 Gas Phase Corona Reactor Prepared by William Heath, Chief Operating Officer, CES The Gas-Phase Corona Reactor™ (GPCR) technology is being developed as a cost-effective and environmentally friendly alternative to thermal treatment for removing pollutants from gas streams. In partnership with Pacific Northwest National Laboratory (PNNL), Current Environmental Solutions™ is tasked with commercializing GPCR for the destruction of volatile organic contaminants (VOCs). The GPCR technology uses gaseous electrical discharges (corona) to form a non thermal plasma capable of initiating chemical reactions. Non thermal plasmas operate at 30 to 120°C but produce the same radicals and other reactive species normally associated with high-temperature (>500°C) reactions. The primary benefits of non thermal plasmas are the potential for low capital costs, low energy requirements, and the ability to treat extremely difficult compounds like perfluorocarbons (PFCs). Because efficiency does not depend on reaching high temperatures, other benefits include rapid start-up and low maintenance costs. Figure 1 is a photograph of a prototype GPCR device capable of treating up to 100 cubic feet per minute of VOCs in air (or other gas streams).
The GPCR process passes high-voltage electrical fields through a packed bed of dielectric pellets to form non thermal plasma in the void spaces between the pellets. The typical GPCR device is a coaxial cylinder with an inner metal electrode, an outer tube made of quartz, and dielectric pellets filling the annular gap, as shown in Figure 2. A screen in contact with the outside surface of the tube serves as the ground electrode. The inner electrode is connected to a high-voltage (20 to 30 kV) alternating current power supply. The quartz tube serves as the reaction vessel and as a dielectric barrier to inhibit direct charge transfer between electrodes.
The packed bed of dielectric pellets performs at least three critical functions. First, the pellets refract high-voltage electric fields so that the local fields between pellets are stronger than the applied field by a factor of 10 to 250 times, depending on the shape, porosity, and dielectric constant of the pellet material. Second, the pellet surfaces catalyze chemical reactions. Catalytic activity appears to affect both the energy requirement for contaminant oxidation (or reduction) and the byproduct distribution (for instance, the ratio of CO to CO2 at the reactor outlet.) Third, physical sorption of contaminants on the pellet surfaces can significantly influence the residence time of contaminants in the reactor. Similar to conventional thermal catalysts, screening tests are performed with various packing materials to evaluate which is the most effective for treating a particular waste stream. In tests performed both at PNNL and the Army's Chemical
Research, Development and Engineering Center (CRDEC), the GPCR process
has been effective in destroying a wide range of hazardous air
pollutants as well as chemical and biological warfare agents. Air
streams with pollutant concentrations ranging from 10's of ppm(v) to
10,000 ppm(v) have been treated. The following specific compounds have
been tested, with destruction efficiencies noted in parentheses:
Compared with quoted costs for equipment, regenerables, and energy, GPCR is projected to be about one-fourth the cost of catalytic oxidation and one-fifth the cost of carbon sorption--the two most common air purification technologies. Figure 3 compares capital and operating costs of the GPCR technology with catalytic and thermal oxidation based on data obtained by PNNL on the destruction of benzene in an air stream. The costs are based on treating a 500 htm air stream contaminated with benzene at a loading of 2000 ppmv. The capital and energy costs for both thermal systems include heat recovery systems.
To validate the GPCR process, a portable demonstration system has been developed for evaluation on actual gas streams at operating plants or field locations. The portable system was created as a test platform to generate the performance and cost data needed to design full-scale systems for deployment on specific waste streams. The portable system, shown in Figure 4, uses a small GPCR device capable of treating VOCs at a rate of up to 10 htm. The portable GPCR device is powered by a linear amplifier connected to a high-voltage transformer sized for 500 W operation at up to 1500 VA. The applied voltage (0 to 20 kV) and power frequency (600 to 1200 Hz) are adjusted using a digital waveform generator connected to the amplifier. The amplifier and reactor enclosure are housed in a portable equipment rack. Together, the power supply and reactor represent the state of the art in GPCR technology. To characterize processing rates and conditions, the system includes a mass flow controller, humidity, temperature and pressure sensors, and an on-board flame ionization detector (FID). The FID is used to measure total VOC concentrations at the reactor inlet and outlet as a means of establishing destruction efficiency. All of the instrumentation signals are captured and analyzed using a computer system mounted in a second portable rack. The system software enables remote control of all operating parameters and real-time access to test data via phone lines or network connections.
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