Method and apparatus for operating basic oxygen furnaces

Abstract

Disclosed is a method and apparatus for simultaneously blowing one basic oxygen furnace and burning in the lining of a second basic oxygen furnace; the waste gases from both operations being handled by a single gas-cleaning system and, by means of proper controls inherent to the method, so that virtually complete burning of all combustibles is assured.

Claims

1. In a system for cleaning waste gases emanating from a first furnace wherein molten metal is being refined and from a second furnace wherein a lining is being burned in, such system including an exhaust hood, a gas-collecting means and an evaporation chamber for each such furnace, the combustion with such system equipment comprising the improvement: a. An exhaust gas conduit leading from each said evaporation chamber; b. a first control valve in each said exhaust conduit; c. A bypass conduit around said control valve said bypass conduit being sized proportionately to said exhaust conduit; and d. a second control valve in each bypass conduit. 2. The invention of claim 1 including: a. means for exhausting said exhaust gases from said first and second furnaces. 3. In the method for simultaneously refining molten metal by blowing oxygen onto the molten metal in a first furnace and generating waste gases therein and by burning in a new lining of a second furnace and generating waste gases therein, the improved method comprising the steps: a. passing all of the waste gases from said first furnace into an exhaust conduit; b. passing a preselected proportionate amount of the waste gases from said second furnace into said exhaust conduit; and c. maintaining the pressure of the mixture of gases in said exhaust conduit at a preselected value. 4. The method of claim 3 including the steps: a. placing a quantity of hot coke in said newly lined second furnace; and b. blowing oxygen into said second furnace thereby generating said waste gases in said second furnace. 5. In a system for cleaning waste gases emanating from a first furnace in which molten metal is being refined and from a second furnace in which a lining is being burned in, the improvements comprising: a. an exhaust conduit communicating with and carrying said waste gases from each furnace and a control valve in each conduit; and b. a bypass conduit with a control valve therein for carrying a portion of the waste gases around the control valve in the exhaust conduit communicating with the second furnace when such control valve is closed, whereby a proportionate portion of the exhaust gases from the second furnace mix with the exhaust gases from the first furnace and the pressure in the exhaust conduit is constant.
ite tales mm Franz .l. Rosentern Pittsburgh, Pa. 8 15, 161 July 28, 1969 Sept. 7, 1971 llfioppers Company, lnc. lnventor Appl. No. Filed Patented Assignee METHOD AND APPARATUS 1 0111 OlPlElltA'llllNG BASlllC OXYGEN FURNACEE 5 Claims, 1 Drawing ll ig. 266/1 llnt. Cl E2116) 5/ 10 Field of Search 266/31, 34, [56] References Cited UNITED STATES PATENTS 1,417,538 5/1922 McGregor 266/18 3,063,219 11/1962 Copcutt 266/15 X 3,224,841 12/1965 Kemmetmuller 266/31 X 3,372,528 3/1968 Hoff 266/15 X 3,490,204 1/1970 Kalika 266/15 X Primary Examiner-Gerald A. Dost Arl0rneysSherman H. Barber and Olin E. Williams ABSTRACT: Disclosed is a method and apparatus for simultaneously blowing one basic oxygen furnace and burning in the lining of a second basic oxygen furnace; the waste gases from both operations being handled by a single gas-cleaning system and, by means of proper controls inherent to the method, so that virtually complete burning of all combustibles is assured. PATENTEU SEP 7 I97! m a i mum N R Q q INVENTOR FRANZ J. IOSt'MS'TiKN METHOD AND APPARATUS FOR OPERATING EASIC OXYGEN FURNACES BACKGROUND OF THE INVENTION This invention relates to steel making and more particularly to a method and apparatus for simultaneously blowing one basic oxygen furnace and burning in the lining of a second basic oxygen furnace. ln meltshops that have two or more basic oxygen converter vessels or basic oxygen furnaces (hereinafter BOF is it customary, when one BOF is shut down for relining, to burn in the new lining and to pass the waste gases from this burn in operation directly into the atmosphere. Heretofore, the usual practice has been to provide a valve in the exhaust gas system of a BOF converter to isolate the inoperative BOF from the gas-cleaning system; thereby preventing the ingress of air through the inoperative BOF hood and conduit, and