Making sense of the sulphur challenge

In recent years, the oil and gas industry has focused on sulphur removal processes and technologies as part of a concerted effort to maximise the profit from sulphur-rich oil and gas resources. This is because many of the world’s remaining hydrocarbon reserves are richer in sulphur than previously exploited fields and governments are imposing ever more stringent limits on the sulphur content of fuels. As these trends continue, refiners will have to find more-powerful new tools and techniques for removing and managing large volumes of sulphur.

What are the main challenges in sulphur separation?

One of our key technology development objectives is improving the quality of crude oil as it reaches the refinery. There are three strands to this: physical separation; chemical separation using catalysts to remove the various contaminants that are bound to the hydrocarbon molecules; and pretreatment of the crude oil, which involves lightly cracking it to produce lighter components.  

We have good technologies for the physical and chemical extraction of the sulphur that is combined with the light components in the crude oil mix. However, some of the sulphur in crude oil is attached to complex molecules and extracting it from these requires more extensive treatment. This is a big challenge, and we are addressing it by focusing much of our research and development effort on separation methods that involve chemical reactions and pretreatment processing.

How does pretreatment help?

Refiners often upgrade heavy crude oil streams by adding hydrogen, usually in the mid stages of their refining operations. But, as the average sulphur content of crude oil continues to rise and the crude slate gets heavier, there are strong arguments for applying the hydrogen treatment at the front end of the refinery process and removing contaminants as early as possible.

Shell is looking at a range of relevant technologies that could, in time, offer further solutions to upgrade the full range of heavy crudes and bitumen.

Where does sulphur fit in the strategic issues that refiners are facing?

Refinery operators are facing a sulphur two challenges. The average concentration of sulphur in crude feedstocks is rising, but the limits for sulphur concentrations in refined products are moving in the opposite direction. There is too much sulphur coming into the refinery when the aim is to produce products with a very low sulphur content.One of our key technology development objectives is improving the quality of crude oil as it reaches the refinery.  

The situation in extracting and processing crude oil has changed dramatically. Two decades ago, a common sulphur content in crude oil was about 0.5% and refined products had similar sulphur specifications. In those days, sulphur was removed from the feedstock to protect the refinery facility from excessive corrosion rather than to meet product specifications. These days, the sulphur content in crude oil has more than doubled while product specifications have been reduced by several orders of magnitude.

How have refinery operators responded to rising sulphur content?

Economic pressures on the refining sector mean that some operators are choosing to process very sulphurous, heavy crude oils because these low-cost feedstocks offer better margins, even with more difficult processing. The downside to this is that high-sulphur oils are more corrosive and can cause more rapid asset deterioration, with its associated costs, at the refinery.

How is Shell preparing for the very high sulphur gases we can expect to see over the coming years?

Today’s technology for gas processing is geared to removing small amounts of sulphur, but these methods become very expensive when applied to hydrocarbons with sulphur concentrations above 20% by volume.

Shell is developing new technologies to address this issue. One of these is the C3Sep centrifugal separator. This device uses the cooling that occurs during pressure reduction to condense and remove sulphur and carbon dioxide from gas mixtures. The C3Sep method has been successful at the laboratory scale, and, in the future, Shell may be seeking to collaborate on the development of this technology. This would combine our expertise in separation processes with support from an organisation that specialises in commercialising process hardware. 

There are few producing gas reservoirs with very high sulphur contents. Why develop this capability now?

It is true that none of the gas reservoirs where Shell currently operates has concentrations of high sulphur, but there are fields around the world that do. These technically demanding reservoirs are likely to be among the last to be developed by their asset holders, but, when the time comes to tap them, technologies such as C3Sep will make it possible. 

How has Shell addressed the issue of desulphurisation within existing refinery operations?

Product regulations have had a profound impact on how refiners conduct their business. Operators have had to introduce new technology and make significant changes to their catalysts and their process and hardware designs. At Shell, we have developed sulphur removal processes, which we apply at our refineries and license to others. This technology portfolio is market proven and includes catalysts, process designs and reactor internals such as trays and other distributors.New product regulations have had a profound impact on how refiners conduct their business. Operators have had to introduce new technology and make significant changes.

One of the major issues in processing heavier crudes is preventing catalyst deactivation. This has made feed preparation and reactor feed handling extremely important and primary economic factors in the refining process. For catalyst manufacturers, the challenge is designing catalysts that resist deactivation and last longer in any given process design. At the same time, a reactor’s hardware design must ensure that the catalyst is used effectively. Shell’s own reactor internal designs facilitate good flow distribution of hydrogen and hydrocarbons to help this.   

We have seen regulations drive down sulphur levels in gasoline, diesel and aviation fuel, but what is the next fuel challenge?

Shell is turning its attention to marine fuels, which are currently the focus for regulatory change. New international and regional shipping emission standards aim to reduce air pollution from marine vessels, and many authorities around the world are implementing or considering emission control areas (ECA).

Many people believe that the ECA regulations will require refiners to produce low-sulphur marine fuel. However, marine emission controls do allow ship operators to comply with sulphur emission levels by either using low-sulphur fuel or implementing a technical solution, for example, a seawater scrubbing system, to remove sulphur from the engine exhaust gas and prevent it being discharged to atmosphere. For gasoline and diesel, the sulphur has been removed at the refinery. In the case of marine fuel, which is the heavy fraction of oil and has a very high sulphur concentration, the solution may be different.

Desulphurisation of marine fuel is one of the hardest technical and commercial challenges that refinery operators have ever faced. Our research and development efforts are exploring both low-sulphur fuels and end-of-pipe  olutions. For the vessel operators, meeting the new emissions standards may involve a combined solution.

What can refinery managers do with the sulphur they extract?

Removing sulphur and meeting product specifications is just one side of the equation. The industry is producing, and will continue to produce, large quantities of sulphur at refineries. In some ways, dealing with this is a bigger technical challenge than developing new separation processes.

As the average sulphur content of crude oil rises, the industry will have much more sulphur than it can find uses for. Shell has done some work in this area and has found niche applications. These include sulphur-enhanced asphalt that offers better performance than conventional asphalts and a durable, fast-setting, sulphur-enhanced concrete binder for the construction industry.

Are there potential environmental issues with the disposal of this sulphur?

Yes. There is the long-term question of what ultimately happens to any products made using recovered sulphur. For example, when a sulphur-rich construction material reaches the end of its useful life what will happen to the sulphur it contains? Will these materials be allowed to degrade and release their sulphur to the atmosphere? We have to take a long-term view on sulphur release when we are looking for a sustainable solution. 

Looking further into the future, what would be the ultimate solution for sulphur removal?

At present, all our sulphur removal work is conducted at surface. If, ultimately, we could develop a process whereby heavy oil was upgraded in the reservoir and the sulphur was captured before the oil or gas came to surface that would be a huge achievement. This would involve developing effective downhole upgrading methods and combining them with sulphur capture techniques. However, I believe that we have to focus on more immediate challenges and see what is achievable by applying existing tools and techniques.

Success in dealing with the sulphur challenge is more likely through incremental improvements rather than by pursuing a single major breakthrough. Excess sulphur production is already a fact and there is a pressing need to develop solutions that address existing challenges. 

For more information, contact Katie Baverstock.