Naßabscheidung von Feinstäuben und Aerosolen

Wet separation of fine dusts and aerosols. Wet scrubbers are frequently employed in the chemical industry for the separation of fine dusts and aerosols from gas streams. In order to choose the most suitable apparatus for a given purpose from the numerous scrubbers available, 35 wet scrubbers of differing construction were examined on full and pilot-scale regarding separating efficiency and operating behaviour. According to their flow conception, the scrubbers can be divided into five fundamental types, providing an almost automatic classification according to separating efficiency. The experimentally determined degrees of fractionation used as apparatus-specific parameters are discussed and a relation between separation efficiency and specific power consumption is presented. The particular requirements of such apparatus in the chemical industry are outlined with the aid of some operational examples.     

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.     

The Role of Minute Droplets in the Separation of Aerosols from Gases

Air pollution is caused to a large extent by submicrometre liquid and solid particles called 'aerosols'. Separation of aerosols from residual gases is a major problem today. Well-known equipment like the venturi scrubber cannot handle submicrometre aerosols successfully. However, enlargement of the aerosols by condensed water vapour and subsequent separation by inertia forces in an air jet containing minute water droplets can lead to an acceptable process with moderate energy consumption. The generation of minute water droplets and their role in the separation of aerosols from gases is described in this paper.     

Neue Wege bei der flotativen Aufbereitung und Abwasserreinigung in der chemischen Industrie

New approaches in flotational processing and waste water treatment in the chemical industry . Flotation has not yet become universally accepted in the chemical industry as a separation technique for the solids/liquid system. This article attempts to discover the reason why. It also presents possibilities enhancing the attractiveness of the flotation technique for recovery of materials and waste water purification in the chemical industry. A brief indication of the phenomena exploited by the flotation technique is followed by a discussion of chemical engineering aspects of this technique in ore and coal flotation and in mechanical waste water purification. A flotation cell without stirrer is presented, as has been designed specifically for the chemical industry. In conclusion, some flotation tasks performed with a laboratory version of this type of cell are presented and discussed. They show that the flotation technique can be a favourable alternative to classical separation techniques in many solids/liquid and liquid/liquid separation tasks, and should therefore be considered in future for appropriate separation problems (particle size ca. 100 μm, solids content ≤ 20 g/l).     

Gaswaschanlagen für saure und basische Abgase unter Berücksichtigung der neuen TA-Luft

Gas scrubbing plants for acid and caustic exhaust gases with consideration of the new TA-Luft . When designing gas scrubbing plants for acid and caustic exhaust gases from manufacturing plants of the chemical and pharmaceutical industry it is important to pay special attention to the aerosol formation which occurs in the exhaust gas systems and absorbers if the emission values should remain under the determined limit values stated in the Technical Instructions for air-pollution control (TA-Luft). The present study explains under what conditions aerosols can occur, how its formation can be prevented, and which gas scrubbers are appropriate for a combined gas-/aerosol separation. A comparison between two exhaust air scrubbing plants of several stages shows that a gas scrubbing plant for an exhaust air pick-up system with separation of the acid and caustic components as well as with source exhaust air pick-up of the highly charged gas flows is considerably more favourable with respect to price than the alternative scrubbing plant for an integrated exhaust air system in which large quantities of fine salt aerosols occur and have to be separated with high energy consumption.     

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.     

Removing 99.99998% of oil aerosols from compressed air and other gases

The oil and water particulates in compressed air and other gases are present as sprays, mists, fogs, smoke, fumes and vapors. The best method found to date for removing the oil and water contaminants from compressed air is a combination of direct impaction, inertial compaction, diffusion (Brownian motion) and coalescence, the latter being the main method of removing them. Baffles, centrifugal flow and flow directional changes of the air stream are helpful in causing coalescence and impingement. Flowing the air through porous media also is effective. The best way to coalesce liquid particulates from compressed air is to control the air flow and velocity as it passes through a fibrous bed that has predetermined porosity and which has minute strands and permanent electrostatic charges. An element designed with a prefilter with tiny pores in a cloth-like layer such as silicon-treated borosilicate enhances coalescing of the liquids. The air passageway between the random microfibers of inert strands located in the next layer through which air travels, and at right angles to the air stream, is very small. he strands must also be very fine (0.5 μ mean diameter). Because of the smaller open area and the smaller diameter of the fibers, this material is more effective as a coalescer of liquid droplets from 5 μ in size down to 0.01 μ in size. This structure also removes small solid particulates by diffusion (Brownian motion) and direct or inertial impaction. As long as air is flowing this design results in an almost continuous film of liquid on the outer layer. Ordinarily excessive air velocities in an element of this kind will cause subdivision of coalesced droplets. An outer cover of a material like a soft plastic, porous foam traps the coalesced film of liquid something like a sponge sleeve would “soak” liquids off a wetted outer cylinder wall. By gravity the liquids migrate down within the foam cover, dropping off the bottom of it and into the sump, out of the gas system.     

