Re: Pressure-Compensating TCs at Regulatory Level ?

Posted by Jim Gunderman on June 08, 1999 at 00:19:16:

In Reply to: Pressure-Compensating TCs at Regulatory Level ? posted by Don Snowden on June 05, 1999 at 17:01:57:

Don,

Those are interesting comments regarding the interaction of a PCT and the pressure controller. I could see how that might happen, however, I have not seen that problem in our refinery (yet). Although it is not a high purity distillation column, we have successfully used PCTs on closed loop control in Depropanizer overhead service.

: Although I have heard of several application that do work, what are people's experiences of implementing PCTs (pressure-compensating temperature) at the regulatory level (e.g. on the TDC-3000 basic regulatory level) ?

: On multicomponent fractionation (e.g. Crude Unit), it is not difficult to implement. But on several applications (Demethanizer lower tray TC and Deethanizer lower TC) I tried in an Ethylene Plant it was not successful. There was too much interaction with the pressure controller. For example, when the pressure would rise the PCT would fall, then the regulatory TC tried to add heat, thus causing the pressure to rise more.

: Since there is always some interaction between a tower's TC and PC, I think one has to be careful implementing PCT's at the regulatory level, particularly in the higher purity distillation columns. Then again, it could be that one needs to make sure the pressure control scheme works very well.

Follow Ups:

• Re: Pressure-Compensating TCs at Regulatory Level ? Dan O'Connor 11:35:48 6/08/99 (5)
  • Regulatory use of pressure compensating temperatures. Tod Peterson 07:22:02 6/20/99 (0)
  • Re: Pressure-Compensating TCs at Regulatory Level ? Don Snowden 22:33:39 6/08/99 (3)
    • Re: Pressure-Compensating TCs at Regulatory Level ? Dan O'Connor 11:03:06 6/09/99 (2)
      • Re: Pressure-Compensating TCs at Regulatory Level ? Don Snowden 00:12:13 6/10/99 (1)
        • Re: Pressure-Compensating TCs at Regulatory Level ? Doug B Robertson 17:08:41 6/17/99 (0)

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Comments:
: Don,

: Those are interesting comments regarding the interaction of a PCT and the pressure controller.  I could see how that might happen, however, I have not seen that problem in our refinery (yet).  Although it is not a high purity distillation column, we have successfully used PCTs on closed loop control in Depropanizer overhead service.

: 
: : Although I have heard of several application that do work, what are people's experiences of implementing PCTs (pressure-compensating temperature) at the regulatory level (e.g. on the TDC-3000 basic regulatory level) ?

: : On multicomponent fractionation (e.g. Crude Unit), it is not difficult to implement.  But on several applications (Demethanizer lower tray  TC and Deethanizer lower TC) I tried in an Ethylene Plant it was not successful.  There was too much interaction with the pressure controller.  For example, when the pressure would rise the PCT would fall, then the regulatory TC tried to add heat, thus causing the pressure to rise more.   

: : Since there is always some interaction between a tower's TC and PC, I think one has to be careful implementing PCT's at the regulatory level, particularly in the higher purity distillation columns.  Then again, it could be that one needs to make sure the pressure control scheme works very well.


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