Practical Guide to Compressor Technology

HEINZ P. BLOCH, MS, is a Consulting Engineer. Previously, Mr. Bloch held the position of regional machinery specialist for the United States at Exxon Chemical. He has authored seventeen books and more than 330 papers and articles and conducted more than 500 technical courses on such issues as practical machinery management, failure analysis and avoidance, turbomachinery, oil mist lubrication, and practical lubrication for industrial facilities.

• PREFACE xiiiACKNOWLEDGMENTS xvPART I POSITIVE DISPLACEMENT COMPRESSOR TECHNOLOGY 11 Theory 31.1 Symbols 31.2 How a Compressor Works 41.3 First Law of Thermodynamics 81.4 Second Law of Thermodynamics 81.5 Ideal or Perfect Gas Laws 91.5.1 Boyle’s Law 91.5.2 Charles’ Law 91.5.3 Amonton’s Law 91.5.4 Dalton’s Law 91.5.5 Amagat’s Law 101.5.6 Avogadro’s Law 101.5.7 Perfect Gas Formula 101.6 Vapor Pressure 111.7 Gas and Vapor 111.8 Partial Pressures 111.9 Critical Conditions 131.10 Compressibility 131.11 Generalized Compressibility Charts 141.12 Gas Mixtures 151.13 The Mole 151.14 Specific Volume and Density 161.15 Volume Percent of Constituents 161.16 Molecular Weight of a Mixture 161.17 Specific Gravity and Partial Pressure 171.18 Ratio of Specific Heats 171.19 Pseudo-critical Conditions and Compressibility 181.20 Weight-Basis Items 181.21 Compression Cycles 191.22 Power Requirement 201.23 Compressibility Correction 211.24 Multiple Staging 221.25 Volume References 231.26 Cylinder Clearance and Volumetric Efficiency 241.27 Cylinder Clearance and Compression Efficiency 27Reference 272 Reciprocating Process Compressor Design Overview 292.1 Crankshaft Design 332.2 Bearings and Lubrication Systems 372.3 Connecting Rods 372.4 Crossheads 382.5 Frames and Cylinders 392.6 Cooling Provisions 452.7 Pistons 472.8 Piston and Rider Rings 472.9 Valves 482.10 Piston Rods 512.11 Packings 552.12 Cylinder Lubrication 552.13 Distance Pieces 562.14 Reciprocating Compressor Modernization 572.14.1 Cylinder Upgrades 592.14.2 Design for Easy Maintenance 592.14.3 Crosshead Designs and Attention to Reliable Lubrication 612.14.4 Materials 623 Reciprocating Compressor Performance and Monitoring Considerations 633.1 Capacity Control 633.1.1 Recycle or Bypass 643.1.2 Suction Throttling 643.1.3 Suction Valve Unloading 653.1.4 Clearance Pockets 673.2 More About Cylinder Jacket Cooling and Heating Arrangements 703.2.1 Methods of Cooling 713.3 Comparing Lubricated and Nonlubricated Conventional Cylinder Construction 733.3.1 Lubricated Cylinder Designs 733.3.2 Nonlubricated Cylinder Design 753.4 Compressor Vent and Buffer Systems 763.5 Compressor Instrumentation 773.5.1 Electric vs. Pneumatic Switches 823.5.2 Switch Set Points 823.5.3 Control Panels 823.5.4 Valve-in-Piston Reciprocating Compressors 833.5.5 Barrel-Frame Reciprocating Compressors 843.6 Condition Monitoring of Reciprocating Compressors 853.6.1 Maintenance Strategies 863.6.2 Justification for Machine Monitoring 863.6.3 What to Monitor and Why 87References 974 Labyrinth Piston Compressors 994.1 Main Design Features 994.2 Energy Consumption 1014.3 Sealing Problems 1045 Hypercompressors 1095.1 Introduction 1095.2 Cylinders and Piston Seals 1115.3 Cylinder Heads and Valves 1155.4 Drive Mechanism 1175.5 Miscellaneous Problems 1195.6 Conclusions 1206 Metal Diaphragm Compressors 1216.1 Introduction 1216.2 Terminology 1216.3 Description 1227 Lobe and Sliding Vane Compressors 1298 Liquid Ring Compressors 1359 Rotary Screw Compressors and Filter Separators 1419.1 Twin-Screw Machines 1419.1.1 Working Phases 1419.1.2 Areas of Application 1459.1.3 Dry vs. Liquid-Injected Machines 1459.1.4 Operating Principles 1459.1.5 Flow Calculation 1479.1.6 Power Calculation 1479.1.7 Temperature Rise 1509.1.8 Capacity Control 1509.1.9 Mechanical Construction 