Rotary air preheater is a crucial heat exchanger in boiler system and its main function is to provide a place for heat transfer between hot flue gas and cold primary/secondary air

thus to realize efficient utilization of waste heat in flue gas. Due to relatively low temperature adjacent to the exit of air preheater

serious ash deposition and corrosion usually happens here

which is related to formation of ammonium bisulfate(ABS). Ammonia escapes from the upstream selective catalytic reduction(SCR) device

the excessive ammonia reacts with sulfur oxides and water at outlet of cold end of the air preheater

which is easy to generate ABS. To solve this problem

there are four solutions: installing air heaters(Scheme 1)

using hot air recirculation technology(Scheme 2)

using air-circulating blocking prevention technology(Scheme 3)

and using flue gas downstream cutting blocking prevention technology(Scheme 4). This study summarizes the four solutions

and compares them with the finite difference calculation method to provide guidance for the fouling prevention retrofit. The results show that

with the increase of the target temperature in Scheme 1

the alert ratio decreases and the cold end wall temperature increases

but the exhaust gas temperature increases. In Scheme 2

the wall temperature increases

but the alert ratio increases much

which is not conducive to the fouling control. Both Scheme 3 and Scheme 4 can effectively improve the fouling and reduce the exhaust gas temperature

but the retrofit parameters cast a great influence on the effect. The latter two options cost more investment but should be preferred when conditions permit. Meanwhile

the Scheme 4 is more effective in controlling air leakage.