Slagging characteristics in the superheater area and K/Ca distribution of biomass-fired grate boiler

The slagging on heating surfaces severely impedes the biomass combustion in grate boiler. Aiming at this situation, the slagging characteristics of a grate boiler firing straw/woody biomass has been investigated. By field sampling of deposition, the slagging mechanisms including gaseous K/Ca condensation, molten ash adhesion and viscous capture of ash particles have been clarified. The severity of slagging is ordered as: mid-temperature superheater > high-temperature superheater > low-temperature superheater > upper furnace. Ca plays a key role in initial layer formation in high-temperature superheater through condensation of gaseous sulfates. In mid-temperature superheater initial layer formed by gaseous KCl condensation and the viscous capture of ash particles lead to serious slagging. The distribution of K/Ca in the boiler during combustion were obtained based on ash collecting and characterization, counter-balance efficiency calculation and fuel consumption calculation. 44.6% of K and 35.8% of Ca contained in the biomass fuel deposited on the heating surfaces inside the boiler, indicating that more K and Ca tend to deposit in the boiler rather than remain in the discharged ash, which also requires more attention to Ca-related slagging. This study can provide basis for slagging predicting and controlling in grate boiler using high K/Ca biomass fuel.