End Point Temperature Control of Basic Oxygen Converter by Sub-lance

Abstract

A new end point temperature control system introducing a sublance has been developed in Steelmaking Plant-II (nominal capacity: 100t×2, 110t×1), Muroran Works, Nippon Steel.
The main body of the sub-lance is a water-cooled steel pipe (2-1/2, O. D.) which moves up and down vertically along the guide rail. The sensor attached to the tip of the lance is a consumable immersion thermo-couple of the same type as that used in the turn-down temperature measurement.
By using the sub-lance, the bath temperature can be measured without stopping the oxygen blow, and “dynamic end point control” has thus become possible. Of every heat, the sub-lance starts to measure the bath temperature at 350 Nm³ (one minute) prior to the calculated total oxygen, and the rising temperature curve is modified accordingly.
Since September 1968, when it was made operative at No3 vessel, the sub-lance has been working quite satisfactorily.
As the result:
(1) The end point temperature control (±10°C) was improved by 15-17% reaching 87% of the on-temperture rate.
(2) Consequently efficiency in steelmaking was improved markedly, and in April 1970 the plant established a world record of 2 762 heats per month.