US2039087A - Method of and means for melting and refining metals - Google Patents

Description

prix 28, w3. A. B. KINZEL 2,3 87

METHOD OF AND MEANS FOR MELTING AND REFINING METALS Filed April 25, 1954 2 Shee'ts-Shee'rI 2 ixw 1 V f2' I Hr *1 f/.Z Z6 f IZ f2 f 2 V2 (ze |-r l l i I l 1 lul-l. Il Il l ll m /4 lNvEN-roR /7 AUGUSTUS BKWNZEL;

l Y BY ,5j ATTORNEY dii Patented lApr. 28, 1936 UNITED STATES amarsi METHQD 0F AND MEANS FOR. mlb

AND REFINING METALS Augustus B. Kinzel, Douglaston, N. Y., assigner, by mesne assignments, to Union @arbide @arbon Corporation, a corporation of New Yorh Application dp t5, liti, Se No. 'lttt t fliaimr.. lill. ttt- 52) 'fthe present invention relates to metal melting and/or refining furnaces, d more particularly' to methods of 'and means for constructing and operating such furnaces in a more economical manner.

an object of this invention is to simplify the construction, operation and control of metallurgical furnaces, and to incrse the number of heats or charges which may be melted and/or rehned by such furnaces in a given unit of time.

.a further object of the present invention is to provide methods of and means for edectively applying the principle of voxygen-enriched air combustion to metallurgical furnaces.

.it still further object of this invention is to provide a method of and means for utilizing the pressure crea by the expansion of compressed oxygen-enriched gases to vaporize or atomlze liquid fuels.

lit has been lrnown heretofore that advantages such as more rapid melting, quiclrer rening, and more direct temperature control in open hearth and other metallurgical furnaces would ensue from higher flame temperatures. There arel several recognized methods of obtaining high de temperatures. One of these is to increase the temperature of the air used. for combustion by recuperating, 1n so-called regenerators, the heat of the waste gases. Another method consists in increasing the oxygen content of the combustion atmosphere in the usualtype of end-port-hred open hearth furnace. The ports are inclined downward at a slight angle so as to direct the name on the slag or bath. This results in producing a slightly higher temperature on the slag than on the roof, but in this type of furnace the considerably higher temperatures which are desirable cannot be practically and commercially achieved because they would result in premature roof failure.v Still another method of obtaining higher name temperatures involves the use of ports or bers in the roof of the furnace, the name being impinged substantially at a right angleto 4and upon the bath or slag surface. This produces a slightly higher temperature at the surface of the metal or slag and increases the temperature differential between the roof and the bath. However, in itself,lthe increase in temperature thus obtained is not sufficiently great and has not proved to be practical due to the great dilculties involved in bringing hot air for combustion into roof ports. These difficulties relate not only to the complexity of the necessary valve mechanism and ducts but also interfere with the cooling of the roof which melts prematurely, so that the ultimate object is not achieved to the desired degree.

Iri'hus, due to the above-stated limitations of furnace construction and methods of operation, it has notbeen feasible heretofore to increase the temperature of combustion beyond the point atwhich it is now used in practice, and no feasible and practical method of obtaining the potential advantages of oxygen-enriched air has been successfully achieved.

.in accordance with this invention, the abovementioned disadvantages inherent in the construction and operation of metallurgical furnaces may be overcome by combining cold-air firing through the roof with the use of oxygen-enriched air and with other features described hereinafter. In this manner, the roof of the furnace is inept cool and is not detrimentally adected by the high temperature of the fuel-oxygen name. At the same time, in accordance with this invention, the gas how in the furnace is so regulated by the proper location of the end ports that a comparatively quiet gas zone is continuously liept in contact with the roof, thus further increasing the temperature gradient between the metal bath and the roof. rihis results in a method of operation in which all the advantages of high temperaturecombustion are achieved, in which the temperature of the roof is maintained as in normal operation, and in which the reversing valves (which are generally unsatisfactory on account of the losses of gases leaking directly into the chimney), and the multiplicity of ducts and other equipment usually necessary for hot air ring through the roof, are eliminated. Furthermore, the construction and use of heat regenerators is avoided and substantial savings in the cost of construction of furnaces are therefore edected.

Experiments have shown that an enrichment of air from the atmospheric 20 per cent oxygen content to about 27 per cent oxygen contentr is sufcient to furnish an extra flame temperature of the same order as obtained by the preheating in the usual open hearth regenerators, of ordinary atmospheric air.

The principles of this invention will now be described with particular reference to the accompanying drawings in which:

Figure 1 represents, in a schematic manner, an embodiment of this invention in which the principles thereof are applied to a metal melting and refining furnace;

Figure 2 shows schematically a section along line 'Ll-f of Figure l;

Figure 3 represents a schematic top plan view of a part of the furnace shown in Figure 1; and

iid

Figure 4 shows, in more detail, a longitudinal sectionithrough the burner shown in Figure 2.'

