Aerosole und ihre technische Bedeutung

Aerosols and Their Technical Significance Aerosols occur in many technical processes. For example, aerosols are formed to generate products of highly disperse solids in gas phase processes. Particle formation and growth in the aerosol state decisively determine the product properties by the size, shape, and structure of the particles. Undesired aerosol formation can also occur in technical processes. These undesired aerosols pollut process gases or products or increase the pollutant content of exhaust gases. If undesired aerosol formation cannot be avoided, efficient separation techniques have to be used. Efficient separators are also required to recover fine product particles from the gas phase. Moreover, aerosols, whether desired or undesired, have to be measured and characterized. This requires high performing measuring techniques. The paper outlines the technical significance of aerosols.     

Aerosol formation by heterogeneous nucleation in wet scrubbing processes

The phenomenon of aerosol formation is often watched in industrial wet scrubbing processes especially if strong acid gases are absorbed in aqueous solutions. Although the basic principles of aerosol formation are well known in general, there exist nearly no specific rules for the design of industrial processes in which aerosol formation can be expected. There are two reasons for the fragmentary knowledge concerning aerosol formation in wet scrubbing processes. Firstly, it is a very complex task to describe the formation and the growth of aerosols theoretically under typical conditions of industrial processes. Secondly, no reliable experimental data, especially for the validation of theoretical work, has been available to date. To bridge this gap, a semi-technical wet scrubbing plant has been developed and erected in which the formation and the growth of aerosols under realistic conditions can be studied and the characteristic aerosol parameters can be measured in situ. It is shown that HCl-aerosols are formed in a quench cooler for hot flue gases of about 200°C even at low HCl feed concentrations of about l000 mg m⁻³, but only in the presence of foreign nuclei. The aerosol droplets in the quench cooler grow up to 1–1.5 μm and can be enlarged in a direct-contact-cooling column up to about 2.5 μm. Furthermore, a strategy for aerosol evaporation is discussed.     

Aerosolbildung durch spontane Phasenübergänge bei Absorptions- und Kondensationsprozessen

Formation of aerosols by spontaneous condensation or desublimation in condensers or absorbers often causes serious problems in industrial processes. The fine aerosol particles, formed under special operating conditions, remain suspended in gases and are carried over into downstream stages or lead to high pollutant concentrations in the exhaust gas. The present paper describe under what conditions aerosols are formed. The characteristic behaviour of aerosols is discussed with the aid of experiments and computer simulation.     

Aerosolbildung bei der Absorption und Partialkondensation

Aerosol formation on absorption and partial condensation. The phenomenon of aerosol or mist formation on absorption and partial condensation has hardly been investigated but causes serious problems in the practice of industrial exhaust air purification, e.g. in the absorption of hydrogen chloride or on low-temperature condensation of solvent vapours. The mist droplets formed in these processes remain suspended in the gas phase and lead to unacceptably high pollutant concentrations in the exhaust air. This present study first surveys currently available knowledge and then goes on to explain under what thermodynamic boundary conditions aerosols are formed by certain substance systems. The author also applies known results relating to nucleation and growth mechanisms from aerosol physics to technical processes. It is seen that aerosols with very small droplet sizes, which are difficult to precipitate, are formed particularly during absorption processes.     

Abscheidung und Messung sehr feiner flüssiger und fester Partikeln in der chemischen Industrie

Separation and measurement of very fine liquid and solid particles in the chemical industry. In comparison to power stations, the total amounts of waste gases emitted by the chemical industry are fairly low. On the other hand, the complexity of the waste gases and their components is far higher. In the chemical industry we can therefore not be content with one overal concept for gas purification, but must use a multitude of individual solutions. These should be applied at source, i.e. to each separate production plant. To solve an aerosol separation problem successfully and economically, a knowledge of the composition, the fineness and the amount of aerosols is essential. Cascade impactors have proved to be the most suitable instruments for a fractionated measurement of solid and liquid particulates in the super and sub-micron size range. The results of these measurements make is possible to choose the right equipment and to calculate its performance. Very complex aerosols, e.g. aerosols which are composed both of liquid and solid particles, or of sticky particles, are likely to present the most difficult problems. This article deals with a small selection of cases by demonstrating the problems of separation and the different ways of solving them. It considers among others acid mists and oil mists as well as organic mists, together with very fine particulates from waste incineration plants.     

