Unsteady-state Operations and Process Control
Introduction
In this chapter, we will introduce unsteady-state operations, which are very common in chemical processing. Since unsteady-state balance systems are transient, we will explore deriving material balances and determining their initial conditions. We will also look at process control strategies, which are used to measure and manipulate processes in plants.
Learning Objectives
By the end of this chapter, you should be able to:
Recognize unsteady-state balance systems.
Derive material balance equations.
Provide initial conditions for well-mixed separable transient single-unit processes.
Solve separable transient balances to find a property of a system at any given time.
Provide initial conditions for well-mixed non-separable transient single-unit processes.
Set-up separable transient balances.
Apply control strategies to control common process variables: flow, liquid pressure, liquid level, and temperature of endothermic process streams.
As you’re going through this chapter, here are some important terms for you to take note of:
- unsteady-state
- input
- output
- generation
- consumption
- accumulation
- transient balances
- boundary conditions
- separable differential equation
- nonseparable differential equation
- continuous stirred tank reactor (CSTR)
- set-point
- disturbance variable
- manipulated variable
- process variable
- controlled variable
- obstruction meter
- rotational or turbine flowmeter
- float measure
- sonic/radar
- manometer
- differential pressure cell
- expansion-based temperature measure
- electrical temperature measure
- endothermic control loop
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