HEAT-TREATMENT OF COKE IN THE TEMPERATURE-RANGE OF 1400-DEGREES-C-1650-DEGREES-C

Coke which is manufactured in the by-product coke oven by heating coal to around 1000-degrees-C in absence of air gets heated to much higher temperatures of 1500-degrees-C or more before taking part in the comb ustion reaction in the raceway region of a blast furnace. It is estima ted that 20 to 30% of carbon in the coke takes part in the Boudouard r eaction in the direct reaction and carburising zones of the furnace in the temperature range of 1000 to 1300-degrees-C and rest of the mass remains more or less intact. Samples collected from the tuyere region of a blast furnace during the off-blast period show 2 to 3% more ash t han the skip coke due to the loss of carbon from the coke and gasifica tion of a part of its silica to silicon monoxide. Coke sample when hea t-treated in the laboratory in absence of any diffusion influx of air did not undergo much changes in its composition and weight upto 1500-d egrees-C but suffered a loss of 12 to 16% in its weight alongwith slig ht lowering of silica in the ash in the temperature range of 1550 and 1650-degrees-C. Results are attributed to the transformation of silica to silicon carbide at around 1540-degrees-C and simultaneous loss of 10 to 20% of silica as silicon monoxide vapours in the gas phase. In a blast furnace, such changes which might take place in the vicinity of the raceway region would lead to recycling of silicon carbide and sub stantial transfer of silicon to the metal in the bosh region.