Process Control: Modeling, Design, and Simulation

2.3. Material Balances

The simplest modeling problems consist of material balances. In this section we use two process examples to illustrate the modeling techniques used. Recall that a model for a liquid surge vessel was developed in Chapter 1 (Example 1.3).

Example 2.1: Gas Surge Drum

Surge drums are often used as intermediate storage capacity for gas streams that are transferred between chemical process units. Consider a drum depicted below (Figure 2-2), where q_i is the inlet molar flow rate and q is the outlet molar flow rate. A typical control problem would be to manipulate one flow rate (either in or out) to maintain a desired drum pressure. Here we develop a model that describes how the drum pressure varies with the inlet and outlet flow ...