The QED family of Passive Skimmers has been designed for product only (LNAPL) recovery applications in sites where active pumping systems are not applicable due to existing conditions or extreme low permeable formations. The floating intake head follows the groundwater fluctuations in the recovery well, allowing only the free-floating phase (LNAPL) to be captured, without taking water, and stored in the built-in reservoir for further manual transfer to a tank.
Passive Skimmers are available for 2” (50 mm) and 4” (100 mm) extraction wells, with different reservoir capacities.
Passive Skimmers are available in two different models: SOS-P (Passive Selective Oil Skimmer), and SPG-P (Passive Specific Gravity Skimmer).
- Simple systems for extreme low recovery applications.
- Choice of floating inlet types.
Choosing the Right Passive Skimmer
Specific gravity and viscosity are two of the most important properties of hydrocarbons (LNAPL) as far as their mobility in the subsurface. At the same time that these parameters affect the migration of the plume, they also play a very important role in the selection of the right skimmer for the cleanup application.
The SPG (specific gravity) inlet uses a float with a controlled specific gravity that causes it to float on water but not in the LNAPL. The SPG float has its fluid inlet port positioned near the top so that it is always above water. If the LNAPL layer gets too thin, the SPG inlet will also be above the LNAPL layer and cease recovery of hydrocarbons until more enters the well. To accommodate a range of final LNAPL layer thickness, the SPG float has multiple, variable inlet ports that can be opened or plugged to adjust the level of the inlet port. Why isn’t the SPG always set for the thinnest possible LNAPL layer? The reason is that any float in a small diameter well has a tendency to occasionally stick as liquid levels move up and down, so setting the inlet port too low increases the chance of allowing water to be pumped instead of pumping only LNAPL. So, a trade-off must be made between achieving desired final LNAPL layer thickness and prevention of pumpingwater.
The SOS inlet uses a float with an inlet port inside a hydrophobic, or water-rejecting, screen. The hydrophobic screen prevents water from being taken in and pumped to the surface, even if the float occasionally sticks or drags as the liquid level fluctuates. While this is a distinct advantage of the SOS inlet over the SPG type, the SOS inlet screen is more subject to plugging due to potential debris or slimes present in the well. The SOS inlet works best on fresh gasoline and jet fuel spills, and less so on weathered diesel.