US3756791A

US3756791A - Al and or coal derivatives method for simultaneously calcining and desulfurizing agglomerates co

Info

Publication number: US3756791A
Application number: US00151323A
Authority: US
Inventors: E Mancke
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1971-06-09
Filing date: 1971-06-09
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04

Abstract

AGGLOMERATES OF COAL AND/OR COAL DERIVAITIVES ARE SIMULTANIOUSLY CALCINED AND DESULFURIZED BY EXPOSURE TO HEATED PARTICLES OF A DESULFURIZING AGENT IN A ROTARY KILN. THE AGGLOMERATES AND HEATED PARTICLES OF THE DESULFURIZING AGENT FLOW COUNTERCURRENTLY THROUGH THE KILN. THE AGGLOMERATES ARE CHARGED INTO THE KILN WITHIN A TEMPERTURE RANGE OF BETWEEN ABOUT AMBIENT TEMPERATURE TO ABOUT 850*F. THE AGGLOMERATES ARE DISCHARGED AT A TEMPERATURE ABOVE ABOUT 1400*F. IT IS PREFERRED TO DISCHARGE THE AGGLOMERATES AT A TEMPERATURE ABOVE ABOUT 1950*F. THE AGGLOMERATES ARE HEATED BY HEAT EXCHANGE WITH THE PARTICLES OF THE DESULFURIZING AGENT WHICH ARE CHARGED INTO THE KILN AT A TEMPERATURE ABOVE ABOUT 1400*F. IT IS PREFERRED TO CHARGE THE PARTICLES OF THE DESULFURZING AGENT AT A TEMPERATURE ABOVE ABOUT 1950*F. THE PARTILES OF THE DESULFURZING AGENT CAN BE AT ABOUT 600*F. AND PREFERABLY ABOUT 1100*F. WHEN DISCHARGED, DEPENDENT UPON THE TEMPERATURE OF THE AGGLOMERATES WHEN CHARGED. THE AGGLOMERATES SO PRODUCED HAVE A RELATIVELY MEDIUM OR LOW REACTIVITY TO CARBON DIOXIDE AT ELEVATED TEMPERATURES, GOOD RESISTANCE TO ABRASION AND SUFFICIENT STRENGTH TO RESIST DEGRADATION WHEN TRANSPORTED AND CHARGED INTO A FURNACE.

Description

Sept. 4, 1973 E. B. MANCKE 3,755,791 METHOD FOR SIMULTANEOUSLY CALCINING AND DESULFURIZING AGGLOMERATES 0F COAL AND/0R COAL DERIVATIVES Filed June 9, 1971 m T m G v e W m m A m a W Y W. I E

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United States Patent METHOD FOR SIMULTANEOUSLY CALCINING AND DESULFURIZING AGGLOMERATES 0F COAL AND/OR COAL DERIVATIVES Edgar B. Mancke, Bethlehem, Pa., assignor to Bethlehem Steel Corporation Filed June 9, 1971, Ser. No. 151,323 Int. Cl. C101 5/00 U.S. Cl. 44-1 1R 7 Claims ABSTRACT OF THE DISCLOSURE Agglomerates of coal and/or coal derivatives are simultaneously calcined and desulfurized by exposure to heated particles of a desulfurizing agent in a rotary kiln. The agglomerates and heated particles of the desulfurizing agent flow countercurrently through the kiln, The agglomerates are charged into the kiln within a temperature range of between about ambient temperature to about 850 F. The agglomerates are discharged at a temperature above about 1400 F. It is preferred to discharge the agglomerates at a temperature above about 1950 F. The agglomerates are heated by heat exchange with the particles of the desulfurizing agent which are charged into the kiln at a temperature above about 1400 F. It is preferred to charge the particles of the desulfurizing agent at a temperature above about 1950 F. The particles of the desulfurizing agent can be at about 600 F. and preferably about 1100 F. when discharged, dependent upon the temperature of the agglomerates when charged. The agglomerates so produced have a relatively medium or low reactivity to carbon dioxide at elevated temperatures, good resistance to abrasion and sufiicient strength to resist degradation when transported and charged into a furnace.

