As the intentionally counter-intuitive industry expression goes, “All processes are batch processes to some degree.” This reflects the reality that even in so-called “continuous” process plants, the units will need to be shut down at some point and then restarted to resume production. And whether performing unit startups or shutdowns (planned or unplanned); making grade or production rate changes; switching feedstocks; or even performing maintenance work during turnarounds, plant personnel must perform specific procedures correctly and in the correct order to ensure smooth plant operation, worker safety and environmental compliance.
To help reduce fuel consumption, improve safety and enhance knowledge transfer at its commercial-scale distillation pilot plant in Stillwater, Okla., Fractionation Research Inc. (FRI, www.fri.org) implemented procedural automation in 2011 with encouraging results. The pilot plant includes two distillation columns (one high-pressure, one low-pressure), plus associated boilers, condensers, cooling water towers, etc.
Commercial refineries typically aim to maintain safe and efficient steady-state conditions for as long as possible (with planned shutdowns only every two to six years). As a research facility, however, FRI typically starts up and shuts down its process units about 20 times per year, performing several operating condition transitions each day. In this type of operating environment, it’s obvious that reducing the number of manual control actions required to shut down the units safely and reach steady state following startups and transitions could provide significant safety and other benefits.
Before initiating the project, FRI controlled and collected operating data in its pilot plant using a small-scale distributed control system (DCS), and performed most analysis using spreadsheets. While the DCS handled steady-state process control, operators performed the relatively frequent startups, shutdowns and transitions manually. As a result, the speed in which steady-state operations could be achieved depended on the skill and experience of the individual operator performing the procedure. This often resulted in less-than-optimum energy consumption and occasionally raised safety concerns.
“Procedural automation appealed to us because we’re interested in safety and we thought this would help our younger, less experienced operators operate the unit in a way that is closer to how our senior operators do it,” says Pete Parker, FRI’s president. “We were also interested in more uniform operation, since natural gas to produce steam is our second largest cost area. We thought procedural automation could reduce our time to steady state and thus reduce energy consumption to a significant degree.”
To determine best practices, a team composed of FRI and Yokogawa personnel carefully evaluated existing procedures, and an experienced FRI board operator documented how he performed startups, shutdowns and setpoint changes. The team then captured these best practices in Yokogawa software, which created the flowcharts needed to develop appropriate automation logic. For those procedures that did not lend themselves to full automation, the software also generated some guided, semi-automatic procedures. The team then jointly reviewed and tested the automated and semi-automated procedures and validated the logic, making adjustments as needed.
For the initial trial runs, the procedures were run in offline mode to ensure that the operator had full control at all times. According to Parker, after further fine-tuning and experimenting with it for several months, the operators finally began to accept the technology and use it with some frequency.
“When developing procedures, it’s necessary to understand why it’s being done the way it is being done,” says Anand Vennavelli, associate research engineer with FRI. “At FRI, we initially get input from all our operators, but the best and most experienced operator always reviews and validates it.”
FRI ultimately succeeded in reducing the time it takes to collect a data point after making a set change in the unit from three hours to about one hour for many of its runs.
Evidence suggests that several well-publicized industrial accidents in recent years occurred because procedures were not followed properly. ARC Advisory Group believes that procedural automation could have helped avoid many of these incidents, or at least significantly minimized the human and environmental consequences.
>> Paul Miller, [email protected], Senior Editor and Content Director at ARC Advisory Group (www.arcweb.com), has been studying and writing about the industrial automation industry for almost 30 years.