For process plant components and equipment, lifecycle costs can dwarf up-front purchase costs. This is particularly true nowadays because of rising energy prices, higher labor costs and the increasing need for uptime. But automation can help monitor, control and cut lifecycle costs.
Lifecycle costs represent the total cost of ownership of an asset, such as a control valve, reactor vessel, boiler or any other piece of equipment. (For a more complete description, see "Lifecycle Cost Definitions.")
How can automation be used to monitor, control and cut lifecycle costs for process equipment and components? The "big three" are reducing stress on equipment, enabling proactive maintenance and cutting energy use.
First is eliminating process upsets. As an anonymous refinery engineer explains, "Improved automation reduces stress on equipment caused by process upsets and unplanned unit shutdowns." Reduced stress obviously leads to fewer equipment breakdowns and lower maintenance costs.
"Our installation of a modern DCS reduced the number of upsets and trips," he continues. "Our operations and maintenance managers noted considerable improvements in production rates and mean time between failure rates. None of these control systems had as their express purpose cutting lifecycle costs, but the net effect of screwing up less often was to reduce lifecycle costs. If you don't break it, it doesn't need to be fixed."
Kenneth Marse, control systems specialist at Galata Chemicals (www.galatachemicals.com) in Taft, La., says his facility reduced lifecycle costs by eliminating the need to shut down the process to perform maintenance or repairs. Fewer shutdowns and start-ups equated to smoother running plants and extended equipment life.
The Taft plant uses four separate DeltaV control systems from Emerson Process Management (www.emersonprocess.com). AMS Device Manager software monitors the smart devices continuously, and raises alarms if any preset operating limits are exceeded. Some parts of the monitoring system rely on wireless communication back to the AMS.
"Every morning I check the alert monitor in AMS," Marse reports. "In one example, AMS gave an alert on a level transmitter that operators thought was working properly. I ran diagnostics on the instrument and found the electronics were going bad. We were able to order new electronics and plan the work while switching production. The result was no unscheduled down time, which means no loss of production. Catching a potential problem before it occurs avoids a great deal of troubleshooting and eliminates downtime."
Energy savings is the third big key to cutting lifecycle costs. Glenn Givens, president of Givens Control Engineering in Burlington, Ontario, Canada (www.givenscontrol.com), has been involved in several projects that simultaneously cut energy costs and increased equipment life.
"We automated the screening process for stock pulp used to fill a large tank at a paper mill," Givens explains.
"The whole system had to be ramped up to about 20 times the existing throughput." The concept was that the pump and screen motors could then be operated for approximately 5% of the time, saving energy and wear and tear." As an additional benefit, pump and motor life would be greatly extended.
"The two motors in question are 200-hp each, consuming 165 kW," Givens says. "Estimated savings were $30K to $40K annually." (See "Automating for Energy Savings," for more on this project.)
Operators Don't Always Buy In
Givens Control Engineering has done other projects that successfully saved energy. In one case, however, reluctant operators gummed up the works.
Refiners are high energy-consumption devices used in paper mills to cut fiber to shorter length. On a paper machine that had two refiners, operators could shut one down in some instances, saving 100 kW per hour.
Givens wrote a program to look at the tonnage, energy per ton and other factors, and display on the DCS when it was permissible to shut down one of the refiners. It couldn't be done automatically because it required manual closing and opening of valves.
Unfortunately, this program wasn't successful because operators didn't implement the shutdown sequence. "Some operators may have felt that quality would be higher running two refiners in parallel, or that there could be a risk of getting out of quality specs when doing so," says Givens. "Or it may have just been easier for operators to ignore it."