US2665200A - Process for the gasification of solid carbonaceous materials - Google Patents

Description

Jan. 5, 1954 UK 2,665,200

M. KWA PROCESS F'OR THE GASIFICATION OF SOLID CARBONACEOUS MATERIALS Filed July l, 1948 i Q n \1 il i `1 B 5 xq u Q a. A

(n LL INVENTOR.

Patented Jan. 5, 1954 PROCESS FOR THE GASIFICATION OF SOLID CARBONACEOUS MATERIALS Monson Kwauk, New York, N. Y., assigner to Hydrocarbon Research, Inc., New York, N. Y., a corporation of New Jersey Application July 1, 1948, Serial No. 36,314

6 Claims. (Cl. 48-197) rlhis invention relates to the gasiiication of a solid carbonaceous material. In one of its more specic aspects it relates to carbonization oi coal. The process of the invention is applicable to gasioation of coal, lignite, oil shale and the like. It is particularly1 useful for treatment of those carbonaceous materials containing volatile constituents which tend to agglomerate on heating, for example, coking coals.

The fluidized solids technique has been applied to processes for the gasification of carbonaceous materials. For example, coal in finely-divided form may be treated in a fluidized bed with hot inert gases to effect removal of volatile constituents or with an oxidizing gas for gasification to any desired extent. Fuid bed gasification is particularly adapted to gasication of coke or hard coal, such as anthracite, which does not 'tend to agglomerate on heating. Coal may be treated prior to gasication to prevent agglomeration. Such pre-treatment may consist of heating the coal to drive off a portion of the volatile constituents therefrom or partial pre-oxidation of the coal with an oxygen-containing gas, nitric acid, or other oxidizing agent. An expedient which is used to some extent involves adu mixing the raw coal with char, ash, or sand to prevent agglomeration of the raw coal particles. The process oi the present invention avoids the difficulties attendant upon these various methods bf handling the coal and provides a method whereby coal may be charged directly to the gasiiier. There is no problem of separating inert material from the residual solid material resulting from the gasication.

The process of the present invention is useful for carbonization of coal, or partial gasification, as well as for complete gasification. Gasification of carbonaceous materials containing volatile constituents may be accomplished by heating, by chemical reaction, or by a combination or both. In carbonization, the volatile constituents are driven off by heat to produce a char or coke residue. Gasication by chemical reaction may be carried to substantial completion leaving only ash or low carbon content char as the residual solid. Elevated temperatures are required for gasification, as is known in the art. The present process is applicable to numerous gasification procedures including dry distillation, or carbonization, and reaction with a gasifying reactant, e. g., free oxygen, steam, carbon dioxide, hydrogen, or a suitable mixture of these gases.

In accordance with this invention, a bed of particles of vsolid inert material of relatively uniform particle size and having relatively high settling rates is fluidized by the action of a stream of a suitable gas passing upwardly therethrough in a gasication zone. The velocity of the iiuidizing gas is such that the fluidized bed of inert material is stationary (like a stationary wave) and substantially no particles of inert material are entrained by the upflowing stream of gas. This bed may be properly referred to as a luidized mixed bed oi particles of solid inert material.

Solid carbonaceous material in particle form is added to he fluidized xed bed in the gasication zone. The carbonaceous material is of a particle size such that it has a lower settling rate than the particles of inert solid. The carbonaceous material may be conveniently supplied to the bed by suspension in the fluidizing gas. Ii the iiuidized iixed bed of inert particles were not present in the gasification zone, the particles of carbonaceous material would be entrained in the gas stream and quickly carried from the gasication zone.

However, due to the resistance oiered by the particles of inert material the residence time of the particles of carbonaceous material in the gasification zone is considerably lengthened. The situation is somewhat analogous to the passage of a gas through a porous medium where the molecules of gas are representative of the fluidized particles of carbonaceous material, and the porous medium, the iiuidized bed of the inert material. By carefully controlling the velocity of the uidizing gas, the bed of inert material can be permanently kept in the gasification zone as a iluidized fixed bed while a stream of uidized carbonaceous material passes through the openings of the fluidized fixed bed of the inert material in the gasication zone. 4

The fluidized iixed bed of inert solid material aids in maintaining the required temperature conditions within rather close limits because it increases the thermal conductivity and thermal stability of the entire bed.

