Page 181 - Fluid Catalytic Cracking Handbook

Unit Monitoring and Control 153

Normalization of the Data
Because a preliminary weight balance seldom has a 100% closure,
it is necessary to normalize the yield to obtain a 100% weight balance,
Example 5-3 shows the preliminary overall weight balance.

Example 5-3
Preliminary Overall Weight Balance

Input = Fresh Feed + Coker Off-Gas
Output = FCC tail gas + LPG + Gasoline + LCO + DO + Coke

• Input = 658,814 + 9,182 = 667,996 Ib/hr

• Output = 34,617 + 93,656 + 326,124 + 134,973 + 46,270 + 27,231
= 662,871 lb/hr

« Difference = 667,996 - 662,871 = 5,125 lb/hr

Error in mass balance = 0.8 wt%

The products are adjusted upward in proportion to theilr rates to obtain a
100% weight balance. The normalized rates:
• Tail gas = 34,883 Ib/hr
• LPG = 94,460 lb/hr = 11,658 bpd
• Gasoline = 328,766 Ib/hr = 30,230 bpd
• LCO = 136,054 lb/hr = 10,077 bpd
« DO = 46,626 Ib/hr = 3,023 bpd
• Coke = 27,440 Ib/hr

Component Yield

The reactor yield is then determined by performing a component
balance. The amount of C 5+ in the gasoline boiling range is calculated
by subtracting the C 4 and lighter components from the total gas plant
products. Example 5-4 shows the step-by-step calculation of the
component yields. The summary of the results, normalized but unad-
justed for the cut points is shown in Table 5-4.