On The Conversion Of Gas Oil In Fluid Catalytic Cracking Risers: Application Of Residence Time Distribution (Rtd) Concept

Risers are considered vital parts on fluidized catalytic cracking (FCC) conversion units. It is inside the riser that the heavy hydrocarbon molecules are cracked into petroleum fractions such as gasoline and liquefied petroleum gas (LPG). A simplified kinetic flow model in combination with the Tank-In-Series model was used to predict the conversion response of an FCC riser to changes in feed temperature, feed flow rate as well as riser diameter and height. The various Residence Time Distribution (RTD) functions and flow-model parameters are used in the characterization of the mixing regime of the riser and the degree of any non-ideal flow behaviour. Conversion was observed to increase with increasing riser height and diameter with values of 95.16% and 94.0% at a riser height of 80 m and diameter of 1.0 respectively. Conversion also increased with increasing feed temperature. A feed flow rate of 10 m 3 /s is converted at 95.95 % whiles a feed flow rate of 40 m 3 /s is converted at 89.72%, indicating an inverse relationship between conversion and feed flow rate. The simulation also revealed that the riser reactor is equal to approximately 1–2 perfectly stirred tanks in series as conversion started to decrease after an N, the number of tanks in the Tank-In-Series model, of 1.5.