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Passive Skimmer How It Works |
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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.
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 SPG Inlet
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.
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 SOS Inlet
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. |
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