Made available in DSpace on 2016-06-02T19:55:43Z (GMT). No. of bitstreams: 1 TeseMCRF.pdf: 11090482 bytes, checksum: acd91fb03f2001e7f8897df596f44b7d (MD5) Previous issue date: 2005-05-24 / Universidade Federal de Minas Gerais / The removal of submicron particles from gaseous streams is becoming an increasingly important operation, both in industrial (nanotechnology) as well as in occupational (inhalation of particula te matter) applications. Among the equipments commonly employed for the removal of particula tes of the gaseous stream, the electrostatic precipitator, ESP, is the one capable of removing particles of such size with high efficiency. Furthermore, it has other advantages as the low pressure drop and the flexibility of working at higher temperatures. Therefore, the objective of this research was to evaluate the influence of operational and design parameters in the efficiency of particle removal of a plate-wire ESP operating in the removal of submicron particles. The precipitator was built in acrylic, with copper plates as collecting electrodes and stainless steel wires as discharge electrodes. The study was divided in two stages: the first studied the collection of PM2.5 (high risk particle matter), using alumina, with median diameter of 0.6 mm and maximum diameter of 2.5 mm as test powder, while the stage 2 focused the nanometric range, utilizing particles of sodium chloride, with diameters between 8 and 100 nm. In stage 1, the project parameters analyzed were duct length (L), diameter of the discharge electrodes (2r) and spacing between them (2c); the operational variables were the electric field (E) and the air velocity (v). Each variable was evaluated in two levels, whose values were Lne = 15 and 30 cm; 2r = 0.045 and 0.025 cm; 2c = 4 and 2 cm; E = 5 and 8 kV/cm and, finally, v = 0.5 and 1.0 m/s. The process performance was evaluated through the analysis of the global efficiency of removal of the particula te matter, obtained through isokinetic sampling. In stage 2, the project parameter analyzed were the duct length (Lne), the ratio s/2c and the distance between the collection plates (2s) and the operational variables were the air velocity (v) and current density (j). Each operation variable was evaluated in three levels, whose values were v = 0.125, 0.25 and 0.50 m/s and j = 1.8, 2.8 and 3.8 mA/m2. The project parameters were studied in two leve ls, Lne = 15 and 30 cm and 2s = 0.04 and 0.06 m. The process performance was evaluated through the analysis of the removal efficiency of the particulates obtained by particle counting, with the use of the Condensation Particle Counter 3007, from TSI. It was observed that the precipitator possesses high collection efficiency, even in the nanometric size range, were efficiencies larger than 99% were obtained, depending on the used configuration. As expected, the increase in air velocity, as well as the decrease of the collecting plate length and of the generated current caused a decrease in the efficiency. Conversely, larger spacing between plates resulted in an increment in the efficiency, phenomenon also observed by some other researchers for larger particles. The ratio s/2c did not show a clear tendency in particle removal. When compared to models from the literature, the one that offered the better adjustment to the experimental data was the classic Deutsch model when used with a drag coefficient given by a modified version of the Li and Wang (2003a e b) equation. / A remoção de partículas submicrométricas de correntes gasosas tem-se constituído numa operação cada vez mais importante, tanto em aplicações industriais (nanotecnologia) quanto ocupacionais (inalação de material particulado). Dentre os equipamentos comumente empregados para a remoção de material particulado da corrente gasosa, o precipitador eletrostático é o que se apresenta mais apto a remover partículas de tal tamanho com alta eficiência. Desse modo, o objetivo desta pesquisa foi avaliar a influência dos parâmetros de operação e de projeto na eficiência de remoção de um precipitador eletrostático do tipo placa-fio, operando na remoção de partículas sub e nanométricas. O precipitador foi construído em acrílico e possui placas coletoras de cobre e eletrodos de descarga de aço inox. O estudo foi dividido em duas etapas: a primeira estudou a coleta de PM2,5 (material inalável de alto risco), utilizando alumina, com diâmetro mediano de 0,6 mm e diâmetro máximo de 2,5 mm, enquanto a etapa 2 focou a faixa nanométrica, utilizando partículas de cloreto de sódio, com diâmetros entre 8 e 100 nm. Na etapa 1, os parâmetros de projeto analisados foram comprimento do duto (Lne), diâmetro dos eletrodos de descarga (2r) e espaçamento entre os mesmos (2c) e as variáveis de operação foram o campo elétrico (E) e a velocidade de escoamento do ar (v). Cada variável foi avaliada em dois níveis, cujos valores foram Lne = 15 e 30 cm; 2r = 0,045 e 0,025 cm; 2c = 4 e 2 cm; E = 5 e 8 kV/cm e, finalmente, v = 0,5 e 1,0 m/s. O desempenho do processo foi avaliado através da análise da eficiência global de remoção do material particulado, obtida através de amostragem isocinética. Na etapa 2, os parâmetros de projeto analisados foram L, relação s/2c e distância entre as placas de coleta (2s) e as variáveis de operação foram v e densidade de corrente (j). Cada variável de operação foi avaliada em três níveis, cujos valores são v = 0,125, 0,25 e 0,50 m/s e jne = 1,8, 2,8 e 3,8 mA/m2. Já os parâmetros de projeto foram estudados em dois níveis, Lne = 15 e 30 cm e 2s = 0,04 e 0,06 m. O desempenho do processo foi avaliado através da análise da eficiência de remoção do material particulado, obtida através da contagem de partículas. Observou-se que o precipitador possui grande capacidade de coletar partículas até mesmo na faixa nanométrica, obtendo eficiências para alguns casos maiores que 99%, dependendo da configuração utilizada. Como esperado, o aumento da velocidade do gás, bem como a diminuição do comprimento das placas coletoras e da corrente gerada, causaram uma diminuição da eficiência. Em contrapartida, o maior espaçamento entre as placas acarretou um incremento na eficiência, fenômeno também observado por alguns outros pesquisadores para partículas maiores. A relação s/2c não apresentou uma tendência clara na remoção do material particulado. Quando avaliados os modelos presentes na literatura, aquele que melhor se ajustou aos dados experimentais foi o modelo clássico de Deutsch, quando utilizado o coeficiente de arraste dado por uma versão modificada da equação de Li e Wang (2003a e b).

