evan7000 cycles is a typical number before the first crack IF, big IF…you do everything right. Most sites do not. So experience varies from cracks after 3 years to barely any after 30+ years. Tons of factors at play here….material, fabrication, operator/process, etc. Also coke drums can be repaired indefinitely for a price of course with automated, engineered weld overlay. Some operators will replace drums after 15~ years while others are still going strong after 30-40 years with repairs….it is an engineering desicison and a economic one. No simple answer…but 7000 cycles is a good rule of thumb to start to expect cracking.
evanHi. I agree with Calvin, there are lots of things to be understood to help you with this issue.
Some initial thoughts,
– If XSO2 is high due to damper control, you may be successful. If it is high due to tramp air, controlling at the burner itself will be hard.
– Corriolis is a good measurement, you get mass and volume and density flow real time. This is the best practice but rare.
– Most refiners now have real time analyzers on the refinery fuel gas network to get composition and heating value. This can be central to the FG ring. But you should also do some QC testing at the DCU to be sure the quality is the same there. Most DCU are at the end of the header and quality changes over the run.
– Generally DCUs like higher XSO2 to prevent heater fouling. If you run too low for heater efficiency, your decoking frequency is likely to increase.
evanI think this is dependent on the pre-TAR inspection looking at
+ steam trends
+ HPU pressure/flow/history
+ boriscope
+ history of operation
The longest I have heard is an overhaul every other TAR but most people do a overhaul each TAR.
Wear sites and locations varies between the TUD and BUD and the various generations of design. Seats, seals, and actuator components can see wear. The gates and body rarely see wear but it has happened for various reason. So it really comes down to your pre-TAR inspection.
evanP-value tests is not really applicable with resid. But I would suggest you use Colloidal Instability Index (CII) is the ticket for resid. You must first get SARA analysis on your feed and ideally on heater charge too.
What values constitute stability are very challenging because of the cracking across the heater. Traditionally CII > 1 is a problem in all cases but CII > 0.5 can be a problem at some sites in the furnace itself. So you will have to find your operating envelope.
Check out this article….
http://www.ogj.com/articles/print/volume-102/issue-34/processing/index-correlates-asphaltene-stability-to-coker-furnace-fouling-potential.html
evanHi. Is the new unit or the existing one? Is your fuel gas coming from an outside source (not refinery fuel gas)?
You should investigate if the fouling is due to entrained amines and pipe corrosion products. That should be fixed up stream of the DCU. You must ensure you have not exceeded the vapor velocity limits for the main fuel gas KO pot in the DCU to prevent entrainment fouling. Some plants use SS piping for the FG system but this is $$$$.
How heavy is the tail end? Are you experiencing burner tip fouling? Consider individual coalescers at each furnace especially if you have Ultra-low NOx burners.
evanRather than cutting all the ubends, you can drill some small holes every few ubends then do a pressure survey to determine which ubends to cut and hydroblast.
evanFurnace flow > fresh feed flow in 90% of cokers. The difference is called recycle or Through-put Ratio (TPR) in FW terms. The reasons why depend on the equipment design and operation.
evanHi. Conical bottom tanks are standard, inverted or normal depends. Taller is better with higher slopes to facilitate draining. Volume should be sufficient to quench and cut 1 drum with no additional water input. Jet pump suction is typically higher than quench pump. Cyclones can work if properly maintained but most sites do not have them. Automated draining valves with some DCS logic is a good approach to draining the system routinely because operators don’t do it……So yes, there are lots of design criteria and I think that’s the short list.
evanJust correcting the link. Great paper
http://www.state.nj.us/dep/dsr/soils/tss%20vs%20ssc%20test%20methods.pdf
evanHow do you know it has collapsed? Internal inspection or gamma testing?
Some ideas include:
+ water ingress with subsequent steam explosion
+ corrosion of trays or bolting clips
+ plugging that results in dP greater than design uplift rating
evanYou can learn more from these patents:
1975 Patent 3917564 Disposal of Industrial and Sanitary Wastes, Mobil Oil
1985 Patent 4666585 Disposal of Petroleum Sludge, Atlantic Richfield
1988 Patent 4968407 Sludge Dewatering and Destruction within a Delayed Coking Process, Foster Wheeler
1989 Patent 5009767 Disposal of Industrial and Sanitary Wastes, Mobil Oil
RE Temperature, yes, that’s during the sludge injection initially in the quench phase after steamout.
RE vendors, all the DCU licensors (AFW, BHTS, Lummus) can design/build the system for you. Veolia and a few other companies can provide the sludge pre-treatment.
evanYou can learn more from these patents:
1975 Patent 3917564 Disposal of Industrial and Sanitary Wastes, Mobil Oil
1985 Patent 4666585 Disposal of Petroleum Sludge, Atlantic Richfield
1988 Patent 4968407 Sludge Dewatering and Destruction within a Delayed Coking Process, Foster Wheeler
1989 Patent 5009767 Disposal of Industrial and Sanitary Wastes, Mobil Oil
RE Temperature, yes, that’s during the sludge injection initially in the quench phase after steamout.
RE vendors, all the DCU licensors (AFW, BHTS, Lummus) can design/build the system for you. Veolia and a few other companies can provide the sludge pre-treatment.
evanYes, there are plants that feed sludge during coking and quenching. The pretreatment requirements vary by the type of sludge being processed. The original systems were called iMOSC for water sludge injection. Most sites will mill the sludge to have a more uniform particle size, typically 650F is a good start.
evanI did not think it was continuous but listen to the OEM not me, I don’t have any details…..
evanyes, wheel wash is normal. Flow is not continuous. It’s hard to say without knowing the details of the compressor design what the flow should be when running. Who’s the OEM for the WGC?
Yes, balance and vibration issues start accumulating without washing. Washing it typically done with the vibration starts coming up. You should look back at the baseline SOR trends. There should be a trip vibration level too. Just a guess but I would think washing should be triggered at approximately 30% of the difference between SOR and trip.
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