Deposition investigation in straw fired boilers

In Denmark straw has been applied as fuel at small combined power and district heating plants since the late 1980`s. New equipment have been developed to handle and burn the straw. However, straw is by no means a trivial fuel, problems like fluctuations, deposition in the furnace, corrosion and a poor burn out have been observed at boiler plants. One of the problems has been, the large differences in the amount of deposition in the furnace chamber and on superheater tubes when applying different fuel parcels. Knowledge of how to characterize the straw for predicting the deposition properties in the boiler is needed. We will here present deposition experiments performed at two straw fired power plants with a fuel input of respectively 18 and 30 MW. Some limited experiments have earlier been performed on smaller scale boilers, no clear correlation between laboratory analyses of the straw and deposition in the boilers was found. Combustion experiments on a combined wood and straw fired 18 MW stoker fired boiler have been performed. Strong indications, of condensation of the mineral matter at different places in the boiler chamber, were seen.