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Question No.:  5452 Category :  Refining Operations
Date Posted:  11/6/2011
Subject: FCC main fractionator disc & donut trays
What will be the effect on main column bottom temperature and column temperature profile if one pair of disc and donut trays is removed? I have experienced that after repairing of damaged disc tray (which was bypassing the liquid to bottom tray) main column bottom temperature has gone high. I would like the forum to share their experience.
Submitted by :
Company Name:

Nikhil Darak

Jamnagar, Gujarat, India


Number of responses : 1
Response 5452-1
Date : 11/14/2011

The purpose of disc and donut trays is to desuperheat and wash catalyst from the reactor effluent entering the Main Column (MC). The desuperheating is accomplished by vaporizing some of the circulating MC bottoms, notably the lighter components. If some of the lighter components are not being vaporized because of poor contact between the entering reactor vapors and circulating liquid, these lighter components will go to the MC bottoms and the average molecular weight will be lower.

Temperature anywhere in a column depends on pressure and composition. Since disc and donut trays have negligible pressure drop the pressure in the bottom of the MC does not change so temperature depends on the composition. Improving contact between the reactor vapors and circulating MC bottoms will result in more of the lighter components being vaporized and a higher average molecular weight in the bottom, which is higher temperature.

The MC temperature profile above the HCO tray should not change.

Name - D. A. Husted
CompanyName - Retired
Location - , USA
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