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?

 

[phex]

i think you should post this question in the petroleum production engineering forum, found here:

forum469 question one, i'd guess the answer is gas hydrate formation, which has to be prevented.

 

[chowles]

Forum469 assumes right. The gas must be dehydrated so no water will drop out in the pipeline and form into hydrates. As the gas travels down the pipeline, it will experience changes in temperature and a drop in pressure that increases with distance travelled. Many subsea pipelines place the gas well within the hydrate formation temperature and so any free water that drops out of the gas due to changes in pressure will form into ice crystals, trapping gas molecules within the crystal structure and hence forming a solid explosive blockage in the pipe. Hydrate formation is quite a well reasearched issue in the oil and gas industry, so a lot of literature exist in the field of flow assurance.

If you have water and carbon dioxide, your problem is then corrosion! Removing the water and injecting a corrosion inhibitor will protect a pipeline from a gas high in CO2. The CO2 will then need to be removed onshore in molesieves if the gas is going into a distribution network.

A brief explaination, but hope it is helpful.

 

[1969grad]

chowles is exactly correct. No free water means no hydrates and no corrosion from CO2.

Run Hysis to determine the water dew point of the gas. It also calculates the hydrate formation temperature. You should be operating above both of these temperatures.

Free water also means you have two phase flow and have to be able to handle the water at the pipeline delivery point.