- Evacuation of Chemical Tankers/Rail Cars: Vacuum pumps are frequently used to effectively evacuate transport tanks
- Methane Gas Recovery: Molecular sieves and vacuum systems are used to recover methane in coalbed methane recovery systems
- Soil Vapor Extraction: Utilizing vacuum and sweep gas to recover volatile organics from contaminated soil
- Vacuum Deaeration: Removing air bubbles from water in boiler systems improves efficiency and boiler lifespan
- Vacuum Distillation of Sea Water: Distilling sea water at vacuum allows for lower energy cost desalination
- Vacuum Priming of Pumps: Vacuum pumps are frequently used to prime large water pumps
- Vacuum Sewer Construction: Vacuum sewer systems use vacuum to quickly move sewage within the system
Soil Vapor Extraction (SVE)
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
Sewerage Vacuum Pumps
Vacuum Sewers offer many advantages over gravity systems including fast installation and lower installation costs due to smaller diameter piping and shallower burial depths. The heart of vacuum sewer systems are the vacuum pumps, which are either liquid-ring vacuum pumps or lubricated sliding vane (Rotary Vane) vacuum pumps. Liquid ring vacuum pumps can be either water sealed (requiring a continual water purge), or oil-sealed (known as Vmax).
Rotary Vane vacuum pumps are the most common type being installed over the last 5 to 10 years, primarily due to an emphasis on electrical efficiency, since rotary vane pumps are approximately 10-15% more efficient (CFM per HP). Per the EPA:”On the negative side, there have been problems with the vulnerability of these pumps should water be carried into (or accumulated in) them. In this situation, the pumps must be taken out of service to remove the liquid; the result is a shortened service life. By contrast the liquid-ring pump can usually withstand an accident of this type with very little damage.”
What is usually not considered in the evaluations, however, is the life cycle costs including maintenance (labor, oil, filters, repairs) of the vacuum pumps. Rotary vane vacuum pumps, on clean service, are recommended to change oil every 500 to 750 hrs of operation (about every 3 weeks for continuous service). The Vmax only requires oil changes once every year (10,000 hrs on clean service); for vacuum sewers- every 6 months. Water accumulation in the oil (very common problem), can damage the rotary vane pump because the vanes and bearings rely on the lubricating oil for operation, whereas the Vmax oil-sealed liquid-ring vacuum pump uses external greased bearings and the oil is used for sealing, not lubrication (see How a Liquid Ring Pump Works).
The oil-sealed Vmax offers many advantages in vacuum sewer applications, when low maintenance and high reliability are important.
- Lower maintenance (oil change once per year)
- Quieter Operation (78 dBA vs. 85 dBA)
- Higher Reliability (able in ingest liquid without damage)
- Small Footprint