US2536365A - Autogenous coking of agglomerates of zinciferous and carbonaceous materials - Google Patents

Description

Jan- 2, 1951 E. c. HANDWERK ET AL 2,536,365

AUTOGENOUS COKING OF' AGGLOMERATES OF ZINCIFEROUS AND CARBONACEOUS MATERIALS Filed July 5l, 1948 Sheets-Sheet 1' ATTO R N EY E. c. HANDWERK ET Al. 2,536,355 AUTOGENOUS COKING OF AGGLOMERATES OF ZINCIFEROUS AND CARBONACEOUS MATERIALS 2 Sheets-Sheet 2 xNvENToRs E/iW//v C//A/vo WERK (Mgg/cf l EN TZ /M/ M/ #Zd/wav ATTORNEYS Jan. 2, 1951 Filed July 51, 1948 Patented Jan. 2, 1951 AUTOGENOUS COKING F AGGLOMERATES 0F ZINCIFEROUS AND CARBONACEOUS MATERIALS Erwin C. Handwerk and Clarence J. Lentz, Palmerton, Pa., assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application July 31, 1948, Serial No. 41,853

Claims. l

This invention relates to the coking of agglomerates of zinciferous and carbonaceous materials and, more particularly, to autogenous coking of such agglomerates for the production of charging material pre-eminently suitable for the vertical retort smelting of zinc ores and the like.

In the vertical retort smelting of zinciferous material, the smelting charge of zinciferous material and carbonaceous material is introduced into the retort in the form of coked agglomerates. The physical requirements of these agglomerates are manifold. For example, such agglomerates :in the form of briquettes must have sufficient strength after reduction of the zinciferous ma. terial therein' to prevent crushing of the briquettes in the lower portion of the charge due to the weight of the charge with the resulting production of nues. The briquettes should also be characterized by a cellular structure in which the particles of zinciferous material are largely enclosed by the coked carbonaceous material. The surface of the coked briquettes should be as smooth as possible and the particles of zinciferous material in the surface should be adequately bonded to the briquette by the coke structure. Roughness of the surface of the briquettes, and particularly roughness caused by selective removal of the coke structure adjacent the surface of the briquettes, results in sanding occasioned by attrition of adjoining rough surfaces of the briquettes and dislodgment of the insufficiently bonded surface particles of zinciferous material. The nes, whether produced by crushing or sanding of the briquettes, tend to settle in the retort more rapidly than the briquettes and cause the 1' briquette charge to bind within the retort. Moreover, a sandy or ashy surface on the briquettes increases corrosion of the retort walls. Accordingly, the briquettes must be of such structure, both with respect to strength and surface smoothness, as to minimize the production of nes which interfere with the proper operation of a vertical retort over prolonged periods.

Coked briquettes of zinciferous and carbonaceous materials having a suitable structure for charging to a vertical zinc smelting retort have been produced heretofore in coking ovens heated by combustion of an extraneous fuel. It has been realized for years that autogenous coking of such briquettes would be highly desirable inasmuch as the coking heat would be provided by combustion of the volatiles reeased from the coal in the briquettes in the course of the coking operation. Nevertheless, to the best of our knowledge, autogenous coking of briquettes of zinciferous and carbonaceous materials has not been accomplished because of the demanding requirements of such briquettes for charging to vertical retorts.

The autogenous coking of coal briquettes is described in the United States patents to Ander- Sen et al., Nos. 2,209,255 and 2,380,930. In accordance with these patents a loose charge of coking coal is maintained in a furnace in the form of a moving bed which passes slowly through the furnace. By passing air upwardly through the bed of coal in the hot furnace, the volatile matter liberated from the coal is burned to produce all of the heat within the furnace required to effect the desired coking of the coal bed. By carefully controlling the amount of air admitted to the various portions of the moving bed of coal, uniform coking of the coal bed may be effected solely by means of the heat of combustion of the volatile matter driven from the coal without objectionable combustion of the solid carbon content of the coal.

