非平衡等离子体技术对有害气体污染物的降解研究进展

由于非平衡等离子体化学过程在增强氧化能力，促进分子离解以及加速化学反应等方面具有很高的效率，因此，近年来利用非平衡等离子技术对气体污染物的破坏分解研究受到了广泛的关注，本文简述了非平衡等离子体技术对气体污染物的降解原理，综述了国内外利用这一技术破坏各种气体污染物的最新进展，讨论了放电功率，停留时间，催化剂，化合物结构等因素对放电反应效率的影响，并展望了其应用前景。     

等离子体技术应用于气相污染物治理综述

近年来利用等离子体技术对气态污染物的氧化分解研究受到了广泛的关注.介绍了等离子体概念、分类及产生方法,简述了非平衡等离子体技术对气体污染物的降解原理,较全面地介绍了等离子体技术在脱硫、脱硝以及降解挥发性有机物(VOCs)等方面的研究.最后指出了今后等离子体处理废气的应用研究方向.     

直流电晕放电降解甲苯的特性研究

利用直流高压电晕产生的非平衡等离子体分解甲苯.考察了各种因素对甲苯降解效率的影响,并对降解机理进行分析.研究结果表明:放电时间的延长、放电电压的提高、适宜的相对湿度和较低甲苯的初始浓度都有利于提高甲苯的降解效率.     

非平衡放电等离子体治理有害气体

重点分析了常温常压下非平衡放电等离子体产生的条件及其物理和化学性能，综合评述了放电技术的理烟气中有害气体ＳＯ２，ＮＯｘ，ＣＯ２的机理和研究现状。     

直流电晕放电降解甲苯的特性研究

利用直流高压电晕产生的非平衡等离子体分解甲苯。考察了各种因素对甲苯降解效率的影响，并对降解机理进行分析。研究结果表明：放电时间的延长、放电电压的提高、适宜的相对湿度和较低甲苯的初始浓度都有利于提高甲苯的降解效率。     

齿轮-筒电极放电处理有机废气及电极优化

放电等离子体技术被广泛用来处理各类有机污染物,其中放电电极的结构是污染物处理效率的关键。通过实验分别研究了在搭载齿轮-筒电极和线-筒电极的等离子体气体处理器下处理甲苯和VOC的效率。此外,还模拟了齿轮-筒电极的放电间距、齿轮齿数、电压大小对于放电特性与效率的影响。结果表明,齿轮-筒电极处理甲苯的效率比线-筒电极具有优势,最高效率可相差8.3%。齿轮-筒电极在处理VOC时的效率也优于线-筒电极2%～5%。放电间距在8～10 mm左右、齿轮为20齿时的电子数密度最大。同时,放电所产生的电子数密度随着电压的增大而增大,但当电压超过-20 kV时增长缓慢。齿轮-筒电极处理有机废气的效率比线-筒电极有提升,此外,电极结构还有优化提升空间。     

非平衡等离子体诱导催化剂吸附单质汞

采用非平衡等离子体诱导γ-Al_2O_3催化剂吸附单质汞,分析了等离子体与催化剂之间的相互作用。结果表明,在放电区域填充催化剂和在气流中加入单质汞均可降低放电的起始放电电压,这是因为放电区域填充催化剂使气体空间放电转变成表面的微放电。催化剂表面可以被等离子放电直接活化,使本身不能吸附单质汞的催化剂产生很强的吸附单质汞的能力。在放电能量密度约为19 J·L-1时,等离子体诱导催化剂吸附单质汞的效率可达94.1%。O2对等离子体诱导催化剂吸附Hg0有促进作用,随着O2浓度的提高,吸附效率随之提高。当气流中含有5%O2时,单质汞的吸附效率可达到98.5%,这是因为气流中存在O2时,经放电生成的等离子体中含有活性氧物种O3和O等,这些活性物质因具有氧化单质汞的能力而增强了单质汞的吸附。此外,催化剂表面O3的分解过程也是强化单质汞的吸附的原因。     

