The Kraft paper process starts with wood chips and includes digesting, washing, delignification, bleaching, sheet forming and drying. “All involve flows through valves, measured by transmitters,” said Keith St. Thomas, systems technologist, Nanaimo Forest Products, “Many processes to be measured, monitored and controlled.”
St. Thomas co-presented “Using AMS Device Manager to reduce downtime and increase process efficiency” at the Emerson Global Users Exchange this week in San Antonio, with Colin Murphy, asset manager, Spartan Controls. Spartan is an Emerson Impact Partner in western Canada.
Harmac Pacific Division of Nanaimo Forest Products is a Vancouver Island, British Columbia manufacturer of Northern Bleached Softwood Kraft (NBSK) pulp. The plant was built in the 1950s and has had a number of owners, most recently a group of 350 workers who invested $25,000 each and, along with some large investors, purchased the mill in 2008.
Harmac decided its historical way of maintaining control valves and instrumentation could be more efficient and less costly. Taking advantage of diagnostic capabilities of smart devices could assist with reducing maintenance costs, improving reliability and minimizing loop variability, resulting in a more efficient process.
Smart devices offer opportunities
All the devices that have smart information can be accessed by Emerson AMS Device Manager and can generate Plantweb alerts on three levels: advisory, maintenance required and failed. An advisory means there is a minor problem that does not affect the process or device. “Maintenance required” means a problem that, if ignored, could eventually lead to failure, so prompt action is needed. A failure is a problem that compromises the function of the device, and requires immediate attention.Receiving and acting on maintenance alerts in AMS Suite prevents process alarms and upsets. Knowing which valves require attention before a planned shutdown helps with scheduling resources, and if necessary, further valve testing can be conducted without pulling the valve for inspection.
“You always want to have this screen on the monitor. Sometimes people don’t see things, and the key is to have this screen up,” said Murphy.
“In the past, we did ad hoc maintenance,” said St. Thomas. “We would shut down and do valve analysis, then if we had a problem, we would have to rush to fix it, or wait until the next shutdown.”
In one example, one of three identical blow line valves on the digester required three times as much torque to stroke as the other two. “We couldn’t get to it during that shutdown, and it failed a few months later,” St. Thomas said.
In another case, a machine room butterfly valve signature was rounded in the seating area and wouldn’t close all the way. “We pulled the valve, and found a wad of emery cloth in it.”
A third example was a steam vent valve with whisper trim. On examination, it had weld slag stuck in the whispers.
“We could collect these signatures during operation using a HART communicator, but at 30 minutes a valve, it would take one person more than a year to do all the valves in the plant,” St. Thomas said. “We can preventively replace valves on a schedule, but that’s a waste of money—if we could have gotten another year from the valve, it wastes useful life. And it wastes time during a shutdown.”
Now, the plant is running valve signature tests on Fisher ValveLink software inside AMS Device Manager. It opens and closes the valve, and checks how it tracks with the signal and actuator. Any offset shows a problem. The key is to know what the valve looks like when it’s good—new or rebuilt—then look for deviations.
“What if you have a sub-par transmitter or a bad pH probe?” said St. Thomas. “Faulty valves and transmitters are harder to detect than ones that have failed, but cause lost efficiency and lost productivity that add up to real dollars.”
Then too, you may have field devices in hard-to-reach and hazardous areas, with corroded covers and screws. Can you get in there to truly and precisely measure valve response?
Getting it going
To convince management that online diagnostics would pay off, the mill did a pilot. “We identified the top 25 valves and did a study of the cost of valves and labor for preventive maintenance,” said Murphy.
They determined that predictive maintenance would save $705 per valve. On a 200-tag system, that would be $141,000 per year. “To recognize that some valves are less critical, we applied a 0.5 factor, to $70,000 per year,” Murphy said. “The payback calculated to less than five months. And that only recognizes the cost of pulling valves during shutdown, not any improvements in the process or reliability.”
They’ve also been collecting examples of how the system could prevent unplanned maintenance and shutdowns, called quantified business results (QBRs). In one QBR, “We had a performance issue causing variations in the process that led to sheet breaks,” St. Thomas said. Each break cost $23,500. “It turns out the actuator on a pulp stock valve had the wrong tuning.”
In another QBR, they found one of the valves on the steam dryer could only open to 80% due to low pressure at the actuator. A second could only open 46%. It’s in a hot environment—the valve diagnostics recorded a peak of 162 °F—and had hardened o-rings. “So, we were slowing down the drying process at an estimated cost of $1,000 per day, and we don’t know for how long,” St. Thomas said.
These examples further support investments in AMS Device Manager.
Implementation is straightforward. Spartan conducted an audit on the existing AMS system, provided a quote for hardware and software, and submitted an implementation plan. Harmac assigned an AMS champion from the valve shop, identified the tags to be monitored, and assigned devices to the proper priorities (1, 2 or 3). Then working together, Spartan and Harmac replaced any non-smart devices on the priority 1 and 2 lists with smart devices, configured the alarms in the devices, set up the database and trained the area champion(s).
Once in operation, they’ll continue to capture QBRs going forward, said St. Thomas. “We’ll continue to reap the benefits, with a tangible effect on our business.”