1. Microwave Soil Vapor Treatment
ØOn-site Carbon Regeneration
ØClosed Circulation System
ØZero Contaminant Discharge
ØChemical Recovery for Recycle or Disposal
CHA Corporation
372 W. Lyon
Laramie, WY
Telephone: (307)
Fax: (307)
Website:
Background
The National Institute for Health has awarded a SBIR Phase I grant to CHA Corporation to build a prototype microwave reactor system capable of recovering chemicals from soil vapors produced during hazardous site remediation without using catalytic oxidation. The field testing has been successfully completed at McClellan Park. The U.S. Air Force Real Property Agency also supported this field demonstration. For the past 13 years CHA Corporation has focused on the utilization of microwaves to induce or enhance chemical reactions. These efforts, made possible through industrial and governmental support, emphasize the development of new technologies for gas and water cleanup through selective destruction in contaminated waste streams.
CHA Corporation
Principles of Technology
The CHA microwave-based gas cleanup process is designed to capture and recover a wide variety of both chlorinated and non-chlorinated volatile organic compounds (VOCs), many of which are commonly found at industrial and military sites. This technology is currently being demonstrated at McClellan Air Force Base.
CHA Corp Microwave Carbon Regeneration & Chemical Recovery System
CHA Corporation
CHA Corporation Field Demonstration Fall 2003

2. Microwave Soil Vapor Treatment
Activated carbon readily adsorbs most VOCs, allowing removal efficiencies near 100% if sufficient carbon adsorbent and appropriate contact times are utilized. As the carbon continues to adsorb VOCs, the available adsorption sites are diminished and the carbon becomes saturated. Microwave energy is used to regenerate the saturated carbon. Rapid on-site regeneration of the carbon facilitates continuous, cost effective removal of VOCs by reusing the carbon in adsorption systems. When using microwaves, VOCs desorbed from the carbon are efficiently condensed in a condenser and recovered as a liquid. Overall, the process uses granular activated carbon (GAC) to remove VOCs from the air stream, continuously regenerates the used GAC with microwaves, and recovers the VOCs desorbed from the GAC by condensation. There are three main components of the CHA Microwave Soil Vapor Treatment System:
Adsorber vessel
Microwave carbon regeneration reactor
Two-stage condenser system
Adsorber Vessel
The inlet and outlet of the adsorber vessel will be connected to an on-site SVE (soil vapor extraction) system. The contaminated air stream from the discharge side of the SVE main blower enters the bottom of the adsorber and passes upward through the GAC adsorption bed. Normally, the cleaned air will exit the adsorber and will be discharged to the atmosphere. However, in this field demonstration, the cleaned air is recycled back to the inlet of the SVE FTO (flameless thermal oxidizer). This provides a closed system for the contaminated air, resulting in zero emissions discharge into the atmosphere. As the GAC in the adsorber becomes saturated, the saturated GAC is transported to the microwave regeneration reactor by means of a pneumatic conveyor system. Consequently, the regenerated GAC above the clean gas outlet moves towards the bottom of the adsorber, allowing continuous operation of the adsorber.
Microwave Carbon Regeneration Reactor
  The moving bed microwave carbon regeneration reactor consists of two stainless steel hoppers with cone-shaped bottoms, a quartz tube reactor, a rotary valve with variable speed drive motor, a multimode cavity applicator, and a 3-kW microwave generator. Saturated carbon is transported from the bottom of the adsorber to the top feed hopper by the pneumatic conveyor system. The carbon passes through the quartz tube reactor, where it is exposed to microwave energy in the multimode cavity applicator. The rotary valve is used to control the carbon flow rate through the quartz tube reactor. The regenerated carbon is stored in the receiver hopper until it is returned to the top of the adsorber.
Two-Stage Condenser System
The two-stage condenser system is used to recover organic chemical vapors as the carbon is regenerated. Nitrogen is used as a sweep gas to remove chemical vapors desorbed from the carbon. If there is accumulation of excess sweep gas, a slight pressure rise in the regenerator is detected, causing a valve to open, venting the excess gas back to the adsorber inlet. Again, no vapors are allowed to leave the closed regeneration system. Condensed liquid in the nitrogen stream is collected in a knockout pot prior to entering the compressor. In order to separate the remaining chemical vapors in the nitrogen stream, the outlet of the compressor flows into the second water-cooled condenser. Chemical vapors in the nitrogen stream are cooled in the second condenser and the condensed liquid is collected in the second knockout pot. Vapor free nitrogen is recycled back to the microwave regenerator.
CHA Corporation
Provide on-site regeneration of GAC, eliminating handling and transporting of hazardous saturated carbon.
Restore the original adsorption capacity of GAC and eliminate the need for supplying fresh GAC.
Reduce the volume of air containing VOCs and other contaminants that require further treatment.
Recover VOCs and other contaminants in soil vapors and avoid the generation of secondary air pollutants.
Provide an effective means to replace the existing catalytic oxidizers and acid gas scrubbers by GAC adsorbers.
Save energy by eliminating natural gas used in catalytic oxidizers and flameless thermal oxidizers.
Recycle valuable recovered chemicals such as fuels and solvents.
Reduce the life-cycle cost for base cleanup significantly.
Technological Advantages