US3384557A

US3384557A - Method of curing of green briquettes by oxidation

Info

Publication number: US3384557A
Application number: US384146A
Authority: US
Inventors: Saller Erik
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1964-07-21
Filing date: 1964-07-21
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21
Also published as: YU31297B; DE1546640B1; BE666910A; AT257536B; GB1056467A; NL139768B; ES315200A1; NL6509227A

Description

E. SALLER May 21, 1968 METHOD OF CURING OF GREEN BRIQUETTES BY OXIDATION Filed July 21, 1954 x0 0 mm a INVENTOR ERIK $14 1.1. 1

ATTORNEY United States Patent 3,384,557 METHOD OF CURING OF GREEN BRIQUETTES BY OXEDATION Erik Sailer, Stamford, Conn, assignor to FMC Corpora' tion, New Yorir, N.Y., a corporation of Delaware Filed July 21, 1964, Ser. No. 384,146 4 Claims. (Cl. 201-22) This invention relates to the curing of briquettes constituted of calcined char derived from coal and a bituminous binder.

In the production of coked briquettes from a bituminous binder and char derived from bituminous coal, it is known to subject the fresh briquettes to a curing treatment prior to coking the briquettes. The char for the briquettes can be derived from coking as well as non-coking coals. In one well known method, known as the FMCoke procedure, disclosed and claimed in US. Patents 3,140,241 and 3,140,242 granted July 7, 1964, bituminous coal, including non-coking coals, of a particle size less than 6 mesh and preferably less than 16 mesh with the average particle size in the range of 40 to 60 mesh, are heated in the presence of oxygen, which may be derived from the coal itself in the case of the so called high oxygen containing coals, i.e., coals having an excess of by weight of oxygen, to a temperature high enough to drive off substantially all moisture but below that at which substantial amounts of tar-forming vapors evolve. Thereafter the coal particles from this heat treatment are heated to a higher temperature at which tar-forming vapors are evolved and for a time interval sutlicient to effect polymerization of the heated coal particles and evolution therefrom of substantially all of the tar-forming vapors to produce a char of markedly lower volatile combustible material content than the parent coal and substantially free of tar-forming vapors. This char is heated to a still higher temperature to produce the calcined char particles for blending with the bituminous binder.

Typical conditions for producing such calcined char particles from a coking coal is to heat in the first stage to a temperature within the range of from 500 F. to 800 F., in an atmosphere containing from 8% to 20% by volume of oxygen; to further heat the hot coal particles from the first stage to a temperature not exceeding 1200" F. to drive off substantially all tar-forming vapors; and to heat in the third or calcining stage to a temperature within the range of from 1400 F. to 1800 F. for a time interval long enough to produce the desired reduction in the volatile combustible content of the calcined char particles, preferably to not exceeding about 5% by weight on a moisture and ash-free basis.

In this specification, all percentage and part values are given on a weight basis, unless otherwise indicated.

All mesh sizes are in terms of the United States Sieve Series (US. Bureau of Standards).

In the case of non'coking coals, preferred for reasons of economy and ready availability in many sections of the world where coking coals are not available, the conditions for the production of the calcined char are to heat the coal particles in the first stage to a temperature within the range of from 250 F. to 500 F. in an atmosphere containing from 1% to 3% by volume of oxygen where the coal treated is not a high oxygen-containing coal (in the treatment of such high oxygen-containing coals, oxygen from an extraneous source need not be introduced). The hot coal particles from the first stage are heated to a temperature not exceeding 1200 F. for a time interval long enough to effect substantially complete removal of tar-forming vapors and the char thus produced heated to a still higher temperature within the range of from 1400 F. to ISO-0 F. to reduce the volatile 3,384,557 Patented May 21, 1968 content to the desired level, preferably to not exceeding about 3% by weight on a moisture and ash-free basis.

