US2021284A - Manufacture of zinc oxide - Google Patents

Description

Patented Nov. 19, 193" yETED S'EATES PATENT FFICE Mahler, Palmerton, Pa.

assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application March 24, 1930, Serial No. 438,462

2 Claims.

This invention relates to the manufacture of zinc oxide and has for its object certain improve:n ments in the method of and apparatus for manufacturing zinc oxide. The nvention relates more particularly to the manufacture of zinc oxide from an agglomerated charge of mixed zinciferous material and carbonaeeous reducing agent.

In our copending application, Serial No. 438,461 led Mar. 24, 1930, we have disclosed a method of and apparatus for manufacturing zinc oxide from an agglomerated charge of mixed zinciferous material and carbonaceous reducing agent confined Within an externally heated retort in which a flow of evolved gases and zinc vapor is induced through the retort by controlled stack draft, withdrawing the resulting mixture of gas and vapor from the retort by the aid of said stack draft, and then directing a blast of com pressed oxidizing gas into said mixture of gases and vapor whereby the zinc vapor is burned to zinc oxide.

As a result of our investigations, we have determined that an oxidizing gas, such as air, may advantageously be brought into contact with an issuing stream of zinc vapor by means of suction draft to produce zinc oxide. The suction draft employed, moreover, preferably provides sufficient air promptly to chill the initially formed particles of zinc oxide. If a suction draft of sucient strength is employed, one that is' adapted to provide in amount and velocityrequired, a zinc oxide pigment of extremely fine size may readily be manufactured.

The present invention accordingly contemplates a method of and apparatus for manufacturing zlnc oxide which involves the step of directing a relatively strong suction draft of oxidizing gas into an issu' ig stream of zinc vapor. The invention more pai cularly comprises inducing a flow of evolved gases and zinc vapor through a reduction retort by controlled stack draft, withdrawing the resulting mixture of gases and vapor from the retort cy the aid of said draft, and then directing' a suction draft of oxidizing gas into said mixture of gases and vapor whereby the zinc vapor is burned to zinc oxide; said suction draft preferably being strong enough to exert a suction cect within the retort.

in the present preferred practice of the invention, we employ a vertically disposed and externally heated retort, open at both ends. en agglomerated charge of mixed zinciferous material and carbonaceous reducing agent is progressively passed through the retort by the action of gravity, spent residues being Withdrawn from the lower end. A nozzle is provided at or near the upper end of the retort for the withdrawal of liberated zinc vapor and retort gases. A device of suitable structure appropriately surrounds the 5 outlet of the nozzle, which is designed to suck in large quantities of surrounding air, the air being directed against the stream of zinc vapor issuing from the nozzle. This device may advantageously consist of a hood connected to a source 10 of suction, such as a suction fan. The device preferably has a slotted opening or openings adjacent to the vapor nozzle, so that air drawn into` the device may be directed against the issuing stream of zinc vapor in the form of a relatively thin layer.

As the reduction process proceeds to completion, the charge materials are progressively moved toward the residue discharge end. The retort itself of suicient length or height adapted to set up a natural or chimney-like draft within the retort, preferably augmented by the applied suction draft, which causes the mixture of liberated zinc vapor and retort gases to pass through the vapor nozzle. The draft employed is advantageously made to draw in controlled amounts of air into the bottom of the retort.

These and other features of the present invention, it is believed, will. be better understood by reference to the accompanying drawing, taken in conjunction with the following description, in which:

Fig. 1 is an elevation in section of an apparatus adapted for the practice of the invention;

Fig. 2 is an elevation in section and in part of a` modified form of apparatus adapted to drect a suction draft of air against an issuing stream of zinc Vapor; and

Fig. 3 is a section on the line 3 3 of Fig. 2.

The apparatus shown comprises a furnace structure le resting upon concrete foundations Il. The furnace proper consists of a bottom I2, side walls i3 and an arched roof il built of suitable hcat-resistant material, such as refractory brick, of poor heat-conducting capacity. These furnace linings define a heating chamber l5. An outer metallic casing l@ completely surrounds the furnace. The space between the arched roof and the top of the furnace structure is filled with suitable heat-resistant material l?, such as da tomaceous earth.

Ports I8 are spaced at various intervals throughout the height of the furnace structure, extending completely through the side walls of the heating chamber. They are adapted for the 55 tegrate.

introduction of air and fuel; such as gas, oil or pulverized coal. An opening I9 is provided at or near the upper end of the chamber for the Withdrawal of spent heating gases. This opening preferably connects with a stack or chimney (not Shown). A number of small openings 2E) extend completely through the side walls of the furnace, and are adapted for taking pyrometric readings of the heating chamber.

A vertically disposed retort 2l extends completely through and centrally of the furnace structure. It is preferably supported by the furnace structure at only one place, which is advantageously at the bottom. When constructed in this manner, the retort may expand or contract independently of the furnace structure.

A sleeve member 2 is attached to the underside of the furnace structure. Its passageway is in substantial alignment with that of the retort above. A revolving platform 23 is located immediately below the sleeve member, and is adapted to be rotated about a vertical axis. A rotative movement of the platform throws off spent residues 2d. In the preferred practice of the invention, regulated amounts of air are permitted to seep into the lower end of the retort. An agglomerated charge is employed that `does not tend materially to break down or disin- Air may therefore pass between the voids or spaces provided between contacting residue agglomerates.