低温等离子体法处理甲醛气体

报道用低温等离子体的方法去除甲醛气体,主要考察了电场强度、进口浓度及填料对于甲醛气体去除效率的影响。实验研究结果表明,随着电场强度的增加,进口浓度的降低和在反应器中加有填料都会提高甲醛气体的去除效率。低温等离子体方法去除甲醛气体的机理可分为2部分:电子与污染物分子的直接碰撞和电场产生的活性粒子与污染物分子之间发生的一系列化学反应。     

介质阻挡放电等离子体技术处理菲污染土壤

采用介质阻挡放电技术对菲污染土壤进行修复处理,研究了电源参数(电压、频率、占空比、放电间隙)对输入能量的影响,考察了电源参数、土壤参数、气体参数对处理效果的影响,并综合考虑处理效果、放电特性及能源利用等因素选取最佳参数以进行后续处理及机理研究。结果表明:在电源输入电压为110 V、脉冲频率为150 Hz、占空比为20%、放电间隙为1.5 cm、气体流速为0.6 L·min-1、初始浓度为200 mg·kg-1、土壤含水率为4%的条件下处理20 min后,DBD等离子体对菲污染土壤的降解率可达到82%,其输入功率为64 W,能源效率为0.04 mg·k J-1。     

低温等离子体氧化氨气影响因素及动力学研究

采用电晕放电低温等离子体处理模拟氨气恶臭气体,考察了输入功率、初始浓度、气体湿度、停留时间等因素对降解效果和能量效率的影响,同时对反应过程进行了动力学研究。研究表明,输入功率以及停留时间对氨气降解的影响是积极的,但能量效率随着两者的增加先增大后减小。氨气的降解率随着初始浓度的增加而降低,而能量效率随着输入功率的增加而增加。氨气降解率和能量效率均随着气体湿度的增加而增加,当气体湿度为45%时达到最大值,然而随着气体湿度的进一步增加,其降解率和能量效率反而降低。反应尾气中臭氧浓度随着输入功率的增加而不断升高,而氨气的存在却使臭氧浓度有不同程度的降低。对电晕放电低温等离子体处理NH3的反应动力学进行了分析,得到NH3的反应速率常数为kNH3=0.0707 m3/(W·h)。     

Data Analysis Procedures for the Ozone NAAQS Statistical Format

The Clear Air Act of 1970 established the authority to control hazardous air pollutants. Section 112 of the legislation requires the Administrator to publish, and from time to time revise, a list of hazardous air pollutants for which he intends to establish emission standards, and to establish emission standards for those pollutants. These national emission standards for hazardous air pollutants are commonly referred to as “NESHAP” standards. All of the NESHAP that have been promulgated as of April 1984 are summarized in the table which accompanies this article. Two types of references are included in the table. The first reference identifies the issue of the Federal Register in which the NESHAP is explained in detail. The second reference identifies the background information document (BID) which contains the technical and economic information developed to support the NESHAP.     

Air quality modeling of hazardous pollutants: current status and future directions

The current requirements and status of air quality modeling of hazardous pollutants are reviewed. Many applications require the ability to predict the local impacts from industrial sources or large roadways as needed for community health characterization and evaluating environmental justice concerns. Such local-scale modeling assessments can be performed by using Gaussian dispersion models. However, these models have a limited ability to handle chemical transformations. A new generation of Eulerian grid-based models is now capable of comprehensively treating transport and chemical transformations of air toxics. However, they typically have coarse spatial resolution, and their computational requirements increase dramatically with finer spatial resolution. The authors present and discuss possible advanced approaches that can combine the grid-based models with local-scale information.     

