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Innovative Natural Gas Purification System Developed
July 23, 2018

New technologies and advanced exploration across the U.S. have combined to make supplies readily available and less expensive, natural gas is being substituted more and more as fuel for power generation plants, industrial facilities as well as the family automobile. However, natural gas, a naturally occurring hydrocarbon gas mixture consisting primarily of methane, contains impurities that must be removed before the methane can be put into transmission pipelines.

To address this challenge, fundamental researchers at the Colorado School of Mines (Mines) have proposed an innovative two-part system for separating impurities from natural gas, according to information provided by the American Institute of Physics (AIP) as published in the Journal of Renewable and Sustainable Energy. The research suggests that a newly proposed purification system, combining two separation methods would improve performance, reduce costs and diminish ecological side effects compared to benchmark technologies.

Natural gas processing typically relies on high-temperature techniques that incur high operating costs. “We propose an integrated process consisting of gas hydrates and membranes, to make the overall process of purifying natural gas potentially more economical without high-temperature driven processes,” explained co-author Moises A. Carreon, associate professor of chemical and biological engineering at Colorado School of Mines and an expert in membrane separating technologies.

Membrane technology applies different types of material to filter out carbon dioxide and nitrogen from raw natural gas. However, propane and hydrogen sulfide are also often present and have the potential to negatively affect membrane performance. Consequently Dr. Carreon’s team, including Carolyn Koh, the William K. Coors Distinguished Professor, Chemical and Biological Engineering at Mines and an expert in hydrates, and Pramod Warrier, a postdoctoral researcher, needed a solution to overcome this problem.

As Dr. Koh explained, “Hydrates form hydrogen-bonded water cages that trap the gases you want to separate. It’s a potentially very selective way of trapping those gases.” Different pressure and temperature conditions are required for impurity hydrates to form compared to methane hydrates. The engineers decided to introduce selective hydrate formation as a preliminary step to the membrane separation process.

In the paper, “Integrated gas hydrate-membrane system for natural gas purification”, the researchers used well-established algorithms to prove the feasibility of specific hydrates’ formation. These conditions have a relatively low energy demand that could make the integrated system economical.

“In this integrated system, we first remove all of the nasty chemicals present in natural gas using gas hydrates to produce a purer mixture,” Dr. Cameron said. He then explained how the purer mixture of gases is easier to separate using membrane technology.

Hydrate formation is not only energy-efficient but also environmentally friendly. Water is the only additional material required for gas hydrate formation, and it effectively sequesters hazardous gases like hydrogen sulfide into the solid hydrate form, which prevents its release into the environment. There are some other contaminants that need to be removed separately, but this newly proposed system reduces environmental impact from the current industrial processes.

“We’re trying to demonstrate that this integrated system can effectively separate natural gas impurities in laboratory experiments,” said Dr. Carreon. Part of that work will involve optimization to ensure that the hydrate structures form easily and rapidly, and can maintain their stability.

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