1539.1.10 Industry Experience 1549.1.11 Maintenance History 1589.1.12 Performance Summary 1589.2 Oil-Flooded Single-Screw Compressors 1609.3 Selecting Modern Reverse-Flow Filter-Separator Technology 1639.3.1 Conventional Filter-Separators vs. SCCs 1649.3.2 Removal Efficiencies 1659.3.3 Filter Quality 1659.3.4 Selecting the Most Suitable Gas Filtration Equipment 1669.3.5 Evaluating the Proposed Configurations 1679.3.6 Life-Cycle-Cost Calculations 1689.3.7 Conclusions 16910 Reciprocating Compressor Performance and Sizing Fundamentals 17110.1 Theoretical Maximum Capacity 17210.2 Capacity Losses 17310.3 Valve Preload 17410.4 Valve and Gas Passage Throttling 17410.5 Piston Ring Leakage 17610.6 Packing Leakage 17710.7 Discharge Valve Leakage 17710.8 Suction Valve Leakage 17810.9 Heating Effects 17810.10 Pulsation Effects 18010.11 Horsepower 18110.12 Horsepower Adders 18110.13 Gas Properties 18210.13.1 Ideal Gas 18210.13.2 Real Gas 18210.14 Alternative Equations of State 18310.15 Condensation 18310.16 Frame Loads 18310.17 Compressor Displacement and Clearance 18410.18 Staging 18610.19 Fundamentals of Sizing 18710.19.1 Number of Stages 18710.19.2 Approximate Horsepower 18710.19.3 Cylinder Bore Requirements 18810.19.4 Frame Load 18810.19.5 Vendor Confirmation 18910.20 Sizing Examples 189PART II DYNAMIC COMPRESSOR TECHNOLOGY 19711 Simplified Equations for Determining the Performance of Dynamic Compressors 20511.1 Nonoverloading Characteristics of Centrifugal Compressors 20511.2 Stability 20511.3 Speed Change 20711.4 Compressor Drive 20711.5 Calculations 20812 Design Considerations and Manufacturing Techniques 21512.1 Axially vs. Radially Split 21512.2 Tightness 21512.3 Material Stress 21512.4 Nozzle Location and Maintenance 21612.5 Design Overview 21712.5.1 Casings 21712.5.2 Flow Path 23012.5.3 Rotors 23412.5.4 Impellers 23412.5.5 Axial Blading 24212.5.6 Seals 24212.6 Bearing Configurations 25012.6.1 Radial Bearings 25012.6.2 Thrust Bearings 25112.6.3 Flexure Pivot Tilt Pad Bearings 25312.7 Casing Design Criteria 25712.8 Casing Manufacturing Techniques 26512.9 Stage Design Considerations 27312.10 Impeller Manufacturing Techniques 28212.11 Rotor Dynamic Considerations 28612.12 Fouling Considerations and Coatings 29212.12.1 Polymerization and Fouling 29212.12.2 Fouling and Its Effect on Compressor Operation 29312.12.3 Coating Case Study 29412.12.4 SermaLon Coating 29612.12.5 Results 29713 Advanced Sealing and Bearing Systems 29913.1 Background 29913.2 Dry Seals 30013.2.1 Operating Principles 30013.2.2 Operating Experience 30213.2.3 Problems and Solutions 30313.2.4 Dry Seal Upgrade Developments 30413.2.5 Dry Gas Seal Failures Avoided by Gas Conditioning 30413.3 Magnetic Bearings 30813.3.1 Operating Principles 30813.3.2 Operating Experience and Benefits 31013.3.3 Problems and Solutions 31113.4 Development Efforts 31113.4.1 Thrust-Reducing Seals 31213.5 Integrated Designs 31413.6 Fluid-Induced Instability and Externally Pressurized Bearings 31813.6.1 Instability Considerations 31813.6.2 Fluid-Induced Instability 31813.6.3 Eccentricity and Stiffness 32013.6.4 Externally Pressurized Bearings and Seals 32113.6.5 Practical Applications 32413.6.6 Rotor Model, Dynamic Stiffness, and Fluid Instability 32513.6.7 Root Locus Stability Analysis 32713.6.8 More About Externally Pressurized Bearings 32813.6.9 Field Data Collection 33113.6.10 Test Stand Data 33413.6.11 Conclusions 336References 336Suggested Reading 33614 Couplings, Torque Transmission, and Torque Sensing 33914.1 Coupling Overview 33914.1.1 Low Overhung Moment 34114.1.2 Low Residual Unbalance Desired 34314.1.3 Long Life and Maintainability 34414.1.4 Continuous Lubrication Not a Cure-All 34514.1.5 Contoured Diaphragm Coupling 34514.2 Coupling Retrofits and Upgrades 34714.3 Performance Optimization Through