Vergleich von Verfahrenskonzepten zur Rauchgasreinigung bei der Rückstandsverbrennung

Comparison of process concepts for flue-gas clean-up in residue incineration. Depending on the residues being dealt with, industrial residue incinerators may produce flue gases having widely varying separation properties. This applies especially to particulate constituents. To determine unknown separation properties, to select suitable separation methods, and to predict the separating behaviour of the envisaged equipment, use can be made of pilot plants or very small test plants. Experiments have been carried out on two residue incinerators of different size using rotary-kiln technology in order to ascertain the suitability of various processes for separating particles from flue gases. For wet treatment a venturi scrubber and a scrubbing column were investigated, and for dry treatment the methods of electrostatic precipitation and cloth filtration. Various alternatives for dust separation have been derived from, and assessed on the basis of, the experimental results. Discussion of the experimental results shows that reliable prediction of the operating behaviour of industrial-scale units will require further basic investigations regarding dust separation and gas scrubbing. The task of enabling cleaned-gas values to be reliably predicted is beyond the development potential of individual manufacturers, individual operators, and individual university institutes. What is essential is the development of a joint concept under which the various tasks will be distributed and coordinated.     

Aerosol formation in gas-liquid contact devices—nucleation, growth and particle dynamics

In gas-liquid contact devices like absorbers, scrubbers, quench coolers or condensers, aerosols can be formed by spontaneous phase transitions, initiated by homogeneous or heterogeneous nucleation, if special process operation conditions lead to a metastable, i.e. a supersaturated state in the gas phase. Aerosol formation can impact severely the mass separation efficiency of gas-liquid contactors. This is demonstrated by experiments performed in semi-technical plants.The paper is aimed to identify strategies for understanding and describing the complex aerosol behaviour in gas-liquid contact devices.Operation conditions are identified under which supersaturation can arise, and the fundamentals of modelling aerosol formation and growth in gas-liquid contactors are discussed.The SENECA code developed by the authors allows to simulate aerosol formation and behaviour in contact devices as well as in multistage gas cleaning processes. Experimental results show that most of all important features of aerosol behaviour in flue gas cleaning and in condensation processes can be predicted with good accuracy by SENECA.     

SIMULATION OF AEROSOL FORMATION IN GAS-LIQUID CONTACT DEVICES

In gas-liquid contact devices like absorbers, quench coolers, or condensers, aerosols can be formed by spontaneous phase transitions, initiated by homogeneous or heterogeneous nucleation, if a supersaturated gas phase emerges due to simultaneous heat and mass transfer processes or chemical reactions. Typical examples are the absorption of acid gases, like HCl or SO₃, the condensation of solvents in the presence of inert gases, and the humidification of cold gases by hot liquids.

In this article the basic principles of aerosol formation in contact devices are briefly described. A strategy for modeling and simulation of aerosol formation and particle dynamics is discussed. Simulation results generated with the process tool AerCoDe for the countercurrent absorption of HCl and the humidification of air are presented.     

SIMULATION OF AEROSOL FORMATION IN GAS-LIQUID CONTACT DEVICES

In gas-liquid contact devices like absorbers, quench coolers, or condensers, aerosols can be formed by spontaneous phase transitions, initiated by homogeneous or heterogeneous nucleation, if a supersaturated gas phase emerges due to simultaneous heat and mass transfer processes or chemical reactions. Typical examples are the absorption of acid gases, like HCl or SO₃, the condensation of solvents in the presence of inert gases, and the humidification of cold gases by hot liquids.

In this article the basic principles of aerosol formation in contact devices are briefly described. A strategy for modeling and simulation of aerosol formation and particle dynamics is discussed. Simulation results generated with the process tool AerCoDe for the countercurrent absorption of HCl and the humidification of air are presented.     

