基于低温等离子体协同催化脱除氮氧化物和碳烟颗粒的研究

文章介绍了等离子体净化柴油机尾气技术的机理和研究状况。研究表明电晕放电和介质阻挡放电等离子体净化柴油机尾气有着能耗过高的缺陷,在应用中不得不结合催化剂同时使用。由于等离子体放电能够产生大量的自由基,能够使柴油机颗粒物PM在较低的排气温度下得到氧化燃烧。同时等离子体常与选择性催化还原技术相结合,作为辅助手段以提升系统去除NOX的效率和提高其选择性[1]。研究发现等离子体协同催化脱除氮氧化物和PM技术对解决柴油车尾气污染问题有着重要的意义。     

柴油车尾气颗粒物净化研究进展

柴油车尾气颗粒物是大气污染物来源之一,尾气颗粒物的净化是后处理的重要组成部分,且技术发展较快。综述了柴油机尾气颗粒物的组成以及柴油机尾气颗粒物的净化方法,包括微粒过滤捕集技术、折叠滤筒、尾气洗涤净化技术、低温等离子体协同催化净化技术、微型旋转超重力机净化技术等。各种技术都有其优势和不足,需要根据柴油车功率和应用环境选择适宜的净化技术和设备,把尾气预处理与深度净化相结合,把颗粒物净化技术与脱除CO、NO_x、碳氢技术协同应用,不影响发动机性能且无安全隐患。     

船舶尾气污染物排放控制研究进展

船舶柴油机排放的SO_x、NO_x、颗粒物(PM)等尾气污染物给人类生活环境和身体健康带来很大危害,对港口城市而言,这一情况更加严重。随着人们对环保的重视,各项环保法规越来越严格,船舶尾气污染物的排放控制也受到更多关注。本文对现有的船舶尾气控制技术进行了梳理,包括机前处理、机内净化以及后处理技术,提出单一后处理技术有望为近期提供更好的解决方案,其中,脱硫塔、选择性催化还原技术(SCR)和颗粒捕集技术(DPF)分别是比较有前景的应对SO_x、NO_x和PM的单一后处理技术。通过分析SO_x、NO_x、PM的不同后处理技术,认为将脱硫、脱硝和除颗粒物结合的一体化处理技术从长远来看是一个主要方向。一体化系统的研究重点可能包括开发新型耐硫、适应低温的催化剂,细颗粒物去除,优化工艺流程,简便和可靠的运行操作以及可接受的空间和费用要求等。     

等离子体去除纳米颗粒物研究

采用活性氧化铝球为吸附剂,利用脉冲介质阻挡放电反应器对煤油燃烧产生的纳米颗粒物(PM)的去除进行了研究,探讨了不同处理方法、脉冲频率和放电电压对纳米PM去除效果的影响。结果表明:(1)煤油燃烧产生的PM粒径在15～150 nm左右;(2)放电结合吸附对纳米颗粒的去除率显著高于单独放电或单独吸附;(3)脉冲频率对纳米PM去除影响不大;(4)随着放电电压的增加纳米PM去除率增加。     

低温等离子体去除VOCs技术研究进展

低温等离子体技术因其高效的去除效率以及较低的运行成本，已被广泛应用于VOCs脱除工艺。首先介绍了低温等离子体去除挥发性有机物的工作原理，其次分析了低温等离子体去除挥发性有机物技术的影响因素，详细阐述反应器电极形状尺寸、放电间隙、气流速度、催化剂等因素对该技术脱除效率的影响作用，最后对低温等离子体技术的发展方向进行了展望。     

低温等离子体氧化技术在废水处理中的应用

低温等离子体氧化法是一种集光、电、化学氧化于一体的新型水处理技术,适用范围广、处理效果好,近年来备受关注。主要阐述了低温等离子体处理废水的基本原理,对现行研究使用的等离子体反应器进行了分类,介绍了低温等离子体技术的国内外研究现状,     

低温等离子体氧化技术在废水处理中的应用

低温等离子体氧化法是一种集光、电、化学氧化于一体的新型水处理技术,适用范围广、处理效果好,近年来备受关注.主要阐述了低温等离子体处理废水的基本原理,对现行研究使用的等离子体反应器进行了分类,介绍了低温等离子体技术的国内外研究现状,分析了催化剂在脉冲放电过程中的作用,并探讨了该技术在废水处理中存在的问题以及应用前景.     

