Reduction of superheater corrosion by co-firing risky biomass with sewage sludge

• Published in: Fuel (Guildford) Vol. 89; no. 9; pp. 2376 - 2386
• Main Authors: Aho, M., Yrjas, P., Taipale, R., Hupa, M., Silvennoinen, J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 2010; Elsevier
• Subjects: Applied sciences; Biomass; Co-combustion; Corrosion; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuels; Natural energy; Sewage sludge; Corrosion; Co-combustion; Sewage sludge; Phosphates; Superheater; Hydroxides; Bark; Aluminium; Combustion; Iron; Biomass; Furnace; Bubbling; Fly ash; Aluminium silicate; Chlorides; Sulfur
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2010.01.023

Iron and aluminium sulphates are added to processes producing sewage sludge (SWS), and SWS also contains aluminium silicates. These compounds can destroy alkali chlorides and prevent Cl deposition on superheaters. Sulphation of chlorides requires formation of SO 3 in the furnace. Raw and digested SWSs were mixed with a fuel containing bark and recycled fuel (REF). Combustion experiments were conducted with a pilot-scale bubbling bed reactor, and concentrations and deposition of critical elements (Cl, Na, K, S…) in the furnace were measured. Change of the iron and aluminium sulphates added to the SWS to phosphates and hydroxides evidently reduced the power of the sulphur to form SO 3. Nevertheless, addition of SWS to the biomass feedstock effectively decreased alkali chloride concentration and Cl deposition, and the alkali sulphates found in the fine fly ash confirmed the contribution of sulphation to alkali capture. The importance of aluminium silicate reaction in alkali capture was indicated.