Transcript Lect. 02 CHE 185 – CONTROL OBJECTIVES
CHE 185 – PROCESS CONTROL AND DYNAMICS
CONTROL OBJECTIVES
CATEGORIES OF OBJECTIVES • PROCESS OBJECTIVES – QUANTITY • MEET PRODUCTION TARGETS • OPERATE AT CONSTANT LEVELS – QUALITY • ALL PRODUCT TO MEET MINIMUM CRITERIA • MINIMIZE PRODUCTION OF OFF-SPEC OR BYPRODUCT COMPONENTS
CATEGORIES OF OBJECTIVES • PROFITABILITY – MAXIMIZE YIELDS – MINIMIZE UTILITY CONSUMPTION • PRODUCTS WITH REDUCED VARIABILITY – REDUCED VARIABILITY PRODUCTS ARE IN HIGH DEMAND AND HAVE HIGH VALUE ADDED – PRODUCT CERTIFICATION (E.G., ISO 9000) ARE USED TO GUARANTEE PRODUCT QUALITY
EXAMPLE OF IMPROVED CONTROL
PLANT OPERATIONAL OBJECTIVES • RELIABILITY – ON-STREAM TIME – MINIMIZE UNSCHEDULED OUTAGES • SAFETY - FAIL SAFE OPERATION – OUT-OF-RANGE ALARMS – EMERGENCY SHUTDOWN – PANIC BUTTON – EMERGENCY INTERLOCKS – AUTOMATIC OPERATION
SAFETY RELIEF SYSTEMS • STANDARDS AND CODES – ASME (AMERICAN SOCIETY OF MECHANICAL ENGINEERS) BOILER & PRESSURE VESSEL CODE, SECTION VIII DIVISION 1 AND SECTION I – API (AMERICAN PETROLEUM INSTITUTE) RECOMMENDED PRACTICE 520/521, API STANDARD 2000 ET API STANDARD 526 – ISO 4126 (INTERNATIONAL ORGANISATION FOR STANDARDISATION)
MODEL DERIVATION • INVENTORY TANK • DESIGN BASES – STEADY STATE FLOWS – DISCHARGE FLOW IS A FUNCTION OF h – CONSTANT AREA A – CONSTANT DENSITY ρ
DERIVE EQUATIONS • MASS BALANCE
d
(
Ah
)
dt
accumulati on
w i
in
w
out
w
q
dh
dt q i
q o A
• ASSUMPTION OF STEADY STATE
h
( 0 )
h
0
DERIVE EQUATIONS • VALVE CHARACTERISTICS LINEAR
q o
C v h
NONLINEAR
q o
C v h
• LEVEL CHANGES – LINEAR ODE – NONLINEAR ODE
MODEL DERIVATION • HEATING TANK • DESIGN BASES – CONSTANT VOLUME – PERFECT MIXING IN VOLUME – PERFECT INSULATION – CONSTANT FLUID PROPERTIES, DENSITY ρ AND HEAT CAPACITY c P
DERIVE EQUATIONS • MASS BALANCE • ENERGY BALANCE
d dt
VC p
(
T
T ref
)
w i C p
(
T i
T ref
)
wC p
(
T
VC p dT dt
dT dt w
V
wC p
(
T i
T
)
Q
(
T i
T
) 1
VC p Q
T ref
)
Q
DERIVE EQUATIONS • AS INITIAL VALUE PROBLEM • GIVEN – PHYSICAL PROPERTIES ( ,
C p
) – OPERATING CONDITIONS (
V
,
w
,
T i
,
Q
) – INITIAL CONDITION
T
(0) • INTEGRATE MODEL EQUATION TO FIND
T
(
t
)
MODEL DERIVATION • CSTR – REACTION A → B • DESIGN BASES – CONSTANT VOLUME – FEED IS PURE
A
– PERFECT MIXING – INSULATED – CONSTANT FLUID PROPERTIES ( ,
C p
, D
H
,
U
) – CONSTANT COOLING JACKET TEMPERATURE
OTHER RELATIONSHIPS • CONSTITUTIVE RELATIONS – REACTION RATE/VOLUME –
r
=
kc A
=
k
0 exp(-
E
/
RT
)
c A
– HEAT TRANSFER RATE: –
Q
=
UA
(
T c
-
T
)
DERIVE EQUATIONS • MASS BALANCE
d
(
V dt
) 0
w i
w
q i
q
• COMPONENT BALANCE ON
A
q i
q V d
(
M A Vc A
)
dc A dt
dt q
(
c Ai M A q i c Ai
c A
)
Vk
0
M A qc A
exp(
E
M A Vr
/
RT
)
c A