温差对气液交叉流PM2.5去除效率影响

针对过程工业尾气PM2.5污染问题,提出以废气废水构建交叉流界面,利用高温工业废气与低温废水之间形成温差发生传热捕集尾气中PM2.5。研究含PM2.5高温工业废气横掠错排降膜阵列的传热传质,分析气液温差对PM2.5去除效率的影响,理论推导PM2.5去除效率表达式,结果表明PM2.5去除效率随气液温差增加而增大。对直径3mm的降膜阵列,气体Reynolds数为140的实例计算显示,气液温差由20oC增加至80oC时,单排降膜阵列PM2.5去除效率由0.33%提高至0.66%,200排降膜阵列去除效率由48.5%提高至73.2%,由350排液柱群组成的分离通道整体去除效率可达到90%。对高温工业尾气横掠降膜阵列进行实验验证,理论分析与实验结果吻合良好。     

废气治理低温等离子体反应器的研究进展

低温等离子体技术用于废气治理成为近年来的研究热点,而低温等离子体反应器的研制正是其重要内容。本文详细介绍了用于废气治理的各种电晕放电反应器、介质阻挡放电反应器以及等离子体-催化反应器的结构特点和放电特性,综合比较了上述反应器在能量效率、降解产物的选择性和工业应用等方面的特点,并提出了今后的研究方向。     

低温等离子体技术用于废水处理的研究进展

低温等离子体水处理技术是一种集活性自由基氧化、臭氧氧化、紫外光辐射、冲击波等效应与一体的新型高级氧化技术,由于其环境友好以及卓越的氧化能力,该技术被称为是最具有前景的高级氧化技术之一。在介绍了具有代表性的等离子体水处理技术,重点归纳并讨论了协同催化氧化以及放电电压、工作气体、初始浓度、p H、电导率、处理时间等特征工艺参数对低温等离子体水处理技术的影响,探讨了不同等离体装置能量利用效率的评价方法,提出了该技术目前的不足及未来的发展方向。     

Advances in the Development of Filterless Soot Deposition Systems for the Continuous Removal of Diesel Particulate Matter

A model catalytic converter system has been developed to investigate and characterize novel catalyst structures for filterless diesel particulate matter deposition and oxidation in modern heavy duty vehicle diesel engine exhaust systems. The particulate traps are designed for low exhaust gas back pressures and to avoid the clogging effects observed in ceramic filters. In experiments under realistic flow conditions deposition efficiencies of up to 70% have been achieved for submicrometer particles in stacks of corrugated stainless steel foil with microsphere surface coating. The model catalytic converter system is also used to study the reaction kinetics of soot oxidation and volatilization by oxygen and nitrogen oxides under a wide range of reaction conditions, for real diesel engine soot, different model soot substances, and different types of converter surfaces.     

Advances in the development of filterless soot deposition systems for the continuous removal of diesel particulate matter

A model catalytic converter system has been developed to investigate and characterize novel catalyst structures for filterless diesel particulate matter deposition and oxidation in modern heavy duty vehicle diesel engine exhaust systems. The particulate traps are designed for low exhaust gas back pressures and to avoid the clogging effects observed in ceramic filters. In experiments under realistic flow conditions deposition efficiencies of up to 70% have been achieved for submicrometer particles in stacks of corrugated stainless steel foil with microsphere surface coating. The model catalytic converter system is also used to study the reaction kinetics of soot oxidation and volatilization by oxygen and nitrogen oxides under a wide range of reaction conditions, for real diesel engine soot, different model soot substances, and different types of converter surfaces.