The production of briquettes from the calcined char thus produced by blending the calcined char with the bituminous binder, desirably in the proportions of from to calcined char to 25% to 10% binder, properly curing the briquettes thus produced and coking the cured briquettes, results in uniform briquettes suitable for metallurgical purposes. These briquettes burn uniformly. When observed, even under relatively lower power of magnification, they are of uniform composition, i.e., as a general rule the carbon derived from the char and that derived from the bituminous binder are indistinguishable. The curing treatment, which effects copolymerization of the bituminous binder with the calcined char so that upon subsequent coking a uniform homogeneous briquette is obtained and in which as noted the carbon derived from the bituminous binder and that derived from the char are, for all practical purposes, indistinguishable, is a most important factor in the production of satisfactory briquettes. This curing stage is also important because it imparts to the green (fresh) briquettes the necessary strength to withstand the subsequent coking treatment without excessive loss, i.e., without having an excessive number of the briquettes spall and crumble during the coking.

The cured briquettes, when properly cured, can be used without subjecting them to a coking treatment before use. For example, cured briquettes of adequate strength are useful in cupola and blast furnaces. Actually the coking of the cured briquettes takes place within the furnace; the temperature conditions in cupola and blast furnaces are such as to effect the coking of the cured briquettes, which are then consumed in effecting the smelting and refining of the charge within the furnace.

As heretofore carried out, curing of the green briquettes is effected by heating in an atmosphere containing 2% to 21% by volume of oxygen to a temperature within the range of from 400 F. to 550 F. The presence of oxygen in the curing medium, it is believed, effects the removal of hydrogen from the carbon matrix derived from the calcined char and from the bituminous binder by dehydrogenation thereof. At the temperature conditions under which the curing is effected, the oxygen promotes copolymerization of the bituminous binder and the char so that upon subsequent coking a uniform briquette is obtained in which the carbon derived from the char and that derived from the binder, for all practical purposes, is indistinguishable.

When the green shapes are subjected to temperatures above the softening point of the binder in the presence of oxygen concentrations below 2 /2% by volume, disintegration of the shapes takes place at a rapid rate. 0n the other hand, at higher temperatures when curing beds of shapes exceeding 24 inches in height are used, combustion of the hydrocarbonaceous volatile components of the binder occurs when the oxygen concentration exceeds 4% by volume of the entering curing atmosphere. With beds of lesser height, oxygen concentrations above 4% by volume can be used; for example, with beds of six inches or less in height, 20% or 21% oxygen, e.g., air, can be used as the curing medium.

Low oxygen concentrations have the objection that it not only requires dilution of air with inert gases and the expense involved in so doing to supply the lower oxygen concentration, but it also results in briquettes of relatively low compressive strength. Using air (about 21% oxygen) as the curing medium, on the one hand, and using a gas containing only 4% oxygen produced, for example, by mixing steam, nitrogen or other inert gas with air, on the other hand, results in a reduction of the crushing strength 3. of the briquettes after coking from 60007000 p.s.i.g. (when using air) to 3500 p.s.i.g.

To accomplish curing with techniques heretofore known, the practice employed was to place the green briquettes in a relatively shallow bed (from about 12" to 18" high) on an .endless grate traveling through an oven maintained at a temperature of from 400 F. to 500 F. while maintaining in the oven an oxygen atmosphere containing about by volume of free oxygen. This shallow grate procedure is objectionable not only because the equipment required is costly and wears out quickly, but also because ofthe limited capacity of a given size installation. The curing time required with this shallow grate procedure are of the order of about 1 to 2 hours.

It is a principal object of the present invention to provide an improved, economically attractive process of curing such briquettes, which process involves the use of undiluted air as the medium for supplying the oxygen required for the curing and yet enables the curing to be conducted in beds of any desired height.

