Workingman's Wireless

More Routine Process Control Applications Are Adopting Wireless to Save Cable, Secure Added Signals, and Transfer Data from Spots Where Wire Can't Go. Here's How Veteran Users Do It Every Day

By Jim Montague

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Communication is what's important. Whether it happens over a cable or through the air is irrelevant, so long as the link is secure and the data transfer is successful. Luckily, there are now plenty of avenues to make that happen, so wireless devices and methods are becoming as routine in process monitoring, data acquisition, automation and even control as sensors, I/O points, hardwiring, PLCs and DCSs--just like the toothbrushes, clean socks, car keys, sack lunches and other items that engineers, operators and other working people use daily.

However, wireless transmitters, antennas, site surveys and wireless protocols remain unfamiliar to many potential users. So it helps to know how those further along the learning curve use wireless to solve mundane, but persistent operational headaches.

Curing Common Complaints

For instance, Thames Power Services' 1,000-MW Barking Power Station near London recently installed 35 Rosemount 708 acoustic transmitters from Emerson Process Management to find more failed steam traps, leaking or misbehaving valves and costly boiler tube leaks, and reduce steam losses, feedwater costs and downtime (Figure 1). If a steam trap fails or a leak develops, an acoustic device in the transmitters reports sound and temperature changes, which are configured to alert operators of a potential problem. Ian MacDonald, Barking's senior control systems engineer, reports the transmitters immediately helped by identifying a leak from a high-pressure, super-heater steam trap, which would have cost £1400 for every day of downtime.

"Improving process performance is all about understanding what's happening around the plant and being able to respond quickly to any problems," explains MacDonald. "Wireless technology enables us to introduce additional measurement points quickly and cost-effectively at any location so we can gather more information to identify potential faults."

Later, Barking installed 15 more acoustic transmitters to monitor other problematic areas, including vent valves that can stick during start-up and pressure relief valves that don't seat correctly. Previous manual monitoring was time-consuming and also failed to indicate when or why a release occurred, increasing the chances of a safety, regulatory or environmental incident. The new wireless devices enable precise monitoring and alert operators when valves have opened for as little as 1 second.

Next, data is fed into Barking's existing Emerson Ovation control system, where noise levels can be trended to identify gradual changes. Repairs can then be scheduled during normal off-times to maintain maximum plant availability and avoid forced downtime. Using its existing wireless networks, more devices can be added at much lower cost than if they had to be individually wired-in. This gives the plant more opportunities for monitoring where it was previously cost-prohibitive, such as identifying blockages in Venturi eductors, which typically use inlet/outlet pressure differences to create suction and rapidly mix injected substances.

"Having already installed Emerson's Smart Wireless THUM adaptors for access to stranded HART diagnostic data in field devices, we were familiar with Smart Wireless," adds MacDonald. "The mobility and flexibility of the battery-powered wireless devices also allow us to run trials and move devices to different areas without temporary cables. As a result, we can spot early problems and improve response to malfunctioning equipment, enabling better planning and use of maintenance resources."

Finding the Right Fit

Probably the most important virtues on the road to wireless are patience and flexibility in researching, designing and implementing the most useful solution.

For instance, engineers at Valero Energy Corp.'s refinery in Wilmington, Calif., were introduced to wireless several years ago when a third-party, point-to-point wireless system was installed to extend process monitoring. However, it was cumbersome and took too much time to deliver data, according to Rick Felix, Valero's associate process control systems coordinator. So the plant's engineers sought improved wireless tools; implemented Honeywell Process Solutions' OneWireless site-wide in 2009; and have been tailoring it to suit their applications and enhancing performance ever since.

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  • <p>I agree both wired and wireless have parts to play in automation. Wired and wireless have different characteristics and thus excel in different applications. They complement each other. Most importantly, the communication shall be digital to enable intelligent devices communicating over a wireless or wired network.</p> <p>Indeed WirelessHART is ideal for fixing problems around the plant with which plants just had to live with before. Modernizing existing plants is the killer application for WirelessHART. Within plants these applications fall into three major areas: essential asset monitoring to improve reliability, HS&amp;E, and energy conservation measures (ECM) for energy efficiency. Outside plants the main application is integrated operations for improved production and recovery at oil and gas wells.</p> <p>Personally I believe the fast uptake of WirelessHART is not due to the low cost, but the low risk of deployment. We hear about savings of tens of thousands of dollars per year, even hundreds of thousands and millions in energy savings and improved production etc. This would be a phenomenal return on investment even on a costlier wired solution. So why was it never done before? I personally believe the reasons are risk and lack of resources. Running wires in an existing plant requires cable trays and junction boxes to be opened; this caries a risk of damaging the existing installation so such mini projects get rejected. And there just aren’t enough people around to manage the logistics of it. WirelessHART is much simpler. You deploy a WirelessHART gateway at the edge of the plant area; then you can deploy wireless transmitters inside that plant area, without running any new wires inside the plant area. No wiring for power. No wiring for signal I/O. That is, electrical installation is non-intrusive. In many cases non-intrusive mechanical installation is also possible: there may be existing thermowells or tapping points for installation of temperature sensors and pressure transmitters. Clamp-on surface temperature transmitters can also be used. Pressure transmitters can be installed where pressure gauges previously were mounted. Valve position feedback bolt onto hand operated valves like bypass valves. Vibration sensors can either be screwed on the outside, glued on, or even use a magnet. Acoustic transmitters for monitoring of valve leaks, relief valve activation, and steam trap health simply strap onto the outside of the pipe using hose clamp. In many cases new process penetrations need not be drilled, cut, or welded. That is, not only low installed cost, but low installed risk.</p> <p>Having said that, high cost of 4-20 mA and on/off cabling and DCS I/O count is often the reason why these points were not automated in the first place when the plant was originally built. But most plants are now very old, and the economics of energy cost etc. has changed greatly since the plant was constructed. All the points which were not automated are now “missing measurements”. WirelessHART provides a “second layer” of automation for points “beyond the P&amp;ID” (on top of the wired automation used for control loops on the P&amp;ID). Use wireless for plant modernization, and deploy wireless gateways in all plant areas on new plants because all Greenfield plants become brownfield after startup.</p> <p>Learn more here: <a href=""></a></p>


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