Investigation of the Diffuse Interfacial Layer of Superfine Pulverized Coal and Char Particles

Superfine pulverized coal combustion is a new pulverized coal combustion technology that has better combustion stability, higher combustion efficiency, and lower NOx and SO2 emissions. In this paper, small-angle X-ray scattering (SAXS) measurements were utilized to calculate the diffuse interfacial thickness of superfine pulverized coal and char particles. Porod’s law was applied to quantitatively analyze the SAXS curves with gray relational analysis (GRA) used for further investigation of the influencing factors on the thickness of the diffuse interfacial layer. Negative deviations from Porod’s law of SAXS curves were found for all the coal samples, indicating the existence of diffuse interfacial layers in the grains. When considered in conjunction with coal pyrolysis experiments and Fourier transform infrared spectroscopy investigations, it is proposed that the interfacial layer is caused by the organic groups linked to the matrix of the coals. As the variation of interfacial thickness is so small, analysis of variance and multiple comparisons were applied to confirm the statistical significance. The effect of inorganic elements on the diffuse interfacial layer of coal particles was also studied using the demineralized samples. Final results indicate that the interfacial thickness of the superfine pulverized coal particles ranges from 0.23 to 0.66 nm and decreases with increasing coal quality and particle size. For the char particles, the interfacial thickness decreases with increasing pyrolysis temperature. Demineralized coal particles in the similar experiments show the same trends as the raw coals; however, the acid washing process increases the diffuse interfacial thickness. The findings from this work will help form the basis of, and provide guidance for, further studies on the chemical and combustion characteristics of superfine pulverized coal particles.