Node temperature of the coupled high-low energy grade flus gas waste heat recovery system

Abstract

Coupled high-low energy grade flus gas waste heat recovery systems (CWHRS) have been applied in power plants to improve unit efficiency. In this study, to evaluate the rationality of waste heat recovery, the energy-grade balance coefficient (EBC) of the CWHRS was derived using the theory of heat balance, exergy balance and energy grade balance. The inlet flue gas temperature (IFT) of the low-temperature economizer was defined as the node temperature of the CWHRS. The optimal node temperature (ONT) was optimal when the absolute value of the EBC was the smallest. The exergy efficiency and EBC of the system installed on a supercritical 600 MW unit were calculated and the result shows that the ONT of the system was about 115 ◦ C, the ONT decreased from about 135 ◦ C to about 113 ◦ C when the IFT increased from 335 ◦ C to 380 ◦ C and the ONT decreased from about 144 ◦ C to about 113 ◦ C when the inlet air temperature increased from −10 ◦ C to 35 ◦ C. The node temperature is recommended as an adjusting parameter of CWHRS to ensure the effect of waste heat recovery.