Test Method and Performance Evaluation of Two-stage Electrostatic air filter

Transcription

1 4 th International Conference On Building Energy, Environment Test Method and Performance Evaluation of Two-stage Electrostatic air filter P. Wang 1, S. Chen 2, Z. W. Zhang 1, S. Zhang 1, J. J. Pei 1 and J. J. Liu 1 1 School of Environmental Science and Engineering Tianjin University, Tianjin, China 2 Tianjin General Hospital, Tianjin, China SUMMARY At present, there is no special performance test standard for civilian electrostatic air filter. This study explored a new method based on the existing air filter standards and assessed the performance of eight electrostatic air filters. Laboratory tests were conducted to determine particle counting and sizing efficiency, PM 2.5 arrestance efficiency, pressure drop, ozone concentration and the change of efficiency in different states (initial, dust loading, after cleaning). The graded particle size counting method with atmospheric dust, fixed dust method and fixed water method are suitable for electrostatic air filter performance test. DEHS aerosol and A2 fine dust can be used as the test dust of electrostatic air filter. Small size particles are more suitable for evaluating the electrostatic air filter performance attenuation after dust holding capacity test. The epm 2.5 calculated by the graded particle size counting efficiency and the quality factor which is positively correlated with efficiency can be used to evaluate the performance of the electrostatic air filter. INTRODUCTION Particulate matter (PM) in indoor environments mainly comes from the outdoor atmosphere and cooking in the kitchen has caused public concerns in recent years. Exposure to suspended particles has significant associations with some diseases and the increased mortality (Morawska and Salthammer 2006). Removal of these contaminants is important for maintaining acceptable indoor air quality. Electrostatic filter originally used in industrial dust removal include corona electrode and collecting electrode, now is widely used in the field of air purification. Performance metrics include particle counting and sizing efficiency, PM 2.5 arrestance filtration efficiency, pressure drop, ozone concentration and the change of efficiency in different states (initial, dust loading, after cleaning). Compared to media filter, the electrical field intensity of electrostatic filter direct action on particulate matter and causes its movement, rather than through the air, which has the characteristics of high efficiency and low energy consumption (Liu 2004).In order to assess electrostatic air filter performance effectively, establish a proper test method and evaluation system is necessary. At present, Chinese standard GB/T is the only standard specifically for electrostatic filter test, but mainly used for industrial electric filter and the test aerosol is flue gas, while civil electrostatic air filter is used to filter the atmosphere dust, and it cannot be directly used to test the performance of civil electrostatic air filter due to the flue gas and atmospheric dust have different composition and particle size distribution. Chinese standard GB/T , European standard EN779:2012, American standard ASHRAE and Japanese standard JISB are now widely used in general media filter performance test. The Chinese and American standards stipulated the efficiency of electrostatic air filter was tested by KCL, ASHRAE dust for arrestance test, ozone and pressure drop test methods are also provided. Both standards use the final pressure drop as a symbol of electrostatic air filter cleaning and replacement, this is suitable for media filter, but not for the electrostatic air filter, because the pressure drop altered not significantly with the dust capacity. In addition, the loading dust for the two standards for testing the filtration device composed, by weight, of 72% SAE Standard J726 test dust (fine), 23% powdered carbon, and 5% milled cotton linters. But powdered carbon would make the electrostatic air filter to the partial discharge phenomena preceding the breakdown. The Japanese standard stipulates DOP as the test aerosol for the efficiency test of electrostatic air filters, while providing resistance and ozone testing methods, but there is no provision for dust containing capacity tests. The European standard (EN779:2012) does not mention the test of electrostatic air filters, which is the standard for Particulate air filters for general ventilation. The filtration efficiency tested by GB/T was arrestance efficiency, counting efficiency for GB/T , ASHRAE and JISB In general, the filtration efficiency of civil electrostatic air filters is as same as the medium efficiency level or even better, and required better filtration efficiency on small particles, so counting efficiency is generally used for electrostatic air filters. Through the analysis of the above five standards, it s impossible to carry out effective test for civil electrostatic air filter by using any standard. In order to reflect the use of electrostatic air filter characteristics, and comparing with media filter better at the same time, this paper puts forward using atmospheric dust counting and sizing efficiency method for the determination of electrostatic air filter efficiency. Combined with China's national conditions, PM 2.5 has got people s extensive attention, PM2.5 arrestance efficiency is tested as an importance performance evaluation index of electrostatic air filter. Resistance test used the same methods for particulate air filters for general ventilation. Civil electrostatic air filters are closely related to human health, and ozone concentration must be controlled. The test method for ozone is used in GB/T or ASHRAE The ASHRAE dust was replaced by iso A2 fine dust as loading dust. To facilitate the electrostatic air filter performance contrast, this article referenced EN779:2012 and adopted the method of fixed loading dust for dust test. The particle counting and sizing efficiency, PM2.5 arrestance efficiency, pressure drop were tested after loading dust, at the same time, adopted the ISBN: COBEE2018-Paper250 page 745

