THE USE OF NATURAL GAS FOR HEATING OF SHAFT FURNACES OF CUPOLA TYPE TO INCREASE THE TECHNOLOGICAL PROCESSES EFFICIENCY OF PIG IRON SMELTING

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 mate rials  with the air flow rate not below 2.5  –  3.0 with formation of a hightemperature 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  %.

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