Photocatalytic elimination of indoor air biological and chemical pollution in realistic conditions

The photocatalytic elimination of microorganisms from indoor air in realistic conditions and the feasibility of simultaneous elimination of chemical contaminants have been studied at laboratory scale. Transparent polymeric monoliths have been coated with sol-gel TiO(2) films and used as photocatalyst to treat real indoor air in a laboratory-scale single-step annular photocatalytic reactor. The analytical techniques used to characterize the air quality and analyze the results of the photocatalytic tests were: colony counting, microscopy and PCR with subsequent sequencing for microbial quantification and identification; automated thermal desorption coupled to gas chromatography with mass spectrometry detection for chemical analysis. The first experiments performed proved that photocatalysis based on UVA-irradiated TiO(2) for the reduction of the concentration of bacteria in the air could compete with the conventional photolytic treatment with UVC radiation, more expensive and hazardous. Simultaneously to the disinfection, the concentration of volatile organic compounds was greatly reduced, which adds value to this technology for real applications. The fungal colony number was not apparently modified.     

Transmissometer Measurement of Participate Emissions from a Jet Engine Test Facility

The body of information presented in this paper is directed toward those individuals involved with handling hazardous materials, whether in actual use of such chemicals, or in monitoring atmospheric emissions. Although specifically relating experience in the design and testing of phosgene emission control equipment, it attempts to establish general guidelines for effectively dealing with emissions of hazardous materials. An approach for handling chemical pollutants having no established air quality emission standards is developed. The paper presents a technique for establishing process emissions at acceptably low levels to insure the health and safety of the general population as well as that of the process workers themselves. Methods, suitable for measuring phosgene at these low levels, have been investigated, and problems associated with such an investigation are discussed. While complete theoretical scrubber design criteria are beyond the scope of this paper, many of the "real world" problems which affected scrubber performance are presented. Finally, the practical aspects of process emissions control are illustrated by actual results from the system test.     

Formation and Removal Reactions of Hazardous Air Pollutants

Current regulatory policies for hazardous air pollutants (HAPs) target the sources of direct emissions. In addition to direct emissions, some of the aromatic, nitrogenated, and oxygenated HAPs can be formed in the atmosphere. Formaldehyde and acetaldehyde, in particular, are produced by almost every hydrocarbon photooxidation reaction. Estimates have been made that, in some urban areas, in situ formation contributes as much as 85 percent of the ambient levels of formaldehyde and 95 percent for acetaldehyde. Over 40 percent of the HAPs being regulated under Title III of the 1990 Clean Air Act Amendments have atmospheric lifetimes of less than one day. The transformation products of these HAPs with low atmospheric persistence are important for assessing risks to human health, especially for cases where the transformation products are more toxic than the HAP itself.     

用于臭氧分解的负载型双金属催化剂

研究了催化剂载体外形和活性成分对催化剂性能的影响和其他污染物的反应对室内空气造成的二次污染。通过XPS分析说明了反应过程中催化剂表面发生的化学变化及反应机理。最终论述了臭氧分解的重要性以及该催化剂的高活性和长寿命。     

Emission factors of air toxics from semiconductor manufacturing in Korea

The development of local, accurate emission factors is very important for the estimation of reliable national emissions and air quality management. For that, this study is performed for pollutants released to the atmosphere with source-specific emission tests from the semiconductor manufacturing industry. The semiconductor manufacturing industry is one of the major sources of air toxics or hazardous air pollutants (HAPs); thus, understanding the emission characteristics of the emission source is a very important factor in the development of a control strategy. However, in Korea, there is a general lack of information available on air emissions from the semiconductor industry. The major emission sources of air toxics examined from the semiconductor manufacturing industry were wet chemical stations, coating applications, gaseous operations, photolithography, and miscellaneous devices in the wafer fabrication and semiconductor packaging processes. In this study, analyses of emission characteristics, and the estimations of emission data and factors for air toxics, such as acids, bases, heavy metals, and volatile organic compounds from the semiconductor manufacturing process have been performed. The concentration of hydrogen chloride from the packaging process was the highest among all of the processes. In addition, the emission factor of total volatile organic compounds (TVOCs) for the packaging process was higher than that of the wafer fabrication process. Emission factors estimated in this study were compared with those of Taiwan for evaluation, and they were found to be of similar level in the case of TVOCs and fluorine compounds.     