     

Kinetics of catalyzed and non‐catalyzed soot oxidation with nitrogen dioxide under regeneration particle trap conditions

BACKGROUND: For compliance with the regulations on diesel particulate matter, car manufacturers have developed diesel particulate filters (DPF). These technologies require a regeneration method which oxidizes soot deposits in the filter. In diesel exhaust emissions there are two suitable oxidizing gases: oxygen and nitrogen dioxide. Nitrogen dioxide is much more active than O₂ and can directly attack the carbon surface. This work describes the kinetics of the oxidation of soot by NO₂ over a wide range of conditions relevant for DPF. RESULTS: The catalyzed and the non‐catalyzed oxidation of soot have been performed in a fixed‐bed reactor. The experimental results show that the overall oxidation process can be described by two additive parallel reactions: a direct C ? NO₂ reaction catalyzed by H₂O and a cooperative C ? NO₂ ? O₂ reaction catalyzed by the Pt/Al₂O₃ catalyst. The results obtained allow to propose the following kinetic law for the specific rates of the catalyzed and the non‐catalyzed oxidation of soot in the regeneration filter conditions: CONCLUSION: The kinetic parameters describing the oxidation rate of soot by NO₂ over a range of temperature and gas composition have been obtained. The extracted kinetics data are relevant for modeling the removal of trapping soot in automotive gas exhaust technology. Copyright © 2009 Society of Chemical Industry     

Distribution characteristics of exhaust gases and soot particles in a wall-flow ceramics filter

An inhomogeneous soot distribution in a diesel particulate filter may deteriorate its behavior and result in higher pressure drops and fuel consumption. This will cause mechanical stresses on the filter due to temperature gradients resulting from the non-uniformly burning of soot during regeneration. The purpose of this paper is to investigate the flow distribution of the exhaust gas entering into a diesel particulate filter, the turbulent motion of diesel soot particles in the inlet header, and their deposition and distribution in the front surface of a diesel particulate filter. A Lagranian continuous random walk (CRW) model is developed to simulate soot particulate motion, which considers a succession of uncorrelated random forcing and drift corrections. The effects of particle inertia, turbulent fluctuation, and lift on the particle motion and trajectory are analyzed. Correlations of the uniformity index of the exhaust gas and soot particles with the flow rate, soot loading, and inlet expansion angle are evaluated. The results show that there is a two-peak phenomenon in the soot distribution at the front entrance of the filter, which is comprised of a peak in the central area due to inertia and a second peak in the periphery owing to diffusion and recirculation action. Exhaust flow rates and the inlet expansion angle have a major influence on the flow uniformity and soot uniformity, while soot loading has a slightly smaller effect on soot uniformity.     

Chemical composition of diesel particulate matter and its control

In this review, we have systematically discussed diesel particulate composition and its formation, understanding of which is essential to design the effective catalyst compositions. The most commonly used after treatment strategies such as diesel oxidation catalysts, diesel particulate filters, and partial flow filters are described followed by chronological and category-wise discussions on various groups of reported soot oxidation catalysts. A detailed review is also presented on mechanistic and kinetics aspects of non-catalytic direct particulate matter (PM) or soot oxidation in air/O₂ and NO₂. Recent progress in catalyst development with a focus on the low-cost catalyst for diesel PM oxidation has been given more emphasis considering their renewed importance.     

Bench Scale Experiments of Diesel Soot Oxidation Using Pr0.7Sr0.2K0.1MnO3 Perovskite Type Catalyst Coated on Ceramic Foam Filters

Potassium and strontium substituted praseodymium manganate type perovskite catalyst coated on ceramic foam filters have been studied for diesel particulate removal. The synthesized catalyst coated filter pieces have been characterized by using XRD, SEM and TG analysis, whereas their catalytic activity towards soot oxidation was tested using a bench scale facility with real diesel engine exhaust. The catalyst coated filters decrease the soot oxidation T_initial value by 150 °C and T_final by 100 °C as compared to bare soot oxidation reaction, which can be considered as high activity under the actual conditions of diesel engine. The catalytic materials show good thermal stability, while their low cost will also add to their potential for practical applications. Although perovskites have been studied for laboratory evaluations of catalytic soot oxidation, present results further substantiate the possibility of using low-cost, supported, non-noble metal based catalysts for diesel exhaust emission control applications, especially for the cost-effective retrofitment of in-use vehicles with old generation engines.     

