US 3185635 A
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Description (OCR text may contain errors)
y 25, 1965 A. CREGLOW 3,185,535
METHOD FOR PRODUCING METALLURGICAL COKE AND METAL-COKE FROM BOTH COKING AND NON-COKING COALS Filed May 10, 1961 4 Sheets-Sheet 1 mmvroa 38 LORAN A. CREGLOW ATTORNEYS May 25, 1965 A. GREG LOW 3,185,635
METHOD FOR PRODUCING METALLURGICAL COKE AND METAL-COKE FROM BOTH COKING AND NON-COKING GOALS 4 Shets-Sheet 2 Filed May 10, 1961 INVENTOR. LORAN A. CREGLOW BY Mfamgg m *WM ATTORNEYS May 25, 1965 1.. A. CREGLOW 3,185,635 METHOD FOR PRODUCING METALLURGICAL COKE AND METAL-COKE FROM BOTH COKING AND NON-COKING GOALS Filed May 10. 1961 4 Sheets-Sheet 5 INVENTOR.
LORAN A. CREGLOW ATTORNEYS United States Patent 3,185,635 METHOD FOR PRODUCING METALLURGICAL COKE AND METAL-COKE FROM BOTH CGKING AND N ON-COKING COALS Loran A. Creglow, Salt Lake City, Utah, assignor to United States smelting Refining and Mining Company, Boston, Mass, a corporation of Maine Filed May 10, 1961, Ser. No. 113,307 27 Claims. (Cl. 202-15) This application is a continuation-in-part of application S.N. 832,204 now abandoned.
This invention relates to a novel and improved method and apparatus :for carbonizing coal, and more particularly, to a novel and improved method for providing coke from poorly coking or normally non-coking coals as well as from moderately and strongly coking coals, and which is also suitable for the production of an integrated ore-fuel charge for use in blast furnaces.
The production of coke normally comprises the heating of a suitable coal in an oven and in the presence of a non-oxidizing atmosphere. The usual coking ovens are often referred to as slot-type ovens, being narrow box-like compartments arranged side by side in batteries of perhaps ten to one hundred ovens. The ovens are commonly built of refractory brick and are separated by a flue within which a gaseous fuel is burned .to heat the oven walls and thus, in turn, heat the coal contained in the ovens. The basic coking operation usually comprises placing the coal in a hot oven and sealing the oven. The oven is then fired for a relatively long time, on the order of sixteen to twenty hours, depending on its dimensions, until the coal has been converted to coke. The coke is then removed from the oven and quenched to cool it below the ignition point.
Another method of producing coke involves the use of what is commonly referred to as a beehive oven. The beehive oven is a round refractory structure with a dome top, quite similar in shape to the traditional beehive. With the oven hot, a batch of coal is charged in through a top opening and leveled off Ito give a bed of around one foot in depth. Air is admitted beneath the dome to burn the gas and the volatile tars given 011 as the coal carbonizes. The burning of these byproducts supplies the heat for carrying on the coking operation. Heat travels downwardly through the bed of coal. When the coal is completely carbonized, the coke is raked out and a new charge of coal is dumped into the oven. There is of course no recovery of gaseous or tar byproducts. For this reason beehive ovens have generally been replaced Iby the byproduct slot ovens described above. However, in recent years there appears to be slight revival of the beehive ovens. This seems to be due to the much lower capital investment for a beehive plant and to reduce value of byproducts as a result of lower cost production of some coal tar chemicals from petroleum.
The usual coking processes may be generally classified in two groups, the high temperature process wherein the coal is heated to a temperature of about 1000 C., and the low temperature process wherein the coal is heated to a range of between 400 C. to 600 C. The high temperature process is generally used to provide a strong, coherent coke suitable for the metallurgical industry and normally requires a good coking coal. A good coking coal may be defined as a coal having the characteristic of caking, which causes the coal to melt or fuse together when heated. A non-coking coal, when heated in a closed container, normally forms a char or powdery residue, which while it may provide domestic fuel or be used in the chemical industry is not suitable for use in the metallurgical industry. It has been a practice in the past to combine strongly coking coals in small amounts with poorly coking coals in order to provide a better blend for making coke. The low temperature method often has been suggested for processing non-coking or poorly coking coal to provide a char for domestic use or for blending with swelling coking coals. In other cases low temperature chars have been agglomerated with tar or pitch in the form of briquettes which were then carbonized at high temperature. In still other cases the low temperature method may be used with a particular coal product which has good coking characteristics but which is not physically suitable for charging into high temperature coke ovens, such a product being provided by the fines which result from breaking and cleaning of the coal. These fines are recovered from the wash Water of the breaking and cleaning process by means of the flotation process.
The reserves of good coking coals available in the United States are, of course, diminishing. On the other hand, there are largely reserves of poorly coking or normally non-coking coals which have heretofore been generally unsuitable for use in providing a good coke, and particularly have not been suitable for providing metallurgical grade coke for use in blast furnaces. An added inducement to the development of efficient processes for providing good coke from poorly coking or non-coking coals is that these coals usually contain a relatively large amount of tars and oils which are dis tilled oif when the coals are carbonized. The byproduct of coal tar contains a multitude of organic chemicals and is generally refined for production of material such as creosote for wood preservatives and pitch for painting and coating of roofs.
The processing of poorly coking or non-coking coal by the low temperature process usually involves a continuous-type furnace wherein the coal is received at one end and the coke is removed from the other end, with the coal constantly moving through the furnace. This is in contrast to the high temperature method, wherein batch ovens are normally used. The continuous process is, of course, to be desired in that usually a higher production rate can be achieved, thus resulting in lower cost of processing. One of the most diflicult handicaps to successful continuous low temperature coking is the tendency of even relatively poor coking coal to soften and become plastic at temperatures in the range of from 350 C. to 500 C. To overcome this handicap, it is in some cases proposed to treat the coal to reduce or substantially eliminate its coking characteristics prior to feeding the coal into the oven. This treatment of the coal may involve oxidation of the coal by heating the same for a long period in the presence of air. This general problem of preventing sticking of the coal as it passes through a low temperature continuous oven has, to a large extent, rendered the low temperature process uneconomical.
The processing of coal fines presents a problem of forming the fines into a suitable mass, such as a briquette, prior to carbonizing. Heretofore it has been usual to form the fines into briquettes or the like utilizing an organic binder such as asphalt or coal tar pitch. However, in the ca-rbonizing process the binder softens and causes the briquettes to become distorted and stuck together, forming a mass which will not pass through the oven. This sticking of the briquettes or the like may occur during the initial heating period of a high temperature process or during a low temperature process of carbonizing. Accordingly, there has not heretofore been provided a fully satisfactory continuous process for carbonizing poorly coking or non-coking coals or for canbonizing briquettes or the like provided from the fines of either coking or non-coking coals.
It is, therefore, the primary object of this invention to provide a novel and improved continuous high temperature process for producing coke from coal fines which may be recovered from what have heretofore been relatively valueless waste products of coal preparation plants, for example, the washery slurries that are usually discarded or stored in slurry or slush ponds.
It is a further object of this invention to provide a novel and improved high temperature process for carbonizing coal which will permit the use of either a coking or a noncoking coal and which, in the case of a poorly coking coal, will permit it to be directly processed without pro-treatment to reduce or eliminate its coking properties.
It is another object of the invention to provide a novel and improved coking process which will have an improved yield of coke and will have a relatively high return of byproducts so as to provide a marked improvement in economy of processing.
It is still another object of this invention to provide novel and improved apparatus for practicing certain aspects of the process of this invention.
it is a still further object of this invention to provide a novel and improved ore-coke pellet providing an integrated ore-fuel charge for blast furnaces whereby the entire charge of fuel and ore for a furnace may be provided by such pellets; included within this object is the provision of a novel and improved method of providing an integrated ore-fuel charge for a blast furnace.
Other objects will be in part obvious, and in part pointed out more in detail hereinafter.
Briefly and in one aspect thereof, the novel and improved process of this invention comprises forming finely divided non-coking coal into porous pellets in the presence of water and an inorganic binder of Wyoming bentonite. The pellets are then partially dried, under conditions which will not cause ignition of the pellets and will not cause oxidation of the coal in the pellets. The pellets are then passed through a continuous shaft retort which is externally heated, and a continuous stream of a crackable hydrocarbon gas such as methane is passed through the retort in a direction opposite the movement of the pellets. This stream of hydrocarbon gas is supplied in addition to any hydrocarbon gas given off by the coal itself during the high temperature coking of the pellets. The pellets are rapidly heated at a rate on the order of C. per minute to a temperature between 1150 C. and 1300 C. During the carbonizing of the coal, the counterfiowing hydrocarbon gas, at least in part, penetrates the porous pellets and is substantially entirely cracked to provide carbon deposited within the porous pellets and deposited on the exterior thereof. The cracking of the gas also provides hydrogen which is removed as a valuable by-product such as for the production of ammonia. The carbon within the pellets and adhering to the exterior thereof assists in providing a hard, strong coke. At the same time, the carbon added to the pellets by the hydrocarbon gas increases the yield of the process by a material amount. The process permits the use of either coking or non-coking coals to provide the pellets and at the same time eliminates the problem of the coal becoming fused and stuck together during the carbonizing step, thus permitting a continuous process with resulting economies in operating costs by reason of increased productivity and reduction in capital equipment. A fuller understanding of the abovedescribed aspect and advantages as well as other aspects and advantages of the invention may be had by reference to the following description when taken in connection with the accompanying drawings, in which:
FIG. 1 is an elevational view of the apparatus for forming pellets for use in the process of this invention;
FIG. 2 is an end view of the apparatus of FIG. 1;
PEG. 3 is an enlarged elevation View, partly in section, of a pelletizing drum forming a portion of the apparatus of FIG. 1;
FIG. 4 is an enlarged elevational view, partly in section, of a pellet conditioning drum forming a portion of the apparatus of FIG. 1;
FIG. 5 is a fragmentary elevational view, in section, of the upper portion of a continuous shaft retort of a type suitable for use in the practice of the process of this invention;
FIG. 6 is a fragmentary elevational view, in section, of the lower portion of the retort of FIG. 5; and
FIG. 7 is a schematic flow sheet illustrating the process of this invention.
