M.G. Grothaus

DESTRUCTION OF HAZARDOUS AIR POLLUTANTS USING A FAST RISE TIME PULSED CORONA REACTOR

Increasingly stringent environmental regulation imposed on both the military and civilian sectors has created a growing demand for alternative abatement methods for a variety of hazardous compounds. One alternative, the nonthermal plasma, shows promise of providing an efficient means for the destruction of dilute concentrations of hazardous air pollutants. The Dahlgren Laboratory of the Naval Surface Warfare Center has extensively investigated one type of nonthermal plasma discharge, the pulsed corona reactor, for the destruction of volatile organic compounds and chemical warfare agents. In this reactor, a fast rise time (∼10 ns), short duration (<100 ns), high-voltage pulse is repetitively delivered to a wire-cylinder electrode geometry, thereby producing a multitude of streamer discharges along its length. The resulting nonthermal plasma contains highly reactive chemical radicals which can interact with and destroy the hazardous molecules entrained in the ambient atmosphere flowing through the reactor v...

A synergistic approach for the removal of NO/sub x/ and PM from diesel engine exhaust

A prototype reactor and diesel exhaust testbed have been assembled to investigate the compatibility and performance of specially developed lean NO/sub x/ catalyst formulations in the presence of a nonthermal plasma as a function of reactor input energy density and specific exhaust conditions. The relative performance of three catalyst formulations acting both alone and in concert with the nonthermal plasma are being compared in preparation for a downselect to the most promising candidate. This formulation will be the subject of subsequent refinement and development. Preliminary results indicate that true synergy does in fact exist between these two aftertreatment approaches.

COAXIAL PULSED CORONA REACTOR FOR TREATMENT OF HAZARDOUS GASES

Abstract : The destruction of hazardous gaseous chemicals has in the past been effectively accomplished using thermal techniques. Pulsed corona reactors are promising candidates for more efficient destruction of hazardous gases using a non-thermal electrical discharge at atmospheric pressure. The energy required for chemical destruction is deposited in the medium by highly energetic electrons present near the streamer head while direct heating of the neutral gas molecules is avoided. The current work emphasizes the construction of an electrically efficient, low cost pulsed corona reactor capable of treating a flow rate of 4 liters/minute. Determining optimum pulse parameters for the discharge and scaling the device to higher flow rates will be the primary focus of future work, with specific emphasis being placed on the use of fast-rising pulses (nanoseconds) of limited pulse-width (10s to 100s of nanoseconds). A testbed for chemical analysis has also been assembled and preliminary results include the electrical efficiency of the device and the chemical destruction efficiency when challenged by small concentrations of hazardous gases in ambient air.

New electrical control methods to prevent power plant fouling

One new nonchemical method for removal of biofouling utilizes pulsed acoustic waves above the cavitation threshold to remove accumulated scale and/or biofouling from the inside walls of piping and other enclosed structures. The pulsed acoustic wave successively removes accumulated deposits as the arc-discharge source is moved down the tube by an operator. We describe a program developing a compact, portable tube-cleaning system for use in utility and US Navy scheduled plant maintenance. Results from a laboratory demonstration with typical heat-exchanger tubing taken from a Tennessee Valley Authority power plant are presented. In addition results from a field experiment conducted at the US Navy Marine Corrosion Test Facility, Ft. Lauderdale, Florida, are presented that demonstrated significant (order of magnitude) reduction in biofouling associated with pulsed acoustic shock wave treatment at intensities below the cavitation threshold.

A crossed-flow pulsed corona reactor

The chemical radicals created during an atmospheric-pressure partial discharge have been shown to be beneficial in the abatement of a variety of gaseous pollutants. These pollutants range from the nitrides of oxygen present in diesel engine exhaust to fluorinated and chlorinated compounds entrained in semiconductor process tool effluent. Despite promising technical advances in the electrical and chemical efficiencies available from this nonthermal technique, achieving the treatment volumes and rates required in practical applications may require large, parallel combinations of existing reactor designs. The pulsed corona reactor (PCR) is one device that is routinely used to create the requisite nonthermal plasma environment. Although simple, this geometry is problematic in accommodating higher treatment rates since the pollutant flow is introduced axially and complex manifolds will be required to direct the flow through numerous parallel reaction chambers. Furthermore, difficulty is anticipated in maintaining the axial alignment of the high voltage inner conductor in the long tubes over time. To solve this problem, the current work describes an alternative reactor geometry, referred to as the crossed-flow PCR (X-PCR), where the pollutant stream is introduced perpendicular to the wire-cylinder reaction chamber through the use of a perforated outer cylinder. The X-PCR has been implemented as part of a plasma-assisted catalysis investigation underway at the Institute for heavy-duty diesel exhaust aftertreatment. The performance of the reactor in a raw diesel exhaust environment will be discussed along with the NO/sub x/ removal efficiencies obtained when used in conjunction with a unique lean-NO/sub x/ catalyst.

Nanosecond pulsed corona reactor for efficient destruction of hazardous gases

Summary form only given. The use of nonthermal plasma reactors for the destruction of hazardous gaseous chemicals shows promise of being highly efficient when compared with thermal techniques. The key to this technique lies in creation of an electric discharge at atmospheric pressure in which the majority of the energy is spent on producing highly energetic electrons rather than on heating of neutral gas molecules. Pulsed corona reactors provide one means of accomplishing this goal. In order to gain some understanding of this approachs economic and operational viability, and attempt was made to determine and improve the total efficiency of these devices. Determining optimum pulse parameters for the discharge and scaling the device to higher flow rates were the primary focus of the work, with emphasis placed on the use of fast-rising pulses (nanoseconds). An electrically efficient prototype reactor and chemical analysis testbed have been assembled. Preliminary results on device electrical efficiency and chemical destruction efficiencies for chlorofluorocarbons and volatile organic compounds in air.