燃料燃烧过程的热力学第二定律分析

发布时间：2018-08-28 14:42

【摘要】：在燃料的所有利用形式中,燃烧过程是将燃料化学能转化为热能的必经过程。由于燃料构成比较复杂,并且燃烧产物多涉及到几种物质的混合,这就决定了在分析燃烧效率时很难用热力学第一定律加以衡量。燃料利用过程需要具体化分析,不能仅局限在过程始末的分析,更要对过程本身的变化加以衡量。本文分别以碳、甲烷、辛烷三种不同状态的燃料为例,并以单耗分析理论为依据对此三种燃料所代表的各种状态的燃料(?)进行简化分析,并以燃料高位发热量来计算在不同温度下这三种燃料燃烧过程的反应焓、反应自由焓、反应熵及不可逆损失占发热量的比重并画出关系曲线图。结果显示,纯碳燃烧的反应熵为正值且不存在水蒸气相变过程,因此以燃料高位发热量来计算会使纯碳实际燃烧过程的熵产增加,对能源利用过程而言,这种影响是符合客观规律的。甲烷在一定燃烧温度范围内以高位发热量来计算反应熵是正值,结果符合真实性。但在高温燃烧时的反应熵出现负值,因此当燃烧温度较高时应重新选取甲烷的发热量来计算过程参数。辛烷燃烧的反应熵均为正值且随燃烧温度的升高不断增大,尽管结果也符合实际情况,但为使燃料的燃烧效率达到最高,应合理控制燃烧温度,使过程不可逆损失降到最低。本文的分析结果可以作为燃料高效燃烧优化设计的理论依据,为能源高效清洁使用的进一步加强提供指导性方向。同样应用单耗分析理论对燃气一蒸汽联合循环某9F等级余热锅炉进行了熵产分析,以热力学等价为前提建立了不同循环系统内部各种不可逆损失所引起的熵产分析模型,并通过实例对此模型进行了验证。结果显示高压水循环系统的熵产占余热锅炉总熵产的份额较大,发掘节能潜力应从高压水循环系统入手。该模型的提出旨在于应用第二定律分析方法对无燃料燃烧的换热过程进行效率评估,为能源利用的第二定律审计工作提供一套集科学性、完整性和严谨性于一体的审计体系。
[Abstract]:In all forms of fuel utilization, the combustion process is a necessary process for converting the chemical energy of the fuel into heat energy. Because of the complexity of fuel composition and the mixing of several substances, combustion products are difficult to be measured by the first law of thermodynamics in the analysis of combustion efficiency. The process of fuel utilization should be analyzed concretely, not only in the beginning and end of the process, but also in the process itself. In this paper, three different fuels, carbon, methane and octane, are taken as examples, and based on the theory of unit consumption analysis, the fuels in different states represented by these three fuels are discussed. The reaction enthalpy, reaction free enthalpy, reaction entropy and the proportion of irreversible loss of heat in the combustion process of these three fuels at different temperatures are calculated by simplified analysis. The results show that the reaction entropy of pure carbon combustion is positive and there is no water vapor phase transition process. This effect is in line with the objective law. In the range of combustion temperature, the reaction entropy of methane is calculated with high calorific value, and the results agree with the reality. However, the reaction entropy of high temperature combustion is negative, so when the combustion temperature is high, the heat of methane should be re-selected to calculate the process parameters. The reaction entropy of octane combustion is all positive and increases with the increase of combustion temperature. Although the results accord with the actual situation, in order to achieve the highest combustion efficiency of fuel, the combustion temperature should be controlled reasonably and the irreversible loss of the process should be reduced to the minimum. The results of this paper can be used as the theoretical basis for the optimization design of fuel efficient combustion and provide guidance for the further strengthening of energy efficiency and clean use. The entropy production of a 9F grade waste heat boiler in a gas-steam combined cycle is also analyzed by using the unit consumption analysis theory. Based on the premise of thermodynamic equivalence, an analysis model of entropy production caused by various irreversible losses in different circulation systems is established. The model is verified by an example. The results show that the entropy production of the high pressure water circulation system accounts for a large proportion of the total entropy production of the waste heat boiler, so we should start with the high pressure water circulation system to explore the energy saving potential. The purpose of this model is to evaluate the efficiency of the heat transfer process without fuel combustion by using the second law analysis method, and to provide a scientific, complete and rigorous audit system for the audit of the second law of energy utilization.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK16

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