The solid inert material is of a particle size suitable for fluidization, generally less than onequarter inch in average diameter and preferably less than about one-tenth inch in diameter. In general, the particle size of the carbonaceous material will be somewhat less than that of the inert material but in some instances, it may be greater.

The composition of the fluidizing gas depend largely upon the type of gasification carried out.

For dry distillation of coal, an inert gas is used or less permanently.

as the fluidizing medium. For gasification under reaction conditions, a gaseous reactant is most suitably included in the uidizing medium. The resulting gaseous products are Withdrawn from the bed together with entrained particles of residual solid material. The solid particles are separated from the product gas either as a product char or ash.

The inert solid particles maintain the dispersion of coal particles in the reactor while at the same time providing all of the advantages of a iiuidized bed. By the process of this invention it is possible to treat an agglomerating coal under gasication conditions in the fiuidized state. Thus materials which have heretofore been unsuited to gasication in a fluidized bed may now be so treated.

Previous attempts at gasication of agglomerating coals and the like in a fluid bed reactor have generally involved admixing the raw coal with the residual solid, such as char or ash. With such an arrangement it is necessary to handle large quantities of residual solid which has unduly complicated the required equipment and resulted in high costs of operation.

The presence of the inert solid material introduces the combined action of dispersion, attrition, and comminution on the carbonaceous material-an action which reduces the chance of the carbonaceous particles contacting one another and forming aggregates. Should an aggregate form, however, it is soon disintegrated by the last two actions of attrition and comminution. This specific characteristic attendant to the presence of the inert particles makes the process applicable to the carbonization and gasiiication of carbonaceous materials which would normally agglomerato.

As mentioned above, the inert material consists of particles having a higher settling rate than the carbonaceous material for reaction. A high settling rate implies a larger particle Weight. Therefore, when in motion, these particles possess a higher kinetic energy, and are more eiective in the dispersing and attritive actions than re-circulated residue, which, as a rule can be considered similar or smaller in size and lighter in weight than the material under reaction. As the bed of the inert material is of a stationary nature, i. e., it is not removed from the gasification zone, it resides in the vessel more This eliminates many costly items of equipment and operational diillculties associated with circulating ash or heat carrier as in prior art processes.

The inert solid material can be chosen to have a .high thermal conductivity and speciiic heat.

Thus the distribution, addition, and removal of heat from the bed as a whole can be greatly facilitated. The danger of forming hot-spots is practically eliminated. Also, the thermal condition of the bed is rendered more stable, inasmuch as it possesses an increased overall heat capacity for withstanding sudden changes in thermal load.

An object of this invention is to provide an improved process for the gasication of solid carbonaceous material.

Another object is to provide a process for the gasification of solid carbonaceous material which vv.is particularly applicable` to carbonization and gasification of coal, lignite, oil shale and similar l materials.

` Still another object is to provide .a process for the gasication of solid carbonaceous materials may take any of various forms.

which tend to soften and agglomerate on heating.

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

The present invention will be described in detail ywith reference to coal as the carbonaceous material as typifying the operation and applications of the process of this invention. It will be understood that coal is used as a specic example and that the apparatus and method described are not limited to the use of Coal as the carbonaceous feed material. Since the gasification of various materials is known in the art, the application of the present invention to other solid carbonaceous materials will be evident to one skilled in the art from the detailed description of this invention and illustrative examples of its application to treatment of coal.

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

With reference to the drawing, coal, for example, is fed through line I into a hopper 2. An inert gas may be supplied to the hopper through line 3 to build up pressure in the hopper. The gas also forms an inert blanket avoiding explosion hazards. The particulate coal is fed from the hopper through a valve 4, suitably a rotary valve conventional for handling solids, into a stream of fluidizing gas in line E. The powdered coal dispersed in the iluidizing gas passes through line B to a reactor l into contact with a iluidized bed of inert solid particles 8 maintained under gasifying conditions.

