Reboiler Duty
Reboiler Duty
(OP)
I am trying to figure what is the right and practical reboiler size for a stabilizer column. I have simulated the Stabilizer Column with a feed/Bottom Exchanger. At steady State the Reboiler Duty required is 5.0 MMBtu/hr. At start up condition (Feed/Bottom Exchanger duty set to zero), the Reboiler Duty is 15.0 MMBtu/hr. How much excess duty above 5.0 MMBtu/hr is reasonable?





RE: Reboiler Duty
Also important is to make sure items like control valves and steam traps are sized for startup and have turndown for normal operation.
RE: Reboiler Duty
Thank for your reply.
If the control valve is sized for the start up condition, Should the reboiler needs to be bigger because the larger amount of heat medium (approximately 3 times) is required due to higher pressure drop? Although the heat transfer area may be sufficient because of higher LMTD and higher heat transfer coefficient due to higher heat medium velocity.
RE: Reboiler Duty
I'm assuming at the 3x duty case that you are starting up is with the column at full rates. Would you actually do this or would you start up at reduced rates and then increase feed as capacity is available?
There's another factor you may want to consider when setting the size of the reboiler design duty. If the feed/bottoms exchanger becomes fouled, what will the site do? Is the column shut down totally so the exchanger can be cleaned? Do you have multiple shells so you can take one out and clean the other at reduced heat transfer? Do you plan on just reducing rates in this configuration until the exchanger is cleaned and back in service.
All of these can be factors in setting the design duty. There isn't a straight forward answer but usually, I've seen minimal additional duty added to exchangers for start up conditions, definitely not adding in 200% additional area. Startup is usually handed by running at reduced rates. However, there is a cost associated with that and that may support adding in additional area.
RE: Reboiler Duty
Thank you for your comment. I guess you are right, during start-up, one would normally start at a much reduced rate, therefore the design at normal operation would be sufficient plus of course the standard design margin.