Innovative, cost-effective technologies are required for the Department of Defense (DoD) and Department of Energy (DOE) air emissions control applications to avoid harmful environmental impacts, major compliance-related issues, or cost escalations.

This project is developing new non-thermal plasma (NTP) reactor technology with reduced energy and power requirements and increased yields of pollutant-attacking species for the abatement of nitrogen oxides (NOx), volatile organic compounds (VOC), and other hazardous air pollutants (HAP). A key goal is to develop an efficient, reductive-mode NOx processor. Our work has led to an NTP-catalytic-converter hybrid system for this purpose.

An NTP is an electrically neutral form of gas containing substantial concentrations of electrons, ions, and other highly reactive species (e.g., free radicals), which may be generated in the polluted gas stream by application of electrical energy. Sequential chemical reactions result in destruction of the pollutants.

A comparative assessment of electric-discharge driven and electron-beam driven NTP reactors has been performed. Bench-top NTP reactors were set up for reactor optimization and for development of reactor scale-up criteria. An initial feasibility study indicated that a novel, hybrid NTP-absorber concept using an atomic-nitrogen-radical injection scheme had potential for reductive NOx removal. Reaction kinetic models and predictive, reactor simulation models also were developed. A chemical-kinetics model was integrated into the Computational Fluid Dynamics (CFD) model to simulate NOx conversion to nitric acid (HNO₃), and spatial and temporal accumulation profiles of HNO₃ were run. A database of chemical kinetics of neutral species in air relevant to NTPs was developed. A field-pilot demonstration of a Corona Radical Shower (CRS) catalytic-converter system was carried out on a small jet engine test facility at Tinker AFB. The CRS system uses many fine nozzles, which spray out a mixture of air and dilute ammonia-nitrogen, connected to a source of high voltage to inject active species formed at the nozzle tips into the process gas stream. In the field tests, 70-100 percent de-NO was normally achieved while, for some cases, radical chemistry, reaction with ammonia, and reactions in the catalytic converters following the CRS unit resulted in 65-80 percent total de-NOx.

This project will provide a flexible NTP technology for emissions control and a basis for selecting the most appropriate NTP technology for specific needs. Using reductive mode processing, the technology offers the potential for low-back-pressure, filter-less, scrubber-less NOx control equipment. Also, NTP could be a promising back-up for other, not yet fully proven VOC-abatement technologies, should emissions standards become more stringent.