Natural gas dehydration

Matjaž Matošec - 19 January 2017

Raw natural gas is saturated with water which must be removed to ensure safe transport. A new technology makes gas dehydration less costly and more efficient.

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Mr Matjaž Matošec
Matjaž Matošec is Editor of Stainless Steel World News and Manager of the Stainless Steel World Conference.
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Natural gas as most of us know it is very different from that lying underground. Raw natural gas must undergo a number of processes before entering downstream equipment, to remove various impurities, including water vapour which increases the corrosiveness of natural gas. As detailed on Naturalgas.org, most of the liquid, free water associated with extracted natural gas is removed by simple separation methods at or near the wellhead. However, the removal of the water vapour that exists in solution in natural gas requires a more complex treatment. This treatment consists of ‘dehydrating’ the natural gas, which usually involves one of two processes: either absorption, or adsorption. Absorption occurs when the water vapour is taken out by a dehydrating agent, while adsorption occurs when the water vapour is condensed and collected on the surface.

The oil & gas giant ExxonMobil recently announced its development of new technology named cMISTTM which dehydrates natural gas using a patented absorption system inside pipes and replaces the need for conventional dehydration tower technology. This ‘in-line’ technology could be deployed at both land-based and offshore natural gas production operations.

The new technology more efficiently removes water vapour present during the production of natural gas. Removing water vapour through the use of dehydration technology, typically accomplished using large and expensive dehydration towers, reduces corrosion and equipment interference, helping to ensure the safe and efficient transport of natural gas through the supply infrastructure and ultimately to consumers.

According to ExxonMobil, cMISTTM reduces the size, weight and cost of dehydration, resulting in reductions of surface footprint by 70 percent and the overall dehydration system’s weight by half, which has significant added benefits on offshore applications.

The cMISTM technology relies on a proprietary droplet generator to break up conventional solvent into tiny droplets that become well dispersed in the gas flow thereby increasing the surface area for the absorption of water from the gas. This is followed by an inline separator that coalesces the water-rich glycol droplets and moves them to the outside wall of the pipe for effective separation from the dehydrated natural gas. The water-rich glycol is regenerated using a conventional system and is sent back to the droplet generator to be used again. The droplet generator uses the energy from the flowing natural gas to create droplets of the right size.

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