II. At Wheeling Steel Corp.

Transcription

1 II. At Wheeling Steel Corp. Basic Oxygen Operations 123 The basic oxygen steel plant under construction at the Steubenville Plant is nearing completion and is scheduled to start operations this summer. This new facility is part of an extensive modernization and expansion program, which includes new primary mills and finishing capacity. The basic oxygen shop will replace a portion of the existing steelmaking units and provide considerable added ingot capacity. LOCATION The plant is located on a green field site east of the new 80 in. wide hot strip mill and west of the existing Mingo Oxygen Co. plant. The shop lies adjacent to three of the company's five blast furnaces (two at North Works), a stripper building, and battery of soaking pits. Including the scrap house the shop W. P. HOLLOWAY is superintendent, basic oxygen furnaces, Wheeling Steel Corp., Steubenville (Ohio) Plant. covers an area 220 ft wide x 2000 ft in length. Fig. 1 shows the south half of the shop where the furnaces are located. Fig. 2 shows the north half of the layout, with additional teeming platforms, the hot metal transfer pits, the track hopper, and the new metallurgical laboratory building. FURNACE DESIGN The first and most important consideration in the plant design was the selection of heat size and the size and shape of the furnaces. In order to fully utilize soaking pit capacity, and avoid partially filled pits, it was desirable that one heat should fill two pits. At the same time the hourly production rate should meet the demands of the primary hot mills. A minimum heat size of 225 net tons was selected to balance out both requirements. The hot metal capacity is sufficient to provide a continuous operation with this size of heat. Provision is made for making and handling larger heats in the future, at which time additional blast furnace capacity will be needed. Furnace design started with the bath depth and the volume inside the brick work.required for 225 net tons heats. Fig. 3 shows the furnace shell and the design of brick work for the start-up lining. The bottom section was designed with a 13 ft 6 in. radius in order to minimize variations in bath depth resulting from lining wear during the course of a campaign. The inverted arch provides proper support at the knuckle joint. The inside diameter of the barrel section is 19 ft 6 in. With the 36 ft bottom lining the height to diameter ratio is 1.6: 1. The barrel section has a 9 in. backup lining, a 4% in. rammed section and a 24 in. working lining. The cone section has a 9 in. back-up lining and a 24 in. working lining. The cone angle is 63" from the horizontal. The mouth diameter is one-half of the bath diameter. The volumes of the three sections are as follows: I t - - -, 4, 9iF C rnt.9.c. -" a, Fig. 1-Equipment layout-south section.

2 124 Open Hearth Proceedings, 1965 Fig. 2-Equipment layout-north section. Volume of cone section Volume of barrel section Volume of bottom section Total Volume Volume per ingot ton Volume of molten steel Bath depth Working volume above metal line working volume per ingot ton 659 cu ft 4790 cu ft 1812 cu ft 7261 cu ft 32.3'~~ ft 1047 cu ft 65% in cu ft 27.6 cu ft The shell is 26 ft-33h in. diameter with a height of 34 'ft-10ys in. After some operating experience with this heavy lining, and larger heats are desired, the 4% in. rammed section may be eliminated and the working lining reduced from 24 in. to 21 in. brick. This will increase the inside diameter to 20 ft 9 in., and raise the working volume required for larger heats. Cranes and auxiliary equipment were designed to make and handle up to 300 ton heats. The shell is solid throughout and of uniform thickness to permit it to expand and contract freely with changes in temperature. For the same reason the trunnion band is separate rather than integral. Integral bands were avoided because actual experience has shown they do not permit free expansion and contraction of the shell and ultimately build up stresses which lead to cracking of the shell and band. TILTING NlECHANlSM Fig. 4 shows the tilting mechanism. The drive is a modified power wheel type with a separate primary and secondary drive. The primary drive consists of two 265 hp dc motors and gear reducers. Both motors are normally used but one motor is capable of rotating the, furnace with a maximum size heat. The secondary drive consisting of a bull gear, two pinions, and gear housing is mounted on the trunnion ring pin on one side. Drive housing is arranged to absorb shocks due to deskulling torque and other unusual shock loads without damaging 'the drives. Primary drive is connected to the secondary drive with two heavy duty rolling mill type drive spindles. This arrangement provides the most flexibility to compensate for any misalignment which may occur between the primary and secondary drives. The arrangement of the bull gear and drive pinicns in a single housing mounted on the trunnion pin permits the bull gear and pinions to remain in correct mesh at all times regardless of deflections or misalignments which may occur. Fig. 5 shows a cross section of the shop through the furnace area. The basic layout consists of three separate aisles-charging, furnace, and teeming. CHARGING AISLE The charging aisle is 91 ft x 550 ft, centerline of columns and is serviced by two 300-ton cranes. Charging is done from the east; tapping from the west side. Scrap is loaded in a separate building to the south and transfered by remote control to the furnace area. Two pans, each of cu ft capacity, are placed on a self-propelled PECOR charging car traveling on rails on the furnace floor level. The pans are dumped by hydraulic mechanism. If the charging car is out of service the pans can be handled by the overhead cranes. Hot metal is received in 200-ton submarine ladles and poured into 220-ton transfer ladles through one of two electronic scale pits at the northeast corner of the aisle. Slag is handled in 500-cu ft pots by rail to a slag dock located south of the scrap house. A transfer track to the teeming aisle is,available for moving hot metal ladles for reline, as well as transferring other materials or equipment from one aisle to another. Fluxing materials are unloaded at a track hopper located east of the hot metal reladling pits. Fluxes, coke, and ore pellets are conveyed by belt to overhead storage bins. FURNACE AISLE The furnace aisle is 50 ft x 550 ft centerline of columns. Two furnaces are spaced on 125 ft centers with space allotted at the south end for a third furnace, or other equipment under consideration. At operating floor level are the operating supervisors' offices, the computer room, instrument repair room, alloy storage and handling