DERIVE EQUATIONS • ENERGY BALANCE
d dt
VC p
(
T dT
VC p dt
T ref
)
w i C p
(
T i
qC p
(
T i
T ref
)
wC p
(
T
T ref
) ( D
H
)
rV
T
) ( D
H
)
Vk
0
e
(
E
/
RT
)
c A
UA
(
T c
T
)
Q
SOLUTION CONSTRAINTS • EQUATION PROPERTIES – 2 ODES – FOR DYNAMIC MODEL TIME IS THE INDEPENDENT VARIABLE – NONLINEAR AND COUPLED – INITIAL VALUE PROBLEM REQUIRES NUMERICAL SOLUTION • DEGREES OF FREEDOM – 6 UNKNOWNS – 2 EQUATIONS – MUST SPECIFY 4 VARIABLE VALUES
MODEL DERIVATION • BIOCHEMICAL REACTOR (GENERAL) • DESIGN BASES – CONTINUOUS OPERATION – STERILE FEED – CONSTANT VOLUME – PERFECT MIXING – CONSTANT REACTION TEMPERATURE & pH – SINGLE RATE LIMITING NUTRIENT – CONSTANT YIELDS – NEGLIGIBLE CELL DEATH
DERIVE EQUATIONS • CELL MASS
V R dX dt
FX
V R
X
dX dt
DX
X
– DEFINITION OF TERMS –
V R
–
F
= REACTOR VOLUME = VOLUMETRIC FLOW RATE –
D
=
F
/
V R
= DILUTION RATE – NON-TRIVIAL STEADY STATE: – WASHOUT:
X
0
D
DERIVE EQUATIONS • PRODUCT RATE
V R dP
FP
V R qX dt
dP
DP
qX dt
• SUBSTRATE CONCENTRATION
V R dS dt
FS
0
FS
1
Y X
/
S V R
X
dS dt
D
(
S
0
S
) 1
Y X
/
S
X
–
S
0 = FEED CONCENTRATION OF RATE LIMITING SUBSTRATE – STEADY-STATE:
X
Y X
/
S
(
S
0
S
)
SOLUTION CONSTRAINTS • EQUATION STRUCTURE – STATE VARIABLES:
x
= [
X S P
] T – THIRD-ORDER SYSTEM – INPUT VARIABLES:
u
= [
D S
0 ] T – VECTOR FORM:
YEAST METABOLISM • BIOCHEMICAL REACTOR (ETHANOL)
glucose acetaldehyde/ pyruvate (S 4 ex ) r 7 degraded products extracellular J 0 J intracellular glucose (S 1 ) ATP (A 3 ) NADH acetaldehyde/ pyruvate (S 4 ) NAD + (N 1 ) glycerol NADH r 6 (N 2 ) r 1 ADP (A 2 ) NAD + NADH G3P/DHP (S 2 ) r 2 ATP r 3 AD P 1,3-BPG (S 3 ) r 4 NAD + r 5 ethanol
MODEL COMPONENTS • INTRACELLULAR CONCENTRATIONS – INTERMEDIATES:
S 1
,
S 2
,
S 3
,
S 4
– REDUCING CAPACITY (NADH):
N 2
– ENERGY CAPACITY (ATP):
A 3
• MASS ACTION KINETICS FOR
r 2
-
r 6 r
2
r
5
k
2
S
2
N
1
k
5
A
3
r r
3 6
k
3
S
3
A
2
k
6
S
2
N
2
r
4
k
4
S
4
N
2 • MASS ACTION KINETICS AND
ATP
INHIBITION FOR
r 1 r
1
k
1
S
1
A
3 1
A
3
K I
4 1
DYNAMIC MODEL EQUATIONS • MASS BALANCES
dS
1
dt dS
4
dt
r
3
J
0
r
4
r
1
J dS
2
dt dN
2
dt
2
r
1
r
2
r r
4 2
r r
6 6
dA
3 • CONSERVED METABOLITES
dt dS
3
dt
2
r
1
r
2
r
3 2
r
3
r
5
A
2
A
3
A t N
1
N
2
N t
• MATRIX
d
x
f
(
x
,
u
)
dt
REVIEW OF OBJECTIVES FOR CONTROL SYSTEMS • PLANT OBJECTIVES - OVERALL PRODUCTION FROM THE FACILITY • COMPONENT OBJECTIVES INDIVIDUAL STEPS IN THE PROCESS • PROVISION FOR OPERATOR CONTROL • OPTIMIZATION OF OPERATIONS
PLANT OPERATIONAL OBJECTIVES • ENVIRONMENTAL PROTECTION – MINIMIZE EMISSIONS FROM PROCESS UPSETS – RELIABLE OPERATION OF ALL POLLUTION CONTROL EQUIPMENT • VENTS – FLARES – SCRUBBERS • PRESSURE RELIEF l http://www.corrocare.com/air_pollution_control_equipment.htm
