- October 24, 2014
- Emerson Automation Solutions
- Case Study
By David Gustafson, Emerson Process Management
It took only two weeks to install the first system, and already it‚Äôs saved $100,000 in maintenance costs and increased production by 5,000 tons per year.
By David Gustafson, Emerson Process Management In 2013, a coffee plant in Mexico increased production by 30 percent to 42,000 tons per year of coffee. The original plan was to reduce energy use by 20% per ton and reduce water consumption by 30% per ton. The company’s engineers quickly identified a way to help meet the energy and water reduction goals by increasing steam system efficiency. Making coffee requires high quality steam, and steam traps are critical to keeping the process running at high performance levels. If a steam trap fails, it can interrupt the coffee production process. The company installed wireless flow, pressure and temperature instrumentation and Model 708 steam trap monitors from Emerson Process Management, and immediately experienced better control of steam, fewer process failures and lower maintenance costs. The results were so significant that the company decided to upgrade all of their other coffee plants in a similar fashion, with a target completion date of 2020. The Cost of Steam The biggest problem the plant had at the beginning of the improvement project was lack of information. Their steam boilers (Figure 1) had little or no instrumentation, and did not connect to the plant’s DeltaV distributed control system (DCS). Adding instrumentation to an existing system is a very expensive process, typically involving a complete process shutdown. Figure 1: The coffee plant has three large steam boilers. Plant personnel needed to know how much energy was being used by each process unit, but because of the lack of instrumentation, they had no information about steam, air and water consumption in the plant. The engineers did know excessive steam trap failures were reducing productivity in the plant by 20% per year because coffee production stopped during those instances. The lack of information didn’t allow proper control of boiler loads which reduced steam capacity during peak plant demand, cutting productivity. Maintenance was done by manual walk-arounds to check for leaks and failed steam traps, but the plant had no way of identifying steam traps failing more frequently than others. The plant has 100 steam traps, of which 60 are critical to production. Monitoring Steam Traps A steam trap’s function is to release excess condensate from steam piping to a sewer or to a condensate return line back to a boiler. When steam is present, the steam trap closes to maintain pressure. Steam traps are fairly reliable, but can fail open or closed. The two primary causes of steam trap failure are dirt, which can plug the trap or cause it to leak; and pressure surges that can damage internal components. Unless the steam trap is leaking, maintenance people have few clues that a trap has failed. If a condensate stack is installed, they might notice a steady plume of steam coming out, but leaking water and steam plumes are the only physical signs of a failure. If a steam trap fails open, it dumps condensate and high-pressure steam to the sewer, resulting in a loss of steam and increased energy costs to generate more steam. Excessive loss of steam can overload the boilers. If a steam trap is plugged or fails closed, condensate will back up into the steam line and reduce the efficiency of the heat transfer process, deteriorate piping, and adversely affect heat exchanger bundles, humidifiers and similar equipment. If the heat transfer process is compromised, it can cause a process shutdown while maintenance corrects the problem. What was needed was a way to monitor all 100 steam traps automatically. Conventional instrumentation was not practical in this installation because of the excessive cost to install instruments and wire them back to the DCS. Also, many things can go wrong in an electrical instrument loop, especially in older plants like this one. For example, water can get inside enclosures after a rainstorm or over time with condensation. Wiring can degrade and cause grounding issues, and terminals can become corroded. The power supply can become unstable toward the end of life. Power supplies that drift or spike in output often indicate that the power supply is faulty and unreliable. These are all issues that can jeopardize process operation due to corrupted 4-20 mA signals or loss of power to the instrument. To save money, speed installation and address reliability issues with wired instrumentation, the plant installed 100 Rosemount 708 Wireless Acoustic Transmitters on their steam traps. The Rosemount 708 (Figure 2) mounts on a pipe and listens for acoustic signatures between 35 and 45 Hz, which means a steam trap is open and releasing condensate. It also has a temperature sensor to detect cold or dropping temperatures from a clogged valve or steam trap. Figure 2: The Rosemount 708 simply clamps onto a steam pipe and transmits acoustic and temperature data to the DCS via WirelessHART. The Rosemount 708 simply clamps onto a steam pipe without cutting pipes or changing pipe configurations for a simple, flexible installation. It transmits the acoustic level (0-255 counts) and temperature of -40 to 260 C via WirelessHART to the plant’s DeltaV control system. In the DCS, Rosemount SteamLogic software monitors the signals from each 708 instrument (Figure 3). The SteamLogic software detects when a condensation release is occurring, when it stops and when turbulence is generated by a leaky steam trap. It monitors this and other information to give immediate notification of a failed steam trap. Figure 3: Indications of steam trap health. The first image shows the proper acoustic signal of a properly functioning trap. The second shows the cold temperature of a plugged trap, and the third shows the acoustic signal of a leaking trap. The plant employed a local mechanical contractor to install the Rosemount 708 steam trap monitors, while Emerson Process Management personnel set up the wireless network and configured the SteamLogic software. It took the contractor a week and a half to install all 100 Rosemount 708s, and Emerson set up the network and software in two days. At no time was it necessary to shut down any of the processes. Pervasive Sensing Prevails Wireless sensors allow “pervasive sensing”—which is the ability to monitor process variables formerly too expensive or too troublesome to instrument. In addition to the steam trap monitors, the company also installed wireless flow, temperature and pressure instruments throughout the plant (Figure 4). Figure 4: Typical wireless instrumentation installed on boilers and steam distribution systems. All of the instrumentation from the three steam systems, including the Rosemount 708 steam trap monitors, connects to the DeltaV DCS via Emerson’s Smart Wireless mesh network. Each sensor transmits its WirelessHART signal which is received by one or more repeaters located around the coffee plant, or—depending on distance—can be received directly by the Smart Wireless Gateway. The Gateway obtains signals from all the transmitters and stores them in a real-time database, where the data is available for processing by SteamLogic or Emerson’s asset management software (AMS). Results Early detection of steam trap problems has reduced required maintenance labor, eliminated the need for walk-arounds, and cut preventive maintenance costs. Personnel get early warning when a trap is leaking or appears to be clogging, allowing maintenance to schedule repairs without interfering with operation. The company estimates savings of $100,000 per year in maintenance costs alone. Early detection and correction of steam trap problems means failed-open traps no longer dump steam to the sewers and waste water and energy. It also means clogged “cold traps” no longer release condensate and allow it to back up, which could reduce heat transfer efficiency and possibly shut down the process in order to avoid water hammer. The company estimates eliminating process shutdowns will increase production by 5,000 tons of coffee per year. The plant is acquiring and analyzing process data from all the instrumentation to determine where further savings are possible. The steam trap monitors were installed in January 2014 and the wireless flow, pressure and temperature instruments later, so they are still evaluating the results. Initial results have been so positive, however, that the company has already begun installing instrumentation at two other plants, and plans to instrument six of its nine coffee plants by 2015. Thanks to wireless instrumentation and results achieved, the company is well on its way to achieving its goals of increasing production while cutting energy and water costs.
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