| The emission of inhalable particulates, especially the fine particulates from coal-fired power plants, which rich in toxic trace elements, not only causes fouling and corrosion, thus affects the safe operation and heat exchange efficiency of boiler, but also causes serious harm to human health and the environment. This study displayed the properties and control technology of fine particulates during coal combustion.In order to study the emission and properties of the particulate matter from coal-fired plant, PM samplings were conducted in two 300 MW coal-fired boilers which equipped with WFGD, firstly. Then, through the coal combustion experiments on drop tube furnace, the formation and properties of particulate matter generated under O2/N2 and O2/CO2 conditions, as well as the effects of mineral element distribution on the formation and properties of particulate matter generated were studied. Since the interactions between different mineral elements may affect the fine particulates generation, kaolin addition and coal blending were employed to reduce the fine particulates generation during coal combustion, finally. The main contents are as follows:Particulate sampling was conducted in two coal-fired boilers equipped with WFGD. The results showed that, the particulate matter generated from these two boilers was trimodally distributed. Fine mode particles mainly contained the elements Na and Mg, while centrol mode and coarse mode particles mainly consisted of the elements Si and Al. The larger the boiler load, the more PM10 generated. After the particulates carried by the flue gas entered into WFGD device, the fine particle emissions increased due to the transformation from external elemental Ca and S into fine particles, while the emission of coarse particulates decreased as the result of physical washing by limestone slurry.Combustion experiments of four pulverized coal samples under O2/N2 and O2/CO2 conditions with different O2 concentrations were conducted. LPI and SMPS-APS were employed to collect the particulates generated, respectively. The results showed that, O2/CO2 combustion may lead a smaller geometric mean size of PM1 generated. Compared to the O2/N2 conditions, the productions of PM1-10 and PM1 decreased under the O2/CO2 conditions. With the O2 concentration increased under the O2/CO2 conditions, the production of PM1-10 increased, however, the PM1 production showed a trend of decreased first and then increased. This is because that, with the O2 concentration increased under the O2/CO2 conditions, the mineral vaporization has been affected both by particle combustion temperature and reducing atmosphere, thus showed a trend of decreased first and then increased. The results from the particulates collected by SMPS-APS showed that, the fine particulates numbers accounted for the majority of total particulates numbers. There is a number concentration peak in the PM size range 0.05-0.1μm and an infection around 1μm.Potassium-rich coal, sodium-rich coal, pretreated coal with different densities and particle sizes, as well as raw pyrite were combusted under different conditions. The particulates collected were analyzed. It is found that, when potassium-rich coal and sodium-rich coal were combusted at 900℃or 1100℃, Na2SO4/K2SO4 was the main potassium compound vaporized and condensed to form the PM1, with an average size of 0.5μm. When the combustion temperature increased to 1300℃, the PM1 production was reduced, due to the form of vaporized Na/K being changed to gaseous NaOH/KOH, most of which may react with aluminosilicates to form coarse particulates (PM10+), the remaining vaporized Na2SO4/K2SO4, and other sulfates/oxides condensed to form the PM1, with an average size of 0.2-0.3μm.Coal density and particle size showed significant impacts on mineral distributions in coal and properties of particulate matter generated from coal combustion. The minerals in low density coal and medium density coal are mainly included, while the minerals in high density coal are mainly excluded. The higher the coal density, the fewer PM1 generated. Except the coal with high density and small particle size, the other pretreated coal with different densities and particle sizes contributed much more PM1 than the raw coal during combustion, which indicated that the interactions between different mineral elements would affect the fine particulates generation. Pyrite combustion had an important contribution to the PM1 generation.Kaolin powder was mixed into raw coal, sodium-rich coal and potassium-rich coal for combustion. The size distribution, concentration and elemental composition of the PM generated before and after kaolin addition were analyzed. It is found that, the peak of fine particulates mode moved to smaller size after kaolin addition. When the raw coal mixed with kaolin was combusted at 900℃,1100℃and 1300℃under O2/N2 conditions, respectively, the maximum capture efficiency of kaolin was obtained at 1100℃, as the result of combined effects of chemical adsorption increase and physical activity decrease with increasing combustion temperature. The interactions between the added kaolin powder and volatile element Ca, Fe in raw coal is thought to be the main reason of PM1 reduction. When the sodium-rich coal mixed with kaolin was combusted under O2/N2 conditions, the maximum PM1 reduction was obtained at 900℃in this study. When the potassium-rich mixed with kaolin was combusted under O2/N2 conditions, the maximum PM1 reduction was obtained at 1100℃. Volatile elements compositions in coal had a significant impact on PM1 reduction after kaolin addition under different combustion temperature.A lignite, a bituminous coal, and their coal blends with different blend ratios (9:1,7:3, 5:5,3:7,1:9), were combusted in a drop tube furnace under the O2/N2 and O2/CO2 conditions to study the effects of coal blending on the formation and properties of particulate matter. The results showed that, the mineral interactions between the lignite and bituminous coal suppressed the fine particulate generation. Blend ratios had significant impacts on the suppression degree of the PM1 generation. In this study, PM1 generation suffered a maximum suppression degree at the blend ratio of 7:3. O2/CO2 conditions affected the formation and properties of the PM1 generated. Compared to the O2/N2 combustion, the interactions of minerals weakened under O2/CO2 combustion, thus the suppression of PM1 generation declined after coal blending. The concentrations and compositions of the element Ca, Fe in PM1 decreased, but the concentrations of the element Ca, Fe in PM10+ increased after the combustion of coal blends. The interactions between the aluminosilicates in bituminous coal and volatile element Ca, Fe in lignite is thought to be the main way to suppress the PM1 generation.
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