TABLE OF CONTENTS Key Learning Objectives
How to use mass balances to understand process flows
How to select a system boundary and design basis
How to estimate reactor and process yields
Material balances are the basis of process design. A material balance taken over the complete process will determine the quantities of raw materials required and products produced. Balances over individual process units set the process stream flows and compositions, and provide the basic equations for sizing equipment.
A good understanding of material balance calculations is essential in process design. In this chapter the fundamentals of the subject are covered, using simple examples to illustrate each topic. Practice is needed to develop expertise in handling what can often become very involved calculations. More examples and a more detailed discussion of the subject can be found in the numerous specialist books written on material and energy balance computations. Several suitable texts are listed in the "Bibliography" section at the end of this chapter.
For complex processes, material balances are usually completed using process simulation software, as described in Chapter 4. Significant time and effort can be wasted in process simulation if the fundamentals of material and energy balances are not properly understood. Careful attention must be paid to selecting the best basis and boundaries for material and energy balances; to predicting yields; and to understanding recycle, purge, and bypass schemes. Shorthand calculations, of the type illustrated in this chapter, should always be used to check process simulation results. Short calculations can...