We have endeavored to use the method of autogenous coking described .in the aforementioned patents for the coking of ore-coal agglomerates destined for use in vertical retort smelting, but we have been unable to obtain the necessary control over the coking operation with this method. When ore-coal agglomerates are heated to a temperature in excess of about 900 C., the coal reduces the ore and Iiberates zinc vapor. In the presence of air, as in the above-described method of autogenous coking, this liberated zinc vapor is oxidized and produces a cloud of zinc oxide. We have found that when air is passed through a heated bed of ore-coal agglomerates in an attempt to autogenously coke the agglomcrates, it is virtually impossible to maintain a uniform briquette temperature close to but not exceeding about 900 C. without sudden rises in temperature, either local or widespread, with the result that appreciable amounts of zinc are lost in the form of zinc oxide and a substantial amount of carbon is burned away from the ore particles on the surface of the agglomerates. As a result, the surface of the coked agglomerates has a sandy or ashy quality, or both, and is not desirable for use in a vertical zinc smelting retort.

We have now discovered that agglomerates of zinciferous and carbonaceous materials may be coked autogenously provided the air used to support combustion of thel liberated volatile matter from the carbonaceous material, which is composed at least in part of cokable carbonaceous material, is introduced in controlled amounts in several stages. Thus, we have found that if only a portion of the combustion-supporting air is passed through the heated bed of agglomerates in amount suilicient only to produce a gentle and protective flame around the agglomerates, the remaining heat required to bring the Aagglomerates up to a. suitable coking temperature not in ecess of 900 C. maybe provided by radiation from a heating zone in which further combustion of unconsumed volatile matter` is effected substantially out of contact with the bed of agglomerates. Accordingly, the method of producing coked agglomerates of Azinciferous and carbonaceous materials in accordance with our present invention comprises moving a bed of cokable agglomerates of zinciferous and carbonaceous materials through a furnace in which coking conditions are established, passing through said bed of agglomerates an amount of air suillcient to support combustion within the bed of only a portion of the voltatile matter liberated from the carbona- .ceous material by the coking thereof and to produce about said agglomerates a gentle, protective, candle-like flame resulting solely from combustion of said volatile matter, and supplying to the unconsumed volatile matter out of contact with said bed but in heat transfer relationship therewith a controlled amount of air sufficient to produce by combustion of at least a portion of said previously unconsumed volatile matter an amount of heat such as to establish said coking conditions and bring said agglomerates to a coking temperature not in excess of 900 C. By charging the resulting coked briquettes to a vertical retort, the zinc smelting operation is facilitated by the smooth passage of the briquettes through the retort as the.

zinciferous material is reduced and as some of the carbonaceous material is consumed in the course of this reduction.

These and other novel features of the invention will be more fully understood from the following description taken in conjunction with the drawings in which Fig. 1 is a side elevation, partly in section, of

Fig. 3 is a sectional plan view taken along lines 3-3 in Fig. 1.

Apparatus suitable for carrying out the autogenous coking operation in accordance with our invention comprises a furnace I0 provided with a suitable traveling grate II in the lower portion thereof. The upper portion of the furnace above the grate is provided with a partition I2 which divides this upper portion of the furnace into two substantially independent but communicating combustion zones. The combustion zone between the grate I I and the partition I2 will be referred to herein as the primary combustion zone, and the combustion zone above the partition I2 will be referred to as the secondary combustion zone. Separate air supplies are provided for introducing air below the traveling grate, for introducing air into the primary combustion zone and for introducing a further quantity of air into the secondary combustion zone. The separate combustion zones with the three independent air supplies make it possible, in accordance with our invention, to autogenously coke agglomerates of zinciferous and carbonaceous material and to completely consume all volatile matter liberated therefrom so that substantially no smoke or fumes are discharged from similarly inclined chute I5 which carries the bri- I quette charge through the furnace opening I6 and onto the charging end of the grate I I. Within thefurnace and above the charging end of the grate II there is provided a leveling bar I1 which, as its position is changed in a vertical plane, controls the thickness of the bed of briquettes distributed on the charging end of the traveling gate. The traveling grate II may advantageously comprise a step grate such as that described in the United States patent to Gailney, No. 2,229,447. Such a step grate provides a downwardly inclined path of travel for the agglomerates from the charging end to the discharging end thereof. We have found that a step grate of this type is particularly well adapted to move a bed of agglomerates uniformly through the coking furnace with sufficient agitation of the bed to promote uniform coking throughout the bed thickness. On the other hand, a conventional coal Stoker grate may be used where the nature of the briquettes is such that a continuously moving but unagitated bed of briquettes is desirable. charges into a hopper I8 formed integrally with the furnace structure. The coked briquettes which accumulate in the hopper may be discharged intermittently or continuously through the discharge gate 20 onto a traveling belt 2| or the like. The coked briquettes removed on the traveling belt may be introduced directly into the charging end of a vertical retort of conventional design.