Another object of this invention is to provide such process which is continuous in character and hence of large capacity or throughput.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In accordance with this invention a bed of green briquettes is moved continuously in a downward direction, countercurrent to an upwardly flowing stream of finely divided solid particles having a size not exceeding about 6 mesh, preferably less than 16 mesh, with the average particle size in the range of 40to 60 mesh, which solid particles fiow through the interstices between the downwardly moving briquettes, the reaction zone of the bed is maintained at a temperature within the range of from 400 F. to 550 F., prefereably 450 F. to 500 F., and the upwardly flowing stream of finely divided solid particles is dispersed in a stream of air which thus supplies the oxygen for the curing and effects the heat transfer from the mass of briquettes subjected to oxidation to the finely divided solid particles so as to maintain the temperature conditions throughout the reaction zone where the oxidation of the briquettes is effected within a relatively narrow range not exceeding about 60 F. throughout the length of the reaction zone. The rate of flow of the air stream and of the bed of briquettes through the reaction zone is controlled to insure the presence of at least 10% by volume, preferably at least by volume, of free oxygen in the solids free gas in the reaction zone where the briquettes enter this zone, or just above this zone. The finely divided solid particles are withdrawn continuously, cooled and recirculated upwardly through the downwardly moving bed of green briquettes, thus acting to remove the heat of reaction and also to effect etficient heat exchange so as to maintain temperature conditions within the reaction zone within the aforesaid narrow range of not exceeding 60 F. as the briquettes move through this reaction zone.

The presence of oxygen during the curing of the green briquettesis essential. Also important is the presence of at least 10% by volume of free oxygen, on a solids free gas basis, where the briquettes enter the reaction zone. Unless at least 10% by volume of free oxygen, on a solids free gas basis, is present where the briquettes enter the reaction zone the oxidative curing of the briquettes does dot proceed rapidly enough to impart sufficient strength to the briquettes to prevent excessive disintegration of the briquettes in their fiow through the reaction zone. The maintenance of the temperature conditions during the curing within the range of from 400 F. to 550 F. is also important. If the temperature is permitted to rise much above 550 F., ignition occurs and the reaction can no longer be controlled, with the result that instead of a curing reaction taking place, the carbon and hydrogen content of the briquette is consumed.

In the present invention, the air suspension of finely divided heat transfer material flows through the interstices of the column of briquettes flowing downwardly through the reaction zone giving good heat distribution and enabling control of the temperature within the bed within a relatively narrow range, not exceeding about 60 F. This is effected by fiowing from 1 to 7 pounds, preferably 3 to 5 pounds, of solid heat transfer material per cubic foot of air up through the briquettes and with the flow of this solid heat transfer material at a superficial velocity of from 1 to 15 linear feet per second.

As noted, the superficial velocity of the solid heat transfer particles should be within the range of from 1 foot per second to 15 feet per second. By superficial velocity of the heat transfer solids is meant the velocity of the air stream in the curing column without any resistance therein to the flow of the heat transfer particles in the column, i.e., the bed of briquettes. As a practical matter, there is no known method of determining the velocity through the bed of briquettes with reasonable accurracy, hence the definition of the velocity of the heat transfer particles in terms of superficial velocity. If the superficial velocity is below about one foot per second, the heat transfer solids tend to settle out of the air and collect on the briquettes,

r plugging he column or bed of briquettes and giving unsatisfactory curing. If the superificial velocity exceeds 15 feet per second, the cost of air compression becomes excessive and the air stream tends to interfere with the downward flow of the briquettes.

Good heat transfer and control are promoted by the solid particles not only because of heat transfer between these particles, but also because these small solid particles circulating in an air transport stream countercurrent to the direction of movement of the briquettes destroy the dead film of gas invariably surrounding the surfaces of the briquettes, thus promoting heat transfer from the briquettes to the fluidized finely divided solids and enabling the latter to remove the heat of reaction, preventing the creation of excessive temperatures within the bed of briquettes and maintaining the temperature within the range of from 400 F. to 550 F. and within a narrow range of not exceeding 60 F. within the reaction zone.

The residence time of the green briquettes in the bed moving through the reaction zone is dependent on the temperature maintained in the reaction zone. Operating at about 500 F. the minimum residence time is about sixty minutes. At 450 F., somewhat longer residence times would be needed to obtain maximum strength. Longer residence times in excess of about three hours, however, 'add nothing to the quality of the final product. Since such longer residence times adversely affect the economics of the process, they are not recommended. Preferred operation is a residence time of from about 60 to minutes at a temperature of from 450 F. to 500 F. within the reaction zone.