BACKGROUND OF THE INVENTION This invention in general is directed to an improved method for continuously simultaneously calcining and desulfurizing agglomerates of coal and/or coal derivatives. Specifically, the invention is directed to continuously simultaneously calcining and desulfurizing agglomerates of coal and/or coal derivatives by contacting the agglomcrates with heated particles of a desulfurizing agent flowing countercurently to the agglomerates in a rotary kiln to thereby control the rate of heat exchanged between the agglomerates and particles of the desulfurizing agent. The method of the invention is particularly adapted to the processing of coal pelletized by a hot pelletizing technique and to form coke.

Modern techniques of smelting iron ores to recover iron values therein include pelletizing the particles of iron ore to obtain a uniform sized agglomerate which is charged into a blast furnace and the like. In order to obtain a more uniform burden in the furnace and to increase the efficiency of smelting and refining, it has been suggested that the iron and steel industry use preformed agglomerates, for example, briquettes and extrusions and pellets of coal and/0r coal derivatives. The agglomerates of coal and/or coal derivatives must have sufficient strength to sustain the burden in the furnace, have good resistance to abrasion to resist degradation during handling and transport and have a relatively low reactivity to carbon dioxide at the temperatures existing in the upper part of the blast furnace.

Agglomerates of coal and/or coal derivatives, for example, form oolee, have been made by several prior art methods. Coal briquettes are made by mixing coal fines or solid coal derivatives such as char and a suitable binder, for example, coal tar pitch and the like,'charging the mix into suitable molds and applying a high pressure to the mix in the molds to compact the mix and bind the coal fines into a coherent form. The pressure can be applied hot or cold. Briquettes thus formed are calcined at an elevated temperature to drive otf a portion of the volatile matter contained therein. Low temperature calcination produces briquettes which have a high reactivity to carbon dioxide at elevated temperatures and poor strength. The reaction between the briquettes and carbon dioxide occurs relatively high in a blast furnace where little reduction of iron oxide is accomplished. Then, too, the reaction between the briquettes and carbon dioxide is an endothermic reaction which cools the furnace. To provide sufiicient fuel and reductant in the blast furnace it is necessary to increase the amount of briquettes charged to the furnace. The increase in the amount of briquettes necessitates a cut-back in the iron ore charged. Obviously, production is decreased and the cost of ironmaking is increased.

Briquettes of coal and/or coal derivatives are calcined at high temperatures in shaft furnaces. In one method, the briquettes and heated solid fine-grain particles of sand are charged into the top of a shaft furnace and move downwardly in a concurrent fiow. The briquettes are heated at a rapid initial rate of temperature rise, that is, the briquettes are shock-heated. With some types of agglomerates, for example pellets, the initial rapid rise in temperature tends to rupture the agglomerates of some types of coal because of the rapid volatilization of the volatile matter in the coal. Other types of coal agglomerates, specifically certain types of briquettes, can be shock-heated. However, the briquettes are generally weak and have a relatively high reactivity to carbon dioxide at elevated temperatures. Countercurrent flow of the briquettes and the particles of sand in a shaft furnace is not a practical way to calcine the briquettes. The sand particles must be entrained in a gaseous medium flowing countercurrently to the briquettes. The problems involved in entraining the particles of sand in the gas, the handling of the entrained mixture, keeping the sand entrained, cleaning the gas for recirculation and reuse are too great to Warrant practical, economical use.

Prior art desulfurization and calcination of carbonaceous solids has been accomplished in concurrent flow in a rotary kiln as exemplified in U.S. Pat. No. 2,824,047 issued Feb. 18, 1958 to E. Gorin et al. No special precautions are taken to prevent rapid heating of the carbonaceous solids by the heated desulfurizing agent added thereto. The solids produced by this method sometimes have good strength but unfortunately also have a high reactivity to carbon dioxide at elevated temperatures. The combination of low reactivity and good strength is not realized.