Referring to the drawings, the furnace shown comprises a bottom or hearth I0 and an arcuate top or roof Il constructed of suitable refractory materials capable oi withstanding temperatures above the melting point of the metals to be melted and/or refined in the furnace. In the roof ii there are provided a plurality of burners such as shown schematically at I2, and in more detail in Figure 4. Each of said burners comprises an inner concentric tubular chamber I3 which is formed by and between a central core Ill and a surrounding tube i5; the chamber i3 is connected to a central gas supply passage i6, as shown, and its lower or left-hand portion terminates in an annular discharge orifice ill having a small cross-sectional area. Ilfhe gas passage I6 is connected to a gas supply line 26 which leads to a source of oxygen-enriched air under pressure, as shown schematically at 29. The wall I5 of the inner tubular chamber iii is surrounded substantially concentrically by another tube or wall 2l" forming a narrow circumferential chamber or passage between the outside of tube l5 and the inner surface of tube 2l'. The tube 2'I is connected, as shown at 2i, to a line 28 which leads to a suitable source or liquid fuel under pressure, shown schematically at 48. Liquid fuel tank 48 is connected to the oxygen gas storage tank 29 through a tank 6i filled with Water. The purpose oi this water tank which is arranged in such a manner that its water level is below the lowest level ofthe fuel tank, is to transmit the pressure prevailing in container 2@ to the fuel tank 48 without there being any physical contact between the highly compressed oxygen-enriched gas and the liquid fuel. Preferably the pressure in the water and liquid fuel containers is given a value below the pressure of the oxygen-enriched gas, for example, by the interposition of a suitable pressure reducing valve such as shown at 62.

The oxygen-enriched gas which is contained in the vessel 29 preferably has an oxygen concentration greater than that of the atmospheric air. In accordance with one embodiment of the invention, use is made of atmospheric air having an oxygen concentration of about 27% or more.

In accordance with a modiiication of this invention there may be provided, in addition to the container 29 for storing an oxygen-enriched gas under pressure, a vessel adapted to hold and vaporize liquefied oxygen-enriched gases. Such a vessel is show n at 3U. This vessel 30 contains voxygen-enriched air in the liquid phase, and is adapted to convert this liquid oxygen-enriched gas into the gaseous phase having any desired substantially constant pressure, for use both for increasing the temperature of combustion of the fuel and for Vaporizing or atomizing the liquid fuel. This may be accomplished by providing suitable means for vaporizing the liqueed gas and for controlling the pressure of the resulting gas. In' order to control the temperature of the liquid oxygen-enriched gas and the rate of its evaporation, the container 30 comprises an inner vessel 3| for holding the liquefied gas, and is substantially completely surrounded by the insulating material 32. An outer jacket or envelope 33 is provided for protecting and supporting the insulation 32. Thc inner vessel 3l is constructed to withstand any desired maximum pressure and is provided with suitable filling means comprising a conduit 34 disposed in the the bottom of the vessel and thus conducts the liquefied gas to a heating coil 3l which may be heated electrically or in any other suitable manner and which vaporizes and heats the gas discharged from conduit 36. The heated gas is then conducted through conduit 38 back into the inner container to eiiect thermal contact with the stored liquefied gas through the walls of the portion of the conduit 38 which is submerged in the liquefied gas. In passing through this portion of conduit 38, the superheat of the gaseous oxygen-enriched gas passing therethrough is substantially all transferred to the stored liquefied gas, thus producing the vaporization oi a. desired portion of the stored liquefied gas, whereby the pressure of the gas within the vessel and in conduits and apparatus in direct connection therewith is increased to any desired Value.

The discharge portion of conduit 3S conducts the gas to a second heat exchange coil 39 where it is i'eheated to any desired temperature. The amount oi' heat applied to the heat exchange coils all and 39 may be controlled in any conventional manner. From the heating coil 3@ a con'- duit il@ conducts the gas to the inlet of an auto matic premure controlling means 4i which maintains the discharge pressure of the gas delivered through conduit d2 at a substantially constant desired value when the inlet pressure is at a varying higher value. The conduit 42 is joined to the conduit 2G which conducts gas at a desired substantiaily constant pressure to the burners I2. A conduit lill, disposed in the upper portion of the vessel it@ and connecting with the space above the stored liquid gas conducts gas when desired to the inlet of an automatic back pressure Valve 45. This valve permits no gas to pass until the pressure of the gas in conduit 4I reaches or exceeds a desired set value.. When this set pressure is exceeded, gas is permitted to flow through the conduit 4d to a second automatic pressure reducing valve lll?. The reducing valve 41 discharges through conduit 26 and maintains any desired discharge pressure of the gas therein at a substantially constant value.

