SPECTRAL EMITTANCE OF IMPORTANT COAL ASH MINERALS AND SELECTED MIXTURES THEREOF: PYRITE, IRON OXID, CARBONATES AND SULFATES

摘要

The current paper presents measurements of the normal spectral and total emittances of mixtures of CaCO_3, CaSCO_4, K_2SO_4, Fe_2O_3 and pure FeS_2 powders. Two size fractions of 0 to 32 μm and 125 to 160 μm were examined. All these minerals are typical constituents of coal ashes, and the goal of the study is to examine whether the emittance of the mixtures can be traced back to the spectral characteristics of the pure minerals. Measurements were made from 500 up to 1000 °C. The spectra were recorded from 1.6 μm to 12 μm, the major wavelength range for radiative heat transfer in boilers. The results show that the larger the particle size, the higher the emittance independent from the mineral considered. In carbonate/sulfate mixtures strong absorption bands are visible in the spectra. Fe_2O_3 shows no absorption bands and seems to dominate the spectra when mixed with carbonates or sulfates.