US3418109A - Method for producing steel by an oxygen lance - Google Patents

Description

l` 24, 1968 J. K.s1'oNE 3,418,109

IIETHOD FOR PRODUCING STEEL BY AN OXYGEN LANCE INVENTOR. FiGl 'JOSEPH nsToNa Dec. 24, 1968 J. K, sToNE 3,418,109

METHOD FOR PRODUCING STEEL BY AN OXYGEN LANCE JOSEPH K. STONE De@ 24, 196s J. K. STQNE 3,418,109

`IE'IHOD FOR PRODUCING STEEL BY AN OXYGEN LANCE Filed um 1s, 1967 4 sheets-sheer s Il' a.

I: O INVENTOR.

JOSEPH K,5TONE ATTO MEY` IBTHOD FOR PRODUCING STEEL BY AN OXYGEN LANCE Filed auch 1s, 19s? 4 sheets-sheet 1 INVENTOR. JOSEPH K. sToNE AT ORNEY United States Patent O 2 Claims. (Cl. 75-60) ABSTRACT OF THE DISCLOSURE Refining iron to produce steel by the oxygen steel process wherein oxygen is blown downwardly onto the surface of a mixed solid and molten ferrous charge contained in a converter by a process where a superatmospheric pressure is maintained in the converter by regulating the discharge of converter gas from the system that includes at least the converter and preferably part of the gas collecting assembly. Superatmospheric pressure favors desirable exothermic reactions, it reduces the volume and velocity of gas for the same mass flow thereby causing less dust entrainment, and it provides a low volume gas stream from which particles can be more readily removed.

Cross reference This application is a continuation-in-part of co-pending application Serial Number 341,376 tiled January 30, 1964, now abandoned.

Background of invention This invention relates to a process and apparatus for refining iron and particularly to a method of employing the basic oxygen conversion process for converting iron to steel.

In the basic oxygen conversion process iron is converted to steel in an open-mouth conversion vessel by blowing a stream of substantially pure oxygen downwardly onto the surface of the ferrous charge within the vessel. The oxygen is introduced through a conduit called a lance which extends into the vessel and discharges a stream of oxygen against the charge. Refining is effected by oxidation of carbon, silicon, manganese, phosphorus, and other impurities the oxides of which are removed from the iron phase by being discharged from the vessel as a gas which is almost entirely CO and CO2, or by entering a slag phase that oats on top of the iron phase.

There are numerous and complex reactions involved in the refining of iron, the net result of which are exothermic. However, heat is advantageous in the process since it promotes rening reactions and since it eifects melting of solid ferrous charge and slag forming ingredients. Particularly it is desirable to melt solid ferrous charge because when more heat is available a greater quantity of relatively inexpensive scrap metal or iron ore may be charged to the process thereby producing a product that is less expensive to produce and more competitive commercially.

Summary of invention The process of this invention includes introducing oxygen into a conversion vessel to refine iron by the reactions described above and to maintain a sealed system between the charge within the conversion vessel and a pressure regulating means in the system including the converter and the gas collecting assembly whereby at least the interior of the conversion vessel is maintained at a superatmospheric pressure. Operating in accordance with this invention results in a change in the composition of the converter gas discharging from the vessel, said change in ICC composition favoring the formation of more carbon dioxide and resulting in the release of more heat within the converter. By operation of this invention, employing the same amount of hot metal charge containing the same amount of carbon, a greater amount of scrap can be charged and therefore a greater amount of product can be produced in that additional heat is produced to melt and convert the added scrap. In the operation of the process of this invention a greatel amount of oxygen will be consumed by converting carbon to carbon dioxide rather than carbon monoxide, or by converting carbon monoxide to carbon dioxide, but this is of little signicance in the oxygen steel process because without the cooling effect of nitrogen typical of older pneumatic conversion processes such as the Bessemer process, the oXygen consumption per unit of heat produced rises an inconsequential amount. However, the production of the same amount of heat in a conventional process requires more carbon in the converter which requires a greater proportion of hot metal in the charge, and therefore less scrap can be used. Stated diiierently, in conventional processes less heat is available from the carbon in the iron charge and less scrap can be charged to the converter which results in smaller steel production per unit of time, per unit of carbon, per unit of hot metal, and per unit of cost.

