US2543420A - Metal smelting process - Google Patents

Description

Feb. 27, 1951 w. A. OGG

METAL SMELTING PROCESS Filed April 3, 1948 .Zi'zvenfon WzZZam d1. 0

I m M k dilfigs Patented Feb. 27, 1951 ,siaizc Nrro res earns Ii Claim.

This invention relates to a smelting process for winning zinc and the like volatilizable metals. In accordance with the invention the charge to be smelted, comprising crude ore and reduction material, is supported on the surface of a bath of hot liquid of relatively high specific gravity and, at the temperatures involved, substantially inert in the sense that it will not react chemically in significant degree with the materials of the charge, from which bath at least a substantial part of the heat required for the endothermic smelting reaction is supplied, and I so manipulate the and charge, for example by the use of the apparatus to be described, as to render the smelting operation particularly efiicient. A molten and superheated meta]. of sufiiciently'high melting point may be used and, because of its properties and for economic reasons, iron of the type of so-called cast iron or pig iron is suitable. In the following description, for convenience, I shall refer to the material of the bath as iron.

I have described in my Patent 1,988,698, January 22, 1935, the use of a quiescent bath of molten iron to support a suitable charge of zinc oxide and reduction fuel to be heated by radiant heat. In this case the bath was in the nature of a liquid hearth over which a thin layer of charge was waited. In the present instance, on the contrary, the bath serves as a source of heat and the operation is such as to render the sensible heat stored therein available for effecting the reduction and also for rearranging the particles of the charge and the lay-products of the reduction in such a way that the continuance of the reaction is not slowed down but facilitated as it proceeds.

My invention will-be well understood by reference to the following description taken in connection with the accompanying drawings wherein:

Fig.1 is longitudinal section through a smelting furnace;

Figs. 2 and 3 are transverse sections on the correspondingly numbered lines of Fig. l; and

Fig. 4 is an enlarged diagram schematically illustrating the movement of the charge within the furnace incidental to the reducing operation.

A characteristic feature of the apparatus disclosed which provdes for the performance of the characteristic step of the novel process is found in the construction of the reduction chamber iii in the form of a long, downwardly sloping chamher in the nature of a covered trough which is formed from suitable refractory material and has its bottom in the form of a flight of low steps 52. These steps have wide treads and, while I have referred to them as low, the risers are of substantial height. The drawing illustrates steps 21 inches wide and 6 inches high, which dimensions,

however, are not critical. At the upper end of the chamber it] there is provided a storage tank i l to which may be supplied superheated iron which is preferably high carbon iron such as is termed cast iron or pi iron because as compared with other ferrous metals it freezes at a relatively low temperature. The molten iron is superheated to a suitable degree so as to have a large available supply of heat units which may be released in the operation of the process Without bringing the iron to the freezing point. It is released from the tank It through a valve [6 to' ilow down the steps i 2 as a shallow stream which plunges over the steps in a series of small cascades or waterfalls, being discharged at the lower end of the flight to a collecting chamber l8 having a vertical series 29, 22 and 24 of tapping openings therein for purposes which will appear. I have not illustrated in the drawing any heating means connected with the chamber it] such as ceous material. The amount of the carbonaceous material need be only slightly in excess of that theoretically required for the reducing reaction.

Such fluxes as are desirable to slag the gangue of the ore and the ash of the carbonaceous material may be included. The charge thus depos' ited on top of the iron may be preheated to lessen the heat demands on the fluid bath. The distribut on of the charge is substantially uniform over the surface of the bath and the layer of charge mixture will be of such thickness that all the zinc may be reduced before the molten iron on which it floats has left the reaction chamber.

The length of chamber i2 is such that the crude zinkiferous material is completely reduced during the passage of the stream carrying the same through the chamber, so that the discharge to the collecting chamber it consists of the partially cold but still liquid iron and incidental liquid slags. The metallic zinc is disengaged as vapor and withdrawn at the port 32 at the upper part of chamber [2 to condenser 34 (see Fig. 2) and is received as liquid spelter in the set tank 36.

