ISA 2011 Fundamentals Distillation

7/31/2019 ISA 2011 Fundamentals Distillation

1/30

Standards

Certification

Education & Training

Publishing

Conferences & Exhibits

Fundamentals ofDistillation Column Control

by Terry Tolliver

ISA Automation Week 2011


2/30

2

PRESENTER Terry Tolliver

Terry is a retired Senior Fellow from Solutia/Monsanto and presentlyprovides contract engineering at ConocoPhillips Wood River refinery.He has 40+ years of experience in process control, simulation,operations, troubleshooting and optimization.

Terry graduated from the Missouri University of Science and

Technology with BS, MS & PhD ChE and was recently inducted intotheir Academy of Chemical Engineers in 2009. He was inducted intothe CONTROL Automation Hall of Fame in 2002.

He has received several ISA awards including the Distinguished SocietyService Award in 1997, the E. G. Baily Award in 1993 and the

Excellence in Documentation award in 1987. Terry has been an adjunct professor for Washington University from

2004-2008, a Lehigh University Biannual Lecturer from 1974-1986, anISA Fellow in 1990, an AIChE Fellow in 2000 and a PE since 1974.


3/30

DISTILLATION CONTROL TOPICS

Levels of control

Classification and pairing of variables

Control objectives and constraints

Dynamic responses Material and energy balances

Separation

Pressure control

Material balance control Temperature control

References

3


4/30

DISTILLATION CONTROL

BASIC

Inventory Control

Composition Control

OPTIMIZING

Floating Pressure

Maximum Profit

SUBOPTIMIZINGFeedforward Control

Two Point Com position Control

4


5/30

CLASSIFICATION and PAIRING of VARIABLES

CONTROLLED

VARIABLESdistillate composition

bottom compositionaccumulator level

sump level

column pressure

YY

X

X

La

La

Ls

Ls

P

P

5


6/30

MANIPULATED

VARIABLESdistillate flow

bottom flow

reflux flow

reboiler duty

condenser duty

D

DB

B

R

R

Qr

Qr

Qc

Qc


6


7/30


DISTURBANCE

VARIABLESfeed flow

feed compositionfeed temperature

reboiler heat supply

condenser cooling

supply and weather

F F

Z Zq

qS

S

W

W

7


8/30


CONTROLLED MANIPULATED DISTURBANCE

VARIABLES VARIABLES VARIABLES

distillate composition distillate flow feed flow

bottom composition bottom flow feed composition

accumulator level reflux flow feed temperature

sump level reboiler duty reboiler heat supply

column pressure condenser duty condenser cooling

supply and weather

8


9/30

CONTROL OBJECTIVES

$/ F

RECOVERY

Cost of Produc t Lost

Cost of Energ y

Tota l Operating Cost

9


10/30

COLUMN CONSTRAINTS

Column Pressure

Boiluprate

Vessel Limit

Weep

Flood

Reboiler

Condenser

10


11/30

COLUMN INTERNALS

TRAYS SIEVE TRAYS

VALVE TRAYS

BUBBLE CAP TRAYS DUAL FLOW TRAYS

PACKING RANDOM PACKING

STRUCTURED PACKING LIQUID & VAPOR DISTRIBUTORS

11


12/30

COLUMN DYNAMICS

RELATIVE RESPONSE TIMES

time

VAPOR - FAST

LIQUID - MEDIUM

COMPOSITION - SLOW

Response

12


13/30


14/30

TOTAL REFLUX

n = [y(1-x)]/ [x(1-y)]

SEPARATION

NORMAL OPERATION

S = ( , N, NF, V/ F, z, E)f

14


15/30

MATERIAL BALANCE and SEPARATION EFFECTS

D/F

LightKeyMoleFrac

tion

0 1.00

1.0

y

X

Z

Increasing S

Increasing S

15


16/30

MATERIAL BALANCE CONTROL

FC

FC

FC

FC

FC

LC

LC

TC

16


17/30


18/30

PRESSURE CONTROL

FCFCLC

VENT

PI

18


19/30

CONDENSER DUTY

Qcond = UA(Tp-Tc)

VENT

CONDENSATE

COOLANT

Tc

Tp

19


20/30

BLOCK & BLEED PRESSURE CONTROL

FCFCLC

VACUUM SOURCE

PC

BLOCK VALVE

BLEEDVALVE

INERTS

20


21/30

MATERIAL BALANCE CONTROL - TYPE 1

FC

FC

FC

FC

FC

LC

LC

TC

21


22/30


23/30


FC

FC

FC

FC

FC

LC

LC

TC

23


24/30


FC

FC

FC

FC

FC

LC

LC

TC

time

response

24


25/30

PROCESS SIMULATION

STEADY STATE PARAMETRIC CASES CONTROL STAGE LOCATION

SENSITIVITY ANALYSIS DISTURBANCE ANALYSIS

DYNAMIC STUDY CONTROL RESPONSE STARTUP AND SHUTDOWN

25


26/30

CONTROL STAGE LOCATION

Benzene-Toluene Column Temperature Profiles

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

70.0 75.0 80.0 85.0 90.0 95.0 100.0 105.0 110.0 115.0 120.0

Temperature, DegC

StageNumber

+1%D/F

-1%D/F

26


27/30

TEMPERATURE SENSITIVITY

CONTROL STAGE TEMPERATURE, degF

98

98.2

98.4

98.6

98.8

99

99.2

99.4

99.6

99.8

100

85 90 95 100 105 110

COMPOSITION,w

t%

BOTTOM PRODUCT

DISTILLATE PRODUCT

27


28/30

DISTURBANCE ANALYSIS

Benzene-Toluene Column Load Effects

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0

Delta Temperature, DegC

TrayNumber

28


29/30

29

REFERENCES


30/30

REFERENCES

ISA 2011 Fundamentals Distillation

Documents