Ash deposition impacts nearly every solid-fuel-fired boiler in major ways. In the case of biomass-coal cofiring, ash deposition problems may be significantly aggravated or somewhat moderated by the biomass component of the fuel. The magnitude of the impact can be very large. The following series of photographs illustrates how ash deposit formation varies with fuel type. Deposits from 100% Pittsburgh No. 8 coal (upper left) and 100% wood chips (upper right) are both quite manageable. By contrast, deposits those from 100% low-chlorine straw (lower left) and a blend of the Pittsburgh No. 8 coal and a high-chlorine wheat straw (lower right) are much less manageable than from either wood or coal. All data are collected in the MFC at surface temperatures of 460°C and 540°C (high temperature probe is on top). All but the cofired blend represent deposit accumulation for one hour. The blend was fired for four hours at the time of this photo.