US2344445A - Material for charging furnaces - Google Patents

Description

.March 14', 1944. B. MANSFIELD MATERIAL FOR CHARGING FURNACES Filed Dec. 22, 1942 O/Q/VE) Patented Mar. 14, .1944

Bernard Mansfield, Tott Nassau smelting & R porated, New York, N.

York

enville, N. Y., assignor to eflning Company, Incor- Y., a corporation of New Application December 22, 1942, Serial No. 469,802

8 Claims.

This invention relates to materials for charging furnaces, and more particularly to materials for charging furnaces for distilling zinc.

Due to the present metal shortage, it is now desirable toutilize zinc bearing by-products,

taining a mixture of zinc material and a reducing agent, such as coal, .both of which are finer than mesh. The percentage of fines is such that the charge has littleporosity and the zinc vapor and reducing gases do not pass freely through the charge, thus slowing up the distillation rate and requiring a high temperature to drive out the zinc vapor. Also when zinc bearing material of the type above described is treated in this manner, the amount of zinc remaining in the residual matter left in the furnace at the end of the distillation process usually is high enough to make such a process economically unfeasible.

The flnely divided nature of the charge causes packing of the-charge, which prevents the reducing gases formed in the furnace from flowing freely through the charge and reducing all of the zinc oxide and other zinc compounds to the metallic state. The gases and zinc vapor also have a tendency to channel andcause certain areas to be more completely reduced than other areas. The finely ground charges generally employed in furnaces for distilling zinc are wetted before being packed in the retorts, and not only require considerable time to become heated to the operating temperature of the furnace, but, of course, cannot be preheated before being fed into the furnace. Perhaps the most serious drawback, however, to these finely ground charges is that they tend to clinker and adhere to the Walls-of the retorts in which they are heated. For this reason, it is frequently necessary to manually remove the residue by scraping or sharply pounding the retort.

An object of this invention is to provide new and improved charging materials for furnaces,

and more particularly to provide new and improved charging materials for zinc distilling furnaces.

are supported by A charge material 'for an inclined, indirectly heated furnace for distilling zinc which is illustrative of the present invention consists of a mixture composed of crushed zinc bearing material, coal screenings, and lumps of coke in sizes varying from about 2 inches to about 6 inches in diameter.

Qtherfeatures and advantages of the invention will become apparent from the following detailed description of one embodiment thereof, when read in conjunction with the accompanying drawing, in which Fig. l is a front elevation of an inclined, indirectly heated furnace for distilling zinc, and

Fig. 2 is a vertical sectional view of the furnace shown in Fig. l.

The furnace shown somewhat schematically in the accompanying drawing comprises a body l0 constructed of a suitable refractory material such as fire brick of a type usually employedin similar furnaces. An arched roof II is provided for the body mits gases to escape from a combustion chamber l3, formed by the body I0 and the roof H. A

number of retorts ll-H made of clay or graphite the body l0 at an angle of about 30 to 45 and are arranged in three rows. Each of the retorts shown in the particular furnace disclosed in the accompanying drawing is capable of refining about 500 pounds of charge materials during each cycle of operation, although the particular shape, size and number of the retorts [4-H may, of course, be varied considerably without departing from the invention. Each retort I4 has a charging opening IS in its upper end, and a smaller discharging opening H in its lower end normally closed by means of a plug I6, which may be removed to allow the charge material within the retorts Il-ll to slide out of the furnace through openings Ill-l8 formed in the body l0. Oil burners (not shown) are associated with openings |9--l9 disposed at the sides of the furnace to heat the combustion chamber 13, and thus indirectly heat the charge material within the retorts l4 l4.

A condenser 2| is placed over the ,end of each retort It to collect the zinc as it is distilled from the charge in the retorts and air tight joints between the condensers and the retorts are effected by fire clay seals 20-20. The particular construction of the condensers 2l2l does not form part of the present invention and the condensers may be of any conventional type. Hence, it is suiiicient to say that each condenser includesa feed hole 22, a collecting chamber 23,

Ill and a flue l2 formed therein perinto the retorts ll-ll through the charging 10 openings l5-|5. The charge fed to each retort may weigh as much as 500 pounds and may be preheated, if desired. After the retorts have been filled with the charge, the feed holes 22-22 are closed by inserting therein the blocks 26-48 of refractory material and luting them in place. The temperature in the combustion chamber I3 is gradually raised during a period of about 2 hours to between about 2400 F. and 25009 F.,

at which temperature the metallic zinc formed by the reduction of the zinc compounds in the charging materials begins to distill into the condenser and the carbon monoxide gas that is formed escapes through the vent hole 24, where the clinkerlng of the charge in the retorts. Normally, the charge should flow by gravity out through the opening in the bottom of the retorts, but when clinkers were formed in the charge, the ejection of the residual charge left after the distillation of the zinc was greatly hindered. As a result, considerable. timeand effort were required to remove the residual charge from the retorts by mechanical means such as pounding and scraping, and the life of the retorts was shortened.

A charge, which illustrates an embodiment of the present invention and which has proven highly satisfactory when used in a furnace such as that shown in the accompanying drawing, consists of a mixture of zinc bearing materials, coal and coke. The zinc bearing materials, in this particular illustration, may consist of zinc ashes, zinc skimmlngs, zinc oxide, sal skimmings, die casting skimmings and other by-products containing relatively low percentages of zinc.

' Both the zinc bearing materials and the coal are it is ignited and burned as it passes into the atmosphere.