催化燃烧技术处理石油化工企业含VOCs废气的工艺研究

石油化工企业工艺装置尾气及污水处理场逸散的废气均含有VOCs,其排放给区域空气质量和人体健康带来严重威胁。针对工艺尾气和污水处理场废气的特点,研究了催化燃烧工艺在处理这两类废气时工艺流程及控制方案。对工艺尾气采用碱洗—催化燃烧组合工艺,对污水处理场废气采用脱硫—均化—催化燃烧组合工艺。研究表明,针对上述两种废气,合理选择催化燃烧组合工艺及控制方案,能够有效处理废气中的VOCs组分,且处理后的气体烃类浓度均可达到国家有关标准。     

Ozonation of Odorous Air in Wastewater Treatment Plants

This study was conducted to evaluate the effects of gas scrubbing techniques for the elimination of odorous compounds in wastewater treatment plants. A pilot plant was installed and operated at Tuzla Wastewater Treatment Plant in Istanbul, Turkey for this purpose. Gas scrubbing experiments conducted using water, ozonated water, caustic and ozone injected caustic revealed different removal efficiencies. The highest and reliable hydrogen sulfide removal efficiencies were obtained in the ozone oxidation experiments.     

湿式氨法烟气脱硫中气溶胶的形成特性研究

气溶胶的形成是湿式氨法烟气脱硫过程存在的主要问题,通过测试分析氨法脱硫前后细颗粒的浓度与粒径分布、颗粒形态及其组成的变化特性,探讨了氨法脱硫中气溶胶的形成机理,并考察了影响气溶胶颗粒形成的主要因素。结果表明:氨水挥发逸出的气态NH3与烟气中SO2发生气相反应是气溶胶形成的主要原因,气溶胶含(NH4)2SO4、(NH4)2SO3、NH4HSO3等组分,粒径集中在0.07～0.70μm范围内,氨法脱硫系统对其难以有效脱除;氨水脱硫液温度及其浓度、烟气中SO2浓度、液气比等对气溶胶形成具有重要影响,形成量随氨水脱硫液及烟气中SO2浓度升高而增多,在保持NH3:SO2化学计量比不变的情况下,随液气比增大,气溶胶颗粒形成量减少。最后,对气溶胶颗粒的控制措施提出了建议。     

用于空气净化的双疏膜制备及应用进展

工业烟气中经常含有大量油性气溶胶,而传统过滤材料基本都是亲油性的,导致吸附污染严重。双疏型膜材料在面向高湿、含油性气溶胶的复杂烟气体系时,具有分离效率高、抗污染性强和易清洁等优点。本文系统总结了用于空气净化过程的双疏膜材料制备方法,通过对应用过程油性气溶胶与膜表面之间的微观作用分析,阐释了影响膜污染形成与控制的表界面作用机理。最后,对双疏膜材料在空气净化领域的发展前景做了分析和研讨。     

Komplementäre Dekarbonisierung der Erzeugung von Elektroenergie und Gewinnung synthetischer Kraftstoffe durch Erneuerbare Energien und fossile Energieträger

The concept of complementary decarbonisation of power generation from renewable energy sources and fossil fuels consists of their integration in one system. A technology network in the form of a CCU‐combined power plant is proposed for the energy generation from fossil fuels by a coal power plant with CO₂ recovery from the exhaust gases and a pyrolysis of natural gas to hydrogen and carbon as a basic technology. This technology network is completed by a reverse water‐gas shift reaction for the conversion of the CO₂ to CO, which will react with the hydrogen in a Fischer‐Tropsch synthesis for synthetic diesel. The recovered energy from the exothermic Fischer‐Tropsch synthesis meets the energy needs of CO₂ scrubbing. The carbon from the pyrolysis can replace other fossil carbon or can be sequestered.     

