ИСПОЛЬЗОВАНИЕ ПРИРОДНОГО ГАЗА ПРИ ОТОПЛЕНИИ ШАХТНЫХ ПЕЧЕЙ ВАГРАНОЧНОГО ТИПА ДЛЯ ПОВЫШЕНИЯ ЭНЕРГОЭФФЕКТИВНОСТИ ТЕХНОЛОГИЧЕСКИХ ПРОЦЕССОВ ВЫПЛАВКИ ЧУГУНА

Abstract

Natural gas can be additionally used to reduce coke consumption in a shaft furnace of cupola type with an open or closed furnace top. Its burning is typically made in the external hearths installed around the perimeter of the furnace shell. Depending on design, the burners provide a partial or complete pre-mixing of gas and air at air flow rate of 1.2 to 1.5. Further, the combustion gas is fed directly to a charge layer. When implementing this method, the coke consumption was 8 – 9 % of furnace charge and fuel gas consumption was 30 – 40 m3/t of melt. For these conditions, there were observed a slight increase in the temperature of the melt (10 – 20 °C) and productivity growth of 15 – 20 % while reducing the amount of harmful gaseous emissions by 20 – 25 % (mostly of CO). In the work of the cupola, periodic disruptions of the gas-dynamical regime were observed accompanied by the suspension of the charge material layer, as well as cooling of the resulting melt, an increase in chemical underburn and deterioration of service conditions of the lining materials. When using the layered method for the gas mixture combustion, it is fed into the heated layer of bulk materials with the air flow rate not below 2.5 – 3.0 with formation of a high-temperature zone of 1350 – 1380 °С and the width of 60 – 70 mm, able to move through the layer at a speed of 15 – 20 mm/min. To implement it in the thick ventilated layer it is necessary to ensure uniform mixing of gas and air, required gas-dynamic conditions and formation of set “gas-air” ratio in the air flow rate more than 2.5 and 3.0. When supplying the cold gas-air mixture in a layer of shaft furnaces by tuyeres, the combustion zone divides the whole layer into two stages: initial and final. The high temperature level of combustion zone provides substantial cooling rate of the materials at the stage of gas-air mixture ignition, which prevents it from fire in free upperlayer space. The absence of direct contact of high temperatures zone with a unit working space increases the reliability and efficiency of this process (no heat losses). The use of the layered method of natural gas burning to heat the cast iron cupola increase the productivity of the melting unit from 10 to 13.6 t/h, or 36 % while reducing specific consumption of coke for 80 kg/t or 33.3 %, decrease in the total consumption of heat for the process by 25 kW, or 18.78 % and heat losses in the exhaust gases by 25.32 kW, or 16.2 %. The overall thermal efficiency of the unit increased from 35.58 to 42.26 % or by 15.81 %. © 2017, National University of Science and Technology MISIS. All rights reserved.