Effects of coal blending on the reduction of PM10 during high-temperature combustion 1. Mineral transformations

Two coals with comparable mineral particle distributions, but different contents of Ca were blended and combusted. Mineral transformations and their effects on particulate matter smaller than 10 μm (PM10) emissions were investigated during the combustion of single and blended coals. Combustion experiments were carried out at 1450 °C in air atmosphere using a lab-scale drop tube furnace (DTF). The particle size distributions (PSD), morphologies, elemental compositions, and chemical composition of minerals in coal and PM were analyzed. The results indicate that emissions of PM smaller than 1 μm (PM1) and particulate matter sized between 1 and 10 μm (PM1–10) are reduced compared to their calculated linear results during combustion. The transformation of P, S, Al, and Si from submicron particles to PM larger than 1 μm (PM1+) reduces PM1 emissions. The transformation of Ca, Fe, Al, and Si from PM10 to particles larger than 10 μm (PM10+) reduce PM1–10 emissions. The high concentration of Ca in coal blends enhances the liquid phase percentage produced during combustion, and as a result, improves both the adhesion of volatilized P, S, Al, and Si on the sticky surface of large particles to be transformed to PM1+, and the probability of collision and coalescence of particles to form larger particles of Ca–Fe–Al–Si, Ca–Al–Si, or Fe–Al–Si. Thus, as Ca, Fe, Al, and Si are transformed into PM10+. PM1 and PM1–10 emissions are reduced accordingly.