Browsing by Author "Bai, HL"

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A theoretical evaluation on the HNO3 artifact of the annular denuder system due to evaporation and diffusional deposition of NH4NO3-containing aerosols
(2002-09-01)
Chang, KF
;
Lu, CS
;
Bai, HL
;
Fang, GC
;
環境工程研究所
(A) mathematical model was developed to evaluate HNO3 artifact of the annular denuder system due to evaporation and diffusional deposition of nitrate-containing aerosols. The model performance was validated by comparing its numerical solutions with laboratory and numerical data available in the literature for evaporation and diffusional deposition of monodisperse and polydisperse NH4NO3 aerosols. Measurement artifacts were evaluated by varying typical sampling ranges of ambient temperature, HNO3 gas concentration, aerosol number concentration, aerosol mass median diameter, and nitrate mass fraction of < 2.5 mum aerosols to see their respective effects. Potential application of the present model on estimating HNO3 artifacts was demonstrated using literature data sampled in USA, Taiwan, Netherlands, Korea and Japan. Significant measurement artifact could be found in Taiwan and Netherlands due either to low HNO3 gas concentration and high nitrate concentration in < 2.5 mum aerosols or to high ambient temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.
Adsorption and desorption characteristics of semiconductor volatile organic compounds on the thermal swing honeycomb zeolite concentrator
(2003-11-01)
Chang, FT
;
Lin, YC
;
Bai, HL
;
Pei, BS
;
環境工程研究所
The use of a honeycomb zeolite concentrator and an oxidation process is one of the most popular methods demonstrated to control volatile organic compound (VOCs) emissions from waste gases in semiconductor manufacturing plants. This study attempts to characterize the performance of a concentrator in terms of the removal efficiencies of semiconductor VOCs (isopropyl alcohol [IPA], acetone, propylene glycol methyl ether [PGME], and propylene glycol monomethyl ether acetate [PGMEA]) under several parameters that govern the actual operations. Experimental results indicated that at inlet temperatures of under 40 degreesC and a relative humidity of under 80%, the removal efficiency of a zeolite concentrator can be maintained well over 90%. The optimal rotation speed of the concentrator is between 3 and 4.5 rph in this study. The optimal rotation speed increases with the VOCs inlet concentration. Furthermore, reducing the concentration ratio helps to increase the removal efficiency, but it also increases the incineration cost. With reference to competitive adsorption, PGMEA and PGME are more easily adsorbed on a zeolite concentrator than are IPA and acetone because of their high boiling points and molecular weights.
An experimental study on the performance of a single discharge wire-plate electrostatic precipitator with back corona
(1999-03-01)
Chang, CL
;
Bai, HL
;
環境工程研究所
;
Institute of Environmental Engineering
The phenomenon of back corona is well known in that it may reduce the collection efficiency of an electrostatic precipitator. In this study, experimental results are presented for the influence of back corona on the performance of a laboratory scale single-discharge-wire ESP system. The effect of back corona under two power controlled methods, constant voltage operation and constant current operation, has been evaluated. The experimental results showed that as back corona occurs, the output current and the power consumption are increased under constant voltage operation. The mass collection efficiency is proportional to the applied voltage. On the other hand, for constant current operation the voltage and the power consumption are decreased under back corona. The mass collection efficiency is independent of the applied current. A lateral mixing model was also applied to assist in the discussion of corona power and particle collection efficiency under normal and stable back corona conditions. Both experimental and theoretical results indicated that the back corona has a large effect on submicron particles. The grade efficiency can be reduced by over 60% for submicron particles. The large reduction of efficiency for submicron particles is due to significant reduction in both particle charge and migration velocity. Since particles in the submicron region are more sensitive to light scattering, the opacity problem may be aggravated under back corona. (C) 1999 Elsevier Science Ltd. All rights reserved.
