Page 139 - Fluid Catalytic Cracking Handbook

114 Fluid Catalytic Cracking Handbook

Where:

P = Fractional Changeover
f = Retention Factor, usually in the range of 0.6 to 0.9
S = Replacement Rate = Addition rate/Inventory
t = Time, day

Example 3-3

The 300- ton inventory unit in Example 3-2 is changing catalyst type
and planning to add 3.5 tons per day of new catalyst. Determine the
percent of changeover after 60 days of operation. Assume a retention
factor of 0.7.
-0.7x0.0117x60

P = 0,387 or 38.7%

Another method of calculating the % changeover is by the use of
alumina balance.

Example 3-4

The example below illustrates the application of the alumina balance
method.
For the same 300-ton inventory unit, assume the alumina (A1 2O 3)
contents of the present and new fresh catalysts are 48 wt% and 38
wt%, respectively. Sixty (60) days after the catalyst switch, the alumina
content of E-cat is 43 wt%. Determine % changeover:

Al 2O 3 (new) - Al 2O 3 (equil.)
Functional Changeover = 1 - — - — - - - — - -
A1 2O 3 (new) - Al 2 O 3 (old)

Fractional Changeover = 1 - - = 0.5 = — >}50%
38 — 48
This method can also be used to calculate the catalyst retention
factor. The above equations assume steady-state operation, constant
unit inventory, and constant addition and loss rate.