Page 45 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

the gas outlets are equipped with demisters, essential filters that will
remove liquid droplets in the gas.

Emergency Valves (EV) are sectioning valves that will separate the process
components and blow-down valves, this will allows excess hydrocarbons to
be burned off in the flare. These valves are operated if critical operating
conditions are detected or on manual command, by a dedicated Emergency
Shutdown System. This might involve partial shutdown and shutdown
sequences since the flare might not be able to handle a full blow-down of all
process sections simultaneously.

A 45,000 bpd design production with gas and 40% water cut will give about
10 cubic meters from the wellheads per minute. There also needs to be
enough capacity to handle normal slugging from wells and risers. This
means the separator has to be about 100 cubic meters, e.g. a cylinder 3
meters in diameter and 14 meters in length at the rated operating pressure.
This means a very heavy piece of equipment, typically around 50 tons for
this size, which limits the practical number of stages. Other types of
separators such as vertical separators or cyclones (centrifugal separation)
can be used to save weight, space or improve separation (see later).
There also has to be a certain minimum pressure difference between each
stage to allow satisfactory performance in the pressure and level control
loops.

Chemical additives will be discussed later.

4.2.3 Second stage separator
The second stage separator is quite similar to the first stage HP separator. In
addition to output from the first stage, it will also receive production from
wells connected to the Low Pressure manifold. The pressure is now around
1 MPa (10 atmospheres) and temperature below 100 degrees C. The water
content will be reduced to below 2%.

An oil heater could be located between the first and second stage separator
to reheat the oil/water/gas mixture. This will make it easier to separate out
water when initial water cut is high and temperature is low. The heat
exchanger is normally a tube/shell type where oil passes though tubes in a
heating medium placed inside an outer shell.

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