Monitoring and modelling of gas-side boiler fouling

Co-firing high shares of biomass with coal in pulverized fuel-fired furnaces may give rise to increased deposition of ash in the convective area (fouling). This paper describes first results of work aiming to develop a mathematical model as well as a system for the on-line monitoring of ash deposition in full-scale plants. Ash deposition experiments have been performed using a new type of deposition probe featuring on-line heat flux measurement. Ash deposits from straw, coal and a 20/80 %/ % mixture are compared. An initial increase of the derived fouling factor is attributed to the radiative properties of the first ash depositing on the probe. The subsequent decrease of the heat transfer is caused by the insulating effect of the growing ash deposit. A mathematical model is formulated to describe the processes of ash deposition in relation to local gas flow patterns; the model is a post-processor which uses the results of CFD calculations for input