Patent GB-1087439-A (GB)
Title: Process measurement system for basic oxygen refining of steel
IPC: C21C5/30
Filed: 1966-03-15
Abstract: 1,087,439. Measuring electrically. LEEDS & NORTHRUP CO. March 15, 1966 [March 30, 1965 (2)], No. 11364/66. Heading G1N. The temperature of molten steel during refinement by the basic oxygen method is inferred from measurements of the rate of loss of carbon from the steel and the rate of production of slag. Integrator 310 receives the carbon loss rate signal on line 312 and the slag formation rate signal on line 320. In addition resistor 300 is preset to supply on line 298 a signal representative of the heat losses by radiation and conduction from the vessel, while resistor 306 is preset to supply on line 304 a signal indicative of the heat carried away by the exhaust gases. Correction signals representative of the amount of carbon dioxide produced in the refining vessel, and of the amount of heat formed by reactions outside the bath are supplied on lines 314 and 324, respectively. The output from integrator 310 is divided by the weight of steel in the vessel by resistor 334, while resistor 333 compensates for the weight of the slag. The voltage across resistor 322 is then indicative of the steel temperature. The initial temperature is measured during a 'turndown' operation, by means of a thermocouple, and the recorder 339 is set to this temperature. The output at 340 then indicates changes in temperature from this datum. Carbon loss measurement. The rate of flow of wet exhaust gases, after cooling at 28, is determined by measuring the pressure drop across orifice plate 54, and the temperature at 68, the wet flow rate being represented by the output at 89. The percentages of carbon monoxide and carbon dioxide in the exhaust gases are determined, on a dry gas basis, by infrared analyzer 100. From the carbon dioxide measurement at 94, the temperature measurement at 74 and a unit reference signal at 108 a signal is obtained at 92 which represents the ratio of dry gas to wet gas in the exhaust gases. The signals at 89 and 92 are multiplied together to give an output a 124 indicative of the rate of flow of dry gas. This is multiplied at 138 by a signal representing the concentration of carbon in the exhaust gases. The signal on line 142 therefore represents the carbon loss rate. This signal is divided by the weight of steel to give an indication of the percentage carbon loss rate on recorder 160, and is also integrated at 182 and divided by the weight of steel at 186 to provide a signal indicative of the percentage carbon loss, which is subtracted from the initial percentage preset on resistor 213 to give an output at 210 indicative of the percentage of carbon remaining. The carbon loss rate signal is applied to resistor 306 to provide the signal at 304 indicative of the heat carried away by the exhaust gases. A proportion of the carbon loss rate signal, preset at 282 is supplied on line 314 to represent amount of carbon dioxide produced in the vessel 10. Slag measurement. The rate of flow of oxygen into the system is measured by differential pressure transducer 220 and static pressure transducer 248 to give an output on line 264. The oxygen flow rate signal is supplied, with the carbon loss rate signal and the carbon dioxide correction signal, to summing amplifier 270, the output of which is indicative of the rate of formation of slag, and which is integrated at 290 to provide an indication of the slag thickness. A preset proportion of the slag rate signal, preset at 321, is supplied on line 320 and is indicative of the heat generated by slag formation. Modifications. Instead of presetting the proportion of carbon dioxide produced, using resistor 282, this proportion may be computed, using the system of Fig. 2 (not shown). In this system analyzer 100 also provides a signal indicative of the percentage of oxygen in the exhaust gases. Using the output on line 126 (derived as in Fig. 1), the signals indicative of the carbon dioxide and oxygen concentrations, and a reference signal and output is produced which, when multiplied by the flow rate signal on line 124, is indicative of the rate of production of carbon dioxide in vessel 10. The computation involves the known relationship between the concentrations of oxygen and nitrogen in the air drawn into the exhaust system at 22, and the assumption that all the oxygen from lance 14 is consumed in vessel 10. A second modification Fig. 3 (not shown) provides a more accurate compensation for water vapour in the exhaust gases, and includes a summing amplifier (88A) instead of sign-reversing amplifier 88 (Fig. 1). The inputs to the amplifier are the signals on lines 74 and 86 and a further signal representing the ambient temperature in the process area. The amplifier output is divided by the output from a further summing amplifier (110A), supplied with signals representing the carbon monoxide and dioxide concentrations, together with a reference signal. The quotient represents the dry gas flow rate and corresponds to the signal on line 120 in Fig. 1. Amplifier (88A) may include a rate circuit shunted across the input resistor connected to the line (74) supplying the temperature signal. If gas analyzer 100 is suitably constructed so as to measure the wet gas concentrations, compensation of the flow rate for water vapour is unnecessary. It is also implied that, since the exhaust gases are converted almost completely to carbon dioxide in duct 20, only the latter concentration need be measured in analyzer 100.