Planning for a pipestill clean
A combination of proven technology, setting expectations and developing a detailed plan helped a refiner achieve optimum results from unit clearing and cleaning plans
Cody Nath, Refined Technologies
Uwe Klingler, BP
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BP’s Texas City refinery and Refined Technologies implem-ented a team strategy on BP’s Pipestill 3A (PS3A) outage and demonstrated that refiners can apply best practices to their owen shutdowns. These practices are related to:
• Selecting the appropriate cleaning technology and vendor personnel for the application
• Defining the key planning deliverables required as part of the clearing and cleaning strategy
• Dedicating the manpower resources required to create a detailed plan to achieve these deliverables
• Communicating the plan to the organisation
• Executing the plan in the field
• Archiving the plan and document-ing lessons learned for future turnarounds.
In 2008, the attitude at BP’s Texas City refinery reflected its corporate performance principles: compliance with law and ethics, continuous improvement, establishing internal targets and incorporating a thorough risk assessment. With a major pipestill turnaround approaching in the autumn of 2008 (PS3A), BP had an opportunity to apply these principles. The fact this turnaround was coupled with other processing units, including a large FCCU, made the opportunity more significant.
The history of turnarounds at BP has been a story of the continuous pursuit of best practice. In the not so distant past, completing a successful chemical cleaning was often like coming home from a trip to the doctor — the best you could hope for was no bad news. In the case of chemical cleaning, this meant no excessive delays, no pyrophoric fires, no hydrocarbon left in equipment and no safety incidents. In the specific case of previous PS3A vacuum tower turnarounds at BP, the chemical cleaning results were poor. In particular, residual hydro-carbons were left inside the vessel.
BP’s management challenged the team to find a better way. By implementing proven technology, setting expectations, establishing communication channels and committing resources during the pre-turnaround phase, a refiner can move beyond decontamination to a predictable, strategic application of chemistry to leave a process unit completely hydrocarbon free and ready for safe work. Furthermore, it is possible for a refiner to hone the process with a lessons learned approach, making the results repeatable in the future.
Select the technology
The PS3A team from BP began planning the turnaround with this in mind. Opportunities for improvement were found in many areas, but perhaps the greatest overall opportunity was in the area of improving the chemical cleaning strategy for the 42ft-diameter vacuum tower. BP had experienced considerable difficulties in the past. The team searched for opportunities to improve performance in clearing and cleaning the unit, targeting a 24–48-hour reduction in the overall clearing and cleaning timeline without compromising safety.
Historically, BP had four methods for cleaning a processing unit: liquid-phase circulation, vapour phase (steam-out), vapour phase with water-based chemistry (com-monly called decontamination) or a combination of these.
For equipment used in heavy hydrocarbon service, such as vacuum towers, the most effective methods had been: a light gas oil or diesel flush performed by operations to dissolve a significant portion of the heavy hydrocarbons; a liquid-phase cleaning to further remove the heavies; and a decontamination step with steam and an aqueous chemical cleaning solution, com-posed of any number of components, from surfactants to oxidising agents or diluted degreasers.
Traditionally, deactivation of pyrophoric materials would occur either concurrently with the degreasing step (usually in the vapour phase), or in an additional liquid-phase step at the end of the process. BP previously used a permanganate product in a circulation loop to address the iron sulphides. The problem with traditional cleaning methods for deactivating pyrophorics is that the prior cleaning steps are not effective at completely removing the hydro-carbons, especially in the packed sections of columns. Often, a hydrocarbon film is left on the surface of the iron sulphide, insulating the pyrophoric material from the oxidiser. When an oxidising agent is introduced, it is impossible to know if it is reacting with residual hydrocarbons or pyrophoric iron sulphides. As a result, pyrophoric reactions in BP’s vacuum column could occur when the tower was opened, even after an extended permanganate flush.
The BP team evaluated the risk of choosing a completely new vendor with new technology set against the option of trying to enhance traditional methods. Relatively low-cost chemistry usually leads to decent decontamination. However, the process is lengthy and there is not a high degree of certainty that the effort will produce a remarkable result. With this in mind, the â€¨BP team established criteria for evaluation of vendors.
chemistry and application method
Refined Technologies’ chemistry, known as QuikTurn, does not contain water, so it is fundamentally different from chemistry commonly applied in the industry. Its high solvency strength enables it to rapidly dissolve heavy oils upon contact and without recirculation. It is applied with steam to greatly reduce the duration of cleaning. The solvency mechanism also increases with temperature, so the result is a hydrocarbon-free tower after 12 hours or less. The same cleaning mechanism works in the vapour phase to remove the light hydro-carbons generally responsible for lower explosive limit (LEL) readings. The chemistry renders the vapour space completely free of hydrogen sulphide.
Refined Technologies was selected to meet BP’s criteria. The decision was followed by discussions and final decisions on the timelines for completing the walkarounds, a mechanical needs list, procedures and all piping and instrumentation diagrams (P&IDs) for the appli-cation. The BP team wanted to eliminate uncertainty in the chemical cleaning timeline and its effective-ness, so it was important to know that the performance promised was predictable.
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