New monograph "The aerodynamics of air treatment devices with a granular charge".
"Introduction" describes the structure of the monograph and the practical values of research results; it overviews the types and structure of granular charges used for air treatment and their physical characteristics that have an influence on the aerodynamic resistance of devices. It presents the methods and laboratory stands used for research on granular charging. It also discusses the aerodynamic processes occurring in industrial air treatment devices. The aerodynamic resistance of granular charging was investigated g by adsorptive, catalytic and biological air treatment methods. Attention is devoted to modelling aerodynamic processes in granular charging. Increasingly stringent environmental requirements encourage the investigations and introduction of new air treatment technologies and charges in devices.
Chapter 1 "Air Treatment Devices" describes air treatment devices that use granular charges, adsorbers, cycles and diagrams of such devices. It also analyses vertical, horizontal and ring-shaped structures of adsorbers.
This chapter describes the catalytic and complex sorbtive-catalytic air treatment devices and their structures as well as the operation principle of the biological air treatment method. It submits the classification of biological air treatment devices with granular charging and their operation principles and analyses membrane bio-reactors, bio-filters, trickling bio-filters and bio-scrubbers.
Chapter 2 "Granular Charging. The Types and Main Physical Characteristics of Granular Charging" presents general information about granular charges. The classification of a granular charge layer, and the equations for determining charge porosity are described. It presents the characteristics of silica gel, activated carbon and zeolite as their granules (diameter 3.32 mm) for the adsorption of gaseous pollutants. It has been determined that the surface area of cylinder-shaped activated carbon reaches 1-268 [m.sup.2]/[m.sup.3] and silica gel--1-140 [m.sup.2]/[m.sup.3].
This chapter analyses granular materials intended for pollutant catalysis, low aerodynamic resistance, resistance to erosion and the possibility of cleaning gas polluted air with suspended particles, when the concentration of suspended particles inside does not exceed 2 mg[m.sup.3].
The advantage of zeolites is their regular structure, a large internal specific surface (around 600-800 [m.sup.2]/g), pores of the same size and good thermal stability. A higher aerodynamic resistance of charging is obtained upon increasing charge humidity and reducing fraction. For a standard bio-filter, pressure losses may reach from 1 to 10 hPa.
Chapter 3 "The Structure of a Granulated Charge Layer" presents the overview literature of this type of charging and describes methods for determining the porosity and structure of a granulated charge layer, methods for research, which can be applied for investigating prospective high-temperature nuclear reactors with gas cooling. The chapter presents the X-ray-gram of ball-shaped granules, the diameter of which reaches 9.5 mm and the dependences of their porosity on a charge form and on the diameters of the granules and device. The advantage of zeolites is the regular structure, a large internal specific surface (around 600-800 m2/g), pores of the same size and good thermal stability. One of the major factors determining the selection of charging is its aerodynamic resistance, which is directly related to the porosity and humidity of charging. A higher aerodynamic resistance of charging is obtained upon increasing charge humidity and reducing fraction. For a standard bio-filter, pressure losses may reach from 1 to 10 hPa. This chapter analyses the structural peculiarities of air treatment bio-filters and presents related proposals aimed at reducing the aerodynamic resistance of these devices. Research produced the expressions of the coefficients of the porosity of granules having forms of balls, cylinders and irregular Raschig rings.
Chapter 4 "The Peculiarities of Gas Distribution in Devices with a Granular Charge Layer" describes various factors that have an influence on gas distribution within a granular charge layer. The chapter examines the ball-shaped granules of different sizes (0.25-8.7 mm) present in the devices of different dimensions (device diameters reaching 40-94 mm). As determined during investigations where the initial airflow rate supplied to the device is from 1-2 m/s, the disparity of gas distribution in the charge layer does not change, airflow rate is below 1 m/s the disparity of gas distribution starts growing. The impact of the non-isothermal layer on gas flow distribution is described. One-cassette and three-cassette devices were analysed. The chapter presents airflow distribution occurring after gas has flown through the granular layer of charging and a theoretical calculation of the distribution of gas flow passed through the charge.
