Deposit Formation in a 150 MWe Utility PF-Boiler during Co-combustion of Coal and Straw

A conventional pc-fired boiler at the Danish energy company I/S Midtkraft has been converted to coal−straw co-combustion, and a 2 year demonstration program was initiated in January 1996, addressing several aspects of coal−straw co-combustion. Deposition trials were performed as part of the demonstration program. A maximum straw share of approximately 20% (energy base) was used in the experiments. For the deposit samples collected, a visual analysis procedure was developed and each sample evaluated according to this. In addition, a number of samples were analyzed by scanning electron microscopy (SEM) combined with energy dispersive X-ray analyses (SEM-EDX) and bulk chemical analyses. In the visual analysis, a significant increase in the amount and tenacity of the upstream deposits was observed as a function of increased straw share, exposure time, and boiler load. The chemical analyses of the deposits show increased amounts of K and S during co-combustion, and the Fe-dominated upstream deposits formed dur...