GasPlant Decon TESTIMONIAL " There is no doubt it cut down on our time compared to traditional water flushing and nitrogen purging from isolation to vessels being ready for entry " Shutdown Manager
No.7 CASESTUDY
SHETLAND GAS PLANT
OVERVIEW This was the first TAR carried out at the Gas Plant since its commissioning in 2016. There was no previous history of TAR performance and site had concerns regarding the levels of fouling and contamination. Expected timings and duration targets were therefore determined based on experience of other similar projects. The decontamination scope of work included MEG Filtrate Vessel & Pre-treatment Filtrate Vessel, Liquid Coalescer and Coalescer Inlet KO Drum, Produced Water Flash Drum and the Closed Drains Drum. CHALLENGES As this was the first TAR at this site, the client had no previous history information to indicate the likely levels of contamination and fouling. The planned TAR duration presented a challenge and it was important to have plant items released quickly for inspection and maintenance to maintain TAR target scheduling. PAST PROCEDURE There was no previous experience at this site for the client to draw on in planning and implementing this TAR since it was the first TAR outage at site. DECON SOLUTION A combination of Vapour Phase and Boil Out processes were applied, with vessels on the MEG unit having a Vapour Phase application of Zyme- Flow® UN657 and all other vessels decontaminated using a Boil Out process. All vessels were drained and prepared by Client Operations personnel then permits issued to Denholm for rigging of decontamination equipment. Zymeflow processing permits were then issued and decontamination commenced. enquiries@denholm-macnamee.com Tel: + 44 (0) 1467 629 933
RESULTS All vessels were decontaminated within the 12- hour time frame (apart from Closed Drain Drum which was interupted by loss of water supply to site) with H2S and LEL levels reduce to Zero and no issues with pyrophoric iron sulphide. The closed drain drum process had to be amended but once this decision was taken the drum decontamination was quickly achieved. The sludge removal from the vessels was achieved much more quickly than expected as the decontamination process also conditioned and reduced the volume of residual solids. All vessels were successfully completed within the 12-hour decontamination window apart from the Closed Drain Drum. This was due to loss of water supply to the whole site half way through the decontamination process which meant that the boilers tripped out on low water and subsequent cooling of the vessel resulted in draw back of contaminants from the flare. A nitrogen purge was applied to prevent further ingress from the flare and analysis indicated that the contaminants were present in the Vapour space of the vessel and were being removed by the Nitrogen purge. It was therefore decided, after discussion between Denholm and the client, that continued purging would be successful in quickly removing the contaminants that had been liberated from the sludge in the vessel base rather than re- commissioning the boiler. Purging continued and H2S and LEL levels quickly dropped to within acceptable limits.
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