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[gastocarbon80]

Dear All,
In the refinery I work, we are having some problems in a VDU due to coke formation in the furnace. We are studing right now the problem but I do not understand one thing.
How should we operate the furnace? I mean, my point is that as the feed is heated up into the tubes, we are getting vapour from the liquid feedstock, so the velocity increase, so the residence time gets lower and coke is avoided. That's the reason behind steam injection in tubes, is it not?
But with these ideas in my mind (which could be not correct), Ive come across with some papers saying that in the furnace you should avoid vaporization, you must get such as pressure profile that you get all the vapour in the transfer line.
What I do not understand is why...in one side getting vapour is goos cos you avoid coke, in other side you need to avoid it. And finally, as you are getting vapour in transfer line, does the temperatura drop in the line? so your are gettind lower temperatura at flash zone therefore less profit?
Any help wpuld be appreciated.
regards