The process of this invention first comprises the forming of coal fines into pellets, with the term pellet being used for the purposes of this invention to define an agglomerate or mass of coal fines which is preferably, although not necessarily, of generally spherical shape. The fines may be provided from the waste products of coal processing plants or by reducing lump coal to the desired particle size by crushing or other suitable means. The coal fines are preferably provided in the size range of percent minus 20 mesh to 25-30 percent minus 200 mesh. The size of the fines necessary to permit pelletizing of the coal will vary, it is believed, generally with the rank of the coal. In other words, a hard, low volatile, bituminous coal or an anthracite may require a finer particle size for pelletizing in that the coal is relatively hard and abrasive and does not attain any appreciable degree of plasticity until the particles are reduced to a fine size. On the other hand, a soft bituminous or lignite coal may be sufliciently plastic with only a moderate percentage of fines. The actual size range for any given type coal may therefore have to be determined by experiment in order to ascertain the optimum particle size for easy and efficient pelletizing.
With reference to FIG. 1, the finely divided coal particles are introduced into a mixer or mill 10 and therein are blended with water and with an inorganic binder which will not be decomposed by the heat of subsequent coking. The amount of water present in the mix should be an amount to give a plastic and moldable mass. It has been found that the size of the pellets formed is generally controlled by the amount of water present; that is, a relatively dry mix will provide small pellets, while the addition of water will provide larger pellets. While the amount of water necessary to add to the fines varies with the moisture content of the fines as Well as the type of coal, it is believed that in most cases the total moisture present in the mixture of coal and binder should be in an amount from 20-30% by weight of the wet mix. It might here be noted that where the coal fines are obtained by a flotation process and then dewatered by filtration, the resulting coal filter cake may contain a sufficiently large amount of water so that it may be used without necessitatmg the addition of further amounts of water. In the case of a lump coal which is ground dry to the proper size for pelletizing, it will be necessary to add water to the pelletizmg mix.
The inorganic binder introduced into the mixing rum 10 is preferably one of the materials commonly referred to as bentonite. For the purpose of this invention, bentonite is defined as a material composed mainly of the clay mineral montmorillonite. Bentonites may be divided into two general classes: (1) those which will absorb relatively large quantities of water, swelling greatly in the process, and which remain in suspension in thin water dispersions; and (2) those that absorb slightly more water than ordinary plastic olays' or fullers earths and do not swell noticeably and settle relatively rapidly in thin water disperslons. In the practice of the present invention it is preferred to use the first or swelling class of bentonites, which is superior to the non-swelling class in dry strength. A bentonite found in the Wyoming-South Dakota district of the United States and commonly referred to as Wyoming bentonite is the preferred material for use as a binder in this invention. It should be noted that the term swelling, as applied to the clay binder, is used herein in the sense that the term is used in ceramic technology, that is to describe a clay which expands or swells when immersed in water. Therefore, the terms swelling clay or swelling bentonite, as used herein, does not include the bloating clays which, in accordance with ceramic technology, are clays which expand when heated to the plastic state, the expansion being caused by the release of gases within the clay body.
In accordance with the invention, a relatively minor percentage of swelling bentonite is added to the coal and water in the mixing drum 10, with the binder being present in an amount of at least 1% by total weight of the mix. The upper limit of the percentage of bentonite is not necessarily critical from the standpoint of the process of this invention. However, it must be realized that ben tonite will add ash to the resulting coke in direct proportion to the amount of bentonite used in the mixture. Inasmuch as the strength of the pellets produced will generally increase with increased amounts of bentonite, a reasonable compromise must be struck between the strength of the pellets and the undesired added ash in the coke. It has been found that the bentonite should be present in an amount of at least 1% by the total weight of the mix with a preferred amount being approximately 2% by weight of the dry coal in the mix. This ratio of bentonite provides a strong pellet while at the same time maintains the ash content of the coke at a satisfactorily low level.
It has been found that in certain cases it may be desirable to add a very minor amount of a disperser to the mixture of coal, bentonite and water in order to assure that the bentonite is in a dispersed condition throughout the particles of coal. It has been found that if salts are present in the pelletizing mix and cause flocculation of the bentonite, the pellets after being formed and dried have substantially reduced strength. While it may be unusual that a coal or the water used in the pelletizing mix contains enough flocculators to seriously affect the strength of the pellets, it may be advisable as a precaution to use a minor amount of disperser in the mix. The disperser may be material such as lignosulfonate, sodium silicate, sodium hydroxide, or other suitable materials. Lignosulfonate is preferred in View of its low cost and the fact that it does not add to the ash content of the coke. It has been found that the addition of lignosulfonate as a disperser in an amount of approximately .2% by Weight of the dry mix assures good dispersion of the bentonite.
With reference to FIG. 1, the mixture from the mixing drum is fed into a pelletizing drum 12 by means of a vibrating feeder or the like 14 disposed adjacent one end of the mixing drum 10 and at least partially extending into the leftward end of the pelletizing drum 12 as viewed in FIG. 1. The pelletizing or balling drum 12 comprises a cylinder 16, which as shown in FIG. 3, it mounted on rollers 13 for rotation about its longitudinal axis. The inlet or leftward end of the drum 16 as viewed in FIG. 3 is positioned slightly higher than the discharge or rightward end of the drum so as to incline the axis of the drum to facilitate passage of material through the drum. The pelletizing drum 16 is provided at its leftward or higher end with a helical reverse flight 2% extending around the inner wall of the drum. More specifically, the reverse flight 20 comprises a member having a generally V-shaped cross section which is arranged in a helix around the inside of the drum and secured thereto. The flight is relatively low; for example, in a drum thirty inches in diameter and sixty inches long, a suitable flight had a height of approximately three-eighths inch. The flight extends only partially over the length of the drum, and more specifically, as shown in FIG. 3, extends for approximately one-third the length of the drum and in this length angularly extends approximately one and three-quarter turns or approximately 630. The length of the flight as well as its pitch and percentage of extension over the length of the drum may be varied, and particularly the flight 6 may be extended up to substantially the full length of the drum while still obtaining proper operation of the drum. The pelletizing drum is rotated in a direction opposite that which would cause the flight 20 to feed the pelletizing mixture toward the discharge or lower end of the drum.
In other words, as the drum is rotated, the inclination of the drum tends to cause the pelletizing mixture to flow toward the lower discharge end. However, the reverse flight 20 tends to move the mixture toward the higher inlet end of the drum. The resulting action causes the mixture to be violently tumbled adjacent the inlet end of the drum, with the result that pellets are formed. While the exact reason for the formation of the pellets is not fully understood, it is believed that the pellets are formed by the compacting of the mixture during the violent tumbling thereof both by engagement of agglomerates of the mixture with each other and with the adjacent surfaces of the inner wall of the drum and the flight. When the pellets have formed a sufficient size, they will roll over the flight and out of the lower end of the drum. With a pelletizing drum having the dimension specified above and rotated at approximately 40 rpm, and with the coal mixture being continuously added to the inlet end of the drum, the pellets will grow until they attain a size of inch or larger before they pass over the flight and are discharged from the lower end of the drum. It has been found that by the use of the reverse flight pelletizing drum the production of the desired size of pellet may be as high as approximately In other words, only about 15% of the pellets produced will be either undersize or oversize and will have to be recirculated through the mixer and pelletizing drum. While the pelletizing drum described above provides very satisfactory results, it will be understood that other suitable means may be utilized to provide the desired pellet.
It has been described above that the water necessary to obtain a proper pelletizing mix is added in the mixing drum prior to discharge of the mix into the pelletizing drum. However, it should here be noted that it is preferred that at least the final portion of the water to be added to the mix be introduced to the mix while the same is in the pelletizing drum. In this manner, the proper proportion of Water may be controlled more accurately by visually observing the ease and speed at which proper size pellets are formed in the pelletizing drum.
With further reference to FIGS. 1 and 2, the pellets, when discharged from the pelletizing drum, fall into a chute 22 which discharges the pellets into suitable sizing means 24 for passing those pellets which are over a certain size and for bypassing undersize pellets onto a conveyor 26 for return to the mixing drum 1t) and reprocessing through the mixing drum and pelletizing drum. The pellets passed by the sizing means 24 are fed into a pellet conditioning drum 28, more clearly shown in FIG. 4, and which in accordance with this invention comprises a generally horizontal rotatably mounted cylinder, the wall of which is corrugated to provide it with an internalspiral or helical groove having an arcuate cross section. As the conditioning drum is rotated, the pellets fed thereinto will be conveyed and tumbled along the helical groove formed by the corrugation of the wall of the drum, from the rightward inlet end as viewed in FIG. 2 to the leftward discharge end. As the pellets are passed through the conditioning drum 28, a flow of air is passed through the drum by a fan 30 having a heater 32 located adjacent the discharge end of the drum so as to slightly dry the surfaces of the pellets to preclude sticking of the pellets to the inside of the drum. However, it should be noted that substantial drying of the pellets during their passage through the pre-dyer is to be avoided since in this case the pellets may tend to develop cracks. The conditioning drum 23 performs the useful function of rounding the pellets discharged from the pelletizing drum. This rounding has been found preferable as in some cases the pellets discharged from the pelletizing drum are generally ovoid or disc shape. However, after the passing along the helically grooved wall of the condi tioning drum :28 the pellets become smooth and more nearly spherical in shape.
