Why is 'excess' gas burned up as fire in an oil rig?

Answer 1

It may be uneconomic to put in a gas pipeline to recover the gas or at least most of it. In some regions gas recovery is mandatory (for environmental reasons) irrespective of economics.

Notwithstanding the above some gas will always be wasted and needs to be burnt off. There are a number of reasons for this:

1 The raw gas may contain impurities such as H2S and CO2 which needs to be separated and the processes produce a tail gas which cannot be used as a fuel because of toxicity/corrosion problems and needs to be flared (although in the North Sea there is one platform where a stream rich in CO2 is reinjected underground)

2 To comply with safety standards process pressure equipment must have pressure control systems and pressure safety relief valves and relieved gas must be disposed of via a flare system. This is the only way to safely engineer such a system to cope with events such as emergency shutdown or equipment or control system failure.

2 A flare system normally requires a small flow of gas to keep it purged (no air egress) and to maintain the flame for when it may be needed for larger flows.

Answer 2

The excess gas is burned off on an oil rig as the quickest way to both relieve pressure to prent an underground or underwater explosion and to just get rid of the gas with flame.

Oil rigs have been around since about 1865 and their design and tradition developed when the concept of 'recycling' hadn't caught on. The 'tradition' of burning off gas on a rig still continues.

Answer 3

Because it's relatively impure and the flow is uneven. There's likely no natural gas pipeline nearby. Purifying it and getting it into a pipeline requires work and money. Cheaper and easier to burn it.

Money is often the answer to: Why don't they....?

It's one small way we could improve our energy efficiency, though.