Torque Monitoring 34915 Lubrication, Sealing, and Control Oil Systems for Turbomachinery 35715.1 Considerations Common to All Systems 35715.2 Seal Oil Considerations 35916 Compressor Control 36316.1 Introduction 36316.2 Control System Objectives 36316.3 Compressor Maps 36416.3.1 Invariant Coordinates 36616.4 Performance Control 36816.4.1 PI and PID Control Algorithms 37016.4.2 Stability Considerations 37216.4.3 Integral or Reset Windup 37316.5 Performance Limitations 37316.5.1 Surge Limit 37416.5.2 Stonewall 37516.6 Preventing Surge 37616.6.1 Antisurge Control Variables 37616.6.2 Antisurge Control Algorithms 37816.6.3 Controlling Limiting Variables 37816.7 Loop Decoupling 37916.8 Conclusions 380Reference 38017 Head-Flow Curve Shape of Centrifugal Compressors 38117.1 Compressor Stage 38117.2 Elements of the Characteristic Shape 38217.2.1 Basic Slope 38217.2.2 Blade Angle 38417.2.3 Fan Law Effect 38517.2.4 Choke Effect 38617.2.5 Mach Number 38717.2.6 Significance of Gas Weight 38717.2.7 Inducer Impeller Effects on Head Output 38817.2.8 Surge 38917.2.9 Vaned Diffusers 39017.2.10 Vaneless Diffusers 39017.2.11 Equivalent Tip Speeds 39117.3 Conclusions 39318 Use of Multiple-Inlet Compressors 39518.1 Critical Selection Criteria 39518.1.1 Head Rise to Surge, Surge Margin, and Overload Margin 39618.1.2 Head per Section 39718.1.3 Compressor Parasitic Flows 39818.1.4 Excess Margins on Other Process Equipment 39918.1.5 Representing Compressor Performance 39918.1.6 Practical Levels of Critical Operating Parameters 39918.2 Design of a Sideload Compressor 40118.2.1 Mixing Area 40218.2.2 Aerodynamics 40318.2.3 Temperature Stratification 40518.3 Testing 40518.3.1 Test Setup 40618.3.2 Instrumentation 40618.3.3 Testing Procedure 40618.3.4 Accuracy of Test Results 40718.3.5 Evaluation of Results 40719 Compressor Performance Testing 40919.1 Performance Testing of New Compressors 40919.1.1 Re-rate Options 41019.1.2 General Guidelines 41019.1.3 Gas Sampling 41119.1.4 Instrumentation 41219.1.5 Sideload Compressors 41419.1.6 Calculation Procedures 41619.2 Shop Testing and Types of Tests 41819.3 Field Testing 42019.4 Predicting Compressor Performance at Other Than As-Designed Conditions 43219.4.1 How Performance Tests Are Documented 43419.4.2 Design Parameters: What Affects Performance 43419.4.3 What to Seek from Vendors’ Documents 43519.4.4 Illustrations and Example 436References 44120 Procurement, Audit, and Asset Management Decisions 44320.1 Incentives to Buy from Knowledgeable and Cooperative Compressor Vendors 44320.2 Industry Standards and Their Purpose 44420.2.1 Typical Scope of Standards 44420.2.2 Disclaimers in Standards 44720.2.3 Going Beyond the Standards 44720.3 Disadvantages of Cheap Process Compressors 44820.4 Audits vs. Reviews 44920.4.1 Staffing and Timing of Audits and Reviews 45020.4.2 Use of Equipment Downtime Statistics 45020.5 Auditing and Reviewing Compressors 45120.6 Compressor Inspection: Extension of the Audit Effort 46520.6.1 Inspection of a Welded Impeller (Wheel) and the Entire Rotor 46620.7 Compressor Installation Specifications 47420.7.1 Field Erection and Installation Specifications for Special-Purpose Machinery 475References 47621 Reliability-Driven Asset Management Strategies 47721.1 Strategy for Reciprocating Compressors 47721.1.1 Process Operating Window 47821.1.2 Breakdown Maintenance 47821.1.3 Time-Based Maintenance 47821.1.4 Equipment Health Monitoring 47921.1.5 Reliability and Maintenance 47921.1.6 Asset Management Strategy 47921.2 Achieving Compressor Asset Optimization 48621.2.1 Input Obtained from Workshops 48621.2.2 Conclusions 496References 497APPENDIX A PROPERTIES OF COMMON GASES 499APPENDIX B SHORTCUT CALCULATIONS AND GRAPHICAL 507COMPRESSOR SELECTION PROCEDURESAPPENDIX C BIBLIOGRAPHY AND LIST OF CONTRIBUTORS 551INDEX 557