Neuere Erkenntnisse und Anwendungen bei der elektrischen Abscheidung von Stäuben und Nebeltröpfchen

New insights and applications in the electrostatic precipitation of dusts and mists. The introduction deals with the basic design, the mode of operation, and the fields of application of dry and wet type electrostatic precipitators. A few important parameters which influence the migration velocity are discussed. Contrary to what the classical theory states, greater passage widths lead to higher migration velocities of the particles and thus to a higher specific efficiency. The methods for conditioning flue gases of power stations are considered, as are the experimental results obtained in an industrial-scale SO₃ conditioning plant. A new field of application is seen in the steel industry through the use of a dry type electrostatic precipitator of special design. New plastic precipitator developments for the chemical industry are discussed, and the articles closes with an account of the efforts invested in developing hot gas precipitators for higher temperatures and pressures in connection with the introduction of new power station concepts.     

Formation of Metal Oxide Aerosols for Conditions of High Supersaturation

High concentrations of submicron particles of inorganic materials are found in the off-gases of various high-temperature processing units such as smelters and coal combustion systems. Metal oxide aerosols can form in combustion systems when hot gases that contain metal vapor species mix with oxygen-bearing gases and when these mixed gases are cooled. Experiments were conducted in an evaporation-oxidation furnace simulating the geometric configuration of a diffusion flame and using zinc as the test substance. The average metal oxide particle size and particle size distribution were measured for various experimental conditions. It can be shown that the conditions under which most metal oxides are formed in combustion gases correspond to extremely high degrees of supersaturation, with respect to the stable solid or liquid oxide phase. For these conditions, the homogeneous nucleation mechanism, utilizing the Becker-Doring theory, does not apply. An alternative approach is the “chemical nucleation” process, starting with an essentially irreversible chemical reaction in the gas phase to form a monomer of the oxide molecule and proceeding through steps of condensation and coalescence that are controlled by the diffusion rate and collision frequencies of the reacting species and the growing oxide particles. The fluid dynamics of the gases in the system are important in the kinetics of the process because they influence the concentrations of precursor species and particles and the lengths of diffusion paths. A chemical nucleation model is proposed to describe quantitatively the formation of zinc oxide particles as a function of process parameters such as partial pressure of metal vapor, oxidation temperature, and characteristic parameters of the gas flow system.     

Adsorbing Flotation of Copper Hydroxo Precipitates by Pyrite Fines

Abstract

The removal of copper ions from dilute aqueous solutions by the addition of mineral (pyrite) fine particles was undertaken by following an adsorbing (scavenging) flotation mechanism. Pyrite generally constitutes a residual or a solid industrial waste by-product in mixed sulfides processing plants. This paper suggests a further utilization for pyrite. The dissolved-air method was applied for solid/liquid separation when the mineral particles were in the fine (subsieve) size range. Various unconventional collectors for pyrite flotation were also examined.     

