At present

the commonly used flue gas waste heat utilization system in domestic coal-fired power plants mainly includes four typical kinds: the flue gas colder system

the water medium gas-gas cooler(MGGH) system

the cold air heater + flue gas cooler system

and the cold air heater + air preheater bypass system. The influence of the cold air heater + air preheater bypass system and the cold air heater + flue gas cooler system on the heat entering into the boiler and the thermal efficiency of the boiler is analyzed in this paper. Moreover

the influence degree is calculated

from both the flue gas side and the air side. On this basis

comprehensive energy conservation effects of the above two systems are calculated and compared. The result shows that

the cold air heater + air preheater bypass system is not the system with the best energy saving effect. Under various conditions

its energy conservation efficiency is lower than that of the coal air heater + flue gas cooler system. Under rated load design condition

the energy conservation efficiency of the cold air heater + air preheater bypass system is 0.797 g/(kW·h) lower than that of the coal air heater + flue gas cooler system. This is because the cold air heater + air preheater bypass system applies the heat with the highest grade(which can be used in the boiler) to the flue gas waste heat utilization system

which violates the principle of energy cascade utilization.