Application of a low pressure economizer for waste heat recovery from the exhaust flue gas in a 600 MW power plant

This paper presents a case study of recovering the waste heat of the exhaust flue gas before entering a flue gas desulphurizer (FGD) in a 600 MW power plant. This waste heat can be recovered by installing a low pressure economizer (LPE) to heat the condensed water which can save the steam extracted from the steam turbine for heating the condensed water and then extra work can be obtained. The energy and water savings and the reduction of CO2 emission resulted from the LPE installation are assessed for three cases in a 600 MW coal-fired power plant with wet stack. Serpentine pipes with quadrate finned extensions are selected for the LPE heat exchanger which has an overall coefficient of heat transfer of 37 W/m2·K and the static pressure loss of 781 Pa in the optimized case. Analysis results show that it is feasible to install LPEs in the exhaust flue gas system between the pressurizing fan and the FGD, which has little negative impacts on the unit. The benefits generated include saving of standard coal equivalent (SCE) at 2–4 g/(kW·h) and saving of water at 25–35 t/h under full load operation with corresponding reduction of CO2 emission.