[Show abstract][Hide abstract] ABSTRACT: Volatile organic compound (VOC) emissions from various sources such as chemical process industry, manufacturing industry, and automobiles have been an environmental and health concern. With the emerging emphasis on using green technologies to minimize greenhouse gas emissions, the use of microwave energy to achieve VOC emissions control with its electric power coming from nongreenhouse-related energy sources, such as wind, geothermal, solar, or even nuclear energy, becomes an attractive option. In this study, an experimental investigation involving the use of microwave energy to accomplish high temperature destruction of p-xylene in a packed bed reactor was performed using a SiC (silicon carbide) foam as the microwave absorbing media with air or nitrogen being the carrier gas. The experimental facilities consisted of a gas cylinder, a mass flow controller, a p-xylene vaporizer, a packed bed reactor packed with a SiC foam, a microwave applicator, and a gas chromatograph/mass spectrometer (GC/MS) for gas analysis. The SiC was found to be an excellent microwave absorber, which efficiently converts the microwave energy into heat energy. It was observed that the SiC temperature rises rapidly upon microwave irradiation and reaches a steady state temperature of higher than 800 °C within 2−3 min depending on the experimental conditions. A semiempirical energy balance model was formulated to describe the dynamic temperature profiles of the SiC in the reactor, and the model was found to simulate the observed profiles reasonably well. The destruction and removal efficiencies (DREs) for p-xylene were observed to reach 100% for all the experiments conducted with air being the carrier gas; however, the DREs never reached 100% with nitrogen being the carrier gas and the major destruction byproducts were observed to be benzene, toluene, styrene, biphenyl, and the unreacted p-xylene. The study has demonstrated that the microwave technology can be effectively developed to control the emissions of low concentrations of VOCs, especially in air.
Full-text · Article · Aug 2010 · Industrial & Engineering Chemistry Research
[Show abstract][Hide abstract] ABSTRACT: Wall-flow diesel particulate filters (DPFs) are considered the most effective devices for the control of diesel particulate emissions. A requirement for the reliable operation of the DPFs, however, is the periodic and/or continuous regeneration of the filters. While microwave heating has been considered a potential active regeneration method for the DPFs, past studies on the technology have identified several technical problems leading to filter failure. The problems are mainly associated with the use of inappropriate filter materials for the microwave system and the generation of local hotspots due to uneven microwave heating, resulting in the physical damage to the filters. The objective of this study was to develop and demonstrate the technology employing a microwave-absorbing filter material coupled with an effective waveguide design for the reliable regeneration of DPFs. In this study, a well-equipped diesel emission control laboratory was established to conduct the experiments. The experimental facilities included a 6-kWe diesel generator, an exhaust flow control system, a diesel particulate filter system, a microwave energy supply system, a soot sampling system, a differential-pressure measurement system, and a temperature measurement system. The DPF was a silicone carbide wall-flow monolith filter enclosed in a quartz filter holder. A commercial 1.4-kWe microwave oven was modified to accommodate the quartz holder and a waveguide was engineered to evenly supply the microwave energy to the enclosed filter to achieve filter regeneration. In the experiments, the diesel engine exhaust was lined up to flow through the filter with a fixed flow rate. The microwave regeneration was triggered after a specific amount of soot loading was reached based on the differential pressure drop reading. The results have indicated that the designed system has been able to achieve uniform temperature profiles both in the radial and the vertical DPF positions. The off-line regeneration of DPF by microwave energy has been observed to be highly efficient in terms of energy consumption and regeneration efficiency. The DPM filtration efficiency has remained comparably high after 150 cycles of filtration/regeneration with no apparent physical damage to the DPF being observed. The on-line microwave regeneration of the DPF, however, is not as efficient as the off-line regeneration due to the insufficient oxygen concentration in the engine exhaust stream.
No preview · Article · Oct 2008 · Industrial & Engineering Chemistry Research