Another advantage of the high pressure basic oxygen process of this invention is that the linear velocity of the gas stream within the converter will be low, even at the same mass flow rate because the same mass of gas occupies a smaller volume. Therefore, the violent churning activity within the converter is substantially reduced and as a result there is substantially less entrainment of solid particles in the converter gas. There results a gas stream less heavily laden with eutrained particles issuing from the converter which requires less extensive particle separation and scrubbing equipment associated with the converter and a diminished loss of ferrous material as flue dust. Further, there is a much smaller volume of gas to be handled within the high pressure portion of the system, which requires smaller conduits and easier control of the gas condition.

In a particularly advantageous embodiment of this invention, the control of pressure is effected in the gas collecting assembly by a valve located downstream of dust separating equipment thereby placing the dust Vsep'- arating equipment in the high pressure side of the system. Gas cooling means may also be in the high pressure side of the system, located either upstream of or downstream of the dust separating equipment. Both the cost of buying and the cost of operating dust separators are related to the size of -the separators, and by placing the dust sep arating equipment in the high pressure side of the system, the gas volume to be handled can be significantly reduced. For example, operation of the high pressure side of the system at about 10 atmospheres gauge pressure will reduce the volume, compared with conventional operation, by at least tenfold for sealed systems and much more for those in which air bleeds into the ducts. It is evident that substantial savings can be realized in the purchase of and operation of a gas cleaning device if only onetenth the volume of gas need be handled. Therefore, the process of the present invention not only reduces the load on the particle-separating equipment by reducing the amount of particle entrainment in the gas stream, but additionally it may reduce the volume of gas to be handled by the particle separating equipment so that it may be `bought and operated substantially less expensively.

This invention also includes apparatus suitable for the practice of this invention. The apparatus includes a converter, a lance, a gas collecting means and a pressure regulating means which may be a valve, a damper, a

3 static pressure leg, a restriction, an expansion engine, or other means, somewhere within a system which includes at least the converter. When the pressure regulating means is in the gas collecting assembly the latter must be sealed to the converter upstream of the pressure regulating means to hold the pressure at which the system is to be operated. The pressure regulating means may =be a restriction at the mouth of the converter when only the converter is to be under pressure, and the restriction may be of predetermined and fixed size or of variable, adjustable size.

In the context of this specification and the appended claims, the terms sealed or sealed system are not intended to mean an absolute seal, ybut are deiined as a seal or system for containing a flowing gas stream that is maintained with no substantial leaks, but which may have relatively small leaks consistent with the volume of gas handled and with the degree of sealing generally associated with equipment of this size and nature. For example, leaks which have no discernable eifect upon pressure within the dynamic system and which do not substantially contaminate the surrounding atmosphere can be tolerated. The apparatus of this invention must be such as to provide a dynamically maintained pressure within the system, that is one that is due to the ow of a large volume of gas; however, the system is not intended and need not be constructed to hold gas pressure if the ow stops.

In one embodiment the pressure regulating means is a restriction in the gas ow system which is provided by cooperatively positioning a portion of the lance assembly with the mouth of the conversion vessel while in another embodiment the pressure regulating means is formed somewhere in the gas handling assembly and a sealed system capable of holding pressure is formed between the gas collecting assembly and the converter.

Detailed description The process and apparatus of this invention can best be described with reference to the accompanying drawings which are presented here to be illustrative of the invention rather than limiting on its scope.

FIG. 1 is a partial schematic representation in section of a basic oxygen converter embodying this invention.

