4 replies to this topic

[PE123]

Hi all,

Currently, I have a heat exchanger ( Tower reboiler) whose heating medium is superheated steam at 27 kg/cm2G.

I am studying the possibility of using medium pressure steam ( 14.5 kg/cm2G) for the same exchanger. Can anyone offer any advice on how to proceed ?

thank you
fsk

[srfish]

What am I missing? Reducing that much steam pressure will cause quite a reducton in heat load for the reboiler.

[PE123]

Hi Srfish,

By design, the heat exchanger area has been overdesigned and the actual duty is also lower than design. As such, it is suspected, the exchanger area ( grossly overdesigned originally) is able to compensate for the reduction in steam pressure.
Kindly note that for both steam pressure grade, the temperature driving force is still available, considering the required process temperature is 160 degC.

How to confirm or check that the exchanger is able to cope with a lower steam grade ?
fsk

[srfish]

Hi fsk,

You need the existing drawings and process information. The existing specification sheet will help. Then use a thermal rating program to see if there is still is excess .surface.

[DB Shah]

Hi fsk,
Measure the chest pressure of the reboiler, cross check this with the condensate temperture leaving reboiler.
Inlet condition of the reboiler =27 kg/cm2g superheated
Exit reboiler condition = saturated condensate at chest pressure.

Rate the reboiler in a simulator (eg HTRI/HTFS) find the operating dirt factor (Vary the Rd to match area ratio=1 ie required area=available area)

Use this Rd and the new conditons at inlet ie MP steam condition.

For reboiler exit condition-
Assume a chest pressure of say 1.0 kg/cm2 less than MP steam condition (to take care of DP in control vavle, FI,piping etc at reboiler inlet. You may need to modify CV,FI, piping to minimize pressure drop in hex inlet)

Reboiler exit condition = saturated condensate at (14.5-1) ~ 13.5 kg/cm2g.

Check the performance of exchanger, if area calculated is less than available area ie Area ratio>1, the hex will perform for new condtions.