Fouling tendency of ash resulting from burning mixtures of biofuels

Specified mixts. of peat with bark and peat with straw were burned in a lab-​scale entrained flow reactor that simulates conditions in the superheater region of a biomass-​fired boiler.  Deposits were collected on an air-​cooled probe that was inserted into the reactor at the outlet.  For both mixts., the deposition behavior followed a non-​linear pattern, which suggests that physico-​chem. interaction between the ashes of the different fuels has taken place.  The results indicate that it is possible to burn up to 30 wt-​% bark (renewable biofuel and pulp mill waste) and up to 70 wt-​% straw (renewable biofuel and agricultural waste) in mixts. with peat without encountering increased deposition rates in the reactor.  The deposit compn. was compared to the fuel ash compn. using chem. fractionation anal. and SEM​/EDX.  While the compn. of deposits obtained from pure fuels resembles the feed compn., a considerable change is obsd. in deposits obtained from mixts.  K and S compds. are attached to Si spheres and the substrate surface.  The deposition rate is significantly lowered when removing K, S, Cl and Na in bark prior to burning by washing and mech.​/thermal dewatering.