| Coal fire is a global disaster,especially in China.In view of the traditional methods of coal field fire control,such as stripping,water injection and grouting,all the thermal energy contained in the fire area is discarded in the process of treatmen.Based on the new idea of "use instead of cure" for coal fire control,a new kind of thermal energy extraction device embedded in the fire extinguishing borehole of coal field fire area based on temperature difference power generation technology is designed and constructed.It is tested and studied.The main research results are as follows:The thermoelectric characteristics of three kinds of thermoelectric power generation modules suitable for the natural conditions of shallow drilling in coal fire area were tested.The differences of thermoelectricity,internal resistance,power generation and thermoelectric conversion efficiency of three kinds of thermoelectric modules were analyzed.And explore the cost-effectiveness of the thermoelectric power generation module,and optimize the thermoelectric power generation module with the best thermoelectric conversion characteristics.A laboratory test device for the in-line thermal energy extraction device for the shallow borehole in the coalfield fire zone was constructed.The test analyzed and analyzed three different cold-end heat dissipation methods,string-connected structure and two different heat-heating methods: heat pipe,air-cooling and water-cooling.The effect of the mode on the thermoelectric conversion characteristics of the device.The results show that in different cooling methods,the highest efficiency is water wall cooling,and the lowest efficiency is heat pipe cooling.In the no-load state,the power generation of the device connected in series is higher than that of the device connected in parallel.When the load is connected,the closer the load resistance is to the internal resistance of the device,the greater the output power will be.For different ways of heat extraction,the way of heat extraction by putting the heat extraction device into the firefighting borehole for direct thermoelectric conversion is better than the way of heat extraction by thermal power conversion after the heat energy in the coal field fire area is extracted to the ground.The in-line thermal energy extraction device for the shallow borehole in the coalfield fire area was designed and constructed.The device mainly consists of copper casing,thermoelectric power generation module,water wall and other components.The thermoelectric conversion characteristics of the device were tested in the field.Subsequently,this paper optimizes the heat extraction device embedded in the fire extinguishing borehole in the coal field fire area from the following aspects: the addition of the soaking system,the utilization of the heat energy between the air and the coal rock under the device,and the reduction of the air gap,aiming at solving the problems found in the field test of the thermal energy extraction device,such as the uneven temperature distribution at the hot end,the failure to effectively utilize the heat energy between the air and the coal and rock at the lower part of the device,and the excessive gap between the high temperature wall surface and the air of the device,etc.The results show that the maximum generating power of the thermal energy extraction device is 207 W and the maximum open circuit voltage is 260 V.The effect of thermal energy extraction device can be further improved by the addition of soaking device,heat energy collection device and the reduction of air gap,and the he maximum output power of the device is increased by 8%,7% and 10% respectively.Finally,the output power of the whole device is increased by 16% compared with that before optimization. |
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