This chapter also analyses the granules of high-porosity materials such as foam, cordierite and ceramics. The chapter presents and analyses five air treatment bio-filters of different structures created, designed and produced at the Department of Environmental Protection of Vilnius Gediminas Technical University. The performed research was aimed at determining the impact the proposed structural solutions of devices have on the treatment efficiency of the bio-filter. In order to extend charging durability and filter treatment efficiency, the conducted research employed not only bio-filters of different structures but also the charges of different origins, composed of wood chips, bark, zeolite granules and foam cube mixtures.
Chapter 5 "Modelling Aerodynamic Processes in Devices with a Granulated Charge Layer" describes modelling performed applying laboratory, pilot, semi-industrial and industrial devices. Treatment devices with thin layers (H<20-30d) are very widely applied by industrial enterprises producing nitrogen, meanwhile very high layers are those with H/d >>100. The mathematical models of research on aerodynamic and bio-filtration processes occurring in bio-filters are also presented and described. The aerodynamic resistance of charging is one of the key factors determining device productivity and treatment efficiency. Software package Phoenics 3.5 was selected for modelling aerodynamic processes in a bio-filter. This software allows evaluating the coefficient of porosity, which has the biggest influence on charge resistance. The charge coefficient of porosity depends on the geometry, form, fraction, layer height and other parameters of charging used for pollutant filtration. Modelling the processes of pollutant bio-destruction in low-capacity bio-filters employs various differential equations, which evaluate the processes of pollutant mass transport, reactions in a bio-film, the adsorption of pollutants, adsorption, the area of a specific surface of charging and a number of other factors. Therefore, the mathematical models--such as those of Monody kinetics and the kinetics of the first and zero degree of mass balance--form a the whole of the mass equilibrium equations, which describe the processes of bio-filtration in a bio-filter. The aerodynamic resistance of a bio-filter charged with the granulated charge of different origins obtained during modelling and presented in this chapter reached 1105 Pa. The aerodynamic resistance of charging after five layers of the charge is lower compared to the experimental results; however, this difference is not big and accounts for 10 %.
Chapter 6 "Aerodynamic Resistance of Industrial Granulated Charges" describes the aerodynamic resistance of adsorbents and catalysts used for air treatment, and pressure losses in round and cylindrical granular charges. The characteristics of the materials such as silica gel, non-platinum catalyst and activated carbon are presented. Pressures not only inside the device but also at the beginning, in the middle and at the end of the charge layer were identified. Gas flowing transition from laminar to turbulent (Re = 40-200) was investigated. Aerodynamic resistance in the cylinder-shaped granular charge composed of activated carbon at an airflow rate of 2.0 m/s can reach around 1200 Pa/m. The chapter analyses ceramic and metal Ranching rings. The dependences of the aerodynamic resistance of charging on the charge surface area were obtained using Eller's criterion. The surface area of silica gel balls with a diameter up to 3 mm reached 968 [m.sup.2]/[m.sup.3]. The surface area of the glass balls of the same diameter but higher porosity reached 1717 [m.sup.2]/[m.sup.3].
The charges of bio-filters have quite low aerodynamic resistance in the majority of cases reaching up to 200 Pa. The resistance of the charge composed of ceramic rings reached 1500 Pa. Bio-filter aerodynamic resistance of 1700 Pa/m was achieved upon using other materials such as a mixture of peat and bark. The lowest aerodynamic resistance was obtained using wood chips for biological treatment.
Chapter 7 "Aerodynamic Peculiarities in Devices with a Granulated Charge Layer" describes devices of different structures used by industries, presents the peculiarities of devices aimed at reducing the aerodynamic resistance of charging. It presents airflow directions in devices with an equalizing partition of gas flow and in devices with an extended air supply branch pipe, which initially diverts airflow in the flow-reverse direction. The chapter presents the directions of gas flows on the basis of the research methods. The distribution of airflow rate within the entire width of a cassette was discussed. To achieve the uniform distribution of airflow, diffusive systems were used in the device and cone-shaped diffusers were investigated. Subject to the type and length of a diffuser, the ratio of airflow rates W/[W.sub.Q] (when [W.sub.0] = 2.5 m/s) may vary from 0.7 to 1.4. It is recommended to use granulated charges composed of silica gel balls of 3-5 mm diameter in cassette filters.
The monograph is written for researchers, environmenta-lists and managers. It is also a valuable reference for doctoral and postgraduate studies.
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|Publication:||Journal of Environmental Engineering and Landscape Management|
|Date:||Jun 1, 2011|
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