Emissions from large-scale medium-speed diesel engines: 2. Influence of fuel type and operating mode

This paper addresses gaseous emissions smoke (soot) and particulate matter in large-scale diesel engine exhaust. The test engine was a large-scale turbocharged, after-cooled mean speed ( 500 rpm) direct-injection diesel engine and the power per cylinder was about 1 MW. Emission measurements were carried out on burning heavy fuel (HFO) and light fuel (LFO) oils. The test modes for the investigation were a propulsion mode (marine application) and a generator mode (power plant application). Gaseous emissions were measured according to the IMO technical code, smoke (soot) emissions were determined optically and particulate matter (PM) was measured by gravimetric impactor designed for five size fractions. In comparison the emissions from HFO and LFO utilisations indicate slightly higher NO and CO emissions for HFO, while LFO gives clearly higher emissions of hydrocarbons (HC). Emissions of soot and CO appeared to correlate very well, being very high for both fuels throughout the propulsion mode and low load, otherwise being similar for both modes. PM emissions are more than three times higher with HFO than with LFO and appear to decrease with the load except for HFO during the generator mode where an increase of PM emissions with the load is seen. Some data on sampled particles is given.     

Examining the Relationship Between Black Carbon and Soot in Flames and Engine Exhaust

This article investigates the black carbon (BC) content of soot formed in premixed and diffusion flames and emitted by light duty gasoline and diesel vehicles. BC is measured photoacoustically and compared with particulate mass collected by filter and calculated from particle size distributions. The BC fraction of soot from rich premixed ethylene flames increases with height above the burner, but can remain well below unity in modestly sooting flames. The BC fraction produced by a propane diffusion flame soot generator (combustion aerosol standard, CAST) falls as the fuel is diluted with nitrogen, the principal means used to adjust the desired particle size. Thermally treating the soot to remove possible condensed semivolatile species does little to change these trends. Transmission electron microscopy (TEM) images show that despite low BC content, these particles display the characteristic fractal-like agglomerate morphology of soot. Particle mass spectra reveal polycyclic aromatic hydrocarbon (PAH) and fullerene fragments associated with low BC soot, which disappear as the BC fraction approaches unity. The results suggest that low BC content reflects immature solid soot that has not carbonized. Particulate matter (PM) measurements from current technology diesel and gasoline vehicles exhibit a high, >80% BC fraction. This is attributed to effective soot carbonization during the expansion and exhaust strokes of the engine, and to the substantial reductions of condensable hydrocarbons by catalytic aftertreatment. These results are discussed with respect to using light absorption-based instruments to monitor engine exhaust PM and using flame-generated soot for PM instrument calibration.     

Kinetics of catalyzed and non-catalyzed oxidation of soot from a diesel engine

To comply with the new regulations on particulate matter, car manufacturers more and more commonly use diesel particulate filters (DPF). The working of these systems needs to periodically burn soot that has been accumulated during the loading of the DPF. This paper describes the kinetics of the non-catalytic and catalytic oxidation of real diesel soot with oxygen. From these experiments, mechanisms for catalyzed and non-catalyzed soot oxidation have been proposed.     

Measurements of diesel soot oxidation kinetics in an isothermal flow reactor–catalytic effects using Pt based coatings

Despite the significant progress in soot oxidation studies, there is still high uncertainty regarding the rate expressions to model the reactions in diesel particulate filters (DPF). This uncertainty arises from inherent difficulties in sampling and measuring the reaction rate in a realistic way, as well as different properties of the examined soot. In this context, the scope of this study is the development of a novel experimental set-up capable of overcoming existing experimental difficulties. The developed set-up allows for real diesel soot oxidation studies in an isothermal flow reactor. The reaction of soot with oxygen and NO₂ is studied with synthetic gas and with real diesel exhaust and the reaction kinetics are derived for both bare and Pt-based catalyzed substrates by combining experimental and model results.