Method for determining blast furnace tuyere zone blackness degree on pulverized coal fuel injection

Abstract

Pulverized coal fuel (PCF) supply is one of the modern methods of improving the cast iron production technology in blast furnaces (BF). It has a significant effect on the heat exchange in the tuyere zone (TZ). The known method of radiant heat transfer calculation in TZ accounts only for the ash particle effect on the TZ blackness degree. The aim of this work is to develop a method for determining TZ blackness degree and to investigate the effect of different factors on this value. The work was based on the elements of the proven method of calculating heat exchange in boiler furnaces. Parametric sensitivity was investigated by alternately simulating an error in each of the input values and determining its effect on the sought value. By analysing the processes, the authors have derived dependences for obtaining the concentration of ash particles and triatomic gases and determined the degrees of TZ blackness by Bouguer’s law simultaneously taking into account the radiation of the burning coke and ash particles, and triatomic gases. It has been established that an increase in the PCF consumption from 0 to 250 kg/t of pig iron changes the TZ blackness degree from 0,067 to 0,243; and a 1 % increase in the pressure, concentration of triatomic gases, ray effective length, TZ temperature and ash particle size changes the TZ blackness by 0,714 %, 0,151 %, 0,72 %, –1,557 % and –0,176 %, respectively. The calculations have shown that the effects of coke particles, triatomic gases and ash particles on the sought value are approximately equal. In contrast, when the conventional method is applied, it results in an approximately 2-time underestimation of the values, while even for evaluation calculations, the maximum permissible error is 10–15 %. The developed method accounting for all factors has the maximum error of 5 %. It is important for designing tuyeres and TZ refrigerators.