Control of Spontaneous Combustion of Sub-Bituminous Coal by Means of Heat Exchanger Submersion inside the Piles

The low-rank coal, such as sub-bituminous and lignite has become a widely used alternative fuel for power generation. During the transportation process from mining location to power plant, coal on the barge might be stored for a long period of time. A control mechanism of spontaneous combustion of coal in barge was simulated in laboratory scale by means of submersing heat exchanger inside the coal bed. The low-rank coal is more prone to self-ignition (spontaneous combustion) which is quite difficult to detect, due to the complex event of spontaneous combustion involving many factors from both intrinsic and extrinsic factors, such as particle size, moisture content, ambient temperature, barometric pressure, etc. A laboratory scale experiment was set up to study the smouldering combustion phenomenon of coal samples and means of control by using heat exchanger submersion in a coal bed. The coal sample was placed inside a wire mesh cube with a coiled copper tube installed in the middle of the coal bed. Fresh water was flowed through the coiled copper tube with controlled intake temperature about 28 °C. Approximately 65 grams of coal is heated in the oven at 210 °C until the temperature in the middle of the pile reaches up to 320 °C, then water is discharged through a copper tube to the middle of the pile and cooling it down. It is found that the temperature of coal sample can be brought down to 200 °C depending on the water flow. Thermocouples are used to measure the coal's temperature in the middle of the pile. This method shows that the heat generated can be reduced to below the critical temperature for spontaneous combustion. The water flow rate has significant impact on temperature reduction of the coal inside the bed. This method has a potential benefit for controlling spontaneous combustion problem during barge transportation of coal.