Fines are removed from the briquette charge throughout its entire path of travel. Thus, the grizzly I4 in the charging hopper effects the separation of fines which are collected in the lower portion of this hopper. The fines so removed are uncoked and still contain the briquetting binder in amount suiiicient to permit return of these fines to the briquetting machine. Fines are also separated from the briquettes as the charge is moved through the furnace on the traveling grate I I. These latter fines ar collected in the hoppers 22 provided immediately below the grate. The fines separated from the charge within the furnace are at least partially coked and have had their binder driven off. Accordingly, these fines are returned to the mixer used in making up the briquette composition.

The separate combustion zones within the furnace are provided, as mentioned hereinbefore, by the partition I2. The partition is advantageously provided with a plurality of openings 23 provided with sliding tiles 24 whereby the openings may be either partially or completely closed in order l to control the temperature of the combustion gases in the various portions of the primary cornbustion zone.v The openings 23 also permit the passage of unconsumed volatiles from the primary combustion zone into the secondary combustion zone where they are completely consumed. The products of combustion are removed from the secondary combustion zone through a stack 25 which operates under a normal stack draft but which may be controlled by a suitable damper26.

The air supply which is passed upwardly through the moving bed of agglomerates is ad- The grate II dlsvantageously admitted under pressure through a suitable supply line 21 provided with valved branches to each of the hoppers 22 disposed below the traveling grate I I. This air supply, which will be referred to herein as the primary air supply, must be carefully controlled in accordance with the invention in order to maintain a gentle, protective, candle-like flame about the briquettes in the moving bed. Each of the air supply branches 28 is separately valved in order that the amount of air supplied to each hopper may be controlled to produce the desired flame characteristics. By proper control of the air supply to each of the zones of the moving bed corresponding to the area of the hoppers therebelow, uniform coking conditions may be established in each zone of the bed. In all events, the amount of air admitted through the grate'to the separate coking zones of the moving bed is so controlled in accordance with our invention that the heat of combustion of volatiles consumed within the moving bed is not sufficient of itself to raise the temperature of the briquettes up to the desired coking range. There is thus avoided any possibility of local overheating of the briquettes in the moving bed to a temperature in excess of 900 C. at which reduction of the zinciferous material will occur as well as deterioration of the carbonaceous bond holding the particles of zinciferous material firmly in place.

'I'he air supply to the primary combustion zone above the moving bed of briquettes is introduced through ports 30 in the side walls of the furnace. The air may be drawn through these ports by the natural stack draft existing within the furnace, in which case the ports 30 are provided with suitable adjustable closures for controlling the volurne of air admitted, or the air may be supplied under pressure to the ports by individually valved supply lines. The amount of air thus introduced into the primary combustion zone should be so controlled as to veffect combustion oi' only that amount of the unconsumed volatiles liberated from the moving bed required to bring the temperature of the bed up to an average coking temperature close to 800 C. with the hottest briquettes not exceeding a temperature of 900" C. The resulting incomplete combustion of volatiles within the primary combustion zone produces a brilliant flame ideally suited for supplying radiant heat to the bed of briquettes. This radiant heat effects uniform heating of the moving bed and does not tend to produce small areas or zones of local overheating. With the primary air supply below the grates so adjusted as to maintain a gentle, protective, candle-like flame about the briquettes, the amount of secondary air admitted through the ports in the primary combustion zone should be kept just below that which will produce, by an excessive amount of heating, orereducing conditions in the bed which are detected by the presence of white clouds of zinc oxide in the exit gases from the stack.