assuring the necessary volumes of air being available for combustion of the operating BOP waste gases. Should such a valve be omitted, the operating furnace would have insufficient air for combustion of its waste gases; combustibles would enter the conduits, causing the danger of an explosion resulting from mixing of the hot gases containing CO with the air drawn in from the inoperative furnace. Those skilled in the art will recognize, from the following description in conjunction with the drawing, that the invention provides a method and apparatus for simultaneously blowing one BOF and burning in the lining of a second BOF in a safe and effective manner; the waste gases from both operations being handled by a single gas-cleaning system. SUMMARY OF THE INVENTION In a system for cleaning waste gases from a first BOF in which molten metal is being refined and from a second BOF in which a lining is being burned in, a bypass conduit and control valve therein regulate the amounts of waste gases that flow from the second BOF into an exhaust conduit in which the gases from the first BOF flow. BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates schematically a system in accordance with the invention for simultaneously refining steel in one BOF burning in the lining in a second BOF and safely evacuating to the atmosphere the waste gases from both operations through a single gas-cleaning system. DETAILED DESCRIPTION One BOF 11 is in use to refine molten iron to steel, and the other BOF 13 has been relined and is ready for burning in the new lining. The BOFs 11, 13 are provided with: oxygen-blowing lances 15, 17; gas-collecting hoods 19, 21; evaporation chambers 23, 25 having emergency relief valves 24, 26; and main exhaust conduits 27, 29 wherein there are isolation and control valves 31, 33. With each main exhaust conduit 27, 29 there is provided a bypass conduit 35, 37 of considerably smaller size relative to the main exhaust conduit 27, 29, and in each bypass conduit there is a control valve 39, 41, The main exhaust conduits 27, 29 merge with a single conduit 43 that leads to a precipitator inlet manifold 44. Branching off of the main inlet manifold Ml are a plurality of smaller-sized conduits 45a-45f that communicate with three double-chambered electrostatic precipitators 49, 51, 53 for cleaning the waste gases. It will be appreciated by those skilled in the art that other types and/or arrangements of gas-cleaning equipment and electrostatic precipitators may be used if they are preferred. Discharge conduits 55a-55f, wherein there are louver dampers 57a-57f, communicate with the precipitators 49, 51, 53, ' and with a discharge manifold 59, as shown in the drawing. Three other conduits, til, b3, b3 branch from the discharge manifold 39 and communicate with induced draft fans a7, 69, 71. Each conduit tall, 63, 63 includes a damper valve Ma, 63a, 63a and a louver damper 61b, 63b, 65b. Exhaust conduits 73, 73, '77 from the induced draft fans 67, 69, 71 communicate through damper valves 73a, 73a, 77a with a discharge manifold 78 leading to a single exhaust conduit 79 that conveys cleaned gases into an exhaust stack 81. In describing the operation of equipment mentioned herein, it will be assumed that only one BOF is blown at one time, that such BOF 11 is refining molten metal to steel, and that BOF 13 has been relined and that the new refractory lining is ready for burning in. Lance 15 is shown in its down or operative position in BOF 11, and a quantity of molten metal in BOF 11 is being blown with oxygen emerging from the lance 15 in a normal manner. The waste gases generated during the blowing period, consisting of approximately 90 percent CO enter the furnace hood 19 where combustion is effected by means of induced air drawn in through the gap between the BOF 11 and hood 19. Gascooling water sprays (conventional) are located in the hood 19 and in the evaporation chamber 23. These water sprays are automatically controlled to maintain the gas temperature leaving the evaporation chamber 23 at approximately 500 F. Control valve 31 is open during the blowing operation and control valve 33 is closed. These control valves 31, 33 are provided with a safety interlock (not shown) that prevents air from being drawn into the gas stream from the inoperative BOF 13 which would reduce the air supply to the operating BOF 11 to such an extent that there would not be enough air for complete combustion of the CO in the hood 19. For the moment, conduits 35, 37 and bypass valves 39, 41 may be disregarded, as they will be