Applying hexagonal nanostructured zeolite particles for acetone removal
(2005-06-01)
Lin, YC
;
Bai, HL
;
Chang, CL
;
環境工程研究所
;
Institute of Environmental Engineering
This study examines the performance of a new adsorbent, hexagonal nanostructured zeolite particles (HNZP) for acetone adsorption and compares the results with that of commercial mobil synthetic zeolite-5 (ZSM-5) type zeolite. The HNZP is a pure siliceous adsorbent with different values of pore diameter and surface area being adjustable by the manufacturing condition. The results indicate that a slight increase in the average pore diameter (d) of HNZP from 2 to 2.5 nm leads to an increase in the acetone adsorption capacity, although its surface area is decreased, in which case (d = 2.5 nm) the adsorption capacity of fresh HNZP is better than that of ZSM-5 zeolite. Even for the fresh HNZP (d = 2 nm) of which the adsorption capacity is less than that of the ZSM-5 zeolite at relative humidity (RH) of 0%, its adsorption capacity is not deteriorated after repeated regeneration, but the adsorption capacity of regenerated ZSM-5 zeolite decays markedly. Thus, after only one regeneration, the adsorption capacity of HNZP (d = 2 nm) becomes better than that of the ZSM-5 zeolite. The decrease in the adsorption capacity of regenerated ZSM-5 zeolite might be because of its aluminum content that catalyzes the acetone into coke and, thus, blocks the adsorption sites. Furthermore, result on the moisture effect shows that because the pure siliceous HNZP was more hydrophobic than the ZSM-5 zeolite, the acetone adsorption efficiency of fresh HNZP (d = 2 nm) is better than that of ZSM-5 zeolite at RH = 50%.
Biotreatment of hydrogen sulfide- and ammonia-containing waste gases by fluidized bed bioreactor
(2001-02-01)
Chung, YC
;
Huang, CP
;
Liu, CH
;
Bai, HL
;
環境工程研究所
Gas mixtures of H2S and NH3 are the focus of this study of research concerning gases generated from animal husbandry and treatments of anaerobic wastewater lagoons. A heterotrophic microflora (a mixture of Pseudomonas putida for H2S and Arthrobacter oxydans for NH3) was immobilized with Ca-alginate and packed into a fluidized bed reactor to simultaneously decompose H2S and NH3. This bioreactor was continuously supplied with H2S and NH3 separately or together at various ratios. The removal efficiency, removal rate, and metabolic product of the bioreactor were studied. The results showed that the efficiency remained above 95% when the inlet H2S concentration was below 30 ppm at 36 L/hr. Furthermore, the apparent maximum removal and the apparent half-saturation constant were 7.0 x 10(-8) gS/cell/day and 76.2 ppm, respectively, in this study. The element sulfur as a main product prevented acidification of the biofilter, which maintained the stability of the operation. As for NH3, the greater than 90% removal rate was achieved as long as the inlet concentration was controlled below 100 ppm at a flow rate of 27 L/hr. In the NH3 inlet, the apparent maximum removal and the apparent half-saturation constant were 1.88 x 10(-6) g-N/cell/day and 30.5 ppm, respectively. Kinetic analysis showed that 60 ppm of NH3 significantly suppressed the H2S removal by Pseudomonas putida, but H2S in the range of 5-60 ppm did not affect NH3 removal by Arthrobacter oxydans. Results from bioaerosol analysis in the bioreactor suggest that the co-immobilized cell technique applied for gas removal creates less environmental impact.
Comparison of ammonia and monoethanolamine solvents to reduce CO2 greenhouse gas emissions
(1999-04-05)
Yeh, AC
;
Bai, HL
;
環境工程研究所
;
Institute of Environmental Engineering
This paper presents experimental results on the evaluation of two reagents, ammonia (NH3) and monoethanolamine (MEA) solvents, for scrubbing carbon dioxide (CO2) greenhouse gas emissions. The scrubbing of CO2 by NH3 solvent is a novel study developed by the authors, and the MEA process is a traditional process for gas purification of removing CO2. The performance of these two solvents are compared in terms of CO2 removal efficiency and absorption capacity. Test results show that both the CO2 removal efficiency and absorption capacity of NH3 solvent are better than those of MEA solvent under the operating conditions conducted in this study. The maximum CO2 removal efficiency by NH3 solvent can achieve 99% and the CO2 absorption capacity can approach 1.20 kg CO2/kg NH3. On the other hand, the maximum CO2 removal efficiency and absorption capacity by MEA solvent are 94% and 0.40 kg CO2/kg MEA, respectively, under the same operating conditions tested by NH3 solvent. Besides, the temperature increases due to exothermal reactions in the NH3 scrubbing process are lower than those in the MEA scrubbing process. This indicates that the energy requirement for the regeneration of NH3 reagent should be less than that for the regeneration of MEA reagent. (C) 1999 Elsevier Science B.V. All rights reserved.
