For double-reheat power generation units applying flue gas recirculation technology

bypass highpressure economizer system and low-pressure economizer system

theoretical analysis on calculation method of economic indexes

such as boiler efficiency

turbine heat rate and coal consumption rate of electricity generation

was performed. In method 1

the heat to the high-pressure and low-pressure economizers is treated as the boiler's heat loss

then the calculated total heat loss of the boiler is 6.42%

and the boiler efficiency is 93.58%. In method 2

the heat to the high-pressure and low-pressure economizers is treated as the heat absorbed by the turbine

then the calculated total heat loss of the boiler is 2.46%

and the boiler efficiency is 97.54%

which is obviously higher than that of the method 1. The boiler efficiency and turbine heat rate calculated by the above two methods differs dramatically

but the difference between the theoretical coal consumption rate calculated by the above two methods is only 0.19 g/(kW·h)

which proved that the two methods are equivalent in calculating the energy consumption index of the unit. However

as the benefits of bypass high-pressure economizer system and low-pressure economizer system given to boiler or to turbine are both feasible for the economic indexes calculation

it can only be calculated once

otherwise

the economic indexes may be higher than the unit's real level.