The briquettes can enter the curing zone at any desired temperature, preferably at the temperature at which they leave the briquetting operation, which is usually Within the range of from F. to 250 F. They soon reach reaction temperature as they move downwardly through the upper portion of the vessel, just before entering the reaction zone therein, due to the heat emanating from the reaction zone and the exothermic character of the curing reaction. The briquettes are maintained.

within the reaction temperature of from 400 F. to 550 F., preferably 450 F. to 500 F., as they pass downwardly through the reaction zone by circulating finely divided solids dispersed in the air stream introduced in the reaction zone and flowing upwardly between the interstices of the briquettes moving downwardly through this reaction zone, these finely divided solids being continuously withdrawn from the upper portion of the reaction zone, cooled and the cooled solids returned to the lower portion, thus removing the heat of reaction from the reaction zone and maintaining the latter within the temperature range of from 400 F. to 550 F. and within a temperature gradient of not exceeding about 60 F. from the inlet to the exit end of the reaction zone. Desirably, the briquettes are introduced into the reaction zone at a temperature near that at the exit end of the reaction zone where the curing is effected. This can be accomplished by flowing the briquettes through a mass of the finely divided heat transfer material 'after the latter leaves the reaction zone to effect partial cooling of the hot heat transfer particles and simultaneous heating of the briquettes.

Storage of the cured briquettes in bulk While the briquettes are at a temperature above 250 P. will cause ignition. Hence when the cured briquettes leaving the curing zone are to be stored in bulk, they are cooled to a temperature below 250 F. before exposure to such atmosphere. Such cooling can be accomplished by water quench or other known cooling techniques employed in cooling hot carbon products. When the cured briquettes are to be coked they are transported from the exit end of the reaction zone directly to the coking stage, without cooling.

Preferred heat transfer solids are the calcined char particles employed in producing the briquettes. The advantages of using these char particles are that they prevent contamination of the briquette product, the char particles are readily available as part of the overall process, and char particles which are converted into fines and separated from the heat transfer particles can be utilized in the process by introducing same into the briquetting operation as part of the char feed, thus eventually contributing to the yield of coked briquettes from the process. The invention, however, is not limited to the use of calcined char particles as the heat transfer material. Instead of char, sand or minerals crushed to a particle size, as, for example, in a hammer-mill having screens passing inch particles, can be used.

The rate of flow of the briquettes downwardly countercurrent to the upwardly flowing heat transfer solid particles suspended in the air stream is dependent upon (1) the size of the vessel, and (2) the height of the reaction or curing zone chosen to give a selected residence time within the curing zone Within the range of from 60 to 180 minutes; this rate of flow must be such as to leave at least preferably at least by volume of free oxygen, on a solids free gas basis, in the gas stream at the point where the briquettes enter the curing zone. The height and cross-section of the curing zone can be chosen to give any desired capacity within limits. Satisfactory curing has been effected in curing zones over 10 feet high; this value is given to demonstrate that the present invention successfully permits the curing to be effected with air in non-shallow curing zones. Curing zone heights of more than 10 feet can be used. The throughput for any given installation depends on the size of the equipment and residence time within the curing zone. The present invention enables the curing to be effected with high throughputs.

The accompanying drawing is a flow sheetshowing one arrangement of equipment for practicing the process of this invention. The invention, however, is not to be limited to this illustrative arrangement of equipment shown in this drawing. In the interest of clarity of illustration, conventional controlling equipment including valves, temperature indicating pyrometers and the like have not been shown.

