Utilising process simulation to reduce SOx emissions Technical guide on designing an effective tail gas treating unit add-on to a sulphur recovery unit
Ganank Srivastava Bryan Research & Engineering, LLC
S ulphur recovery units (SRU) have long been seen as the ‘emission controls’ unit of a refinery or gas plant. Contaminated off-gases and wastewater streams generated by various refinery hydroprocessing units are usually first sent to an amine treatment and sour water stripping unit for H2S scrubbing. Instead of incinerating all this recovered H₂S directly, most operators first send these acid gases to an SRU. The primary function of an SRU is to recover useful and harmless elemental sulphur (Sx) from H2S. The Claus process is the industry standard for sulphur recovery, converting H2 S to elemental Sx through partial combustion (thermal) and catalytic reactions. However, a straight-through Claus process typically achieves only around 95% sulphur recovery efficiency (SRE). The remaining sulphur-containing molecules, such as unrecovered H2S or unreacted SO2, all exit with the Claus tail gas and eventually still make their way to the back-end flare stack contributing to overall SOx emissions. As refineries look to expand and process more sour crude, the emissions footprint (especially compounded on an annual basis over time) is only going to rise. SOx emissions pose serious environmental threats by contributing to acid rain, air toxicity, and ground-level ozone formation. Therefore, it is imperative to look beyond the 95% SRE and push the target towards 99.9% or higher to not only ensure social responsibility but also meet regulatory compliance. Solution In the hydrocarbon processing industry, especially in sulphur block operations, tail
gas treating units (TGTUs) have been widely accepted to bridge this gap and play a critical role in ensuring environmental compliance and enhancing SRE. The need for cleaner technologies and stricter environmental regulations has made the design and operation of TGTUs not just optional but essential for sustainable operations. TGTUs are usually installed downstream of the Claus unit to capture and convert residual and unconverted sulphur compounds in the tail “ The need for cleaner technologies and stricter environmental regulations has made the design and operation of TGTUs not just optional but essential for sustainable operations ” gas to increase overall SRE towards 99.9%. It ensures the plant remains compliant with stringent emission standards. As environmental regulations become more stringent, this article aims to provide an in-depth guide for process engineers to effectively design TGTUs to ensure their refineries’ SOx emissions are well managed. Process scheme A standard TGTU configuration typically adheres to the following scheme after the acid gases pass into the straight-through SRU: • Hydrogenation reactor : Converts all remaining unconverted sulphur-containing species back into H2S. • Quench or cooling system : Reduces gas temperature.
Refining India
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