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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.
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.
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.
Performance of the annular denuder system with different arrangements for HNO3 and HNO2 measurements in Taiwan
(2000-01-01)
Bai, HL
;
Wen, HY
;
環境工程研究所
;
Institute of Environmental Engineering
Experiments on different annular denuder system (ADS) arrangements for sampling nitrous acid (HNO2) and nitric acid (HNO3) gases were conducted in this study to evaluate their sampling artifacts. The evaluation basis is the one that employed one sodium chloride denuder for sampling HNO3 gas and two sodium carbonate (Na2CO3) denuders for sampling HNO2 gas, which is a commonly employed ADS arrangement in many field applications in the United States. A field study was conducted in Hsinchu, Taiwan, and the results indicated that this ADS arrangement may yield over 80% relative errors for HNO3 gas. It also showed that the relative errors for HNO2 gas can be less than 10% as sampled with only one Na2CO3 denuder. This is attributed to the fact that the ambient HNO3 concentration measured in this study was relatively low while the HNO2 concentration was high, as compared to typical concentrations of these two gases measured in the United States. The sampling error of HNO3 gas may be due to high concentrations of N-containing interfering species present in Taiwan's atmosphere. Because the relative sampling errors of HNO3 and HNO2 gases depend mainly on their concentrations in the atmosphere as well as concentrations caused by interfering species, the risk for high error while measuring low HNO2 concentrations by only one Na2CO3 denuder is also possible. As a result, it is suggested that pretests are necessary to evaluate possible sources and degrees of sampling errors before field sampling of HNO2 and HNO3 gases. The sampling errors of these two gases can, therefore, be minimized with a better arrangement of the ADS.
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.
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.
Energy-effectiveness of nonthermal plasma reactors for toluene vapor destruction
(2001-07-01)
Lin, CH
;
Bai, HL
;
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.
Field study, design, and catalyst cost of selective catalytic reduction process
(2001-08-01)
Bai, HL
;
Lee, SH
;
Lin, CH
;
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.
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.

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