The tertiary air for the secondary combustion zone above the partition I2 is supplied through Doris 3| in the side walls of the furnace adjacent this zone. The air may be drawn into the furnace by the stack draft existing therewithin, or the air may be supplied under pressure from an air line. The amount of tertiary air so introduced through the ports 3| need not be carefully controlled insofar as the success of the coking operation is concerned. This secondary combustion zone is separated from the primary combustion zone by the partition I2 and its temperature has little elect upon the coking temperature established in the moving bed of briquettes on the grate II. However, in order to minimize the smoke-like discharge from the stack, due tothe presence therein of unconsumed volatile matter from the coking operation, the amount of tertiary air admitted to the secondary combustion zone should be suillcient to effect substantially complete combustion of those volatiles not previously consumed in the moving bed or in the primary combustion zone.

We have found it advantageous to provide a take-off line 32 from the stack 25 through which, with the aid of a motor-driven fan I3 and an auxiliary air line 34, a mixture of warm stack gases cooled and diluted with a controlled amount of cool air from the auxiliary air line may be delivered through a. branched line `35 to the charging hopper I3 below the grizzly Il. These warm gases serve to dry the briquettes while they are still in the charging hopper so that they may be raised quickly to a coking temperature as they slide down the chute I5 into thefurnace. These drying gases, together with any furnace gases which may escape through the furnace opening I6, may be removed by a suction hood 36 positioned immediately above the charging hopper.

It will be seen, therefore, that the coking furnace used in the practice of our invention provides careful control of the air supply to separate zones within the furnace (the moving bed and the primary combustion zone) in order to control the coking temperature and conditions in the bed of briquettes containing zinciferous and carbonaceous materials. Such control of the air supply makes it possible to coke the briquettes without reduction of the zinciferous material and without deterioration of the carbonaceous bond on the surface of the briquettes. The small amount of air uncontrollably admitted through the discharge gate 20 as the coked briquettes are discharged from the hopper may be removed therefrom without gaining access to the furnace interior by the provision of a suction line 31 connected to the hopper I8.

'I'he operation of the coking apparatus shown in the drawings for the autogenous coking of agglomerates of zinciferous and carbonaceous materials in accordance with our invention is as follows. The briquettes are preferably produced as described in the patents to Bunce No. 1,810,070 and Bunce et al. No. 1,835,460. The zinciferous material used in preparing such briquettes may, for example, comprise zinc ore, such as Willemite, or zinc blende (roasted zinc sulfide ore), or mixtures thereof, with or without further enriching additions fof refuse zinc oxide, such as Waelz oxide, and the like. The briquettes should contain from 18 to 30% by weight of bituminous coal of the free-swelling type, and of good coking quality, and preferably not more than 27% of such coal. Amounts of bituminous coal below 18% do not provide enough volatiles to supply the heat required for autogenous coking and produce briquettes of unsatisfactory strength. Amounts of such bituminous coal above 30%, or better 27%, tend to produce excessive swelling. The amount of the bituminous coal used generally varies with the fineness of the coal particles, the nner the particle size the less coal is required. Thus, 20% of extremely finely divided bituminous coking coal will be as effective as 25% of a coarser grind of the same coal. The balance of the carbonaceous material in the briquettes is composed generally of non-coking coal such as anthracite.

The briquettes are delivered to the charging hopper I3 and are discharged by the grizzly I4 and the chute I5 onto the traveling grate I I. The

position of the leveling bar I1 is so chosen as to provide on the grate a bed of briquettes of sulcient depth to insure uniform coking. We prefer to so adjust the thickness of the bed with respect to the grate area and the bed speed as to produce between 0.4 and 1.2 tons of coked 'briquettes (output) per day per square foot of grate area. Although operation within this range will produce briquettes autogenously coked to a satisfactory uniformity, we havel found it best to adjust the output of coked briquettes to 0.6-0.7 ton per day per square foot of grate area.

