The Improved Method And Application Of Boiler Entropy Analysis

In this paper,the entropy generation model of boiler system is improved based on the second law of thermodynamics.And the entropy generation is calculated indirectly by the endothermic and endothermic average temperature,instead of the traditional entropy calculation method with thermodynamic parameters.The method is succincter and it is more propitious to the engineering application of the entropy analysis method.Then this paper selects the boiler system of 600 MW subcritical boiler,600 MW supercritical boiler and 1000 MW ultra supercritical boiler and makes the calcution of the entropy generation distribution.The entropy generation of each process is analysed under different working conditions..Starting from the efficiency of each heating surface in the boiler system,the heat transfer process of each heating surface is a heat transfer process from fuel to flue gas to working fluid.Based on this process,the heat of each heating surface can be traced back to the amount of fuel consumed with heat analysis of each heating surface.The conclusions of this paper include the following aspects:1.Improved model of boiler entropy generation is divided into the entropy generation process of the furnace and boiler heat transfer.Entropy generation in the furnace process includes the combustion process and the exothermic process of the flue gas,including entropy generation of air preheater,incomplete combustion,burned coal adiabatic combustion,heat loss of boilers,ash heat loss and flue gas exothermic process.The heat transfer process entropy generation of the boiler mainly includes the of the process of heat absorption and flow in the working fluid,including entropy generation of feedwater flow resistance,steam flow resistance of the reheater and boiler heat transfer process.2.The entropy generation of burning coal,boiler heat transfer process,flue gas exothermic process and air preheater account the most parts in entropy generation distribution of boiler system.The reduction of the irreversible loss in the heat transfer process of the boiler system is one of the important reasons for the increasing of the the second law efficiency(exergy efficiency).The exergy efficiency of the economizer is the lowest among all the heating surfaces of the boiler,and the highest is the high temperature superheater and the high temperature reheater.With unit parameters improving,the economizer can play a less obvious role.Economizer has the the lowest efficiency in the boiler heating surface.Therefore,the role of boiler economizer need to be re-recognized.