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 ASSUMPTION OF STEADY STATE

DERIVE EQUATIONS VALVE CHARACTERISTICS 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

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,  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 COMPONENT BALANCE ON A

DERIVE EQUATIONS ENERGY BALANCE

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 –DEFINITION OF TERMS –V R = REACTOR VOLUME –F = VOLUMETRIC FLOW RATE –D = F/V R = DILUTION RATE –NON-TRIVIAL STEADY STATE: –WASHOUT:

DERIVE EQUATIONS PRODUCT RATE SUBSTRATE CONCENTRATION –S 0 = FEED CONCENTRATION OF RATE LIMITING SUBSTRATE –STEADY-STATE:

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) extracellular intracellular glycerol NAD + NADH G3P/DHP (S 2 ) ATP (A 3 ) NADH (N 2 ) NAD + (N 1 ) ADP (A 2 ) ethanol acetaldehyde/ pyruvate (S 4 ex ) 1,3-BPG (S 3 ) AD P NAD + NADH ATP acetaldehyde/ pyruvate (S 4 ) degraded products glucose glucose (S 1 ) r2r2 r6r6 r1r1 r5r5 r3r3 r4r4 J0J0 J r7r7

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 MASS ACTION KINETICS AND ATP INHIBITION FOR r 1

DYNAMIC MODEL EQUATIONS MASS BALANCES CONSERVED METABOLITES MATRIX

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

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 process.aspx workspace.aspx