Page 88 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

shore. This will also avoid local power generation at each facility and
contribute to low manning or remote operation.

6.4 Flare and atmospheric ventilation

Flare subsystems include flare, atmospheric ventilation and blowdown. The
purpose of the flare and vent systems is to provide safe discharge and
disposal of gases and liquids resulting from:

• Spill-off flaring from the product
stabilization system. (oil,
condensate etc.).
• Production testing.
• Relief of excess pressure caused
by process upset conditions and
thermal expansion.
• Depressurization either in response
to an emergency situation or as
part of a normal procedure.
• Planned depressurization of
subsea production flowlines and
export pipelines.
• Venting from equipment operating
close to atmospheric pressure (e.g.
tanks).

The systems are typically divided into a High Pressure (HP) Flare and a Low
Pressure (LP) flare system. The LP system is operated a little above
atmospheric pressure to prevent atmospheric gases such as oxygen flowing
back into the vent and flare system and generating a combustible mixture.
With low gas flow, inert gas is injected at the flare nozzle to prevent air
ingress.

Traditionally, considerable amounts of hydrocarbons have been more or less
continuously flared. In these cases, a continuously burning pilot is used to
ensure ignition of hydrocarbons in the flare.

Stronger environmental focus has eliminated continuous flaring and the pilot
in many areas. Vapors and flare gas are normally recovered, and only in
exceptional situations does flaring occur. To avoid the pilot flame, an ignition
system is used to ensure safe ignition even when large volumes are

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