A multistage boiler heat exchange apparatus has a combustion furnace and at least one boiler set. The combustion furnace is used to produce a heat source and has a furnace base and a hot-air passage. The at least one boiler set is connected to the combustion furnace, and each has a preheater and a boiler. The preheater is deposited adjacent to the combustion furnace, and is connected to and communicates with the hot-air passage to adjust temperature of the heat source that enters the preheater. The boiler is an uprightly-deposited cylinder, is connected to the preheater, and has a conducting pipe and an exchange tube. The conducting pipe is deposited on and communicates with the boiler to enable the heat source to enter the boiler. The exchange tube is deposited in the boiler and has an exchange medium to exchange heat with the heat source in the boiler.

A thermal power plant has an exhaust gas system, a feed-water system, a high-pressure feed-water heater provided to the feed-water system, a main economizer, a catalytic NOx removal equipment, and a sub economizer. The main economizer is provided to the secondary side of the high-pressure feed-water heater of the feed-water system and increases the temperature of the feed-water by using the residual heat of the combustion gas from the boiler. The catalytic NOx removal equipment is provided to the secondary side of the main economizer of the exhaust gas system. The exhaust gas is supplied to the catalytic NOx removal equipment at a required temperature or higher. The sub economizer is provided between the high-pressure feed-water heater and the main economizer and increases the temperature of water by using the exhaust gas on the secondary side of the NOx removal equipment.

A thermal power plant has an exhaust gas system, a feed-water system, a high-pressure feed-water heater provided to the feed-water system, a main economizer, a catalytic NOx removal equipment, and a sub economizer. The main economizer is provided to the secondary side of the high-pressure feed-water heater of the feed-water system and increases the temperature of the feed-water by using the residual heat of the combustion gas from the boiler. The catalytic NOx removal equipment is provided to the secondary side of the main economizer of the exhaust gas system. The exhaust gas is supplied to the catalytic NOx removal equipment at a required temperature or higher. The sub economizer is provided between the high-pressure feed-water heater and the main economizer and increases the temperature of water by using the exhaust gas on the secondary side of the NOx removal equipment.