Referring to the drawing, green briquettes as produced in the briquetting equipment are transported to the storage hopper 10. From this hopper 10 the green briquettes flow down through conduit 11 at a given and desired rate into the upper portion 12 of a fluidized bed of particulate heat transfer solids 13 reaching the interface 14 of the downwardly moving bed of briquettes 15. Such feed of the briquettes from the storage hopper 10 through the conduit 11 can be effected by a vibratory feed mechanism (not shown) or other suitable mechanism for effecting the feed of the briquettes at a controlled rate. The interface 14 between the particulate heat transfer solids 13 and the downwardly moving bed of briquettes 15 is controlled to be positioned at about the outlet 16 for the spent heat transfer solids 13. This outlet 16 forms the inlet or head of conduit 17 leading into the cooler vessel 41.

The green briquettes move down through the reaction zone 19, the extent of which is indicated by the arrows on the drawing. From the reaction zone 19 the cured briquettes continue downward by gravity past the distributing cone 21 into the exit section 22. The latter comprises a lock hopper system 26 which consists of three

slide valves

27, 28 and 29 operated in timed relation to permit flow of briquettes through the lock hopper system while maintaining the exit section 22 sealed. The cured briquettes pass out of valve 29 onto a conveyor belt 31 where they are transported to a vibrating screen 32 for the purposes of the removal of pieces of briquettes and particles of heat transfer material, in the embodiment illustrated calcined char, which exit through valve 29. The screenings are discharged from the vibrating screen 32 to chute 33 from which they are returned to the feed stock for the formation of the green briquettes. The screened briquettes are discharged from the vibrating screen 32 onto a conveyor 34 which moves them to transport container 35 for transport to the locale of intended use or for further processing, e.g., feed to the coker.

The heat transfer material, in the preferred embodiment calcined char, of the desired particle size, not exceeding about 6 mesh, preferably less than 16 mesh, is stored in hopper 36 and fed therefrom by means of a vibrating screen or other suitable feed mechanism into a conduit 37 leading into the disengaging space 38 of the reaction vessel shown in the drawing. In the disengaging space 38 they mix with the gases which are heated by passage through the reaction zone and have been disengaged of most of the heat transfer solids. These gases are in a turbulent state in the disengaging space of chamber 38. Feed of the heat transfer material through these gases effects cooling of the gases with consequent heating of the incoming heat transfer solids fed into the disengaging chamber 38 from storage hopper 36. The heat transfer material moves down in a dense phase by gravity through conduit 17 which is screened at its inlet 16 in order to prevent the flow of briquettes into conduit 17. The heat transfer solids 13 exiting through the conduit 17 pass in a dense phase by gravity into the fluid bed 41 maintained in vessel 42. In the fluid bed the heat transfer solids are cooled by an incoming stream of cold air introduced through line 43 or by circulating a cooling medium through a jacket (not shown) surrounding vessel 42 to cool the contents of this vessel. 44 is a meter for metering the air supplied through line 43.

The heat transfer material can be cooled by other procedures, for example, by direct water injection into the circulating stream of heat transfer material at a point in its circulation after leaving the reaction zone to remove enough of the heat of the curing reaction to maintain the reaction zone 19 within the range of 400 F. to 550 F.

The heat transfer solids are thus picked up by the air stream supplied through line 43 and conveyed through conduit 47 into the distribution chamber 48 where the suspension of heat transfer solids is dispersed in the annular conical chamber constituting the distribution chamber 48 and flow upward through the downwardly moving bed of briquettes into the disengaging chamber 38. Thus the heat transfer solids, dispersed in the air stream flowing upwardly and enveloping the downwardly moving bed of briquettes, are cycled through the reaction zone 19 removing the heat of reaction, maintaining the briquettes within the reaction zone within a narrow temperature range not exceeding about 60 F., and maintaining a free oxygen concentration of at least 10% by volume, on a solids free basis Where the green briquettes enter the curing zone.

Cold air is introduced through line 54 provided with a meter 55. The volume of air introduced through line 54 plus that introduced through line 43 controls the loading of the heat transfer solids in the air stream passing through the reaction zone 19, i.e., pounds of heat transfer solids per cubic foot of air passed through the reaction zone 19. The volume of air introduced through line 43 controls the rate of recycle of heat transfer solids through the reaction zone 19, i.e., pounds of solids per minute passed through reaction zone 19.

