We have a kettle type ammonia vaporiser. Shell side is ammonia and tube side is steam to vaporise the ammonia. We have observed that tube side (steam side ) remains filled with condensate almost 80% due to its low load operation against the design. Is this operation is correct to run the vaporiser with filled tube condensate?
Answers
|
10/05/2015
|
A:
|
Karan Shah, Armstrong International, karan5188@gmail.com
i would suggest please check the steam trap down stream of steam line for proper functioning.
Also please let me know the ammonia temp so that i can suggest you some better system.
|
|
20/02/2014
|
A:
|
S Banik, Centre for High Technology, sbdr@rediffmail.com
There is nothing wrong in this type of operation. In fact we used to operate a large kettle re-boiler for a 1200mm dia. research distillation column. For achieving turn down of the column load,we used to control level of condensate in the condensate drum so that desired no of tubes would remain flooded with condensate. You may be controlling steam flow rate in line with vaporization rate of ammonia. Better way could be condensate level control.
|
|
19/02/2014
|
A:
|
Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
It would not be unusual if your steam control valve is on the condensate side of the vaporizer. For a heat exchanger Q=UAdelta T. When running at reduced duty the control will pinch closed causing condensate to back up in the tubes. This effectively reduces the area available for condensation to occur over thus bringing the heat exchanger effective area in line with what is needed to meet the duty needs. If you put the control valve on the steam in, lower duty demand again causes the CV to pinch down. This time though the extra DP across the control valve lowers the pressure of the steam, thus reducing the condensing temperature. Duty is then controlled by lowering the delta T between the vaporizing fluid and the condensing steam temperature. The downside to this latter scheme is that if the duty is low enough the steam pressure will drop so low that you can't get the condensate out of the exchanger. It then starts to back up into the exchanger until enough pressure builds to push it out.
|
|
19/02/2014
|
A:
|
Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Allowing steam condensate to "back up" in kettle evaporators is a very traditional control approach. The h,i-steam and potential heat flux [BTU/hr-ft2 in English units] for condensation of "clean" steam can be very high [incredibly high at times]. So condensate has to "back up" in order to reduce the surface area available for evaporation. I do NOT recommend this traditional control approach. I postulate that this can cause more aggressive fouling and corrosion on both sides and may cause shell side boiling to switch among several modes cyclically.
My recommended control approach is to include external condensate pot with its own local LI/LC/LCV with "gravity drainage" of the tube bundle to the condensate pot. Condensate pot does require an equilibration vent back to steam-side channel and this may or may not be available in cheaped down exchangers. Then the pressure of the steam in the tube side is controlled via PI/PC/Trim PCV reset by primal controller for mass / volume flow of evaporated ammonia.
|
|
19/02/2014
|
A:
|
Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
If the boiler feed water is properly treated, there should be no problem. If you were using circulating hot oil for a heating medium, the tubes would be 100% full, wouldn’t they? If circulating hot water were hot enough for the service, again liquid full.
|