antonio saura Cebrian
my first question is Why you increase the quench oil?, (I suppose that the used fluid is HCGO at 650 ºF), Before that you increased the flow the velocity was relatively high (Delta P approx = 7psi/100 feet and greater to 10 f/sec), although, this line is of chromium material, the HCGO, is considered that it has solids ( less a 500 ppm , with a good section of washing), but nevertheless yo u have to keep speeds lower on 10 f/sec (preferably 6-8 f/sec).
In the units where I have been worked, we have maintained this quench flow as a relation between quench and feeding to the furnaces and this value this between 3 to 6 % and the same one we have fit it of way to maintain the line free of coke (this is verifies, by a monthly inspection of the line, removing the bridle 24 “or 36¨ ,where this quench is injected), Additionally to this, we have cut the quil (piping injection) until half of the diameter of the exit line of the drum (these movements of flow can take to the maximun possible as long as you do not increased the recycle in the unit
In some opportunities by problems in the zone of washing , we have been increased this flow, which has allowed us to decresae concarbon, until the problem is solved
I request your pardon by my English