Flue gas waste heat utilization is of great significance to the improvement of comprehensive energy efficiency of coal-fired power plants. By taking a supercritical condensing unit firing coal with high and medium moisture fraction as an example

this study carried out thermodynamic calculation for two approaches recovering the waste heat of flue gas

namely using low temperature economizer to heat the return water and using flue gas cylinder drying device to heat the input coal. On this basis

the waste heat recovering mechanism of the above two approaches was analyzed

and the economic efficiency of them was discussed. The results show that

by utilizing waste heat of flue gas

the exhaust gas temperature reduces from 130 ℃ to 95 ℃

and the additional electric power output of these two flue gas waste heat utilization systems increases by 3.14 MW and 10.85 MW

respectively

and the net annual benefit increases by 4.643 4×106 yuan and 1.401 1×107 yuan

respectively. Using the flue gas to heat the input coal has higher economic efficiency.