As the pellets are discharged from the conditioning drum 28, they drop onto suitable sizing means 34 which separates the pellets over a predetermined size and returns the same by suitable means (not shown) to the mixing drum. The properly sized pellets are then fed onto a converyor 36 which, as shown in FIG. 1, comprises a perforated endless belt or screen 38, the upper flight of which passes over a plurality of air ducts 40 connected to a manifold 42 which is suitably connected to a source (not shown) of warm, pressurized air. As the pellets are carried along by the conveyor in a leftward direction as viewed in FIG. 1, warm air is exhausted through the ducts 40, through the screen 38, and thence upward through the pellets for drying of the same. The wet pellets after being formed will develop strength as the water is removed therefrom. It has been found that removal of water to the extent that the pellets contain below 3% moisture will result in a dry pellet with sufficient strength to be handled and processed without breakage or undue degradation by attrition. It has been found that pellets provided in accordance with the process of this invention will have a drop strength in many cases exceeding that of natural lump coal of a comparable size.
With respect to the drying of the pellets, the conditions under which the pellets are dried will be dependent upon the type of coal utilized in the preparation of the pellets. Generally speaking, when a poorly coking coal is utilized, the drying of the pellets must be carried out in a manner to assure that oxidation of the coal in the pellets will not occur to any substantial extent. If the coal of the pellets made from poorly coking coal is oxidized, during the drydog operation or otherwise prior to the coking of the pellets, the resulting coke pellet will have a much reduced strength and may, during the coking operation, break up into a pulverulent char, which is not suitable for metallurgical furnaces. On the other hand, in the case of pellets manufactured from moderately or strongly coking coal, the coal in the pellets must be oxidized in order to prevent the pellets from fusing together during the high temperature coking operation. It has been found that the determination of the requirement for either preventing oxidation or providing oxidation of the coal pellets can be made with reference to the free swelling index of the coal utilized. The value of the free swelling index of the coal is hereby defined as that obtained according to the ASTM Standards on Coal and Coke published in September of 1959. A specific description of the process involved in determining the free swelling index may be had by reference to Standard Method of Test for Free-Swelling Index of Coal, ASTM Designation: 13720-57.
It has been found that pellets made from coal having a free swelling index of approximately 4%. or less will provide good strong coke pellets so long as the coal in the pellets is not oxidized, while the coal in the pellets made from coal having a free swelling index of greater than approximately 4 /z must be oxidized. This requirement of the oxidation of coal pellets made from coals having a free swelling index of greater than approximately 4 /2 may be satisfied by oxidizing the coal in the pellets prior to coking or by compounding the pellets with an internal oxidizer which will during coking, even in a non-oxidizing atmosphere provide oxygen to oxidize the coal in the pellets during the carbonization thereof. The aspects of preoxidizing the coal pellets or of compounding the pellets with an internal oxidizer will be dealt with in more detail herein after.
Turning back to the provision of coal pellets from coals having a free swelling index of approximately 4 /2 or less, the drying of such pellets, following the pelietiz'ing opera tion, may be achieved without oxidation of the coal by two general processes. The pellets may be dried under heat in an atmosphere which is non-oxidizing, or the pellets may be dried in air so long as the temperature and time of heating is controlled. When the pellets are dried in air, it has been found that the temperature must be maintained below approximately 150 C. However, if the pellets are dried in a neutral or reducing atmosphere a higher temperature could be used.
It has been found that when the green coal pellets formed in accordance with the invention are held in air from eight to twelve hours at approximately 160 C., prior to coking, the resulting coke pellets will be relatively weak and generally unsuitable for use as metallurgical coke. On the other hand, it has been found that when the same green coal pellets are dried for the same period at approximately C. prior to coking the resulting coke pellets are satisfactory in strength for metallurgical use. It has been found that optimum results may be achieved by forcing a relatively large volume of warm air through a bed of coal pellets and that the time of drying is dependent upon the volume of air force through the bed rather than the temperature of the air. For example, it has been found that wet pellets fabricated in accordance with this invention and arranged in a bed approximately six inches deep can be dried in approximately thirty minutes by air having a temperature of approximately C. passed upward through the bed at the rate of approximately 300 cubic feet per minute per square foot of bed area. The pellets will not ignite or oxidize to any appreciable extent when exposed to such a moving current of air having a temperature of approximately 130 C. However, if the pellets are placed in an open topped container while at this temperature or even somewhat lower, they may soon begin to shoulder and give off a pungent smoke. Therefore, it is preferable, if not necessary, to cool the pellets discharged from the end of the conveyor 36, preferably down to a temperature of 40 C. to 50 C., before the pellets are stored. This cooling may be accomplished in a variety of ways, one of which may be the provision of cooling air at the discharge end of the conveyor 36 so as to cool the pellets prior to their removal from the conveyor. This cooling is only necessary if the pellets are to be stored for any appreciable time prior to carbonization. In the event that the pellets are to proceed directly to the carbonization step following their drying, then cooling may not be necessary and in fact may be undesirable.
A very economical way of drying the pellets is to utilize the waste heat from the coking step. For instance, the waste products of combustion of the fuel used for heating the retort are at a temperature around 1000 C. They consist mainly of carbon dioxide and nitrogen with a very minor percentage of oxygen. In a large scale operation, this gas may be diluted with air to bring the temperature down to about C. This warm gas may then be blown through a bed of moist coal pellets contained on a travelling screen belt conveyor to dry the pellets.
With regard to the fabrication of pellets compounded from coal having a free swelling index of greater than approximatey 4 /2 preoxidation of the coal in the pellets may be most easily accomplished by heating the pellets in air at a temperature and for a time sufficient to accomplish the desired oxidation of the coal in the pellets. It has been found that the coal pellets made from the mod erately to strongly coking coals can be sufiiciently oxidized by passing a stream of air at a temperature of from C. to 220 C. through a bed of pellets for 15 to 30 minutes. The exact time and temperature utilized will vary somewhat with the coal utilized. Generally speaking, the longer times and high temperatures are necessary with the coals having higher free swelling indexes. The exact time and temperature relationship necessary to provide sufficient oxidation should be determined empirically for the specific coal used. It will be noted that the preoxidizing of the coal is accomplished after formation of the pellets and preferably during the drying of the pellets. Attempts to oxidize the coal prior to forming the same into pellets has not resulted in a satisfactory pellet.
Following the drying step, and any necessary preoxidizing of the coal in the pellets, the pellets may be fed into a continuous oven for coking. Generally speaking, an oven suitable for use in the process of this invention comprises an elongated hollow shaft or retort through which the coal is moved during the coking process. The shaft or retort may be externally heated, and the interior of the retort sealed against entrance of air. In a vertical shaft oven, the coal is introduced at the top of the oven and feeds by gravity through the retort to exit at the lower end of the oven as coke. Preferably an initial preheating level should be provided in the oven to raise quickly the temperature of the incoming coal pellets to within the range of from approximately 250 C. to 450 C. The initial preheating level or low temperature coking portion of the oven provides for distillation of the volatiles of the coal which may be then collected and condensed to provide valuable lay-products. After leaving the low temperature zone of the oven, the coal p'as'ses through a high temperature level or portion of the oven wherein the temperature is, for example, approximately 1200 C. The coal is passed through the shaft in the high temperature level of V the oven at a rate sufiicient to assure that when the coal reaches the lower end of the shaft it will have been coked.
A continuous shaft oven suitable for use in coking pellets of this invention is shown in FIGS. and 6. The oven comprises a hopper 50 for receiving coal such as in the pellet form heretofore described. The coal is fed from the hopper through a pipe 52 to an elongated cylindrical retort 54. The retort 54 in the specific embodiment comprises a pair of elongated Carbofrax tubes joined end to end. Carbofrax is a high grade silicon carbide refractory of at least 85% 82C. The retort is received in radially spaced relation within a housing having an upper section 56 and a lower section 58. Both the upper and lower portions of the oven housing are lined with refractory material 60. The upper and lower portions 56 and 58 are further sealed from each other by means of refractory material to separate the oven into a low temperature portion corresponding to the housing section 56 and a high temperature portion corresponding to the housing section 58. As seen in FIG. 5, the upper end of the retort 54 is sealed while the lower end is open to provide for passage of coke downwardly and out of the lower section 58 of the oven and into a collector pipe 64 leading to a coke extractor 66 shown in FIG. 6. The coke extractor comprises a hollow metal housing 68 in which is mounted a pair of paddle wheels or the like 70 disposed adjacent the lower end of the pipe 64. The housing 68 is sealed against the entrance of air and is provided at its lower end with means such as the weighted ball 72 for permitting coke to move out of the housing for depositing in a suitable receptacle 74. A poke rod 76 slidably extends through a seal in the housing 68 for movement generally coaxially into the pipe 64 for breaking up undesirably large masses of coke which might impede flow through the oven. i
Returning to FIG. 5, the upper portion 56 of the oven is provided with heating means, such as the gas burner '78, for externally heating the upper portion of the retort 54. A flue 86 is provided on the upper section 56 externally of the retort for exhaust of the products of combustion of the burner. The lower oven portion 58 is provided with gas burners 82 or the like for externally heating the lower high temperature portion of the retort. The lower portion 58 is also provided with a flue 87 externally of the retort for exhausting the products of combustion of the burners 82. The refractory lining 60 of the lower portion 58 of the oven is sealed about the lower end of the retort 54 to provide an enclosed heating area around the lower portion of the retort.
