Operator's Guide to Process Compressors

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

Robert X. Perez is mechanical engineer with more than 40 years of rotating equipment experience in the petrochemical industry. He has worked in petroleum refineries, chemical facilities, and gas processing plants. Currently, he provides engineering consulting services and rotating equipment training. He earned a BSME degree from Texas A&M University at College Station, an MSME degree from the University of Texas at Austin and holds a Texas PE license. Mr. Perez has written numerous machinery reliability articles for magazines and conferences proceedings and has authored 4 books and coauthored 4 books related to machinery reliability. He resides in San Antonio, Texas.

Preface xv

1 Introduction to Gases 1

1.1 Ideal Gases 4

1.2 Properties of Gases 5

1.3 Temperature 5

1.4 Pressure 6

1.5 Gas Laws 7

1.6 Gas Mixtures 10

1.6.1 Dalton’s Law of Partial Pressures 10

1.7 Molecular Weight of a Gas Mixture 11

1.8 Gas Density 13

1.9 Density of Mixtures 14

1.10 Heat of Compression 15

2 Commonly Used Compressor Flow Terms 19

2.1 Ideal Gas Law 20

2.1.1 Example of How to Convert from SCFM to ACFM 22

2.2 Visualizing Gas Flow 23

2.3 Compressibility Factor (Z) 25

2.4 Sizing Compressors 27

3 Compression Processes 31

3.1 Adiabatic Compression 33

3.2 Polytropic Compression 37

3.2.1 Polytropic Example #1 40

3.2.2 Polytropic Example 2 40

4 What Role the Compression Ratio Plays in Compressor Design and Selection 43

4.1 Compression Ratio versus Discharge Temperature 44

4.2 Design Temperature Margin 46

4.2.1 Design Trade-Offs 49

5 An Introduction to Compressor Operations 53

5.1 Compression Basics 53

5.2 Defining Gas Flow 55

5.3 Compressor Types 56

5.4 Multistaging 59

5.5 Key Reliability Indicators 60

6 Centrifugal Compressors 63

6.1 Centrifugal Compressor Piping Arrangements 66

6.2 Start-Up Configuration 68

6.3 Centrifugal Compressor Horsepower 68

6.4 Troubleshooting Tips 70

6.5 Centrifugal Compressor Start-Ups 71

6.6 Centrifugal Compressor Checklist 72

7 How Process Changes Affect Centrifugal Compressor Performance 75

7.1 Baseball Pitcher Analogy 75

7.2 How Gas Density Affects Horsepower 78

7.3 Theory versus Practice 80

8 How to Read a Centrifugal Compressor Performance Map 83

8.1 The Anatomy of a Compressor Map 85

8.1.1 Flow Axis (See Figures 8.2 and 8.3) 85

8.1.2 Head or Pressure Ratio Axis (See Figures 8.2 and 8.3) 86

8.1.3 Predicted Surge Line (See Figures 8.2 and 8.3) 86

8.1.4 Predicted Capacity Limit (Figures 8.2 and 8.3) 86

8.1.5 Surge Margin (See Figure 8.2) 87

8.1.6 Speed Lines (See Figures 8.2 and 8.3) 88

8.2 Design Conditions 88

9 Keeping Your Centrifugal Compressor Out of Harm’s Way 91

9.1 Compressor Operating Limits 93

9.2 Compressor Flow Limits 93

9.3 Critical Speeds 95

9.4 Horsepower Limits 96

9.5 Temperatures 97

10 Troubleshooting Centrifugal Compressors in Process Services 101

10.1 The Field Troubleshooting Process—Step by Step 105

10.1.1 Step 1: Define the Problem 105

10.1.2 Step 2: Collect All Pertinent Data 105

10.1.3 Step 3: Analyze the Body of Data as a Whole 106

10.1.4 Step 4: Act and Confirm 106

10.2 The “Hourglass” Approach to Troubleshooting 108

10.3 Thinking and Acting Globally 109

10.4 Troubleshooting Matrix and Table 110

10.5 Centrifugal Compressor Troubleshooting Example 110

11 Reciprocating Compressors 117

11.1 Reciprocating Compressor Installations 124

11.1.1 How Process Conditions Affect Reciprocating Compressor Performance 126

11.2 Reciprocating Compressor Start-Ups 128

11.3 Reciprocating Compressor Checklist 129

11.4 Criticality 131

