If you have worked around a delayed coker unit for any amount of time, you have heard some of the debates around fired heater fouling and tube metal temperature (TMT) as measured by welded on thermocouples. During our Coker Process, Design, and Troubleshooting training course, this topic comes up repeatedly with surprising variation across the industry. Let’s talk about a few DO’s and DON’Ts when it comes to this measurement.
- DO understand that shielded and unshielded designs will report vastly different temperatures at the same location. Differences within 20-30F can be expected.
- DO have a good layout of instrument housing or extra expansion stress will cause premature failure. Follow the OEM guidelines for routing and expansion loops.
- DO have good welding procedure and inspection to ensure the weld is strong with no air gaps. Weld failures lead to higher than actual readings.
- DON’T just install TMTs in the lower radiant section and in one vertical section. Coverage of lower, middle, and upper radiant plus shield tubes and maybe 1-2 per pass in the convection is better.
- DON’T just rely on TMTs but do regular IR thermography. Look for relative temperature changes and hot spots.
Talk to your local TMT vendor, like Daily Thermetrics and Gayesco as a start, about their technology, especially if the TMTs are failing regularly.
There is much more to be said about this topic and it can all be heard at any of the RefComm® conferences and training events each year. Safety concerns for tube overheating and rupture is a very real concern. Not to mention some monetary gains possible through crude, reduced down time, and higher yields related to optimization. Take a hard look at the data coming from your TMTs and their installation in the firebox. You will be surprised at what you might learn.
Additional Reading
Optimizing Strategies for Temperature Instrumentation in Delayed Coking Units
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