The mixture of fluidizing gas including the reaction gases formed in the reaction zone and the heat transfer solids move upwardly through the bed of briquettes at a rate so designed that for each unit passage of briquettes through the reaction zone 19, about 10 passes of the heat transfer solids through the reaction zone 19 are effected. In other words, the number of recycles of heat transfer solids per single pass of briquettes through the reaction zone 19 is of the order of 10 to 1. p

The disengaging space 38 aids in effecting separation of the gases leaving the reaction zone 19 from the heat transfer solids by the cyclone separator 57. The gases thus separated in the cyclone separator 57 enter the condenser 58 where condensables such as tars are condensed. The condenser 58 can be in the form of the well known direct scrubber Where the gases are scrubbed by a suitable aqueous medium, e.g., water, to condense the condensables in the gas stream. Tars so condensed are removed through line 59. Liquor is decanted from the tars and removed through line 61. Clean gases exit through line 62 and flow through meter 63 from which they can be passed to storage for use, or otherwise disposed of, for example, by venting to the atmosphere.

In placing the equipment in operation, the air flowing through meter 55 and introduced through line 54 to effect the fluidization of the heat transfer solids introduced from hopper 36 into chamber 38 and reaction zone 19, initially is preheated to a temperature of about 450 F. to insure that the curing reactions take place within the reaction zone 19. However, once the reaction is initiated, as indicated by suitable temperature control instruments associated with the reaction zone, the preheating of the air introduced through line 54 is discontinued and air at atmospheric temperature introduced at this point. The curing reaction is maintained by the heat generated in the reaction zone 19. This heat is more than suflicient to heat the incoming air and the down-flowing bed of briquettes as well as the heat transfer solids flowing upwardly through the down-flowing bed of briquettes. Actually, once the reaction has reached steady state operation, heat must be removed from the reaction zone 19 to maintain the temperature therein within the desired range of from 400 F. to 500 F, preferably 450 F. to 500 F. Also, once steady state operation is reached, the amount of heat transfer solids supplied to reaction zone 19 from hopper 36 is the amount required to replace the solids exiting through valve 29.

The cured briquettes produced in accordance with this invention have sufficient strength for use in cupola and blast furnaces. When so used coking of the briquettes takes place in the cnpola and blast furnaces; the cured and uncoked briquettes are sumeiently strong to provide adequate support for the burden and this without excessive crumbling so as to plug up the charge in the furnace. The cured briquettes in the uncoked state can also be used as a smokeless fuel.

The following example is given to illustrate a preferred embodiment of the invention. It will be understood that this invention is not limited to the example.

The example was carried out in equipment of the type shown in the drawing. The briquettes were supplied to storage hopper 10 at a temperature of 80 F. The heat transfer solids, which were calcined char particles, the

same as those employed in producing the briquettes, were supplied from storage hopper 36 at F. and air at 80 F. was supplied through line 54 and 44 once steady state operation commenced. Initially, preheated air heated to a temperature of about 450 F. was supplied through line 54. The green briquettes contained 81.9% calcined char and 18.1% bituminous binder, which was a tar binder obtained from the carbonization of the coal (Elkol coal) employed in forming the calcined char. Elkol coal, as is well known, is a sub-bituminous grade B coal, mined at Kemmerer, Wyoming, having an approximate fixedcarbon weight percent on a dry basis of 53.2%; volatile matter content on a weight percent dry basis of about 42.7%; and an approximate elemental analysis on a weight percent dry basis as follows: carbon 70.8; hydrogen 5.2; oxygen 18.8; nitrogen 0.9; sulfur 0.8; and ash 3.4.