Competition between the charge ordered and ferromagnetic states in (La,Nd)(0.75)Na0.25MnO3 manganites
(2004-05-24)
Li, ZQ
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Zhang, XH
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Yu, JS
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Liu, XJ
;
Liu, XD
Structural, magnetic, and transport properties of (La1-xNdx)(0.75)Na0.25MnO3 (0 less than or equal to x less than or equal to 1) are studied. The system exhibits a rhombohedrally distorted perovskite structure for x less than or equal to 0.2 and it convert to an orthorhombic structure for x greater than or equal to 0.4. Re-entrant ferromagnetic type charge ordering transitions are observed in the narrow bandwidth samples (x greater than or equal to 0.6), while charge ordering transition is not observed for these samples with rhombohedral structure. Combining with the published results related to the charge ordering transition, we argue that the rhombohedral structure likely favor double exchange interaction and suppress charge ordering interaction. The compounds show metal to insulator transitions except Nd0.75Na0.25MnO3. The resistivity data above the metal to insulator transition temperature for the charge ordered sample are discussed in the frame work of variable-range hopping model. (C) 2004 Elsevier B.V. All rights reserved.
Control of VOCs emissions by condenser pre-treatment in a semiconductor fab
(2005-04-11)
Lin, YC
;
Chang, FT
;
Bai, HL
;
Pei, BS
;
環境工程研究所
The performance of a modified design of local condensers to pre-treat a variety of volatile organic compounds (VOCs) emitted from the stripping process of a semiconductor fab was tested in this study. The reaction temperature of the condensers was controlled at around 10 degrees C, it is relatively higher than the traditional condenser reaction temperature. Both VOCs and water vapors were condensed and formed liquid films. This resulted in an enhancement of the VOCs removals, especially for VOCs of high boiling points or solubility. This can help to prevent the follow up zeolite concentrator from damage. The performance of the integrated system of condenser/zeolite concentrator could, therefore, remain highly efficient for a longer operation time. Its annualized cost would also be lower than installing the zeolite concentrator only. (c) 2005 Elsevier B.V. All rights reserved.
Design model for selective catalytic reduction process: Solution of convective diffusion and NOx reaction
(1998-12-01)
Bai, HL
;
Chwu, JW
;
環境工程研究所
;
Institute of Environmental Engineering
A simple model for the design of selective catalytic reduction (SCR) process is presented. The two-dimensional mass transfer equation shown in Bai and Chwu (1997) is simplified and the analytic solution is obtained. The analytic solution is verified by the solution of the numerical two-dimensional model as well as published experimental data. Then it is applied for the design of the SCR reactor. Effects of operating temperature, inlet molar ratio of NH3/NO, channel pitch, and gas flow rate on the SCR reactor volume are evaluated based on a designed NO removal efficiency. The NH3 slip problem of a given inlet ratio of NH3/NO also is discussed. It is shown that the injection ratio of NH3/NO must be slightly higher than the desired NO removal efficiency so that the reactor volume can be reduced and the problem of NH, slip is not a major concern.
Design model for selective catalytic reduction process: Solution of convective diffusion and NOx reaction
(1998-12-01)
Bai, HL
;
Chwu, JW
;
環境工程研究所
;
Institute of Environmental Engineering
A simple model for the design of selective catalytic reduction (SCR) process is presented. The two-dimensional mass transfer equation shown in Bai and Chwu (1997) is simplified and the analytic solution is obtained. The analytic solution is verified by the solution of the numerical two-dimensional model as well as published experimental data. Then it is applied for the design of the SCR reactor. Effects of operating temperature, inlet molar ratio of NH3/NO, channel pitch, and gas flow rate on the SCR reactor volume are evaluated based on a designed NO removal efficiency. The NH3 slip problem of a given inlet ratio of NH3/NO also is discussed. It is shown that the injection ratio of NH3/NO must be slightly higher than the desired NO removal efficiency so that the reactor volume can be reduced and the problem of NH, slip is not a major concern.
