Compressors

Lesson 1 — ABOUT COMPRESSORS

Lesson Objectives
- In order to complete this lesson, you must:
- Describe the basic functions of compressors.
- Describe three common types of compressors.
- Identify common types of compressors in the field.

Lesson Introduction
This lesson identifies three common types of compressors used in the process industry: the reciprocating compressor, the centrifugal compressor, and the liquid ring compressor. Other types of compressors are not as common and will not be discussed in this module. When the general principles of gas compression are understood, the design of most compressors should become be readily comprehensible.
This training is important because understanding how compressors are used in your process is essential to understanding your job. Compressors are capable of building very high pressures, and are subject to other inherent hazards. Understanding the types of compressors and their particular hazards is essential to operating your process in a safe manner.
In this lesson, you will learn the basic function of compressors and the three most common types of compressors.

Basic Functions of Compressors
Compressors are used throughout the process industry to compress and move a wide variety of gases and vapors safely and efficiently.

Function of Gas Compressors
Compressors increase the pressure of gases or vapors in a process system so that these materials will flow through the process at the required rates. Medium to high pressure is required for some processes to properly operate. Compressors are frequently the primary source for pressurizing these kinds of processes. For example, gas recovery plants, hydrogen processing units, and many chemical manufacturing processes all depend on compressors to develop the needed operating pressure.

Operating Conditions Vary the Design
Gas compressor design varies with the operating conditions of the gas. The design variations create types of compressors that perform one or more of the following services:
- Create very high pressure.
- Pump very high flow rates.
- Move hazardous gases without endangering personnel or the environment because of any external leakage.
- Create a vacuum. Compressors in this application are commonly called vacuum pumps and must maintain an extremely high vacuum.
No one design can simultaneously perform every service efficiently. Compressors must be carefully chosen for the type of service the process requires. Most process operators must be familiar with several types of compressors.

Three Common Types of Compressors

There are many variations in the design of compressors. This section will describe three common types and their features. These compressor types are:
1. Reciprocating
2. Centrifugal
3. Liquid Ring

Reciprocating Compressors

Reciprocating Compressors Reciprocating compressors compress gas by the action of a piston moving in a back-and-forth motion within a cylinder. These types of compressors are best suited to generate very high pressures and to move low volumes of gas.

Centrifugal Compressors

Centrifugal CompressorsGas in a centrifugal compressor is compressed by a series of impellers rotating at very high speed, often in excess of 10,000 rpm. Their unique sealing system makes these compressors ideal for handling hazardous and toxic gases. There is virtually no leakage to contaminate the environment or create a health hazard. Centrifugal compressors are best suited for pumping very high flow rates.

Liquid Ring Compressors

A liquid ring compressor consists of a rotor that spins a liquid inside a cylindrical casing. As the liquid spins, centrifugal force shapes it into a donut-like ring. Gas is compressed within the donut hole by the interaction between the liquid and the rotor. Liquid ring compressors are highly efficient, with virtually no internal recycling of the discharge gas back into the suction. This feature makes them suitable for vacuum pumps for high vacuum service. They are often used for vacuum distillation columns, for steam turbine surface condensers, for evaporators, and for vacuum boilers for crystallization.

Summary

In this lesson, you learned the basic functions that compressors perform. You also learned about three common types of compressors. You have learned to identify the common types of compressors.
In the next lesson, you will learn the major components of the three common types of compressors.