2 4 th International Conference On Building Energy, Environment method of fixed quantity water for electrostatic air filter cleaning, and test the filters performance after then. The particulate air filters for general ventilation adopts the quality factor (Li 2009.) proposed by Jiayong Chen to carry out performance evaluation. However, this parameter only considered the performance of the new particulate air filters, without the consideration of the loading capacity and the performance after the process of using. Based on this, the initial quality factor and the whole process quality factor were put forward to evaluate the initial performance and the whole process performance for electrostatic air filter. Both particle counting efficiency and arrestance efficiency were used in the calculation of the quality factor of electrostatic air filter, which were generally obtained by experiment. International standard ISO/DIS putted forward a method of atmospheric dust counting efficiency converting into arrestance efficiency, the calculation method to consider the particle counting and sizing efficiency comprehensively, at the same time, to some extent, overcome the influence of unstable atmospheric dust distribution in the process of testing(zhang and He 2015), the arrestance efficiency calculated in this way are more accurate than test directly with test aerosol directly, and more suitable for electrostatic air filter performance evaluation. METHODS The characteristics of eight different brands of civil electrostatic air filters evaluated in this study are shown in table 1. Table 1. Characteristics of the electrostatic air filters evaluated in this study No Dimension Windward area Face velocity Test volume # mm mm mm m/s m 3 /h W Power Figure 1 presents the filter efficiency test facility which is based on European standard EN779:2012. The test duct size was mm 2 with a flow control system and test particles of potassium chloride were supplied in the test duct using an atomizer(figure 2). The particle concentrations at the upstream and downstream of the test filter were measured using an aerosol spectrometer (APS3321, Dusttrak8533 TSI). The pressure drop across the test filter was measured using a micro-manometer (Testo 510). Filtered air was supplied to the test duct by a HEPA filter installed at the entrance of the test duct. API T400 ozone sampling instrument was used to measure the difference in the concentration of ozone in the downstream and downstream, as the ozone quantity released by the electrostatic air filter. The detailed parameters of the instrument used in the performance test of electrostatic air filter are shown in table 2. Figure 1. Schematics of the filter test system [Hyun and Baek 2017] Table 2. Test instrument parameter Name Model Parameters Range Precision Aerodynamic particle size spectrometer Aerosol monitor Ozonometer Vortex flowmeter Analytical balance APS 3321 Dusttrak 8533 API T400 Testo 510 XY- LUGB HR-120 Particle counting and sizing efficiency Weight concentration of particle Ozone concentration Resistance Air flow Load quality dust μm <10000/cm 3 ±5.0% PM1.0/2.5/4. 0/ mg/m 3 ±0.1% 0-10ppm ±5.0% 0-100hPa m 3 /h Micromanometer ±( )hPa ±1.5% 0-120g ±0.2mg In the loading dust test, the fine dust of 30g A2 is placed in the dust feeder device, as shown in fig.2 (2). The dust was sent to the tested filters at a concentration of 70 mg/m 3. After then, particle counting and sizing efficiency and PM2.5 efficiency were measured again. After the dust holding capacity test, the electrostatic air filter is cleaned with high pressure cleaning machine, as shown in Fig.1 (3). We keep the cleaning methods (cross cleaning), cleaning time (10min) and water consumption (30L) remain the same. After cleaning, leaved in the ventilated place for six hours, and tested particle size counting efficiency and PM 2.5 efficiency. ISBN: COBEE2018-Paper250 page 746

