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1. By Rebecca Mwaura
CENG0016 - Present 21/05/24
Detailed design
phase for a
Benzene-Toluene
Distillation column
1

2. Presentation
Overview
Optimised Design Parameters
Control Scheme
Safety Integrity Level Analysis
Sustainability Considerations
Separation problem1
2
3
4
5
2

3. Minimum 99.5wt% of
Benzene in distillate
required.
Feed enriched in Light
gases
The Separation Problem1
Figure 1: BFD of the Benzene Toluene distillation unit 3

4. Design Variable Value
Number of stages 17
Feed Stage 7
Reflux ratio 1
Reboiler duty (MW) 2.16
Column internals Nutter Ring (by SULZER)
Table 1 : Summary of design variables
Optimised Design Parameters 2
4

5. Optimised Design Parameters 2
Figure 2.1 : Benzene distillate purity against molar reflux ratio
5

6. Optimised Design Parameters 2
Figure 2.3 : Reboiler duty against feed stage
6

7. Optimised Design Parameters 2
Figure 2.2 : Reboiler duty against the number of stages
7

8. Of liquid flows
out of the
thermosyphon
reboiler
Control Scheme3
Feed and Liquid Level changes were the most critical disturbances.
Of liquid flows
into the column
32405
kg/hr
27210
kg/hr
8

9. Pressure
Loop
Reflux drum
to liquid
level loop
Reflux to
feed ratio
loop
Column
bottom liquid
level loop
Steam to
feed ratio
loop
1 2 3 4 5
Control Scheme3
SISO feedback
control
PI controller
SISO feedback
control
PI controller
SISO feedback
control
PI controller
Ratio control
PID controller
Cascade control
PID controller
9

10. Mitigation
E.G: Planned emergency escape
routes
Layer 6
Physical protection
E.G: Pressure safety valves
Layer 5
Safety instrumented/ Emergency shut
down systems.
E.G: Forced closure of steam valve
Layer 4
Two-level alarm system
E.G: Low and High level
temperature alarms
Layer 3
Basic process control system
E.G: Control loops
Layer 2
Process design
E.G: ensuring
Layer 1
01
02
03
06
05
04
Control Scheme3
10

11. Safety Integrated level analysis4
Overpressurization
was identified as
the main hazard
Figure 4.1: Risk Matrix in process industry context. [1]
ESDV were
implemented as part of
the Safety Integrated
System.
11

12. 12
Safety Integrated level analysis4
For the
protected
hazard
For the
unprotected
hazard
0.12 f/yr 0.066
f/yr
Implementing the Safety Integrated System caused the failure rate
to decrease
Both hazards achieved a SIL 3 rating.

13. 13
Sustainability considerations 5
Recycle streams
Recruit local talent
Liaise with local fishermen

14. References
[1] : AIChE , “Guidelines for hazard evaluation procedures”, Centre for
Chemical Process Safety (CCPS), AIChE, New York, 2nd Edition, 1992.
14