Influence of Sewage Sludge Addition on Coal Ash Fusion Temperatures

• Published in: Energy & fuels 2005-11, Vol.19 (6), p.2562-2570
• Main Authors: Folgueras, M. Belén, Díaz, R. María, Xiberta, Jorge, García, M. Purificación, Pis, J. Juan
• Format: Article
• Language: English
• Subjects: 01 COAL, LIGNITE, AND PEAT; Applied sciences; ASH CONTENT; ASHES; BENCH-SCALE EXPERIMENTS; BINARY MIXTURES; BITUMINOUS COAL; CALCIUM OXIDES; CHEMICAL COMPOSITION; COCOMBUSTION; Combustion of heterogeneous mixtures. Incineration; Combustion. Flame; Energy; Energy. Thermal use of fuels; EUTECTICS; Exact sciences and technology; MELTING POINTS; MINERALOGY; MIXING; MIXING RATIO; SEWAGE SLUDGE; TEMPERATURE MEASUREMENT; Theoretical studies. Data and constants. Metering
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef058005a

The ash fusion characteristics of three types of bituminous coal (A, B, and C), one type of sewage sludge (W), and the corresponding coal−sewage sludge blends (10 and 50 wt % of sludge) were studied. The ash fusibility temperatures of samples in oxidizing atmosphere were measured, and their chemical and mineralogical compositions were determined. The addition of sludge to coal in certain proportions produces blends whose ashes have lower fusibility temperatures than those of coal and sludge. This is related to the differences in chemical composition and modes of elemental combination in both types of materials. The main differences are associated to the elements P, Fe, and Ca. As the sludge is much richer in Ca than the coals, the compositions of the blend ashes pass through low-temperature eutectic regions of the ternary phase diagrams SiO2−CaO−Al2O3 and SiO2−CaO−Fe2O3. As a result, for the sludge−coal blend ashes series (one for each coal), the relationships between ash fusibility temperatures and the percentage of sludge ash in blend ashes fit to second-order polynomial functions. The minima of these functions, as well as some sludge−coal blend ashes, are located in the above-mentioned low fusion regions. Differing from coal ashes, in the sludge and 50 wt % blend ashes, the minerals calcium ferrite, larnite, and chloroapatite were found.