2 replies to this topic

[Estiqaatsi]

I’m simulating a column in Hysys in dynamic mode, trying to take into account the effect of static heads (nozzle elevations). When I switch to the dynamic mode (and Hysys uses information relating to elevations) suddenly the pressure of the last tray, as shown in the “pressure vs tray position” graph, drops. A quick check led me to conclude that Hysys calculates the last tray pressure from the reboiler pressure, taking into account the static head of the line “ToReboiler”. But the value used as starting point for the reboiler is not necessarily correct, because there is no information about the pressure drop in the boilup line, and it is actually this pressure drop which allows to build up a higher pressure in the reboiler. If the reboiler pressure is underestimated, then subtracting the static head the bottom tray pressure becomes lower and unrealistic too. Has anyone ever faced similar problems?

 

[Pilesar]

Did you model the reboiler separate from the column before switching? That may allow putting pipe units in for the reboiler lines. I'm not a Hysys user, but I know dynamic software makes some simplifying assumptions internally.

[Estiqaatsi]

Did you model the reboiler separate from the column before switching? That may allow putting pipe units in for the reboiler lines. I'm not a Hysys user, but I know dynamic software makes some simplifying assumptions internally.

 

Pilesar, unfortunately the simulation was already set to a lower level of detail. The condeser has been modeled outside of column environment, but the reboiler is inside.