This example involved a run of approximately 38 hours duration during which 9100 pounds of green briquettes were passed through the reaction zone 19. The briquettes introduced into the reaction vessel had a size of 1 /8 x x A. The exiting briquettes, i.e., the cured briquettes, were dimensioned 1% x /3 x A, the same as the green briquettes introduced into the reaction vessel. The calcined char employed as the heat transfer solids had the following mesh analysis:

Mesh size,

U.S. Sieve Series Percent +14 17 0 -14+2s 2s 5 2s+100 42 6 100 ll 9 These calcined char particles contained 4.5% volatile matter. 9100 pounds of the green briquettes were passed downwardly through the reaction zone 19 to form a bed approximately 10 feet long having a cross-sectional area of approximately 144 square inches. 8500 pounds of cured briquettes were removed. The residence time of the briquettes in reaction zone 19 was about minutes. Oxygen consumption during curing was about 0.07 pounds per pound of green briquettes.

Air was introduced just below the annular distributor 48 through lines 43 and 54. Total air flow was 60 s.c.f.m. and the superficial velocity in the reaction zone 19 was 1.76 feet per second. The volumetric composition of the exit gas leaving the top of the unit was 15.6% 0 1.8% CO 0.5% CO and 82.1% N (by difference) on a dry and solid-free basis.

The calcined char particles were circulated upward through the reaction zone 19 at a rate of 1944 pounds per hour, equivalent to about 8.2 pounds of calcined char per pound of green briquettes. The gas flowing through the reaction zone contained about 0.3 pounds of calcined char per cubic foot. The temperature at the top of the reaction zone 19 during steady state operation was 430 F.; at the exit end just above the annular distributor 48 the temperature was 400 F.; and the temperature at the approximate middle of the reaction zone was 460 F. The hot heat transfer particles entered conduit 17 at a temperature of 460 F., were cooled in vessel 42 before returning to the bottom of the reaction zone 19. The vessel 42 serves to remove the excess heat generated in the reaction zone and thereby provides a convenient way of controlling temperature in the reaction zone.

The cured briquettes thus produced were of excellent quality. Their resistance to crushing after coking was approximately 30% greater than coked briquettes produced from the same green briquettes but cured on an endless grate passing through an oven in which an atmosphere containing from 4% to 5% by volume of oxygen was maintained by the introduction of air and recycle of reaction gases through the grate.

It will be noted that the present invention provides an economically attractive process of curing green briquettes constituted of calcined char derived from coal and a bituminous binder in which air is employed as a medium for supplying the oxygen required for the curing and in which green briquettes are passed through the curing zone in a bed of any desired capacity, thus enabling the curing to be effected with large throughputs of the briquettes. The residence time for the briquettes in the curing zone is relatively short and the process is continuous in character and hence the equipment required for the practice of the process can be tailored to meet the requirements of commercial installations where the capacity must be relatively large.

The expression briquettes is used herein in a broad sense and includes compressed blends of char and binder in all forms including extrusions, pellets and other shapes.

Since certain changes can be made in carrying out the above disclosed method of curing green briquettes without departing from the scope of this invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of curing green briquettes consisting essentially of calcined char derived from coal and a bituminous binder, which process comprises continuously passing a bed of green briquettes downwardly through a reaction zone; continuously supplying green briquettes to the upper portion of said bed; continuously introducing a stream of air having heat transfer solid particles dispersed therein in the neighborhood of the exit end of said reaction zone and flowing the said stream of air and heat transfer particles upwardly through said reaction zone countercurrent to the down-flowing bed of briquettes with the stream of heat transfer solids enveloping the briquettes in the down-flowing bed, the rate of flow of the bed of briquettes downwardly and the rate of flow of 3 the stream of air having the heat transfer solids dispersed therein upwardly being controlled to provide in the portion of the reaction zone where the green briquettes enters at least 10% by volume of free oxygen, on a solids free basis; continuously withdrawing heat transfer solids from an upper portion of said reaction zone, cooling the solids thus withdrawn and continuously returning to the reaction zone the cooled solids thus removing the heat of reaction and maintaining the temperature within the reaction zone within the range of from 400 F. to 550 F.; and removing cured briquettes from the exit end of said reaction zone.