Destruction of styrene in an air stream by packed dielectric barrier discharge reactors
(2005-12-01)
Chang, CL
;
Bai, HL
;
Lu, SJ
;
環境工程研究所
;
Institute of Environmental Engineering
This study presents the decomposition rates of styrene vapors with non-packed and packed bed dielectric barrier discharge reactors. The concentrations of intermediate byproducts at various plasma operation conditions were evaluated. The results showed that although styrene vapors could be almost completely removed at low styrene inlet concentration of 132 ppm, the selectivity of CO2 as the major product was rather low in a non-packed bed reactor. It was found that solid carbon containing compound was the major byproduct. An increase in the styrene inlet concentration tended to reduce the styrene removal efficiency, it also led to increase in the solid byproduct. The reactors that packed with glass, Al2O3 or Pt-Pd /Al2O3 pellets could improve the styrene decomposition efficiency and reduce the formation of intermediate products, of which the best oxidation of styrene to CO2 could be achieved with a Pt-Pd /Al2O3 packed bed reactor. The carbon byproducts could also be reduced if the rector length was increased. The concentrations of ozone formed during the plasma process were also evaluated for the non-packed and packed bed reactors. The plasma reactor that packed with Pt-Pd /Al2O3 pellets was proved to have the lowest O-3 concentration.
Direct quantitative analysis of phthalate esters as micro-contaminants in cleanroom air and wafer surfaces by auto-thermal desorption-gas chromatography-mass spectrometry
(2005-04-08)
Kang, YH
;
Den, W
;
Bai, HL
;
Ko, FH
;
環境工程研究所
This study established an analytical method for the trace analyses of two phthalate esters, including diethyl phthalate (DEP) and di-n-butyl phthalate (DBP), known as the major constituents of cleanroom micro-contamination detrimental to the reliability of semiconductor devices. Using thermal desorption coupled with a GC-MS system, standard tubes were prepared by delivering liquid standards pre-vaporized by a quasi-vaporizer into Tenax GR tubes for calibration. This method was capable of achieving detection limits of 0.05 mu g m(-3) for 0.1 m(3) air samples and 0.03 ng cm(-2) for 150-mm wafer surface density. Actual samples collected from a semiconductor cleanroom showed that the concentration of DBP in a polypropylene wafer box (0.45 mu g m(-3)) was nearly four times higher than that in the cleanroom environment (0.12 mu g m(-3)). The surface contamination of DBP was 0.67 ng cm(-2) for a wafer stored in the wafer box for 24 h. Furthermore, among the three types of heat-resistant O-ring materials tested, Kalrez((R)) was found to be particularly suitable for high-temperature processes in semiconductor cleanrooms due to their low emissions of organic vapors. This analytical procedure should serve as an effective monitoring method for the organic micro-contamination in cleanroom environments. (c) 2005 Elsevier B.V. All rights reserved.
Effects of some geometric parameters on the electrostatic precipitator efficiency at different operation indexes
(2000-09-01)
Chang, CL
;
Bai, HL
;
環境工程研究所
;
Institute of Environmental Engineering
The performance of electrostatic precipitators (ESPs) was usually obtained under different geometric parameter values and operation indexes. Hence different conclusions were made in the literature and similar improvements may not be obtained for other applications. In this paper the effects of some geometric parameters on the performance of a wire-plate ESP at different operation indexes are evaluated theoretically. The geometric design parameters include discharge wire diameter, wire-to-wire distance, and plate-to-plate spacing. And the operation indexes considered are the electric field strength, the average current density at plates, and the corona power ratio. The results show that the collection efficiency is increased with a decrease in the wire diameter under the same electric field strength. But opposite results are observed under the same average current density at plates or the same corona power ratio applying to the ESP. The optimal wire-to-wire distance and plate-to-plate spacing vary as the electric field strength is changed. On the other hand, high collection efficiencies are always obtained with decreases in the wire-to-wire distance and the plate-to-plate spacing under the same average current density at plates or the same corona power ratio.