12 Troubleshooting Reciprocating Compressors in Process Services 133

12.1 The Field Troubleshooting Process—Step by Step 137

12.1.1 Step 1: Define the Problem 137

12.1.2 Step 2: Collect All Pertinent Data 137

12.1.3 Step 3: Analyze the Body of Data as a Whole 138

12.1.4 Step 4: Act and Confirm 138

12.1.5 Troubleshooting Matrix and Table 140

12.1.6 Reciprocating Compressor Troubleshooting Example 140

13 Screw Compressors 147

13.1 Oil Injected Screw Compressors 150

13.2 Screw Compressor Modulation 151

13.3 Pressure Pulsation Issues 152

13.3.1 Absorptive Type Dampeners 154

13.3.2 Reactive Type Dampeners 154

13.3.3 Combination Type (Reactive and Absorptive) 154

13.3.4 Oil Contamination 155

13.3.5 How Process Conditions Affect Screw Compressor Performance 156

13.4 Troubleshooting Screw Compressors 156

14 Compressor Start-Up Procedures 159

14.1 Compressor Start-Up Risks 160

14.2 Generic Start-Up Procedure 162

14.3 Centrifugal Compressor Start-Ups 165

14.4 Reciprocating Compressor Start-Ups 167

14.5 Screw Compressor Start-Ups 170

15 Compressor Trains: Drivers, Speed Modifiers, and Driven Machines 173

15.1 Driven Process Machines 174

15.1.1 Drivers 175

15.1.1.1 AC Electric Motors 176

15.1.2 Steam Turbines 177

15.2 Gas Turbines 178

15.2.1 Natural Gas Engines 179

15.2.2 Speed Modifiers 180

15.2.2.1 Gear Boxes 180

15.3 Useful Gearbox Facts 182

15.4 Combination Machines 182

15.4.1 Turboexpanders 182

16 Compressor Components 185

16.1 Bearing Types 185

16.2 Rolling Element Bearings 187

16.3 Plain Bearings 188

16.4 Compressor Bearings 189

16.5 Modeling Fluid Film Bearings 190

16.6 Thrust Loads 192

16.7 Kingsbury Thrust Bearing 193

16.8 Compressor Seals 194

16.8.1 Labyrinth Seals 194

16.8.2 Oil Film Seal 194

16.8.3 Face Contact Wet Seals 196

16.9 Seal Oil System 197

16.10 Dry Gas Seals 197

16.11 Seal Gas Quality and Control 198

16.12 Reciprocating Compressors – Packing 199

17 The Importance of Lubrication 201

17.1 Lubrication Regimes 203

17.2 Lubricating Oils 206

17.3 Compressor Lubricating Oil Systems 206

17.3.1 Lubrication Monitoring 209

17.4 Oil Foaming 210

17.4.1 Excessive Foam 211

Table of Contents xiii

18 Inspection Ideas for Operators and Field Personnel 213

18.1 Equipment Field Inspections 213

18.1.1 Audible Inspections 215

18.1.2 Visual Inspections 216

18.1.3 Tactile Inspections 217

18.1.4 Smell 219

18.2 Tools Available to Quantify What You Have Detected 220

18.2.1 Audible Inspection Methods 220

18.2.1.1 Ultrasonic Gun 220

18.2.1.2 Stethoscope 220

18.2.1.3 Metal Rod 220

18.3 Visual Inspection Methods 221

18.3.1 Infrared or IR Gun 221

18.4 IR Camera 222

18.4.1 Strobe Light 223

18.5 Inspection Methods Using Vibration and Temperature Measurement Equipment 224

18.5.1 Vibration Meter with Accelerometer 224

18.5.2 Temperature Measurement Equipment 226

18.6 Generic Monitoring Guidelines 227

19 Addressing Reciprocating Compressor Piping Vibration Problems: Design Ideas, Field Audit Tips, and Proven Solutions 229

19.1 Piping Restraints 232

19.2 Pipe Clamping Systems 233

19.3 Guidelines 233

19.4 Piping Assessment Steps 235

19.4.1 First, Perform the Following Pre-Field Analysis Steps 235

19.4.2 Next 235

19.4.3 Problem Locations 236

19.5 Attaching Pipe Clamps to Structural Members 237

19.5.1 Installation Examples 240

19.5.2 Here Are a Few More Pipe Clamp Tips 240

20 Collecting and Assessing Piping Vibration 243

20.1 Piping Analysis Steps 245

20.2 Piping Vibration Examples 246

Appendix A: Practice Problems Related to Chapters 1 Through 4 Topics 249

Appendix B: Glossary of Compressor Technology Terms 261

Index 273

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