Turning Sour Gas Sweet To Meet Growing Gas Demand

Researchers from the Gas Research Center are Patenting Technologies that Turn Sour to Gas Sweet Efficiently and Affordably

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The “sweet” natural gas that provides power to nearly all of the UAE’s co-generation power and seawater desalination plants is very different from the “sour” gas that fills the region’s underground hydrocarbon reservoirs.

The sour label applies to over 60% of the natural gas found across the Middle East due to its high concentrations of carbon dioxide and hydrogen sulfide. This sour gas is extremely poisonous, flammable and corrosive and is extremely challenging to process.

Only recently has the technology that enables processing sour gas in an economically feasible way been developed, which explains why the UAE’s Shah Gas Field – the largest sour gas project in the world – has only just began processing operations in 2016, even though the field was discovered over 50 years ago.

The process of removing hydrogen sulfide and carbon dioxide is known as “sweetening,” but it is anything but sweet. Sweetening is very expensive and can often lead to costly plant shut-downs.

Because natural gas plays a key role in the UAE Energy Strategy, there is a pressing need for innovative technologies that will further reduce the financial and environmental cost of turning the country’s sour gas sweet.

Responding to this need is a team of researchers from the Gas Research Center (GRC), located in Khalifa University of Science and Technology’s Saas Al Nakhl Campus. The GRC was established by the Petroleum Institute, now part of Khalifa University of Science and Technology, with the support of GASCO, ADNOC, Shell Abu Dhabi B.V., Total S.A. and Partex Gas Corporation. Researchers there have been developing technologies that aim to make the sweetening process cheaper, easier, and more efficient.

Their research has yielded intellectual property in the form of six patent applications filed with the United States Patent and Trademark Office. Additionally, fifteen research articles and one book chapter have already been published on the research, with one of their projects receiving Best Poster Award in the Abu Dhabi International Petroleum and Conference (ADIPEC) in 2013.

“The strong portfolio of intellectual property (IP) generated through this research project demonstrates the great value of GRC and the Khalifa University of Science and Technology’s commitment to developing innovative breakthroughs with high commercial potential that will give the ADNOC group a competitive advantage in the oil and gas sector and support the UAE’s innovation goals,” said Dr. Steve Griffiths, Interim Vice President for Research, Khalifa University of Science and Technology.

THE FOAMING PROBLEM

The main focus of the team’s research has been on optimizing chemicals designed to either reduce or remove the compounds that trigger perhaps the biggest obstacle faced during gas sweetening: foaming.

Foaming occurs as an unintended consequence of the sweetening process. It is the sudden build-up of bubbles inside the amine contactor – the tank where the sweetening takes place.

Traditional sweetening uses ammonia-based chemicals known as amines to adsorb the acid gases from sour natural gas. As the amines flow through the processing tank, the hydrogen sulfide and carbon dioxide molecules attach themselves to the amines. The amine solvent then flows out of the tank, and the acid gases are removed. The recovered amines are then reused to adsorb more acid gas molecules from the next batch of sour gas. Over time, the amines begin to degrade. In the process, they release compounds that cause the natural gas to get trapped inside of the amine solvent, forming bubbles and eventually foam.

“There are many factors that cause foaming, such as traces of other hydrocarbons and water vapor. But another factor is the amine solvent. The traditional practice has been to inject anti-foam into the amine contactor. However anti-foam is expensive and accumulates in the liquid, which can actually exacerbate the foaming problem,” explained Dr. Fawzi Banat, Professor and Department Chair of Chemical Engineering at the Khalifa University of Science and Technology.

Dr. Banat is leading the research team, which includes Dr. Pal Priyabrata and Dr. Emad Alheseinat, along with six graduate student interns. His team has been developing and patenting technologies over the past five years to help reduce the operating costs for the project’s key sponsor – GASCO, the national gas producing company of Abu Dhabi and one of the world’s largest gas processing operations.

IDENTIFYING FOAMING OFFENDERS

Dr. Banat’s approach to overcoming the foaming challenge has been two-pronged. First, the team has focused on identifying and analyzing the contaminants that cause foaming, which was aided by a novel ‘foaming fractionation’ apparatus. Second, they developed different techniques for removing the identified contaminants through the application of optimized adsorbents and ion exchange processes.

“Analysis of the foam was key to understanding how to prevent its buildup in the first place,” Dr. Banat remarked. “We used a range of analytical instruments to analyze the chemical properties of the amine solution. The foaming apparatus was particularly helpful, because it allowed us to run experiments and simulate foaming conditions. We were able to collect samples of the solution and analyze its physical and chemical properties to identify the foam-creating substances.”

Now, a similar foaming apparatus has been installed at the GASCO plant site to monitor foaming behavior of the amine solution being employed there.

Dr. Banat’s research is a major contribution to the natural gas field, as there was previously very little literature available on the causes of foaming and how to remove foam-causing contaminants from traditional amine solutions. His team has identified major contaminants in the degraded amine solution, including organic acid anions, metal ions and organic degraded products such as dissolved hydrocarbons. This work was published in the Journal of Natural Gas Science and Engineering in 2014.

REMOVING CONTAMINANTS

Removing the contaminants that generate foam is considered to be the only efficient solution to the foaming problem. Once Dr. Banat’s team was able to determine what compounds were triggering the foaming, they set to work fabricating adsorbents that could successfully remove the contaminants once they emerged.

The adsorbents fabricated by Dr. Banat’s team are made of alginate, which is a biopolymer gel, with fillers made of kaolinite, quartz and carbon. The gel and fillers are prepared as beads so they can be inserted into the amine contactor during the sweetening process.

The adsorbents demonstrated significant removal of heavy metal ions as well as organic degraded products present in the amine solution. The adsorbents’ successful performance prompted Dr. Banat to file a patent on the novel chemical technology with the US Patents and Trademark Office earlier this year.

The technology has been successfully demonstrated at the laboratory scale, and now, in collaboration with GASCO, studies to scale up the technology are underway to validate the process and its cost for industrial use in the field.

The technologies being developed by Dr. Banat and his team are helping GASCO better exploit the UAE’s low-quality sour gas reserves in order to meet increasing gas demand while decreasing production costs.

As a key project of the Gas Research Center, Dr. Banat’s team is directly supporting the Center’s vision to develop, build and strengthen the UAE’s research capabilities and bolster GASCO’s technology know-how, enabling the national gas processing company to solve current and emerging challenges in the gas industry.

Source : Masdar Institute