It is an object of this invention to provide a method for producing agglomerates of coal and/or coal derivatives wherein the agglomerates are calcined and desulfurized by heated particles of desulfurizing agent, said method including feeding the agglomerates and the heated particles of the desulfurizing agent counter-currently in a rotary kiln to thereby control the rate of heat transfer from the heated particles of the desulfurizing agent to the agglomerates and to produce agglomerates which have,

good resistance to spalling, internal fracturing and degradation to fines.

It is an object of this invention to provide a method for producing agglomerates of coal and/or coal derivatives which are coked at relatively high temperatures, have a relatively low reactivity rate when exposed to carbon dioxide at elevated temperatures, have good resistance to abrasion and degradation when handled and which are of a size suitable for charging into a blast furnace and the like.

It is another object of this invention to provide a continuous method for producing agglomerates of coal and/ or coal derivatives suitable for charging into a blast furnace and the like wherein the agglomerates are calcined and desulfurized at a controlled heating rate by heated particles of a desulfurizing agent flowing countercurrently to the agglomerates in an atmosphere containing hydrogen.

It is another object of this invention to provide a continuous method for producing agglomerates of coal and/or coal derivatives wherein the agglomerates will not spall or fracture internally or be reduced to fines by avoiding rapid increases in temperature in a sensitive temperature range.

It is another object of this invention to provide a continuous method for calcining and desulfurizing agglomerates of coal and/or coal derivatives wherein the temperature of calcination and desulfurization is sufiiciently high to produce agglomerates having medium or low reactivity rates when treated by the standard test hereinafter described.

It is another object of this invention to provide a method for simultaneously calcining and desulfurizing coal which has been formed into pellets by a hot pelletizing technique, wherein said hot pellets of coal are heated to a temperature of at least about 1400 F. at a rate of not greater than 7 /2 F. per minute, particularly within a temperature range of about 110 F. to about 1400 F.

SUMMARY OF THE INVENTION The invention is directed to a continuous method for simultaneously calcining and desulfurizing agglomerates of coal and/or coal derivatives by heated particles of a desulfurizing agent flowing countercurrently to the agglomerates in a rotary kiln. The agglomerates so manufactured have a medium or low reactivity rate when exposed to carbon dioxide at elevated temperatures and a major portion of the sulfur therein is removed therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of an apparatus which is suitable for use in performing the method of this invention.

FIG. 2 is a sectional view through 2-2 showing a cross-sectional view of the furnace in FIG. 1.

PREFERRED EMBODIMENT OF THE INVENTION I have found a method for manufacturing agglomerates of coal and/ or coal derivatives suitable for charging into blast furnaces, cupolas and the like. The agglomerates are heated to a temperature and are calcined and a major portion of the sulfur contained therein is removed. The heat and material necessary for calcination and sulfur removal are provided by heated relatively fine particles of a desulfurizing agent. The agglomerates which are within a temperature range of about ambient temperature to about 850 F. and particles of a desulfurizing agent heated to at least about 1400 F. are charged into opposite ends of a rotary kiln. The agglomerates and desulfurizing agent pass through the furnace countercurrently to each other. During the countercurrent fiow of the charged materials, a heat exchange occurs at a controlled rate between the agglomerates and the heated particles of the desulfurizing agent. The agglomerates are heated to a temperature of at least about 1400 F. at discharge and the heated particles of the desulfurizing agent are reduced to any temperature below about 1100" F. at discharge. Simultaneously with the heat exchange, the sulfur in the agglomerates reacts with hydrogen (H formed in the furnace as the coal agglomerates are heated to elevated temperatures. The hydrogen reacts with sulfur present as organic sulfur and pyritic sulfur in the agglomerates to produce hydrogen sulfide (H 8). The hydrogen sulfide (H con acts and reacts with the heated particles of the desulfurizing agent to form a sulfide with the material therein. The sulfur is thereby removed from the gas. Free hydrogen gas is reformed which can then react with sulfur in the agglomerates. It can be seen that the hydrogen acts as a vehicle to transport a portion of the sulfur originally in the agglomerates to the heated particles of the desulfurizing agent. Of course, it is not possible to remove all the sulfur from the agglomerates since sulfur is difficult to remove, but the amount removed is sufiicient to reduce the sulfur content in the agglomerates to an acceptable amount. By agglomerates, I mean briquettes, extrusions or pellets of coal and/or coal derivatives formed by charging coal particles and/or coal char to a press and applying pressure thereto at ambient temperature or temperatures of about 300 F. to about 950 F. or forming balls thereof on a balling drum and the like. The method of the invention is particularly adapted to the processing of balls of coal which are formed by a hot balling technique. The technique, which is not part of this invention, includes heating the particles of coal and char separately so that a mixture thereof attains a temperature within the range of about 700 F. to about 850 F. and forming the particles into balls in a balling drum or the like. The heated particles of the desulfurizing agent can be either solid or porous so long as the particles are of a size smaller than the agglomerates and have sufficient surface area available for reacting with H S to thereby remove sulfur from the agglomerates.