The removal of electrostatic precipitator (ESP) ash by solving the ash in water constitutes an environmental problem if heavy metals, such as cadmium, present in the ash remain in the outgoing effluent streams. The ESP ash solution is alkaline, meaning cadmium is present as the insoluble salt Cd(OH)2, cadmium hydroxide. The aim of this work is to reduce the amount of cadmium released to water recipients from pulp mills by investigating different precipitation mechanisms in ESP ash/ water solutions. Solutions with different concentrations, pH and added process chemicals were prepared and the Cd content in the supernatant measured with atomic absorption spectroscopy. The Cd removal through precipitation reached the highest values when ESP ash concentrations were >150 g/l, pH was above 11.5 and the ash solution was allowed to precipitate for 24h. The addition of polymers was found to reduce needed precipitation time. The effect of concentration on Cd removal could be caused by maximum solubility for the Cd2+ ion being reached at roughly 100 g/l ash concentration. The need for higher pH values could be caused by Cd forming complex ions with other solutions at pH<11 and theoretical maximum Cd2+ ion concentration decreasing from pH 10 to pH 13. / Uttag av elfilteraska där askan löses i vatten utgör ett miljöproblem om tungmetaller i elfilteraskan, till exempel kadmium, finns kvar i det avloppsvatten som lämnar systemet. Elfilteraskan är basisk, vilket innebär att kadmium bildar det olösliga saltet kadmiumhydroxid, Cd(OH)2 när askan löses i vatten. Målet med detta examensarbete är att reducera mängden kadmium som släpps ut till vattenrecipienter från massabruk genom att undersöka fällningsmekanismer i vattenlösningar av elfilteraska. Lösningar med olika koncentration, pH och fällningstid förbereddes och kadmiumhalten i klarfasen mättes genom atomabsorptionsspektroskopi. Avskiljningsgraden för kadmium var som störst när koncentrationen >150 g/l, pH var över 11,5 och fällningstiden för hydroxidsalterna var 24h. Polymertillsats visades reducera nödvändig fällningstid. Koncentrationens påverkan på kadmiumhalt i klarfasen kan tänkas bero på att maximal koncentration för Cd2+-jonen nås vid ungefär 100 g/l koncentration. Högre pH-värden kan leda till att komplexbildning med andra joner i asklösningen, vilket sker vid pH<11, undviks. Den teoretiskt maximala lösligheten för Cd2+-jonen minskar från pH 10 till pH 13, vilket kan förbättra avskiljningsgraden.

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With the increase in population and industrial growth, the need for power has increased manifold. A major share of India’s power generation is coal-based generation. Thermal power generation through coal combustion produces minute particles of ash that causes serious environmental problems. Most of the thermal power stations in India use bituminous coal and produce large quantities of fly ash. Fly ash is produced primarily by thermal power plants and, to a lesser extent, by cement and steel plants and railways. This poses problems in the form of land use, health hazards, and environmental dangers. Today the fly ash from thermal power plants is utilized to make cement. Cement industry needs fly ash with more fine particles. If these fine particles (of diameter in micro-meter range) are left out to atmosphere, it will be easily breathed into lungs, creating health hazard to human as well as animal life. If properly collected, it forms a valuable by product. Hence collecting fly ash is important to reduce pollution and also to increase revenue. Even though there are many devices like cyclones, fabric filters etc. the Electrostatic Precipitator (ESP) is the most efficient device to capture the fly ash. It is at this juncture a need for such a simple ESP model was felt to facilitate prediction of the V-I characteristics of dust loaded precipitators, be it cement dust or fly ash. Given the fact that 99% of Indian ESPs are operated under DC energization and most of them are running inefficiently due to lack of proper diagnostic tools and also due to lack of interest to invest on an ESP. In such circumstances, the free availability of a simple model that combines the V-I curves with collection efficiency serves to improve the ESP performance in our Indian industries. In an ESP Voltage-Current (V-I) characteristics are used to diagnose any electrical problems occurring in it. Mathematical model of V-I characteristics under clean air and dust laden conditions will be helpful in diagnosing the ESP problems as well as in designing the ESP. The model will also indirectly reflect upon the collection efficiency of the ESP. The collection efficiency should be as high as possible not only to prevent pollution but also to collect maximum fly ash which is a valuable by-product. The modeling of collection efficiency will help the industries to design a new precipitator as well as to improve the performance the collection efficiency to meet the changing restrictions set by the government to reduce pollution. In this thesis a mathematical model of ESP based on Finite Difference Method is developed. The modeling is done in three sections. 1. Simulation of clean air V-I characteristics. 2. Simulation of dust laden V-I characteristics. 3. Simulation of collection efficiency. Simulation of clean air V-I characteristics is done by iteratively solving the Poisson’s equation and current continuity equation, using FDM in one quarter region of the ESP. Just by introducing the effect of particle charge into this solution the dust laden V-I characteristics are simulated. Finally, the collection efficiency is calculated using average charge density at the plates obtained from the above solution. The developed model is validated at first against published experimental and simulated data and then, with the data obtained through conduction of experiments, by the author, on commercial precipitators situated at a thermal power station and a cement plant, in India. The thesis discusses in detail these theoretical and experimental studies.