3 th 4 International Conference On Building Energy, Environment Where Q is the quality factor, is the filter pressure drop. is the filter efficiency, P RESULTS (1) Aerosol generator The initial efficiency of the eight electrostatic air filters is shown in Figure 3. With the increase of particle size, particle counting and sizing efficiency increases gradually, and the efficiency of the differences between the electrostatic air filters decreases, to reflect the differences between the electrostatic air filter, small particle size (e.g., 0.3 to 0.5 μm) particles are more suitable for electrostatic air filter performance evaluation. Figure 3 (2) is the PM2.5 arrestance efficiency of all electrostatic air filters under different test aerosol. The PM2.5 arrestance measured by DEHS is more efficient than atmospheric dust. This is because the volume distribution of DEHS is single peak distribution, mainly concentrated in between 0.3 and 2.5μm. However, the volume distribution of atmospheric dust is distributed by the bimodal distribution, mainly concentrated in between μm and μm, and the average particle size of atmospheric dust under 2.5μm is smaller. At the same time, the relative permittivity of DEHS is greater than that of atmospheric dust, which leads to the power of DEHS in electrostatic field is stronger than atmospheric dust, so it has a higher efficiency of PM2.5. (2) Dust feeder (3) High pressure cleaner Figure 2. Physical drawing of experimental device The particle counting and sizing efficiency and PM2.5 arrestance efficiency was estimated by Equation (1). n Ei 1 i 100% Ni (1) Where Ei is the counting or arrestance efficiency for certain particle size. ni and N i are the particle concentrations at the upstream and downstream of the test filter, and i is the particle size. Equation (2) is a simple equation used to estimate the concentration of ozone. C=C2-C1 (2) 1 Classification efficiency of partical count Where C is the ozone emission of electrostatic air filter. C1 is the ozone concentrations at the upstream and C2 for downstream. The particulate matter efficiencies epm10, epm2.5 and epm1 are calculated from the average fractional efficiencies Ei and the standardized particle size distribution q3(d). For the meanings of the parameters in Eq. (3), see the standard ISO/DIS n n 1 1 epm1(2.5) Ei q3u (di ) ln di / q3u (di ) ln di n epm10 Ei q3r (di ) ln di / q3r (di ) ln di (3) 1 The quality factor was estimated by Equation (4). Q ln(1 ) P ISBN: (4) 2 PM2.5 arrestance Figure 3. Initial efficiency of electrostatic air filters COBEE2018-Paper250 page 747

4 th 4 International Conference On Building Energy, Environment Figure 4(1) is the curve of pressure drop with the face velocity. When the face velocity is 2.5 m/s, the resistance of most electrostatic air filters is below 60 pa, and the resistance of the filter is very small compared to that of the media air filter. The ozone emission amount of each electrostatic air filter is shown in figure 4 (2), which is far smaller than the specified value(0.16mg/m ³ ) of Chinese standard GB/T PM2.5 arrestance efficiency 1 Pressure drop across the electrostatic filters increases as a function of the face velocity μm counting efficiency Figure 5. The efficiency of electrostatic air filter under three test conditions 2 Ozone emission amount Figure 4. Resistance and ozone emission amount of electrostatic air filters Figure 5 shows the performance change of electrostatic air filters under three test conditions (initial, dust holding and after cleaning), the electrostatic air filter efficiency are decreased after dust holding test, but the arrestance efficiency of PM2.5 decreased less than 0.3 to 0.5μm counting efficiency, so electrostatic air filter for filtering performance of small diameter particles attenuation is more obvious, suggested to choose small diameter particles to evaluate electrostatic air filter attenuation performance. The efficiency of electrostatic air filter after cleaning is basically restored, but slightly below the initial efficiency. ISBN: The initial quality factor for the electrostatic air filter was evaluated by PM2.5 arrestance efficiency and μm counting efficiency respectively, as shown in FIG. 5 and FIG. 6. Among them, FIG. 6 shows the comparison between the calculated values and the test values of initial quality factor and PM2.5 arrestance efficiency. It can be seen that the measured PM2.5 efficiency is more efficient than the calculation of PM2.5, which may be due to the difference between the size distribution of atmospheric dust and standard atmospheric dust. The change trend of them is the same, and the quality factor has the same change trend, which indicates that the calculation of PM2.5 efficiency can be used to evaluate the performance of electrostatic air filters. COBEE2018-Paper250 page 748

