Investigation of the Influence of Metallic Fuel Improvers on Coal Combustion/Pyrolysis

The influence of iron-, aluminum-, and silicon-based oxides (fuel improver) toward coal combustion was investigated in a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrophotometer, temperature-controlled two-stage bench reactor (TSBR), and 100 kW(th) combustion test facility (CTF). The metallic oxides, 5, 15, and 33% by weight, to prepare overall 20 mg of sample blends were mixed with pulverized coal for the TGA FTIR study. The individual unblended samples of fuel improver and coal were also analyzed separately. The analysis of fuel improver samples revealed no evidence of hydrocarbon release or weight change; however, substantial changes in the weight as well as the release of hydrocarbons (HCs) and CO were observed for coal. More importantly, the study of the combustion data shows a distinct change in the peak intensities for CO and HCs, especially when the coal sample was blended with 5, 15, and 33% (by weight) of fuel improvers. This suggests enhanced cracking of the coal matrix in the presence of fuel improvers. This impact of the presence of the fuel improver was also confirmed to increase the gas/oil yield in the temperature-controlled two-stage fixed-bed reactor. In this study, a schematic mechanism for the interaction of the fuel improver with sub-bituminous coal and NOx reduction chemistry along with volatile carbon production pathways has also been presented. The increase in the combustion zone temperature, improvement in NOx reduction, and loss on ignition of fly ash samples collected from a 100 kW(th) CTF proved the enhanced combustion characteristics of coal with a studied metallic fuel additive. Hence, these fuel improvers can be used in the heat power engineering related to solid hydrocarbon fuels.