The Modern Problems of Electrostatics with Applications in Environment Protection

The common denominator of established industries owing success to electrostatics, involves small forces acting on micron and sub-micron particles. While such forces appear insignificant, they are enormous when compared to gravity acting on the same particles in air. Furthermore, designed electric fields can move them along any desired paths, without affecting the gaseous medium. Considering that the earth air is shared by its entire population, and that particulates present major health hazard, the properties of the electric forces put them in the forefront of effort to restore our air environment. The encouraging results of gaseous pollution abatement research in world laboratories, with corona induced oxidation and/or plasma chemical processes, cost wise, are not yet acceptable to industry. The Canadian industrial developments in minimizing particulate emissions is presented together with the limited research in gaseous pollution abatement.

The technologies based on the principles of electrostatics that enable both modernizing certain equipment and developing new facilities acquired new functions in the environmental protection policy, due to implementation of the last scientific developments. In conception with equipment development, research and technology had a main contribution in developing high performance techniques for environmental protection alongside with modification of certain technologies meant for reducing noxious emissions. The aim of the paper is to present a series of elements favorably influencing development of “electrostatic precipitators”, ozone generators for water treatment and technological equipment to limit air, water and soil pollution. Including a series of results obtained in the Romanian research and industry for equipment manufacturing the paper could open new directions of interest offering industrially — tested solutions that plead for a generalization of positive results.

Some significant aspects on environmental state in Romania are presented together with priority goals included in the national environment action strategy and programs. In the context of the gradual association and integration of Romania in the European Union there are put in evidence the connection and harmonisation of these documents with the priorities of the European politics and of the international conventions for environment.

Electrostatics encompasses many areas of science and technology, and one of these areas, the field of environmental protection, makes liberal use of electrostatics within its framework. Information relevant to environmental protection needs to be distributed throughout the environmental community, and there are many groups throughout the world that serve that purpose. Often, the information is of such a nature that the electrostatics contribution is relegated to a few passing words. The Electrostatics Society of America provides a platform for the dissemination of a wide variety of electrostatics information including information relevant to the environmental community. A review of the ESA and the activity of its membership in environmental protection are presented in this paper.

Starting from the statistical data of the pollutants level from the Romanian Thermal Power Plants and from the legal norms referring to the pollution, the paper presents the ICEMENERG principal research and practical implementations in the fields of: fossil fuel cleaning; advanced steam generation technologies; flue gases SOx, NOx and dust reduction in order to respect the legal norms. Technological, economical and implementation aspects are discussed for every presented solution: low NOx burners, electrical and thermal energy co-generation, SOx and NOx reduction technologies, flue gases temperature reduction. The conclusions refers to the necessity of the rehabilitation and modernisation of electrical and thermal energy generation sector, measures for the reduction of the flue gases pollution and required founds for the technological transfer from the research field to the industrial field.

The thermo-electric power stations represent one of the important polluting sources in Romania. For this reason, the analysis of the parameters and of the operation processes of the electrostatic filters is of a theoretical and experimental interest. As to the theoretical analysis, the paper deals with: DC corona discharge between two conductors, a general case being taken into consideration; the characteristics of the corona discharge external area for bidimensional fields specific to the electrostatic filters from unit 3 of the power station Turceni; calculation of the current-voltage characteristic for a structure specific to the electrostatic filters used for the power station in Turceni. The experimental results refer to the current dependence on the voltage for the filters 1 and 2 from the thermo-electric power station, Turceni; the experimental results harmonize well enough with the theoretical ones.

Uncertainty is one of the greatest opponents of the scientists and engineers. Construction and operation of an equipment are usually based on well defined parameters which can be measured with adequate accuracy. Nevertheless, there are several situations, where the physical parameters of a process or a phenomenon are unknown or can not be determined accurately, therefore the correct use of these data is uncertain. Some examples are given, how and where can uncertainty be taken into consideration. In complicated industrial systems the determination of the prospective risk of a failure plays an important role in the design period. The complex relationship between the parts of the whole system makes the determination of the risk extremely uncertain. Furthermore, this complex relationship in case of operator controlled systems hinders operators in decision making. The decision can be assisted by the use of the risk assessment and failure diagnosis.

