FCC fundamentals: turnaround best practices
Basic procedures and activities are presented for the unit engineer and other support personnel, designed to ensure a successful and safe FCC turnaround
Ziad S Jawad
Shaw Energy & Chemicals Group
Viewed : 10085
The term “turnaround” was coined as oil refining itself was just being developed. Large barrels were used to heat and process crude oil, and periodically these barrels had to be turned as the metal exposed to the heating element degraded; hence, the term “turnaround”. Today, a turnaround has a much more involved meaning. Wikipedia describes “turnaround” as follows:
“In petroleum refining and chemical manufacturing, a term meaning a scheduled large-scale maintenance activity wherein an entire process unit is taken off stream for an extended period for comprehensive revamp and renewal. This operation involves a lot of preparation, and many precautions are taken because this is a dangerous operation (especially at startup).”
This article presents a collection of best practices and examples of pitfalls to avoid, which, if taken into account in advance or incorporated into the planning and work scope, will help to guarantee a safe and successful turnaround. This is the third article in a series entitled FCC fundamentals, designed to help unit engineers and other support personnel maximise a scheduled FCC shutdown. Just as in the early days of refining, thoughtful planning and execution will result in an efficient turnaround, saving time and money, and ensuring a long and profitable run. Above all, advance preparation is critical for the safe execution of the plan, as, in the end, finishing the job safely is the factor of most value.
Advanced turnaround preparation
As with most difficult tasks, advanced preparation is the key to successful completion. Unit engineers should be engaged early in the preparation stages, including the development of capital projects, work scope and shutdown/startup plans. It is important to baseline normal operations pre- and post-turnaround with an equipment evaluation that includes a complete pressure survey and material balance. This will help to quantify the success of the turnaround, in addition to being a valuable tool when providing input to the work scope. Keep in mind that work scope recommendations must be accompanied by solid justification.
The unit engineer’s time during the turnaround is valuable. There tends to be a waiting period, followed by several activities that require immediate and simultaneous attention. The result could be missed inspections or concerns that are not addressed. The execution of the turnaround work must not be delayed. To avoid these situations, prepare an inspection plan in advance of the shutdown. Include checklists and assemble all required mechanical drawings. Table 1 shows a checklist for a distillation tower. This checklist can be duplicated for each tray in the tower. The purpose is not to capture everything that could possibly be inspected, but to ensure a thorough inspection and help document the findings. Keep a master copy, either electronic or paper, and make copies to capture findings and notes during each trip inside the unit. An “attrition source checklist” is specific to FCC and includes a list of aeration or steam connections and associated restriction orifice diameters for quick verification during the shutdown. Steam/air rings and cyclones are other possible candidates to thoroughly inspect when searching for potential attrition sources, including checklist items.
Similar to checklists, equipment drawing packages can be prepared well in advance of the turnaround and tailored to specific inspection tasks. Keep a master copy of the drawings that reflect existing equipment and new equipment to be installed. The master should be kept in the office, where additional copies can be reproduced for use during the inspection. One example is a separate drawing package for the equipment accessible via each manway on the reactor or regenerator. Knowing the scaffolding plan in advance is also helpful. During the inspection, it is usually busy, noisy, dirty and dark. Simplify the task by cutting out important parts of the drawings. Group these parts on a smaller piece of paper and highlight important items for quick reference when inside the vessel. For example, mechanical drawings of the reactor stripper can be simplified on one or two pages, showing steam rings and important dimensions. Main fractionator drawings can be simplified to just a few pages, showing odd, even, draw or feed trays each on their own sheet. These should accompany a checklist and can also be used to take inspection notes.
Shutdown and startup procedure
The job of managing the FCC catalyst inventory, which is particularly important, immediately preceding and following a turnaround, is commonly assigned to the unit engineer. At shutdown, the capacity of the hoppers must be adjusted to allow enough room for all of the catalyst in inventory to be unloaded. Similarly, enough catalyst must be available at startup to completely inventory the unit and sustain any losses until the next fresh shipments arrive. These tasks can be tricky at times due to losses during shutdown and startup and usually involve selling or disposing of equilibrium catalyst before shutdown and purchasing it during the shutdown.
The FCC shutdown procedure usually begins several days before the actual point of feed out; early activities include the discontinuation of the use of additives or addition of fresh catalyst. Similarly, the startup procedure does not end at feed in, but continues for several days until the unit is completely “lined out” and operating normally. The unit engineer should be familiar with all of the shutdown and startup procedure steps and, at times, work closely with operations to assist with the development or optimisation of these procedures. One possible task is the evaluation of special procedures such as washing or decontamination procedures. Part of this task is the selection of speciality solvents or other cleaning agents. There are several products that are useful when attempting to properly clean for entry to the main fractionator or gas plant equipment. These products are very effective for vessels in dirty or sour services and accelerate the steam-out time considerably. The chemical vendor should be contacted as well regarding recommended procedures, setup and the safe use of the chemical.
Technical support during critical steps of the startup procedure is invaluable. Operational problems must be quickly resolved and constant troubleshooting is usually required. Another important task is the monitoring of catalyst levels during loading to minimise stack emissions or carryover to the main fractionator. New equipment startup will not be familiar to operations support personnel, and additional technical support is almost always required.
Unit shutdown and startup are excellent learning opportunities for the FCCU engineer. Time should be taken to sit on the board during this period and learn more about unit operations. The unit will experience many transient operating conditions that are not normal and only seen as the unit shuts down or starts up.
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