Page 134 - Fluid Catalytic Cracking Handbook

FCC Catalysts 109

C a = Catalyst Addition Rate, Ib/day
M 0 = Initial Metals on the E-cat, ppm
t = Time, day
I = Catalyst Inventory, Ib

At steady state, the concentration of any metal on catalyst is:

(W x M f)
M = A =

141 5
' -x 350.4 x M f
M =
B

B = Catalyst addition rate, pounds of catalyst per barrel of feed

Figure 3-14 is the graphical solution to the above equation and can
be employed to estimate metals content of the E-cat, based on feed
metals and catalyst addition rate.

Carbon (C)
The deposition of carbon on the E-cat during cracking will tempor-
arily block some of the catalytic sites. The carbon, or more accurately
the coke, on the regenerated catalyst (CRC) will lower the catalyst
activity and, therefore, the conversion of feed to valuable products
(Figure 3-15).
The CRC is an important parameter for a unit operator to monitor
periodically. Most FCC units check for CRC on their own, usually
daily. The CRC is an indicator of regenerator performance. If the CRC
shows signs of increasing, this could reveal malfunction of the regen-
erator's air/spent catalyst distributors. It should be noted that the MAT
numbers reported on the E-cat sheet are determined after the CRC has
been completely burned off.

CATALYST MANAGEMENT

Depending on the design of a cat cracker, the circulating inventory
can contain 30-1,200 tons of catalyst. Fresh catalyst is added to the
unit continually to replace the catalyst lost by attrition and to maintain