Electrostatic separation is extensively used for the selective sorting of granular mixtures, by means of the electric forces, which act on charged or polarized bodies. The roll-type separator with combined corona-electrostatic field has been proved to be the most advantageous solution when the purpose is to isolate conductive particles form nonconductive ones. The paper presents the contributions of the High Intensity Electric Fields Laboratory of the Technical University of Cluj-Napoca to the development of this technique for various applications in the recycling industry. A multitude of factors inffluence the efficiency of the separation process and the authors show how the results of numerical modeling guided the design of new installations and the optimization of their operating conditions. Laboratory and pilot plant brought evidence of the effectiveness of the proposed technology.

The cumulative effects of small and stable pollution sources became comparable with similar effects of the large pollution sources. A new vertical precipitator type with cylindrical collector is presented as an adequate mean for local treatment of the small pollution and as a new step in electrostatic precipitators miniaturization. The pseudo-electret filter novelty appears as a possible ultimate and miniature solution for the micron particles and small flow rates pollution abatement.

The International Atomic Energy Agency (IAEA) has been laying great emphasis on technologies, which are environmentally friendly, and would lead to sustainable development. Some areas of technology in which modern electrostatics (as electron beam accelerators) play an important role, and which have been supported by the IAEA, include: radiation based processes which minimize the use of toxic chemicals, processes for treatment of industrial and municipal wastes, electron beam treatment of combustion flue gases, and research for fusion energy. Countries from all regions of the world have participated in the development effort and the developing Member States have benefited by having access to advanced technologies developed by the developed Member States. Development of radiation based processes is always complimented by the establishment of suitable radiation safety regime where necessary. The paper gives a brief review of the research in radiation technology where the IAEA has played a supporting role.

The Electron Beam (EB) process removes SO₂ and NOx simultaneously from flue gas. The irradiation with accelerated electrons generates OH - radicals who oxidize SO₂ and NO_x into sulphuric acid (H₂SO₄) and nitric acid (HNO₃). These acids are neutralized by ammonia (NH₃) and a submicron aerosol consisting of ammonium sulphate and-nitrate is formed. The product is collected using filters and may be used as agricultural fertilizer. The main advantage of the process is, that besides removing SO₂ and NO_x in one process step, it yields a usable product.The technical feasibility of the process was proven in pilot plants in Japan, U.S.A., Germany and Poland. Meanwhile large-scale demonstration plants have been constructed in China and Japan. The application of the process for high sulphur conditions was investigated. Based upon the experimental data and an engineering study it was shown, that the process has the potential to be significantly less expensive, than current state of the art systems, depending upon the cost of the accelerator and the market value of the fertilizer by-product.

The paper concerns modelling of the effects produced when nitrogen plasma is injected into atmospheres containing nitric oxide with characteristics similar to flue gas. The basis of the model is that the nitrogen atoms generated by low voltage DC discharge emerge into a process gas while located initially within relatively small “pockets” of very hot gas. Experimental evidence for these pockets has been published elsewhere by Weinberg and co-workers. Following the concepts of N.N. Llepojevic the processes of diffusion of chemical species into and out of such pockets are computed, as are also the rates of competitive reactions in which N atoms react respectively with NO (removal) and with O₂ (generation) of NO. By these calculations profiles are predicted in concentrations of N, NO, and O₂ as functions of the temperature field around these pockets. The main findings of the investigations can be summarized as follows: the time during which the chemical reactions are accomplished for temperatures examined in this work was found to be roughly 10^-4s; higher plasma temperatures lead to shorter reaction times; diffusion processes take place at a much slower pace. A greater presence of oxygen enhances the effect of the build-up of nitric oxide inside the plasma pocket, since the N-radicals and O₂ combine to NO. The concentration of NO in the outside gas mixture has, with the present model, only very little influence on the production of nitric oxide inside the plasma pocket. Smaller plasma pockets lead to less formation of NO inside the pocket, and furthermore they tend to affect the outside gas to a larger extent than bigger pockets. The results are discussed in relation to experiments in which net removal/production of NO have been measured. Finally, suggestions are made on future adaptations of the model employed in the programme.

