Sulphur retention during co-combustion of coal and sewage sludge

• Published in: Fuel (Guildford) 2004-07, Vol.83 (10), p.1315-1322
• Main Authors: Belen Folgueras, M, Maria Diaz, R, Xiberta, J
• Format: Article
• Language: English
• ISSN: 0016-2361
• DOI: 10.1016/j.fuel.2004.01.0l5

The aim of this work is the study of the S retention in ashes from combustion of three bituminous coals and a sewage sludge, processed with lime from an urban wastewater treatment plant, that uses FeCl(3) as a coagulant. The effect of the sludge addition during co-combustion of sludge-coal blends in the proportions 10 and 50 wt% of sludge is analysed. The combustion was carried out in an electric furnace at different temperatures (800, 900, and 1100DGC). The results have confirmed that sludge addition to coal enhances S retention at any temperature due to the high CaO contents of the sludge and the formation of CaSO(4). However, the addition of FeCl(3) may be prejudicial, since it produces Na and K volatilisation during co-combustion. Moreover, the presence of Fe(2)O(3) from FeCl(3) can reduce the amount of retained sulphur due to its reaction with CaO to produce calcium ferrite. Another element with a similar effect to Fe is Si, since it forms larnite (2CaO-SiO(2)) in coal-sludge blends with high Si and Ca contents. Lineal relationships have been found between S retention and the above oxide contents.