Temperature of the CDU feed is always less than 370'C because temperature further than that will cause cracking. Cracking of what? Cracking of Diesel? Or cracking of heavier ends? I'm asking because FBP of Diesel is 370'C.
Answers
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07/03/2018
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Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Temperature of the flash zone or CDU column feed entrance zone is always maintained between 355 to 365 deg.C approx. Above these temperatures cracking of hydrocarbons can happen and coke deposition will take place. It also depends on the type of feedstock i.e crude oil type .
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05/03/2018
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Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Cracking is a function of the oil, the temperature and the residence time. The amount of cracking that takes place in a crude or vacuum unit is miniscule compared to the total amount of oil present so it has no impact on the boiling range of the crude and doesn't make a difference from a yield stand point which fraction the cracked material comes from.
Cracking is a problem in crude units because they are not really designed to handle much coke. Any coke formed tends to build up slowly over time and can plug things like pump suction lines. There are some design details that can be used to help better manage coke formation and limit its impact in the crude unit.
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05/03/2018
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Krishna Rao Pulugurti, Retired/Consultant, pkrao2012@yahoo.com
Cracking of paraffins and cyclic compounds with long paraffinic side chains in the residue
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05/03/2018
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Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
There are CDU units that operate at heater outlet temperatures as high as 393 degrees C and run for more than 5-6 years without coking or fouling problems. The major concern is coke formation in the wash section (which is a product of thermal cracking). Some units have suffered wash section fouling due to a combination of poor operation, processing cracked material slop / synthetic crudes, and having the wrong column internals.
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