As digital plants continue to deploy large numbers of sensors to improve productivity and process operations, they are also taking advantage of digital networks to facilitate that deployment. Article by Jonas Berge, Senior Director, Applied Technology, Emerson Automation Solutions Asia Pacific.
Wireless and expanded fieldbus networks are often the most practical and cost-effective means of deploying and connecting sensors in plant operations, because they don’t require installation of I/O cards, the use of spare I/O channels or additional 4-20 mA wiring. But what makes these digital networks most appealing is the way they enable the automation and reduction of many time-consuming manual tasks that often hinder operational effectiveness. Here are some of the most common yet critical areas where digital networking can enhance productivity in digital plants:
Traditionally, field operators manually collect data around the plant at each shift, on a daily or weekly basis, by reading mechanical instruments like pressure and temperature gauges or sight-level glasses. Sometimes, they might use a dip stick to take the reading and a clipboard or handheld terminal to record it. Manual data collection is non-productive, slow and often susceptible to human error. In addition, it also adds concerns over personnel safety. Fortunately, automating manual operator rounds with pervasive sensors is easy with wireless or fieldbus networking and results in greater productivity, as well as more accurate and timely data for a more predictive operation.
Local Control Panels (LCPs)
Another case for digital networking is the automation of mechanical pressure gauges at the local control panels (LCP) from which operators manually start and stop pumps, fans and compressors in the field. In this application, replacing the mechanical gauge with a wireless pressure gauge transmitting to the historian or DCS for indication, trending and alarming enhances the situational awareness around manual procedures to reduce mistakes. At the same time, a large dial gauge is provided on the field instrument to support local operation when necessary.
Offsite Storage Tank Farms
Storage tank farms are typically located away from the control room, and many of them offer little or no instrumentation due to the high cost of running wiring for each individual signal over long distances. As a result, operators must go all the way to the tank farm and climb each individual tank to retrieve the data – a process that is very time consuming. By modernizing the tank farm with digital networking, a tank can be fully instrumented with little or no wiring, thereby improving productivity at minimal cost.
Valve and Damper Monitoring
Due to the high cost of 4-20 mA and on-off signal wiring and associated DCS I/O cards, several actuated instruments within the plant (eg: control valves, on-off valves, dampers, vanes, louvers) were often not fitted with actual position feedback when the plant was originally built. As a result, operators often have no way of confirming the valve or damper is moving correctly, if it is limited in movement, or even if it is completely stuck – all of which can negatively impact control performance. Operators can benefit from receiving actual position feedback via digital networking to properly gauge equipment position and health – whether a valve is unable to open fully or if a louver arm is bent out of shape – to ensure any issues are corrected in order to restore production performance. The same applies to position feedback from manual valves to ensure those that are supposed to be closed are not left open, and that valves are lined up correctly for product transfers.
Rotating Kiln and Reactors
Assets that revolve around their axis, such as rotating kilns, combustion chambers, dryers, and reactors, often require instrumentation for monitoring, principally to get a temperature profile to detect hot spots that could damage the equipment. Traditionally, 4-20 mA instrumentation is used in this application, but because the equipment is revolving, it also requires the use of a slip-ring to transmit signals from the rotating equipment to the system. However, these slip-rings often suffer wear and tear and are prone to failure, resulting in a loss of measurement and visibility. Instrument engineers can bypass the use of slip-rings by instead using wireless instrumentation to solve the problem and procure a trustworthy measurement for monitoring and control.
These are just few of the digital productivity solutions digital plants are now deploying as part of digitalizing their operations. They all demonstrate the value wireless networking can contribute to hardwired plants and especially to those built on fieldbus networks that are rarely loaded to their full capacity. A single wireless gateway can handle 100 devices, and each device can support multiple measurements, translating to a significant amount of additional I/O capacity. By putting digital networking to good use, plants can make more effective use of scarce manpower, and personnel can spend less time collecting data and more time acting on the information.
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