A review of chemical absorption of carbon dioxide for biogas upgrading

Significant attention has been given to biogas production, purification and upgrading as a renewable and clean fuel supplement. Biogas is a product of an anaerobic digestion process comprising methane, carbon dioxide, and trace amounts of other gases. Biogas purification removes trace gases in biogas for safe utilisation. Biogas upgrading produces methane-rich biogas by removing bulk carbon dioxide from the gas mixture. Several carbon dioxide removal techniques can be applied for biogas upgrading. However, chemical absorption of carbon dioxide for biogas upgrading is of special significance due to its operation at ambient or near ambient temperature and pressure, thus reducing energy consumption. This paper reviews the chemical absorption of carbon dioxide using amine scrubbing, caustic solvent scrubbing, and amino acid salt solution scrubbing. Each of these tech-niques for biogas upgrading is discussed. The paper concludes that an optimised implementation of the chemical absorption techniques for biogas upgrading requires further research.     

污水处理厂除臭装置设计实例

本文介绍城市污水处理厂致臭气体的化学吸收装置设计实例。采用硫酸溶液和碱性氧化剂溶液作吸收介质．恶臭气体氨气、硫化氢、甲硫醇通过三级吸收塔被吸收,气体达标后排放。     

Facing the Sulfuric Acid Aerosol Problem in Flue Gas Cleaning: Pilot Plant Experiments and Simulation

Experimental and simulation results of sulfuric acid aerosol formation during absorption of sulfuric trioxide in a wet flue gas scrubber (quench cooler) are presented. The complete characterization of the volatile aerosol with respect to number concentration and droplet size distribution is only possible by combining experimental and theoretical methods. Both experiments performed in a pilot plant and simulation results, reveal high number concentrations. A simulation tool predicts the formation of very small droplets that remain even submicron after coagulation in typical residence times of scrubbing systems and thus are difficult to precipitate.

Copyright 2013 American Association for Aerosol Research     

表面活性剂吸收法治理甲苯废气的中试实验

采用添加表面活性剂的填料塔来吸收治理甲苯废气，探讨了水-吸收剂的吸收机理，筛选出适合吸收甲苯的表面活性剂。考察了喷淋量、入口废气中的甲苯浓度和表面活性剂添加量这3个因素对甲苯去除率的影响。通过实验分析所得到的结果表明，对甲苯来说表面活性剂对去除率的影响最大，喷淋液体流量次之，入口浓度的影响最小。当条件满足时，最高去除效率可以达到90．6％(质量)，甲苯废气可以达标排放。     

Application of a FIGAERO ToF CIMS for on-line characterization of real-world fresh and aged particle emissions from buses

On-line chemical characterization of real-world particle emissions from 13 transit buses was performed using a chemical ionization mass spectrometer (CIMS) equipped with a filter inlet for gases and aerosols (FIGAERO). In addition to the fresh emissions the emissions were artificially aged using a potential aerosol mass reactor (Go:PAM). The buses studied were running on different fuel types (diesel, compressed natural gas, and rapeseed methyl ester) and exhaust after-treatment systems (selective catalytic reduction (SCR), exhaust gas recirculation (EGR), and a three-way catalyst). When evaluating emissions from passing exhaust plumes using the FIGAERO ToF-CIMS, two technical features were highlighted from this work, the use of high mass calibrants and the factor enhancement method to be able to filter important compounds from mass spectra including hundreds of species. Here, acetate was used as the reagent ion to enable detection of highly oxygenated species in the exhaust particle emissions with potential high toxicity and/or secondary organic aerosol formation (SOA) potential. The acetate ionization scheme accounted for 4% to 46% of the total emitted particulate mass through identification of 61 species in the spectra. For aged emission the various fuel types provided overlapping species that could explain up to 19% of the aged emissions. This is hypothesized to come from the oxidation of engine lubrication oil, thus a common source for various fuels which was further supported by laboratory measurements. Specific markers from the SCR technology, such as urea oxidation products and further byproducts from hydrolysis were identified and attributed to reactions of isocyanic acid.

Copyright © 2019 The Author(s). Published with license by Taylor &; Francis Group, LLC