August 4, 2007 at 6:07 pm #3975
Our Feed Valve(Make: Velan 14″) got stuck up recently…gradually with each passing cycle the problem has aggravated….Initially the torque was raised and now the valve is opearated fully manually…involving lots of labor….
Our guess is that because of improper flushing the Switch valve-feed valve spool piece has coked up & the same coke has entered/striking against the ball valve face causing the valve to take up excess torque. We plan to take a shutdown to attend the valve/clean up the spool piece
We have 4 drum coker, With my 1st block in service…. can I risk dropping the 2nd Block’s Feed Valve(relying solely upon the Switch Vavle for isolation)…. then drop the spool piece & blind the switch valve face?
What is your take on the problem at hand and if anybody would like to share their views/experience on this problem
What is the ideal time for flushing switch valve spool piece & would 1.5″ blocking steam line suffice for a 14″ spoolpiece & whether I should do away with the RO on the blocking steam line/ Feed Valve Purges?
August 5, 2007 at 11:52 am #7333
Sticking of the valve is most likely due to inadequate steam purging of the valve. It is important to verify that your steam piping arrangement is proper and that you are not losing flow to the valve purges due to steam being used preferentially in another part of the process.
You can install a blind to do work as long as the switch valve is holding and is deenergized and locked in place while the blind is being installed.
Feed line spool flushing should start before moving the switch valve (3″ steam line is best)and should continue for 5 – 10 minutes, then shut the downstream isolation feed valve. The amount of flow should be ~ 5klb/hr or more if the MF can handle it.
August 6, 2007 at 9:48 pm #7331
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August 9, 2007 at 10:32 am #7330
I have to agree with Mitch. It sounds like the valve is coked up and will only get worse. You can monitor the situation by taking amp readings from the actuator. As the amps increase the valve is continuing to coke up. I would suggest you call Mark Fucich at Southern Valve 713-443-9642.
August 15, 2007 at 3:51 am #7325
Thanks you Mitch & others for your replies……
Last week we had to bring down the coker block,…because the feed valve would not open….The valve was dropped…and guess what…the seat was COMPLETELY filled with coke fines…which had got compounded over a period of time & had gradually lifted the ball up…so much so that it had hit the roof & had completly prevented the ball movement..In a record time do 2 days… 2 nos….of 14″ ball valves……were dropped cleaned & boxed up again….the vendor was citing improper flushing of spool piece…but upon dropping the valve the feed line was completely clear with no coke deposition whatsoever…..This foxes us….we feel it is more to do with the valve steam purges & not with feed line flushing (which we already do for 5-10 minutes)…also we have removed the feed line RO that we initially had…..your comments please
One more query: Why do you suggest to start flushing before moving Switch valve to final position…does it help much ?
August 15, 2007 at 11:06 am #7323
I believe that it is important to avoid the resid from being stagnant at over 900F. Coke can form rapidly. For that reason, I recommend having line purges on before the switch. Better safe, than sorry. Valve purge block valves should all be open all the time. Again it is important to verify that the steam piping arrangement is proper and that the line purge is not robbing from the valve seat purge.
September 6, 2007 at 5:54 pm #7297
A purge steam pressure gage near each switch valve is useful, so the operator can check it before switching.
Restriction orifice size is also important, so that you have enough purge rate.
Also, if you have steam traps in this piping, they should be in working order.
September 19, 2007 at 1:46 pm #7273
September 22, 2007 at 2:34 am #7271
Please ensure proper purge steam to all the valves (feed line isolation , switch or vapor valve) on routine basis. Not passing of purge steam to the valves has caused coke deposition in your case finally resulting in non operation or jamming of valve. Failure of feed line flushing steam will cause coking of the spool piece between switch & isolation valve.This will result in increased pressure at switch valve inlet during switch over to the concerned coke drum & will lead to unit interruption immediately.
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