described hereinafter. The exhaust gases from BOlF 11, after passing through the evaporation chamber 23, flow through conduit 43 into the precipitator manifold 44, and thence through conduits 45a 45finto the electrostatic precipitators #19, 51, 53; the damper valves 47a 47fbeing open. From the electrostatic precipitators 49, 51, 53 cleaned waste gases flow through conduits 55a -55f, louver valves 57a S7f, into the exhaust manifold 59 and into the exhaust fans 67, 69, 71; the gases passing through open dampers 61a, 63a, 65a and louver dampers 61b, 63b, 65b. From the exhaust fans 67, 69, 71 the gases pass into the fan discharge manifold or breaching 73 and pass through the exhaust conduit 79 into the exhaust stack 31. It should be noted that dampers 47a -4l7f, 61a, 63a, 65a, and 73a, 75a, 770 provided for isolating inoperative equipment only, and they provide no controlled function in the operation of the system. Likewise, the louver dampers 57a 57f are used for manual remote adjustment of the gas flow through each precipitator chamber only and have no controlling function in the operation of the system. Fan inlet louver dampers 61b, 63b, 65b operate automatically to maintain a preselected subatmospheric pressure in the conduit 43. The isolation and control valve 31 functions to control the draft in the hood 19 during the oxygen flow, and such draft is measured at a selected point, such as conduit 27. Should the pressure in conduit 27 drop below a preselected minimum, the isolation and control valve 31 will close, emergency relief valve 24 will quickly open, the oxygen flow to lance 15 will be stopped, and the lance will be retracted from the furnace. All of these functions are automatically initiated in response to a control signal indicating a drop in pressure in conduit 27. The operation and control of the fan inlet dampers 61b, 63b, 65b, and the isolation and control valves 31, 33 described hereinbefore is only one of various methods of gas flow control presently employed. However, it will be apparent to those skilled in the art from the following description, that this particular type of control is preferred in a system constructed in accordance with the invention. As mentioned previously, in a typical two-furnace meltshop, one BOF operates while the other BOF is being relined; thus, the gas cleaning system handles the gases from one BOF only and is sized accordingly. It should be noted, however, that although many shops operate both BOFs by blowing them al' ternately, nevertheless, the gas cleaning system handles the gases from only one BOF at a time and is sized accordingly. The new refractory lining of a BOF is usually burned in by placing hot coke in the relined furnace and then blowing a nominal amount of oxygen through a lance that has been lowered into the furnace. In the drawing, the lance 17 would be lowered into the BOF 13 and a nominal amount of oxygen would be blown through lance 17 onto the hot coke. Depending on shop practice, the burn in may take from one to several hours. At the present time, the gases generated by the burn in are discharged directly to the atmosphere through the emergency relief valve 26 or 24, depending upon which BOF is being burned in. The discharge of dirty waste gases through emergency relief valves 24, 26 is a violation of air pollution codes in some areas, and it has become necessary to pass the waste gases generated during the blowing of molten metal in a BOF such as in BOF 11, and the burning in of a lining in BOF 13, through a gascleaning system. The system shown in the drawing can operate satisfactorily even if one precipitator chamber and one exhaust fan are inoperative. Thus, the one precipitator and one exhaust fan provides spare capacity for burning in a new furnace lining while blowing oxygen in the normal manner in the other furnace. Referring again to the drawing, it is understood, that while BOF 11 is blowing a heat and BOF 13 is burning in a new lining, control valves 31 and 41 are opened and valves 24, 26, 33, and 39 are closed. Bypass valves 39, 41 are so sized that when the subatmospheric pressure in conduit 43 is a maximum, the flow through both valves 39, 41, will not exceed a precalculated amount. Thus, the flow of waste gases from the operating BOF 11 is not reduced below a safe level. In actual practice this may not be possible, and adjustments to the open position limit switches on valves 39, 41 may be required to assure accurate settings. Actuation of these valves can be accomplished by means of pushbuttons from the respective