Page 184 - Fluid Catalytic Cracking Handbook

156 Fluid Catalytic Cracking Handbook

Adjustment of Gasoline and LCO Cut Points
As discussed earlier in this chapter, gasoline and LCO yields are
generally corrected to a constant boiling range basis. The most com-
monly used bases are 430°F TBP gasoline and 640°F TBP LCO end
points. Since TBP distillations are not routinely performed, they are
often estimated from the D-86 distillation data. The adjustments to the
end points involve the following:

+
* Adding to the raw LCO all the 430°F in the raw gasoline and
subtracting the 430°F in the LCO stream.
« Adding to the raw LCO all the 650°F~ in the raw decanted oil
and subtracting the 650°F~ in the decant oil stream.
* Adding to the raw gasoline all the 430°F~ in the raw LCO and
subtracting the 430°F* in the gasoline stream.
+
• Adding to the raw decanted oil all the 650°F in the raw LCO
and subtracting the 650°F~ in the decant oil stream.

Table 5-5 illustrates steps used to convert ASTM D-86 data to TBP.
The laboratory usually converts D-1160 and reports the data as D-86,
Extrapolation of the TBP data indicates the following:
+
« The 430°F content of the FCCU gasoline is 3 vol%, or 859 bpd.
« The gasoline (430°F~) content of LCO is 8 vol%, or 806 bpd.
+
« The 650°F content ofLCO is 12 vol%, or 1,209 bpd.
• The LCO (650°F~) content of the decanted oil is 17 vol%, or
514 bpd.
Therefore, the adjusted rates are as follows:

+
Gasoline (C 5 to 430°F TBP end point) = 28,650 - 859 + 806
= 28,597 bpd

LCO (430°F to 650°F TBP end point) = 10,077 + 514 - 1,209 - 806

+ 859 = 9,435 bpd

+
DO (650°F ) = 3,023 + 1,209 - 514 = 3,718 bpd
Table 5-6 shows the normalized FCC weight balance with the adjusted
cut points.