The Technology Solution That Enabled Pdo’S Yibal Khuff Sudair Project To Meet Oman’S Highly Stringent Emissions Regulations
Much depends on Petroleum Development Oman’s (PDO) Yibal Khuff Sudair integrated development project. When it comes online in 2019, it will produce oil and gas to sustain the Sultanate of Oman’s industrial growth and provide gas for enhanced oil recovery techniques to boost the amount of crude oil that can be extracted from the country’s other oilfields.
As with any mega-project, there are significant challenges. Chief among these at Yibal Khuff Sudair are the nature of the gas produced, which will contain about 3% hydrogen sulphide, 5% carbon dioxide and other contaminants such as mercaptans, carbonyl sulphide and nitrogen, and the export gas total sulphur specification of <5 ppmv.
Even more challenging, though, is the combination of the ultra-high sulphur-recovery efficiency (SRE) specification of 99.9%, and sulphur dioxide (SO2) emission regulations, which, at 35 mg/Nm3, are among the most stringent in the world.
“The SRE requirement is in line with many other countries’ regulations,” says Rajiv Srinivasan, Senior Process Engineer, PDO. “However, the SO2 emission requirement is much lower than the International Energy Agency World Bank guidelines for sulphur recovery units (SRU), which stipulate less than 150 mg/Nm3. The Omani government was probably ahead of the game with this one.”
The combination of these two regulatory requirements, Srinivasan says, made the design of the gas treatment and sulphur recovery facilities extremely challenging.
It was clear to PDO that best-in-class solutions would be necessary for the project to comply with the standards. Cost would also be an issue, as achieving ultra-high SRE levels typically sees costs increase dramatically.
Working with Shell Global Solutions, PDO investigated the potential of various sulphur-recovery technologies and flue gas desulphurisation solutions.
“There were only a few technology choices available on the market to meet the stringent regulatory framework, and just two that could do it at a reasonable cost,” says Srinivasan.
One of these involved a regenerable SO2 scrubbing process: Shell Global Solutions’ CANSOLV® tail gas treating plus (TGT+) technology, which is based on a Cansolv Technologies Inc. process.
This post-combustion regenerable wet scrubbing process uses a proprietary aqueous amine solvent to remove SO2. The captured SO2 is recycled as a pure stream to the SRU reaction furnace, where it reacts with incoming hydrogen sulphide in the acid gas to form elemental sulphur. SRU tail gas and other sulphur-containing gas streams are directed to a thermal oxidiser where all the sulphur compounds are converted to SO2. The incinerated gas is cleaned and cooled in a wash tower before entering the CANSOLV SO2 absorber, where SO2 is selectively removed.
Crucially, the CANSOLV solvent is highly selective to SO2. No other compounds in the gas are absorbed: they are discharged directly to atmosphere through the stack. The SO2-containing solvent leaves the absorber and is regenerated using steam to produce a concentrated SO2 stream that can be accommodated by the SRU.
The other technology was flue gas desulphurisation. However, there were concerns about this: the large volumes of caustic necessary and the disposal requirements would lead to onerous logistics. In addition, as a specialist technology, the flue gas desulphurisation unit would have to be sourced from a different licensor to the rest of the gas treating block. That meant that the 35 mg/Nm3 SO2 requirement would be extremely difficult to guarantee.
Srinivasan explains that the project team was keen to avoid sourcing units from different licensors. “We have been in similar situations on other projects: the battery limit conditions of one unit did not match the battery limit conditions of another because different licensors supplied them.”
Instead, Shell was able to license and take design responsibility for the entire gas treating and sulphur recovery block. “The package we have licensed from Shell Global Solutions involves a relatively complicated line-up of seven technologies, which are all heavily interlinked,” Srinivasan explains. “For PDO, as the customer, having an integrated licence is a major advantage. It means that Shell Global Solutions assumes responsibility for making sure that the interfaces between the various units are robust. It also maximises the scope for optimisation.”
At Yibal Khuff Sudair, this optimisation extended beyond the gas treating block; many of the decisions that Srinivasan’s team made had positive impacts on the overall central processing facility, not just the gas treating complex. “For instance, we were able to move the compression requirement of the project from the sour gas side to the sweet gas side by reducing the facility landing pressure,” he says. “Shell wanted to understand our needs very clearly, and we worked together extremely closely to arrive at this solution.”
To facilitate the transfer of knowledge and best practices, some PDO process engineers were seconded to the Shell project team. One of these was Ahmed Azizi, who relocated to Amsterdam, the Netherlands, during the preparation of the basic design package.
Here, Azizi was heavily involved in the simulation of the project’s SRU and the incinerator. As a result, he has captured and documented the key operating philosophies, constraints and best practices associated with the technology. PDO will leverage this information to help overcome operational difficulties or optimise the units in the future. This secondment, he says, has given him a better feel for the sensitivities in the design and the design decisions that the project team took.
“It was also a fantastic experience,” he adds. “Being in such an environment full of multidisciplinary expertise was just wonderful. If you have any technical issues you can work them through with a seasoned professional and develop solutions with them.”
The technologies that PDO has licensed and the design that the two organisations developed through such close collaboration are set to achieve ultra-high sulphur-recovery levels and adhere to some of the most stringent emissions standards that the industry has seen. “We have pushed the technological boundaries with this line-up and, as a result, we are able to set new standards,” says Srinivasan. “The project has been an enormous success.”
For more information contact Alexandra Anghel
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SO2 emission control specialist Cansolv Technologies Inc. is a wholly owned subsidiary of Shell Global Solutions International BV.
Cansolv is a Cansolv Technologies Inc. trademark.