Document Type : Research Paper
Energy 2050 Group, Department of Mechanical Engineering, Faculty of Engineering, University of Sheffield, Sheffield, S10 2TN, UK.
Oil & Gas Refinery Engineering Department, Al-Farabi University College, Baghdad, Iraq.
Biomass is a clean alternative fuel to coal in terms of carbon, NOx, and SO2 emissions in the power generation sector. However, ash deposition problems have been a concern with biomass fuels due to the high alkali and residual sulphur contents in the ash forming particles. In this study, the influence of oxy-fuel firing conditions of wood pellets combustion on ash partitioning and deposit formation, were investigated experimentally on a 250-kW pilot scale pulverized furnace and theoretically through chemical equilibrium modelling using the FactSage program. Oxy-fuel combustion case was compared with air-fuel case in this assessment. The results of this study showed that wood pellets had a low tendency for radiation zone slagging, but, had a high fouling tendency in the convective passes. It is possible that oxy-fuel combustion inhibited the release of volatile elements to the gas phase in the initial stages of the combustion, thus reducing the alkali sulphates slagging, increasing however, the alkali sulphate fouling tendencies on the convective passes. Moreover, the effect of the oxy-fuel environment on the ash formation was significant. The chemical equilibrium modelling showed reasonable predictions of the ash behaviour of wood pellets in terms of alkali behaviour and explained to some extent the influence of the oxy environment on ash deposit formation.
- Deposition tendencies of wood pellets are predicted by the ash stream compositions.
- Wood pellets have a low tendency for slagging and high tendency for fouling.
- Oxy-fuel combustion reduces slagging yet increases fouling tendencies of alkali sulphates.
- Oxy-fuel combustion can reduce the propensity of high-temperature corrosion problems.
- Ash behaviour of wood pellets is significantly changed when replacing air-fuel with oxy-fuel conditions.