In normal operation, the controlled combustion of volatiles within the furnace will provide the desired coking conditions. For the purpose Y o f starting the furnace, however, these coking conditions may be established by burning any suitable fuel introduced into the primary combustion zone. The briquettes entering the charging end of the furnace on the chute I5 are exposed to the radiant heat of the primary cornbustion zone and are thereby brought nearly to the coking temperature before they are deposited on the grate II. The amount of primary air supplied under pressure through the valved inlet lines 28 is so regulated as to maintain a gentle, protective, candle-like flame about the briquettes, and within this limit the amount of air deliveredwto the several bed zones corresponding to the hoppers 22 are adjusted so as to maintain uniform coking conditions throughout the entire moving bed. With the amount of primary air thus established, the amount of secondary air admitted through the ports 30 to the primary combustion zone is adjusted so as to provide, by partial combustion of the volatile matter in this zone, an amount of heat just below that which will produce reducing conditions in the bed of agglomerates. From a practical operating point of view, this amount of secondary air can be determined by observing through a sight hole 38 in the end of the discharge hopper the color of the lowermost layer of briquettes leaving the discharge end of the grate. The amount of secondary air is increased to give the highest temperature for these briquettes without reduction of the zinciferous ore. The point at which such ore reduction commences may be observed readily by the presence of a cloud of white zinc oxide in the stack gases. Such ore reduction occurs whenever the temperature of a briquette exceeds 900 C. For this reason, the temperature of the hottest briquettes should be limited to about 900 C. with the average bed temperature approximating a temperature of 800 C. The amount of tertiary air supplied through the ports 3| in the secondary combustion zone is preferably adjusted to admit a sufcient quantity of air to completely burn the sired physical strength to resist crushing in the lowerportion of the vertical retort but they are further characterized by exceptionally good surface characteristics which minimize sanding Briquettes produced in accordance with the coking process of our invention promote improved operation of the vertical smelting retorts. The strength of the briquettes and their desirable surface condition minimize the production of nes and insure smooth and uninterrupted ow of briquettes downwardly through the retorts as the zinciferous and carbonaceous materials are consumed. The non-sandy, non-ashy surface of these briquettes also reduces corrosion of the vertical retort walls to a minimum. It will be seen, therefore, that we have devised an improved vertical retort smelting operation characterized by theuse, as a charging material. of agglomerates of zinciferous and carbonaceous material autogenously coked by the method described hereinbefore.

We claim:

1. In the production of coked agglomerates of zinciferous material and carbonaceous material wherein a body of cokable agglomerates of said zinciferous material containing between 18 and 30% by weight of bituminous coal is passed through a coking chamber maintained at an elevated temperature sufcient to effect coking of .said coal, the improvement which comprises movingr said cokable agglomeratesin the form of a bed through the coking chamber, passing through said bed of agglomerates an amount of air sufficient to support combustion within the bed of only a portion of the volatile matter liberated from the carbonaceous material by the co-.:ing thereof and to produce about said agglomerates a gentle protective ame resulting solely from combustion of vsaid volatile matter, and supplying to the unconsumed volatile matter out of Contact with said bed but in heat transfer relationship therewith a controlled amount of air suicient to produce by combustion of at least a portion of said previously unconsumed volatile matter an amount of heat such as to establish said colrin' conditions and bring said agglomerate; to a coking temperature not in excess of 900 C.

2. In the production of coked agglomerates of zinciferous material and carbonaceous material wherein a body of cokable agglomerates of said zinciferous material containing between 18 and 30% by weight of bituminous coal is passed through a coking chamber maintained at an elevated temperature suiiicient to effect coking of said coal, the improvement which comprises moving said cokable agglomerates in the form of a bed on a grate through the coking chamber, passing through said bed of agglomerates an amount of air suiiicient to support combustion within the bed of only a portion of the volatile matter liberated from the carbonaceous material by the coking thereof and to produce about said agglomerates a gentle protective iiame resulting solely from combustion of said volatile matter, and supplying to the unconsumed volatile matter out of contact with said bed but in heat transfer relationship therewith a controlled amount of i air suflicient to produce by combustion of at least a portion of said previously unconsumed volatile matter an amount of heat such as to effect colringr of said cokable agglomerates at a rate of 0.4 to 1.2 tons of coked agglomerates per day per square foot of grate area at a coking temperature not in excess of 900 C.

