CHE 185 – PROCESS CONTROL AND DYNAMICS P&ID’S AND CONSTRAINTS FOR ROUTINE OPERATIONS

Model for Product Composition for CSTR with a Series Reaction

Model for Cell Growth in a Fed-Batch Reactor

Class Exercise: Dynamic Model of a Level in a Tank Model equation is based on dynamic conservation of mass, i.e., accumulation of mass in the tank is equal to the mass flow rate into the tank minus the mass flow rate out.

Solution: Dynamic Model for Tank Level Actuator on flow out of the tank. Process model Level sensor since the level sensor is much faster than the process and the actuator

PIPING AND INSTRUMENT DIAGRAMS (P&ID’s) DESIGN DOCUMENTS PROVIDE THE PRIMARY CONTROL LOGIC FOR A PROCESS ALSO USED TO PROVIDE PIPING DESIGN INFORMATION REFER TO APPENDIX b

P&ID SYMBOLS STANDARD LETTERS ARE USED FOR FUNCTIONS AND VARIABLES STANDARDIZED SYMBOLS ARE USED FOR CONTROL EQUIPMENT STANDARD SYMBOLS ARE USED FOR CONNECTIONS

SIMPLIFIED P&IDS USE THE PROCESS FLOW DIAGRAMS TO SHOW PRIMARY CONTROL LOOPS CONSIST OF LOOPS THAT SHOW LOCATIONS OF SENSORS, A CONTROLLER OR INTERLOCK, AND THE ACTUATOR CAN BE PRODUCED FOR A SINGLE UNIT OPERATION OR FOR AN ENTIRE FACILITY

EXAMPLE simplified p&id

EXAMPLE simplified p&id TC AND LC REPRESENT TEMPERATURE AND LEVEL CONTROLLERS, RESPECTIVELY THESE INDICATE THE TEMPERATURE OF THE MIXED TANK IS MAINTAINED BY THE FLOW OF STEAM TO AN EXTERNAL HEAT EXCHANGER THAT HEATS A SIDESTREAM FROM THE MIXING TANK THE LEVEL OF THE VESSEL IS MAINTAINED BY CONTROLLING THE FLOW THROUGH A DRAIN VALVE

EXAMPLE simplified p&id PT REPRESENTS A PRESSURE INDICATION LOOP THIS INDICATOR IS NOT USED TO CONTROL PROCESS VARIABLES THROUGH A CONTROLLER IT MAY BE USED TO PROVIDE imFORMATION DURING NON-ROUTINE OPERATIONS, SUCH AS STARTUP/SHUTDOWN OR TO FOR OPTIMIZATION THE LOOPS ARE NOT NUMBERED

CONCEPTUAL DIAGRAMS INCLUDE ALL CONTROL LOOPS AND INSTRUMENTATION FUNCTIONS THESE SUMMARIZE THE RESULTS OF DESIGN CALCULATIONS

FORMAL P&IDs INCLUDE DETAILS FOR ALL STEADY STATE CONTROL, BATCH CONTROL, INTERLOCK, SAFETY, AND STARTUP/SHUTDOWN OPERATIONS THESE INCLUDE ALL THE DETAIL USED FOR SPECIFICATION EACH LOOP IS NUMBERED WITH DESIGNATIONS THAT WILL BE USED FOR ALL DETAILED DESIGN THERE MAY BE STANDARD INSTRUMENTATION DIAGRAMS THAT SUPPORT THE P&ID PRESENTATION

FORMAL P&IDs LOOP IDENTIFICATION USES ISA STANDARD DESIGNATION FOR EACH COMPONENT AND FUNCTION CONTROL VALVES ARE NORMALLY DESIGNATED ACCORDING TO THE CONTROLLED VARIABLE, PCV, TCV, LCV, FCV - THOUGH THEY ALWAYS CONTROL FLOWS PNEUMATIC, ELECTRONIC AND COMPUTER CONNECTIONS ARE DIFFERENTIATED

OTHER INSTRUMENT DOCUMENTATION LOOP DIAGRAMS ARE MADE FOR EACH SEPARATE LOOP WITH DETAILS FOR ALL COMPONENTS AND REFERENCES TO CALCULATIONS OVERALL DCS DIAGRAMS ARE PREPARED ON THE SUPERVISORY LEVEL TO SHOW HOW THE PLANT NETWORK CONNECTS WITH THE LOCAL I/O PANELS LADDER LOGIC DIAGRAMS ARE PROVIDED FOR PLC’s ELECTRICAL ONE-LINE DIAGRAMS SHOW THE RELAYS THAT ARE INCLUDED IN THE CONTROL SYSTEMS

CONSTRAINTS FOR ROUTINE OPERATION DYNAMIC CONTROL MODELING TENDS TO EMPHASIZECONTINUOUS AUTOMATED CONTROL - STEADY STATE OPERATION THERE ARE OTHER NON-ROUTINE CONDITIONS WHERE OTHER CONTROL METHODS ARE APPLIED AND DYNAMICS ARE SECONDARY NO CONTROL - SOME FUNCTIONS ARE NOT CONTROLLED DIRECTLY RAW MATERIAL QUALITY UTILITY QUALITIES

CONSTRAINTS FOR nonROUTINE OPERATION MANUAL CONTROL - SOME SYSTEMS HAVE SUCH LARGE TIME DELAYS, THAT MANUAL CONTROL IS ADEQUATE ON/OFF CONTROL - THIS IS INTERLOCK OPERATION WHERE THE SYSTEM MAY BE ACTIVATED OR DEACTIVATED IN RESPONSE DUE TO OUT-OF-RANGE OPERATION END OF A TIMER CYCLE

CONSTRAINTS FOR nonROUTINE OPERATION STARTUP/SHUTDOWN OPERATION MAY INCLUDE OPERATION UNDER A SEPARATE SET OF TUNING CONSTANTS MAY INCLUDE SHORT-TERM INTERRUPTION AS WELL AS LONG-TERM PROCESS SHUTDOWN NON-ROUTINE CONDITIONS WHERE OTHER CONTROL METHODS ARE APPLIED AND DYNAMICS ARE PRIMARY

FAIL-SAFE INTERLOCK OPERATION THE POTENTIAL INCIDENT NEEDS TO BE DYNAMICALLY MODELED TO PREVENT SECONDARY FAILURES THAT COMPROMISE SAFETY FOR EXAMPLE IF A RELIEF VALVE DOES NOT HAVE ADEQUATE CAPACITY, THE SYSTEM MAY OVER-PRESSURE IF A FLARE DOES NOT PROVIDE A FLAME RAPIDLY, THERE MAY BE A RELEASE TO ATMOSPHERE.

CONSTRAINTS FOR ROUTINE OPERATION Personnel protection ENVIRONMENTAL PROTECTION EQUIPMENT PROTECTION