Page 190 - Fluid Catalytic Cracking Handbook

162 Fluid Catalytic Cracking Handbook

VIII. Energy required to heat the spent catalyst from its reactor to the
regenerator temperature =
6
481.9 - 108.0 - 39.5 - 4.4 - 3.7 - 2.6 - 19.3 = 304.4 x 10 Btti/hr
IX. Calculation of catalyst circulation

6
^ , „. . . 304.4 xl0 Btu/hr
Catalyst Circulation =
(0.285 Btu/°F-lb) x (1,309 - 972)°F
6
= 3.169 x 10 Ibs/hr = 26.4 short tons/min.

Where: 0.285 is the catalyst heat capacity (see Figure 5-6)
6
Cat/oil ratio = 3.169 x 10 /658,914 = 4.8
.„ , Coke Yield, wt% 4.2 A 0_ „
ACoke = = — = 0.87 wt%
cat/oil ratio 4,8

Reactor Heat Balance

The hot regenerated catalyst supplies the bulk of the heat required
to vaporize the liquid feed (and any recycle) to provide the overall
endothermic heat of cracking, and to raise the temperature of disper-
sion steam and inert gases to the reactor temperature.

Heat In Heat Out

Fresh Feed Reactor Vapors
Recycle Flue Gas
Air Losses
Steam

The calculation of heat balance around the reactor is illustrated in
Example 5-6. As shown, the unknown is the heat of reaction. It is
calculated as the net heat from the heat balance divided by the feed
flow in weight units. This approach to determining the heat of reaction
is acceptable for unit monitoring. However, in designing a new cat
cracker, a correlation is needed to calculate the heat of reaction. The
heat of reaction is needed to specify other operating parameters, such