Heat Economy Analysis Of Low-pressure Economizer In Power Plant

With the increasingly prominent contradiction between economic development andenergy and environment in China, energy conservation and emission reduction ofthermal power units becomes an issue of great concern. In order to achieve theenergy-saving emission reduction better, power plant and new design of thermal powerplant project were built and there are many projects that use the low press economizerfor flue gas waste heat recovery. Because of the different method of calculation, theeconomic evaluation of flue gas waste heat recovery and utilization has beencontroversial. In this background, it’s urgent to figure out reasonable evaluationmethodology, thus we can improve the energy conversion efficiency of flue gas wasteheat and lower the energy consumption rate accordingly.Flue gas waste heat recovery and utilization, which belongs to the external heatutilization system, could be quantitatively analyzed through the cycle function method.The paper is based on the cycle function method, sets up the complete mathematicalmodel of local quantitative calculation from the angle of anti balance. The model isapplied in partial quantitative analysis, such as the replenishment system, condensatesubcooling etc. Respectively based on a300MW subcritical unit and based on a1000MW ultra supercritical unit, calculating and analyzing the thermal economic.Based on a300MW subcritical unit, mathematical model of local quantitativecalculation is applied in heat economy analysis of low-pressure economizer, havingstudied the operating characteristics and the best installation position of low pressureeconomizer.The main research results are as follows:①The last water intake coefficient for the unit is the irreversibility of system,reducing the last water intake coefficient for the unit or increasing circulation heat,could improve the efficiency of the unit. Quantitative calculation model of the cyclefunction method is clear in concept, strong versatility, convenient computer programetc..②The operation optimization mathematical model of low pressure economizerwas built, and there is an optimal water flow, at rated conditions, when the water flow is69.2kg/s, there is a maximum relative increment of efficiency, which is0.722%. Bycomparing the experimental data and the theoretical calculation results, certify the accuracy and reliability of quantitative calculation model of cycle function method.③Having studied the main operating characteristics of low pressure economizer,these characteristics are universal, and could guide the practical production. Studyingthe best installation position of low pressure economizer, the results show that, thereview and selection of the scheme should comprehensive analysis from the materialprices and energy supply and the other aspects.