FIG. 2 is a partial schematic representation in section illustrating another embodiment of the present invention in which pressure is maintained only in the converter and FIG. 3 is a partial schematic representation illustrating still another embodiment of the present invention in which pressure is maintained only in the converter, and

FIG. 4 is a partial schematic representation illustrating still another embodiment of this invention wherein dust separating and gas cooling devices are in the high pressure portions of the system.

Referring to FIG. 1, a converter generally designated 10, and a gas collecting assembly generally designated 11 are in sealed relationship with respect to one another by virtue of their mating flanges illustrated as 12 and 12'. The converter is an open-mouthed vessel formed from a steel shell 13, and a refractory lining 15, and it is supported on trunnions 16 which are held in stationary members, not shown, and adapted with means for eifecting rotation of the vessel, which are also not shown.

The gas collecting assembly 11 includes a jacketed conduit 17 with an outer wall 20, and an inner wall 21, and a space 22 .between the walls which is supplied with a cooling medium such as water admitted through conventional means which are not shown. The gas collecting assembly illustrated is also provided with a control valve 24 connected lby line 25 to conventional pressure control means which are not shown. Gas discharging from valve 24 expands to atmospheric pressure and discharges into a hood 27 which may or may not be sealed to the line 26 passing from the valve and which conducts the gas to a gas handling system which includes particle separation and cooling.

A lance generally designated 30, which is a conventional lance consisting of at least three concentric tubes, passes through opening 14 in ange 12 into the interior of converter 10. The lance is supplied with cooling water through line 31 and with oxygen through line 32, while line 33 is employed to remove the cooling water after it has circulated through the lance. The lance terminates in an opening 3S through which oxygen discharges within the converter 10. The opening 14 is also provided ywith means to receive the lance slidably without substantial leakage of converter gas, and conventional seals in ange 12 are contemplated for this purpose. During normal operation, the converter 10 will contain a molten iron phase 40 upon which a molten slag phase 41 is oating. The molten iron phase will consist at least in part of pig iron containing more than the amount of carbon desired in the final product. Oxygen impinging on the charge reacts with the carbon to produce carbon dioxide and carbon monoxide, and in conventional processes more than of the gas produced is carbon monoxide. This gaseous reaction product discharges from the converter 10 and passes through the gas collecting assembly 11 into a gas handling system which cools, scrubs and disposes of the gas thus formed. When reiining reactions are completed, the ange 12 is separated from the converter 10, the converter 10 is rotated on trunnion 16, and the molten steel product is discharged through the open mouth or a top hole into suitable ladles or ingot molds and treated conventionally.

In the embodiment of FIG. 1 the valve 24 is adjusted to provide a 4back-pressure within converter 10. Higher pressure in converter 10 favors the formation of CO2 instead of CO thereby providing additional heat to the process. Roughly, each pound of carbon burned to CO2 instead of CO provides an additional 10,000 B.t.u.s and, accordingly, any significant increase in pressure will provide additional heat to the process. Thus, maintaining the interior of converter 10 at gauge pressures of from one atmosphere to ten atmospheres or substantially higher will improve the conversion in the manner stated hereinabove.

To illustrate this advantage even further, the conversion of one pound of carbon to CO2 instead of CO will permit approximately an additional pounds of `scrap or other solid ferrous material to be charged to converter, and by changing the pressure from one atmosphere to ten atmospheres the amount of CO2 in the converter gas can be changed at least several percentage points.

FIG. 2 illustrates another embodiment of the present invention. In this embodiment only the converter is maintained under pressure while the entire gas collecting system may operate at atmospheric or even sub-atmospheric pressure. In FIG. 2 a converter generally designated as 50 is employed in conjunction with a hood generally designated as 51. The hood, although shown schematically, is of conventional double-walled water-cooled construction. The converter comprises a steel shell 53, lining 55, `and trunnions 56 which function as described in conjunction with the description in FIG. l. The lance assembly of FIG. 2 comprises the usual lance designated `60 which is supplied with a water inlet 61 and Oxygen inlet 62, and a water outlet 63. However, in the lance assembly of FIG. 2, a second water-cooled element is present which is generally designated as 65 and this water-cooled element is concentric with the lance and independently movable so that it may slide -up and down along the lance. The movable element 65 consists of a hollow cylindrical element 66 which terminates in a conical portion 67. The interior of the movable element 65 is hollow and it preferably contains a cylindrical baille connected to the top thereof but terminating short of the bottom. The bae 68 is provided to direct the flow of cooling fluid. Cooling fluid is introduced through line 70, and it travels downwardly along the outside of the baie 68, around the bottorn thereof, then upwardly in the interior space ultimately discharging through line 71.

