Clean Power Generation from the Intractable Natural Coalfield Fires: Turn Harm into Benefit

Abstract

The coal fires, a global catastrophe for hundreds of years, have been proved extremely difficult to control, and hit almost every coal-bearing area globally. Meanwhile, underground coal fires contain tremendous reservoir of geothermal energy. Approximately one billion tons of coal burns underground annually in the world, which could generate ~1000 GW per annum. A game-changing approach, environmentally sound thermal energy extraction from the intractable natural coalfield fires, is being developed by utilizing the waste energy and reducing the temperature of coalfield fires at the same time. Based on the Seebeck effect of thermoelectric materials, the temperature difference between the heat medium and cooling medium was employed to directly convert thermal energy into clean electrical energy. By the time of December 2016, the power generation from a single borehole at Daquan Lake fire district in Xinjiang has been exceeded 174.6 W. The field trial demonstrates that it is possible to exploit and utilize the waste heat resources in the treated coal fire areas. It promises a significant impact on the structure of global energy generation and can also promote progress in thermoelectric conversion materials, geothermal exploration, underground coal fires control and other energy related areas.

Heat losses in a smouldering system: The key role of non-uniform air flux

“…Moreover, as seen in barbeques, smouldering will propagate as a reaction wave through the bed until the fuel is exhausted or the air flow is eliminated. There is a wide range of fuels that smoulder, from natural materials such as peat [20], coal [21], and forest litter [22] to anthropogenic materials like polyurethane foam [23], oil-soaked insulation [24],…”

“…and coal tar-contaminated soil [18,25]. In uncontrolled smouldering scenarios, such as underground coal seam fires, smouldering proceeds in a runaway manner since the air flow cannot be eliminated, fuel load is in excess, and the system geometry is uncontrolled [21,26]. In applied engineering scenarios, air flow is strictly managed, and fuel load and system geometry are carefully controlled to effectively destroy wastes and capture the released energy [8,10,18].…”

“…The underlying causes are positive energy balances both locally (at the reaction front) and globally (across the fuel bed), where the rate of heat generated reaches thermal equilibrium with the heat lost (e.g., to endothermic processes and to the external environment) at temperatures above quenching [16,19,43]. The self-sustaining nature of smouldering is what makes natural smouldering problems so intractable, such as peat forest and underground coal fires [21,22,26], and what makes applied smouldering waste-to-energy systems so green and sustainable [8,10,18,25].…”

Waste heat recovery, utilization and evaluation of coalfield fire applying heat pipe combined thermoelectric generator in Xinjiang, China

“…with very limited information being reported at realistic scales. Recently, a HP exchanger system was tested for TEG in a sub-surface coal fire [17,44]. The authors report that the maximum installed capacity was of 1600 W when using Bi2Te3 thermoelectric modules.…”

“…The importance of this work stems from a change in approach towards the recovery of the energy produced by combustion while enabling control and suppression. Given that nearly one billion tons of coal combusts underground annually worldwide, releasing heat that could potentially generate almost 1000 GW electricity (the current nuclear power and hydropower capacity is currently 400 GW and 900 GW, respectively [17]), achieving any form of energy recovery will be a very positive outcome. .…”