External Temp measurement probes for columns control

[mrtangent]

I'm looking for advice here.

Has anyone used an external temperature probe (fitted to the wall of a carbon steel column to indicate temps).

We have a packed column with temperature probes in the packing in the top section but none in the bottom section. For control the ASPEN model shows the greatest % composition change with temperature in middle of the packing not the bottom of the column where an exsiting probe is located.

So in short. To get better column control we need an Analyser in the base or a TT inthe bottom packing. We dont have DP ether.

So I'm looking for advice / suggestions has anyone tried using an external temperature probes on columns to indicate process temp. The column is lagged and inside a building so the temp should be pritty constant. The feed to the column is fixed its tank to tank.

James

 

[pmureiko]

I've done this to troubleshoot column problems and not for control. It is fairly accurate and will you will improve column control column using the proper stage.

The external temperature will be delayed due to conduction through the vessel walls and will be offset because of heat losses to the surroundings. The delay can be compensated for in tuning the control loop.

The affect of heat loss on temperature can be determined by looking at the difference between where you do have an internal temperature reading and an external measurement. This offset can be applied to your external TI's to determine the interal temperature.