As an example of an apparatus which can be used to accomplish the process of the invention, a rotary kiln is shown generally at 10 in FIG. 1. The rotary kiln 10 comprises two concentrically aligned cylinders, an outer shell 11 and an inner apertured tube 12. The shell and tube may rotate in the same direction or in opposite directions. A worm conveyor 15 is fixedly attached to the inner surface of the outer shell 11. A plurality of lifter bars 14 are fixedly attached to the inner surface of the outer shell 11 and are longitudinal to and parallel with said inner surface. The free ends 14a of the lifter bars 14 can be curved to form a cup-like portion. The apertures in the inner tube 12 can be any shape, for example, circular, oval, rectangular, etc. The apertures 13 are sufficiently large to allow the small particles of the heated particles of the desulfurizing agent to pass through and into the inner tube 12 but sufficiently small to retain the agglomerates inside the tube 12. The agglomerates, A, are charged into one end of the inner tube 12 of rotary kiln 10 by any suitable means, for example a conveyor 16. The agglomerates A pass downwardly to the discharge end of the inner tube 12. The agglomerates are discharged into a chamber 12a where they are cooled. The heated particles of the desulfurizing agent, B, are charged into one end of the outer shell 11 by any suitable means, for example a conveyor 17. As the rotary kiln slowly rotates, the heated particles of the desulfurizing agent B are carried upwardly toward the apex of the outer shell 11 by the lifter bars 14 and are also transported in a direction opposite to the flow of the agglomerates. The heated particles of the desulfurizing agent fiow uphill in the kiln. As the heated particles B are lifted toward the upper portion of the outer shell 11, they fall downwardly from the lifter bars 14 through the apertures in the inner tube 12 into the interior of the inner tube 12. A sufiicient amount of the heat particles are retained in the inner tube 12 to form a relatively deep bed therein. The agglomerates flow downwardly in the inner tube 12 through the relatively deep bed of heated particles B of the desulfurizing agent. A controlled rate of heat exchange occurs between the agglomerates A and the heated particles B of the desulfurizing agent whereby the agglomerates A are heated and the particles B of the desulfurizing agent are cooled. Simultaneously, as the agglomerates A lose volatile matter with increasing temperature, hydrogen is formed and desulfurization of the agglomerates A occurs. A portion of the heated particles B falls downwardly through the apertures in the inner tube 12 to the lower portion of the outer shell 11. The heated particles B are transported upwardly in the rotary kiln by the worm conveyor and eventually are discharged from the kiln 10 into hopper 18. The worm conveyor 15 is in spaced relationship with the outer surface of the inner tube 12 to thereby allow the passage of gases fed to the kiln or formed by heating the agglomerates therein. The heated particles B of a desulfurizing agent, for example manganese ores in which a major of the manganese is manganous oxide (MnO), calcined dolomite, calcium oxide (CaO), and magnesium oxide (MgO), smaller in size than the agglomerates A, are heated to a temperature above about 1400 F. and preferably above about 1950 F. to about 2200 F. prior to being charged into the kiln 10 by conveyor 17. The agglomerates A are within a temperature range of about ambient temperature to about 850 F. when charged into the kiln. As the kiln 10 rotates, the agglomerates A and the particles B of the heated desulfurizing agent flow in countercurrent directions to one another.

