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I am currently working in Exxon Flexicracking FCC model. During start-up of the unit, when we establish catalyst circulation, sour water received in the MF O/H drum is acidic. When we introduce feed to the reactor, it becomes neutral. Why is it so? I am interested in the chemistry of the process leading to acidic boot water. Can we reduce the acidity by changing operating conditions of the MF or R-R section?
16/10/2019 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
During restart of an FCC unit, residual ammonium chloride and iron chloride salts in the fractionator overhead system dissolve in steam condensate forming dilute HCl acid which makes the pH of the reflux drum boot water less than 7. After feed is introduced, organic nitrogen compounds in the feed break down to form NH3 and cyanides. If the nitrogen content of the feed is high enough, sufficient NH3 is generated to increase the pH of the condensed of the reflux drum boot water to 8 or more.