Soil Vapor Extraction
Soil Vapor Extraction (SVE) is a general term for pulling a vacuum on contaminated soils to remove volatile organic compounds (VOCs). The process has several different names including SVE, Soil Vacuum Extraction and variations which includes removing groundwater along with the vapors: High Vacuum SVE, Multi-Phase, Dual Phase, 2-Phase™. The choice of vacuum pump used depends upon the vacuum level, desired reliability and cost.
Straight “SVE” only pulls vapors from the vapor or “vadose” zone above the water table. Vacuum levels are typically measured in “H2OV or ”HgV with vacuum levels less than 10”HgV. Typical systems include an inexpensive entrainment tank and filter before the vacuum pump. Since water carryover is not anticipated, there is usually no allowance for water accumulation. The standard pump used in this range is a regenerative blower.
High Vacuum SVE, Multiphase SVE, Dual Phase SVE, and 2-Phase™ are designs which include groundwater entrainment carryover with the vapor flow (the different names have more to do with the well configuration than with the above ground vacuum system), and will include inlet KO Pots, water transfer pumps. Many times the purpose of pulling the higher vacuum on the soil is to increase the water yield from the well for treatment. Depending how tight the soil formation, high vacuum can increase the water yield by a factor of 10 times. Vacuum levels for these designs are typically in the 10”HgV to 28”HgV range. In the 10” – 15”HgV range you will typically see rotary lobe blowers, and liquid ring vacuum systems (water and oil), but in the 15-28”HgV range, you will find mostly liquid ring vacuum system (water and oil) as the vacuum source. Capacities can range from 100 to 4,000 CFM.
Water-Sealed vs. Oil-Sealed Liquid Ring Vacuum Pumps
Wintek supplies both for SVE applications, but in terms of long term reliability, we recommend the oil sealed version. Although it is not intuitive to use an oil sealed pump on an environmental clean up site, this design overcomes many of the problems encountered with water sealed pumps. Liquid ring pumps are very rugged and can take lots of “abuse”, but they also can have their drawbacks. The problem with water sealed liquid ring pumps is the quality of the water (typically dirty and high in minerals – hard water) available at most sites. The minerals tend to plate out (especially with air-cooled versions) on the pump internals, valves, and switches causing system problems and down-time, usually starting in the 2nd year of operation. It is not uncommon to hear of water sealed pumps only getting 50% uptime. Wintek’s oil-sealed liquid ring systems typically get 90-95% uptime over the 1st five years of operation, based on customer comments.
Integrated Humidity Control Option
This option may be desired when operating at vacuum levels in the 15”-28”HgV range if you are utilizing vapor phase carbon on the system discharge.By nature of activated carbon, for optimal adsorption, the vapor stream to the carbon should be controlled in temperature and humidity at 50% RH and 90-110oF. High vapor temperatures and high humidity can impede adsorption of VOC’s on activated carbon, increasing a site’s on-going operating costs. Wintek’s Integrated Humidity Control System (US Patent 5,441,365) optimally conditions the vapors for carbon adsorption, thus keeping operating costs down.
2-Phase™ is a trademark of Xerox Corporation