PLANT OPERATIONAL OBJECTIVES • FLEXIBILITY - DYNAMIC RESPONSE – SYSTEM TO ADJUST AUTOMATICALLY TO ANTICIPATED CHANGES IN: • PRODUCTION RATES • QUALITY SPECIFICATIONS • COMPOSITIONS OF FEED • INTERMEDIATE STREAMS
PLANT OPERATIONAL OBJECTIVES • USER FRIENDLY OPERATOR INTERFACE – MINIMIZE NUMBER OF VARIABLES NECESSARY TO CONFIRM THE PROCESS STATUS – DESIGN THE SYSTEM SO THE “NATURAL” OPERATOR REACTION TO PROCESS VARIATIONS IS ANTICIPATED – PROVIDE AN INFORMATION INTERFACE FOR OPERATION/ENGINEERING
PLANT OPERATIONAL OBJECTIVES • MONITORING AND OPTIMIZATION – DETERMINE THE CONTROL LIMITS FOR THE PROCESS – DETERMINE THE OPTIONS FOR COST REDUCTION
PLANT OPERATIONAL OBJECTIVES • STARTUP/SHUTDOWN – ROUTINE START-UP CONTROL – MINIMIZE START-UP TIMES – ROUTINE SHUTDOWN CONTROL – RESPOND TO SHORT TERM SHUTDOWNS WITH MINIMUM RESTART TIME – SAFE EMERGENCY SHUTDOWN
PLANT OPERATIONAL OBJECTIVES • EQUIPMENT PROTECTION – INTEGRATE DESIGN SO FAILURE OF ONE PART OF THE FACILITY DOES NOT TRANSFER TO FAILURE IN ANOTHER PART – INTERLOCK SYSTEMS TO PREVENT EQUIPMENT DAMAGE IN THE EVENT OF A PROCESS INTERRUPTION
COMPONENT OPERATIONAL OBJECTIVES.
• SIMILAR TO PLANT OBJECTIVES • COMPONENT RELIABILITY – MINIMIZE COMPONENT DEGRADATION OR FAILURE.
– REDUNDANCY WHEN PRACTICAL.
– MINIMAL LOCAL ADJUSTMENT FOR NORMAL PROCESS VARIATIONS
COMPONENT OPERATIONAL OBJECTIVES.
• SAFE OPERATION – COMPONENT DESIGNS FOR SAFE OPERATION WITHIN THE ANTICIPATED OPERATING RANGES FOR THE PROCESS – RELIEF SYSTEMS TO AVOID CATASTROPHIC FAILURE IF THE PROCESS EXCEEDS THE SAFE OPERATING RANGES.
COMPONENT OPERATIONAL OBJECTIVES.
• ENVIRONMENTAL PROTECTION – DESIGNS TO AVOID LEAKS OF PROCESS MEDIA – DESIGNS TO INDICATE LEAKS OF PROCESS MEDIA – DESIGNS TO AVOID SUPERSONIC FLUID CONDITIONS OR OTHER FORMS OF SOUND POLLUTION
COMPONENT OPERATIONAL OBJECTIVES.
• EASE OF OPERATION – LOCAL OPERATION – REMOTE OPERATION • MONITORS – TO DETERMINE CURRENT STATUS OF COMPONENT – TO DETERMINE THE NEED FOR MAINTENANCE OR REPLACEMENT
COMPONENT OPERATIONAL OBJECTIVES.
• PROVIDE THE OPERATOR WITH ADEQUATE INFORMATION – FOR ROUTINE START-UP AND SHUTDOWN FROM A REMOTE LOCATION.
– FOR LOCAL OPERATION DURING STARTUP OR SHUTDOWN
COMPONENT OPERATIONAL OBJECTIVES.
• EQUIPMENT PROTECTION – DESIGNS TO INDICATE OUT-OF-RANGE CONDITIONS SO OPERATORS CAN TAKE PROPER ACTION • DESIGNS TO INITIATE AUTOMATIC SHUTDOWN SEQUENCES FOR OUT OFCONTROL CONDITIONS.
TYPES OF CONTROL • CONTINUOUS • BATCH • SEMI-CONTINUOUS • COMBINATIONS OF THE ABOVE http://www.controlloopfoundation.com/continuous-chemical-reactor process.aspx
http://www.controlloopfoundation.com/batch-chemical-reactor workspace.aspx