Effect of Flue Gas Recirculation on Multi-Cyclones Performance in Reducing Particulate Emission from Palm Oil Mill Boiler

The effect of recirculating the flue gas on the performance of a multi-cyclones unit as particulate collector in an actual plant scale was studied. The existing multi-cyclones unit was modified by connecting a recirculation duct between the inlet and outlet gas stream of the multi-cyclones attached with an external induced (ID) fan. The particulate samplings were done following the U.S. EPA method at boiler outlet (before multi-cyclones), stack (after multi-cyclones) and recirculation duct. Result shows that the amount of recirculated particulates increases with ID fan suction power. The collection efficiency increased slightly from 68% (0% or without recirculation) to 74% (at 11% recirculation) and dropped to 67% (at 17% recirculation). Moreover, the amount of the fine particulate size fraction emitted able to be reduced one fold at 11% recirculation flow rate. However, high amount of recirculated particulates results in re-entrainment of particulates into the outlet of the multi-cyclones, hence, results in increase of particulate emission in the stack.