Transfer of Sulphur in Petrochemical Applications with Inert Surface Coatings

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The Advantage of Inert Coatings

When adsorption of sulphur containing compounds is prolonged (during priming for example), desorption of sulphur from the surface can slowly cause disruptive false readings in process, refining and down-hole sampling applications. This ‘memory’ of adsorbed sulphur compounds can cause long delays in equilibrating a sample stream. Figure 3 demonstrates the memory effects of three types of tubing used to transfer streams containing sulphur compounds. The inert coating (SilcoNert 2000) shows less retention of sulphur compounds by several orders of magnitude, indicating very high sulphur inertness. Passivated or primed electropolished and stainless steel tubing desorbs or release sulphur compounds. This memory effect can disrupt sample quality, and prevent accurate monitoring of process and environmental conditions.

Priming or passivation can also significantly slow or extend accurate sample transfer in petrochemical plants. Figure 4 compares the sulphur transport properties of 100 feet (30.5 metre) lengths of electropolished, raw commercial grade and inert coated (SilcoNert 2000) 1/8in OD x 0.020 in wall stainless steel tubing. Uptake of 500 ppbv methyl mercaptan sulphur compound by the three tube surfaces shows – the SilcoNert 2000 coated tubing did not significantly adsorb the methyl mercaptan, while delivering a representative sample with no delay. The untreated surfaces completely adsorbed the methyl mercaptan for up to 90 minutes and did not stabilize until up to 140 minutes.

Coatings Provide 'Out-of-the-Box' Solutions

Commercially available inert coated components have eliminated the need for passivation, and are now recognized as a ‘use out of the box’ solution to sulphur sampling and transport reliability. This eliminates the need for working with dangerous materials such as high concentration H2S to passivate or prime the sampling pathway. The value delivered by coating solutions cannot be taken for granted in comparison to passivation techniques, which increase the risk of obtaining poor analytical results. Inert pathways, such as SilcoNert 2000 treated stainless steel, results in more accurate sampling and faster cycle times. Shorter sampling cycles translate directly into more samples collected and analyzed. Process upsets can be detected faster, while false readings, associated with passivation, can be eliminated. Typical savings can be calculated by looking at average per-hour cost of operating a process that relies on accurate quantification of sulphur compounds. A one hour delay in operations can cost an 800,000 ton per year ethylene plant $50,000 USD. A 250,000 ton per year LDPE unit will cost operations $36,000 USD for a one hour upset.

* The authors are from SilcoTek Corp., USA. Tel.: (814) 353-1778

* E-mail contact: silcod@silcotek.com.

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