3 ;I Basic Oxygen Operations 125 facilities, the main operating pulpits and auxiliary pulpits, sample carrier stations, the furnace hoods and spark boxes, and a personnel elevator to the service floor above. The service floor over the furnaces is designed to provide adequate floor space for the storage of the furnace rebrick tower and handling furnace refractories, coolant scrap, and the incandescent coke system for furnace lining burn-in. The lance cranes are wall type, pivoting on the center line of each furnace and providing immediate lance replacement. Suspended in this area at each furnace are the flux surge weigh hoppers which feed materials through the furnace hood. A 25-ton crane services this aisle. This includes lance handling, the unitized rebrick tower, and other miscellaneous work. Fig. 6 shows a longitudinal crosssection of the layout. The flux batching floor carries the reversing conveyor, individual weigh hoppers for each material, and emergency flux batching controls. Above are the storage bins fed by a top side shuttle conveyor. There are two ore, one spar, one coke and five lime bins. The end bins at either extreme can bypass the re- versing conveyor and go directly to the furnace via the surge hopper. The entire flux handling system is covered, with the dust control effected by means of a vacuum dust collecting system. This system exhausts into the waste gas system and assists in PH control of the recirculating water for the Venturi scrubbers. Fig. 7 shows a flow diagram of the materials handling system for the entire operation-the hot metal handling starting at ground level on the left, the scrap handling on the right. The upper left part of Fig. 7 shows the track hopper for fluxing materials being moved by inclined conveyors to the shuttle conveyor over the bins. Fig. 8 shows the gas scrubber system. The waste gas system, after leaving the furnace hood and spark box, consists of a stack with downcomers crossing over the teeming aisle into a common header and a variable Venturi scrubber located 27 ft 6 in. above the ingot tracks west of the teeming aisle. OXYGEN FLOW Oxygen of high purity produced by the adjacent Mingo Oxygen Co. units at 200 psig enters the BOF Fig. 4-Furnace tilt drive. I I( I through an 8 in pipe. It is reduced to 150 psig by a pressure regulating station. Total oxygen flow is measured through a dual flow meter section located in the valve room. Both flow sections are pressure and temperature compensated. The main flow section will conduct a maximum of 1,800,000 std cu ft hr through the 8 in. pipe. The rate of oxygen flow to the lance is measured, recorded, and controlled, using a pressure and temperature compensated flow system. Maximum supply flow to be 1,800,000 std cu ft hr. The maximum blowinh rate is to be 23,000 std cfm. The opi erator manually sets the rate of flow on the set point control station and the total flow on the oxygen batch counter. As the blowing lance is lowered into the converter, limit switch contacts on the hoist actuate the oxygen shut-off valve permitting oxygen to flow at the rate set on the flow controller. A second pen records the oxygen pressure to the lance. Fig. 3-Furnace DIA. shell and lining. W E T V LINING WRRING LINING BURN-IN OXYGEN CONTROL 1 Oxygen is automatically controlled with a separate flow measuring system for burn-in of a new lining. The rate of maximum flow is 420,000 std cu ft hr with pressure and temperature compensated. Burn-in can be controlled from either one of two control stations. One being in the main operating pulpit and the othek on the auxiliary platform. A ternr perature recorder is located in the main pulpit and a temperature indicator is located at the auxiliary station. NATURAL GAS Natural gas enters the shop at 115 psi and is reduced to 30 psi by a reducing station in the valve room. It will be used primarily for fuel for incandescent coke oven service, heatl ing, ladle and stopper rod drying, and service stations. Space for instrumentation is available for future preheating of scrap.

4 126 Open Hearth Proceedings, 1965 Fig. 5-Equipment layout-cross section at converter. Fig. &Equipment layout-longitudinal cross section.

5 Basic Oxygen Operations 127 Fig. 7-Flow diagram-material charging and dust collecting. STEAM FLOW water return is measured and re- any one of which will actuate a corded. High temperature, or low Steam will be used in the hood of warning light on high temperature. each operating furnace as a flame arin flow, will actuate the Water flow per hood is 6000 gpm. annunciator. rester. Maximum flow will be 6000 PPH at 220 psi and 500 F. SPRAY WATER FLOW LANCE COOLING WATER The pressure and temperature of the lance cooling water (treated city water) supply is measured and recorded on a two-pen recorder. Flow is also measured on the supply water. The flow is 1000 gpm and the temperature of the lance cooling Filtered raw river water will be measured to each furnace with a minimum flow of 2000 gpm. HOOD COOLING WATER Clarified river water in a closed loop will cool the hood of each furnace. There are 20 temperature elements located throughout each hood, WASTE GAS TEMPERATURE CONTROL SYSTEM The temperature of the waste gas from the furnace is measured, recorded, and controlled using two high speed thermocouples with high automatic selection to operate the recorder and spray water valves. The controller opens or closes spray water valves (nine per hood) in successive steps. In event of excessive temperature, the annunciator will be actuated, the relief damper opens, and the oxygen shut-off...lfl :.y:s: *::!=E=.,.: c: FL. Fig. 8-Gas scrubber system. COMPUTER The application of a computer do this process was included in all the design considerations from the start. Although no digital system was functioning in a basic oxygen shop at the stage of final design (late 1962) it was decided that since full dynamic control may eventually be achieved, the conduit lines, wiring, sensing points, etc., had to be installed at this time. Later, in 1963, the decision was made to install the instrumentation and data logging center. The start-up will be under as complete control as possible. Programming will be accomplished by trained corporation personnel.