The influence of insufficient recirculating pipe’s flow-passing capability on boilers with coal-powder sending system by exhaust gas upon economic operation of the coal pulverizing system has been calculated and analysed. The calculation shows

reasonable selection of recirculating pipe’s diameter of said boilers has comparatively large influence upon the operation of coal pulverizing system. Hence

the diameter of recirculating pipe should be calculated and designed strictly according to the flow velocity of medium recommended in related stipulations

to ensure economic operation of the coal pulverizing system under optimal air flow conditions.