Flame analysis for prediction of thermocouple temperature and quality of sponge iron at TATA steel long products limited

Abstract

Abstract The temperature profiles of the gas and charge in a coal-fired rotary sponge iron kiln affect both the iron ore reduction process and accretion formation. The temperature profile of charge is estimated from the eleven thermocouples (TC1-TC11) placed along the 80 m length of the kiln. The quality prediction models are heavily dependent upon the accuracy of the measurement of TC10. However, slowly, as the kiln’s campaign life increases TC10, and other thermocouples too, get corrupted due to deposition of material (accretions) on the thermocouples. At the beginning of the campaign, however, there is no accretion on TC10. In the present work, an attempt is made to directly correlate flame characteristics with TC10 and with quality of iron produced so that when TC10 is corrupted due to accretion or breakdown, we can still survive by using flame characteristics as a guide to control quality. The flame inside the rotary kiln has been analysed by using image analysis procedures for the first time in a sponge iron plant. The flame’s estimated average temperature and pixel intensity information are correlated with (a) the temperature measured by the thermocouple TC10 (which is installed at a distance of 20 m from the rotary kiln outlet hood) and (b) with quality of iron produced. It is found that use of average flame temperature for quality prediction has several advantages in terms of increased accuracy of prediction and quicker response time of flame to short-time changes in coal quality (particle size, moisture, ash content, etc) whereas TC10 thermocouple takes much longer to reflect these changes due to slow process of heat transfer to charge. In addition, the adverse effect of accretion formation on TC10 for quality prediction has been overcome.