In this study, pulverized coal bias ignition experiments were conducted in a 250 kW pilot-scale bias combustion simulator to investigate the effects of the combustion conditions on the particulate matter (PM) formation characteristics in a reducing atmosphere; the amount of PM10 was determined using an electrical low-pressure impactor. The particle size distributions of PM10 from pulverized coal bias ignition under various combustion conditions in a reducing atmosphere differ from those in the tail flue gas of a coal-fired boiler. Mainly PM0.38 is produced when the pulverized coal concentration (PCC) is 0.53, the lowest amounts of PM0.38 and PM0.38–10 are produced when the PCC is 0.4, and mainly PM0.38–10 is produced when the PCC is 0.33; the PCC significantly affects formation of PM0.5–0.794. As the bias concentration ratio (BCR) of the pulverized coal increases, the pulverized coal jets are prone to releasing viscous minerals, which easily coalesce into supercoarse particles of size greater than 10 μm; this decreases the formation of PM0.38 and PM0.38–10. The released viscous minerals are the main sources of PM0.38, and the BCR significantly affects PM0.205–0.5 formation. Volatiles and char burn most intensely at a primary air velocity (PAV) of 17 m/s, resulting in maximum production of PM0.38 and PM0.38–10. PM0.38 was mainly produced in the volatile combustion stage, and PM0.38–10 was mainly produced in the char combustion stage; the PAV significantly affects the formation of PM0.041–0.317. More PM10 with a larger fraction of ultrafine PM was produced at the optimum PAV, which was selected based on the ignition characteristics.

In this work, the PM 2.5 emission characteristics, the comparison of the morphological characteristics, and the sizeclassified elemental composition of PM 2.5 are determined experimentally before and after the fabric filter at an industrial circulating fluidized-bed boiler. Measurement in situ was taken with an electrical low-pressure impactor equipped with a two-stage dilution sampling system. The morphological characteristics and size-classified elemental composition were performed by scanning electron microscopy and energy-dispersive X-ray analysis. The size distribution was measured in the range from 0.029 to 2.38 μm. Before and after the fabric filter, the number size distribution displays a bimodal distribution. The fabric filter total removal efficiency of PM 2.5 without pulse back blowing cleaning is 99.449%, and that with pulse back blowing cleaning can reach 99.029%. The minimum size-classified removal efficiencies appear in the particle size range from 0.1 to 1 μm. In this size range, the fabric filter size-classified removal efficiencies are 99.15−99.59%, and the pulse back blowing cleaning can result in the lowest value of 98.46%. The morphological characteristics before and after the fabric filter are nearly the same, except channels 3−5. Sodium, potassium, and zinc show enrichment with decreasing particle size; calcium and titanium show clear enrichment with increasing particle size; however, silicon, aluminum, magnesium, iron, and manganese show no enrichment with particle size variation.

In this research, the emission characteristics, morphological characteristics and size-classified elemental compositions of PM 2.5 are determined experimentally before and after a fabric filter (FF) at an industrial pulverized coal boiler. Sampling and measurement of PM 2.5 in situ were taken with an ELPI with a two-stage dilution sampling system. The morphological characteristics were analyzed by scanning electron microscopy. The size-classified elemental compositions were analyzed by energy-dispersive X-ray analysis and inductively coupled plasma−atomic emission spectrometry. The number size distribution of PM 2.5 before the FF displays a unimodal distribution. The mass distribution of PM 2.5 before the FF displays a unimodal distribution with the peak near 0.1 μm, but the mass distribution of PM 2.5 after the FF shows no peak. The pulse back blowing of the FF exerts significant influence on PM 2.5 number and mass concentrations after the FF, especially on the number and mass concentrations of PM 0.007−0.029 . There appears a penetration window in nearly 0.1−1 μm; however, the removal efficiency of PM 0.007−0.029 is lowest. The pulse back blowing of the FF can reduce the removal efficiency of PM 0.007−0.029 from 99.37% to 97.80%. The microstructures of super-micrometer and sub-micrometer particles are different before and after the FF; however, the ultrafine particles in 0.007−0.029 μm are nearly the same before and after the FF. The fractional mass distributions of silicon, aluminum, iron, calcium, and magnesium vary little with variation of the particle size. Cadmium, arsenic, and selenium are enriched with the particle size decreasing.

No abstract

Ion-exchanged Na (INa) and adsorbed Na (ANa) concentrations have significant impact on the physicochemical properties of coal-derived aerosol, and product yields of soot and tar. INa effectively reduced tar release during primary pyrolysis, thus reducing soot yield. ANa had no clear effect on primary pyrolysis, but was easier to gasify. During the secondary pyrolysis, lowconcentrated gasified Na promoted aggregation of aromatics to form soot disordered core and increased soot yield. However, at sufficiently high concentration, Na mainly catalyzed tar cracking. Gasified Na can change size distribution of soot aggregates and promote the conversion of SO 2 to SO 4 2− . These two effects of Na were affected by Cl in pyrolysis gas. Na in soot can change the arrangement of graphite-like layers and increase sp 3 hybridized carbon bonding. INa can couple to carboxylate (COO − ) and promote formation of ether C−O structures in soot or tar.