I highlighted some of the challenges North American refiners face in an earlier post with tight oil from shale formations. Emerson’s Michelle Weimert has Hydrocarbon Processing article, Leverage diagnostics to keep production running smoothly, which looks at the role of temperature measurement diagnostics can play in reliable refinery operations.
The continuing trend to increase production of crude oil from shale deposits in the US and oil sands of Canada has brought new opportunities in production. Production of tight-oil in the US is projected to grow from the current 1.5 million barrels per day (bbl/d) to between 2.8 and 4.2 million bbl/d. As a result, new technical issues have come to the surface as refineries optimize their product mix.
Unplanned shutdowns can significantly reduce the refinery output. Heat is a fundamental element in converting crude oil to refined fuels and other products. Diagnostics from temperature transmitters:
…can identify an issue before it causes process upsets, dangerous conditions, or measurement failure.
Temperature transmitters have different levels of diagnostics beyond the temperature process variable (PV) that they provide to the control system. Michelle explains that:
Most have internal diagnostics that monitor transmitter memory, functionality and output validity. They also offer external diagnostics for monitoring the measurement signal for such things as drift, degradation, measurement validity, and broken or damaged leads among others.
Digital communications protocols including HART/WirelessHART, Foundation fieldbus, and Profibus carry these diagnostics from the transmitter back to the handheld device, process automation system, or asset management software.
She highlights the difference between alerts and alarms from a transmitter:
Alerts do not affect the transmitter’s ability to output the correct measurement signal and therefore will not interrupt the 4-20 mA output. An example is “Process Variable Out-of-Range”… Alarms, on the other hand, will drive the transmitter output either high or low depending on user’s configuration choice.
Some temperature transmitters, such as the Rosemount 3144P, have diagnostic logging to capture:
…what caused the transmitter to go into an alarm, even if the event has disappeared. For example, if the transmitter detects an open sensor from a loose terminal connection, the transmitter will emit an alarm. The diagnostics logging feature keeps track of what caused the transmitter to go into alarm.
The main issues these diagnostics help refinery personnel spot include measurement failure, poor measurement reliability, and suboptimal process control. Failures occur when components in the transmitter fail. Tough operating environments found in refineries can accelerate these failures. Transmitter redundancy, drift detection, and monitoring the diagnostics can help avert unplanned shutdowns and quickly address the situation.
Sensor degradation, electrically noisy environments and instrument failure can impact measurement reliability. Transmitter noise filtering, measurement validation, sensor signal drift identification, loose/broken sensor lead alerts can help improve overall measurement reliability.
Control systems that can read the transmitter diagnostics can incorporate these diagnostics to help identify:
…situations where these limits are violated and identify and quantify the deviations. They can identify intermittent sensor failures, record minimum and maximum process temperatures, and log failures and their causes.
Judicious use of the diagnostics provides a return on this investment (ROI) in proportion to the criticality of the measurement. The investment is mostly in time spent and the ROI may be measured in increased throughput, higher product quality, less downtime, less product waste, lower energy costs or more subjectively, by the prevention of an explosion.
See some of the specific diagnostics described in the article and connect with the Rosemount Temperature experts in the Temperature Instrumentation track of the Emerson Exchange 365 community.
Also, if you haven’t already ordered your complimentary copy of The Engineer’s Guide to Industrial Temperature Measurement, follow the hyperlink to the ordering page.