The Formation and Emission of Particulate Matter during the Combustion of Density Separated Coal Fractions

Abstract

The present study is a further effort to extend our knowledge of the included and excluded mineral characteristics responsible for the formation of particulate matter (PM). A Chinese bituminous coal was first separated into three density fractions using the float-sink method: heavy (>2.0 g/cm 3 ), medium (1.4-2.0 g/cm 3 ) and light (<1.4 g/cm 3 ). Then, combustion and pyrolysis of coal with different density fractions were carried out in a laboratory-scale drop tube furnace to understand the formation mechanism of inhalable particulate matter, less than 10 µm (PM 10 ) and less than 1 µm (PM 1 ). PM 10 was collected with a 13-stage low pressure impactor (LPI) having aerodynamic cutoff diameters ranging from 10.0 to 0.03 µm for a size-segregated collection. The experimental results indicated that the light fraction of the coal produced 44 wt % of total PM 10 and 45 wt % of total PM 1 . The medium fraction of the coal contributed 52 wt % of total PM 10 and 49 wt % of total PM 1 . The heavy fraction contributed 4 wt % of total PM 10 and 6 wt % of total PM 1 . The light fraction and the medium fraction of the coal contained mostly included mineral and the heavy fraction contained largely excluded minerals. The PM 10 and PM 1 contents formed by the excluded minerals were very low compared to those formed primarily from included minerals. The proportion of the minerals in the light density fraction converted into PM 1 and PM 10 was the highest, with their weight percentages being 9.59% and 43.49%, respectively. There were three reasons for this. One of reasons was the mineral particle size. The median mineral size in the light density fraction coal was smallest. However, the median size of each coal fraction was almost the same. Another reason was mineral transformation during combustion. The light fraction and the medium fraction of the coal contained mostly included minerals, and the heavy fraction contained largely excluded minerals. The transformations of included and excluded minerals were largely different and played a different role during coal combustion. The last reason was char fragmentation. Char formed by the light coal fraction was easier to fragment and subsequently formed more fine ash particles. This was because the swelling ratio, BET surface area, and total pore volume of char decreased with increasing parent coal density.

Field Measurements on the Emission and Removal of PM2.5 from Coal-Fired Power Stations: 3. Direct Comparison on the PM Removal Efficiency of Electrostatic Precipitators and Fabric Filters

“…Briefly, a stream of flue gas (flow rate: 10 L/min) was isokinetically extracted from the center of the duct section via a high-temperature (kept at 130 °C) sampling probe, and then introduced into a low-pressure impactor (LPI) sampling system for PM collection. The LPI sampling system consists of a Dekati cyclone (SAC-10), a Dekati low-pressure impactor (DLPI), a pressure gauge (KELLER LEO 2), and a vacuum pump (SV-25B). ,, The whole sampling system was heated to 130 °C to prevent acidic gases condensation. During PM sampling, PM of aerodynamic diameters >10 μm was first separated in the cyclone before the DLPI, and that smaller than 10 μm (i.e., PM 10 ) was size classified into 13 stages via the DLPI and collected on the collection filters (either aluminum foils or polycarbonate membranes).…”

“…The LPI sampling system consists of a Dekati cyclone (SAC-10), a Dekati low-pressure impactor (DLPI), a pressure gauge (KELLER LEO 2), and a vacuum pump (SV-25B). 27,40,41 The whole sampling system was heated to 130 °C to prevent acidic gases condensation. During PM sampling, PM of aerodynamic diameters >10 μm was first separated in the cyclone before the DLPI, and that smaller than 10 μm (i.e., PM 10 ) was size classified into 13 stages via the DLPI and collected on the collection filters (either aluminum foils or polycarbonate membranes).…”

Field Measurements on the Emission and Removal of PM2.5 from Coal-Fired Power Stations: 2. Studies on Two 135 MW Circulating Fluidized Bed Boilers Respectively Equipped with an Electrostatic Precipitator and a Hybrid Electrostatic Filter Precipitator

“…Both of the two LPI sampling systems were made up of a Dekati cyclone (cyclone-10), a Dekati low-pressure impactor (LPI), a pressure gauge (LEO-2), and a vacuum pump. 15,16 In the LPI sampling systems, PM with aerodynamic diameter larger than 10 μm (PM >10 ) was separated in the cyclone upstream of the LPI. And PM 10 (PM less than 10 μm) was fractionated into 13 stages according to particle size and collected on the aluminum foils in the LPI.…”

“…Two different LPI sampling systems were employed to obtain the detailed mass size distribution and concentration of PM, including a dilution system (termed as “LPI-D”) for PM before the dust collectors and a heating system (termed as “LPI-H”) for PM after them. Both of the two LPI sampling systems were made up of a Dekati cyclone (cyclone-10), a Dekati low-pressure impactor (LPI), a pressure gauge (LEO-2), and a vacuum pump. , In the LPI sampling systems, PM with aerodynamic diameter larger than 10 μm (PM >10 ) was separated in the cyclone upstream of the LPI. And PM 10 (PM less than 10 μm) was fractionated into 13 stages according to particle size and collected on the aluminum foils in the LPI.…”

“…Total fly ash samples before the dust collectors were also collected through a smoke analyzer (Laoying 3012H smoke/gas analyzer). 16 During the fly ash sampling, flue gas was first isokinetically extracted into the sampling probe at the center of the duct section and then the fly ash was collected with a glass fiber cartridge filter embedded in the probe. Both the fractionated PM and the total fly ash samples were dried at 45 °C and saved for further analysis.…”