In the combined system of low pressure economizer and air heater

when the ambient temperature is low and the unit is running at low load

it is prone to the problem that the heat exchanger tube is cracked and the heater system can't be put into operation. The cause of the cracking of the heat exchanger tube in the air heater was analyzed

and the improvement measures for antifreeze of the air heater were proposed from the aspects of structure and system

such as thickening the heat transfer pipe elbow of the air heat

increasing the design working medium speed in the heat transfer tube

adding quick drainage system and compressed air purge device

switching operation along the flow/counterflow direction

and so on. The combined system of low pressure economizer and air heater that had been put into operation could reduce the risk of frost cracking of the air heater through operation control. Taking the antifreeze retrofitting of secondary air heater in a 600 MW as the example

on the basis of analyzing the cause and improvement methods of the cracking of heat exchanger tube in the air heater

considering the difference in ambient temperature between different units and the antifreeze requirements

the design principles of antifreeze for the air heater were proposed

which can provide reference for transformation of combined system of low temperature economizer and air heater.