exporting gas from a platform. 1

[eng9901375]

Why is it essential to dehydrate gas before it is compressed and exported from the platform?

Also, what special considerations must be given to the design and operation of the gas export pipeline if the gas contains substantial amounts of carbon dioxide?

Thanks to everyone.

 

[SooCS]

Natural gas tends to crystalize with water under pressure (usually above 1500 psi)to form hydrate even at room temperature. These hydrate crystal can grow in size and cause the pipeline to plug.

Hydrate will only form if there are liquid water. That's why dehydrate the gas to ensure no liquid water under the worse condition.

Also CO2 form acid when mixed with liquid water which is corrosive to the pipeline material. Therefore removing the water helps remove the corrosion problem.

Read more about it in GPSA Engineering Data Book.

 

[Mark62]

Another issue is that if the gas is to be exported through a flexible pipe line then dry gas can be transported at higher temperatures than wet gas. this is due to the fact that most offshore flexible lines have a PA11 barrier which suffers from hydrolosis problems (goes hard and brittle) at temperatures arround 70°C with wet gas, but is good for dry gas for temperatures up to 90°C.

 

[narenr]

Wet gas export is possible if the pipeline is designed with corosion allowance and provision of corrosion inhibition. Partial dehydration can also be done by glycol inhibition. Most wet gas pipelines are CRA clad which is big$$$$. If the pipeline is not designed for corrosion, it could vanish in no time due to high CO2.

Rgds Naren

Narendranath R
Pipeline engineering is made easy with state of the art computer software, visit

http://www.narendranath.itgo.com.