Energy-effectiveness of nonthermal plasma reactors for toluene vapor destruction
(2001-07-01)
Lin, CH
;
Bai, HL
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環境工程研究所
;
Institute of Environmental Engineering
The energy-effectiveness of packed-bed and nonpacked-bed plasma reactors for the destruction of toluene vapors is evaluated on the basis of the power consumption of the reactor system. The operation and design parameters being evaluated include the applied voltage, inlet gas flow rate, and toluene concentration. The optimal operational conditions for the target destruction of toluene vapors, with minimum power consumption, are determined. The results showed that a packed-bed plasma reactor has a higher toluene destruction efficiency and a lower power consumption than a nonpacked-bed plasma reactor. The toluene destruction efficiency is increased as both the inlet gas flow rate and the toluene gas concentration are decreased. For a plasma reactor 2 cm in diameter and packed with 5-mm glass pellets, > 90% of toluene destruction can be reached at an applied voltage of 8.7 kV, inlet toluene concentrations <1,000 ppm, and gas flow rates of < 680 cm(3)/min. The corresponding energy-effectiveness is about 15 g toluene/kW (.) h.
Estimation of PAHs dry deposition and BaP toxic equivalency factors (TEFs) study at Urban, Industry Park and rural sampling sites in central Taiwan, Taichung
(2004-05-01)
Fang, GC
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Chang, KF
;
Lu, CS
;
Bai, HL
;
環境工程研究所
The concentrations of polycyclic aromatic hydrocarbons (PAHs) in gas phase and particle bound were measured simultaneously at industrial (INDUSTRY), urban (URBAN), and rural areas (RURAL) in Taichung, Taiwan. And the PAH concentrations, size distributions, estimated PAHs dry deposition fluxes and health risk study of PAHs in the ambient air of central Taiwan were discussed in this study. Total PAH concentrations at INDUSTRY, URBAN, and RURAL sampling sites were found to be 1650 +/- 1240, 1220 +/- 520, and 831 +/- 427 ng/m(3), respectively. The results indicated that PAH concentrations were higher at INDUSTRY and URBAN sampling sites than the RURAL sampling sites because of the more industrial processes, traffic exhausts and human activities. The estimation dry deposition and size distribution of PAHs were also studied. The results indicated that the estimated dry deposition fluxes of total PAHs were 58.5, 48.8, and 38.6 mug/m(2)/day at INDUSTRY, URBAN, and RURAL, respectively. The BaP equivalency results indicated that the health risk of gas phase PAHs were higher than the particle phase at three sampling sites of central Taiwan. However, compared with the BaP equivalency results to other studies conducted in factory, this study indicated the health risk of PAHs was acceptable in the ambient air of central Taiwan. (C) 2004 Elsevier Ltd. All rights reserved.
Field study, design, and catalyst cost of selective catalytic reduction process
(2001-08-01)
Bai, HL
;
Lee, SH
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Lin, CH
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Hwang, JF
;
Hsieh, CL
A pilot TiO2/V2O5 based selective catalytic reduction (SCR) system was installed in a glass manufacturing factory. The effects of important operation parameters such as the reaction temperature, space velocity, and inlet NH3/NOx molar ratio on the NO removal were evaluated. It was observed that >1 mol of NO, is reacted for every 1 mol of NH3 injected. This observation is different from that reported in the literature for laboratory experiments. The key design parameter values of the reaction rate and the NH3 adsorption rate were determined based on results of the pilot tests using a theoretical SCR model developed by the same research group. The SCR model is a simple analytical solution that accounts for the simultaneous mass transfer and chemical reaction of an SCR reactor. The model results were compared to field data of NOx conversion efficiency and NH3 slip, and they were in reasonable agreement. The required catalyst volume and the cost of catalysts were then determined with the assistance of the design model.
Measurement of atmospheric particles and anionic species across central Taiwan
(2003)
Fang, GC
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Chang, KF
;
Lu, CS
;
Bai, HL
;
環境工程研究所
The ambient air concentrations and fluxes of various anionic species were sampled by MOUDI, TSP and dry deposition plates at a traffic sampling site in Taichung, central Taiwan. In the sampling period, from September to December 2000, the ambient air particle concentrations (PM1, PM2.5, PM10 and TSP) were lower in the September than in the other three months (October to December). The reason is that the northwest wind brought more particles (diameter less than 10 mum) and the higher wind speed caused higher dry deposition fluxes and TSP concentrations in the last three months. The anion species percentages of TSP were 0.24%, 13.7%, 0.52%, 12.0%, 18.9% and 54.6% for F-, Cl-1 Br-1 NO2-1 NO3 and SO42-, respectively. The results revealed that SO42-, NO3, Cl- and NO2- were the dominant species at the traffic sampling site. The ion-size distributions of Cl-, NO2- and NO3 were unimodal, the main peak being between 3.2 and 5.6 mum. In contrast, the size distribution Of SO42- was bimodal, with the main peaks in the particle size ranges 0.32-0.56 mum and 3.2-5.6 mum. The ambient average particle dry deposition flux was 6.28 mug/m(2)/s, and the dry deposition fluxes were 0.01, 94.6, 0.05, 34.7, 72.2 and 376.4 ng/m(2)/s for F-, Cl-, Br, NO2-, NO3- and SO42-, respectively. The dry deposition velocities were 3.10, 0.03, 3.67, 0.05, 1.54, 2.03 and 3.67 cm/s for F-, Cl-, Br-, NO2-, NO3- and SO42-, respectively.
