Patent GB-1131311-A (GB)
Title: Optimized blowing control for basic oxygen furnace
IPC: G01N33/20
Filed: 1966-07-18
Abstract: 1,131,311. Controlling oxygen steelmaking. LEEDS & NORTHRUP CO. July 18, 1966 [Aug. 16, 1965; Feb. 14, 1966], No.32199/66. Heading C7D. In a basic oxygen process of steelmaking the oxygen flow is controlled during the silicon removal phase at a level such that undesirable side reactions are avoided, and then when this phase is complete, as detected by the carbon loss efficiency ratio reaching a preset level, the oxygen rate is steadily increased subject only to an overriding upper limit. Provision is however made for the carbon loss rate to be monitored, any sudden increase being caused to reduce the oxygen flowrate. Provision is also made for the lance to be lowered as the reaction proceeds and the slag layer builds up, except that a rapid increase in oxygen flow will cause the lance to be raised. Finally the control mechanism may cause the oxygen flow to be cut-off and the lance to be raised when the preset final carbon content and/or bath temperature is reached. In the particular apparatus shown in Figs. 1A and 1B the carbon monoxide and dioxide contents of the exhaust gases leaving converter 10 through hood 30 are determined by analyzer 100, while the temperature and rate of flow are determined at 72 and 50 respectively. From this information there is produced a signal on line 142 representing the carbon loss rate, this signal operating carbon loss recorder 160 and through an integration means and in conjunction with inputs of initial carbon and bath weight a bath carbon recorder 212. The pressure of oxygen and the differential pressure across an orifice, are measured at 248 and 220 respectively and from these is produced on line 264 a signal indicative of oxygen flow-rate. This signal in conjunction with that on line 142 and appropriate inputs, is used to produce at 294 a record of the slag produced (based on the difference between total oxygen supplied and that used to oxidize carbon) and a record of bath temperature at 339. Furthermore the signal representing carbon loss rate is divided by that representing oxygen flow rate to produce a signal representing a quantity known as "carbon removal efficiency"; this quantity gives, at low carbon contents, a more accurate indication of bath carbon than does recorder 212, and is reported at 463. In the control mechanism, amplifier 410 compares the signal on line 412, representing actual oxygen flow, with that on line 416, representing the desired value, any discrepancy causing the controller to operate valve 42 through motor 42A. During the initial stage of blowing the set point signal on 416 is governed by the limiting silicon removal rate fed in at 420B and initial silicon content fed in at 428B, although there may be provision for feedback of a carbon removal rate signal 142 whereby increasing carbon removal rate results in an increase in oxygen input. There is however a limit circuit to prevent the maximum permissible oxygen rate (input at 450B) from being exceeded. Termination of the first stage is detected by comparison of carbon removal efficiency (line 460) with final silicon (input at 462B); at this point relay 470 is energized so that the initial control signal on line 430 is progressively increased according to the carbon loss rate increase preset at 472B. However to avoid slopping of the bath carbon loss rate signal 142 is fed to a rate type network 500 from which emanates on 510 a signal representing rate of change of the signal on 142; thus signal will produce through dead band circuit 518 a signal on 520 bringing about any necessary change in oxygen flow-rate. The height of the lance is adjusted by controller 600 through motor 15 according to a comparison between signals 21 representing actual position, and 612 representing that desired. Initially the lance is at its maximum height, as preset at 614B, but is then lowered according to the slag build-up as reported on 293 at a rate preset at 630B. Any sudden change in oxygen flow appearing on 416 will however result in modifying the lance height through rate type circuit 642 and dead band circuit 662; furthermore a minimum lance height is preset at 690B, this minimum height being increased by increasing oxygen flow indicated on 412. The desired final carbon content is preset at 720B in terms of carbon removal efficiency, while the minimum final bath temperature is preset at 732B. When these conditions are both met relay circuits cause zero potentials to appear on lines 416 and 612, whereupon the oxygen flow is cutoff and the lance raised to its highest position.