Abstract
NOx is emitted in the flue gas from semiconductor manufacturing plants as a byproduct of combustion for abatement of perfluorinated compounds. In order to treat NOx emission, a combined process consisting of a dry plasma process using nonthermal plasma and a wet chemical process using a wet scrubber is performed. For the dry plasma process, a dielectric barrier discharge plasma is applied using a blade-barrier electrode. Two oxidation methods, direct and indirect, are compared in terms of NO oxidation efficiency. For the wet chemical process, sodium sulfide (Na2S) is used as a reducing agent for the NO2. Experiments are conducted by varying the gas flow rate and input power to the plasma reactor, using NO diluted in air to a level of 300 ppm to simulate exhaust gas from semiconductor manufacturing. At flow rates of ≤5 L/min, the indirect oxidation method verified greater removal efficiency than the direct oxidation method, achieving a maximum NO conversion rate of 98% and a NOx removal rate of 83% at 29.4 kV and a flow rate of 3 L/min. These results demonstrate that the proposed combined process consisting of a dry plasma process and wet chemical process is promising for treating NOx emissions from the semiconductor manufacturing industry.
Highlights
Since 1950, the semiconductor manufacturing industry has continued to grow, raising concerns about the increasing emissions of perfluorinated compounds (PFCs) [1]
Gas together with such fuels as oil and natural gas to decompose it into hydrogen fluoride and carbon dioxide [2,3], and catalytic methods, which use catalysts to decompose the gas into hydrogen fluoride and carbon dioxide by means of the hydrolysis reaction [4,5]
The hydrogen fluoride generated during treatment is dealt with by dissolving it in water and processing it as hydrogen fluoride solution, or by causing it to react with calcium hydroxide to immobilize it as CaF2 [6]
Summary
Since 1950, the semiconductor manufacturing industry has continued to grow, raising concerns about the increasing emissions of perfluorinated compounds (PFCs) [1]. The HF can sometimes poison the catalyst for the SCR [7,8], which poses a problem for the treatment of the NOx generated during processing of the PFCs. Plasma–chemical methods that use nonthermal plasma have been proposed as a method of removing the NOx at low temperatures [9,10,11,12,13,14]. Our research group has achieved highly efficient removal of NOx through treatment by a combined process of indirect oxidation by nonthermal plasma together with a sodium sulfite (Na2 SO3 ). In the blade-barrier electrode-based plasma reactor proposed in this study, the discharge direction is parallel to the gas flow, making it suitable for high-flow treatment of exhaust gas with no limit on the flow rate, and promising a highly efficient treatment of exhaust gas. NO in the simulated exhaust gas is oxidized to NO2 by using a blade-barrier electrode reactor as a plasma reactor, and NOx reduction is performed by Na2 S scrubber
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