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.
Highlights
About 70% of the generator sets are coal-fired units in China, consuming nearly half of the produced coal every year [1]
There are are two two problems problems to to be be solved: solved: how the exhaust exhaust temperature, the inlet and outlet air temperature are determined by adjusting some parameter of temperature, the inlet and outlet air temperature are determined by adjusting some parameter of the system; and how to optimize waste heat recovery when the changes and the the system; and how to optimize waste heat recovery when the inlet flue gas temperature (IFT) or the inlet air temperature (IAT) changes and the exhaust temperature were solved in the paper by exhaust temperature and andout outair airtemperature temperatureare areconstant
Theproblems problems were solved in the paper theoretical analysis of using the theory of heat balance, energy balance and exergy balance, by theoretical analysis of CWHRS using the theory of heat balance, energy balance and exergy and calculating the optimal of a CWHRS
Summary
About 70% of the generator sets are coal-fired units in China, consuming nearly half of the produced coal every year [1]. Huang et al [10] proposed an improved waste heat use system for power plant boilers based on the traditional bypass flue heat recovery system, in which low-pressure steam is extracted from the low-pressure cylinder to preheat the air, replacing high-temperature flue gas to heat the feed water of the boiler, and the calculation showed the unit’s exergy efficiency was increased to 45.46% on a. Liu et al [11] introduced a coupled high-low energy grade flus gas waste heat recovery system (CWHRS) applied to a 1000 MW double-reheat unit, which has produced good energy-saving effects All these flue gas waste heat recovery systems were analyzed under the designed condition. Given a determined inlet flue gas temperature (IFT) and outlet exhaust gas temperature of the waste heat use system and IAT of the boiler, it is necessary to find methods of improving the effectiveness of waste heat recovery systems. The effects of different IFT and IAT on EBC were analyzed to determine the ONT under different conditions
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