Filtration Characteristics of Control Devices and Management Strategy of Cooking Oil Aerosol Emission
Date Issued
2016
Date
2016
Author(s)
Hung, Hsiao-Yi
Abstract
In recent years, the fine particulate matter (PM2.5) pollution has become a major environmental concern in Taiwan. According to the Taiwan Emission Data System, TEDS 8.1, more than 37.5 % of PM2.5 concentrations were contributed by emissions from both restaurants and accommodations in Taipei city. Therefore, efforts to reduce PM2.5 levels would be impeded if cooking oil emissions are not addressed. However, the use of air pollution control devices (APCDs) is not required in kitchen hood systems nowadays in Taiwan. Accordingly, the main purpose of this study was to develop a feasible filtration test method for evaluating the efficiency of APCDs in kitchen exhaust systems. The results might be helpful for environmental policy implementing and reducing the PM2.5 levels eventually. To determine the particle penetration as a function of particle size in the range of 0.02~0.7 µm, a salt atomizer (model 8118A-EN, TSI Inc., St. Paul, MN) and an oil generator (model 1081414R, TSI Inc., St. Paul, MN) were used to generate polydisperse sub-micrometer-sized challenge aerosol particles for laboratory and field study, respectively. For laboratory tests, the generated particles were then passed through an aerosol neutralizer (25 mCi, Am241) to neutralize the aerosol particles to the Boltzmann charge equilibrium. Next, the neutralized aerosols were mixed with ambient air to obtain the desired flow rates. A scanning mobility particle sizer (SMPS, model 3936, TSI Inc.) was used to measure the aerosol concentrations and size distributions. Particle number concentration data, obtained upstream and downstream of an APCD, were used to assess the penetration of aerosol particles. In this work, filtration characteristics of filter media and electrostatic precipitators (ESPs) were measured both in the laboratory and field. Moreover, the efficiency curves of commercial grease filters were also evaluated. In this part of test, an aerodynamic particle sizer (APS, model 3321, TSI Inc.) incorporating with an ultrasonic atomizing nozzle (model 8700-120, Sonotek Inc., Highland, NY) was used to measure the aerosol penetration in the size range of 0.7~5 µm. The APCD’s initial filtration efficiency is a function of the size of the particles, and is not dependent on whether they are solid or liquid. The results showed that the commercial grease filters were effective only at capturing particles with diameter larger than 2.5 µm at the face velocity of about 2 m/s. In contrast, ESPs and filter media tested in the present study were more effective in collecting PM2.5 particles. Experimental results showed that aerosol penetration through the ESP decreased with decreasing air flow rates. The most penetrating particle size (MPPS) of the ESP ranged from 0.2~0.3 µm. Although the collection efficiencies of ESPs decreased significantly for particles less than 20 nm due to the partial charge effect, those particles did not contribute significantly to emission based on mass. On the other hand, aerosol penetration through the filter media depended not only on air flow rates, but also on fiber charges. The data showed the tested filter media had an initial MPPS around 50 nm. When electrostatic charges are removed by dipping the filter in isopropanol or loading with oil particles, aerosol penetration increases substantially and the MPPS increases to 200~400 nm, which is the range expected for filters relying solely on mechanical collection mechanisms. The laboratory and the field tests both showed the same trend. In order to comprehensively regulate the emission of cooking oil aerosols, it is proposed that the aerosol penetration ranging from 20 to 700 nm is a required test for all APCDs, and aerosol penetration of the MPPS should not exceed 10%. Theoretical analysis results showed that using challenge aerosol with count median diameter (CMD) of MMPS and geometric standard deviation (GSD) less than 1.4, the worst efficiency of the ESP or filter could be obtained correctively within 5% error regardless of evaluating based on total number, surface, or mass.
Subjects
air pollution control devices (APCDs)
range hood
most penetration size
collection efficiency
SDGs
Type
thesis
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