It is well known since several decades that an electrical discharge produces a plasma which may induce chemical reactions that otherwise would not occur. However, only few decades ago, scientists started to investigate the possibility to use the plasma generated by the electrical discharges for treating gaseous pollutants. The first pollutants to be considered were the nitrogen and sulfur oxides produced by the combustion of fossil fuels in the power stations. Later on, scientists investigated the applications of plasma generated by electrical discharges to the treatment of volatile organic compounds like organic solvents. Presently there is some interest in investigating the application of such plasmas to the treatment of pollutant in liquid phase. The catalyzing performances of the plasma depend on its characteristics, which depend on the type of discharge. The discharge itself depends on the shape of the electrodes, on the nature of the inter-electrode region, on the voltage and current waveforms used for producing the plasma. The paper will briefly report on the important steps of the researches in this field; it will propose some features, which should characterize the different plasmas and illustrate the different discharges investigated. Finally taking into account the most recent results, a tentative economic evaluation of the processes based on this technology will be discussed.

In this work, we report several new approaches of non-thermal plasma processing for the environment protection including dioxins (PCDDs+PCDFs) removal. Hybrid plasma reactors were tested for NOx removal, indoor pollutant and dioxin removal. The hybrid plasma system is the process which combines discharge plasma with catalyst or chemical scrubber. For the treatments of diesel exhaust and flue gas from an incinerator, it is demonstrated that the hybrid plasma systems with photocatalyst (TiO₂) or chemical scrubber significantly enhance the performance. Especially for the treatment of an incinerator flue gas, this combination is effective to reduce not only NOx emission but also dioxin emission, which causes serious damage to human health. Plasma reactor combined with TiO₂ catalyst is found to be effective in the cleaning of indoor air pollutants as well as NOx removal.

The emission of environmental pollutants such as SO₂ and NO_x into the atmosphere from heavy industrial activities, and in particular from fossil fuel burning in electricity production, is creating increasing concern. One of the three areas of the world most affected by the resultant acid rain lies in eastern and central Europe. A major contribution to this pollution comes from the burning of poor quality pit and brown coal with a high sulfur content. Many countries around the world have imposed industrial emission limits and this move has generated renewed interest in finding viable and cost effective solutions to SO₂ and NO_x pollution control. Conventional technologies - wet scrubbing for SO₂ and selective catalytic reduction for NO_x have reached their full potential. New technologies are being investigated for industrial scale commercial viability. One of them is the electron beam dry scrubbing process, which allows the simultaneous removal of SO₂ and NO_x from industrial flue gases. Institute of Nuclear Chemistry and Technology (INCT) started research on the electron beam flue gas treatment process ten years ago. A laboratory unit with a gas flow of 400 Nm³/h and a pilot plant with a gas flow 20 000 Nm³/h have been constructed. The laboratory unit uses a 20 kW, 2 MeV accelerator and two accelerators, 50 kW each, 700 keV are applied in the pilot plant. An industrial plant with a gas flow of 270 000 Nm³/h and 1200 kW beam power is now under development and construction. During the years of the research, double gas irradiation, non equal two stage energy delivery, high/low humidity and high/low SO₂ content have been investigated, which resulted in low dose requirements, and reduced electrical consumption. High removal efficiencies for SO₂ (up to 98%) and NO_x (up to 80%) have been demonstrated during the testing. Continuous operation of the pilot plant has been demonstrated as well. Agricultural tests performed by three independent institutions have proved full fertilizer applicability of the by-product. Industrial tests concerning the application of the by-product for NPK fertilizer production have been performed successfully. Economical and technical comparison with conventional technologies have demonstrated the competitiveness of this technology.