Fiber Glass Fabric Filters for High Temperature Dust and Fume Control

Foliar markings on vegetation have proven a highly sensitive criterion for the presence of many air pollutants; proper evaluation of such effects can serve as a valuable and inexpensive tool for delineating an air pollution condition. Injury symptoms from fluoridt, sulfur dioxide, photochemical oxidants and other pollutants have been described and can be recognized by experienced observers. Field studies provide a valuable technique for appraising an air pollution problem when diagnosis is not confused by other factors. Careful inspection can avert difficulties arising in diagnosis where similar symptoms are produced by agents other than air pollutants. Several factors must be considered in appraising injury. These include a knowledge of the relative sensitivity of plant species to various pollutants, the syndrome of injury on a number of plants and species, and distribution and geographic relation of affected plants to the suspected source. Background information on cultural, environmental, disease and insect conditions which might be responsible for, or modify, foliar markings or chronic effects in question must also be understood. For some pollutants a chemical analysis of foliage and air may prove helpful. When these factors are studied, the presence, distribution and magnitude of an air pollution situation can be evaluated, thus providing a sensitive criterion of air quality.     

Emissions and risks associated with oxyfuel combustion: State of the science and critical data gaps

Oxyfuel combustion is a promising technology that may greatly facilitate carbon capture and sequestration by increasing the relative CO₂ content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants (e.g., acid gases, particulates, metals and organics) is not well studied. It is possible that combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry (e.g., by changing the valence state of metals). The data available for addressing these concerns are quite limited and are typically derived from laboratory-scale or pilot-scale tests. A review of the available data does suggest that oxyfuel combustion may decrease the air emissions of some pollutants (e.g., SO₂, NOx, particulates) whereas data for other pollutants are too limited to draw any conclusions. The oxy-combustion systems that have been proposed to date do not have a conventional “stack” and combustion flue gas is treated in such a way that solid or liquid waste streams are the major outputs. Use of this technology will therefore shift emissions from air to solid or liquid waste streams, but the risk management implications of this potential change have yet to be assessed. Truly useful studies of the potential effects of oxyfuel combustion on power plant emissions will require construction of integrated systems containing a combustion system coupled to a CO₂ processing unit. Sampling and analysis to assess potential emission effects should be an essential part of integrated system tests.

Implications: Oxyfuel combustion may facilitate carbon capture and sequestration by increasing the relative CO₂ content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants has not been well studied. Combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry. Therefore, before moving further with oxyfuel combustion as a new technology, it is appropriate to summarize the current understanding of potential emissions risk and to identify data gaps as priorities for future research.     

Emission Factors of Air Toxics from Semiconductor Manufacturing in Korea

Abstract

The development of local, accurate emission factors is very important for the estimation of reliable national emissions and air quality management. For that, this study is performed for pollutants released to the atmosphere with source-specific emission tests from the semiconductor manufacturing industry. The semiconductor manufacturing industry is one of the major sources of air toxics or hazardous air pollutants (HAPs); thus, understanding the emission characteristics of the emission source is a very important factor in the development of a control strategy. However, in Korea, there is a general lack of information available on air emissions from the semiconductor industry. The major emission sources of air toxics examined from the semiconductor manufacturing industry were wet chemical stations, coating applications, gaseous operations, photolithography, and miscellaneous devices in the wafer fabrication and semiconductor packaging processes. In this study, analyses of emission characteristics, and the estimations of emission data and factors for air toxics, such as acids, bases, heavy metals, and volatile organic compounds from the semiconductor manufacturing process have been performed. The concentration of hydrogen chloride from the packaging process was the highest among all of the processes. In addition, the emission factor of total volatile organic compounds (TVOCs) for the packaging process was higher than that of the wafer fabrication process. Emission factors estimated in this study were compared with those of Taiwan for evaluation, and they were found to be of similar level in the case of TVOCs and fluorine compounds.