The requirement to meet ultra-low SO2 emission standards, even lower than World Bank limits, is becoming more and more prevalent for new natural gas developments and/ or certain regions. At the same time, more-complex, sour gas fields are being developed as sweet fields become depleted.

Addressing these challenges while ensuring that increasingly stringent SO2 emission limits are met in the future, requires technology capable of ultra-high levels of sulphur recovery, even when dealing with difficult gas streams. Next to meeting the increasingly stringent SO2 emission limits, proposed technology should also satisfy the requirement of lowest life cycle cost. In this respect, Shell Global Solutions is continuously developing and/ or improving its portfolio of gas treatment technologies.

Shell Global Solutions has utilised its extensive knowledge and experience of designing and operating Shell Claus off-gas treating (SCOT*) units since the 1970s to hone the technology for this purpose. The company has also extended its tail gas treating portfolio with the addition of the Shell CANSOLV* TGT+ technology and with the current development of the next generation SCOT.

These technologies are capable to meet stringent SO2 emission limits for a range of emission requirements (even better than World Bank limits). Depending on the case, e.g. feedstock composition, required SO2 emission, each of these technologies has its own competitive edge.

Shell CANSOLV TGT+ technology can be part of an integrated sour gas treating solution, enabling ultra-low SO2 emissions and the capture of 99.9+% of the overall sulphur present in sour gas streams while minimising the complexity of the process line-up. This system sits at the back end of the gas processing line-up and serves as the final destination to capture SO2 from all the plant’s sour gas streams routed to the incinerator, as illustrated in Figure 1.

Figure 1 shows the different off-gases routed to the Shell CANSOLV unit via the incinerator from the acid gas enrichment unit (AGEU) and the degasser. These gases are combined with the flash gas from the acid gas removal unit (AGRU) and disulphide oils generated in caustic treating of extracted natural gas liquids (NGL) or condensate, following treatment in the molecular sieve unit (MSU). Without the Shell CANSOLV technology, each of these individual streams would have required dedicated treatment or would have been emitted to atmosphere after incineration and thus contributed to higher levels of SO2 emissions.

The Shell CANSOLV TGT+ process centres on the Shell CANSOLV SO2 Scrubbing System, which has been used worldwide to capture post-combustion SO2 and recycle it back to the thermal stage of a Claus sulphur recovery unit.

“This tail gas treating unit uses a Shell CANSOLV proprietary solvent that can achieve even greater levels of sulphur recovery for more complex applications than conventional SCOT applications. This enables us to be well within the most stringent emission levels mandated in different jurisdictions at competitive capital and operating costs while minimising process line-up complexity,” says Dr Lydia Singoredjo, Licensing Technology Manager Upstream Gas Processing at Shell Global Solutions.

“The Shell CANSOLV TGT+ technology’s ability to improve on World Bank emission standards gives operators the reassurance that they have a flexible and future-proof technology. Even if you only need to meet a certain limit now, the technology is flexible enough to accommodate future tightening of emission regulations relatively easily, without the requirement of hardware changes. This puts the technology ahead of the curve.”

The Shell CANSOLV TGT+ unit is being introduced in several new projects across the Middle East and Europe, where SO2 emission regulations are very stringent. Some of the projects are now in the construction phase and due to start up soon.

This system has bolstered an already successful tail gas treating technology portfolio. Shell Global Solutions has more than 40 years’ experience of designing and operating SCOT units. The SCOT process uses catalytic conversion and amine absorption processes, which are familiar to plant operators, downstream of a Claus unit. The conventional SCOT system can achieve sulphur recovery levels of up to 99.98%. 

Shell Global Solutions has licensed more than 300 SCOT units, which has enabled the team to build up a strong background in using tail gas treating as a means of meeting SO2 emission limits. As both a designer and an operator of these units, Shell is well equipped with the knowledge and expertise necessary to get the best out of them and offers more than just a design and delivery service.

“We have a closed loop whereby we design a unit, operate it and then collate all the operating experience and feed it back into our research and development. We can then feed our research and development results back into our design approach,” explains Singoredjo.

“By repeating that loop over and over again, we are always optimising our designs and, ultimately, improving our operations. This knowledge and operational experience are, therefore, vital parts of our technology offer to clients. Other companies have developed similar versions of the SCOT design, but Shell has the ability to look back over a history filled with many reference cases and operational and design experience,” she adds.

Based on the extensive knowledge in the area of tail gas treating, Shell is currently developing the next generation SCOT, aiming for step change performance of sulphur recovery level of 99.9%+. Figure 2 represents the SCOT line-up and the potential benefits of the next generation of SCOT technology.

Based on the extensive knowledge in the area of tail gas treating, Shell has developed the SCOT ULTRA process, which offers a step change in the performance of the well-established SCOT process. Learn more about the SCOT ULTRA process by reading the article “A step change in tail gas treating unit performance at low cost with SCOT ULTRA" or refer to the SCOT ULTRA section on this website.

*CANSOLV, SCOT and SCOT ULTRA are Shell trademarks.

** Criterion Catalysts & Technologies LP (Criterion) is a wholly owned affiliate of CRI/Criterion Inc. and an affiliate of the Shell Global Solutions network of companies.

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