5 th 4 International Conference On Building Energy, Environment Figure μm counting efficiency and quality factor of electrostatic air filters 1 PM2.5 arrestance efficiency Figure 8. epm2.5 and quality factor in the whole process 2 Initial quality factor Figure 6. The comparison between the calculated values and the measured values This article selects the average value of initial efficiency and efficiency after dust holding capacity as the efficiency in the whole process of using electrostatic air filter, and the whole process performance of electrostatic filter ware evaluated by the μm counting efficiency and epm2.5. As shown in figure 7 and figure 8. The whole process quality factor is positively correlated with the μm counting efficiency and epm2.5, and the change trend is the same. CONCLUSIONS This study put forward the performance testing method of electrostatic filter based on the different test standards, and the conclusions are as follows: (1) The counting efficiency of the civil electrostatic air filter can be tested uses the atmospheric dust, and the PM2.5 efficiency measured by DEHS is better than that of atmospheric dust to evaluation the performance of electrostatic air filter. (2) Final pressure drop is not suitable as a symbol of the end of the electrostatic air filter dust holding capacity test, and the method of fixed dust can be used to access the performance, at the same time, small diameter particles is more suitable for the evaluation of electrostatic filter efficiency attenuation after the dust holding capacity test. (3) epm2.5 considered the average fractional efficiencies and the standardized particle size distribution, to some extent, overcome the unstable atmospheric dust distribution in the process of testing. (4) Initial quality factor and whole process quality factor can be used to evaluate the initial performance and whole process performance of electrostatic filter. ACKNOWLEDGEMENT This work was supported by the National Natural Science Foundation of China (No ), National Key R&D Program of China (No. 2017YFC ) ISBN: COBEE2018-Paper250 page 749

6 4 th International Conference On Building Energy, Environment REFERENCES Liu P Study on the test method of electrostatic air filter. Master. Thesis, Tianjin University, China, 97 pages. SAC GB/T , Performance test of electrostatic precipitator. Standardization Administration of China. SAC GB/T , Air filter. Standardization Administration of China. ECT EN779: 2012, Particulate air filters for general ventilation - Determination of the filtration performance. European Committee for Standardization. ASHRAE ASHRAE Standard , Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. Atlanta: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. JIS JIS B , Test Method of Air Filter Units for Ventilation and Electric Air Cleaners for Ventilation. Japanese Industrial Standards. Hyun O, Baek M, Moon J, and Ahn Y, Performance evaluation of two-stage electrostatic air filter with lowozone emission corona charger, Particulate Science and Technology. 35:1, Morawska L, and Salthammer T Indoor environment: airborne particles and settled dust. John Wiley & Sons. Li Y. Y General ventilation for air filter performance evaluation. Master. Thesis, Tianjin University, China, 67 pages. ISO ISO/DIS : 2014, Air Filters for General Ventilation -Part1: Technical specifications, requirements and efficiency classification system based upon particulate matter (PM). International Standards Organization Zhang W. Y. and He T. L, The PM 2.5 efficiency of air filters in general ventilation is studied. Refrigeration and air conditioning, 15(10): ISBN: COBEE2018-Paper250 page 750