Just because your plant's control system is decades old—obsolete and in constant need of maintenance—doesn't guarantee that your company will be eager to throw $10 million your way for a new system. You might have all kinds of good reasons for an upgrade, but you'd better make a solid case for it. And you'd better deliver on the promised results too, or don't count on a second round of funding.
Charlie Watson, process controls manager for Koch Fertilizer in Wichita, Kan., recently went through the process of upgrading the control system in a 1960s-era ammonia plant. Speaking at the Yokogawa Users Group Conference in New Orleans today, he advised session attendees to carefully plan their arguments and justifications.
Watson's role for the past four years has been to design and implement DCS/SIS automation upgrades of equipment built in the ‘60s and ‘70s. Although the desire to upgrade might seem a legitimate request, engineers are likely to get some resistance nonetheless. "If you go to management and say your system's 20 years old and it needs to be replaced, the response might be, 'It's still running; why would you mess with it?'" Watson said, adding that other common responses include that there's no benefit to upgrading, and that people are used to the old system and don't want any changes.
Age and obsolescence do matter, however, Watson said. "It's old and needs to be replaced. That is a valid reason to do it." But of course there's more to the argument.
When the Bathtub Curve Starts to Climb
Watson showed a typical "bathtub curve" chart—a trend that every piece of equipment in a plant tends to follow in which there are typically some maintenance issues at the beginning of equipment life, then a (hopefully) long period during which the equipment runs relatively maintenance-free, and then the equipment begins to break down regularly.
"Predicting where the right-hand point of inflection is can be difficult," Watson said. Some general guidelines, however, are five years for HMI equipment, 10 years for field I/O and 20 years for DCS/SIS system components. "As your systems approach this age, you do have a very valid reason to start looking at upgrading those components."
Ignoring aging equipment will result in more frequent plant trips and upsets, Watson warned. "A couple spurious trips will buy a new system."
There are other reasons to upgrade as well. "If the DCS/SIS is really obsolete, you might not be able to get spare parts after you use up what you have," Watson gave as one. Another is that you are likely to find some major economic benefits to doing an upgrade. "There have been so many advances over the years [that] there are additional economic benefits that can be realized."
Performance Improvements Count Too
For example, a single-loop controller typical of the 1960s and 1970s being upgraded to a second-generation DCS today will gain advanced process control capability that will typically yield a 1% to 3% efficiency improvement. The new system will also likely add a historian, alarm logs and trends for optimization and troubleshooting; enhanced reliability due to support of redundant instrumentation and I/O cards; ease of future expansion; and a host of benefits that come from upgrading from a first-generation to a second-generation DCS.
Upgrading from a Gen 1 to Gen 2 DCS can provide enhanced reliability of the plant as a whole due to the integration of smart devices; better SIS integration; integrated model- predictive control, which typically yields a 2% to 3% capacity improvement; ISA18.2-compliant alarm management systems; easier FDI integration via Modbus TCP; powerful IEC1131 programming languages; hardened I/O that be located outdoors; and secure remote access capability and better ERP integration.
"The best thing of all is that the equipment is new again," Watson stressed. "You're back to the good side of your bathtub curve. It will be relatively maintenance-free for many years, and spare parts will be available."
Watson listed more benefits pertaining to other types of upgrades, but the gist of it was better performance and significant savings over time. He outlined the savings to be gained in a hypothetical ammonia plant that produced 1200 tons per day. On a yearly basis, that plant could save $700,000 for each 1% efficiency gain; $900,000 for each 1% capacity gain; $500,000 for each spurious trip that's avoided; $100,000 in instrument maintenance; and $1.3 million if the major turnaround frequency can be increased from two to three years.
"Your experience and benefits will be different, but those are typically the big hitters if you're trying to define the benefits," Watson advised. In his own batch plant, when the automation upgrade was done, they actually achieved a 30% increase in production, he added.
Don't Neglect the Human Factor
Delivering results is important, but it's not just the technical gains that need to be considered. "Human factors are every bit as critical to success as the technical factors," Watson said. "If you don't do this part right, you won't get funded for your second project."
Consider that you will be taking away a control system that operators have been used to for 20 years, regardless of how well it may or may not work. They will be dealing with big changes. "If you want money for your second project, you've got to get this right on the first one," Watson warned.
To do that, be sure to plan for:
- Operator involvement in the graphics design. "As engineers, we may think we know how to design graphics, but you'll get a much better project if you have operators work on it with you," Watson said.
- Operator involvement in software factory acceptance tests. "They'll help catch what's not right."
- Operator training is critical. Be sure to develop a simulator too.
- Maintenance technician training is important too.
- Alarm management. In a new control system, the number of alarms jumps into the thousands, Watson noted.
- DCS/SIS management of change procedures. "If you don't have a good change management process, it'll be a nightmare."