Comprehensive energy-saving and efficiency improvement retrofits for in-service units are helpful to achieve the peak of carbon emission as soon as possible. In order to improve the energy efficiency level of subcritical 300 MW-level W-flame boiler unit burning high sulfur anthracite in service

the main influencing factors and technical route are analyzed

and the feasibility study is carried out on the main efficiency improvement technologies such as rasing steam parameters

improving combustion efficiency

reducing exhaust temperature

and coupling turbine with boiler. The overall transformation scheme is formed as: retrofit of heating surface with lifting parameters + addition of gas-air heater + air leakage treatment of rotary air preheater + capacity increase of coal mill + air distribution uniformity retrofit for air box + adaptability retrofit of combustion system + addition of lowtemperature economizer. The results show that

for the case unit with design parameters of 540 ℃/540 ℃

the overall efficiency improvement scheme of increasing the parameters to 574 ℃/572 ℃ can reduce the power supply coal consumption by more than 25 g/(kW·h).