Safe Process Start-up Procedures Based on an Operator Training Simulator: a Case StudyFlavio Manenti and Davide MancaDipartimento di Chimica Materiali e Ingegneria ChimicaPolitecnico di Milano – ITALY

18-23 May 2008 – Hong Kong, CHINA

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Presentation outline

Definition of start-up and shutdown procedures

Process transient simulations

Alternative start-up procedures and control schemesto improve process safety

Operator Training Simulator withdetailed simulation packages

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Widespread Simulation Toolkits

• Dynamic simulation features• Batch dynamic simulations• Control strategies• Start-up and shutdown• Distributed Control Systems• Operator Training Simulators

• Control-room and fieldoperator training

• Dynamic simulation features• Batch dynamic simulations• Control strategies• Start-up and shutdown• Distributed Control Systems• Operator Training Simulators

• Control-room and fieldoperator training

• SimSci-Esscor (Dynsim)• Honeywell (HYSYS)• Aspentech (Aspen HYSYS)• PSE (gPROMS)• CreateaSoft (Simcad)• Simulation Solutions (Virtual Refinery)• …

• SimSci-Esscor (Dynsim)• Honeywell (HYSYS)• Aspentech (Aspen HYSYS)• PSE (gPROMS)• CreateaSoft (Simcad)• Simulation Solutions (Virtual Refinery)• …

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Dynamic Simulation Implementation

DYNAMIC MODEL BUILDING

Flow-Sheet definition

Thermodynamic methodselection

Definition of reaction and kinetic schemes

Process unit geometries and boundary conditions

Flow-conductance factorsand valve caracteristics

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Dynamic Simulation and Control

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Presentation outline

Definition of start-up and shutdownprocedures

Process transient simulations

Alternative start-up procedures and control schemesto improve process safety

Operator Training Simulator withdetailed simulation packages

7

Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Start-up and Shutdown Procedures

“Cold”plant

Steady-stateconditions

Start-up

Shutdown

• Decrease of off-spec periods

• Increase of plant productivity

• Start-up and shutdown operating conditions are significantly

different from the steady-state conditions

• Relevant safety and operability problems

• Decrease of off-spec periods

• Increase of plant productivity

• Start-up and shutdown operating conditions are significantly

different from the steady-state conditions

• Relevant safety and operability problems

Importance of the analysis of unsteady conditions

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Start-up ProcedureBubble conditions

(feed tray)

Liquid holdup on thelower trays

Liquid holdup in the reboiler

Enoughliquid level in the

reboiler?

no

yes

Switch-on the reboiler exchanger

Vapor holdup at every tray

Switch-on the top condenser section

Enoughlevel in the reflux

drum?

Refrigeration

no

yes

Switch-on the reflux pump

Liquid holdup onhigher trays

Column stabilization

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Shutdown Procedure

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Presentation outline

Definition of start-up and shutdown procedures

Process transient simulations

Alternative start-up procedures and control schemes to improve process safety

Operator Training Simulator withdetailed simulation packages

11

Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Conventional control scheme

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Modified Control Scheme

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Safety and Reliability Issues

• Loading

• Flooding

• Weeping

• Pressure shots

• Entrainment

• Wet Bundles

• Smooth dynamics

• …

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Condenser

0

10

20

30

40

0 30 60 90 120

Time [min]

Tem

pera

ture

[°C

]

SET-POINT

0

0.4

0.8

1.2

1.6

0 30 60 90 120

Time [min]L

iqui

d H

oldu

p [m

]

SET-POINT

Conventional control structure

Modified control structure

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Reboiler

-20

20

60

100

0 30 60 90 120

Time [min]

Tem

pera

ture

[°C

]

SET-POINT

0

0.4

0.8

1.2

1.6

0 30 60 90 120

Time [min]L

iqui

d H

oldu

p [m

]

SET-POINT

Conventional control structure

Modified control structure

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Bottom composition

Conventional control structure Modified control structure

0

0.2

0.4

0.6

0 30 60 90 120

Time [min]B

otto

m C

ompo

sitio

n [-

].

iC4nC4C3

0

0.2

0.4

0.6

0.8

0 30 60 90 120

Time [min]

Bot

tom

Com

posi

tion

[-].

iC4nC4C3

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Manipulated variables of the modified control structure

Reboiler

0

4

8

12

16

0 30 60 90 120

Time [min]

Flow

rate

[kg/

s]

COOLANT

GAS

LIQUID

0

10

20

30

0 30 60 90 120

Time [min]

Flow

rate

[kg/

s]

HOT UTILITY

BOTTOM

Condenser

Modified control structure

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Davide Manca – CMIC POLIMI – PSAM-9, 18-23 May 2008, Hong Kong CHINA

Conclusions

• A detailed simulation of process transients allows:

designing new control structures;

quantifying the performance of start-up and shutdown procedures;

assessing the safety issues and risky conditions of start-up and shutdown procedures;

training both control-room and field operators;

improving process safety and performance.