The Second Law Of Thermodynamics Analysis In The Process Of Fuel Combustion

In all forms of fuel using, the combustion is a necessary process that converte the fuel chemical energy into heat energy. Since the fuel mix is more complex, and combustion products in the form of multi-mix for several substances, this determines when analyzing combustion efficiency is difficult to measured by the first law of thermodynamics. The combustion process analysis requires more specific, so when analysis not only limited in the process of the whole story, but also measured change process itself. Taking carbon, methane, octane which three different states fuels as example, on the basis of the analysis of the theoretical basis of consumption to simplify analysis fuel exergy which this three fuels represent the various states, calculate the reaction enthalpy、reaction freedom enthalpy and reaction entropy and energy compensation value accounted for the proportion of heat in the higher heating value of this three fuels combustion process under different temperatures and draw the relationship graph. The results show that the pure carbon combustion reaction entropy is positive and there is no vapor phase transition, thus, it will increases the entropy generation of pure carbon actual combustion process in the higher heating value of carbon, in terms of energy use process, this effect is consistent with objective law. Methane combustion in a certain temperature range, its reaction entropy is positive if calculated in the higher heating value, the results is authenticity. But the reaction entropy is negative when combustion at high temperature, so it need to re-select the heat of methane to calculate process parameters when in high combustion temperatures. Reaction entropy of octane combustion is positive and rises with combustion temperature increases. Although the results are also consistent with the actual situation, however, in order to achieve maximum efficiency of fuel combustion, it should be control the combustion temperature reasonably, making the process irreversible losses to a minimum. This conclusion can be used as fuel efficient combustion optimization design theory and provide guidance direction about further strengthen the clean and efficient use of energy. Conduct the entropy generation analysis of a 9F grade HRSG in gas—steam combined cycle on the same theoretical, established entropy generation analysis model caused by different irreversible loss in different internal circulation system on thermodynamic equivalence, and through examples to validated this model. The results showed that the entropy generation in high-pressure water system accounted for a larger share of total entropy generation in HRSG, tap the energy potential should start with high-pressure water system. The model proposed intending to apply the second law analysis methods to assessment the efficiency of non-fuel combustion heat transfer process, so as to provides a complete set with scientific、integrity and rigor of the audit system for the second law of energy audits.