During the conversion reactions, the element 65 may may be raised or lowered forming a variable restriction with mouth 54 of converter 50 which is capable of increasing and decreasing the back-pressure within converter to achieve the change in equilibrium between CO2 and CO to varying degrees.

The slidable element as Well as the valve 24 -illustrated in FIG. l may be controlled manually or may be controlled with conventional instrumentation whereby the size of the restriction may be regulated responsive to the pressure in the conversion vessel. Since such instrumentation is conventional it will not be described in detail herein. The means for regulating valve 24 and the means for adjusting the position of sliding element 65 are also conventional and are neither shown nor described in detail. FIG. 2 also illustrates the charge -in the vessel which includes an iron phase and a slag phase 76.

FIG. 3 illustrates another embodiment of the present invention. In FIG. 3, a converter generally designated and consisting of a steel shell 82 and a refractory lining 83 is provided with an unusually small opening 85 which preferably is formed of a heat resistant material 86. The converter is shown containing a normal charge including a molten iron phase 100 and a molten slag phase 101 floating on the iron phase. The converter operates in conjunction with a gas collecting hood 81 which is shown schematically but intended to be a Water-cooled double-walled conventional hood. Finally, the lance 90 passes through the hood 81, and through the open mouth 85 of the converter 80 so that the opening 91 is in position above the charge in the converter. In the embodiment of FIG. 3, a xed sleeve 92, preferably of heat resistant material and water-cooled through internal communication with the water-cooled portion of lance is provided. The sleeve 92 is of such dimensions that the opening between sleeve 92 and element 86 is a restriction in the system of predetermined size. The pressure may be controlled by regulating the oxygen yfeed rate through the lance 90 and thereby the rate of production of CO2 and CO.

FIG. 4 illustrates another embodiment of the present invention. In FIG. 4 a converter generally designated 120 is tted with a discharge pipe 124 surrounded with a Water jacket 121 to provide cooling so that it is not destroyed by hot gases. Lines 122 and 123 supply and remove cooling water to the jacketed portion of discharge pipe 124. The discharge pipe is sealed into a flanged connection 125 that forms a pressure tight seal between the gas-collecting assembly and the converter 120. A llance 126 is also fitted into flange 125 as described hereinabove so that it may be adjusted slidably through a seal capable of holding the operating pressure within the converter. Fluid-carrying lines generally designated as 127 are employed to supply oxygen and cooling water to the lance 126.

The hot gases discharging from converter 120 pass through line 124 and into cooler 128 which is supplied through line 129 with a cooling uid that is discharged through line 130. In normal operation lthe cooling jacket 121 will produce a very small amount of cooling of the gases since that jacket is provided to protect the discharge pipe 124, however, cooler 128 is for the purpose of cooling the gases and will be constructed so that a great deal of heat can be extracted from the owing gas stream. Cooling means 128 may he a sheet and tubetype cooler, preferably with the cooling fluid in the tube side or it may be a spray which introduces a vaporizable liquid into the flowing gas stream so that sensible heat and -heat of vaporization drastically reduce the temperature of the gases. Cooler 128 is an optional piece of equipment in this embodiment and may be eliminated altogether.

