Implementing wireless process sensing

Installing a wireless sensing system may seem complicated, but following these four basic steps can simplify the required effort.

08/04/2017


Oil and gas, chemical, refining, food and beverage, power, and other process industries are under pressure to increase production, make processes more efficient, reduce energy usage, cut maintenance costs, improve safety, and meet dozens, if not hundreds, of federal, state, and local regulations. To accomplish these goals, plants must monitor all aspects of a process, acquire data from new instrumentation, analyze the data to turn it into actionable information, and take steps to remedy problems.

Figure 1: A combined cycle power plant in California implemented a wireless architecture to monitor cooling towers, turbines, and other equipment. Courtesy: Emerson Automation SolutionsMany process plants are huge, with many opportunities to improve operations. Where do plant personnel start? What follows is a four-step process for employing strategies to monitor anything, anywhere. 

Step 1: Identify areas for improvement

The first step in identifying investment opportunities is determining the economic value associated with improved operational visibility. For example, what's it worth to know an asset is about to fail or is operating inefficiently? After economic value is estimated, the measurements and variables needed to make an informed decision can be determined.

A way to accomplish this is to do a walk-through and/or piping and instrumentation diagram (P&ID) review of the plant with the help of a wireless system supplier. Wireless experts and key plant personnel walk the site and/or review P&ID drawings; examine equipment and processes; note available instrumentation, wiring, and input/output (I/O) infrastructure; and evaluate areas for improvement. The experts identify areas where improvements will result in a quick return on investment (ROI), such as monitoring steam traps or pressure relief valves.

In some cases, plant experts already know what's needed. For example, a utility in California wanted to implement a wireless architecture throughout its combined cycle plant to access data previously unattainable through traditional wired solutions (see Figure 1). "We needed to monitor the performance of our cooling towers," said the plant engineer. "Cooling tower riser temperatures are critical to an efficiency calculation used for cooling tower performance."

The plant also wanted better monitoring of its turbines. This included temperature monitoring to prevent overheating, and air filter monitoring to reduce the impact of clogged filters on turbine efficiency. "We wanted to monitor turbine compartment temperatures for leak detection of forced air cooling the turbine exhaust," the plant engineer said. "We had switches that would close if they got hot, but we didn't know the temperature inside the compartment. When the switches closed, we knew something was happening, but we did not have any other information." Mechanics were sent to do inspections much more frequently than necessary, because experience had proven that leaks in this turbine exhaust cooling application were a problem and needed to be found quickly.

The power plant analyzed its needs, determined what processes would yield the best ROI, and installed wireless transmitters to acquire the information it needed.

Step 2: Acquire data

The key to a successful wireless implementation is executing a strategy where wireless sensors are used to acquire data from all parts of the plant at a reasonable cost. Many older, existing plants could benefit from adding many more measurement points, given the proven financial benefits. One reason they don't is that, in the past, these inputs would have to be wired from the sensing point, such as a pressure instrument installed at a pump, to a control and monitoring system.

Adding this wiring to an existing facility usually is a very expensive undertaking because wired sensors require power, wiring to I/O systems, and additional I/O points at the control and monitoring system. Such modifications often require significant downtime, which isn't an option as many plants operate at or near full capacity.

WirelessHART sensors, on the other hand, have built-in power modules, so they don't require power wiring. And, being wireless, they don't require additional I/O capacity from the plant's control and monitoring systems. These sensors are connected through a plant-wide wireless mesh network to control and monitoring systems via a gateway. WirelessHART sensors allow points of measurement to be added at a fraction of the cost and time required for their wired equivalents, and sensors not requiring process penetrations can be installed without any downtime.

After a WirelessHART infrastructure is in place, adding more sensors is quick and inexpensive. In this case, the aforementioned California power plant discovered it could add a wireless temperature transmitter on fire pumps to protect against pump damage, and added wireless sensors to the remote rainwater pond feeding the cooling towers. Both tied into the new WirelessHART infrastructure.

Figure 2: A modern wireless installation will have many of WirelessHART sensors in its pervasive sensing system. Data from these sensors can be analyzed quickly using Emerson’s Plantweb software applications. Courtesy: Emerson Automation Solutions

"We have a level transmitter warning us before the pond overflows to the river," the plant engineer said. "This gives us time to go to the pond, take measurements, and prove compliance." Another wireless measurement point continuously monitors pH to ensure there is no issue with the water feeding the cooling towers. 

