By Kevin Root, Harcros Chemicals
At our facility in Kansas City, Kan., four manufacturing units are situated on approximately 100 acres. Our alkoxylation unit adds ethylene oxide or propylene oxide to produce our T-DET surfactants and other specialty adducts. The surfactants are shipped in current form or further processed into phosphate ester surfactants, ether sulfate surfactants or our T-MULZ emulsifiers. We do about 200 different products at this unit, and a lot of the products are dissimilar enough that they require washouts during a changeover.
A valve left open after a washout can have dangerous and expensive consequences.
Primarily, we wanted to minimize employee exposure because we're around some pretty severe chemicals. On the environmental side, there would be serious issues if these valves were left open and we put material on the ground. We deal with some dangerous chemicals, so this could have a severe impact on the environment.
Test the Waters
In the fall of 2008, Harcros decided to eliminate the risk of an employee putting a foot in a dangerous chemical spill by dipping its own toe in the wireless water.
"We put the wireless on to verify the valve position," says Lloyd Hale, director of manufacturing at Harcros. "It was cost-prohibitive to hardwire because of location. We're a batch operation, so these valves are open after each batch when we do washouts, and these valves are tough to get to. A person has to reach up through the piping. We turn reactors around almost every day, so the potential to miss a valve is always there when you're dealing with the human factor, and we needed to verify the valves were closed prior to a batch. We also wanted to put wireless into a non-critical application to build our confidence in its reliability."
A lot of opportunities for wireless applications exist at our site. Before we undertook any major capital improvements, we wanted to prove the reliability of wireless so we can approach other applications with confidence.
The only alternative to wireless that Harcros considered was switching to positive-close, spring-loaded valves that would have to be held open and then would self-close. "But during washouts that would be hazardous to the employee holding open the valve," explains Hale.
Because the DeltaV control system already was in place, Harcros turned to Experitec (www.experitec.com), its local Emerson representative. "We wanted to be sure we could communicate with our current control system, DeltaV," explains Hale. "Experitec put us in contact with Emerson to evaluate the right valve monitors. Emerson sent a rep down from the Fisher division in Marshalltown, Iowa. We're at capacity, so we couldn't shut the unit down very often. It's a 5/24 plant, but we normally work every other weekend. The contractor scheduled for its people to come in when the unit was down. It took about five months."
Valve Feedback Without Wires
Most process plants have situations similar to Harcros Chemicals, relates Terry Buzbee, president of the Fisher division at Emerson Process Management (www.emersonprocess.com/fisher). "They might have hundreds or even thousands of valves that aren't connected to the control system because of high wiring costs," he says. "These valves therefore provide no feedback on their actual positions, even though incorrectly positioned valves represent a significant cause of safety-related incidents."
Harcros' use of manual valves for sampling, directing, injection and extraction processes at its facility means many of the valves are in remote, hard-to-reach locations too costly to access with wires. "Monitoring them was a difficult process, requiring operators to enter hazardous areas or climb ladders to check the valves' state or position," adds Buzbee.
Harcros installed the Fisher 4320 wireless position monitors, which were integrated with an Emerson Smart Wireless Gateway and AMS wireless configurators to form a Smart Wireless network communicating with the site's existing DeltaV digital automation system. The self-organizing wireless network passes signals along to the gateway, creating a redundant network that bypasses obstructions as needed. Frequent performance updates occur without any involvement by the user. With redundant communication paths, wireless networks provide reliability between individual devices and a receiver.
"In the past they had to send someone out to the valve to check on it," explains Kurtis Jensen, Fisher instrument product manager at Emerson Process Management. "These valve monitors update every minute. They know the state of the valves at all times. The critical periods in production occur after they have rinsed the reactors and are ready to fill with the product mixture." A valve in the wrong position is the cause of product spills or a bad product.
Emerson configured everything. When they left, it was all online and operational, and the redundancy of the mesh network was critical to its reliability.
"Harcros, like most, if not all, customers, is looking to increase confidence in its processes," says Jensen. "Coming to them with less-than-reliable products would be a disservice. Of paramount importance is reliability in communications. The only way to get that today is with a wireless network that builds a mesh between the wireless gateway and each and every device. The devices must be able to reroute communications in case there are changes or interruptions in the network. The only network that can do that is WirelessHART. The 21 devices at Harcros form a mesh and route traffic to the gateway. Most of the devices communicate directly with the gateway, but they also formed secondary, tertiary links between themselves to build the meshing."