In the operation of the oven as shown in FIGS. 5 and 6, coal in the form of pellets fabricated in accordance with the invention and in the manner heretofore described are placed in the hopper 50 and transferred to the retort 5d. The retort is preferably initially provided with a starting bed of metallurgical coke and is purged with a suitable atmosphere such as nitrogen. The pellets are removed at a predetermined rate from the lower end of the pipe 64 by means of the rotation of the paddle wheels '70 at a predetermined speed. The pellets flow smoothly downwardly through the column formed by the retort and the pipe 64, passing through the low temperature zone corresponding to the upper portion 56 of the oven and subsequently through the high temperature zone corresponding to the lower portion 58 of the oven. As the coal pellets are passed through the low temperature zone, distillation of the volatiles of the coal is provided with these by-products passing outwardly of the retort through the pipe 83, whereupon they may be condensed by suitable means (not shown). The pro-heating of the coal in the upper zone of the oven assures that the volatiles will not condense upon the incoming cold coal which might cause the coal to become stuck together in a semi-plastic mass and impede the desired flow downwardly through the retort. In this connection, it has been found that the temperature within the low temperature zone of the oven should preferably be at least 250 C. as measured adjacent the point where the coal enters the oven. On the other hand, if the temperature in this region of the oven is too high, it may cause softening and sticking of the coal. With a temperature within the range of from 250 C. to 450 C., as measured adjacent the entrance of the coal into the retort, it has been found that condensing of volatiles on the incoming coal may be eliminated while at the same time the coal is rapidly preheated without causing softening or sticking of the coal. As the coal passes downwardly through the retort 54 and into the high temperature zone of the oven, the temperature of the coal is raised to within the range of from 1150 C. to 1300" C. It is in this high temperature zone of the oven that the coking process is completed to form coke pellets of high strength.
It might here be noted that in spite of the relatively intense thermal shock that the coal undergoes on entering the retort, when the coal is in a pellet form, in accordance with the teachings of this invention, substantially all of the pellets remain intact and relatively few are cracked. It is believed that this high resistance to thermal shock is because of the relatively loose compacting of the pellets as compared to the compacting of briquettes. It is believed that this also makes possible the use of a rapid heating rate. For example, a coal pellet made in accordance with this invention may be heated to a coking temperature of 1200 C. in one hour or less and rates of 2200 C./l1our have been utilized with satisfactory results.
Another aspect of the invention of providing coke pellets from poorly coking coal having a free swelling index of less than 4 /2 is concerned with contacting the coal pellets with a crackable hydrocarbon gas during the high temperature coking of the pellets. With reference to FIG. 6, a valved conduit 86 is connected to the housing 68 of the coke extractor and is adapted to be connected to a source of pressurized crackable hydrocarbon gas for passage of the gas upwardly into and through the pipe 64 and retort 54 and then outwardly through a valved conduit 88, which as shown in FIG. 4 is connected to the top of the retort. As the gas is passed upwardly to the retort, it will be dissociated into carbon and hydrogen. The carbon will be deposited on and/or in the coal pellets to increase the free carbon content thereof and thus the yield of the process. The hydrogen provided by the dissociation of the gas will be passed off, with the volatiles of the coal, from the upper portion of the retort whereupon it may be separated from the coal tars and the like and effectively utilized, such as for the production of ammonia. It has been found that in order to provide a strong coke pellet from coal having a free swelling index 1 1 weak and easily crumbled or in some cases the pellets may stick together at their points of contact and impede their passing through the retort.
It is, of course, realized that during the coking of the pellets, the coal will give off dissociable hydrocarbons. However, it has been found that the hydrocarbons volatilized from the coal are not sufiicient in quantity to accomplish the desired result. Accordingly, a stream of dissoeiable hydrocarbon gas is passed through the retort in counter flow relation to the coal passing through the retort with this gas being separate from and in addition to any such gas volatilized from the coal in the high temperature zone. The amount of gas which must be passed through the retort will vary depending on the type of coal being used and the carbonizing temperature. F or instance, a low rank coal with a free swelling index of l to 1 /2 will require a large volume of gas and generally a higher coking temperature to produce a strong coke pellet than will a coal having a free swelling index of, say 3 /2 to 4. The volume of volatilized gases given off by the coal may range from a few thousand cubic feet up to more than ten thousand cubic feet per ton of coal. However, the hydrocarbon content of the volatilized gases generally is a minor constituent, varying from about 30% of the volume in the low temperature range to about 15% in the high temperature zone. It is presently believed that the additional hydrocarbon gas introduced should be between 5,0G to 10,000 cubic feet per ton of coal being processed. Depending on the type of coal being used, the amount of added dissoeiable hydrocarbon gas should be varied until the desired strong pellets are achieved. It is conceivable that conditions might prevail in which the amount of dissociable hydrocarbon gas introduced into the bottom of the retort might be less than the total amount of gas volatilized from the coal in the high temperature zone. However, in all cases the amount of additional hydrocarbon gas introduced would be substantially greater than the amount of crackable hydrocarbon gases derived from the coal during high temperature coking. The crackable hydrocarbons which volatilize from the coal while the coal pellets are in the low temperature zone of the retort will not be cracked or dissociated and will pass off with the oil gas through the pipe 88. On the other hand, essentially all of the crackable hydrocarbons volatilized in the high temperature zone of the retort will be cracked caused by the high temperature in this zone. If desired, the crackable hydrocarbon volatilized in the low temperature zone of the retort may be utilized in providing the additional crackable hydrocarbon gas at the bottom of the retort.
As noted above, when the hydrocarbon gas dissociates into carbon and hydrogen, free carbon is deposited within the porous pellets and is deposited on the surfaces of the pellets. This free carbon in the presence of the high temperatures of the oven becomes graphitized, at least to some extent, into a hard, strong form of carbon that adds to the strength and hardness of the coke pellets. Also, of course, the added carbon becomes an integral part of the coke produced by the oven and substantially increases the yield obtained from a given quantity of coal. The extent of graphitizing of the carbon depends on the temperature in the oven as well as the time the carbon is exposed to high temperature. Accordingly, the carbon will be graphitized to a relatively large extent at the higher portion of the preferred temperature range of the high temperature zone. The hydrogen released by the dissociation of the gas provides an atmosphere for the entering coal pellets in the lower temperature zone which is advantageous in enhancing the coking properties of poorly coking coals. Also, as the hydrocarbon gas enters the retort, it engages the hot coke leaving the retort and cools or dry quenches the coke. The gas, in turn, is quickly heated by the coke to a temperature approaching the coking temperature by the time the gas passes through the pipe 64 of FIG. 5 and reaches the high temperature zone of the retort. As the gas passes upwardly through the retort, it is believed that it assists, at least to some extent, in distributing heat across the retort, thus improving uniformity of heating and efficiency of the retort. It should also be noted that it is believed that the rate of flow of the erackable hydrocarbon gas in counterflow relation through the retort, at least to some extent, affects the permissible low temperature limit in the low temperature zone of the retort. The volatiles which are given off in the low temperature zone may condense as they pass outwardly through the retort. This could be particularly true where the temperature at the upper end of the retort was at the lower end of the range. However, when the stream of crackable hydrocarbon gas is passed through the retort at an appreciable rate, the stream of gas remaining after dissociation of the original gas assists in sweeping out of the upper end of the retort any condensed volatiles which are in mist form and tends to prevent these condensed volatiles from falling back upon the incoming coal pellets. Thus, the minimum permissible temperature in the low temperature zone of the retort may, at least to some extent, be a function of the rate of flow of gas into the bottom of the retort. While there is an element of cost involved in utilizing a eountertlow of hydrocarbon gas as aforedescribed, the cost is minimized by the fact that the hydrogen may be collected for its valuable use in the production of ammonia or, if desired, for providing heat for the oven as well as other obvious and known uses. It might even be expected that in areas where dissociable hydrocarbon gas is readily available, the cost of using the gas may be more than oliset by the value of the increased yield of coke and the value of the hydrogen collected.
It might here be noted that the hydrocarbon gas preferred in this aspect of the coking process of this invention is natural gas, which is readily available at a relatively low cost in certain areas where large amounts of poorly coking coals are also readily available. The majority of natural gas available in the United States consists principally of methane with low percentages of higher hydrocarbons. Methane begins to decompose slowly at about 800 C., and the decomposition becomes quite rapid when the temperature reaches 1100" C. to 1300 C. The rate of decomposition of the methane is, of course, dependent on the material in contact with the gas, which material may act catalytically to promote decomposition. For example, it is known that materials such as silica and carbon act as catalysts in the thermal dissociation of methane. Thus, when methane is used in a coking proc ess involving pellets formed in accordance with this invention, the silicate bentonite binder used in the pellets as well as the carbon deposited on the coal pellets during the process may provide a catalytic action to enhance the dissociation of the methane. For example, in the coking of pellets comprising 2% bentonite, an increase of 36% in the rate of gas flow produced an increase of 36% in the increased yield of the coke. By the increased yield of the coke is meant the increase in yield obtained by the use of the counter-flowing hydrocarbon gas over the yield normally to be expected from prior processes which did not use the gas counterfiow. When pellets comprising 1% bentonite were similarly processed, an increase of 87% in the gas rate produced an increase of 33% in the yield. Thus, it would appear that bentonite is an etfective catalyst for decomposition of the hydrocarbon gas.
While natural gas or methane is to be preferred, primarily for reasons of economy, it is, of course, understood that other hydrocarbon gases such as ethane, butane, and propane may be utilized. The higher hydrocarbons will dissociate more readily and at lower temperatures than methane, and therefore, at the temperatures utilized in the high temperature zone of the coking oven any higher hydrocarbons will also be dissociated.
When coking pellets made from poorly coking coal having a free swelling index of 4 /2 or less, the temperature at which the high temperature zone of the oven is maintained will depend primarly upon two factors: first, the desired hydrogen content of the oil gas from the retort; and secondly, the desired quality of the coke produced. It has been found that the percentage of the hydrogen in the oil gas from the retort varies substantially directly with the temperature within the high temperature coking zone. However, the percentage of hydrogen in the elf gas appears to be substantially independent of the flow rate of the gas through the retort, although the flow rate of the gas affects the total quantity of hydrogen produced. As previously noted, rapid dissociation of methane occurs at from 1100 C. to 1300 C., with substantially complete dissociation at the high temperatures. Further, it has been noted that the quality of the coke produced drops ofi" appreciably when the coking temperature in the high temperature zone drops below approximately 1150 C. At this temperature, the residual methane in the off gas has also been noted to increase. Therefore, the temperature of the high temperature zone of the retort should be maintained at a level not lower than approximately 1150 C. in order to achieve a satisfactory quality of coke as well as a satisfactory percentage of hydrogen in the off gas.