The inert solid particles are iluidized by the gas passing upwardly therethrough. The particles of inert solid material have a higher settling rate than the particles of coal undergoing gasication, that is, the inert particles are of greater density, or larger particle size, or both. The coal particles are dispersed in the fluidized bed, and brought rapidly to reaction conditions. As the coal particles pass upwardly through the bed they are gasied to the desired extent.

The relative proportions of coal and inert particles in the reactor may vary considerably but preferably the inert solid particles are present in excess. For example, from one to ten parts of inert solid may be present per part of coal, the larger relative proportions being preferred.

'Ihe particles of residual solid material resulting from the gasication are entrained in the effluent gas stream and carried overhead from the reactor 1 through line I0 with the eiiluent to a separator I I. The residual solid material is separated from the gas and discharged from the separator through line I2. The resulting gas passes through line I3 for a further treatment or utilization in other processes. A portion or all of the fluidizing gas may be a recycle gas separated from the gas stream discharged through line I3. This recycle gas, which preferably is a selected fraction of the gas discharged through line I3, is supplied to line 6 through a recycle gas line I5. A portion or all of the uidizing gas may be supplied from an outside source through line I6 as desired.

Heat may be supplied to the reactor from an outside source by means of a suitable furnace I8. Hot gases are Supplied to the furnace through duct I9 and the residual flue gases discharged through duct 20. Furnace I8 is optional and The furnace is useful for dry distillation of the carbonaceous material and for endothermic reactions, e. g..

5 with steam or carbon dioxide. When free oxygen or hydrogen is supplied to the reactor for chemical reaction with the carbonaceous material, furnace I8 may be unnecessary.'

When the particles of coal are brought intol 'the particles of coal and where heat is transferred by indirect heat exchange facilitates the heat exchange between the particles of coal and the hot metal surfaces.

The carbonaceous particles mix readily in a mechanical way with the added solid particles. However, since the inert solid has a higher settling rate than the carbonaceous particles, the latter work steadily upward through the fluidized bed. Under these conditions the residual solid particles from the carbonaceous material are selectively eliminated from the fluidized bed and carried out of the reactor by the efliuent gases. Thus by choice of an inert material of requisite size and density, relative to the size and density of the carbonaceous particles, the relative proportions of carbonaceous material and inert material in the iiuidized bed is readily ccntrclled. The fluidizing gas may be made up sclely of inert gas or may comprise gaseous reactants utilized in the reactor for gasification of the solid carbonaceous material.

In the carbonization of coal, for example, a hydrocarbon gas which is inert with respect to the distillation products is most suitably used as the fluidizing gas. This may comprise methane and other gases including light hydrocarbons resulting from the distillation of the coal itself. Often it is desirable that the fluidizing gas contain some Water Vapor to prevent deposition of carbon on the inert material.

The temperature of the distillation is suitably within the range of ll to l300 F., and the pressure, from atmospheric to about 60 pounds per square inch gauge.

The luidizing gas may be at an elevated temperature prior to contact with the coal sufficient to supply part or all of the heat of distillation. The remaining heat is supplied by furnace lil to the fluidized bed by indirect heat exchange through the Wall of the reactor l. The inert solid material having a higher thermal conductivity than the carbonaceous material enhances the rate of heat transfer from the Walls of the reactor to the solid carbonaceous material undergoing treatment.

The distillation products withdrawn through lines it and i3 may be treated to separate the normally liquid coal tar hydrocarbons and tar. A portion of the normally gaseous fraction of the volatile constituents, comprising principally methane, may be recycled through line I as the fluidizing gas. In this case it is not necessary to supply gas through line le.

