Fluid Catalytic Cracking Unit Reactor Regenerator Control

1. Fluid Catalytic Cracking Unit
Reactor Regenerator Control
TEAM M-
KAUSTUBH.A.DESHPANDE

2. Objective
• The project aims at designing a control strategy for the process variables of
a FCC unit which have to be controlled when change occurs in any of the
following :
1) Feed stock composition
2) Ambient temperature
3) Preheat temperature
which are the external disturbances for this system.

3. Process Flow Diagram

4. Manipulated Variables
Variable Description Tag Limit Values
Combustion Air Flow U1 140-155 TPH
Hot Gas Oil Flow U2 90-110 m3/h
Combined Cold Gas and
Recycle Oils
U3 90-110 m3/h
Feed Preheat Temperature U4 230-250 °C
Riser Outlet Temperature U5 515-535 °C
Recycle Oil Flow Controller
Output
U6 20-80 %

5. Process Variables
Variable Description Tag Limit Values
Flue Gas O2
Concentration
Y1 1.0%
Regenerator Bed Temp. Y2 705-735 °C
Fuel Gas Flow Y3 15 T/H
Wet Gas Compressor
Suction Pressure
Controller Output
Y4 70%
Riser Outlet Temperature
Controller Output
Y5 80%
Regenerated Catalyst Slide
Valve Pressure
Differential
Y6 22KPA
Spent Catalyst Slide Valve Y7 24KPA

6. Design Analysis
• For finding the best loop pairing we use singular value
decomposition (SVD) and relative gain array (RGA).
• RGA analysis cannot be performed directly on our system as we
have a non-square gain matrix.
• The RGA indicates how the input should be coupled with the
output to form loops with the smallest amount of interaction.
• RGA = K*(inv K) T

7. • RGA = 1.0000 0 0 0 0
• 0 1.8378 -0.8318 -0.5260 0.5201
• 0 -0.5615 1.8318 0.2046 -0.4749
• 0 -0.6637 0 1.7491 -0.0854
• 0 0.3874 0 -0.4276 1.0402
• The best loop pairings were found to be U1-Y1,U2-Y6,U4-Y5,
U5-Y4,U6-Y2. We added the U1-Y1 loop since it was missed by
the SVD analysis.
• We observed that λ<2 which means that interaction between
loops is small and multiloop control is realizable.

8. Best Control Design
• With the best RGA pairings, a multivariable feedback control
system was developed.
• All the PI controller parameters were calculated by using FODT
model followed by open loop Fertik method for controller
design.

9. Results of Best Design

11. Additional Designs
• An additional design with the inclusion of feed forward
controller for disturbance D3 only was also implemented since
D1 which is the change in feed temperature cannot be measured.

14. Conclusion
• We were successfully able to maintain all the PVs within limits
by applying the designed PI controllers.
• An additional design which included feed forward control along
with the PI controllers was also tried out but the overall
improvement wasn’t sufficient to warranty its implementation.