Master thesis deals with design of electrostatic precipitator for domestic wood-burning appliances. In the opening chapters, principles of electrostatic precipitation are described and a study of existing electrostatic precipitators for domestic combustion devices is made. In the practical part of the thesis, a mathematical model of electrostatic precipitator was created. Based on the mathematical model, electrostatic precipitator was designed and its performance parameters predicted.

New emission legislation regarding air pollution control, as instructed by the Department of Environmental Affairs (DEA) to Eskom Generation Power Stations, implies a particulate emission limit of 100 mg/Nm3 for all existing power stations by 2015 and 50 mg/Nm3 for all new and existing power stations by the year 2020. Some of Eskom’s power stations which are equipped with Electrostatic Precipitators (ESP’s) were not designed for this stringent legislation. It is also experienced that ESP’s and coal quality in Eskom have deteriorated over time, resulting in the performance of the ESP’s not meeting the legislative requirements. Eskom is in the process of introducing various ESP enhancement projects to improve performance and aligning the operating philosophy to comply with the more stringent particulate emission legislation. An ESP efficiency test was conducted at Lethabo Power Station to determine the current state of the plant and performance. The results of the test were compared with the original design base specifications to determine the relevant deficiencies which contribute to high emissions and poor ESP performance. It was aimed to develop an ESP simulation model and validate the outputs with the test data. This study endeavours to demonstrate the greater impact on ESP performance when the ESP is operated outside the design specification. It is further aimed to demonstrate that a solution to the problem of high emissions is not only contributed by the variables within the ESP itself. This study is a coal to stack evaluation considering the ESP variables and the upstream conditions of the ESP that form part of the entire process. The intention of this study is to demonstrate the importance of operating an ESP at the designed parameters and highlight the significance of proper maintenance. It was learned that before any ESP enhancement technology can be implemented, the ESP and upstream conditions must be in accordance with design specifications. The implementation of an ESP enhancement technology will have no merit or justification on a unit that is being operated outside of its design specifications. The results obtained from the ESP simulation model correlated well with the ESP efficiency test data. The expectation of the model to assist operators and engineers to operate ESP’s according to the designer’s specifications was conceded. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

New emission legislation regarding air pollution control, as instructed by the Department of Environmental Affairs (DEA) to Eskom Generation Power Stations, implies a particulate emission limit of 100 mg/Nm3 for all existing power stations by 2015 and 50 mg/Nm3 for all new and existing power stations by the year 2020. Some of Eskom’s power stations which are equipped with Electrostatic Precipitators (ESP’s) were not designed for this stringent legislation. It is also experienced that ESP’s and coal quality in Eskom have deteriorated over time, resulting in the performance of the ESP’s not meeting the legislative requirements. Eskom is in the process of introducing various ESP enhancement projects to improve performance and aligning the operating philosophy to comply with the more stringent particulate emission legislation. An ESP efficiency test was conducted at Lethabo Power Station to determine the current state of the plant and performance. The results of the test were compared with the original design base specifications to determine the relevant deficiencies which contribute to high emissions and poor ESP performance. It was aimed to develop an ESP simulation model and validate the outputs with the test data. This study endeavours to demonstrate the greater impact on ESP performance when the ESP is operated outside the design specification. It is further aimed to demonstrate that a solution to the problem of high emissions is not only contributed by the variables within the ESP itself. This study is a coal to stack evaluation considering the ESP variables and the upstream conditions of the ESP that form part of the entire process. The intention of this study is to demonstrate the importance of operating an ESP at the designed parameters and highlight the significance of proper maintenance. It was learned that before any ESP enhancement technology can be implemented, the ESP and upstream conditions must be in accordance with design specifications. The implementation of an ESP enhancement technology will have no merit or justification on a unit that is being operated outside of its design specifications. The results obtained from the ESP simulation model correlated well with the ESP efficiency test data. The expectation of the model to assist operators and engineers to operate ESP’s according to the designer’s specifications was conceded. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

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