In view of troublesome problems influencing upon the safety of lowgrade bituminous coal firing boilers with hot air for sending pulverized coal and centralized allocatioin of the primary air

such as firecarrying in the primary air jet orifice

and slagging on the waterwall in zone of burners etc.

occured after enhancement of volatile and heat value in the coal

a scheme for solving the said problems by admixing exhaust gas has been put forward. The results of design calculation combined with typical boilers

as well as test and study on the admixer of exhaust gas and hot air show that the exhaust gas can be admixed with hot air in a large proportional range

making the implementation of the said scheme to be possible.