Discharge Plasma Supported Mariculture and Lignite Waste for NOx Cleaning in Biodiesel Exhaust : Direct and Indirect Methods

Abstract

One major aspect of environmental pollution affecting human life and climate is air pollution. The harmful pollutants in the air include mostly hydrocarbons, carbon monoxide, carbon dioxide, nitrogen oxides as well as soot and other particulate matter. These pollutants result in several damaging effects on environment and living beings which include acid rain, photochemical smog, global warming and various health hazards in human beings even cancer. Major contribution of these pollutants is from man-made sources such as industrial and automotive emissions that employ fossil fuels. In our country, diesel constitutes more than 40% of the fossil fuel consumption. Studies show that diesel engine emissions contribute to 80% of nitrogen oxides amongst other air pollutants. In the context of stringent emission regulations being implemented all over the world, exhaust emission control, in general and nitrogen oxide emission in particular, is gaining significant importance. A review of recent literature indicates the significance and popularity of electrical discharge based non thermal plasma for exhaust cleaning applications in general, and NOx cleaning in particular. While the existing pre-combustion and catalyst based post-combustion nitrogen oxides (NOx) abatement techniques have inherent disadvantages owing to short shelf life, saturated engine modifications, cost concerns etc., the electrical discharge based non- thermal plasma techniques offer certain advantages in terms of cost and life factors. Several non-thermal plasma techniques viz., pulsed plasma, surface plasma, dielectric barrier discharge plasma etc., have been studied under different laboratory conditions. Interestingly, due to the high oxidizing environment that prevails in the discharge plasma zone, complete reduction of NOx by the plasma alone is becoming a challenging task. This has led the researchers to utilize additional processing techniques in cascade with discharge plasma. This additional gas cleaning technique may involve the use of adsorbents, catalysts or some other secondary treatment for eliminating the nitrogen oxides produced due to oxidizing reactions in the plasma chamber. One such additive can be an adsorbent, which can be commercially obtained or prepared from industrial wastes. In this thesis the adsorption properties of two industrial wastes were explored for the first time in conjunction with discharge plasma. The synergistic effect of plasma combined with an adsorbent shows promising results in NOx removal thus offering an effective solution to two environmental issues namely air pollution and open waste dumping. While the plasma, generally, refers to direct plasma treatment of exhaust, it can also be used for generation of ozone in a separate reactor which can subsequently be injected into the exhaust stream resulting in indirect plasma treatment. The current work focuses on both direct and indirect dielectric barrier discharge plasma treatment for NOx reduction in diesel engine exhaust cascaded with either oyster shells, a mariculture waste or lignite ash from lignite coal fired plant. Instead of conventional petro-diesel, biodiesel produced from the seeds of pongamia pinnata is used as the fuel. This biofuel, on one hand, causes considerable reduction in volatile organic compounds, particulate matter, soot, oil mist etc., but on the other hand may have higher concentrations of nitrogen oxides, an aspect that has motivated us to take up the research work envisaged in this thesis. It was observed in the laboratory environment that for a given power, both direct and indirect plasma treatments have resulted in NOx removal to the tune of 85 to 95% when cascaded with the adsorbents studied.