Introduction

This chapter explains how the various components are combined into a production system. The material is in no way meant to be all-inclusive. Many things must be considered in selecting components for a system, and there is no substitute for experience and good engineering judgment.

A process flowsheet is used to describe the system. Figure 2-1 is a typical flowsheet that will be used as an example for discussion purposes. Another name for a process flowsheet is a process flow diagram (PFD). Regardless what it is called, either a flowsheet or a diagram, the information contained on both is the same. Figure 2-2 defines many of the commonly used symbols in process flowsheets.

Figure 2-1: Typical flowsheet.

Figure 2-2: Common flowsheet symbols.

Controlling the Process

Before discussing the process itself, it is necessary to understand how the process is controlled.

Operation of a Control Valve

Control valves are used throughout the process to control pressure, level, temperature, or flow. It is beyond the scope of this chapter to discuss the differences between the various types of control valves and the procedures for their sizing.

This section focuses primarily on the functions of this equipment. Figure 2-3 shows the major components of a typical sliding-stem control valve. All control valves have a variable opening or orifice. For a given pressure drop across the valve, the larger the orifice is, the greater the flow through the valve will be.

Figure 2-3: Major components of a typical sliding stem control valve. (courtesy...