节能量计算的第二定律方法及其应用

An Energy-saving Calculation Method Using the Second Law of Thermodynamics and its Applications

鉴于第一定律的节能分析方法存在的问题,本研究基于热力学第二定律,推导出节约能量计算的一般化方法,从热力学实质上揭示节约能量正比于节能技术改造带来的能源利用系统总熵产的减少。针对火电机组,给出了系统总熵产计算模型。以输入燃料一定为条件,推导出超超临界机组锅炉烟气余热回收用于加热凝结水的节约能量计算公式,进一步揭示机组总熵产的减量正比于总热损失的减量,这意味着基于热力学第二定律的节能量计算和审计可以通过改造前后的系统总体热平衡分析进行,案例分析验证了本研究提出方法的正确性和实用性。

In view of the problems related to the energy conservation analysis using the first law of thermodynamics,a general method of energy-saving calculation was deduced based on the second law of thermodynamics in this paper. It was demonstrated that the energy-saving is essentially proportional to the reduction of the total entropy production from the improved energy utilization system. Specifically for the thermal power unit,the corresponding calculation model of the total entropy production was given. For an ultra-supercritical unit with constant fuel input,the calculation formula of energy-saving through reusing the exhaust waste heat to heat the condensed water was deduced,and it further showed that the reduction of the total entropy production of the unit is proportional to the reduction of the total heat loss. It implies that the energy-saving calculation based on the second law of thermodynamics can be made through comparing the overall thermal balances of the system before and after the energy-saving improvement is applied. Case analyses have verified the validity and the practicability of the method proposed.