In the recent years the experience of successful solution of ecological problems using the radiation technologies based on powerful electron accelerators attracts more and more attention. The report presents the brief data of the industrial electron accelerators produced in the Budker Institute of Nuclear Physics and used for this application. The possibilities of cleaning the various gases from SO₂, H₂S, NO_x, etc., using the electron beam and stimulated corona discharge are described. The possibility of deactivation of the chemical warfare using the radiation technologies is considered. The report also describes the experience of operation of the industrial installation (based on the accelerators produced in BINP) for the cleaning of industrial wastewater from nekal. The results of the investigations of cleaning of municipal and industrial wastewater from other harmful additives, including the heavy metals, are given. The radiation technology permits to produce the enzymes immobilized on the stable carrier. The radiation-immobilized enzymes can be used for the ecologically pure lines for treatment of hides and leather, washing of raw wool, decomposition of organic wastes. The examples of accelerators’ usage in the ecologically pure production are given.

Many authors have investigated simultaneous reduction of SO₂ and NOx from flue gas stack emissions. Because of his high costs, this technology has been applied only in few countries (Japan, China, and Poland). Small countries, consumers of cheap combustibles, produce a great deal of atmospheric pollutants: SO₂ and NOx. For this reason there is a great interest for implementation of cheaper technologies, with same impact as electron beams processing has. The paper presents a series of experimental data for SO₂ and NOx removal of flue gas by electron beams, electric discharge. It also presents an economic study for an installation of simultaneous SO₂ and NOx removal pilot plant at a 550 MWe power plant (CET-SOUTH-Bucharest), with an electron beam device and processing capacity of about 10,000 Nm³/h and 10⁶ Nm³/h, respectively.

Ozone is widely used for water purification. Since it cannot be stored without decomposing it must be generated as required. The preferred methods of generation using the silent electric discharge are described as well as conditions required for maximizing the efficiency. Alternate methods of generation are discussed and two recent developments are reviewed. In the first the ozone generation takes place at an air-water interface through the novel use of an ac electric discharge from the water surface. The second describes an automated method for the accurate measurement of electric power dissipated in the silent electric discharge in ozone generators.

A summary is given about applications of ozone in water treatment. Advantageous and disadvantageous reactions of ozone are shown in potable water, surface water, contaminated ground water, cooling water, and industrial effluents and in leachate of landfills. Traditionally ozone is used for disinfection and removal of odour, smell, colour, iron and manganese in drinking water treatment, by what you can save flocculating chemicals, chlorine and activated carbon. Combinations with ozone increase the ratio of BOD/COD in a biological system. Selective degradation reactions are possible with ozone to remove for example surfactants and dyes.

The industry is facing new stricter environmental demands concerning the wastewater discharge into the environment. New methods for internal and external waste minimization and treatment has to be used in order to find economically feasible and environmentally friendly solutions. The complete mineralization of pollutants by chemical oxidation is rare due to the high consumption of oxidants. Usually partial oxidation is achieved. Ozonation or ozone combined to addition of hydrogen peroxide or UV radiation could be the method chosen for different types of wastewaters. Ozonation can be used as a pre-treatment step to enhance biodegradability or as a post-treatment method for removing residual refractory organic matter and toxicity before water is released to recipient water. We have compared the efficiencies and the costs of ozonation and related techniques for the treatment of paper, pulp and textile industry effluent.

