Article pubs.acs.org/EF
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 Yishu Xu,† Xiaowei Liu,*,† Yu Zhang,† Wei Sun,† Zijian Zhou,† Minghou Xu,*,† Siwei Pan,‡ and Xiangpeng Gao§ †
State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan 430074, China ‡ Electric Power Research Institute of Guangdong Power Grid Corporation, Guangzhou 510080, China § Discipline of Electrical Engineering, Energy and Physics, School of Engineering and Information Technology, Murdoch University, 90 South Street, Murdoch, WA 6150, Australia ABSTRACT: This contribution reports direct comparison of the particulate matter (PM) removal efficiencies of electrostatic precipitators (ESPs) and fabric filters (FFs) installed in two 300 MW coal-fired power station units that are equipped with identical boilers and DeNOx units. Field PM measurements were carried out at the horizontal ducts at the inlets of the DeNOx units, as well as the inlets and outlets of the two dust collectors when the two boilers burned the same coal under identical combustion conditions. The PM and total fly ash were collected via a low-pressure impactor (LPI) and/or a smoke analyzer. The collected samples were then subjected to analysis for chemical composition and morphology using an X-ray fluorescence (XRF) probe and a field emission scanning microscope with an energy-dispersive X-ray analyzer (FESEM-EDX). The results show that both the ESPs and the FFs can effectively capture PM, with a PM2.5 collection efficiency of 99.63% and 99.95%, respectively. For the PM with similar properties, the collection efficiencies in the FFs are only marginally higher than those in the ESPs. The most notable discrepancies between the fractional PM removal efficiencies of ESPs and FFs are observed for PM in the size range 0.3− 2 μm. The PM removal performance of both the ESPs and the FFs is related to particle size. At 0.3−2 μm, the performance of the ESPs is more sensitive to particle size than the FFs. The PM collection efficiency of the FFs is inversely related to particle size, and the capture of PM around 0.4 μm is slightly weak, most likely due to the transition of capture mechanisms from impaction to Brownian diffusion. are more difficult to be captured.14,24 Ash particles of high specific resistivity, which depend strongly on their chemical composition, would lead to back corona, while PM of low specific resistivity would cause the re-entrainment of the collected particles on the collection plate.9,17,23,25,26 In our previous field study, decreasing flue gas temperature by ∼40 °C led to the PM2.5 collection efficiency of the ESPs increasing from 99.24%−99.48% to 99.79%−99.86% as the resistivity of the ash particles decreased.27,28 The particle size distribution of the PM may be changed by various devices (e.g., low-pressure economizer, acoustic agglomeration devices, and aerodynamic agglomeration devices) ahead of the ESPs, which would also affect their performance.28−30 Moreover, the mass concentration of the PM would also significantly affect their removal in the ESP.9,20,25,31 Therefore, at least the size distribution, concentration, and chemical composition of ash particles should be considered when analyzing and evaluating the particle removal characteristics of ESPs. Besides ESPs, FFs (also called baghouses) are another widely used dust collection technology, especially in the power stations burning low-sulfur coal.8,32,33 In FFs, PM is separated through
1. INTRODUCTION China has been suffering from severe atmospheric pollution caused by particulate matter (PM) and, in particular, fine PM with aerodynamic diameters 10 μm was first separated in the cyclone before the DLPI, and that smaller than 10 μm (i.e., PM10) was size classified into 13 stages via the DLPI and collected on the collection filters (either aluminum foils or polycarbonate membranes). Hightemperature Apiezon (Apiezon-H) grease was coated on the aluminum foils to avoid particle bounce. The mass of PM was obtained by weighing the filters before and after an experiment using a microbalance (SARTORIUS MSA6.6S-0CE-DM). To collect an adequate amount of PM samples for analysis, different sampling durations were set when sampling at different sites. Samplings at sites 1# and 2# before the dust collectors lasted 1 min, and samplings at site 3 after the dust collectors lasted 2.5 h. To ensure the reproducibility of the data, three parallel runs were conducted under each condition, with the average values being reported. The power plant units were operated at constant load (90% of the full load) during the PM collection period. Total fly ash samples at the inlet of dust collectors were also collected with a Laoying 3012H smoke/gas analyzer. During the sampling of total fly ash, flue gas was extracted into the sampling probe isokinetically and the fly ash entrained in it was collected in an embedded glass-fiber cartridge filter. Both the total fly ash collected in the filter and PM samples collected on the polycarbonate membranes were dried at 45 °C prior to analysis. The collected PM and total fly ash samples were tested with an Xray fluorescence (XRF, EAGLE III, EDAX Inc.) probe to obtain their chemical composition. The morphology and composition of the PM collected at the outlet of the ESPs and the FFs were further characterized using a field emission scanning electron microscope coupled with an energy dispersive X-ray analyzer (FESEM-EDX, Sirion 200, FEI Inc.). A thin layer of Pt was coated onto the PM samples to improve their conductivity.
Table 3. Concentrations of PM0.3, PM1 and PM2.5 at the Inlet of the SCR, as Well as the Inlet and Outlet of the Dust Collectors and Their Removal Efficiencies Boiler E1
Boiler E2
PM
PM0.3
PM1
PM2.5
PM0.3
PM1
PM2.5
SCR inlet, mg/Nm3 Collector inlet, mg/Nm3 Collector outlet, mg/Nm3 Removal efficiency of collector, %
18.43
57.07
387.10
20.43
65.69
451.03
18.60
68.41
265.46
16.12
62.63
303.29
0.04
0.20
0.99
0.03
0.08
0.15
99.77
99.71
99.63
99.83
99.88
99.95
of
