深部煤层地下煤气化原位点火的CFD模拟

CFD simulation on in-situ ignition of UCG in deep coal seam

地下煤气化(Underground Coal Gasification,UCG)作为一种新型采煤技术受到了广泛的关注,但UCG的实验成本较高,在开展UCG实验之前应当对煤层的演变机理进行深入的探究。计算流体力学(Calculated Fluid Dynamics,CFD)可以凭借计算机强大的计算能力,以较为低廉的成本模拟UCG的生产过程。采用Ansys公司开发的CFD软件Fluent模拟了1000 K烟气加热下深部煤层的原位加热着火过程,重点分析了温度、氧气摩尔分数和孔隙度的变化。结果表明,泵入500 s的1000 K烟气不足以点燃煤层,1000 s的烟气加热时间足以点燃煤层,该结果在时间上与劳伦斯实验室的点火时间相当。在煤层内表面,高温主要集中在靠近入口0~0.6 m内的煤层。着火前的最高温度低于加热烟气入口温度1000 K,而着火后的最高温度超过1000 K,最高温度约1250 K。O_(2)在高温区几乎全部消耗,而在其他温度较低的区域,到达煤层内表面的氧气摩尔分数不到2%。高温区孔隙度迅速增长,在1000 s时部分煤层孔隙度可达0.9左右。在煤层内部,煤层越厚,温度上升越低。在1000 s和2000 s时,7 cm线上煤层的最高温度仅为500 K左右,远低于相同加热时间下煤层内表面的最高温度。在2000 s的点火过程中,渗入7 cm和14 cm煤层中的氧气较少,内部煤层孔隙度均在0.4以下。较低的孔隙度是由较低的温度和较低的氧气摩尔分数共同造成的。对温度、氧气摩尔分数和孔隙度的模拟可为如何促进煤层内部的反应提供参考。

Underground coal gasification(UCG)as an alternative coal mining technology is attracting much attention.However,due to the high experimental cost of UCG,the evolution mechanism of coal seam should be deeply explored prior to the implement of experiments.By virtue of the great computational power of computers,the computational fluid dynamics(CFD)is able to simulate the production process of UCG at a relatively lower cost.The in-situ ignition and combustion of deep coal seam heated by 1000 K flue gas is simulated and the changes of temperature,molar O_(2) fraction and porosity are analyzed by the CFD software,Fluent,developed by Ansys cor-poration.It is elucidated that pumping 1000 K flue gas for 500 s is inadequate for coal seam ignition,while 1000 s heating has been enough for coal seam ignition.On the internal surface of coal seam,the high temperature is accumulated in the 0−0.6 m coal seam near inlet.The maximum temperature before ignition is below inlet temperature of heating flue gas,1000 K,while the maximum temperature after ignition exceeds 1000 K and reaches up to 1250 K.Almost all O_(2) is consumed in the high-temperature zone,while less than 2%molar O_(2) fraction arrives at the internal surface of coal seam in other lower-temperature zones.The porosity rap-idly increases in high-temperature zone and at 1000 s the porosity in the part of coal seam reaches up to 0.9.In the interior of coal seam,the thicker the coal seam is,the lower the temperature rises.The maximum temperature on 7 cm line is only 500 K at 1000 s and 2000 s,much lower than that on the internal surface of coal seam when it is heated for the same time.During 2000 s ignition,little O_(2) penetrates 7 cm and 14 cm coal seam and the porosities of interior coal seam are all be-low 0.4.The low porosities are attributed to the low temperature and low molar O_(2) fraction.The simulation on temperat-ure,molar O_(2) fraction and porosity may provide a reference for how to promote the reaction in the interior of coal seam.