Case Study 1 Boiler Control Lei XIE Institute
Case Study #1: Boiler Control 锅炉控制 Lei XIE Institute of Cyber-Systems & Control, Zhejiang University, Hangzhou, P. R. China
Contents n n n Process Diagram and Control Problems of Boiler (锅炉设备的生产流程与控制问题) Characteristic Analysis & Three-element Control for Drum Level (汽包水位特性分析与 三冲量控制) Cross-limiting Air/Fuel Ratio Combustion Control (双交叉空燃比燃烧控制)
Simplified Process Diagram of a Boiler Main equipments ? Decompose the process into several subsystems ?
Boiler Control Problem Select the best pairing of MVs & CVs ? System decomposition: (1) drum-level control; (2) combustion control; (3) steam-temperature control.
Drum-level Control Problem n n n Controlled variable: drum level, in H (s) Manipulated variable: feedwater flow, in F (s) Main disturbances: Steam flow, in D (s) Please explain the reason why it is a difficult problem
Drum-level Characteristics Disturbance path characteristic (Why? ) Models ? Control path characteristic (Why? )
Non-minimum phase Characteristics There will be a zero in right side of the complex plane if The process will be called “non-minimum phase system (非最小 相位系统)”
One-element (单冲量) Control Simple PID Control
Two-element (双冲量) Control Problem discussion: (1) Point out the kind of control methods ? (2) Obtain control diagram of the scheme. (3) Select the controller action, the symbol and the value of C 2, if the valve is a fail-open valve and C 1=1.
Three-element (三冲量) Control Diagram ?
Two Simplified Connections of Three-element Systems Which differences between two connections ?
Combustion Control Problem MVs and CVs Pairings: Flue gas →Furnace pressure, Air → Excess Air (O 2% in flue gas), Fuel → Steam pressure
Simple Control Scheme for Combustion Control Existing main problem ?
Cross-limiting Air/Fuel Ratio Combustion Control Analyze the control scheme Advantage: (1) Decoupling design (2) Protect against excess of fuel under all conditions
Feedforward/Feedback Control for Furnace Pressure Analyze its design principle
Steam-temperature Control Scheme Which kind of control methods ?
Problem Discussion n 《 业过程控制 程》思考题与习题 23 -2~23 -4, P. 420
Exercise 9. 1 To control drum level, the threeelement control scheme shown in left figure is common used. If the feedwater valve is failed-open, then (1) describe the complete control diagram, and note the inputs and outputs for each block; (2) determine the symbol and the value C 1, C 2, C 3 as well as the action of level controller LC.
Next Topic: Distillation Control (精馏塔控制) n n n Description of Distillation Column Distillation Control Objectives Steady-state Characteristic Measurement of Composition Decomposition of Control Problem Basic Control Schemes
Next Topic: Problem Discussion CVs (被控变量): P, LD, LB, TR/x. D, TS/x. B MVs (操作变量): D, B, L, QH, QC, DG DVs : F, x. F, TF To design your multi-loop control system to satisfy the above requirements and reduce interaction
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