Most plants are familiar with the cost of what some might call a lost profit opportunity (LPO)—when an unplanned unit shuts down and production is lost. “We define another kind of opportunity—a loss avoidance opportunity (LAO)—when proper use of smart instruments and AMS prevents an LPO,” said Ben Krueger, instrumentation engineer at LyondellBasell’s Channelview, Texas plant. “The object is to increase LAOs and reduce LPOs.”
Together with John Scott, executive account manager in Emerson’s Rosemount business, Krueger presented the session, “LyondellBasell Works to Prevent Unplanned Unit Shutdowns and Saves Money Utilizing Transmitter Diagnostics and AMS Alert Monitor on SIS Systems,” at Emerson Global Users Exchange 2016, this week in Austin, Texas.
One of several LPOs occurred when 3051SMV pressure transmitters in a two-out-of-two (2oo2) interlock tripped on RTD failure, causing a hard shutdown of five furnaces. Both of the dual-element RTDs failed simultaneously, and shutdown triggered a flaring event, “which we call, ‘burning money,’” Krueger said. A review of records from the plant’s Asset Management Suite (AMS) records showed both transmitters had sent alerts for two days before the event. “We didn’t see the alerts, because we weren’t monitoring frequently enough,” he said. “It was a learning experience—a step on the journey.”
[sidebar id =1]On the positive side, Krueger cited several LAO successes. One was associated with the first example above, where AMS captured all the information needed to understand the incident. Since the temperature (RTD) was not part of the process information on those pressure transmitters, they were able to reconfigure the temperature values in the transmitters. “Two days later, that prevented a second shutdown worth $953,000,” Krueger said.
A little bit about smart instruments
Rosemount 3051S pressure transmitters provide information about their condition and the condition of the loop by tracking pressure, differential pressure and temperature (using external RTDs). They monitor loop integrity by measuring the voltage needed to provide the milliamp signal: if the loop wiring is damaged or connections are corroded, the voltage will rise out of range for the current. If the loop resistance falls due to a short or the power supply fails, voltage will be detected as too low.
The 3051S can detect plugged lines through statistical process monitoring (SPM). The transmitter takes readings 22 times per second; theyreport the mean to the DCS, but watch the standard deviation—if it falls, it indicates damping that may be caused by plugged lines.
The 3144 temperature transmitters use the readings from dual RTDs to track sensor drift, and detect thermocouple failures by measuring the resistance across the thermocouple. “The default resistance setting is 5,000 Ohms,” added Emerson’s John Scott. “If resistance rises due to loose connections, vibration, corrosion or a failing thermocouple, it sets an AMS alarm.”
Transmitters can be configured for appropriate voltage, temperature and current limits for the individual application, and for what they’ll do when a deviation occurs, for example, to signal instead of drive high on RTD failure. “That’s what we did on the furnaces to prevent the second incident, to save that $953,000,” Scott said. “By the way, those were not Emerson RTDs.”
Decrease LPOs, increase LAOs
“These potential savings cannot be ignored,” Krueger said. “Emerson has developed powerful tools to save millions of dollars, but it’s up to us to use them.”
Grasping that advantage is a three-part process, Krueger says. The first is to adjust job duties. “Instrument techs are now required to configure alerts on AMS Monitor. Alert configuration sheets for each device are printed out and put in binders at each station.”
As an engineer, “I am now the AMS champion,” Krueger said. “I regularly report the number of smart devices, which are monitored and which are not, and report the LPOs and LAOs.”
The second part is to redefine organizational roles “to monitor AMS alerts and generate timely and effective response,” Krueger said. This role is distributed among the instrument technicians at this plant, but may be assigned part- or full-time to an “AMS technician,” or even automated through AMS and a CMMS.
The third part is to work with local experts and Emerson to make an effective implementation, Krueger said. “We’re now changing a unit from RS3 to DeltaV, and we’re adding online monitoring before we start up.
“I can’t emphasize this enough. Just spending millions of dollars on smart instruments will not do it alone. You make must make some form of these changes to gain the benefits.”