In Fig. 4 I have diagrammed what occurs when the stream of molten iron with the smelting charge floating thereon is precipitated from one step to a lower one. As seen at the left, the relatively light materials of the charge (marked Charge and indicated by stippling) float on top of the molten iron (marked Fe). As the stream plunges over the edge of the upper step and is precipitated on the lower step, the materials are intimately mixed, the condition being analogous to that of the whirlpool at the base of a waterfall. The reduction charge is thus intimately mixed with the iron to be heated thereby. By convection uniformity of temperature of the vertical layer is brought about. For clearness in the diagram the stream is shown as striking the lower tread at some distance from the foot of the upper riser. This is not intended as an indication of a particular horizontal velocity of the stream.

As the mixed material flows along the tread of the lower step, further intimate contact is provided by the tendency of the lighter materials to float up to the top of the iron, and as they again approach the edge of a tread they may have more or less completely resumed the position of a supernatant charge, only to be mixed again as they are precipitated downwardly onto the succeeding step,

It will be seen that the mixing described is effected very simply and, as it were, automatically as the materials pass through the reaction chamber IE1. The power required is provided by the simple operations of elevating the molten iron and the smelting charge to the containers l4 and 26 respectively.

It would be apparent that if the stream of iron were quiescent throughout its course through the chamber, its upper surface would tend to chill and heat from the lower portions of the stream would be relatively slowly transferred to the supernatant charge. In the present instance this tendency toward what we might term thermostratification of the heat reservoir is avoided. A desirable action is also exerted on the charge itself. The materials delivered to the collecting chamber I 8, including the slag, are all liquid, which is desirable. As the stream traverses the reduction chamber, the ash of the reduction fuel and the gangue of the roasted zinc ore become slag and form a layer of liquid on top of the molten iron. The remaining solid zinc oxide is heavier than the slag and would therefore be at the under side of the slag, whereas the solid carbon particles would be on top. The two materials which react to effect the reduction would thus tend to become separated and the zinc oxide placed in a position where it would not be possible for either carbon monoxide gas or solid carbon to come into efiicient reducing contact therewith. However, when the iron with the supernatant materials plunges over from an elevated step to a lower one the mixing which 4 and will gravitate to the bottom of the contents of the chamber and may be removed from tap hole 20. The slag floats on top of the iron and may be tapped 01? by a tap hole 24. The excess iron is withdrawn from tap hole 22. The molten iron may be taken to an open hearth furnace or Bessemer converter for conversion to steel, or it may be reheated, recarbonized if necessary, and returned to the tank I4.

I have referred to the stream of iron passing through the chamber as shallow and to the supernatant layer of the molten charge as thin. In view of the nature of iron, its weight and cost, obviously we are not constructing a cascade comparable to the falls of Niagara. In general reference to a shallow stream here means a fraction of an inch, an inch, or two or three inches. The volume of iron at a given elevated temperature forming a stream or pool of given depth will have a certain number of heat units per square foot of exposed surface available for use in effecting the reducing action without danger of freezing the iron, due consideration being given to the losses incidental to any commercial process and to the provision of an adequate margin of safety.

We may then calculate the thickness of a layer of crude zinc oxide containing the amount of zinc that the available heat would reduce. Thus for a layer of iron one-half inch thick where the temperature is to be permitted to fall from 1500 C. to 1300 C. the charge layer (zinc oxide and carbon) would be roughly one-sixteenth of an inch thick. In the absence of extraneous heating means there would be no use in loading a markedly greater amount of zinc bearing material on top of the molten iron, as there would not be heat enough to reduce the additional zinc except at the risk of reducing the temperature of the iron to its freezing point. The thickness of the charge will generally be much smaller than the thickness of the layer of iron on which it is supported.

I claim:

The process of smelting zinc or the like wherein a charge of crude zinlciferous material and solid reduction material is deposited on the surface of a bath. of hot, inert liquid of relatively high specific gravity and the endothermic reduction reaction is eifected at least in substantial parr at the expense of the excess heat of the bath, the reduced metal being withdrawn as vapor, characterized by flowing the bath with its supernatant charge as a stream under gravity down a flight of steps to effect mixing of the materials and of the materials and the bath as the stream plunges from step to step.

WILLIAM A. OGG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 833,472 Mehner Oct, 16, 1906 894,383 Imbert July 28, 1908 1,938,582 Davis Dec. 12, 1933 1,988,608 Ogg Jan. 22, 1935 2,100,264 Perrin Nov. 23, 1937 FOREIGN PATENTS Number Country Date 27,754 The Netherlands Sept. 15, 1932

Images