3. In the production of coked agglomerates of zinciferous material and carbonaceous material wherein a body of cokable agglomerates of said zinciferous material containing between 18 and 30% by weight of bituminous coal is passed through a coking chamber maintained at an elevated temperature suiiicient to effect coking of said coal, the improvement which comprises moving said cokable agglomerates in the form of a bed through the `coking chamber, consuming by combustion in said bed an amount of the volatile matter liberated from the carbonaceous material by the coking thereof insufficient to provide the heat required for said coking, and supplying the remainder of the heat required to bring the agglomerates up to the coking temperature but not in excess of 900 C. by radiation from a combustion zone in which the heat is obtained by combustion of volatile matter liberated from the carbonaceous material and not consumed in said bed of agglomerates.

4. In the production of coked agglomerates of zinciferous material and carbonaceous material wherein a body of cokable agglomerates of said zinciferous material containing between 18 and 30% by weight of bituminous coal is passed through a coking chamber maintained at an elevated temperature sufiicient to effect coking of said coal, the improvement which comprises moving said cokable agglomerates in the form of a bed through the coking chamber, and providing said coking conditions by the radiant transfer of heat to said bed from a combustion zone in which the heat is provided by combustion of at least a portion of the volatile matter liberated from said carbonaceous material by the coking thereof, the amount of heat transferred to said bed being insuicient to heat the agglomerates to a temperature in excess of 900 C.

5. In the production of coked agglomerates of zinciferous material and carbonaceous material wherein a body of cokable agglomerates of said zinciferous material containing between 18 and 30% by weight of bituminous coal is passed through a coking chamber` maintained at an elevated temperature suiiicient to effect coking of said coal, the improvement which comprises moving said cokable agglomerates in the form of a bed on a grate through the coking chamber, and providing said coking conditions by the radiant transfer of heat to said bed from a combustion zone in which the heat is provided bv combustion of at least a portion of the volatile matter liberated from said carbonaceous material by the coking thereof, the amount of heat transferred to said bed being suflicient to effect coking of said cokable agglomerates at a rate of 0.4 to 1.2 tons of coked agglomerates per day per square foot of grate area at a coking temperature not in excess of 900 C.

ERWIN C. HANDWERK. CLARENCE J. LENTZ REFERENCES CITED Ihe following references are of recordi in the le of this patent:

UNITED STATES PATENTS Guardian, July 7, 1944. pages 26-28.

Claims (1)

1. IN THE PRODUCTION OF COKED AGGLOMERATES OF ZINCIFEROUS MATERIAL AND CARBONACEOUS MATERIAL WHEREIN A BODY OF COKABLE AGGLOMERATES OF SAID ZINCIFEROUS MATERIAL CONTAINING BETWEEN 18 AND 30% BY WEIGHT OF BITUMINOUS COAL IS PASSED THROUGH A COKING CHAMBER MAINTAINED AT AN ELEVATED TEMPERATURE SUFFICIENT TO EFFECT COKING OF SAID COAL, THE IMPROVEMENT WHICH COMPRISES MOVING SAID COKABLE AGGLOMERATES IN THE FORM OF A BED THROUGH THE COKING CHAMBER, PASSING THROUGH SAID BED OF AGGLOMERATES AN AMOUNT OF AIR SUFFICIENT TO SUPPORT COMBUSTION WITHIN THE BED OF ONLY A PORTION OF THE VOLATILE MATTER LIBERATED FROM THE CARBONACEOUS MATERIAL BY THE COKING THEREOF AND TO PRODUCE ABOUT SAID AGGLOMERATES A GENTLE PROTECTIVE FLAME RESULTING SOLELY FROM COMBUSTION OF SAID VOLATILE MATTER, AND SUPPLYING TO THE UNCONSUMED VOLATILE MATTER OUT OF CONTACT WITH SAID BED BUT IN HEAT TRANSFER RELATIONSHIP THEREWITH A CONTROLLED AMOUNT OF AIR SUFFICIENT TO PRODUCE BY COMBUSTION OF AT LEAST A PORTION OF SAID PREVIOUSLY UNCONSUMED VOLATILE MATTER AN AMOUNT OF HEAT SUCH AS TO ESTABLISH SAID COKING CONDITIONS AND BRING SAID AGGLOMERATES TO A COKING TEMPERATURE NOT IN EXCESS OF 900* C.

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