The effects of coal blending on the formation and properties of particulate matter during combustion

The control of particulate matter (PM) emissions from coal combustion becomes an urgent work due to their adverse effects on human health. Coal blending is a promising option for submicron particulate (PM1) reduction. This study addressed the effects of coal blending on the formation and properties of particulate matter in combustion process. Coal blends from lignite and bituminous coal, with different blend ratios (9:1, 7:3, 5:5, 3:7 and 1:9), were combusted in a drop tube furnace. The mass size distribution, concentration, elemental composition and morphology of the particulate matter generated under O-2/N-2 and O-2/CO2 conditions were characterized. Particulate matter was collected by a low pressure impactor (LPI), which aerodynamically segregated particulates into thirteen fractions with sizes ranging from 0.03 to 9.8 mu m. The results showed that coal blending reduced PM1 generation, compared with the calculated average values from the combustion of constituent coals. This indicated that the mineral interactions had a great effect on PM1 reduction. The blend ratio also played an important role in the suppression of PM1 generation. In this experimental study, PM1 generation suffered a maximum suppression at the blend ratio of 7:3. The O-2/CO2 atmosphere affected the formation and properties of the PM1 during coal blends combustion. Compared with the O-2/N-2 combustion, the interaction of minerals was weakened under O-2/CO2 combustion, thus the suppression of PM1 generation decreased after coal blending. Compared with the calculated values, the concentrations and percentages of Ca, Fe in PM1 decreased, but the concentrations of Ca, Fe, Si and Al in coarse particulates (PM10+) increased after coal blends combustion. The interactions between the aluminosilicates in the bituminous coal and volatile elements Ca, Fe in the lignite were thought to contribute to the suppression of PM1 generation during the combustion of coal blends.