As the temperature of the high temperature zone is raised, the quality of the coke increases as well as the percentage of hydrogen in the OE gas. On the other hand, the increasing of temperature in this zone tends to result in the depositing of carbon from the dissociated methane on the inside of the retort. Also, at higher temperatures there is an increase in the rate of graphitizing of this deposited carbon which results in the formation of hard crusts on the inside of the retort which may not be abraded oil by the descending coke. Such crusts may seriously impede movement of the coke through the retort and necessitate a shut-down of the oven in order to burn out the crusts by admission of air through the retort. It has been found that the rapid development of crusts occurs above a temperature of approximately 1300 C. Accordingly, the temperature in the high temperature zone is preferably maintained at a level of 1150 C. to 1300" C. in order to achieve satisfactory dissociation of the methane and good quality coke and at the same time minimize the formation of crusts on the retort. This temperature range will also apply where higher hydrocarbon are utilized as a counterflow gas inasmuch as they will be even more easily dissociated at these temperatures.
The flow rate of the dissociable hydrocarbon gas through the retort will, of course, directly affect the yield of the coke; and it has been found that it will also affect the rate at which the crusts build up on the inner wall of the retort. Therefore, the flow rate of the gas will be determined by a balance of the advantage of providing a relatively large amount of hydrogen and high yield of 'coke while at the same time minimizing the build-up of crusts. For example, if the ofl? gas were to be used for the production of ammonia, it would be desirable to provide relatively large amounts of oil gas having a high hydrogen content. Accordingly, the gas flow rate would be at a higher level and the temperature in the high temperature zone would be maintained at the higher end of the range. While the tendency of crust formation would be increased, there would be a corresponding increase in the gas rate as well as the percentage of hydrogen in the off gas; and, further, the resulting coke would be harder and stronger and accordingly more valuable in some instances. On the other hand, in the case where there was a minimum demand for hydrogen, the flow rate of the gas could be adjusted to produce only enough ofi gas for firing the retort and perhaps other process uses. In such a case, the feed rate of the coal as well as the coking temperature in the high tempertaure zone would be adjusted to give a maximum production of coke of the desired strength and at the desired yield.
By way of illustration, there will now be described a specific example of the practice of the process of the present invention utilizing coal having a free swelling index of less than 4 /2. A batch of non-coking coal, which was a flotation concentrate recovered from the waste slurry of a preparation plant, was prepared by floating the coal away from the mineral ash constituents in the slurry and then dewatering the coal by filtration to provide a coal filter cake. The coal was then mixed with water in an amount sufficient to bring the Water in the mix to a value of approximately 21 to 26 percent by weight of the mix. Further, a quantity of ground Wyoming bentonite was added to the mix in an amount equal to approximately 2% by weight of the dry coal in the mix. The mixing was continued until the mix attained a proper consistency for pelletizing, whereupon the mix was processed through pelletizing apparatus of the type previously herein described. After drying, the pellets were processed through a coking oven of the type herein previously described, with the coking temperature as well as the rate of fiow or natural gas through the retort being varied while the feed rate of the pellets was maintained substantially constant. The following table illustrates the results achieved in various runs of the pellets at given generally average coking temperatures in the high temperature zone of the oven and at different rates of flow of the natural gas in cubic feet per minute per square inch of cross section of the retort. The results indicate the coke yield of the oven in terms of percent by weight of the coal feed, the hydrogen yield in terms of the percentage of hydrogen by volume in the off gas, and a tumbler index rating indicating the hardness and strength of the coke produced.
Coking Coke yield, Hydrogen, temp, Gas rate, percent of percent by Tumbler Run 0. (high c.f.1n./in. coal feed vol. in index zone) As can be seen from the foregoing table, run A at 1150 C. and a gas rate of .075 c.f.rn. per inch square provided a coke yield of 66.3%, a percentage hydrogen in the off gas of 67.4, and a tumbler index of 95.8. This coke yield, even at the low end of the temperature range, is substantially in excess of that normally achieved by conventional coking methods. A usual good yield to be expected by conventional methods is approximately 55% The tumbler ind ex is equivalent to what the ASTM designates as the hardness factor and was provided by the use of a modified tumbler machine based on the ASTM standard. Specifically, the tumbler index represents the percentage of a 2000 gram plus 8 mesh sample of coke that remains on an 8 mesh screen after being tumbled for eighty-six minutes in a tumbler barrel revolving at twenty-three r.p.m. The tumbler index of 95.8 on the coke of run A is substantially better than that provided by a good metallurgical coke provided by conventional methods. A specific example of such conventional coke had a tumbler index of 90.3.
As will be seen from run B, with a slight rise in coking temperature and a substantial decrease in the gas rate, the coke yield fell off while the percentage hydrogen in the off gas rose slightly due to the increase in coking temperature. The tumbler index was reduced but still remained higher than that of conventional coke. In run C the coking temperature was increased still further to approximately the mid-point of the preferred range, and the gas rate was increased to that which was the same as in run A. In this case the coke yield increased over run B, as was predicted, and the percentage hydrogen in the oii gas rose sharply. Further, there was :1 corresponding increase in the tumbler index. In run D, the coking temperature was increased to a value near the high end of the range, while the gas rate was maintained the same as in run C Here again, the coke yield increased as did the percentage hydrogen in the off gas as well as the tumbler index. In run E, with the same coking temperature as run D, the gas rate was decreased appreciably, causing a decrease in the coke yield, while the percentage hydrogen in the off gas remained substantially the same as in run D. The tumbler index showed a slight decrease over run D. In run F, the gas rate Was approximately doubled over run E. The coke yield and percentage hydrogen in the off gas were, however, less than run D, wherein the same coking temperature was utilized and a lesser gas rate provided. It is believed that these lesser values in the coke yield and percentage hydrogen were brought about by a lesser percentage dissociation of the natural gas by reason of the increased rate of flow resulting in the gas being exposed to the high temperature zone for a lesser period.
The heating rate of the coal passing through the oven during all of the runs described was approximately C. per minute. In other words, the coal pellets were raised to coking temperature in approximately one hour or less. Accordingly, it can be seen that the through-put rate of the coking process of the invention is considerably greater than that achieved with conventional coking processes wherein the heating rate is on the order of 1 to 2 C. per minute. Further, it can be seen from the above example that a yield approaching 70% may be attainable with noncoking coal in a continuou operation.
It can be seen that the marked improvement in productivity provided by this coking process together with the obvious advantage of using heretofore unusable coal waste in the pelletizing process of the invention provides an over-all process whereby wasted coal refuse may be processed into coke which is superior to that now provided from good coking coals. The economy of the process will be apparent when it is considered that the increase in value of the final coke by reason of the addition of carbon from the natural gas used in the process will be substantial equal to if not greater than the cost of the gas used. Further, the hydrogen and condensible volatiles in the off gas will provide an additional source of substantial revenue. In this latter connection, the coal tars are distilled at or near the minimum distillation temperature and carried by the ascending gas into cooler zones of the retort, thus minimizing cracking of the tars and resulting in a more valuable primary or low temperature tar.
The coking of coal pellets prepared in accordance with this invention has thus far been described primarily in connection with coal having a free swelling index of less than 4 /2. When the coal utilized has a free swelling index of 4 /2, the green coal pellets are prepared in the same manner as those made from coal having a free swelling index of less than 4%.. However, the pellets may be coked while passing a stream of crackable hydrocarbon gas through the retort as described above, or by utilizing a stream of a non-crackable reducing or neutral gas to provide a non-oxidizing atmosphere in the coking oven. It is to be understood that when the term noncrackable reducing gas is used hereinafter, and in the appended claims, in connection with a counterflow through the retort, the term is used to indicate a gas which will not be cracked at the coking temperature as distinguished from the crackable hydrocarbon gas previously described which is also a reducing gas. When using a crackable hydrocarbon gas, the yield will be somewhat higher. However, it is not necessary to use the crackable hydrocarbon gas counterflow in order to provide strong coke pellets. Whenthe coal utilized has a free swelling index of greater than 4 /2, the green coal pellet mix may be prepared in the same manner as the mix of poorly coking coals. In coking these pellets the use of a countertlow of additional crackable hydrocarbon gas may not be desirable as it may cause the pellets to fuse together so as to prevent their passing through the retort. In such an event, the use of a counterfiow of a non-crackable reducing gas or a neutral atmosphere has been found to alleviate the problem. For example, carbon monoxide, hydrogen and nitrogen have been used with satisfactory results. Also, if desired, the off gas from the top of the retort may be recirculated in counterflow relation through the bottom of the retort.
An example of the production of satisfactory coke pellets from coal having a free swelling index of greater than 4 /2 involved the use of coal from the Sewell Seam in Pennsylvania. This coal had an analysis of 64.1% fixed carbon, 29.9% volatile matter, 5.1% ash, .94% water, and .63% sulphur. The pellets were prepared using 2% bentonite based on the dry weight of the coal in the pellet mix. The pellets were dried in air at approximately 214 C. for 30 minutes to achieve the desired reduction in water content and pro-oxidation of the coal in the pellet. When pellets thus prepared were coked at 1200 C. in the presence of a counterfiow of natural gas very strong coke pellets were provided. Strong coke pellets were also provided when similarly prepared pellets were coked at the same temperature in the presence of a counterllow of a non-crackable, non-oxidizing gas; for example, nitrogen. In the case of the coke pellets provided from the process utilizing a counterflow of natural gas, the resulting coke pellet analyzed had 89.6% fixed carbon, 9.97% ash, .44% sulphur, and .43% volatiles. The yield in the case of the operation using natural gas was approximately 2.7% greater than the operation utilizing nitrogen. The yield here expressed is the weight of coke expressed in percent of the weight of the coal pellets after oxidation. The quality of the coke in both cases was substantially the same. There appeared to be little difference in the strength of the pellets. However, those made in the presence of nitrogen were somewhat more easily abraded by rubbing than were those which were coked in the presence of the counterfiow of natural gas. Therefore, while the use of natural gas is not essential as is the case where coal having a free swelling index of less than 4 /2 is utilized, a counterllow of dissociable hydrocarbon gas may in some cases be advantageous.
