Page 138 - Fluid Catalytic Cracking Handbook

FCC Catalysts 113

Example 3-2 below illustrates the use of the above equations.

Example 3-2

Assume a 50,000 bpd cat cracker with:

* Catalyst inventory of 300 tons
» Makeup rate of 4.0 tons per day
* Fresh catalyst MAT conversion 80 vol%
* E-cat MAT number 71.5 vol%

Determine:
a. New E-cat MAT conversion if the addition rate is reduced to 3.0
tons/day:

4 0
si ?5 — — U.ulj33 days
300

t = 300/4 = 75 days

Deactivation Constant = K = ^—— ^ = 0.001498 days' !
-75.0

3 0 1
New Fractional Replacement = —— = 0.01 days"
300

The revised E-cat = '• = 69.5 vol%
0.01333 + 0.001498

b. The new E-cat MAT conversion if the fresh catalyst MAT number
is reduced from 80 vol% to 75 vol%:

75x0.01333 ^ ,„
A = = 67 vol%
0.01333 + 0.001498

When a refiner changes the FCC catalyst, it is often necessary to
determine the percent of the new catalyst in the unit. The following
equation, which is based on a probability function, can be used to es-
timate the percent changeover.
fxsxt
p = 1 - e~