Page 230 - Fluid Catalytic Cracking Handbook

198 Fluid Catalytic Cracking Handbook

Where:

CI = Cetane index
T = Mid boiling temperature, °F
°API = °API gravity at 60°F

For Example:

T = 550°F (288°C)
°API = 19
CI = 28.9

Source: ASTM Standards, Method D-976-80
LCO is highly aromatic (50 wt% to 75 wt%) and has a low cetane
index (20-30). The cetane number and sulfur content determine the
amount of LCO that can be blended into the diesel or heating oil pool.
Most (30-50 wt%) of the aromatics in the LCO are di- and tri-
aromatic molecules. Hydrotreating the LCO can increase its cetane
number. The degree of improvement depends on the severity of the
hydrotreating. Mild hydrotreating (500 to 800 psig/3500 to 5500 K p)
can partially hydrogenate some of the di- and tri-aromatics and
increase cetane by a 1 to 5 number. Severe hydrotreating conditions
(> 1,500 psig/10,300 K p) can increase the cetane number above 40.
Other conditions-that improve cetane are:
» Undercutting the FCC gasoline
« Reducing the unit conversion
* Using an "octane" catalyst
« Processing paraffinic feedstock

HCO and Decant Oil

HCO is the sidecut stream from the main column that boils between
LCO and decanted oil (DO). HCO is often used as a pumparound
stream to transfer heat to the fresh feed and/or to the debutanizer reboiler.
HCO is recycled to extinction, withdrawn as a product and processed
in a hydrocracker, or blended with the decant oil.
DO is the heaviest product from a cat cracker. DO is also called slurry
oil, clarified oil, bottoms, and FCC residue. Depending on the refinery
location and market availability, DO is typically blended into No. 6 fuel,
sold as a carbon black feedstock (CBFS), or even recycled to extinction.