The coal utilized in the last described example had a free swelling index of 7. When using other coals having a free swelling index of 5 to 7 similar satisfactory results were obtained. However, when utilized, a Pennsylvania coal from the Pittsburgh Seam having a free swelling index of 8, the coke pellets produced were fairly weak when coked in either natural gas or nitrogen and even though the coal pellets were pre-oxidized by drying the same in air. However, it was found that satisfactory pellets could be provided from such coal when oxidation of the pellets was accomplished through the use of an internal oxidizer, and the pellets coked in nitrogen. More specifically, pellets are compounded from an aqueous mixture of coal, bentonite, and an oxide, such as magnetite or oxidized manganese ore which is reducible during high temperature coking of the pellets. The pellets thus prepared are not pro-oxidized but rather are merely air dried at low temperatures in the manner described in connection with pellets made from coals having a free swelling index of 4 /2 or less. When these pellets are coked, the oxide will be reduced, or in other words, the coal in the pellets will be oxidized to a substantial extent sufiicient to provide that the resulting pellets are strong and of good quality. When iron ore is utilized as the internal oxidizer, the iron ore will be reduced to metallic iron in the coking process. Thus, the resulting pellet will inelude metallic iron as well as coke. However, where the coke is to be used in an iron blast furnace operation, the presence of metallic iron in the pellet will not adversely affect the blast furnace process. Further, where oxidized manganese ore is utilized as an internal oxidizer, the resulting coke pellet will contain metallic manganese which might be useful as a source of manganese in an iron blast furnace operation.
As previously described, the use of an internal oxidizer, rather than a pre-oxidizing step has been found to be necessary with a coal having a free swelling index of 8. It has also been found that the inclusion of an oxide, such as magnetite, in the original pellet mix will provide a good strong coke pellet in the case where the green coal pellets are made from coals having a free swelling index of greater than 4 /2. Where magnetite was incorporated into a pellet mix using coal having a free swelling index of 4 /2, the resulting coke pellet was relatively weak and not particularly suited for blast furnace operation. When magnetite was incorporated into a green pellet mix of coal having a free swelling index of less than 4 /2, the pellets coked in a counterilow of natural gas, the resulting coke product was not satisfactory. These last two results are, of course, consistent with the above-described requirement of precluding oxidation of the coal in pellets made from coal having a free swelling index of 4 /2 or less.
The primary advantages of utilizing iron ore as an internal oxidizer for the pellets are two-fold: first, the preoxidizing step is eliminated, although the green pellets should be dried after pelletizing and before coking; secondly, the percentage of coal and iron ore in the green pellet mix may be selected to provide that the resulting iron-coke pellets can be used to provide the entire ore and coke charge for a blast furnace. In the preparation of pellets for use in providing an integrated ore-coke charge, the pellet mix will be prepared in essentially the same manner as was initially described in connection with poorly coking coal. However, as stated above, iron ore will be added to the mix prior to pelletizing. Also, a flux may be added to the mix. Specifically, natural limestone (CaCO may be added to the pellet mix in an amount determined by the amount of iron ore in the mix. It should be here noted that it is essential that natural lime stone be utilized and not burnt lime (CaO). Where burnt lime is utilized, the lime becomes hydrated to Ca(OH when water is added to the pellet mix. When pellets utilizing burnt lime are carbonized, the result is a spongy pellet which is quite weak. On the other hand, when natural limestone is utilized, the self-fiuxing iron-coke pellets provided are very strong although not perhaps quite as strong as the pellets provided when limestone is not used. Where a natural limestone is utilized, it is apparently decomposed during carbonization of the pellet to provide CaO with expulsion of CO Evidently, however, this occurs at a temperature (around 700800 C.) at which coke has become hardened and is not susceptible to expansion with evolution of the carbon dioxide. Given below in tabulate form are the results obtained when using various coal and various percentages of iron ore in the coal pellet mix.
Iron cokes The coal pellets represented in the above table were coked generally in the same manner as described in connection with coal pellets made from coals having a free swelling index of 4 /2 or less, except that it is not necessary to utilize a counterflow of a crackable hydrocarbon gas. Rather, a suitable neutral or non-crackable reducing gas such as nitrogen may be utilized; also, if desired, the off gas from the retort may be recirculated. It should here be noted that in any case Where a crackable hydrocarbon gas is not passed in counterfiow relation through the retort, the lower limit of the temperature range in the high temperature portion of the retort may be reduced somewhat, for example, to about 1100 C. This reduction is permitted because of the fact that there is no necessity for cracking of additional hydrocarbon gas as in the case of the process involving a poorly coking coal. However, it will be apparent that in all cases, the coking operation is one which should be referred to as a high temperature operation as opposed to a low temperature operation.
From the table above, it can be seen that the percentage reduction of the iron ore varies with the ratio of ore to coal in the original mix. It has been found that in most cases where the percentage of iron ore in the pelletizing mix is approximately by weight of the total dry mix, about of the iron ore is reduced. On the other hand, where the pellet mix is approximately 50% iron ore, the iron ore is substantially completely reduced. In the case of the 70% iron ore mix, the resulting pellet was deficient in carbon with respect to providing a complete, integrated charge of iron and coke for a blast furnace. Where the pellet mix contained approximately 50% iron ore there was too much residual carbon. However, with pellet mixes having approximately 60% iron ore and 40% coal, it is believed that the resulting iron coke pellet would provide very close to the correct amount of iron and coke necessary for an integrated complete charge for a blast furnace. With this mix, the iron ore should be substantially reduced to the metallic state during the coking of the pellet. It will be realized that the exact ratio of iron ore to coal in the mix which will provide a complete integrated charge will be dependent upon the analysis of the particular ore and coal utilized.
' The advantages of the use of an iron coke pellet provided by this aspect of the invention are several. In the conventional blast furnace operation, the tonnage of iron produced is dependent to a large extent on the amount of air which can be passed through the stock column in the furnace; this, in turn, is dependent upon the permeability of the column. For this reason, in modern blast furnace practice, efforts are made to prepare the constituents of the charge so as to obtain a loose permeable column. The coke must be of good size pieces and of such strength that it will not break down into fines under the pressure of the column. Likewise, the limestone flux must be in lump form. The iron ore is generally screened Iron coke pellet analyses Coal used Iron ore 1 Yield 2 Ore red.
Volatile Fixed Ash Metallc S carbon Fe Pittsburgh Seam, Pa.
(FSI S) 4 50. 0 69. 7 3. 0 37. 3 11. 9 47. 8 47 100. 00 Do 70. 0 68. 0 1. 2 18.1 15. 7 65. 0 62 94. 7 Sewell Seam, P (F 7)- 50. 0 73.2 2. 2 42. 2 9. 0 46. 6 45 100. 00 Frederick Mine, Colorado (FSI 7) 70. 0 70.1 7 12. 7 23. 5 63.1 44 95.0 Allen Mine, Colorado (FSI 5) 70.0 73. 6 l. 0 15.5 13.0 60. 5 33 95. 8
1 Amount of iron ore in pellet mix expressed by percent of total weight of dry mix. 2 Weight of iron-coke pellet expressed in terms of percent by weight of dried green pellets prior to coking. 3 Percentage of total iron present in the admixed iron ore which is reduced to metallic iron.
4 Free swelling index of coal used in pellet mix.
prior to charging in the furnace and the fines are agglomerated by sintering. The lump sinter, coarse ore, limestone and coke are charged to the blast, and hot air blown into the furnace through tuyeres near the bottom burns the coke to carbon monoxide with intense heat. The hot carbon monoxide rising in the column reduces the iron oxide of the ore to metallic iron. Also, the heat generated by the burning of the coke melts the iron and causes the gangue constituents of the ore and the ash from the coke to be fluxed by the limestone into molten slag. The molten slag and iron flow downward to the hearth of the furnace where they separate according to their specific gravity and are periodically tapped, separately, from the furnace.
A recent improvement in blast furnace operation has been the development of iron ore pellets. These pellets are largely the product resulting from beneficiating so called taconite iron ore. These ores as mined are too low a grade to be smelted directly. The iron occurs in the ore mostly as magnetite. The ores are ground to a very fine size, and the magnetite is separated from the waste by magnets to provide a concentrate having an iron content of about 65%. Even though the concentrate is very fine, it must be ground further to an extreme fineness in order to permit its being pelletized. The extremely finely ground concentrate is pelletized using water and generally with a binder and the moist pellets are then coated with fine coke or anthracite and fired either on a travelling grate or in a shaft furnace. The heat treatment converts the green pellets into stronger harder pellets consisting essentially of iron oxide. None of the iron is reduced to the metallic state during the production of the pellet. It should also be noted that the coke or anthracite which is dusted over the pellets is merely for the purpose of providing fuel for the hardening step. are then charged to the blast furnace with the usual amount of coke and limestone flux. It has been reported that the capacity of blast furnaces utilizing such pellets is substantially greater than that obtained when natural iron ore is utilized. It is believed that the improved results are obtained in part because of the higher iron content of the charge and also because of the greater permeability of the stock column which permits an increase in the volume of blast air.
