Utilization of the waste heat of boiler flue gas has important significance for power plant.For single-stage low pressure economizer using in regenerative system of steam turbine

there are such problems as low temperature difference

large heat transfer area and low-temperature corrosion.So the two-stage low pressure economizer technology was proposed.Taking a 300 MW unit as an example

general computational model of the turbine side was established according to the energy conservation principle and matrix method.Economic calculation and comparison for four different design schemes was performed.Results showed that

the two-stage low pressure economizer system was superior to the single-stage technology in aspects of unit efficiency enhancement

coal consumption cut down and cost saving etc.For the two-stage system

it will enhance much more efficiency if using the low pressure economizer in the higher heater but not the lower one.For scheme 4

the coal consumption of the unit decreased by 6.4 g/(kW·h)

the efficiency increased from 46.29%(with no low pressure economizer) to 47.15%

each unit can save 1.215 82×107 yuan per year.The economic benefit was huge and the CO2 emission can be reduced by 9.83×107 yuan every year.