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AnonymousHi
We have some problem during the drum warm up. The gas in the drum bottom has some dificulties to flow to the main tower. We have a vessell that receives the gas and liquids from the drum during the warm up and sends to the main tower.
In order to solve the problem of flowing gas from the warm up vessel to the main tower we are studying to install a control valve in the pipe of the set of two drums from the top to the main tower. We will keep the drum pressure and decrease the main tower pressure. With the increase of the pressure difference between the drums and the main tower will be possible to increase the gas flow from the warm up vessell to the main tower.
We have a plug valves in the top drums pipe but it is very hard to control the pressure.
Anybody has this kind of design ?
If I replace my plug valves to Ball Valves on the drums it will be possible to control the pressure ?
Regards -
the liquid and gas that is generated during the warm up, is going directly to the coke condensate or to the blowdown (some unit dont have coke condensate)?
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AnonymousThe liquid and gas that is generated during the warm up is going directly to the coke condensate vessel. After the gas from de condensate vessel goes to the main tower and the liquid from the same vessel goes to the blowdown vessel.
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Yes, as Antonio (espana2005) said, some DCU’s do not have a coke condensate drum.
In the coker I worked some years ago, the coke drum overhead lines had ball valves, and after the point the lines from two drums would join, we had a butterfly valve. This butterfly valve was normally open 100 %, and when we were going to warm up a drum, we would partially close this butterfly valve to force the hot vapors from the online coke drum into the “cold” coke drum. Some older cokers do not have this set up, while some newer ones use a “ring valve” instead of a butterfly valve.
There is some information on ring valves here: http://www.velan.com/products/pdfs/vel-cbv-2002-web.pdf
Hope this helps,
Regards,
CG -
AnonymousMr: Butterfly valves are not recommended unless they have special design for coking process conditions (the valve may stick in the close position)
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The butterfly valves in the coker I worked had a mechanical stop in the actuator that would prevent closing the valve completely.
We did experience sticking in these valves a couple of weeks after start-up, because of the resid would get in between the shaft and the bushing and coke up.
To correct this we had to drill the valve body and weld 1/2″ pipe with flanges to inyect steam into the bearing to keep them clean.
This was done back in 2001, and my friends there tell me the valves are still OK.
Regards, CG -
AnonymousMr: mech stops are usually a feature included in the actuation mechanism and they are not reliable. Valves in coker service always require steam flushing to avoid sticking (they have to be ordered with steam injection ports from the beggining).
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All these valves are called SP’s (steam purge) because they must be specified with steam purge. In the specific case of the SP-3 (in the FW design) that valve is located on the line that goe to the fractionator, There are units were have installed butterfly valves or gate valves. That valves can generally tend to stick (formation of coke in its internal, due to the loss of steam into the purge)
The main function of that valve is to help send more gas to the top of the drum to warm; close this SP-3 valve allow to force the hot vapors to the drum
As Clauss said in the new designs are being installed the valve that is called “ring valve,” prevent closing the valve completely (due its internal design, see velan page), almost all the new design (FW design) have installed ball valve in all this sytems like SP-1/2, also the valve going to the blowdown
I understand that problem is present from the initial startup of the unit, This may be due to poor design of the line of gases coming out of coke condensate drum (might be small) or that the blowdown system has a lot of pressure (less drive force)
What is the method or procedure to warm up the drum, I meant, for how long do you send the gas to the blowdown and to the fractionator. or how do you do to warm up the coke drum?
Excuse my English, Best Regards
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Anonymousthx
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AnonymousI have heard this 1st drum warm up problem happening during start up, mainly in FW units.
During startup very light feed is circulated back to fractionator, while keeping 700 Deg.F Heater outlet by procedure, which increase vaporization; but, normal procedure for first drum warm-up, as said before, requires a good design for the coke condensate balance line, which typically is too small since it is designed for normal operating conditions. I have seem cokers almost closing SP3 as much as possible (restricted by miminum mechanical stop) and still getting very long warm-up times.
Has anybody tried different warm-up procedures (other than FWs) for first drum during start up?
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Sure
150# superheated steam is much better option for initial drum warm-up; , but your going to be it can be done for as long as needed, while heating up main fractionator and drying out the whole system with hot oil circulation at the same time. -
Has anyone tried warm up/ heating of coke drum with medium pressure steam (available 14 kg/cm2g, 290 deg C) instead of vapour heating. May share their experiences please.
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