煤化工有机废渣萃取处理的研究进展

煤化工有机废渣是煤化工生产过程中产生的有毒有害的有机固体废弃物,有强烈的刺激性气味,对人类及环境都有巨大的危害,一般归属于危险废物。为了更加有效地处理这些废渣,在分析国内外煤化工有机废渣处理技术的基础上,对煤化工有机废渣的各种萃取处理技术——普通溶剂萃取分离法、超临界萃取分离法、溶剂油萃取分离法、离子液体溶剂萃取分离法、切换溶剂萃取法等进行了详细介绍,并比较了各方法的优缺点,对比分析了各类萃取溶剂、萃取工艺,以期为未来煤化工有机废渣的处理提供参考。     

Particle Bounce During Filtration of Particles on Wet and Dry Filters

This paper experimentally examines the bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (precake formation) by wet and dry fibrous filters. PSL and DEHS were the solid and liquid aerosols, respectively, used in four monodisperse sizes of 0.52, 0.83, 1.50, and 3.00 w m. Three different fibrous filters were used to filter the aerosol streams, and the efficiency of the filtration process for each aerosol type under dry and wet regimes was measured. It was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles, although this difference decreased in the smaller size fractions. The difference between solid and liquid efficiencies was found to be greatest in the 1.5 w m size range. As particle sizes of liquid/solid aerosols and filtration parameters were similar, this difference is most likely to be due to the effect of particle bounce and or immediate re-entrainment occurring inside the filter, with the greater efficiency of filtration of the liquid particles being due to their greater capacity to plastically/elastically deform in order to absorb the impact forces. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Therefore, the conclusion can be drawn that the either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture.     

Application of Ultrafiltration and Complexation to the Treatment of Low-Level Radioactive Effluents

Abstract

This paper addresses certain aspects of the design and development process aiming at reducing the radioactivity of liquid low-level waste streams (LLLW) to a very low level. Two types of membrane processes are being examined: ultrafiltration (UF) and seeded ultrafiltration (SUF). The UF membrane enables the removal of very fine particles of solid material from liquid radioactive waste. Only the particles with molecular weight above the cut-off of the UF membrane are retained. Much greater radioactivity removal may be achieved if the effluent is treated with high-molecular-weight ligands that form complexes with radioactive ions or small-sized radioactive molecules. This paper presents results of experiments consisting of decontamination of model radioactive effluents, simulated waste, and original LLLW by using several ligands for binding the radioactive ions of Cr, Co and Cs.     

Zukunftssichere und umweltneutrale Beseitigung von Industrieabfällen

Low environmental-impact disposal of solid, liquid and semisolid industrial residues . In many production plants, waste residues are formed which must be treated before their disposal so as to safeguard against environmental pollution. Industrial methods for the treatment and disposal of residues are so multifarious that each disposal problem requires careful consideration so as to ensure selection of the most suitable method, both from the ecological and economical point of view. Dumping grounds cannot accommodate all waste materials without endangering or disturbing the environment. For incineration, proven methods are available which can be modified to suit the particular waste problem at hand. After a suitable pretreatment every effort must be made to achieve a waste free from organic materials, an optimum utilization of heat and a flue gas purification without inadmissible loading of waste gases and waters. In recent years there has been a considerable increase in research and development activities in the area of thermal treatment of solid, liquid and semi-solid wastes. Worth mentioning are the high-temperature methods giving favourable emission values and methods for degasification and gasification directed at the recovery of important raw materials. Plants based on these principles are currently being operated on the pilot scale.     

Anwendung von Flockungsmitteln bei der mechanischen Flüssigkeitsabtrennung

Use of flocculants in the mechanical separation of liquids . The mechanical separation of liquids from turbid water or sewage sludges depends primarily on the size and density of the suspended particles. The process of separation by sedimentation, filtration, or centrifugation becomes increasingly difficult with decreasing size of the suspended particles and decreasing density difference between solid and liquid. The addition of flocculants in ppm amounts destabilizes the dispersion and flocculation sets in. Thus flocculants agglomerate suspended particles, improve the separation, and accelerate the overal separation process. The synthetic organic high polymers used in the treatment of municipal and industrial waste water are characterized by their chemical composition, their molar mass, and their charge density.     

Dampfstrahl-Vakuumpumpen in der Öl- und Fettindustrie Energieverbrauch und Abwassertechnik

Steam Ejectors in Oil and Fat Industry: Energy Consumption and Waste Water Technology Steam ejectors convey gases and vapours from distillation and deodorization columns via intermediate condensers to atmospheric pressure. Inspite of utmost care taken for the separation of liquid or solid particles at the point of suction, some of these particles are carried over into the vacuum lines and are deposited at the cold surfaces of the vacuum system. Measures to prevent this carry over by scrubbing, freezing or heating need additional energy. Minimizing such energy requirements is one of the tasks of the processing engineer, plant manufacturer and plant operator. In the presented work, the influences of suction pressure, intermediate pressure, boosting steam pressure, cooling water temperature and temperature of the surroundings were correlated. Different possibilities of connection are shown, which can be chosen depending upon local requirements in order to minimize environmental pollution.     

