Features: Features: - Tanker Operator

TECHNOLOGY - VAPOUR CONTROL
Pressure developed during a vapour balanced lightering.
into the atmosphere, and compact
recovery equipment can bring
losses down further:
Ensure that the gas hose is not
restricting the gas flow.
Usually, 16 inches diameter is
required.
Control the receiving ship's
pressure and keep it as high as
can be permitted (80% of
lowest relief valve setting,
usually 1120 mm WG)
throughout the transfer.
Run an absorption unit in the
latter part of the transfer, when
liquid levels and the
hydrocarbon concentration in
the return gas are right.
Ideally, a unit will be installed
on the discharge ship in
addition.
Any gas releases into the
atmosphere should be throttled
to keep ships' pressures
constant.
Again, abrupt releases produce
greater hydrocarbon and H2S
losses. Venturie recommends the
employment of a PLC to control
the pressure, so that it can be
kept stable and thus higher. A
first step would be to use a
portable valve unit on the gas
transfer line.
The service vessel should have
an absorption unit fitted on
board, Dr Haagensen explained.
By fitting this unit, pressure
control software is available for
the valves. The absorption
process is shown schematically
below - a pipe circuit with a
venturi unit, served by a pump.
During and after the oil transfer,
surplus gas is drawn in from the
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