Dual Phase Extraction Description:

 Dual phase extraction (DPE) is increasingly popular because it combines two groundwater remediation technologies, soil vapor extraction and pump/treat, into one piece of equipment. A dual phase extraction system generates a high vacuum, 28-29 in-Hg, which is applied to the recovery wells through a sealed well cap and drop tube. The drop tube, generally 1”-2” PVC, extends through the well seal into the well to the depth to which the water table is to be drawn down to. The drop tube acts like a straw in a glass of water. The high vacuum generated by the dual phase extractor literally pulls the water/product out of the well just like drinking liquid through a straw. When the water table is drawn down to the bottom of the drop tube, the well casing above the water table now becomes exposed to the vacuum. Vapors are drawn out of the well and surrounding soils. Any additional water or product that enters the well due to recharge is immediately drawn into the drop tube and therefore the water level in the well is maintained at the bottom of the drop tube.

Product Recovery Management’s most common DPE skids utilize a Atlantic Fluidics, oil flooded rotary vane vacuum pump in conjunction with a moisture knock out tank. Vapors extracted from the well first enter the moisture separator tank through a side inlet. This creates a vortex in the tank, which helps to drop out liquids. Vapors then exit the top of the tank and pass through an inline filter, which removes any particulates. The vapors then pass through the vacuum pump and are discharged either to the atmosphere or treated with off gas equipment.

The moisture separator has a clear site tube on the side to visually note the liquid level and consistency. Float switches are included to notify of high liquid level conditions in the tank and to control a transfer pump. The pump most commonly used by PRM for this application is a Liberty or Moyno progressive cavity type. This type of pump is designed to operate against the high vacuum conditions that exist inside the tank. Using this type of pump means that the system does not have to be shut down to empty the moisture separator.

A Atlantic Fluidics pump is a very simple piece of equipment, which requires little maintenance, yet is very powerful and reliable. There are other types of groundwater remediation equipment to generate high vacuums, such as water sealed liquid ring pumps, but they have very complex piping and cooling systems and require a great deal of maintenance. Product Recovery Management’s DPE system is unitized onto a painted steel skid and is a self contained unit ready for connection to other system components such as Oil/Water Separators and Air Strippers. The most commonly used dual phase extraction systems are capable of generating vacuums in excess of 29 in-Hg and air flows in excess of 440 cfm. This vacuum allows liquids to be drawn up from about a 33 foot depth maximum.

Dual Phase Extraction (DPE) Applications:

Dual phase high vacuum technology is most applicable at sites where pump and treat in addition to soil vapor extraction is desired to be conducted. In particular, sites that have low hydraulic conductivity and yield low vapor recovery rates (under lower vacuum pressures) are most suited to this technology. Where a standard vapor extraction system, regenerative or vaccupoint, may only generate 5-10 in-Hg vacuum, an Atlantic Fluidics vacuum pump is designed to operate at higher vacuums (28-29 in-Hg) and low flows without overheating. This allows a constant high vacuum to be applied to the soils to extract vapors that the soils will yield. It also, over a period of time, will help develop new pathways to increase vapor extraction.

Sites with low hydraulic conductivity yield little water from the recovery wells. For this reason a down-well pump type of system is a waste as it is not utilized to its capacities. The pump is off most of the time waiting for the well to recharge. The high vacuum extraction system has the ability to draw in water as it enters the well. The water recovery though is a “free” benefit of having the high vacuum. The water is recovered basically as a side effect of the vapor extraction effort.