Electro-Acoustic Dewatering (EAD) a Novel Approach for Food Processing,and Recovery

Abstract

Separation of liquids from fine particle suspensions plays an important role in many industrial processes. In the past few years a number of technologies have been developed for the separation of slurries with coarse particle suspensions and intermediate particle sizes. However, separation of fine particles from their suspensions can be difficult and prohibitively costly.

Battelle has developed a solid/liquid separation technology that utilizes differences in electro-kinetic and acoustic properties to enhance the efficiency of conventional solid/liquid separation techniques such as vacuum filters or presses. This method can dewater colloidal stable suspensions better than conventional techniques. Typical applications of this technology to food processing will be presented. Mechanisms involved during separation will also be discussed.     

MADM-A New Multicomponent Aerosol Dynamics Model

A Multicomponent Aerosol Dynamics Model (MADM) capable of solving the condensation/evaporation equation of atmospheric aerosols is presented. Condensable species may be organic and/or inorganic. For the inorganic constituents the equilibrium model ISORROPIA is used to predict the physical state of the particle, i.e., whether the aerosol is liquid or solid. The mass transfer equations for the fluxes for solid atmospheric particles are developed. MADM is able to simulate aerosol deliquescence, crystallization, solid to solid phase transitions, and acidity transitions. Aerosols of different sizes can be in different physical states (solid, liquid, or partially solid and partially liquid). Novel constraints on the electroneutrality of the species flux between the gas and aerosol phases are presented for both liquid and solid aerosols. These constraints aid in the stability of the algorithm, yet still allow changes in aerosol acidity. As an example, MADM is used to predict the dynamic response of marine aerosol entering an urban area.     

Charakterisierung von Suspensionen nanoskaliger Partikel mittels Ultraschallspektroskopie und elektroakustischer Methoden

Technical control over dispersions with particles in the nanometer size realm should bring about a boost in innovations for some parts of industry. Requirements for the development of these new products is the accurate characterization of the various materials systems. A characterization should always include a determination of the particle size distribution, since it is coupled to the specific effects of these systems. Ultrasound measurement techniques and electroacoustics are two if the available techniques that allow determination of the size distribution and zeta potential of particles with dimensions up to 10 nanometers. A further fundamental advantage of the method is the possibility of carrying out measurements in high‐concentration materials systems. This report describes ultrasound spectroscopy for the measurement of fine‐ and very‐fine‐dispersion particles, and the known theoretical concepts for the interpretation of spectra. In addition, experiences in the use of currently available measurement techniques are presented.     

Highly selective synthesis of propylene glycol ether from methanol and propylene oxide catalyzed by basic ionic liquid

BACKGROUND: Propylene glycol ether is expected to be a safe substitute for toxic ethylene glycol ether usually used in industry owing to its negligible toxicity. Although catalysis of solid acids or bases for the synthesis of the ether can avoid separation of catalysts, liquid waste treatment and corrosion problems, it suffers from drawbacks, e.g. lower activity and selectivity to target product, high reaction pressure and temperature. In order to solve these problems, a basic ionic liquid, namely choline hydroxide was prepared and used as a catalyst for synthesis of the ether via atom‐economy reaction from propylene oxide and methanol. RESULTS: The ionic liquid showed excellent catalytic performance exhibiting 95.4% conversion of propylene oxide (PO) and 94.6% selectivity to 1‐methoxy‐2‐propanol. It is also an effective catalyst for the reaction of PO with other primary alcohols to yield corresponding ethers. In addition this catalyst can be recovered and reused. CONCLUSION: The high activity and selectivity can probably be ascribed to its basicity and/or the strong polarity and electrostatic field of the reaction medium caused by the ionic liquid. These findings are very rare in synthesis of propylene glycol ether to our knowledge. Copyright © 2010 Society of Chemical Industry