When the present process is operated, for example, for gasication of coal by reaction with free oxygen to produce either synthesis gas or producer gas, the iiuidizing gas comprises free oxygen and steam. Methane, tail gas from the synthesis reaction, or the like may be used to supplement the primary reactants. The gases lib- ,leased may be admixed, where permissible, or introduced separately into the reactor. With free oxygen as a reactant it is generally not necessary to supply heat from an outside source due to the exothermic nature of the oxidation reaction. Steam and carbon dioxide enter into endotherrnic reactions with heated carbon. Heat rein the exothermic reaction may be utilized by these endothermic reactions. By choosing conditions such that a proper balance is attained, the process may be made self-sustaining on a heat basis. Gasiiication with oxygen land steam is generally carried out at 1800 to 2000 F. at pressures up to about 400 pounds per e square inch gauge.

The inert material aids in the heat transfer between the exothermic and endothermic reactions. The heat released by the exothermic reaction taking place upon introduction of the reactants into the reactor, e. g., burning of the vcoal to form carbon dioxide and Water, is rapidly transmitted by the inert material in the uid bed to carbon throughout the bed. Thus there is e'cient heat transfer to the reactants in that portion of the reactor where carbon dioxide and water vapor react with carbon. These endothermic reactions take place subsequent to the initial oxidation reaction and at a point removed from the point of introduction of oxygen to the reactor.

Entirely endotherinic reactions may be carried out in the reactor, for example, reaction of hot carbon with steam or carbon dioxide. Part or all of the heat requirements for such reactions may be supplied by heat exchange as in the case of distillation. lt is generally preferable to supply at least a part of the heat required for the endothermic reaction by preheating the reactants. The inert material aids the transfer and distribution of heat to the gases and solid carbonaceous reactants,

The inert solid material employed is subject to considerable variation in choice. The following general conditions may be set as determining factors in selecting the inert solid material. The average size of the inert particles should be of about the same order of magnitude as the carbonaceous particles; preferably the inert particles are larger. The density of the inert particles should be higher than that of the carbonaceous material so that they are retained in the reactor when the velocity of the lluidizing gas is greater than the average terminal velocity of the carbonaceous particles. Preferably, the inert material has high thermal conductivity and high specific heat. The inert particles should be refractory and resistant to attrition and spalling. Among the materials which. may be mentioned as suitable for use in accordance with the process of this invention are smooth compact pieces or pellets of alumina, silica, zirconia, magnesia, compositesI of these materials, silicon carbide, high melting point ferrous alloys, and the like.

The raw carbonaceous solid may be introduced into the reaction zone separately from the reactant gas where undesirable preliminary reaction is likely to take place. This may be accomplished by dispensing the carbonaceous particles in a stream of innocuous gas which may be inert or relatively unreactive under conditions prevailing prior to introduction of the suspension into the reaction zone. Steam, carbon dioxide, and other endcthermic reactants generally fall in the latter category and may be premixed with the carbonaceous material.

-Obviouslyxmanyjfmodifications and variations :offthe inventionfas hereinabovesetforth may be rceous .material which tends tofagglomerate on sitory mass-of unreactiveasolid contact material .in thepformof particles having a relatively high settling rate in gaseous suspension, continuously introducing into theilower portion'of said zone vsolid carloonaceousmaterial in the form of par- -ticles ha-ving a relatively low settling rate in gaseous suspension, continuously introducing to vthe lower-portion lof said zone a stream of iuidizinggas Which is unreactive with said solid contact ymaterial under conditions prevailing Within the zone, passing said stream upwardly through said mass of particles with sufcient velocity to eiect entrainment of saidparticles of carbona ceous material and'to maintain said particles of contact material inhighly agitated condition but Without substantial entrainment of said particles of contact'material, eiecting'substantial gasication of said solid carbonaceous material during its passage through said contact material Within said zone, continuously removing from the upper portion of said zone an effluent stream of gaseous reaction products containing entrained residual solid material resulting from gasification of said solid carbonaceous material.

'2. A process as defined in claim l wherein the solid carbonaceous material is coal.

3. A process as defined in claim 1 wherein the luidizinggas comprises a gas reactive with the solid carbonaceous material.

4. A'process vas'dened in claim 1 wherein the fluidizing gas comprises a gas'selected from the group consisting of oxygen, hydrogen carbon dioxide and steam.

