Optimization Research On Waste Heat Generation For Organic Rankine Cycle

The low temperature waste heat, which is discharged into the environment, is aboundant in the industry of China. The waste heat power generation of organic Rankine cycle(ORC), which has a simple structure, high thermal efficiency, long life, good economy, and environment-friendly features, is currently considered to be one of the most promising heat recovery technologies.The research on the waste heat power generation of ORC has important significance on the energy saving, emission reduction and ecological balance.Firstly, the basic ORC(BORC) was as a research object. The economy of the ORC system was studied. The pinch point temperature difference, evaporating temperature, cooling water and gas flow were selected as independent variables. The optimization mode was established, in which the minimum electric production cost was the object function. The influence of parameters on electric production cost was analyzed. And the system parameters were optimized. Meanwhile, the influence of gas temperature on optimal parameters was compared. The results showed that because the pinch point temperature difference, evaporating temperature, gas and cooling water flow had a complex influence on net output power and equipment price, which had an optimal value to make electric production cost a minimum. When the gas temperature was 170℃ and cooling water 20℃, the economy of R245 fa was the best. And the corresponding electric production cost was about 0.4339 yuan/(k W·h). If the gas temperature could increase, the system economy would improve. And the best evaporating temperature, pinch point temperature difference, gas flow would also increase.On the basis of BORC thermodynamic and economic model, on the basis of the thermodynamic and economic model on BORC, the mayhmatical model with internal regenetation on ORC(IHORC) was established to compare the thermal economy and economy of two systems. Thermal efficiency, exergy efficiency, electric production cost and payback period were analyzed at different evaporating temperature. The results showed that with the increase of the evapotating temperature, the thermal efficiency of two systems increased and the exergy efficiency decreased after an initial increase. There existed a certain evaporating temperature that made exergy efficiency a maximum. And with the increase of the evapotating temperature, the electric production cost and payback period increased after an initial decrease. And on certain conditions the thermal economy of IHORC was better, while the economy of BORC was better.According to the comparison results of thermal economy and economy of BORC and IHORC, a comprehensive objective function consisted of exergy efficiency and electricity production cost was established. The optimization model was established, in which the maximum exergy, minmum electric production cost and minimum comprehensive objective function were respectively as the object functions. And the two systems were optimized. The influence of evaporating temperature, condensing temperature and gas temperature on comprehensive economy was analyzed. And the influence of gas temperature on optimal parameters was analyzed. The better performance system was found in different gas temperature and evaporating temperature. The results showed that thermal economy and economy could be taken into account by the comprehensive objective function reasonably. The comprehensive objective function could evaluate the comprehensive economy. On certain conditions the suitable evaporating temperature range existed respectively in two systems. IHORC was suitable for high temperature and BORC was suitable for low temperature. With the increase of the evapotating temperature, the comprehensive objective function increased after an initial decrease. There existed a certain evaporating temperature that made the comprehensive economy good. With the increase of the condensing temperature, the comprehensive economy decreased. And With the increase of the gas temperature, the optimal evaporating temperature increased.