2. The process of curing green briquettes as defined in claim 1, in which the temperature difference between the temperature of the briquettes at the inlet and exit end of the reaction zone does not exceed about 60 F.

3. The process of curing green briquettes as defined in claim 1, in which the heat transfer solids are calcined char particles derived from coal.

4. The process of curing green briquettes as defined in claim 1, in which the heat transfer solids are calcined char particles derived from coal, the amount of said solids passed through the downwardly moving bed of briquettes is from 1 to 7 pounds per cubic foot of air passed through the downwardly moving bed of briquettes and the superficial velocity of said solids is from 1 to 15 linear feet per second.

References Cited UNITED STATES PATENTS 2,776,935 1/1957 Jahnig et a1 20131 3,018,226 1/1962 Batchelor et al 201--22 3,051,629 8/1962 Gorin et al 201-22 3,117,064 1/1964 Friedrich 201- 12 3,140,242 7/1964 Work et al. 201-31 3,172,823 3/1965 John et al 4410 3,117,918 1/1964 Batchelor et a1 20l9 3,140,985 7/1964 Schmalfeld 20l-9 NORMAN YUDKOFF, Primary Examiner.

D. EDWARDS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,384,557 May 21, 1968 Erik Saller It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the drawing, and in the heading to the printed specification, title of invention, "METHOD OF CURING OF GREEN BRIQUET'IES BY OXIDATION", each occurrence should read METHOD OF CURING GREEN BRIQUETTES BY OXIDATION Column 3, line 13, "time" should read times line 65, "dot" should read not Column 4, line 25, "he" should read the Column 7, line 55, "500 F." should read 550 F.

Signed and sealed this 30th day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

Claims

1. THE PROCESS OF CURING GREEN BRIQUETTES CONSISTING ESSENTIALLY OF CALCINED CHAR DERIVED FROM COAL AND A BITUMINOUS BINDER, WHICH PROCESS COMPRISES CONTINUOUSLY PASSING A BED OF GREEN BRIQUETTES DOWNWARDLY THROUGH A REACTION ZONE; CONTINUOUSLY SUPPLYING GREEN BRIQUETTES TO THE UPPER PORTION OF SAID BED; CONTINUOUSLY INTRODUCING A STREAM OF AIR HAVING HEAT TRANSFER SOLID PARTICLES DISPERSED THEREIN IN THE NEIGHBORHOOD OF THE EXIT END OF SAID REACTION ZONE AND FLOWING THE SAID STREAM OF AIR AND HEAT TRANSFER PARTICLES UPWARDLY THROUGH SAID REACTION ZONE COUNTERCURRENT TO THE DOWN-FLOWING BED OF BRIQUETTES WITH THE STREAM OF HEAT TRANSFER SOLIDS ENVELOPING THE BRIQUETTES IN THE DOWN-FLOWING BED, THE RATE OF FLOW OF THE BED OF BRIQUETTES DOWNWARDLY AND THE RATE OF FLOW OF THE STREAM OF AIR HAVING THE HEAT TRANSFER SOLIDS DISPERSED THEREIN UPWARDLY BEING CONTROLLED TO PROVIDE IN THE PORTION OF THE REACTION ZONE WHERE THE GREEN BRIQUETTES ENTERS AT LEAST 10% BY VOLUME OF FREE OXYGEN, ON A SOLIDS FREE BASIS; CONTINUOUSLY WITHDRAWING HEAT TRANSFER SOLIDS FROM AN UPPER PORTION OF SAID REACTION ZONE, COOLING THE SOLIDS THUS WITHDRAWN AND CONTINUOUSLY RETURNING TO THE REACTION ZONE THE COOLED SOLIDS THUS REMOVING THE HEAT OF REACTION AND MAINTAINING THE TEMPERATURE WITHIN THE REACTION ZONE WITHIN THE RANGE OF FROM 400$F. TO 550F.; AND REMOVING CURED BRIQUETTES FRO THE EXIT END OF SAID REACTION ZONE.