Step 3: Analyze data

When a plant adds pervasive sensing technology, the wireless ecosystem generates a large amount of raw data, and it may be difficult for plant operators and engineers to decide what's relevant and actionable (see Figure 2). Expensive enterprise level software management systems often require six-figure investments, extensive training, and months to deploy. Such systems usually require expensive outside consultants for startup, and significant IT resources in terms of server hardware, dedicated computers, etc.

Figure 3: Emerson’s Plantweb Insight analytics software can be accessed via a browser running on PCs, smartphones, or tablets. Courtesy: Emerson Automation SolutionsRecent developments in analytical software—now available as an app that can be accessed from Web browsers on a desktop computer, laptop, tablet, or mobile device—make analysis simpler and less expensive (see Figure 3). Each app takes data from the wireless gateway or other data and monitoring systems. And each app addresses specific equipment, such as steam traps, pumps, heat exchangers, or pressure relief devices, with simple, inexpensive, plug-in solutions that can run independent of a plant's control system. These apps use pre-built analytic models and strategic interpretation to turn the raw data into information that plant personnel can use to make decisions and take action.

Because each of these solutions is purpose-built for a specific asset, they are quick, easy, and inexpensive to implement. And with a wireless infrastructure in place, additional applications can be added quickly.

Step 4: Take corrective action

Figure 4: A Rosemount 708 WirelessHART acoustic transmitter can monitor steam traps, detecting if they fail open or closed, or if they are leaking. Courtesy: Emerson Automation SolutionsThe fourth and final step is for the plant to take the appropriate corrective action.

Because of their locations, steam traps often are not monitored in most plants. Instead, many plants rely on manual rounds, where maintenance technicians test traps once or twice a year and look for signs of leaking. Manual rounds are often ineffective, and many problems go undetected. Estimates indicate 18% of the steam traps in petrochemical plants fail every year, with each trap failure causing about $16,000 in fuel and steam costs.

By installing WirelessHART acoustic sensors, plants quickly can identify steam traps failing open or closed, leaking, or working improperly (see Figure 4). The annual savings from monitoring 112 steam traps in one ethylene plant amounted to $342,578.

Installing WirelessHART acoustic sensors downstream of pressure relief devices (PRDs) enables maintenance personnel to identify leaking or sticking valves, repair them, and avoid U.S. Environmental Protection Agency fines due to fugitive emissions of up to $350,000 per incident. In one petrochemical plant with 200 PRDs, the annual energy savings obtained by identifying and repairing leaking PRDs was $1,487,040.

A power plant in California had no riser temperature measurements before wireless temperature sensors were installed on the cooling towers (see Figure 5). These measurements are now used in the efficiency calculation to confirm whether fans are running at correct speeds. "With confirmation that the fans are at the right speed, we do not have to over-compensate, which gives us better thermal efficiency. As a result, we have increased the throughput of the cooling towers," a plant engineer said. "The information provided by the wireless measurements has enabled the plant to lower the amount of current used by the fan motors, lengthening their lifetimes."

Figure 5: Installing wireless temperature sensors on these cooling towers and analyzing the data improved operations, saved energy, and increased the lives of fan motors. Courtesy: Emerson Automation SolutionsWireless temperature transmitters were installed to provide online turbine compartment temperatures to detect leakage of hot air, an inexpensive early detection strategy. "We track temperature over time to help with preventive maintenance scheduling and troubleshooting. This has allowed us to cut our preventive maintenance on the turbines in half," said the plant engineer.

For air filter monitoring, two wireless differential pressure (DP) transmitters were installed to monitor inlet air filter efficiency on two units. "The wireless DP transmitters allow us to see if the filters are getting clogged with dust," said the engineer. "With better DP information across the filters, we can clean them at the proper time. This significantly improves turbine efficiency and reduced megawatt usage. We saved $15,000 to 20,000 for each DP transmitter compared to a wired solution because of the long distances from the measurement point to the control room."

"One of the great benefits of wireless devices is that we can install them ourselves in a fraction of the time it takes to wire an instrument," the power company plant engineer said. "We typically need to hire contractors for wired instrument installation because we do not have a big staff. Being able to do it ourselves in a fraction of the time was a big savings to the company. It takes about an hour to install a wireless device, compared to two weeks to run wire and completely install a wired transmitter." 

Overcoming challenges

Installing wireless transmitters and analytics software in a plant improves efficiencies, finds problems, cuts maintenance costs, and extends the life of valuable equipment. While such a solution may appear challenging, with the help of a wireless supplier and following this basic four-step procedure, a wireless solution can be installed at a reasonable price with a quick ROI. 

Brian Joe is a wireless product manager for Emerson Automation Solutions in Shakopee, Minn.

This article appears in the Applied Automation supplement for Control Engineering 
and Plant Engineering

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