in excess of about 1000 P. will cause appreciable carbonization of the coal, i. e., an appreciable quantity of volatilizable constituents will be distilled from the coal. The pressure may vary from about atmospheric to about 500 pounds per square inch gauge and is determined largely by subsequent process requirements, the

pressure having no appreciable eifect upon the efiiciency of the present process. Thus the pressure is dependent upon the desired reaction, if any, within the treating zone and upon the desired pressure at which the effluent gas and treated coal are supplied to associated processes. For example, in the gasification of coal it is often desirable to operate the gasification reactor at a pressure within the range of from about 50 to 500 pounds per square inch gauge. The treating step of the present invention may be operated at a comparable pressure so that the treated coal may be supplied directly to the gasification zone without any diificulties in feeding the treated coal due to the pressure at which the gasification zone is operated.

When the present process is operated for treatment of the coal with a reactant gas which undergoes an ex0- thermic reaction with. the coal, for example oxygen or hydrogen, the process may be made self-sustaining on a heat basis. Thus, free oxygen, for example, may be supplied with the fiuidizing gas stream to provide all or part of the required heat within the treating zone 6. The fluidiz ing gas may, of course, be preheated to any desired extent.

It is well to observe that the pretreating process of this invention can serve the dual function of rendering caking solid fuels non-agglomerating and simultaneously preheating them prior to charging them into a gasification zone or other processing zone maintained at an elevated temperature.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In a process for treating a coal, which becomes tacky and cakes on heating, to substantially eliminate its caking tendencies without efiecting substantial gasification of said coal, the improvement which comprises introducing relatively coarse pieces of said coal into the upper portion of a dense phase fluidized bed of solid particles of a non-agglomerating material having an average particle size considerably less than the average particle size of the pieces of coal, passing a fiuidizing gas upwardly through said bed at a rate sufficient to maintain said particles of non-agglomerating material in a highly agitated condition but insufiicient to cause substantial fluidization of said pieces of coal or entrainment of said particles of non-agglomerating material from said bed while permitting said pieces of coal to settle to the bottom of said bed, maintaining said pieces of coal in contact with said fluidized particles in said bed at a temperature above about 600 F. and below about 1,000 P. to ensure tackiness of the surface of said pieces, and to render said pieces substantially non-agglomerating by the adhesion of a thin coating of said particles of non-agglomerating material to the surface of said pieces, and withdrawing the thus coated pieces of coal from the lower portion of said fluidized bed substantially free of the tendency to cake on heating.

2. A process as defined in claim 1 wherein the average particle size of said non-agglomerating material is not greater than about one-tenth the average particle size of said coal.

3. A process as defined in claim 1 wherein there are at least five parts by volume of non-agglomerating particles in the fluidized bed for each part by volume of coal undergoing treatment in said bed.

4. A process as defined in claim 1 wherein the pieces of coal are of a size in the range of A5 to 2 inches in average diameter and the particles of the non-agglomerating material are of a size smaller than about mesh.

References Cited in the file of this patent UNITED STATES PATENTS 1,984,380 Odell Dec. 18, 1934 2,396,036 Blanding Mar. 5, 1946 2,471,119 Peck et al. May 24, 1949 2,480,670 Peck Aug. 30, 1949 FOREIGN PATENTS 578,711 Great Britain July 9, 1946 299,936 Great Britain Nov. 8, 1928 394,747 Great Britain July 6, 1933

Claims

1. IN A PROCESS FOR TREATING A COAL, WHICH BECOMES TACKY AND CAKES ON HEATING, TO SUBSTANTIALLY ELIMINATE ITS CAKING TENDENCIES WITHOUT EFFECTING SUBSTANTIAL GASIFICATION OF SAID COAL, THE IMPROVEMENT WHICH COMPRISES INTRODUCING RELATIVELY COARSE PIECES OF SAID COAL INTO THE UPPER PORTION OF A DENSE PHASE FLUIDIZED BED OF SOLID PARTICLES OF A NON-AGGLOMERATING MATERIAL HAVING AN AVERAGE PARTICLE SIXE CONSIDERABLY LESS THAN THE AVERAGE PARTICLE SIZE OF THE PIECES OF COAL, PASSING A FLUIDIZING GAS UPWARDLY THROUGH SAID BED AT A RATE SUFFICENT TO MAINTAIN SAOD PARTICLES OF NON-AGGLOMERATING MATERIAL IN A HIGHLY AGITATED CONDITION BUT INSUFFICIENT TO CASE SUBSTABTIAL FLUIDIZATION OF SAID PIECES OF COAL TO SETTLE PARTICLES OF NON-AGGLOMERATING MATERIAL FROM SAID BED WHILE PERMITTING SAID PIECES OF COAL IN CONTACT TOM OF SAID BED MAINTAINING SAID PIECES OF COAL IN CONTACT WITH SAID FLUIDIZED PARTICLES IN SAID BED AT A TEMPERATURE ABOVE ABOUT 600* F. AND BELOW ABOUT 1,000* F. TO ENSURE TACKINESS OF THE SURFACE OF SAID PIECES, AND TO RENDER SAID PIECES SUBSTANTIALLY NON-AGGLOMERATING BY THE ADHESION OF A THIN COATING OF SAID PARTICLES OF NON-AGGLOMERATING MATERIAL TO THE SURFACE OF SAID PIECES AND WITHDRAWING THE THUS COATED PIECES OF COAL FROM THE LOWER PORTION OF SAID FLUIDIZED BED SUBSTANTIALLY FREE OF THE TENDENCY TO CAKE ON HEATING.