Paper presents and comments a lot of experimental results obtained by a small ozone generator (50 gO₃/h) as for: ozone generation (gO₃/h); ozone concentration (g0₃/m³); ozone generation Efficiency (g0₃/kWh); concentrations of the nitrogen oxides: NO and NO₂ (mg/Nm³), etc, function to the applied voltage, gas flow, pressure, etc, for two cases: with air and with oxygen supply. Also are presents the conditions favoring occurrence of nitrogen oxides as well as occurrence of nitrates and nitrites subsequently to ozone treatment of certain surface waters containing ammonium.

A technique of electrical decontamination of soil using electrokinetic phenomenal has been developed. The method is based on the application of an electric field between electrodes placed in the ground. By this process it is possible either to remove pollutants contaminating the soil or to contain them to that they do not spread to the surrounding subsoil. The paper discuses the principal mechanisms, which can induce the motion of contaminants under the effect of the electric field: electromigration, electroosmosis and electrophoresis. The results of several experiments are presented. The rate of extracted pollutant increases as the electric field intensity increases and as pore thickness decreases. The importance of 3D morphological analysis of soil emphasized.

Mobility is the most important parameter in the separation of pollutant particles from surrounding fluids, especially air. The basic model of the mobility process reveals three key factors in determining mobility. These are particle size, particle charge, and fluid viscosity. The particle size is often increased by the attachment of neutral particles. The charge magnitude ranges from zero up to a limit determined by the limiting electric field at the particle’s surface, which is turn depends on the fluid at the particle size. The effective viscosity of the fluid may be significantly altered if the fluid is rarefied may be significantly altered if the fluid is rarefied or conductive, or if the particle moves fast enough to generated compressibility or inertial effects in the fluid. The interaction of these influences is examined for particles in air with a size ranging from atomic to macroscopic.

Conventional hydrodynamic nozzle produces rather large size of droplets (200~400um) in order to get reasonable inertia force from a nozzle. Since the insects live on the back of leaves and stems the crop itself must be completely covered by the excess amount of pesticide. The residual pesticide drips down to ground causing the contamination of soil and finally goes into underground water. Electrostatic pesticide spraying might be one of the most promising method to solve the problem described above. The electrostatic force could act as a driving force for disintegration of liquid and produces uniform fine droplets. The finer charged droplets are driven by electrostatic force to plant, that is several 10 times greater than gravitational force. These charged droplets are transported toward the plant by following the electrostatic field lines even to the backside of leaves. Some field tests indicated that half rate of treatment with electrostatic method could produce equivalent effect in insect and disease control of plant. Thus, over spraying to plant could be avoided with electrostatic spraying.

Paper presents an electrostatic crop spraying with rotary atomizers which has been used to apply pesticides; comments the results obtained of a three year period to different crops and with different pesticides. The aim of the work was to render evident the advantages of both electrostatic spraying and ultra low volume spraying carried out by help of land equipment as compared to classical methods.

The use of charged liquid aerosols (CLA) is perspective method for improving of existed technologies and design of new effective ones. It is mentioned that among the traditional technological processes (electropainting, electroseparation, electrostatic purification of exhausted gases, electrostatic pesticide spraying, disinfecting and disinsecting of premises etc.) last time the charged liquid aerosols are paid more attention to due to appearance of real possibilities for solution of ecological problems by CLA use - reduction of environment pollution, improvement of working conditions in highly dusted and smoked industrial halls, improvement of process of fuel combustion with low NO_x and SO_x generation. It is shown that the most important part of the designed electroaerosol technologies is the use of the effective methods of liquid, in particular water, charged aerosols. The results of investigations of electrostatic sprayers based on the new methods of liquid film spraying and charging in external electric field are presented. The basis criteria which determine the charged aerosol effective generation are determined, the numerical programs for calculation of electrostatic sprayers with verified functional parameters are developed, electrostatic sprayers with pneumatic and pneumocavitative spraying of liquid film in electric field are designed. The results of practical use of designed electroaerosol technologies and electrostatic sprayers for solution of different ecological problems are presented.