Microwave Soil Vapor Treatment

1
Microwave Soil Vapor Treatment
CHA Corporation 372 W. Lyon Laramie, WY
82072 Telephone [phone] Fax (307)
742-3415 Website www.chacorporation.com Email cc
ha_at_chacorporation.com
ØOn-site Carbon Reactivation ØClosed Circulation
System ØZero Contaminant Discharge ØChemical
Recovery for Recycle or Disposal
CHA Corporation
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. Early Phase I
work included designing and fabricating a
prototype system to be field-tested, which was
completed in the summer of 2003. In the second
year the prototype was transported to the former
McClellan Air Force Base, where it was operated
for two months to obtain data needed to evaluate
the technical and economical feasibility of the
microwave process. The field demonstration was
completed in December 2003. The results proved
that this microwave technology is a viable
alternative to conventional catalytic oxidation
that will result in significant cost savings and
environmental benefits.
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. AFRPA at
McClellan has completed a cost-benefit analysis
for replacing the currently operating oxidizers
with a central microwave carbon reactivation
system and vapor carbon adsorbers. Due to
favorable results from this evaluation, URS Corp.
and CHA Corp. are currently conducting additional
field testing for AFRPA to gather additional
information about this microwave system.
CHA Corp Microwave Carbon Regeneration Chemical
Recovery System

• CHA Corporation

• CHA Corporation Field Demonstration WINTER 2004

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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
  reactivate the saturated carbon. Rapid on-site
  reactivation 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 reactivates 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 reactivation 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
  reactivation reactor by means of a pneumatic
  conveyor system. Consequently, the reactivated
  GAC above the clean gas outlet moves towards the
  bottom of the adsorber, allowing continuous
  operation of the adsorber.

• Microwave Carbon Reactivation Reactor
•   The moving bed microwave carbon reactivation
  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 reactivated 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
  reactivated. Nitrogen is used as a total recycle
  sweep gas to remove chemical vapors desorbed from
  the carbon. If there is accumulation of excess
  sweep gas, a slight pressure rise in the
  reactivator 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 reactivation 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
  reactivator.

• CHA Corporation