Information from wireless transmitters saves energy

Cover Story: Wireless transmitters provide process information and increase energy efficiency in facilities.
By Jesse Dodge July 2, 2016

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. 

Figure 3: An example of cooling towers at a refinery. Courtesy: Emerson Process ManagementEnergy-efficient cooling towers with wireless transmitters

A cooling tower’s energy efficiency (see Figure 3) often depends on the ambient temperature. During hot days, if the cooling tower’s capacity is limited, cooling water temperatures may rise. This causes column condensers to overload and product coolers, requiring process units, to be slowed down. During periods of cold weather, cooling towers can freeze and damage equipment. Manual readings of temperatures and other variables can provide required information to deal with these issues, but are expensive to make and present a potential safety risk to personnel.

Typically, cooling towers are poorly instrumented, and fans and pumps are checked manually or left unmonitored. Because evaporation is dependent on air temperature, humidity, pH of the water, and fan efficiency, cooling towers present an ideal opportunity to reduce energy and chemical consumption with wireless monitoring.

A refinery near Mexico City relied on manual rounds to check cooling tower operations. Although operators performed three rounds per day, slowdowns and shutdowns from failed cooling towers were costing $1.6 million a year. Instrumentation was old, most of it was out of service, and the data was poor—making it difficult to calculate energy efficiency and optimize operations.

It was necessary to install wireless temperature, pressure, level, pH, and vibration transmitters to fully monitor the cooling towers’ complex processes. As a test, the refinery installed 122 wireless transmitters and five gateways on four cooling towers.

The next step in improving cooling tower control is analyzing the data gathered from the wireless transmitters. Various software packages exist which provide early limited cooling warnings. The software can also provide diagnostics to help operators spot bearing, lubrication, or alignment problems in cooling tower pumps and fans. Automatic alerts flag personnel to cooling water conditions to adjust blowdown rates and minimize the use of water treatment chemicals. Analyzing this data helps refinery operators recognize and prevent cooling failures before they occur.

The first installation of wireless transmitters and analysis software improved energy efficiency by 10%. Due to these results, the company is adding wireless instrumentation on all of the remaining cooling towers at the refinery and implementing the same solution at other refineries.

When all of the savings are added—$4.8 million in decreased fan maintenance, $1.8 million in reduced chemical costs, $1.6 million in fewer production losses, 87% reduction in manual operator rounds, and $5.9 million in reduced downtime at the Alkylation plant—the company estimates that the payback time for each cooling tower wireless transmitter installation is about two weeks. 

Upgrading power plants for energy efficiency

Steam lines and other equipment near the outside walls of the turbine buildings can be subjected to sub-zero temperatures, freeze up, and cause a power trip.

Figure 4: Rosemount 702 wireless discrete transmitters provide real-time data for electric power consumption. Courtesy: Emerson Process ManagementA power plant in New Hampshire experienced up to five power trips per year in cold weather due to frozen equipment. The company suffered a power trip costing up to $250,000 whenever the plant went down, up to five per year, because the temperature in the turbine buildings wasn’t monitored.

The power plant is a 60-year-old facility with limited instrumentation, cable trays, and wiring infrastructure. The large plant needs personnel to measure temperature in several widespread turbine buildings. However, wiring instruments weren’t available in many locations, so installing wired temperature transmitters and the supporting infrastructure was too expensive.

The initial installation of continuous, temperature measurement monitoring for freeze protection used five wireless temperature transmitters and a wireless gateway. The company now has more than 60 wireless devices installed to measure temperature, pressure, flow, vibration, and level across the plant. Currently, the plant is continuously monitoring remote turbine control boards and boiler drum level indication areas for freeze protection. The control room is alerted to adverse conditions to take corrective action before a problem arises. Since the first installation in 2010, the power plant has not suffered any more freeze-related trips and saves up to $1.25 million per year. 

Awareness of energy efficiency

As electric utilities move more toward time-of-day pricing, there will be a wider differential between peak and off-peak power pricing. Installing wireless power monitoring transmitters can help a plant adjust its operations to reduce energy costs by using power at the right time.

For example, a corn wet mill in Indianapolis, Ind., receives a monthly bill from its utility detailing electrical usage, but doesn’t have daily, real-time measurements to accurately forecast and budget the energy bill each month.

Controlling and forecasting costs is important to avoid demand energy charges by adjusting the use of various energy-consuming processes to run during periods of lower rates or shut off equipment during peak hours that would lead to additional costs.

When portions of the plant were shut down for maintenance, it was discovered that some large motors and process equipment were still running. A walk-through of the plant took place and, in conjunction with a local power company, determined that they could integrate wireless discrete transmitters with the utility’s existing power meters to detect when these machines were operating (see Figure 4).

The mill uses the data to make accurate power consumption calculations. Its accounting department used to require three manual power meter reads per month on the same day at all six locations for forecasting, but now the data is available automatically in real-time with improved accuracy. The data also is used to forecast monthly power costs.

Future plans are to use the power monitoring data to detect when the plant is approaching a consumption level that would trigger power demand charges from the electric utility. With a sufficient advanced warning, they will be able to take advantage of lower off-peak rates and avoid demand charges by shutting down equipment, postponing operations to a period of lower electrical rates, and/or rescheduling processes to minimize consumption. [subhead]

Wireless makes it feasible

Figure 5: Jesse Dodge is the director of wireless business development for Emerson Process Management. Courtesy: Emerson Process ManagementIn the examples cited, it is possible to install wired transmitters. And, if a wired infrastructure existed near the measurement points, making it easy to add another wired transmitter, then it might have made sense to use a wired solution.

But in these cases, and in many others, wired transmitters were not the best option and were often not economically feasible. Wireless transmitters with integral power modules require no wiring infrastructure or power source and no input points at the control system. At one-third to one-fifth the cost of a wired transmitter, wireless devices make it possible to obtain the measurements needed to cut energy costs.

Jesse Dodge is the director of wireless business development for Emerson Process Management. Edited by Emily Guenther, associate content manager, CFE Media, Control Engineering, eguenther@cfemedia.com.

MORE ADVICE

Key Concepts

  • Install wireless transmitters for energy savings.
  • Improve energy efficiencies at a facility with wireless transmitters.
  • Wireless transmitters help improve a facility’s preventive maintenance schedule.

Consider this

How many wireless transmitters are necessary for accurate data analysis?