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LNAPL Skimmers How It Works |
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The LNAPL enters the skimmer system through the floating inlet, flows down through a flexible tube, then is pulled upward by the pump’s suction action during the fill cycle.
During the discharge cycle, the bladder is squeezed by the compressed air and the LNAPL is pumped to the collection system at the ground surface. Then, during the fill cycle the compressed air around the bladder is exhausted again and the bladder expands, resuming its original shape. This pulls fluid into the bladder through the check valve at the bottom ofthe pump.
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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 pumping water.
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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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