Monodisperse nanoparticle synthesis by an atmospheric pressure plasma process: An example of a visible light photocatalyst
(2004-10-27)
Bai, HL
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Chen, CC
;
Lin, CS
;
Den, W
;
Chang, CL
An atmospheric pressure plasma-enhanced nanoparticle synthesis (APPENS) process was proposed to produce a titania-based visible light photocatalyst. The titanium tetraisopropoxide (TTIP) precursor was vaporized with a N-2 carrier gas and entered a nonthermal AC plasma system. The N-2 gas was dissociated into N atoms by the plasma energy, and then they were doped into the precursor vapors. The produced TiO2-xNx nanoparticles were highly uniform and adjustable in size. The titania-based particle sizes ranged from 25 to 40 nm, and they depended on the precursor ratio of TTIP/H-2O. In addition to producing the photocatalytic particles, the APPENS process has a potential application as a continuous-flow nanosize monodisperse aerosol generator.
Organic airborne molecular contamination in semiconductor fabrication clean rooms - A review
(2006)
Den, W
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Bai, HL
;
Kang, YH
;
環境工程研究所
;
Institute of Environmental Engineering
Monitoring of airborne molecular contamination (AMC) has become a crucial element of cleanroom management as the production phase of semiconductor devices marches deep into sub-100-nm range. The current understandings of the AMC, particularly those with organic origins, are presented comprehensively in this article based on the research reports within the past ten years. Starting with a review of the chronological development of AMC problems and several approaches for the AMC classifications, this article also examines the merits of several available ambient sampling and surface analytical methods. The focal point of the article is to address the surface deposition potential of organic AMCs by experimentally correlating the surface speciation and abundance of the organic AMCs with their physical and chemical characteristics, together with the kinetic models delineating the rates of deposition for both single-and multiple-contaminant scenarios. In addition, the current progress of the AMC control strategies, especially the development of the chemical filtration technology, is also examined in the paper. (c) 2006 The Electrochemical Society.
Particle size distribution and anion content at a traffic site in Sha-Lu, Taiwan
(2001-11-01)
Chang, KF
;
Fang, GC
;
Lu, CS
;
Bai, HL
;
環境工程研究所
Ambient air particle concentrations were sampled by two total suspended particle (TSP) samplers, PM10/PM2.5 specific sampler and micro-orifice uniform deposit impactor (MOUDI) during July-October 2000 at a traffic sampling site in central Taiwan. The average TSP concentration (194 mug/m(3)) was about a factor of two higher than that of the fraction <2.5 mum (93.2 mug/m(3)). The mean level of the fraction < 10 mum collected by MOUDI (93.2 mug/m(3)) was about 11/2 times higher than that of the size class <2.5 mum (43.8 mug/m(3)). Furthermore, this fraction showed a certain correlation with the TSP concentration. The particle size distribution was bimodal in the ambient air at the traffic site. The major peaks appear at particle diameters between 0.56-1.0 and 3.2-5.6 mum. The percentages of anions contained in TSP were 0.23% F-, 13.7% Cl-, 0.52% Br-, 12.0% NO3-, 18.9% NO2-, and 54.6% SO42-. The Cl-, NO2-, and NO3- size distributions were all unimodal and the major peaks appeared at 3.2-5.6 mum. The SO42- size distribution was bimodal, with major peaks at 0.32-0.56 and 3.2-5.6. (C) 2001 Elsevier Science Ltd. All rights reserved.