3 replies to this topic

[mannan]

Dear friends,

We have vertical reboiler is using heating MTBE and C4 raffinate by MP steam. Normally the MP steam is entered before desuperheated by MP condensate water. At normal unit running MP steam inlet Flow control valve was opening 60 to 65 percent. but nowadays the control valve open fully and less flow , we opened the bypass suspect control valve chock.. that time also .. flow less. only ..
we have 2 steam traps is available for removing condensate from reboiler out let which both are working well .. at present we put both on service. we checked flow transmitter also found working perfect.

what are the reasons steam flow less ? Need your help.. Thank you in advance.

[trilok_sontakke]

before going to your problem.I wish to ask you some questions.

how you know that steam is flowing less?
are you distilling something from raffinate?what is the distillation rate?
have you checked the stean consumption?and if so is it same as calulated for reqiured distillation rate?
have checked steam pressure and temperature? is it same as before when your things are working?

Actually ther is no stean flow as you are saying.More important is steam pressure and temperature.




Thanks
Trilok

[djack77494]

Mannan,
You have not adequately described your problem, so I'm forced into some assumptions in replying. It sounds as if you are seeing less steam flow now than you've seen in the past. That, I suspect is a problem if for no other reason than that you've lost control of your process. (If your control valve is operating at its full open position, then you have no control.) It sounds as if you desuperheated your steam at some time in the past but are not doing so now. (Please clarify this, since it is a key factor.)

Based on the above, you may be getting less effective use of your heat exchange surface. Heat is readily released by condensing steam, so surface area where steam is condensing is very effective (high U). On the other hand, heat transfer in cooling superheated steam to its saturation temperature is MUCH less easily accomplished. If you are doing more of the latter today than you were doing in the past, this could explain an apparent degradation of the reboiler's performance. If I'm wrong in these assumptions, please clarify and I'll give it another shot. Also, be careful with your use of the word "normal". It's not clear if you mean as designed or actual past performance or something else. And let us know what's happening on the process side of the reboiler.
Regards,
Doug

[Pronab]

If process side temperature is not maintaining, reboiler fouling is one of the main reason of steam control valve fully open. It seems that steam is not condensing fully but passing through the reboiler, which is useless. We faced the same problem of our condensate stabilizer, where steam flow control valve( out let of horizontal reboiler) was full open and process side temperature was not sufficient. We found tube surface was fully deposited of thick black materials(mostly FeS deposition).
Mr. Doug is absouletly correct, Saturated steam is to be always used in reboiler.

Pronab.