Energy Consumption and Optimal Reactor Configuration for Nonthermal Plasma Conversion of N 2 O in Nitrogen and N 2 O in Argon Gui-Bing Zhao, † Xudong Hu, † Ovid A. Plumb, ‡ and Maciej Radosz* ,† Department of Chemical & Petroleum Engineering and College of Engineering, University of Wyoming, Laramie, Wyoming 82071-3295 Received January 29, 2004. Revised Manuscript Received June 21, 2004 The analysis of experimental data, chemical reaction mechanisms, and kinetic modeling data is used to determine the power input and pulsed-corona-discharge reactor configuration that minimizes energy consumption for converting N 2 O in nitrogen and N 2 O in argon, which are model binaries reminiscent of more complex NOx in flue gas systems. Specifically, it is found that in- series reactors are much more energy efficient than a single reactor and more energy efficient than parallel reactors. For example, 12 reactors in series are needed to remove 90% of N 2 O if its initial concentration in nitrogen is about 200 ppm. 1. Introduction Nonthermal plasma processing is a promising tech- nology for the conversion of NOx and SOx pollutants in flue-gas streams. Compared to thermal methods, non- thermal plasma techniques are more efficient because a majority of the electrical energy goes into the produc- tion of energetic electrons rather than into gas heating. 1 The electrical energy supplied by the discharge is used preferentially to create energetic electrons, which are then used to produce radicals by dissociation and ionization of the carrier gas in which the pollutants are present. These radicals then decompose the pollutants. Compared to the selective catalytic reduction process, direct decomposition of NOx into nitrogen and oxygen using nonthermal plasma techniques has the advan- tages of relative simplicity, scalability, and lower capital cost as demonstrated by a study committee of MITI in Japan. 2 Almost all of the currently tested catalysts in the selective catalytic reduction process suffer from such problems as easy catalyst deactivation, poor thermal and hydrothermal stability, and unsatisfactory activity. 3 There are several issues that affect the practical application of nonthermal plasma processes including (1) energy cost, (2) byproduct emission, (3) power delivery method, and (4) reactor design. Different types of electrical discharge techniques (dc, ac, pulsed, and arc) have been exploited for facilitating discharge of nonthermal plasma with low energy consumption. Com- pared to the other nonthermal plasma technologies using dc, ac, and arc discharge, pulsed corona discharge is energy efficient and is expected to be developed for dry DeNOx/DeSOx processes for utility power plant boilers. 2 Recently, Hackam and Akiyama 4 reviewed different electrical discharge techniques including dc, ac, pulsed, and arc discharge used in the conversion of the major polluting constituents, NOx and SOx, encoun- tered in flue gases and exhaust emissions. The consis- tent conclusion is that nonthermal discharges using very fast rise and short duration pulses are likely to be promising technologies. To be competitive for remediation of diesel engine emissions, the energy cost for an idealized nonthermal DeNOx reactor should be lower than 10-20 eV/NO for concentrations ≈ 1000 ppm. This would correspond to an overall power consumption of lower than 5% of the total engine power. 5,6 For pulsed-corona-discharge reac- tors (PCDRs), energy costs that have been reported vary considerably, for example, from 10 to 500 eV/molecule. 6 The approaches to reducing electrical energy con- sumption can be divided into three categories. (1) The first category of approaches is activation of pollutant conversion reactions by chemical additives. Additives are introduced into the feed of flue gas reactors in order to enhance the conversion of the pollutants and neutralize nitric and sulfuric acids. One of the most widely used additives is ammonia. 7-11 Other additives such as lime, methane, ethylene, propylene, * Corresponding author. E-mail: radosz@uwyo.edu. Tel: 307-766- 2500. Fax: 307-766-6777. † Department of Chemical & Petroleum Engineering. ‡ College of Engineering. (1) Penetrante, B. M.; Hsiao, M. C.; Merritt, B. T.; Vogtlin, G. E.; Wallman, P. H. IEEE Trans. Plasma Sci. 1995, 23, 679-687. (2) Masuda, S. Report on novel dry DeNOx/DeSOx technology for cleaning combustion gases from utility thermal power plant boilers. In Nonthermal Plasma Techniques for Pollutuion Control; Penetrante, B. M., Schultheis, S. E., Eds.; Springer-Verlag: Berlin, 1993; Part B. (3) Luo, J.; Suib, S. L.; Marquez, M.; Hayashi, Y.; Matsumoto, H. J. Phys. Chem. A 1998, 102, 7954-7963. (4) Hackam, R.; Akiyama, H. IEEE Trans. Dielectr. Electr. Insul. 2000, 7, 654-683. (5) Penetrante, B. M. Plasma Chemistry and Power Consumption in Non-thermal DeNOx. In Nonthermal Plasma Techniques for Pol- lution Control; Penetrante, B. M., Schultheis, S. E., Eds.; Springer- Verlag: Heidelberg, Germany, 1993; Part A. (6) Puchkarev, V.; Gundersen, M. Appl. Phys. Lett. 1997, 71, 3364- 3366. (7) Chang, J. S.; Looy, P. C.; Nagai, K.; Yoshioka, T.; Aoki, S.; Maezawa, A. IEEE Trans. Ind. Appl. 1996, 32, 131-137. (8) Mok, Y. S.; Nam, I. S. IEEE Trans. Plasma Sci. 1999, 27, 1188- 1196. 1522 Energy & Fuels 2004, 18, 1522-1530 10.1021/ef049966c CCC: $27.50 © 2004 American Chemical Society Published on Web 08/05/2004