Continuous Monitoring of Distillation Exchangers with Fluctuating Rates
Continuous Monitoring of Distillation Exchangers with Fluctuating Rates
(OP)
Hello All!
I'm creating monitoring tools for our distillation columns and I am trying to determine the best way to monitor the Condensers (CW and Propane Refrigerant) and Reboilers (75# IPS and 25# LPS) on multiple towers for fouling. From school, my understanding is a trend of the UA curve would let you know at what rate your Overall Heating Coefficient is degrading. However, when I graph the UA curve it is constantly jumping around due to our constantly changing feed rates into these towers. I am currently trying to graph the steam valve % Open vs tower feed to determine if the Reboiler is degrading, but it seems very "Hand-wavy." What is generally used to continuously monitor these types of heat exchangers with constantly changing rates? Any other tips you have I would greatly appreciate :)
Note: All are S&T exchangers, counter-current. Attached is an example that comes out of my current Reboiler graph that I made, that I can't really make any sense of.
Have a wonderful day and thank you for your insight!
AlbusTheEngineer
I'm creating monitoring tools for our distillation columns and I am trying to determine the best way to monitor the Condensers (CW and Propane Refrigerant) and Reboilers (75# IPS and 25# LPS) on multiple towers for fouling. From school, my understanding is a trend of the UA curve would let you know at what rate your Overall Heating Coefficient is degrading. However, when I graph the UA curve it is constantly jumping around due to our constantly changing feed rates into these towers. I am currently trying to graph the steam valve % Open vs tower feed to determine if the Reboiler is degrading, but it seems very "Hand-wavy." What is generally used to continuously monitor these types of heat exchangers with constantly changing rates? Any other tips you have I would greatly appreciate :)
Note: All are S&T exchangers, counter-current. Attached is an example that comes out of my current Reboiler graph that I made, that I can't really make any sense of.
Have a wonderful day and thank you for your insight!
AlbusTheEngineer





RE: Continuous Monitoring of Distillation Exchangers with Fluctuating Rates
Similarly, the condensing side pressure (dT) is a direct indication of load (Q) as long as the U is constant (fouling isn't occurring).
So, dT (condensing side pressure) varies with load and fouling. If both are occurring (fouling and load changes) then dT can't be used to distinguish between the two.
RE: Continuous Monitoring of Distillation Exchangers with Fluctuating Rates
RE: Continuous Monitoring of Distillation Exchangers with Fluctuating Rates
RE: Continuous Monitoring of Distillation Exchangers with Fluctuating Rates
If you've got the process / thermal datasheet for each of these units, try to compute the clean U value (or the design case h values with given values of fouling coeff for each of tube and shellsides) for the HX for a range of process side flows and corresponding utility side flows, assuming you have a fixed target temp for the process side temp for all operating flows. Then compute overall U. To gain some confidence on the calculation routine, first see if you can match the design case overall U for the design case flows stated on the thermal datasheet. Dont forget to take into account tubeskin temps and how film coeff changes with viscosity, where applicable. Finally compute the clean UA value for each case given this flow adjusted clean value of U. Then compare with the field derived UA value.
What may make data reconciliation more difficult is when temperature transmitters show considerable response lag ( due to the thermal inertia in thick wall thermowells) to actual process temp for transient process / utility side flows. So you should only jot down process parameters when stream temperatures on both sides have had some time to stabilise.
RE: Continuous Monitoring of Distillation Exchangers with Fluctuating Rates