5, In a process for vtreating a solid carbonaceous material to eiect"gasication thereof in a gasiiication izone, the improvement comprising f disposing within said zone' a substantially nontransitory mass of unreactivel solid contact material in the form of particles having a'relatively high settling rate inigaseous suspension, continuously introducing into the lower portion of said mass solid carbonaoeous material in the form of 'particles having a relatively low settling rate 'in gaseous suspensiony supplying heat to said reaction zone from an external source by heat transfer through a wall of said reaction zone to said mass of particles contained therein, continuously introducing into the lower portion of said zone a stream of fluidizing gas which is unreactive with said solid contact material under conditions prevailing Within said Zone, passing said stream upwardly through said mass of particles with sufficient velocityto eiect entrainment of said particles of carbonaceous material and to maintain said particles of contact material in highly agitated condition but without substantial entrainment of said particles of contact material, effecting substantial gasiication of said solid carbonaceous material during its passage through said contact material within said zone, continuously removing from the upper portion of said zone an eiiluent stream of gaseous reaction products containing entrained residual solid material resulting from gasification of said solid carbonaceous material.

5. A process as defined in claim 5 wherein said solid carbonaceous material is a caking coal.

MOOSON KWAUK.

References Cited in the file 0f this patent UNITED STATES PATENTS Number Name Date 1,873,941 Hillebrand -Aug. 23, 1932 2,443,673 Atwell June 22, 1948 FOREIGN PATENTS Number Country Date 321,422 Great Britain Nov. 4, 1929 586,391 Great Britain Mar. 18, 1947 OTHER REFERENCES Lange, Handbook of Chemistry,`5th Edition, pp. 1374-1375.

Claims (1)

1. IN THE PROCESS FOR TREATING A SOLID CARBONACEOUS MATERIAL WHICH TENDS TO AGGLOMERATE ON HEATING TO EFFECT GASIFICATION THEREOF IN A GASIFICATION ZONE MAINTAINED UNDER GASIFICATION CONDITIONS, THE IMPROVEMENT WHICH COMPRISES DISPOSING WITHIN SAID ZONE A SUBSTANTIALLY NON-TRANSITORY MASS OF UNREACTIVE SOLID CONTACT MATERIAL IN THE FORM OF PARTICLES HAVING A RELATIVELY HIGH SETTLING RATE IN GASEOUS SUSPENSION, CONTINUOUSLY INTRODUCING INTO THE LOWER PORTION OF SAID ZONE SOLID CARBONACEOUS MATERIAL IN THE FORM OF PARTICLES HAVING A RELATIVELY LOW SETTLING RATE IN GASEOUS SUSPENSION, CONTINUOUSLY INTRODUCING TO THE LOWER PORTION OF SAID ZONE A STREAM OF FLUIDIZING GAS WHICH IS UNREACTIVE WITH SAID SOLID CONTACT MATERIAL UNDER CONDITIONS PREVAILING WITHIN THE ZONE, PASSING SAID STREAM UPWARDLY THROUGH SAID MASS OF PARTICLES WITH SUFFICIENT VELOCITY TO EFFECT ENTRAINMENT OF SAID PARTICLES OF CARBONACEOUS MATERIAL AND TO MAINTAIN SAID PARTICLES OF CONTACT MATERIAL AND TO MAINTAIN SAID PARTICLES OF WITHOUT SUBSTANTIAL ENTRAINMENT OF SAID PARTICLES OF CONTACT MATERIAL, EFFECTING SUBSTANTIAL GASIFICATION OF SAID SOLID CARBONACEOUS MATERIAL DURING ITS PASSAGE THROUGH SAID CONTACT MATERIAL WITHIN SAID ZONE, CONTINUOUSLY REMOVING FROM THE UPPER PORTION OF SAID ZONE AN EFFLUENT STREAM OF GASEOUS REACTION PRODUCTS CONTAINING ENTRAINED RESIDUAL SOLID MATERIAL RESULTING FROM GASIFICATION OF SAID SOLID CARBONACEOUS MATERIAL.

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