1. Case Study #1: Boiler Control 锅炉控制
Lei XIE
Institute of Cyber-Systems & Control,
Zhejiang University, Hangzhou, P. R. China

2. Contents
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)

3. Simplified Process Diagram of a Boiler
Main equipments ?
Decompose the process into several subsystems ?

4. Boiler Control Problem
Select the best pairing of MVs & CVs ?
System decomposition: (1) drum-level control;
(2) combustion control; (3) steam-temperature control.

5. Drum-level Control Problem
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

6. Drum-level Characteristics
Disturbance path
characteristic (Why?)
Control path
characteristic (Why?)
Models ?

7. 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)”

8. One-element (单冲量) Control
Simple PID Control

9. 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 C2, if the valve is a fail-open valve and C1=1.

10. Three-element (三冲量) Control
Control Diagram ?

11. Two Simplified Connections of Three-element Systems
Which differences between two connections ?

12. Combustion Control Problem
MVs and CVs Pairings: Flue gas →Furnace pressure, Air → Excess Air (O2% in flue gas), Fuel → Steam pressure

13. Simple Control Scheme for Combustion Control
Existing main problem ?

14. Cross-limiting Air/Fuel Ratio Combustion Control
Analyze the control scheme
Advantage:
Decoupling design
Protect against excess of fuel under all conditions

15. Feedforward/Feedback Control for Furnace Pressure
Analyze its design principle

16. Steam-temperature Control Scheme
Which kind of control methods ?

17. Problem Discussion
《工业过程控制工程》思考题与习题 23-2~23-4, P.420

18. Exercise 9.1
To control drum level, the three- element 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 C1, C2, C3 as well as the action of level controller LC.

19. Next Topic: Distillation Control (精馏塔控制)
Description of Distillation Column
Distillation Control Objectives
Steady-state Characteristic
Measurement of Composition
Decomposition of Control Problem
Basic Control Schemes

20. Next Topic: Problem Discussion
CVs (被控变量):
P, LD, LB, TR/xD, TS/xB
MVs (操作变量):
D, B, L, QH, QC, DG
DVs : F, xF, TF
To design your multi-loop control system to satisfy the above requirements and reduce interaction