Heating energy-saving system and method for deeply utilizing waste heat of boiler plant

A heating energy-saving system for deeply utilizing waste heat of a boiler plant, wherein a plurality of forced draft fans are arranged at an upper part of the boiler plant, an operation level relay induced draft fan is installed on the operation level, and communicates with a bottom level of the boiler plant below the operation level, and an air preheater is installed in the bottom level of the boiler plant;

• the air preheater communicates with an air outlet of a boiler forced draft fan through a first air supply duct, and an air inlet of the boiler forced draft fan communicates with an air inlet device through a second air supply duct;
• the air inlet device penetrates through a sidewall of the boiler plant;
• and an outdoor air inlet control valve is installed at an opening of one end of the air inlet device located outside the boiler plant, and an indoor air inlet control valve is located at an opening of a sidewall of the air inlet device located in the boiler plant.