With an iron coke pellet fabricated in accordance with this invention there is, of course, the primary advantage that the pellet may be used to provide the total charge to the blast furnace, thus facilitating the handling of constituents. Also, iron ore fines are utilized directly in the production of the pellet thus eliminating any sintering operation. It is not necessary that the iron ore be provided in as fine a size as that necessary to provide the iron pellets described above. For example, an iron ore size of minus 50 mesh is satisfactory. Further, the iron ore in the ore-coal pellets of this invention is completely reduced to the metallic state during the coking step. Accordingly, when the charge is fed to the blast furnace less coke is present, and consequently less air for its combustion is required inasmuch as it is not necessary to reduce the iron oxide to metallic iron. For example, in standard blast furnace operation where the iron charge consists of iron oxide (Fe O approximately 1400 pounds of coke is required per ton of iron produced. Roughly, 45% of this coke is consumed in the reduction of the iron oxide to metallic iron and the remaining 55% is burned to supply heat. When using an integrated corn plete ore-fuel charge of this invention, it is obvious that the coke normally required for the reduction of the ore in the furnace will not be needed. The air required to burn the remaining coke will be reduced in proportion to the coke saved. In other words, a given volume of air blast should result in a greatly increased melting rate when the iron is charged into the furnace in the metallic form rather than in the oxide form. Also, the iron coke pellets provided by this invention will be relatively uni- The iron pellets 2% form in size, or at least more so than the usual charge into a blast furnace. Accordingly, the stock column should be somewhat more permeable to the passage of gas than in the case where either iron taconite pellets or lump ore are charged together with lump coke and lump limestone.
From the above, it can be seen that the various aspects of this invention are each based upon the concept of providing a coke pellet by pelletizing finely divided coal with bentonite and water to provide a coal pellet which is then carbonized in a high temperature coking process. As will be apparent from the above, certain aspects of the green coal pellet preparation and coking operation, as well as the suitability of various coals in providing an integrated ore coke blast furnace charge, are dependent upon the free swelling index of the coal utilized. For this reason, a summary of the relationship of the free swelling index of the coal to various aspects of the invention will now be given. Where a coal having a free swelling index of less than one is utilized, the green coal pellets must be compounded with a percentage of bentonite which is higher than that previously specified. For example, it has been found necessary that at least 3% of bentonite be used with such coal. The green coal pellets must be dried at low temperatures (not over C.) to avoid oxidation of the pellet. Also, the coal pellet must be coked with a counterfiow of a crackable hydrocarbon gas in order to provide a stronge coke pellet. With a coal having a free swelling index of approximately 1, the coal pellets are sufficiently strong when bentonite in an amount of 2% by weight of the coal is utilized in the pellet mix. The green coal pellets must be dried at a low temperature to avoid oxidation and must be coked with a counterfiow stream of crackable hydrocarbon gas. Where the free swelling index of the coal is 2 /2 to 3 /2, the pellets have the same requirements for coking. Also, these pellets, as well as those made from coals having a free swelling index of less than 2 /2, may not be used for making iron coke. Where the coal used has a free swelling index of 4 /2, the coal pellets must still be dried under conditions selected to avoid oxidation of the coal. The resulting coke pellets are very strong, whether coked in a crackable hydrocarbon gas or in a counterfiow of a non-crackable, non-oxidizing gas such as nitrogen or in a counterfiow of off gas from the coking operation. Where such coal is utilized to provide iron coke, the resulting pellets are relatively weak and fairly easily abraded. Where the free swelling index of the coal used is from 5 to 7, the green coal pellets are provided using a mix of coal, water, and approximately 2% by weight of the coal of bentonite. Green coal pellets from this coal, dried at low temperatures (below 150 (3.), so as to prevent any substantial coal oxidation, fuse together when coked. Accordingly, where the pellet is not used for the production of iron coke pre-oxidation is required before coking. This oxidation may be provided by air drying the pellets at C. to 220 C. In order to provide a strong coke pellet, the oxidizing of the coal should be done after the pellets are formed and not prior to forming the pellets. The pre-oxidized pellets are then coked either in a neutral or non-crackable reducing gas or in recycled off gas passed in counterfiow relation to the coke charge. The resulting coke pellet is quite strong. Where iron coke pellets are desired, the pre-oxidizing step is eliminated. Again, the coal pellets may be coked in a suitable non-crackable reducing or neutral gas or in off gas passed in counterfiow relation to the passage of the coke through the retort. The iron coke pellets provided while all being sufiiciently strong do vary in strength, with the pellets made from the coals having the higher free swelling index giving the stronger iron coke pellets. With a coal having a free swelling index of 8, and presumably higher, the pellets are provided again using approximately 2% by weight of the coal of bentonite. The green pellets when dried at low temperatures to prevent any substantial coal oxidation may fuse into a solid mass When coked in either natural gas or nitrogen. Pre-oxidation of the green coal pellets by drying in air at 220 C. eliminates the fusing. However, the coke pellet provided from the subsequent high temperature coking operation is fairly weak and is easily abraded whether the coking is conducted with a counterflow of natural gas or nitrogen. However, iron coke pellets of excellent quality can be provided from such coal with the coking being accomplished with either a counterfiow of off gas or a neutral or reducing gas. Pre-oxidation of the green pellets is not required in providing iron coke pellets from such coal.
In the use of coal having a free swelling index of 4 /2 and higher to provide an iron coke pellet, it should be emphasized that the coal in the green coal pellet is provided for later use as a fuel and not merely as a binder for the iron ore in the coal pellet. In pelletizing the coaliron ore mixture bentonite has been used as a binder with the bentonite being in an amount of about 2% of the combined dry weight of the coal and ore. It is believed that when bog type ores are used, their bog-like characteristics may permit the ore to act as a binder and eliminate or reduce the bentonite. Also, the coal is carbonized to a true coke in the coking operation and not merely to a char. In this connection, it may be noted that the coal is not ignited at any time during the preparation of the coal pellet or during the coking operation. While the iron coke aspect of this invention has been described in connection with the provision of a complete integrated charge for a blast furnace, it will, of course, be understood that if desired, the iron coke pellet could be provided with an excess of iron ore or an excess of carbon. In this connection, satisfactory iron coke pellets may be provided utilizing anywhere from -75% iron ore in the pelletizing mix. These percentages are based on the total weight of the dry mix for the pellets. For reasons of economy of operation based on either the ore or the coal not being readily available at the pellet processing plant, it might be desirable to utilize either a high ratio of coal to ore or a high ratio of ore to coal in the green pellet. The necessary additional iron ore or coke would then be provided at the blast furnace site. Therefore, on the range of from -70% of iron in the iron-coke pellets may be used. This percentage is based on the total weight of the iron-coke pellet. While this range may seem large, in keeping with the intent to provide an integrated iron-coke charge for a blast furnace, it is desirable since the percentage of iron in the pellets will depend at least to some extent on the volatile and ash content of the coal used, assuming a constant amount of iron ore in the original pellet mix. For instance, a coal having a low volatile and ash content will be able to support a higher content or iron in the iron-coke pellet. Such coal will give, in the iron-coke pellet, a higher yield of fixed carbon to furnish fuel for smelting the iron.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efliciently attained and, since certain changes may be made in carrying out the above process, in the described product and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
Having thus described my invention, I claim:
1. In a high temperature process for producing coke from coal, the steps of applying heat to a quantity of coal in a non-oxidizing atmosphere to carbonize the same, and during the carbonizing of the coal contacting the coal with a stream of dissociable hydrocarbon gas, the temperature of the carbonizing being maintained at a value of from about 1100 to 1350 C. to cause rapid dissociation of said hydrocarbon gas, said coal maintained in contact with said hydrocarbon gas for a sufi'icient time at said temperature to cause a substantial amount of free carbon to form on the coal, and said hydrocarbon gas being provided separate from any dissociable hydrocarbon gas evolving from the coal during high temperature carbonizing thereof.
2. A process as described in claim 1 wherein the separately provided gas consists essentially of methane.
3. A process for producing coke from finely divided particles of coal comprising the steps of providing a pelletizable aqueous coal mixture by mixing water, bentonite and particles of coal having a free swelling index of no greater than 4 /2, with the bentonite being present in a minor amount which is however at least 1% by weight of the total weight of the mix, pelletizing said mixture to provide green coal pellets, coking said pellets in a continuous two zone coking process wherein the pellets are sequentially passed first through a low temperature zone for distillation of the majority of the volatiles of the coal in the pellets and then are passed through a high temperature zone providing high temperature coking of the coal in the pellets, and during the high temperature coking of said pellets passing a dissociable hydrocarbon gas in contact with the pellets, said dissociable hydrocarbon gas being provided separate from and in addition to any such gas evolved from the coal in the pellets during the high temperature carbonization thereof, the temperature of said high temperature zone being maintained at a value of at least about 1100 C. to cause rapid dissociation of the separately provided dissociable hydrocarbon gas, and said pellets being maintained in contact with said hydrocarbon gas for a sufiicient time at said temperature to cause a substantial amount of free carbon to form on the pellets.
4. A process for producing coke from finely divided particles of coal having a free swelling index of no greater than 4 /2 comprising the steps of mixing finely divided particles of such coal with water and a minor amount of an inorganic binder to provide a pelletizable mixture, pelletizing the aqueous mixture of coal and inorganic binder to provide green coal pellets, drying said green coal pellets without causing any substantial oxidation of the coal in said pellets, coking said pellets in a continuous two-zone coking process wherein the pellets are sequentially passed first through a low temperature zone for distillation of the majority of the volatiles of the coal in the pellets and then are passed through a high temperature zone providing high temperature coking of the coal in the pellets, and during the high temperature coking of said pellets passing a counter flow of dissociable hydrocarbon gas through said high temperature zone, said dissociable hydrocarbon gas being provided separate from and in addition to any such gas evolved from the coal in the pellets during the high temperature carbonization thereof, the temperature in said high temperature zone being maintained at a value of at least about 1100 C. to cause rapid dissociation of the separately provided dissociable hydrocarbon gas, and said pellets being maintained in contact with said hydrocarbon gas for a sufiicient time at said temperature to cause a substantial amount of free carbon to form on the pellets.
