Characteristics of novel synthetic fuels using coal and sewage sludge impregnated bioliquid applying for a coal combustion system

- The new synthetic fuel (HSF) using coal and sewage sludge impregnated bioliquid was investigated.
- HSF properties were similar to sub-bituminous and bituminous coal on the van Krevelen diagram.
- HSF showed single-stage combustion characteristics from the thermogravimetric analysis.
- HSF presented higher fuel reactivity in comparison with low reactivity coal.
- HSF had a higher hydrophobicity on the surface.

The application of biomass resources and sewage sludge is currently the most important issue in the field of coal combustion systems. The main drawback for operating a boiler system is its varied firing characteristics and low heating value. In this study, we have developed new synthetic fuels, namely hybrid sludge fuel (HSF), using coal and sewage sludge impregnated bioliquid (molasses) and evaluated their properties by comparison with conventional fuels. To prepare the HSF, it was treated in a carbonization system at 250 °C. Depending on the van Krevelen diagram, the fuel quality of HSF was superior to that of raw bioliquid and sewage sludge. In addition, its fuel characteristic was similar to sub-bituminous and bituminous coal. Thermogravimetric analysis (TGA) indicated only a single-stage combustion pattern for HSF during non-isothermal heating. To clarify the unburned carbon (UBC) content, an ultimate analysis was conducted. The amount of UBC of the HSF was much more than that of sewage sludge, but less than that of coal. To investigate the surface hydrophobicity of HSF, Fourier transform infrared spectroscopy (FT-IR) analysis and a moisture re-adsorption test were carried out. The HSF possessed high hydrophobicity and presented a low moisture re-adsorption rate compared to conventional fuels.