furnace-operating pulpits. An electrical interlock will be provided as part of the equipment of BOF 11 so that valves 24 and 31 must be closed in order to open valve 39. Likewise, electrical interlocks will be provided as part of the equipment of BOF 13 to ensure that valves 26 and 33 are closed in order to open valve 41 when the lining of BOF is being burned in. Those skilled in the art will recognize several features of the invention among which are: That the method of the invention accomplishes the simultaneous blowing of a melt in one BOF and the burning in of a lining ofa second BOF That the handling of waste gases from both BOFs by a single waste gas cleaning system and by means of proper control is easily accomplished by the system of the invention, thereby assuring the supply of adequate excess air for the blowing BOF for burning virtually all of the combustibles in the furnace hood and evaporation chamber; That the invention described herein can be adapted to other types of BOF equipment and to waste gas cleaning systems which use an excess of combustion air for burning all combustibles in the waste gas emitted from the BOF That the invention makes it possible, in a two-furnace or a three-furnace meltshop, where it is operating practice to alternately blow two furnaces, to have a certain amount of draft available through the hood of the BOF being charged or poured while the other BOF is being blown, provided the gascleaning system associated with the BOF equipment is properly sized. A nominal amount of air flowing into the hood between blows is desirable in order to reduce smoke emission into the meltshop building. What is claimed is: 1. In a system for cleaning waste gases emanating from a first furnace wherein molten metal is being refined and from a second furnace wherein a lining is being burned in, such system including an exhaust hood, a gas-collecting means and an evaporation chamber for each such furnace, the combustion with such system equipment comprising the improvement: a. An exhaust gas conduit leading from each said evaporation chamber; b. a first control valve in each said exhaust'conduit; c. A bypass conduit around said control valve said bypass conduit being sized proportionately to said exhaust conduit; and d. a second control valve in each bypass conduit. 2. The invention of claim 1 including: a. means for exhausting said exhaust gases from said first and second furnaces. 3. In the method for simultaneously refining molten metal by blowing oxygen onto the molten metal in a first furnace and generating waste gases therein and by burning in a new lining of a second furnace and generating waste gases therein, the improved method comprising the steps: a. passing all of the waste gases from said first furnace into an exhaust conduit; b. passing a preselected proportionate amount of the waste gases from said second furnace into said exhaust conduit; and c. maintaining the pressure of the mixture of gases in said exhaust conduit at a preselected value. 4. The method of claim 3 including the steps: a. placing a quantity of hot coke in said newly lined second furnace; and b. blowing oxygen into said second furnace thereby generating said waste gases in said second furnace. 5. In a system for cleaning waste gases emanating from a first furnace in which molten metal is being refined and from a second furnace in which a lining is being burned in, the improvements comprising: a. an exhaust conduit communicating with and carrying said waste gases from each furnace and a control valve in each conduit; and b. a bypass conduit with a control valve therein for carrying a portion of the waste gases around the control valve in the exhaust conduit communicating with the second furnace when such control valve is closed, whereby a proportionate portion of the exhaust gases from the second furnace mix with the exhaust gases from the first furnace and the pressure in the exhaust conduit is constant. wag UNITED S'I'A'IES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,605,572 Dated September 7, 1971 Inventor(s) Franz J. Rosenstern It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Claim 1, lines l8, 19, change "combustion", to---combination--- Inventor's Name change Franz J. Rosentern" to Franz J. Rosenstern-- Signed and sealed this 13th day of June 1972. (SEAL) Attest: EIZWARD MJLETCHERJR. ROBERT GOTTSCHALK testlng Officer Commissioner of Patents

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    US-8979980-B2March 17, 2015Alstom Technology LtdGas cleaning unit and method for cleaning gas