Tim Skelton takes a closer look at ExxonMobil’s cMIST gas dehydration technology – a smaller, lighter alternative to steel towers
Following successful field trials, US oil and gas giant ExxonMobil now says its compact in-pipe dehydration technology is ready for commercial launch. The new proprietary cMIST™ technology is aimed at improving the efficiency of offshore gas production, which the company modestly describes as a “step-change in operational efficiency.” It uses the absorption of moisture inside the pipes themselves to dry the extracted gas, bringing significant savings in size, weight and costs.
Conventional dehydration Drying extracted gas by removing the water vapour mixed with it is not a new concept. Dehydration technology is already a well-established standard part of processing natural gas on onshore and offshore rigs. But the conventional manner of achieving this normally involves bulky and expensive steel dehydration towers. These can be as much as 30 metres in height, they are heavy, and – perhaps most importantly – they take up a great deal of valuable room on the rig. This can be a particular issue at offshore facilities, where space is always at a premium. The new technology effectively does away with the need for this large equipment, dehydrating the gas using an innovative patented absorption system located inside the pipes.
How does it work? In its most basic form, the cMIST process involves two key technologies: the first stage uses a patented droplet generator that was developed in-house by ExxonMobil Upstream Research following what was said to be around 6,500 hours of research.
The droplet generator’s passport to success is that it can improve the effectiveness of what is otherwise a conventional glycol solvent. One innovative feature is that the energy it requires is harvested from the fast-flowing gas within the pipe. It uses this to break up the solvent into tiny micro-droplets of the desired size. These droplets are small enough to be easily dispersed throughout the whole pipe diameter when sprayed into the gas flow. The decrease in droplet size also greatly increases the relative surface area of the solvent that can be exposed to the gas. This in turn enhances the solvent’s ability to absorb water, boosting the efficiency of the process as a whole.
After the solvent has become saturated, the second process stage involves an in-line separator. This re-coalesces the tiny water-laden glycol droplets back into a cohesive whole, and moves the solvent to the outside wall of the pipe, whereupon it can be more easily separated from the dry gas and removed. Once it has been syphoned out of the system, the solvent is regenerated using a conventional drying system to remove the water. As this point it is recycled and returned to the droplet generator to begin another cycle. The separator ExxonMobil chose to use is a special compact HiPer™ in-line model developed and patented by the Chemtech division of Swiss engineering giant Sulzer. Chemtech is an established player in such technologies, and its HiPer line already has a proven track record in the field. The resulting droplet generator and separator combination is able not only to remove water vapour from gas more effectively; it also reduces both corrosion and interference in the equipment. This, the developers say, will help to ensure safer and more efficient transport of gas through the entire supply infrastructure.
Reducing the footprint By moving much of the process inside the pipes and effectively removing the need for a conventional drying tower, cMIST reduces burdens of the system in several ways. According to the developers, the compact size of the new technology means it decreases the surface footprint of the dehydration system by as much as 70%. Moreover, the weight of the new system is no more than half that of its conventional predecessors. These reductions could have a significant impact in terms of lowering the cost of materials, as well as offering the tangible benefit of space savings – especially useful for offshore platforms. “With cMIST we’ve eliminated a large and cumbersome piece of equipment and replaced it with a solution that fits into a few pipe segments,” Norman Yeh, a member of the cMIST development team at ExxonMobil Upstream Research, told the parent company’s own corporate news site Energy Factor. “The space and weight reduction is important because we could, for example, use the freed-up space to deploy devices that could help increase output,” he added.
“Our researchers were able to create this advanced natural gas dehydration technology, which represents a step-change in operational efficiency and a significant reduction in footprint,” Tom Schuessler, president of ExxonMobil Upstream Research said in a statement when the process was unveiled to the press.
Ready to launch The company launched the cMIST process at the beginning of this year. ExxonMobil says it is suitable for deployment at both land-based and offshore natural gas production operations. As a result of the technical tie-up between the two companies, it has also selected Chemtech to be the exclusive worldwide licensee of the technology. Chemtech will use its expertise in the specialist field to facilitate commercial deployment of the technique across the industry.
The developers say they are confident the new technology will provide the industry with much-needed reductions in capital expenditures for both new projects and at existing facilities. This will come as welcome news at time when margins across the upstream industry are being squeezed at both ends by a combination of higher production costs and low oil and gas prices.