Qc
Tower T1
Tower T2
Top
Top
T2
A
A
A
T1
Feed A, B, C
B
B
B
C
C
Qr
Bottom
Bottom
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
C
Composition mole fraction
Composition mole fraction
Figure 2 Composition profile for a DWC
• Operational pressure variation between column sections is not possible • Increased temperature difference between reboiler and condenser • Increased pressure drops • Increased length and diameter of the vessel • Increased complexity for modelling in the process simulation • Increased complexity for the hydraulic design of the mass transfer components • Lower operational flexibility. Existing naphtha splitter The existing naphtha splitter is a conventional distillation column with a side draw. It splits the full naphtha coming from the bottom of a depentaniser located at the GasCon of the fluid catalytic cracking (FCC) unit, into three streams: light naphtha, middle naphtha and heavy naphtha.
The column is heat integrated with the FCC unit. The heat duty to the column is provided by two reboilers: upper reboiler, where the heating medium is the light cycle oil (LCO) coming from the reboiler of the debutaniser, and lower reboiler, heated with the heavy cycle oil (LCO) coming from the FCC main fractionator. The top condensation system provides the cooling duty to draw off the light naphtha and generate the internal reflux required for the fractionation of the cuts. The feed is preheated at the preheat exchanger by means of the side-cut draw before entering the tower in the middle section (see Figure 3 ). The three cuts are further processed to the downstream MOG and SCANfiner units to meet the quality of the gas - oline pool. Revamp motivation All three cuts were initially used for gasoline. The existing tower was able to achieve the required performances both
1.2
0.8
16.5
Light naphtha to SCAN finer
From De-C bottom
Middle naphtha to MOG
138
LCO from De-C reboiler
XX
Pressure kg/cm g
To De-C reboiler
YY
Temperature ˚C
HCO from FCC MF
1.5
Heavy naphtha to SCAN finer
To FCC MF
Figure 3 Simplified process flow diagram of the tower before revamp
34
PTQ Q2 2024
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