PURPOSE: To increase a dust removing capability and enable to prevent a clogging in air preheater with acid ammonium sulfate by a method wherein a supporting beam is arranged between a hot temperature area thermal conduction element and an intermediate temperature area thermal conduction element and a pressure of the injected medium into the adhering area is increased.

CONSTITUTION: A supporting beam 12 is arranged between a high temperature area thermal conduction element 14 of a regenerative rotary type air preheater 10 and an intermediate temperature area thermal conduction element 15, thereby a pressure of the injected medium can be increased more than that of the prior art when the beam is reached to the adhering area of the medium injected form the soot blower 13, resulting in that a dust removing capability is increased. That is, a distance between the soot blower 13 at the low temperature area thermal conduction element 16 and the acid ammonium sulfate adhering area is made short and an attenuation of injecting pressure is low, so that a ratio M1/M0 between an injecting original pressure M0 of the soot blower 13 and a pressure M1 of the medium injected from the soot blower 13 is increased and a adhered material removing capability is increased. Therefore, a possibility of clogging caused by acid ammonium sulfate adhered material in the air preheater is reduced.