Enhancing THC/NOX removal efficiency in diesel exhaust through catalyzing industrial wastes in the presence of electric discharge plasma /

Includes bibliographical references

PhD;2025;Electrical Engineering

The consistent rise in air quality index in various cities has risen a worldwide concern toward the critical situation of air pollution and climate change. Despite the implementation of stringent regulations, the usage of petroleum products in developing nations like India, has seen an increase of 4.6% in financial year 2023-24 and diesel contribution is nearly 40% of the total consumption. Given the reliance on diesel due to its high energy density, fuel efficiency, durability, reliability, and heavy-duty application, completely eliminating its use remains an impractical goal at present, necessitating continuous improvements in diesel exhaust cleaning processes. Concurrently, solid waste management poses a significant challenge for developing nations like India, with industrial waste constituting a substantial portion of the overall waste stream, necessitating urgent attention for sustainable management practices. Despite existing recycling methods, a considerable volume of solid waste remains untreated and ends up in landfills. This untreated disposal of waste can result in air pollution, water pollution, soil pollution and land pollution. By exploring non-conventional and innovative techniques, this research endeavors to mitigate environmental pollution and safeguard public health, offering a holistic approach to sustainable development. The mitigation of gaseous pollutants emitted from diesel engines can be achieved through control strategies implemented either at the engine design stage (pre-combustion) or via after treatment methods applied to the exhaust stream (post-combustion). While pre-combustion strategies are constrained by the extent of feasible engine design modifications, post-combustion techniques offer greater flexibility by leveraging advanced technologies such as plasma discharges, catalysts, and adsorbents. One such promising post-combustion approach involves the treatment of nitrogen oxides (NOX) and total hydrocarbons (THC) using non-thermal plasma (NTP) generated through dielectric barrier discharge (DBD). This technique has demonstrated significant potential at the laboratory scale for pollutant reduction. Non-thermal plasma operates at atmospheric pressure and ambient temperature, creating a highly oxidative environment consisting of energetic electrons, excited molecular species, ions, and radicals. When the exhaust interacts with this reactive plasma, nitrogen oxides undergo oxidation, leading to the formation of higher-order nitrogen oxides, while hydrocarbons are converted into intermediate oxidation products. However, to achieve effective pollutant removal, these oxidation byproducts necessitate subsequent treatment using adsorbents or catalytic materials. Recent advancements in plasma-assisted exhaust treatment have led to the emergence of plasma catalysis, wherein a plasma reactor is integrated with catalytic materials to enhance pollutant degradation. This synergistic process facilitates chemical reactions at significantly lower temperatures compared to conventional thermal catalysis, improving overall conversion efficiency. Studies on plasma catalysis for gas treatment applications have primarily relied on expensive, commercially available catalysts, often incorporating noble metals. However, the high cost and frequent replacement requirements due to catalyst deactivation and surface fouling present economic challenges for large-scale implementation. To address this issue, the exploration of industrial waste-derived catalysts has gained traction as a cost-effective and sustainable alternative. Utilizing waste materials as catalysts not only reduces the dependency on expensive noble metals but also contributes to environmental sustainability by repurposing industrial byproducts. The development of such low-cost, eco-friendly plasma-catalytic systems for NOX and THC abatement holds immense promise for practical diesel exhaust treatment applications, offering a viable solution for long-term emission control. In the current research work, which is mainly laboratory oriented, diesel exhaust is treated using a DBD reactor energized with a unipolar repetitive pulses at 80 Hz. The plasma reactor, housing different design of corona electrodes, is packed with industrial waste-derived pellets for plasma catalysis applications. Initially, the study is conducted to determine the optimal pellet diameter for the selected reactor configuration. Once the optimal size is identified, both the reactor geometry and pellet dimensions remain constant for subsequent experiments. To enhance THC abatement, eight novel composite waste materials are synthesized by combining two distinct individual wastes mixed in equal proportion. Additionally, an extended gas treatment zone technique for NOX/THC abatement is explored by comparing single and double plasma energization modes using lignite ash, red mud, waste tiles, and oyster shells as catalyst supports. Furthermore, the impact of multiple plasma energization (single to triple energization) on pollutant degradation is examined specifically for iron tailings and foundry sand pellets. A comparative analysis is also performed between commercially available catalysts and industrial waste-based materials under plasma catalysis conditions to evaluate their relative efficiency in THC reduction. Three distinct experimental modes—plasma-alone, plasma adsorption, and plasma catalysis—are implemented to assess their effectiveness in pollutant abatement. Preliminary findings indicate that THC adsorption is minimal due to the low boiling points of several hydrocarbon species. Results further demonstrate that an extended gas treatment zone significantly improves NOX and THC degradation by increasing the residence time of pollutants within the reactor and facilitating the conversion of residual emissions that remain untreated in the initial reaction phase. Finally, two additional industrial wastes—steel slag and manganese waste, sourced from Tata Steel—are investigated for their catalytic activity under extended gas treatment conditions. Maximum THC removal efficiencies of 96% and 95% at an energy density of 241 J/L, and NOx reduction efficiencies of 97% and 90% at 23 J/L, are achieved using manganese waste and steel slag, respectively, under plasma catalysis mode. These findings highlight the potential of waste-derived catalytic materials as cost-effective and sustainable alternatives for plasma-assisted diesel exhaust treatment, paving the way for scalable emission control solutions.