The operation of the heating system described is substantially as follows:

Assuming the pressure of the reducing valve 4l' to be set for a Value of say 150 lbs. per square inch, and the heat exchange coils or rheostats 3l and 39 to be set for a corresponding heat value, oxygen-enriched gas having this pressure is conducted to the conduit 26 and to theburners I2, and issues from the annular orifice I'I thereof in the form of a spray of very high velocity. The pressure of the liquid fuel being preferably adjusted to a value less than that of the oxygenenriched gas, say to about to 100 lbs. per square inch, liquid fuel is caused to flow, by virtue of the pressure exerted upon it through conduit 52, valve 62, tanks 6I and 48,-into supply line 28, and issues from the orifice of burners I2 in a direction substantially at a right angle to the direction of ow of the compressed oxygen-enriched gas. Owing to the impact of the highly compressed gas upon the liquid fuel, the fuel is vaporized and the vaporized fuel and the gas of combustion are intimately mixed in the combustion chamber. This mixture of fuel and oxygen-enriched gas burns with the production of a long flame whose temperature may be of the order of 2000 C. or more. The zone of maximum temperature occurs substantialiy at the end points of the flame, that is at the point of contact of the flame with the metal or metal bath upon the hearth of the furnace. v

By causing a plurality of high-temperature llames to impinge upon the charge, during and after the melting thereof, it is possible to oxidize the various impurities contained in the charge considerably more rapidly than is possible with the use of lower llame temperatures. A considerable shortening of the melting and refining operation is thus obtained, which results in an increased number of heats per unit of time, and in considerable savings in overhead expenses. The method of providing a plurality of long and hot yflames which are directed downward upon the metal or metal bath together with the design and the location of the end ports, permits the accumulation of an inert layer of gas directly underneath the roof, and enables a furnace construction in which the roof is at a considerably greater height from the surface of the bath than would be possible otherwise. Thus the roof may be maintained cool very eiectively, and consequently its useful life is increased several fold.

Although the advantages and applications of this invention are not limited to the use of liquid fuel, since gaseous fuel has other obvious advantages, when using fuel oil instead of gas fuel. no generators are required for the production of the oil fuel. In view of the high temperature of the oxygen flame, the length of time required for melting and refining a heat or charge is considerably reduced. and no regenerators are needed for recuperating the heat content of the escaping waste gases. Consequently, the cost of constructing and operating a furnace in accordance with this invention, as well as the cost of maintaining such a furnace in repair and operation, is considerably reduced.

Furthermore, owing to the complete vaporization or atomization of the liquid fuel, use may be made of the heavier and more economical types of fuel oil which heretofore have been considered unsatisfactory as fuel oil on account of the diiiiculties experienced in their vaporization or atomization. g

By increasing the oxygen to nitrogen ratio from the normal ratio of l to 4 to approximately 1 to 3,

or l to 2, the proportion of the nitrogen in the waste gases and consequently the volume ofthe waste gases is considerably decreased, thus cor'- respondinglyreducing the amount of heat which is abstracted from the furnace chamber in the form of waste gases. Furthermore, if desired, in any particular case, the amount of heat wasted may be reduced still further by utilizing at least one portion of the escaping flue gases for heating steam boilers. and using the resulting steam for the operation of steam engines, or for the operation of the oxygen-concentrating apparatus, or for any other purpose. This utilization of the waste gases may be particularly advisable in all cases in which the temperature of the waste gases is sufficiently high to warrant any of these methods of operation.

What I claim is:

1. Method of producing high temperatureswithin a combustion chamber which comprises projecting an ignited finely divided jet, consisting of a mixture of fluid fuel and oxygen-enriched air, downward through the roof of said chamber, and maintaining a relatively thick layer of substantially quiescent gas adjacent to the under side of said roof.

2. lA furnace for melting or refining metals and the like which comprises a hearth; a roof; sidewalls; means for'projecting an ignited mixture of fiuid fuel and oxygen-enriched air from one or more points a substantial distance below said roof downwards onto said hearth; and one or more ports in said sidewalls for discharging gaseous products of combustion, said port or ports being located in a lower portion of said sidewalls; whereby, a relatively thick layer of substantially quiescent gas is maintained between the roof and the zone of combustion in said furnace.

3. A heating system which comprises, in combination with the furnace claimed in claim 2, a vessel adapted to hold liquefied oxygen-enriched air under pressure; a vessel adapted to hold liquid fuel; means for transmitting pressure from said first-mentioned vessel to said second-mentioned vessel without permitting oxygen-enriched air to enter said second-mentioned vessel; means for vaporizing the lsaid liquefied oxygen-enriched air to create said pressure; and one or 'more liquid fuel atomizers and meansI for conducting said liquid fuel and said vaporized oxygen-enriched air

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