The distillation of the zinc iscontinued for about 20 hours, so that one complete cycle of operation requires about 24 hours. During the distillation of the zinc it is necessary to withdraw the molten zinc that condenses in the bottom of the collecting chamber 23 in each of the condensers 2l-2I through the tap hole 25 approximately every 8 hours. When the distillation process has ended, the oil burners are shut off and the plugs lB-IS are removed from the retorts 14-44 to permit the residual material from the charge-to slide out of the retorts through the openings l|-l| and throughthe openings lt-il in the furnace body Ill into a suitable receptacle. The plugs i6|6 are then reinserted in the lower ends of the retorts ll-ll, and a second charge is fed into charging openings |5--| in the retorts through the feed holes 22-22 in the condensers 2l2l to commence the following cycle of operation. As an alternative procedure, the charge may be fed directly into the retorts "-14 through the openings zinc containing materials to metallic zinc which l5-l 5, in which case condensers which may have no feed holes are sealed to the retorts after the charge has been'fed into the retorts and are removed from the retorts when another charge is I to be fed thereto.

The type of charge generally employed in furnaces somewhat similar to that shown in the accompanying drawing consisted of zinciferous materials, usually in the form of oxides, and suitable reducing material, such as coal or coke.

These ingredients were usually ground to ap- 6 proximately t4 inch mesh or finer. Since the ingredients of the charge were fairly uniform in size and quite small, they tended to become packed, thus preventing free movement through the charge of the reducing gases formed during the heating of the retorts. As a result of the non-uniformity of the reduction and the distillation and the packing of the charge, the time and temperature required for distilling the zinc therefrom were increased considerably, which 7 was undesirable both because it consumed valuable time and because it increased the amount of fuel required to distill a given quantity of zinc. Perhaps the most undesirable effect resulting from the abovementioned type of charge was 75 ground sufficiently fine to pass through a 10 mesh screen. The coal used may be what is known in the art as screenings, which are generally composed of coal particles that will pass through a 10 mesh screen. I

The coke, in the form of lumps of from about 2 inches to about 6 inches in diameter, is mixed with the ground zinc bearing materials and coal screenings in the proportion of about 5% coke, about 25% coal, and about zinc bearing materials. These proportions, of course, will vary somewhat with the particular zinc bearing material or materials used.

The charge is then thoroughly mixed and preheated, if' desired, before it is introduced into the retorts ll-ll in order to considerably shorten the cycle of operation of the furnace and increase its output. After the charge has been fed into the retorts lC-il, the furnace is operated as above described.

Due to the uniform mixing of the zinc containing material with the other ingredients of the charge, suillcient reducing materials are intermixed with the zinc containing ingredients to reduce all of the readily available zinc in the distills into the condenser. The large coke particles make the mix quite porous and permit free movement of the reducing gases through.

the entire charge. As a result, the cycle of operation of the furnace is further shortened, less fuel is required for a given quantity of zinc distilled and only a small amount of zinc, generally less than 5%, is left in the residual charge.

The large coke lumps also prevent clinkering of the charge and permit the removal of'the charge by gravity alone at the bottom of the retorts, thus lengthening considerably the life of the retorts and shortening the time required to remove the charges.

The use of a charge like thatdescribed makes the above outlined process economically feasible by increasing the amount of zinc obtained from the zinc containing materials, by shortening the cycle of operation of the furnace, by reducing the amount of fuel required to distill a given amount of zinc, and by facilitating the discharge of the residual charge material, thus lengthening the life of the equipment considerably.

What is claimed is:

i. A charge for an inclined, indirectly heated 2. A charge for an inclined, indirectly heated furnace for the distillation of zinc, which consists of a uniform mixture composed of crushed zinc bearing materials, coal particles capable of passing through a screen of approximately 10 mesh, and lumps of coke in sizes varying from about 2 inches to about 6 inches in diameter.

3. A charge for an inclined, indirectly heated furnace for the distillation of zinc, consisting of a uniform mixture composed of crushed zinc bearing materials ground to at least about 10 mesh fineness, coal ground to at least 10 mesh fineness, and about 5% coke in the form of lumps varying in size from about 2 inches to about 6 inches in diameter.

4. A charge for an inclined, indirectly heated furnace for the distillation of zinc having inclined retorts, which consists of a uniform mixture composed of about 70% crushed zinc bearing materials, about 25% coal screenings, and about 5% coke in the form of lumps varying in size from about 2 inches to about 6 inches in diameter.

5. A charge for an inclined, indirectly heated furnace for the distillation of zinc, which consists of a uniform mixture composed of about crushed zinc bearing materials, about 25% coal of at least about 10 mesh fineness, and about 5% coke in the form of lumps varying in size from about 2 inches to about 6 inches in diameter.

6. A charge for an inclined, indirectly heated furnace for the distillation of zinc, which consists of a uniform mixture composed of about 70% crushed zinc bearing materials of at least about 10 mesh fineness, about 25% coal of at least about 10 mesh fineness, and about 5% coke in the form of lumps varying in size from about 2 inches to about 6 inches in diameter.

'7. A charge for an inclined, indirectly heated furnace for the distillation of zinc, which consists of a uniform mixture composed of about 70% of crushed materials which have been passed through a screen of approximately 10 mesh fineness and which contain a low percentage of zinc, approximately 25% coal which has been passed through a screen of approximately 10 mesh fineness, and about 5% coke in the form of lumps varying in size from about 2 inches to about 6 inches in diameter.

8. A charge for an inclined, indirectly heated furnace for the distillation of zinc, which consists of a uniform mixture of crushed materials containing'a low percentage of zinc, coal screenings, and lumps of coke varying in size from about 2 inches to about 6 inches in diameter;

BERNARD MANSFIELD.

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