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My question is related to indications of channeling or bypassing in a catalyst bed.
An indication of bypassing or channeling is the Radial Spread (T.peak - T.min) of the multi-point thermocouples provided at the outlet of the bed i.e. difference between peak temp and min temp.
However, it is measured as Radial Spread divided by the Temperature difference across the catalyst bed:
RS/dT = (Tpeak-Tmin) / (Tpeak-Tinlet)
Where Tinlet is the average inlet temperature to the catalyst bed and the value of the ratio RS/dT should be below 0.5. Any value greater than this indicates channeling in the catalyst bed.
How is RS/dT an indication of Channeling?
Why is its limit 0.5?
 
Answers
03/06/2019 A: Ed Ouwerkerk, Catalyst Intelligence Sarl, ouwerkerk@catalyst-intelligence.com
Any RS or Radial dT >> 2C (typical measurement accuracy) is a sign of local maldistribution or TI-error. The time response of TI's give you more information of the nature of the problem, see for example www.catalyst-intelligence.com blogs.
29/05/2019 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Where are you located?
29/05/2019 A: Xavier Ruiz Maldonado , Haldor Topsoe, Inc, xerm@topsoe.com
The radial temperature spread (RTS) to axial temperature ratio (AT) is a quick and easy way to get the radial temperature spread (RTS) normalized no matter the height of the bed. If we look at RTS values only, the bed height may cause an amplified effect on the RTS which is difficult sometimes to interpreter and compare with other units sized differently. Having the RTS normalized, the definition of <0.5 value for a "proper distribution" means that per every degree developed by the bed, it should result into less than 0.5 ºC measured at the axial level. Therefore, this is just another way to say there is a minimum temperature spread across the bed.
In order to apply this method, it is highly important to verity the real position of the TC's above the OC, and the reliability of the TCs.