Process Control: Introduction and Applications
Explore the concept of automatic control, common process variables, benefits of automatic control, feedback control principle, and practical examples in the field of process control. Learn about software requirements for running simulators and the significance of maintaining process variables near setpoints. Discover how automatic control can enhance product quality, safety, and efficiency in various industries.
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Course: Process Control, NMBU Dec 2017 - April 2018 Introduction to process control By Finn Aakre Haugen, PhD, TechTeach (finnhaugen@hotmail.com) F. Haugen. Process Control. NMBU. 2017. 1
Software requirement for running SimView simulators Most of the lectures and exercises of this course include running simulators. These simulators have been developed in LabVIEW. Here are the requirements for the simulators to run. F. Haugen. Process Control. NMBU. 2017. 2
What is automatic control? F. Haugen. Process Control. NMBU. 2017. 3
Automatic control is making process variables stay sufficiently near their setpoints (references) - automatically (i.e. without manual operations): Without control or with poor control With good control Specifications about control error not satisfied! Less error! (Smaller variance) Max limit Min limit Setpoint, ySP Control error, e = ySP - y Process output, y t t F. Haugen. Process Control. NMBU. 2017. 4
Common process variables to be controlled to follow setpoints: Temperature (heat exchanger, reactor, room) Pressure (reactor, oil/water/gas-separator) Flow (gas or liquid flows in pipe) Level (tank) Position (ship, robot) Rotational speed (motor) F. Haugen. Process Control. NMBU. 2017. 5
Areas where automatic control can make large benefits: Product quality Product economy Safety Environment protection Comfort Feasibility Automation F. Haugen. Process Control. NMBU. 2017. 6
The principle of feedback control F. Haugen. Process Control. NMBU. 2017. 7
Think about how you you act while you are controlling the temperature of the water in the shower to make the temperature become equal to the desired temperature (aka. the temperature setpoint or reference), even under disturbances like reduced availability of hot water and variations of air temperature in the room. F. Haugen. Process Control. NMBU. 2017. 8
I guess you act like this (text on next slide): Room temperature = process disturbance or environmental variable Shower = process Control loop. Feedback Brain = controller incl. temp.- setpoint (brain) Water temperature = process variable Hand = sensor Hand and valve (tap) = Actuator F. Haugen. Process Control. NMBU. 2017. 9
You manipulate the actuator (tap) until the difference between the temperature setpoint and the temperature measurement is sufficiently small. This is error-driven control! It is the fundamental control principle in technical, industrial, biological, social system. More common terminology than error-driven control: Feedback control Closed loop control Automatic control F. Haugen. Process Control. NMBU. 2017. 10
Temperature control system implemented with industrial components: Aktuator Sensor Regulator F. Haugen. Process Control. NMBU. 2017. 11
Piping & Instrumentation Diagram (P&ID) for the temperature control system: Room temperature = process disturbance or environmental variable Temperature setpoint Measurement signal Control signal Water temperature = process variable TC TT Actuator Controller Sensor (TT = Temperature Transmitter) (TC = Temperature Controller) F. Haugen. Process Control. NMBU. 2017. 12
So, how does the controller act? It manipulates the process variable by changing the control signal to the actuator until the control error has become zero. So, it continually improves, until the aim is reached: Zero error. In practice it is the mean error which will be zero as there will always be some disturbances making the error vary somewhat, see the figure below. Process variable Setpoint Control error = Setpoint - Process variable t F. Haugen. Process Control. NMBU. 2017. 13
Example of industrial feedback control system: Level control of wood chip tank (Process & Instrumentation Diagram - P&ID) Conveyor belt Feed screw Actuator win [kg/min] ws[kg/min] Chip tank Process variable Control signal Controller Level sensor h [m] u LC LT Wood chip Setpoint hSP [m] 0 m Outflow to subsequent process units wout [kg/min] Process disturbance F. Haugen. Process Control. NMBU. 2017. 14
Simulator (Run the exe-file in the link.) F. Haugen. Process Control. NMBU. 2017. 15
Another example: Simulator F. Haugen. Process Control. NMBU. 2017. 16
A third example (see comment on next slide): Simulator F. Haugen. Process Control. NMBU. 2017. 17
The third example (see previus slide) resembles the inlet equalization basin upstreams VEAS wrrf: F_ut u [m3/s] Tunnel F_vaskevann [m3/s] F_tunnel [m3/s] u [m3/s] LC 1 h_sp [m] Settpunkt A [m2] V skespeil Kanal h [m] LT 1 Totalt: F_inn = F_tunnel + F_vaskevann LC = Level Controller LT = Level Transmitter (sensor) F. Haugen. Process Control. NMBU. 2017. 18
Symbols in Piping & Instrumentation Diagrams (P&IDs) F. Haugen. Process Control. NMBU. 2017. 19
Standards for P&IDs: ISO 3511-1 ISA S5.1 F. Haugen. Process Control. NMBU. 2017. 20
Letter codes (for P&IDs): F. Haugen. Process Control. NMBU. 2017. 21
Instrumentation symbols: Instrument mounted in the field (at the measurement point) FC 1 Instrument mounted in a central place available for the operator, e.g. in a control room FC 1 F. Haugen. Process Control. NMBU. 2017. 22
Process fluid and signals: Process fluid (liquid or gas) General (undefined) signal Pneumatic signal Electrical signal F. Haugen. Process Control. NMBU. 2017. 23
Valves: Valve with membrane actuator (Is also used as a general symbol for control valves.) Valve with electrical motor Magnetic valve (On/Off) Hand (manually) operated valve Valve with fixed opening F. Haugen. Process Control. NMBU. 2017. 24
Tanks: Absorption/stripping column Open tank Distillation column Closed tank Stirring motor Reactor Autoclave Jacket for heating or cooling F. Haugen. Process Control. NMBU. 2017. 25
Heat exchanger: Process fluid CW Heat exchanger (CW = Cold Water HW = Hot Water) F. Haugen. Process Control. NMBU. 2017. 26
Pumps: General pump symbol P-1 Centrifugal pump Displacement (dosing) pump Compressor Turbine F. Haugen. Process Control. NMBU. 2017. 27
Block diagrams of control systems F. Haugen. Process Control. NMBU. 2017. 28
A simplified block diagram showing the most essential parts: We will relate this block diagram to the level control system of the wood-chip tank. Process disturbance (environmental variable) Process variable or process output Control error d Setpoint or reference Control signal e y u ySP Controller (function) Actuator Process E.g. [m] or [%] or [mA] E.g. E.g. [m] [kg/min] or [%] or [mA] Feedback control loop ym Sensor Feedback Process measure- ment E.g.[m] or [%] or [mA] F. Haugen. Process Control. NMBU. 2017. 29
