Over a period of many years the engineers on the sour water stripper (SWS) had noticed that the overhead FinFans were becoming heavily fouled and losing efficiency. This was causing deterioration in the level of performance of the fans. The reduction in exchanger duty had led to excess steam being sent to the sulphur units. Excess steam, especially when excess ammonia is in the system, leads to operational difficulties and corrosion of pipe work.
During the clean, the refinery would need to keep the overheads on the Sour Water Stripper online to allow the process fluids to keep circulating. Conventional methods such as water blasting would have cooled the circulating medium in the tubes, thereby causing the deposition of ammonia salts. If the temperature in the tubes is reduced it can lead to ammonia blockages.
After working closely with the Operations Team to understand the issues, and come up with a solution, ProDecon was given the contract to perform the clean. ProDecon’s technique of using a specially modified inert crystal media, driven by compressed air, proved highly effective. The non-abrasive method effectively cleared out all of the detritus between the fins, but was gentle enough to ensure that there was no damage. Moreover the overheads could be kept online, improving productivity and avoiding the risk of internal plugging.
After the clean, the refinery was able to report that the improved efficiency of the fans was allowing for increased sulphur recovery. This had the knock-on effect of significantly reducing the amount of steam and ammonia that was passing downstream. As a result, there were reduced levels of corrosion downstream. Additionally, a refinery engineer believes that, “one of the additional benefits of this performance increase is that it might lead to a reduction in the downtime of the SWS during the October turnaround. During that event, the refinery’s sour water will accumulate in tankage. If this volume can be reduced, this will limit the amount of tankage required and speed up the removal of the water after the event.”
The Customer’s View
“The results have exceeded our expectations; with our exchanger outlet temperature well under control....... their operation is much more stable” – A Client Treating Development Engineer.