Nitrogen oxide decomposition by barrier discharge

Nitrogen oxides have been linked to numerous air pollution problems including the production of ozone in the troposphere and acid rain. Annual nitrogen oxides emissions in the United States exceed 21 million tons and are primarily a result of the high temperature combustion of fossil fuel. Recent regulations in the U.S., both federal and state, require that nitrogen oxides emissions be reduced over the next several years. Control of nitrogen oxide emissions is difficult in combustion exhaust gases because of their low concentration and reactivity. Numerous technologies have been developed to reduce emissions but the costs are generally high and the technologies are not applicable to many of the combustion systems in use today. Electrical discharges provide a means of producing active chemical species such as ions, radicals and metastable compounds that can react with oxides of nitrogen and cause their decomposition and removal from the gas stream. This study investigates the use of one such electrical discharge technique, barrier discharges. Experiments were conducted in a bench top apparatus and in a larger scale process development unit. The variables controlling the operation of the barrier discharge process and the products produced were identified and studied. They included electrical parameters such as applied voltage and frequency, the chemical composition of the gas stream, and flow conditions in the barrier discharge reactor. Experimental results showed that greater than 95% conversion of nitric oxide could be achieved using both simulated and combustion generated flue gas. Products of the reactions leading to nitric oxide destruction were non-polluting nitrogen and oxygen when dry, simulated flue gas was used. Nitric acid was produced when the gas stream contained water vapor. Operation of the barrier discharge system established on the bench scale apparatus was verified on the process development unit. Results of this work have the potential to establish the foundation for a nitrogen oxides control technology that is more versatile and may cost less to install and operate than existing control techniques