Information from wireless transmitters saves energy

Cover Story: Wireless transmitters provide process information and increase energy efficiency in facilities.


Every process plant has hundreds if not thousands of measurements it would like to make to save energy. However, installing wired pressure, flow, temperature, or other transmitters in a process plant is expensive. A wired 4-20mA, Profibus, or Foundation Fieldbus transmitter requires power, cabling, conduit, junction boxes, marshalling cabinets, and control system inputs or fieldbus communications. And if the device to be measured is in a hazardous area, this can add even more expense. If the measurement has to be made in a remote area or the top of a tank, the cost of making the measurement with a wired transmitter can be astronomical.

For about one-fifth to one-third of the cost of a wired transmitter-depending on the specific application-a wireless transmitter can be installed and connected back to the control system. Many organizations are taking advantage of wireless transmitters for significant energy savings, with payback periods as quick as two weeks. 

Monitoring steam traps for energy efficiency

A steam trap is an example of a device that is difficult to monitor with a wired transmitter. They are often located in hard-to-reach areas, far from other instrumentation while supporting wired infrastructure, and sometimes located in a hazardous area. For decades, the best known method to identify failures was conducting manual steam trap audits using acoustic and temperature sensing methods. Many plants use this practice annually, which leaves the plants vulnerable to long periods of failures between audits. Process plants with preventive maintenance plans typically experience failures in about one in five steam traps. There is an expected 12% to 25% failure rate for process plants that perform these annual audits.

Wireless transmitters with integral power modules (see Figure 1) measure the ultrasonic acoustic behavior and temperature of steam traps and send this information to a control or monitoring system via a wireless mesh network. Because no wiring is required to the transmitters, installation is more cost-effective compared to a wired instrument.

Figure 1: A wireless Rosemount 708 steam trap monitor sends acoustic and temperature information to the control system. Courtesy: Emerson Process ManagementIt's difficult to measure the financial impact of failed cold steam traps, although it's easy to find examples of everything from steam line ruptures causing millions of dollars of damage, to unplanned outages for equipment repair. For example, one large company experienced severe water hammer because of four plugged steam traps, resulting in a six-hour site shutdown and $250,000 in repairs. Another manufacturer was unable to accurately control the temperature of a vital manufacturing process because of steam trap failures. This resulted in batches of product being reprocessed, costing millions of dollars of lost production.

For further example, a chemical plant in Leverkusen, Germany, had to cut energy costs to meet the European Commission's June 2012 Energy Efficiency Directive. It was determined that failed steam traps were causing loss of steam and inefficient heat transfer and therefore wasting energy. With more than 300 steam traps in three areas at the Leverkusen plant, it was difficult to test them all on a regular basis. As a solution, Wireless steam trap transmitters were installed on 100 critical steam traps, and software was used to analyze data from the transmitters.

The wireless transmitters and software were installed in September 2014 for a three-month test. The system immediately found several failed steam traps in addition to detecting several undersized steam traps during the trial period.

By repairing or replacing failed steam traps, the three plant areas immediately began to see substantial reductions in energy costs. Failed traps were no longer venting valuable steam, resulting in lower energy consumption to produce steam and process shutdowns. The increased energy efficiency made the plant compliant with Energy Efficiency Directive and ISO 500001 Energy Management Standard requirements.

"We calculated a return on investment of less than two years, thanks to savings in energy costs," said the project engineer. "We also reduced the number of process shutdowns because of steam trap failures and eliminated the need for maintenance technicians to make regular rounds, resulting in further substantial savings."

Finding fouled heat exchangers in refineries

Many refineries are trying to maximize the use of discounted crude oils; however, using this type of feedstock often presents significant processing challenges. For crude unit preheat exchangers, some crude blends can be incompatible with varying crude oil properties, which causes an accelerated rate of unexpected fouling. Fouling causes reduced energy efficiency and limits production.

Figure 2: An illustration of how a heat exchanger operates with a wireless transmitter for increased energy savings. Courtesy: Emerson Process Management

By adding wireless temperature measurements to exchanger banks (see Figure 2), the increased data from the instruments sent to process analytics software can alert operations of excessive fouling conditions and rates. This information can be used to determine incompatible crude blends and also indicates when an exchanger bundle requires cleaning.

Corrective action and optimized cleaning schedules can produce an improved energy intensity index and capacity utilization for a return of over $3 million per year in an average-sized refinery. Heat exchangers can use wireless temperature measurement and analytics software to check the equipment's health status. 

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Jonas , Singapore, 08/08/16 12:14 PM:

Relief valves, cooling towers, and air cooled heat exchangers are other kinds of equipment which can be monitored for passing and fouling using wireless sensors. ISO 50001 energy management can be automated using wireless sensors. They share the same wireless network as mentioned in the article above.
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