Q & A > Question Details
We are facing problem of low heat duty of the debutanizer reboiler. Tube side heating media is saturated high pressure steam. Our steam flow was decreased gradually. We opened steam flow supply valve more to increase the heat duty, but still we did not succeed. We use saturated high pressure steam as heating medium and operating temperature is 482 Deg F (250 C). We as of now ruled out the reason of polymerization because of the low heating medium temperature, but question is that higher shell side tube wall temperature due to low pressure drop and it may lead into polymerization. Can it happen?
One more point is that, we have one online sealing clamp at steam inlet line and we injected sealing material three times to arrest leak. I thought that this sealing material might have blocked the control valve upstream cadge/ filter and reduce the steam flow. We had reduced the condensate pot pressure and we observed that the steam flow was increased.
What can be the reason for low reboiler heat duty? Is it because of polymerization or chocking of the steam control valve? How can we conclude this problem?
 
Answers
13/02/2014 A: Marcello Ferrara, ITW SrL, mferrara@itw.it
In case you are facing polymerization problems, please be aware we have a technology for dissolving polymers in debutanizer/depropanizer columns/reboilers. This can be performed without opening the equipment in 24 hours on an oil-to-oil basis.
02/02/2014 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
One other thing you didn't mention is it a kettle type reboiler with a weir... if so check that the balance line is closed (used to drain during shutdown) if it is closed try raising the level on the weir side to ~90%.. If the duty of the reboiler increases the weir is damaged... The weir ensures the tubes are covered if it is damaged your tube will only be half covered..
02/02/2014 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
These are latent heat reboilers..If the steam is not condensing you can open the valve wide it wont make any difference. Are you sure of the level in the condensate pot... empty or full will both prevent heat transfer.... If the level is good...run an IR heat gun over the end plate to see if the tubes are flooded (condensate backing up into the exchanger) in which case you are probably plugging of on the outlet. Any chance of a tube leak..remember if it is a leak, hydrocabon will build up on the bottom half of the exchanger channel head (assuming a single pass), venting the top will not show anything. The build up of hydrocarbon will restrict the flow of steam.
29/01/2014 A: Kalpesh Unadkat, L&T-Chiyoda Limited, unadkatkc@hotmail.com
Problem may be due to condensate side back pressure as by decreasing pressure on condensate side, flow is able to increase.
29/01/2014 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Can you e-mail a sketch showing the valves and instrumentation around the reboiler?
Ralph
28/01/2014 A: Jignesh Refinery, EOL, jignesh.joshi1980@gmail.com
We do not have bypass facility across steam control valve, but steam flow was increased from 20 kg/hr to 30 kg/hr, when we reduced the balancing line (Condensate pot) pressure from 38 kg/cm2G to 34 kg/cm2g. From this can we say something about valve chocking.
28/01/2014 A: Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
For debutanizer reboiler the practice is to keep the hot fluid temperature below 550 F, so your steam temperature is good.
Can you measure the pressure and temperature on the condensate leaving the reboiler, If steam flow is limited by hydraulic restriction, then you should see a higher pressure drop on the steam/condensate side of the reboiler.
27/01/2014 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Can the steam line filter be bypassed? If the filter is not the problem, if you open the control valve bypasses at both the steam and condensate control valves, and the reboiler duty does not increase, then the problem is on the shell side.