In Rankin cycle, the heat accounting for more than 50% of the total heat of working medium is taken away by cooling water in the condenser, resulting in loss. Feedwater heating is an effective way to reduce this loss. This cycle with feedwater heating is called regenerative cycle. In order to maximize the effect of feed water regenerative, the feed water heating stages of modern high parameter and large capacity intermediate reheat units generally adopt 7 or 8 stages.
The feed water heater includes Low pressure heater And deaerator. Low pressure heater is located between condenser and deaerator, and high pressure heater is located behind feed pump heater 。 Feedwater heaters can be divided into surface type and mixed type according to steam water heat transfer mode. Low pressure heaters are mostly surface type High pressure heater All are surface type. The surface heater can be divided into two types according to the structural form: coiled incense tube type and U-shaped tube type. The U-tube type can be divided into vertical type and horizontal type according to the water inlet position and layout mode, and can also be divided into vertical type and side vertical type according to the water inlet position. In order to increase the outlet water temperature of the heater under the condition that the extraction pressure remains unchanged, the heater of the large capacity intermediate reheat unit is equipped with superheated steam cooling section and drain cooling section. 