The upper end of the retort extends completely through the furnace structure Va, convenient distance, and preferably has a substantial extension or prolongation This extension or prolongation may rest upon the retort; or, it may be separately supported. In our copending application, Serial No. 244,401, filed January 4, 1928, we have disclosed and claimed a process of eliminating lead from zinc vapor contaminated with the same. According to the process therein outlined, the zinc vapor is conducted from the reduction retort to a hot body of( agglomerates about to be subjected to the reduction operation. Under suitably controlled temperature conditions, the hot agglomerates tend selectively to retain lead, and the like, while permitting the ltered zinc vapor to pass on. This process is advantageously employed in the practice of the present invention, particularly when it is desired to manufacture a zinc oxide product substantially lead-free. The extension or prolongation is frequently referred to as an eliminator, because it functions to eliminate lead and the like from zinc vapor contaminated with objectionable amounts of the same.

The eliminator structure 26 comprises an outer metallic casing 2l spaced from and completely surrounding the eliminator, thus providing a free space that is filled with a suitable heat-insulating material .28, such as coal dust. A number of doors 2S are advantageously located at or near the lower end of the metal casing for the removal of coal dust. The upper end of the eliminator structure is preferably open so that heat-insulating material may be introduced or with-drawn.

A charging device 3u ts into the upper end of the eliminator, and extends downwardly a convenient distance. This device is adapted to receive fresh agglomerated charge materials 3l of mixed zinciferous material and carbonaceous reducing agent. A removable cap 32 rests above the charging device. It may be removed from time to time for the introduction of fresh charge materials. If the process and apparatus are to be operated substantially continuously, the cap may be removed and suitable connection made with a source of charge materials adapted to keep the charging device filled.

An off-take conduit 33 is provided at or near the upper end of the eliminator. If desirable, it may be appropriately insulated to avoid undue dissipation of heat. This conduit 'is equipped at its discharge end with a clean-out 33 and a nozzle 3ft adapted to discharge issuing zinc vapor into an oxidizing environment.

An oxidizing chamber 35 is built around the vapor discharge nozzle. It consists of a box-like device with a door 36 in a side wall thereof, to provide access to the interior. connects with an off-take pipe 3l that leads to collecting chambers, where zinc oxide particles may be permanently separated from their accompanying gases. A strong suction fan (not shown), such as is well known to those working in this industry, is employed in association with the pipe and is adapted to exert a strong suction draft. This suction draft is preferably adapted to exert an appreciable suction effect within the retort. An annular space 38 is provided between the upper end of the nozzle and the boxlike device. An upwardly extending and inclined lip S9 of the device, running substantially parallel to the outer face of the nozzle, gives depth to the annular space; which is adapted to give 3 direction to and to cause a relatively thin layer of inrushing air to be directed against zinc vapor issuing from the nozzle. The size of this space may be regulated to accord with optimum oxidizing conditions. In this way the amount of the gas admitted through this space varies inversely as the amount of gas drawn into the base of the retort, the total amount of gas drawn in at the two points tending to remain constant.

A modified form of apparatus for oxidizing an issuing stream of zinc vapor is shown in Fig. 2. The annular space 38 is not provided with a guiding lip, as in the case of the apparatus described above. A number of holes or vents 40 The chamber 1 are located in the bottom of the box-like device 5 to a level preferably at or above the opening leading into the off-take conduit 33. then replaced.

Suitable air and fuel, such as oil, are introduced into the heating chamber l5 through the ports ill. The combustion gases circulate around The cap 32 is the retort and ultimately nd their way through the exit iii to a stack or chimney (not shown). Pyrometric readings of the temperatures prevailing within the heating chamber are taken from time to time through the openings 20. Suitable regulation of the amount and quality of the heating gases is made from time to time to provide for optimum reduction temperatures.

As the heating operation continues, heat is gradually driven through the retort walls and into g the agglomerated charge materials confined creates a draft through the column of agglomerates to sweep out the zinc vapor evolved therein, and adjusting the size of said aperture so that the amount of the blast of oxidizing gas varies inversely With the amount of the current of air drawn into the base of the column, whereby optimum oxidizing conditions producing a substantially uniform product are maintained in said chamber to burn the zinc vapor to zinc oxide.

2. In a method of making zinc oxide by introducing a blast of oxidizing gas into a stream of zinc vapor and gaseous products of combustion issuing into an oxidizing chamber from the upper end portion of an elongated vertical porous column of agglomerated zinciferous material and carbonaceous reducing agent, the base of the column being in communication with a source of gas under approximately atmospheric pressure, the sides of the column being enclosed and the upper end portion of the column being in communication with the oxidizing chamber, the improvement which comprises producing a reduced pressure in the oxidizing chamber. With a source of suction to draw the blast of oxidizing gas into the stream of zinc vapor, simultaneously producing a reduced pressure Within the base of the porous column by means of the same source of suction to draw gas into the base of the column and to sweep out zinc vapor formed in the column and prevent its condensation within the column, and varying the quantities of gas drawn into the stream of zinc vapor, issuing from the column and into the base of the column inversely to each other, whereby optimum oxidizing conditions are maintained in said chamber to burn the zinc Vapor to zinc oxide and a substantially uniform zinc oxide product results.

EARL H. BUNCE. CLARENCE J. LENTZ, GEORGE T. MAHLER.

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