5. A process for producing coke from finely divided particles of coal having a free swelling index of no greater than 4 /2 comprising the steps of providing a pelletizable mixture by mixing finely divided particles of such coal with water and a minor amount of swelling bentonite which however is present in an amount of at least 1% by weight of the total mix, pelletizing the aqueous mixture of coal and bentonite to provide green coal pellets, drying said green coal pellets in air at a temperature of no greater than C. and for a time insuflicient to cause any substantial oxidation of the coal in said pellets, coking the dried pellets in a continuous two-zone coking process wherein the pellets are initially exposed to a temperature of from 250 C. to 450 C. as they enter the first zone and are subsequently exposed to a high temperature of from l150 to 1300 C. to provide high temperature coking of the coal in the pellets, and during the high temperature coking of said pellets continuously passing a stream of dissociable hydrocarbon gas through the high temperature and low temperature zones in counter flow relation to the movement of the pellets, said stream of dissociable hydrocarbon gas being provided separate from and in addition to any such gas evolved from the coal in the pellets during the high temperature carbonization thereof, and said pellets being maintained in contact with said hydrocarbon gas for a sufiicient time at said high temperature to cause a substantial amount of free carbon to form in the pellets.
6. The process defined in claim wherein said dissociable hydrocarbon gas essentially consists of methane.
7. A process for producing coke from finely divided particles of coal comprising the steps of mixing finely divided particles of coal having a free swelling index of greater than 4 /2, a reducible metal oxide and an inorganic binder with water to provide a pelletizable mixture, said inorganic binder being present in a minor amount of at least 1% by weight sufficient to provide a binder for the pellets, pelletizing said mixture, and carbonizing the coal in the pellets by processing the pellets through a continuous two-zone high temperature coking process comprising a first low temperature zone for distillation of the volatiles in the coal and a high temperature zone for high temperature carbonization of the coal in the pellets, said oxide having the characteristic of being reducible during said coking process and being selected and being provided in said mixture to provide oxygen in an amount sufiiciet to oxidize the coal in said pellets to an extent sufficient to prevent the pellets from fusing together during the coking process.
8. The process as defined in claim 7 wherein the reducible metal oxide is iron ore.
9. The process defined in claim 7 in which said binder is swelling bentonite which is present in the pelletizable mixture in an amount of at least 1% by total weight of the mix, in which the temperature of said low temperature zone is from 250 C. to 450 C. at the entrance of the pellets into said low temperature zone and the temperature of said high temperature zone is at least approximately 1100 C. to 1300 C. and wherein a stream of reducing gas is passed in counter flow relationship to the movement of the pellets through the high temperature and low temperature zones to provide a non-oxidizing atmosphere therein.
10. A process for producing iron-coke pellets for use in providing an integrated iron-fuel charge to a blast furnace, comprising the steps of providing an aqueous pelletizable mixture of finely divided particles of coal having a free swelling index of greater than 4 /2, bentonite and iron ore, pelletizing said mixture, and carbonizing the coal in the pellets by processing the pellets through a continuous two-zone high temperature coking process comprising a first low temperature zone for distillation of the volatiles in the coal and a high temperature zone for high temperature carbonization of the coal in the pellets, said ore being at least partially reduced to metallic iron and the coal in said pellets being oxidized sufi'iciently during said coking process to provide strong integrated pellets of metallic iron and metallurgical grade coke.
11. The process defined in claim 10 in which the hentonite is swelling bentonite which is present in the pelletizable mixture in an amount of at least 1% by total weight of the mix, in which the temperature of said low temperature zone is from 250 C. to 450 C. at the entrance of the pellets into said low temperature zone and the temperature of said high temperature zone is at least approxi- 2 mately 1100 C. to 1300 C., in which said ore is magnetite, and wherein a stream of a non-crackable non-oxidizing gas is passed in counter flow relationship through the high temperature and low temperature zones to provide a non-oxidizing atmosphere therein.
12. A pellet for use in a high temperature coking process comprising a quantity of finely divided coal having a free swelling index of greater than 4 /2 bound by swelling bentonite in at least 1% by total weight of the mix, the pellet further including a metal ore which is reducible at the temperatures normally associated with a high temperature coking process, the metal of said ore being compatible with the use of said pellet in a furnace after the pellet has been processed through a high temperature coking process, the coal in said pellet not being oxidized to any substantial extent.
The pellet as defined in claim 12 wherein the metal ore is iron ore. 14. A coke pellet comprising a porous mass of carbonized coal particles and ash from an inorganic binder of at least one percent by weight of the pellet and the pellet having a substantial amount of free carbon deposited in its pores and on its surface.
15. The coke pellet as defined in claim 14 wherein the porous mass includes a reduced metal.
16. The coke pellet as defined in claim 14 wherein the porous mass includes reduced iron and the inorganic binder is swelling bentonite.
17. A metallurgical grade coke pellet comprising a porous mass of carbonized coal and ash of swelling bentonite and the pellet having a substantial amount of graphitized free carbon deposited in its pores and on its surface.
18. An ore-coke pellet for use in a blast furnace operatron the constituents of said pellet consisting essentially of substantially completely reduced metal ore, metallurgical coke, and at least one percent by weight of the pellet of ash IIOIIl an inorganic binder.
19. The ore-coke pellet as defined in claim 18 wherein the metal ore is iron ore.
20. The ore-coke pellet as defined in claim 18 wherein the metal ore is iron ore and the iron is present in an amount of from 30 to 70 percent of the total weight of the pellet, said pellet providing an integrated iron-coke charge for a blast furnace.
21. The ore-coke pellet as defined in claim 18 wherein the pellet also includes limestone in an amount sufiicient to provide the fiux necessary when the pellet is used to cnarge a blast furnace.
22. The ore-coke pellet as defined in claim 18 wherein the metal ore is reduced iron ore and the inorganic binder is the ash of swelling bentonite in an amount of from about 1 to 2 percent by weight of the green ore-coke pellet.
21f. A process for producing coke from finely divided particles of coal comprising the steps of mixing finely divided particles of coal having a free swelling index of greater than 4 /2 with water and a swelling bentonite to provide a pelletizable mixture, pelletizing said mixture; gry ng the green pellets provided from the last step, oxiizmg the coal in said green pellets, and carbonizmg the coal in the oxid' d l e 1 ize pedcts by processing the pellets tnrough a continuous two-zone high temperature coking process comprising a first low temperature zone for distillation of the volatiles in the coal and a high temperature zone for high temperature carbonization of the coal in the pellets, said oxidizing being sufficient to provide strong coke pellets and prevent excessive sticking of the pellets during carbonization thereof, and during said passage of the pellets through the high temperature zone contacting the pellets with a dissociable hydrocarbon gas, the temperature of the high temperature zone being maintained at a value of about 1100 C. to 1350 C. to cause rapid dissociation of said hydrocarbon gas, said pellets being maintained in contact with said hydrocarbon gas for a sufficient time at said temperature to cause a substantial amount of free carbon to form on the pellets, and said gas being provided separate from any dissociable hydrocarbon gas evolving from the coal pellets.
24. The process defined in claim 23 wherein the coal pellets include a reducible metal oxide in an amount sufficient to oxidize the coal in said pellets and to prevent the pellets from fusing together during the coking process.
25. The process as defined in claim 23 wherein the coal pellets include a reducible iron ore.
26. The process as defined in claim 23 wherein the coal in the pellets is oxidized in air at a temperature of from about 180 C. to 220 C.
27. A process for producing coke from finely divided particles of coal comprising the steps of mixing finely divided particles of coal having a FSI of greater than 4 /2 with water and swelling bentonite, said bentonite present in an amount of at least 1% by total weight of the mix to provide a pelletizable mixture, pelletizing said mixture without the application of molding pressure to form loosely compacted porous green pellets, drying and oxidizing the green pellets in air at a temperature of from about 180 to 220 C., carbonizing the oxidized green coal pellets by passing the pellets sequentially through a low temperature zone of from 250 C. to 450 C. for distillation of a majority of the volatiles of the coal in the pellets, and then passing the pellets through a high temperature coking zone at a temperature of approximately '1 100 C. to 1350 C. wherein the pellets are directly contacted with a gaseous reducing stream in a counter current flow to the movement of the pellets, the pellets being heated in the high temperature zone at a rate of 20 C. per minute or greater.
References Cited by the Examiner UNITED STATES PATENTS 987,554 3/11 Coggeshall 202-25 XR 1,602,128 /26 Smith 202-109 1,756,896 4/30 Wisner 20235 1,838,882 12/3 1 Trent 20234 1,875,287 8/32 Weber 20234 1,886,350 11/32 Nielsen et a1 202-15 1,899,809 2/ 33 Kern et al 202-34 1,913,121 6/33 Kern 20234 1,913,122 6/33 Kern 202-34 1,924,819 8/33 Van Ackeren 202-121 1,929,408 10/ 33 Bunce 20215 1,939,457 12/33 Merkel 202-15 1,941,462 1/ 34 Bunce 202-15 2,015,336 9/35 Bunce 202-15 2,131,702 9/38 Berry 202-16 2,167,099 7/ 39 Benezech 202-15 2,376,760 5/45 Elsey 202-26 2,377,518 6/45 Records et al 202-121 2,429,416 10/47 Lesher 20234 2,582,386 1/52 Komarek et al. 44-26 2,674, 5 81 4/54 Balcar et a1 252-1883 2,675,307 4/54 Klugh et a1 202-120 2,695,221 11/54 Klugh et a1 252-1883 2,728,940 1/ 56 Yesberger et a1 18-1 2,778,056 1/ 57 Wynne 18-1 2,825,679 3/58 Baum 202-26 2,914,395 l1/ 59 Davies 75-3 2,923,965 2/ 60 Djuvik 18-1 2,956,868 10/60 Burgess 44-26 2,961,411 1 l/60 Klugh 4 3,010,882 11/61 Barclay 202-26 FOREIGN PATENTS 660:374 11/51 Great Britain.
OTHER REFERENCES Egloif: Reactions of Pure Hydrocarbons, Rheinhold Publishing Corp., New York (1937), pp. 53-56.
MORRIS O. WOLK, Primary Examiner. MILTON STERMAN, Examiner.