Having structured, written procedures not only meets regulatory requirements but also aids in the efficient and economical operation of a process plant. A U.S. Gulf Coast refinery with an average-sized fluid catalytic cracking unit of 80,000 bpd will lose over $75,000 a day for a downed unit. Therefore, it is critical to maximize efficiency when executing start-up procedures on a unit.
A procedure sequence flow diagram (PSFD) is designed to help users logically organize information relating to a complex process providing a graphical outline of tasks. The PSFD makes it easy for personnel to visualize the entire sequence of performing a complex unit operation, such as a unit start-up or shutdown from an operator’s perspective.
The PSFD follows a left to right flow with logic sequence lines connecting the blocks. Blocks that appear parallel to one another are independent and can be performed simultaneously, resulting in an acceleration of the event, although the blocks themselves do not represent time.
These diagrams do not reveal information about resource usage. A key design consideration is the PSFD preparation assumes “unlimited resources.” Thus, if multiple blocks are shown in parallel, then logically they can all commence at the same time. Obviously, this may not be the case if there are personnel constraints for a unit.
The PSFD is a tool that can be used in:
- Consensus building.
- Planning.
- Coordination and communication.
- Training.
The PSFD becomes a common mental model for system experts to refine over time. During development of the PSFD, system experts on various parts of the unit discuss their approaches to operating the unit, decide on the best approach to use and then revise the PSFD to reflect their consensus best practice.
The unit may be partially operating with some systems operating and others shut down for maintenance. Planners can easily identify which tasks appearing on the PSFD apply and then develop a customized plan using only those tasks necessary to accomplish the desired objective.
Complex unit operations like start-ups and shutdowns almost always extend beyond one shift. An added advantage of using PSFDs is shift changeover is accelerated and the likelihood of inadvertently omitting a key unit status element is reduced. As each task is completed, personnel can check it off on the master copy of the PSFD. An oncoming shift can then rapidly integrate what took place during the previous shift and quickly visualize the current status of the unit. On-shift supervisors can then determine their shift priorities, divide their personnel into appropriate teams and provide clear instructions on which tasks each team needs to complete.
The PSFD serves as a mental map that helps new operators visualize the “big picture” and see how each task fits into the operational scheme. It also facilitates the development of training materials and standard operating procedures by helping to determine their overall scope. The logical grouping of common tasks facilitates efficient data collection of the steps necessary to successfully complete each task and when similar tasks can be combined
Many tools provide performance support for operators, but having a PSFD available can assist in providing a safe and cost-effective unit start-up.
For more information, visit http://oilgas.gpstrategies.com, call Joe Janney at (713) 284-1816 or email jjanney@gpstrategies.com.