Co-firing biomass and coal experimental investigations of deposit formation

The work aimed to find upper limits for successful application of biomass cofired with coal focused on deposits on superheaters. The experimental investigations reported here were conducted using the Multifuel Combustor at Sandia National Laboratories. Mixtures of biofuel and coal were chosen to establish limits for co-firing primarily with regard to chlorine contents of the fuels. Deposit growth rates and deposit chemical composition were measured, The tests are compared to short-term and long-term full scale results from cofiring tests at Vestkraft Power Plant and Studstrup Power Plant in Denmark to determine the degree of similarity between rig scale and full-scale tests. The results demonstrate that deposit growth is hest determined by the available alkali in the fuels. Ln the transfer of species from ash to deposits relative enhancement of sulphur is seen as well as relative depletion of chlorine in the deposits. This indicates that sulfation of the alkali chloride formed during combustion occurs. Limits for fuel combinations for cofiring resulting in chlorine-free deposits are suggested. For the mixed-fuel combinations tried at rig-scale and full-scale the observations are identical.