The Shell Off-gas Treating (SCOT) process has been developed to remove sulfur compounds from Claus tail gas to comply with stringent emission regulations. The LT SCOT process is a design that reduces energy consumption, improves system reliability and operability (for revamp units) and can be installed for a lower investment cost in new installations compared to a normal SCOT.
Jacobs Comprimo® Sulfur Solutions pioneered a low temperature innovation for the (SCOT) technology known as Low Temperature SCOT or LT SCOT. This technology advancement provides the dual advantage of reduced energy consumption and lower capital investment requirements.
The LT SCOT process utilizes the same steps as conventional SCOT but with several key differences.
The hydrogenation reactor for LT SCOT operates at 220 C versus 300 C in the conventional mode. At this low temperature, the LT SCOT reheater can be a steam heat exchanger instead of an in line burner. Steam heating eliminates the need for fuel gas and reduces the total gas flow to the LT SCOT process.
The resulting lower gas flow volume, due both to lower operating temperature and by eliminating the added combustion gases, means that the LT SCOT reactor size and catalyst bed is smaller relative to a conventional unit. This reduces capital cost.
The gas leaving the reactor proceeds to the quench stage. Because the gas temperature is lower, the LT SCOT design does not utilize a heat recovery boiler ahead of the quench column, providing further TIC savings. Since this boiler would only provide LP steam, the lost steam production is rarely an issue.
The LT SCOT process has operational advantages as well as cost advantages. The traditional line burner is a significant maintenance item and usually the largest cause of unit trips. Eliminating the line burner in the LT SCOT design means improved system reliability. Next, because there is no flame in the LT SCOT process, the risk of soot generation within the system is eliminated, again improving reliability and system flexibility. Finally, steam reheating improves the unit turndown capability, generally from 30% for conventional SCOT to 15-20% for LT SCOT based on proper attention to the quench and absorber stage design.
As with the conventional SCOT, the LT SCOT design can be integrated with the amine treating system upstream of the Claus plant to achieve equipment cost savings. The rich amine from LT SCOT can be routed to a common regenerator for the two systems; this is called a Cascaded SCOT. The common regenerator must be sized to handle the two streams. The cascaded SCOT design is also available for LT SCOT. The partially loaded solvent from the LT SCOT can be routed to an intermediate tray of another absorber where its remaining acid gas loading capacity can be used.
(as compared to conventional SCOT and other amine treating designs)
- Improved turndown, as low as 15%
- Lower Equipment Count reduces TIC and maintenance costs
- Eliminating the line burner improves reliability
- No fuel gas required - energy saving and lower CO2 emissions
- Lifecycle cost savings greater than 10%
The first LT SCOT unit was commissioned at a refinery in Germany in mid-2004. The system was tested, optimized and fine tuned through a wide range of temperature regimes. Since that time, 25 other LT SCOT units have been designed.
More than 200 conventional SCOT units are operating throughout the world ranging in capacity from 3 t/d up to 4,000 t/d sulfur production.
Jacobs Nederland B.V., Leiden, The Netherlands, and Jacobs Canada, Calgary together forming Jacobs Comprimo® Sulfur Solutions is one of the three authorized licensors on behalf of Shell Research Ltd. since 1981.