不同体积分数氧气气化剂下煤炭地下气化过程[火用]分析

Exergy analysis of underground coal gasification with different oxygen concentrations

开展煤炭地下气化过程中能量转化环节效率优化,有利于提高煤炭地下气化系统实际生产效率和经济性。利用煤炭地下气化模型试验系统,进行了不同气化剂氧气体积分数条件下的地下气化模型试验,并结合热力学第1定律和热力学第2定律建立了煤炭地下气化系统[火用]评价模型。结合实际试验数据和物料平衡、热量平衡、[火用]平衡等理论模型,分析了不同氧气体积分数的气化剂对煤炭地下气化系统[火用]效率及不可逆[火用]损的影响。结果表明,煤炭地下气化系统是具有较高有效能量转化效率的系统;气化剂氧气体积分数是影响煤炭地下气化系统[火用]效率的主要因素之一。在气化剂氧气浓度为40%,60%和80%条件下,煤炭地下气化炉的综合[火用]效率分别为67.47%,73%和78.52%,外供[火用]效率分别为47.36%,61.00%和57.73%,不可逆[火用]损分别为32.53%,27.00%和21.48%。提高氧气体积分数可以显著提高系统的[火用]效率并降低不可逆[火用]损失;在利用纯氧作为气化剂时,地下气化系统[火用]效率可达到84.72%,外供[火用]效率可达68.86%,不可逆[火用]损可低至15.28%。对比地面气化系统,煤炭地下气化系统的有效能转换率大于高炉系统和发生炉系统、低于焦炉煤气的生产过程。水碳比是影响外供[火用]的主要因素之一,通过提高绝热燃烧温度、减少煤炭地下气化系统的热量损失和提高传热系数可以降低不可逆[火用]损。

In order to optimize the efficiency and economy of underground coal gasification(UCG)system in actual production,the efficiency of energy conversion in the process of UCG was optimized.A model test system was used to simulate the UCG under the conditions of 40%,60%,80%and pure oxygen concentration of gasifying agent respectively.Exergy evaluation model of UCG was established by combining the first law of thermodynamics and the second law of thermodynamics.The influence of gasifying agent with different oxygen concentration on exergy efficiency of UCG gasifier was analyzed.The concentration of gasifier oxygen is one of the main factors affecting exergy efficiency of UCG system.Under the condition that the concentration of gasifier oxygen is 40%,60%and 80%,the comprehensive exergy efficiency of UCG gasifier is 67.47%,73%and 78.52%,respectively;the efficiency of external exergy gasifier is 47.36%,61.00%and 57.73%,and the irreversible exergy loss is 32.53%,27.00%and 21.48%,respectively.When pure oxygen is used as gasifying agent,the exergy efficiency of UCG system can reach 84.72%,the exergy efficiency of external exergy can reach 68.86%,the concentration can significantly improve the exergy efficiency of the system and reduce irreversible exergy,and the rate of irreversible exergy can be as low as 15.28%.Irreversible exergy can be reduced by increasing adiabatic combustion temperature,reducing heat loss in gasifier,and increasing heat transfer coefficient.