Effect of Feedstock Moisture Content on Biomass Boiler Operation

Burning feedstock with high and constantly varying moisture contents is a challenge in the operation of the stoker-grate type biomass boiler in pulp and paper mills. A fundamental two part study was performed to systematically investigate the effect of moisture content on the combustion behaviour of woody biomass. The first part involved a thermogravimetric combustor controlled at different temperatures, and the second part involved collecting and analyzing operating data of 3 biomass boilers. The laboratory results show that combustion occurs through three stages: time-to-ignition, volatile burning, and char burning and samples containing 40% moisture ignite and burn readily at 800°C, but they take longer to ignite at lower temperatures and do not ignite at 400°C. For the field studies, the moisture content of the feedstock was back calculated by a material and energy balance. The relationship between moisture content and the other operating data was studied. The results suggest that changes in moisture content mainly affect the lower furnace temperature and excess O2.M.A.S