Experimental Study on Operation Regulation of a Coupled High–Low Energy Flue Gas Waste Heat Recovery System Based on Exhaust Gas Temperature Control

Jiayou Liu,Fengzhong Sun

doi:10.3390/en12040706

Abstract

Controlling the exhaust gas temperature (EGT) of coal–fired boilers at a reasonable value is beneficial to ensuring unit efficiency and preventing acid corrosion and fouling of tail heating surfaces in power plants. To obtain the operation regulation of coupled high–low energy flue gas waste heat recovery system (CWHRS) under a given EGT, experimental equipment was designed and built. Experiments were carried out to maintain the exhaust gas temperature under different flue gas flow, flue gas temperature and air temperature conditions. As the flue gas flows, the flue gas temperatures and air temperatures increased, and the bypass flue gas flow proportions or the water flows of the additional economizer were increased to maintain the EGT at about 85 °C. An improved low temperature economizer (LTE) and front located air heater (FAH) system were put forward. As the flow of the crossover pipe increased, the EGT and the inlet water temperature of the LTE increased. As the flow of the circulating loop increased, the EGT and the inlet water temperature of the LTE decreased. Operation regulations of LTE–FAH system under four cases were given. The operation regulations of CWHRS and LTE–FAH system can provide references for power plant operation.

Highlights

For coal–fired boilers in power stations, the heat loss of flue gas represents a high proportion of the total heat loss [1]
If the exhaust gas temperature (EGT) was higher than 85 ◦ C, the heat recovered by additional economizer (AE) was increased by increasing the bypass gas flow to decrease the inlet temperature of low temperature economizer (LTE), by which the EGT was reduced to 85 ◦ C
An improved LTE–front located air heater (FAH) system was put forward and the relationship between the crossover pipe flow, circulating loop flow and EGT, inlet water temperature was studied through experiments

Summary

Introduction

For coal–fired boilers in power stations, the heat loss of flue gas represents a high proportion of the total heat loss [1]. With the rising exhaust gas temperature (EGT), more heat is taken away by the flue gas, resulting in decreased boiler efficiency and increased coal consumption. Measures to reduce EGT to improve the boiler efficiency and reduce consumption of coal and water are necessary. There are numerous methods to recover the waste heat from flue gas and reduce the EGT. The organic Rankine cycle system can convert the flue gas waste heat to electricity and improve the unit efficiency [3]. The low–temperature flue gas heat can be used to dry fuel such as lignite for utility boilers [6], saving steam consumption for fuel drying [7]. The traditional way to reduce the EGT is to add a heat exchanger at the tail of the flue to heat the turbine condensate or the inlet air of an air preheater (AP)

Methods

Results

Conclusion