1. Workshop for Flipped Class
Based on students having completed the Chapter 14 e-Lesson before class
Chapter 14
Cascade Control
Copyright © Thomas Marlin 2016

2. Workshop 1 – Cascade design
CHAPTER 14: CASCADE CONTROL
Workshop 1 – Cascade design
The stirred tank is cooled via a jacket through which water flows. The key goal is content temperature control. Evaluate cascade control for a disturbance in the warm water inlet temperature. You may add a sensor and controller but may not make other changes to the equipment.
Feed
Cold water
Effluent jacket water
KM: Here is a very realistic process design challenge. The stirred tank reactor in the figure includes cooling via cool water in the vessel jacket; the cooling water is prepared as a mixture of warm and cold water. The reactor temperature cannot be too low because we need to prevent crystallization on the walls of the vessel. Therefore, the entering cooling water temperature is adjusted by TC1.
TM: One of the main disturbances is the warm water temperature. Improve the control design shown in this figure by introducing cascade control. You may add one sensor and controller, but you may not change piping and valves.
KM: When you have prepared your answer, please advance to the next slide. TC 1 LC
Warm water
Product FC

3. Workshop 2 – Cascade design
CHAPTER 14: CASCADE CONTROL
Workshop 2 – Cascade design
Evaluate cascade control for a disturbance in the heating medium inlet temperature. You may add a sensor but make no other changes to the equipment. TC 2 T 1 F 3 L
feed
product
heating stream

4. Workshop 3 – Cascade thought questions
CHAPTER 14: CASCADE CONTROL
Workshop 3 – Cascade thought questions
Why do we retain the primary controller?
Which modes are required for zero steady-state offset for the primary controlled variable?
Which modes are recommended?
What is the additional cost for cascade control?
Normally, each PID controller represents one independent controlled variable. Is anything different in a cascade structure?

5. Workshop 4 – Design cascade designs to improve control performance
CHAPTER 14: CASCADE CONTROL
Workshop 4 – Design cascade designs to improve control performance FT 1 2 PT AT TI 3 4 PI 5 6 7 8 9 FI 10 11
feed
air
fuel
Flue gas
burner TC FC AC PC
These four loops were introduced in Chapter 7

6. Let’s improve the performance of the flash drum control design by adding cascade control.
Vapor
product
PC-1 T5 T1
Feed
Methane
Ethane (LK)
Propane
Butane
Pentane T2
FC-1 T3 v3
LC-1
Liquid
product F5 v1 v2 F2 F3 v4
AC-1
Process
fluid
Steam
L. Key