As shown in FIG. 2, the outer shell 11 rotates in a counterclockwise direction as shown by arrow C, while the inner tube 12 rotates in clockwise direction, as shown by arrow D. Of course, the outer shell 11 and the inner tube 12 can be rotated in the same direction. The apertures 13 are shown as elongated slots and the lifter bars 14 are shown as having curved ends to form a cup-like portion.

While I have shown a rotary kiln with an inner tube 12 having apertures therein, it must be recognized that an inner tube 12 made of screening having appropriate sized openings between the strands forming the screen can be used. The inner tube 12 may also be made up in which portions of the tube 12 are screens and portions are apertured. Then, too, the lifter bars 14 can be attached to the outer surface of the inner tube.

As the agglomerates A and the heated particles B of the desulfurizing agent flow countercurrently to each other, there is a heat exchange at a controlled rate between the two materials. The temperature of the agglomerates A is raised from the temperature at which they are charged into the kiln 10 to not less than about 1400 F. and can be preferably above about 1650 F. when discharged from the kiln. The calcined and desulfurized agglomerates A are discharged from the kiln 10 into a storage bin 12a. The agglomerates A are susceptible to spalling, internal cracking, rupturing or dusting of heated rapidly within a temperature range of about 1100 F. to about 1400" F. I have found that spalling, internal cracking, rupturing or dusting can be virtually eliminated by heating the agglomerates A at a temperature rate not exceeding about 10 F. per minute and preferably about 75 F. per minute through the critical temperature range of 1100" F. to 1400 F. In the process of the invention, the rate of heating the agglomerates is within a temperature range of 1 F. per minute to 10 F. per minute. Generally the heating rate is about 4.0 F. per minute but in no instance exceeds the critical rate of about 10 F. per minute and preferably does not exceed 7 /2" F. per minute. To obtain the full benefits of the controlled heating rate, the particles of the desulfurizing agent can be at a temperature of not more than 1100 F. when discharged from the kiln. Discharging the particles of the desulfurizing agent at a temperature of not more than 1100 F. will prevent a rapid rise in temperature in the agglomerates as they are heated through the sensitive temperature range of 1100 F. to 1400 F. The controlled heating rate of between about 1 F. and about 10 F. is realized.

Generally, all the heat necessary to calcine the agglomerates A is provided by the hot particles B of the desulfurizing agent. However, if necessary, additional heat can be provided by blowing a limited amount of air into the kiln. Since the hydrogen-containing atmosphere is hot, the ox gen in the air will burn thereby providing heat.

The amount of sulfur contained in many coals is about 2%. This amount of sulfur renders the agglomerates undesirable as charge material to a metallurgical furnace. It is, therefore, necessary to reduce the sulfur content of the agglomerates to an acceptable amount. Simple heating of the agglomerates results in the removal of a portion of the sulfur. However, the amount of sulfur thus removed from the agglomerates is insufficient to make the agglomerates a desirable fuel for use in metallurgical furnaces. It is therefore necessary to provide means to remove a suflicient amount of sulfur from the agglomerates to make them acceptable as charge material for metallurgical furnaces. One means is to provide a material which will accept sulfur. Several materials are well known as sulfur acceptors, for example, manganese ore in which a major portion of the ore is manganous oxide, calcium oxide (CaO), manganous oxide (MnO), magnesium oxde (MgO) and calcined dolomite. I therefore provide heated particles B of at least one or mixtures thereof of the above mentioned desulfurizing agents in the rotary kiln to reduce the sulfur content in the agglomerates A to an acceptable amount. As noted previously, the agglomerates A are heated, free hydrogen (H forms in the kiln 10 to provide a vehicle for sulfur transport and to provide an inert atmosphere in the kiln. The sulfur in the agglomerates A reacts with the hydrogen to form hydrogen sulfide (H 8). The hydrogen sulfide in turn reacts with the hot particles B of the desulfurizing agent, for example, manganous oxide (MnO), to form manganese sulfide (MnS) hydrogen (H and some water vapor (H O). It can be seen that the hydrogen (H is regenerated and the sulfur transported from the agglomerates A to the hot particles B of the desulfurizing agent. Of course, it is within the scope of this invention to provide means to add a hydrogen-bearing gas to the atmosphere in the kiln 10 to improve the desulfurization of the a-gglomerates A.