Line 131 carries the converter gases from cooler 128 through venturi 132 into particle separator 133 wherein the dust carried within the flowing gas stream is `for the most part removed. Particle separator 133 may be any of the conventional dust separating -rneans and it is shown here as a device which operates by accelerating the total stream of gas and particles through venturi 132 so that the accelerated stream impinges on the surface of a liquid into which the particles in the ilowing gas stream are discharged while the gas stream reverses direction 180 and flows out of the particle separator through line 134. Line 134 connects to pressure control valve 135 which preferably is an adjustable valve operated by means 136 which controls the pressure in the system through means such as tap 137 shown here schematically. The valve discharges gas in excess of that required to maintain pressure in the system into line 138 from which it expands into the portion of the gas-collecting device shown as 140 which normally is a conduit of approximately the size of the hood system in a conventional oxygen steel process. Of course, the gas in 140 is cool and substantially dust free so that the diicult problems of gas handling associated with such conduits in conventional oxygen steel processes are substantially diminished. It may be seen from the embodiment illustrated in FIG. 4 that substantially smaller conduits, valves, cooling jackets, and other portions of the gas handling part of the system are normal tubes and pipes of readily obtainable sizes that are easily formed to maintain pressure. The high pressure system makes building and operation of equipment to handle hot gases substantially easier and it reduces substantially the size of particle separator 133. It also diminishes the size of many of the other pieces of equipment such as cooling jackets, etc. that would normally have to jacket a conduit the size of element 140. As stated hereinbefore pressures in lthe range of 10 atmospheres will cut down the volume of converter gas by a factor of about ten and will permit gas handling conduits to be one-third the diameter or less than similar conduits operated at atmospheric pressure which are conventional in the prior art.

Within the scope of this invention there may be many ways for effecting the process and for controlling conditions other than the means described in conjunction with the drawings. Whatever means are employed to provide a superatmospheric pressure in the system, the advantages of such high pressure conversion will be obtained, including the production of more heat to provide improved refining conditions and the ability of the process to accept more solid iron and iron oxide charge, the production of :a converter gas containing lesser loading of particles as well as other process and product advantages.

It is also intended that the descriptions given in conjunction with the drawings be considered as illustrative and that process variations other than the specic examples are within the scope of the invention. For example, although the pressure in the system should be at least one atmosphere gauge and preferably about l0 atmospheres, there is no limit on the pressure at which this process `may be effected nor is the equipment necessarily of conventional design. Converters that are spherical, cylindrical or other shapes which are adapted with various means to supply oxygen and exhaust the converter gas may be employed.

What is claimed is:

1. In a basic oxygen process of rening a charge of carbon-containing ferrous metal including molten and solid portions in a converter having a mouth by blowing oxygen toward the charge through a lance which projects into the converter through said mouth thereby to produce a converter gas including both carbon monoxide and carbon dioxide in the converter above said charge, said gas emerging from the converter through said `mouth and having entrained dust particles therein, and conducting substantially all of vsaid emerging gas through a substantially air-tight gas conducting system away from the converter and into a particle separator wherein dust particles in said gas are removed, and conducting substantially dust-free gas out of said separator; the steps of restricting the flow of gas being conducted out of said separator thereby to build-up gas pressure in the separator, the converter and said system during said blowing of oxygen to greater than about one atmosphere gauge thereby to convert carbon monoxide to carbon dioxide to produce heat in the converter whereby greater quantities of said solid portion per total charge can be used and melted, to reduce gas volume, to minimize entrainment of solid particles in the emerging gas, and whereby the size of the separator is minimized; and introducing oxygen into the converter through said lance at a pressure greater than the pressure built up in the converter by said restricting step.

2. The process of claim 1 wherein said restricting step is carried out to build-up said pressure in the converter and separator to an amount between about one atmosphere and about ten atmospheres gauge.

References Cited UNITED STATES PATENTS 117,248 7/ 1871 Bessemer 75-60 2,855,194 10/1958 Konig 75-60 3,084,039 4/1963 Baum 75-60 3,134,835 5/1964 Okaniwa 75-60 10 3,170,017 2/1965 Namy 75-60 HYLAND BIZOT, Primary Examiner.

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