Coal to biomass (wood pellets) mill conversion

To convert a pulverised fuel (suspended) boiler into one that burns biomass, one modification required, is on the coal mills/pulverisers. Existing attempts, such as using an existing coal classifier with blocked off areas for increased throughput, seems to not be the solution. With biomass, the flakes (broken pellets) will react differently to the air due to a flake having a very low density, therefore conventional classifiers will over classify the flakes causing a reduced throughput to the boiler.