Simultaneously with the transport of the sulfur from the agglomerates A to the heated particles B of the desulfurizing agent, the agglomerates A are heated to a temperature of not less than about 1400 F. and generally above about 1650 F. to about 1950 F. and preferably above about 1950 F. by heat transferred from the hot particles of the desulfurizing agent. It will be noted that the lower calcining temperatures result in agglomerates with medium reactivity rate, and the higher calcining temperature, above about 1950 F., results in calcined agglomerates which have a low reactivity rate when measured by carbon dioxide tests.

Although the agglomerates are heated to temperatures above 1700 F., the coked agglomerates produced by the process are of sufficient strength to resist abrasion and can be transported. It is known that carbonaceous agglomerates heated to temperatures above 1800" F. in those cases where the unit is heated by combustion of fuels containing hydrogen and/or carbon, lose strength because of the reaction with carbon dioxide and water vapor formed by combustion of fuels required to obtain the higher temperatures. Since in the present invention substantially all the heat required for calcination and desulfurization is provided by the heated particles of the desulfurizing agent, no fuel is normally burned. Therefore, carbon dioxide and water vapor are not formed. The introduction of supplemental air to provide additional heat can result in a small amount of combustion products to form. The quantities of the combustion products thus formed do not weaken the coked agglomerates. Since no carbonaceous fuel is fired, carbon dioxide is not formed. The small amount of water vapor formed if air is admitted for supplementary heating is not sufficient to weaken the agglomerates.

The reactivity of coke can be tested as described below. A SO-gram sample is ground to a particle size of 18 x 40. The sample is placed in a quartz tube which is placed in a tube furnace. A nitrogen atmosphere is established in the furnace. The sample is heated to and held at about 1825 F. for the duration of the test. After ten minutes at temperature, the nitrogen atmosphere is replaced with a carbon dioxide atmosphere. The sample at 1825 F. is exposed to the carbon doxide atmosphere for two hours. The reaction tube is removed from the furnace and cooled in a stream of nitrogen. The sample is weighed. The reactivity of the coke is reported as the percent loss in weight of the sample corrected for volatile matter in the coke. It has been found that at temperatures below 1600 F. little reaction takes place between coke and carbon dioxide. At high temperatures, for example above about 2200 F., the reaction is so rapid that cokes made from various coals or admixtures thereof react at essentially the same rate. Between the extremes of the temperature range of about 1600 F. to about 2200 F. various cokes have different reactivity rates.

Of course, the temperature at which the agglomerates are calcined is the highest temperature which is practical and economical to use and to produce agglomerates which have the lowest reactivity rate which is practical while still retaining their strength.

The calcined agglomerates can be cooled to as low as about 200 F. in an inert atmosphere, which can be hydrogen, nitrogen or relatively non-oxidizing gases and mixtures thereof, in a chamber outside the kiln and are then passed to storage or use. A portion of the desulfurizing agent is regenerated on any given cycle by any one of several known methods. The regenerated portion can be recharged into the kiln for reuse.

Of course, a portion of the particles of the desulfurizing agent becomes spent after a time and is regenerated. It is, therefore, necessary to add particles of the regenerated desulfurizing agent; it is also necessary to add particles of unused desulfurizing agent from time to time to replenish that portion which is lost. The particles so added are heated to the desired temperature prior to their addition.

