Thermodynamic analysis of a low-pressure economizer based waste heat recovery system for a coal-fired power plant

• An evaluation method of the LPE (low-pressure economizer) system is established.
• Impacts on the original thermal system by installing LPE are investigated.
• A theoretical guideline is provided to improve the thermal system efficiency by LPE.
• A detailed case is presented to demonstrate the energy saving of the LPE system.

An LPE (low-pressure economizer) based waste heat recovery system for a CFPP (coal-fired power plant) is investigated thermodynamically. With the installation of LPE in the flue before the FGD (flue gas desulfurizer), the heat contained in the exhaust flue gas can be recovered effectively and the water consumption can be reduced in the FGD resulted from the temperature dropped flue gas. The impacts on the related apparatuses after installing LPE in a CFPP are analyzed and the internal relationships among correlated parameters are presented. The efficiencies of LPE installed in a CFPP evaluated by the first law, the second law and the thermal equilibrium efficiencies are also compared and analyzed. A detailed case study based on a 350 MW CFPP unit is presented and the variations of the thermal performance after the installation of LPE are investigated. The results show that the second law and the thermal equilibrium efficiencies are increased which can be indicators to evaluate the performance of the LPE system while the first law efficiency is decreased after installing LPE. Results also show that the saving of SCE (standard coal equivalent) is 3.85 g/(kW·h) for this CFPP unit under full load after installing LPE.