Optimization of fuel and air use in a tunnel kiln to produce coal admixed bricks

In the present work, optimization of the fuel and air use was done around a tunnel kiln producing bricks with low calorific value coal as an additive. The objective function is the cost of fuels together with heat lost through the stack. The mass and energy balance computations to calculate the energy to be supplied by fuels, were computed based on the plant data. The process constraints are the energy to be supplied by the fuels, air required for complete combustion, the SO2 emission to the atmosphere, the relative humidity of the stack gases and the percentage of carbon in the brick body.Using admixed coal (AC) as an energy source in the brick body is beneficial when either pulverized coal (PC) or natural gas (NG) is used as the fuel fed in the firing zone. Whatever the heating value of the AC, it has a substantial contribution varying from 15% to 39% of the energy required for brick production. The energy to be supplied is the highest when fuels used are NG and low calorific value admixed coal (LCV AC) in the brick body. This is due to the risk of condensation in the stack which should be prevented by increasing the flow rate of the ambient air.