By the use of the described apparatus it is possible to charge about 1.1 tons of agglomerates A of coal containing about 2% sulfur at a temperature of about 700 F. into the inner tube 12 at one end of a rotary kiln and about 2.6 tons of heated particles of manganous oxide at a temperature of about 1950 F. into the outer shell 11 at the other end of the kiln 10. As the kiln 10 rotates, the agglomerates A and heated particles B of manganous oxide will flow countercurrently to each other. The temperature of the agglomerates A will be raised to a temperature approaching 1950 F. and the heated particles B of manganous oxide will be cooled to about 850 F. to about 950 F. The agglomerates A will be charged into a cooling chamber (not shown) wherein an inert atmosphere will be maintained. The heated particles B of manganous oxide will be discharged from the other end of the kiln 10. The total time for the agglomerates A to pass through the kiln 10 wherein they are calcined and desulfurized could be about four hours. The sulfur in the calcined agglomerates will be decreased to acceptable levels. All the hydrogen required for desulfurization can generally be formed during the heating of the agglomerates A.

It will be understood in this specification and claims that wherever percentages are referred to, such percentages are on a weight basis unless otherwise noted.

I claim:

1. An improved method for producing agglomerates of coal and coal derivatives which are characterized by having low to medium reactivity to carbon dioxide at elevated temperatures, wherein said agglomerates are simultaneously calcined and desulfurized in a hydrogen atmosphere by heat exchange from relatively small heated particles of manganous oxide in a rotary kiln comprising an outer shell and an inner apertured tube concentrically aligned with said outer shell and means attached to the inner surface of said outer shell to transport said heated particles of manganous oxide countercurrently to the passage of said agglomerates in said inner tube of said rotary kiln, said apertures in said inner tube being large enough to allow passage of said heated particles of manganous oxide into and through said inner tube but not large enough to allow said agglomerates to pass out of said inner tube, said method comprising:

(a) charging said agglomerates into one end of said inner tube in said rotary kiln, said agglomerates being at a temperature between ambient temperature and 850 F.,

(b) charging said relatively small heated particles of manganous oxide into one end of said outer shell in said rotary kiln, said relatively small heated particles of manganous oxide being at a temperature of not less than 1400 F.,

(c) rotating said rotary kiln to cause said agglomerates to pass to the other end of said inner tube and to pass said heated particles of manganous oxide countercurrently to the fiow of said agglomerates to the other end of said outer shell, said heated particles of manganous oxide being transported to the apex of said outer shell by said means attached to said inner surface of said outer shell, said heated particles of manganous oxide passing downwardly through said apertures in said inner tube to thereby intimately contact said agglomerates therein and subsequently passing downwardly through said apertures in said inner tube to the bottom of said outer shell, said agglomerates being heated at a controlled rate through a temperature range of 1100 F. to 1400 F. while simultaneously being desulfurized by hydrogen in the atmosphere in said rotary kiln and the temperature of said heated particles being reduced to below about 1100 F., and

(d) discharging calcined and desulfurized agglomerates from one end of said rotary kiln and said cooled particles of manganous oxide from the other end of said rotary kiln.

2. The method of claim 1 in which the agglomerates are heated at a controlled rate of between 1 F. per minute to 10 F. per minute in step (c).

3. The method of claim 1 in which the agglomerates are heated at a controlled rate of between 4 F. per minute to 7 /2 F. per minute in step (c).

4. The method of claim 1 in which the heated particles of manganous oxide in step (b) are solid. I

5. The method of claim 1 in which the heated particles of manganous oxide in step (b) are porous.

6. The method of claim 1 including the additional step (e) of cooling the agglomerates to a temperature below 500 F. in a chamber having an inert atmosphere.

7. The method of claim 1 in which the agglomerates of step (a) are heated to a temperature range of 1950 F. to 2200 F. in step (c).

References Cited UNITED STATES PATENTS 3,640,016 2/1972 Lee et al 441 R 2,966,400 12/1960 Lykken 442 X 3,018,227 1/1962 Baum et al. 441 R 3,101,303 8/1963 Batchelor et a1. 201-17 CARL F. DEES, Primary Examiner U.S C1. X.R.