Flare Design: Staged flare designs

How is the flare designed to minimise methane? > Flare Design: Staged flare designs

A staged flare design utilizes a smaller capacity flare to handle flaring requirement during normal operation, maintenance, and start-up cases; and a larger capacity flare to handle emergency flaring requirements.

How it works

A staged flare systems consisted of two or more flares so that the number of flares in operation is proportional to the gas flow.
The first stage in a staged flare system is typically designed to handle the normal operation, maintenance, and start-up cases. The second stage is generally designed for emergency relief cases.
Staged flares operate based on pressure or flow. A staging valve or liquid sealDevice that directs the flow of relief gases through a liquid (normally water) on the path to the flare burner, used to protect the flare header from air infiltration or… drum is used for staging between the first stage and the second stage.

Types of staged flares

Staged flare systems can include the following:

Multi-point ground flares (Figure 1)
Enclosed ground flares
Combination of multi-point ground flares/ enclosed ground flares and elevated flares (Figure 2)

Advantages

Low purge ratesThe flowrate of flare purge gas – most stages are typically closed until required to open for an emergency relief scenario. A continuous purge flow is only required for the first stage; therefore, lowering emission from purging
Design variability – each stage can be designed to meet the process requirements
High turndown capacity – limit equipment downtime
Long equipment service life – equipment associated with second and successive stages operate less often; hence, increasing the life span of these items

Limitations

Sufficient plot space would be challenging, especially for existing facilities

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Case study

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Improve efficiencies

Maintaining effective cobustion efficiency and destruction efficiency are key to minimising methane from flaring. This can be achieved through improving the mixing of flare gas and air to enable complete combustion and/or by only lighting the flare when required using ignition and pilot-light systems that avoid the risk of venting.

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