Operator's Guide to Process Compressors

Robert X. Perez

• Publisher: Wiley-Scrivener
• Year: 2019
• ISBN:
  9781119581345
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

The perfect primer for anyone responsible for operating or maintaining process gas compressors.

Gas compressors tend to be the largest, most costly, and most critical machines employed in chemical and gas transfer processes. Since they tend to have the greatest effect on the reliability of processes they power, compressors typically receive the most scrutiny of all the machinery among the general population of processing equipment. To prevent unwanted compressor failures from occurring, operators must be taught how their equipment should operate and how each installation is different from one another.

The ultimate purpose of this book is to teach those who work in process settings more about gas compressors, so they can start up and operate them correctly and monitor their condition with more confidence. Some may regard compressor technology as too broad and complex a topic for operating personnel to fully understand, but the author has distilled this vast body of knowledge into some key, easy to understand lessons for the reader to study at his or her own pace.

This groundbreaking new work is a must-have for any engineer, operator, or manager working with process compressors.

The main goals of this book are to:

• Explain important theories and concepts about gases and compression processes with a minimum of mathematics
• Identify key compressor components and explain how they affect reliability
• Explain how centrifugal compressors, reciprocating compressors, and screw compressors function.
• Explain key operating factors that affect reliabilityIntroduce the reader to basic troubleshooting methodologies
• Introduce operators to proven field inspection techniques
• Improve the confidence of personnel operating compressors by teaching them the basics of compressor theory
• Improve compressor reliability plantwide by teaching operating and inspection best practices
• Improve communication between operating and supporting plant personnel by providing a common vocabulary of compressor terms
• Help processing plants avoid costly failures by teaching operators how to identify early compressor issues during field inspections

Chapter 1
Introduction to Gases

Gases represent a state of matter that has no fixed shape or fixed volume, which consist of tiny, energetic particles, i.e., atoms or molecules, that are widely spaced (Figure 1.1). Compared to the other states of matter, solids and liquids, gases have a much lower density, i.e., they have a small mass per unit volume, because there is a great deal of empty space between gas particles. At room temperature and pressure, the gas inside a container occupies only 0.1% of the total container volume. The other 99.9% of the total volume is empty space (whereas in liquids and solids, about 70% of the volume is occupied by particles). Gas particles move very fast and collide with one another, causing them to diffuse, or spread out, until they are evenly distributed throughout the volume of their container. You will never see only half of a balloon filled with air.

Figure 1.1 Gas atoms or molecules are constantly moving and colliding with one another.

Although both liquids and gases take the shape of their containers, gases differ from liquids in that there is so much space between gas molecules that they offer little resistance to motion and can be compressed to smaller and smaller volumes. As seen in Figure 1.2, as a gas is compressed, the molecules making up the gas get closer together and create a higher internal pressure.

Figure 1.2 As gas is compressed, the gas molecules get closer together.

Hydrogen is the lightest known gas. Any balloon filled with hydrogen gas will float in air if the total mass of its container is not too great. Helium gas is also lighter than air and has 92% of the lifting power of hydrogen. Today all airships, i.e., blimps, use helium instead of hydrogen because it offers almost the same lifting power and is not flammable.

Gases can be monatomic, diatomic, and polyatomic. Monatomic gases are gases composed of single atoms, diatomic gases are those composed of two atom molecules, and polyatomic gases are those made up of molecules with more than two atoms. Noble gases such as helium, neon, argon, etc., are normally found as single atoms, since they are chemically inert. Gases such as nitrogen (N₂), oxygen (O₂), and carbon monoxide (CO) tend to be found as diatomic molecules (Figure 1.3). Carbon dioxide (CO₂), and methane (CH₄) are examples of polyatomic gas molecules (Figure 1.3).

Figure 1.3 Oxygen, nitrogen, and carbon monoxide are examples of diatomic molecules. Carbon dioxide, water, nitrogen monoxide, methane, sulfur dioxide, and ozone are examples of polyatomic molecules.

Gases can be found all around us. In fact, the earth’s atmosphere is a blanket of gases composed of nitrogen (78%), oxygen (21%), argon (1%), and then trace amounts of carbon dioxide, neon, helium, methane, krypton, hydrogen, nitrous oxide, xenon, ozone, iodine, carbon monoxide, and ammonia.

Because of the large distances between gas particles, the attractions or repulsions among them are weak. The particles in a gas are in rapid and continuous motion. For example, the average velocity of nitrogen molecules, N₂, at 68 °F is about 1640 ft/s. As the temperature of a gas increases, the particles’ velocity increases. The average velocity of nitrogen molecules at 212 °F is about 1886 ft/s. The particles in a gas are constantly colliding with the walls of the container and with each other. Because of these collisions, the gas particles are constantly changing their direction of motion and their velocity. In a typical situation, a gas particle moves a very short distance between collisions. For example, oxygen, O₂, molecules at normal temperatures and pressures mo...