Abstract
Recovering flue gas waste heat is beneficial to improving the unit efficiency in power plants. To obtain the change rules of performance parameters of a flue gas waste heat cascade recovery system (FWCRS) under variable working conditions, an experiment bench was designed and built. The variation laws of the inlet temperature and exhaust flue gas temperature of a low temperature economizer (LTE), the inlet and outlet air temperature of an air preheater (AP), the heat exchange quantities of the AP, LTE, and front-located air heater and an additional economizer (AE), as well as the waste heat recovery efficiency, the system exergy efficiency, and the energy grade replacement coefficient were obtained as the flue gas flow, flue gas temperature, bypass flue gas ratio, air temperature, and circulating water flow in AE changed. Using an orthogonal test, the flue gas temperature, bypass flue gas ratio and air temperature were proved to be the significant factors affecting the performance parameters of FWCRS, and the bypass flue gas ratio was suggested as an adjusting parameter of FWCRS under variable working conditions.
Highlights
With the rapid development of the world economy and increase of the population, the demand for energy sources is growing
For coal-fired power plant units, the exhaust flue gas temperature of boilers can reach more than 120 ◦ C, and about 50–80% of boiler heat loss is due to the exhaust flue gas energy loss, which accounts for 3–8% total energy input of the units [3]
Song [23] used the thermodynamic analysis method to study the off-design operating performance of an low temperature economizer (LTE) system, and the results indicated that the energy-saving effect of the system was stable under high-load conditions
Summary
With the rapid development of the world economy and increase of the population, the demand for energy sources is growing. Yang [22] proposed a conceptual waste heat recovery system on a 1000 MW coal-fired unit, in which the AP was divided into high-temperature AP, main AP and low temperature AP, the flue gas waste heat was used to heat condensed water by LTE and heat the combustion air by the APs, and 13.3 MW additional net power output was produced. Zhang [25] studied the energy-saving potential of an exhaust gas heat recovery system on a 600 MW unit by developing a calculation model of steam turbine and heat exchangers under off-design conditions, and the ratio of bypass flue gas was proved to have the greatest influence on the saved coal amount of the unit.
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