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Troubleshooting Vacuum Systems: Steam Turbine Surface Condensers and Refinery Vacuum Towers

ISBN: 978-1-118-29034-7
280 pages
December 2012
Troubleshooting Vacuum Systems: Steam Turbine Surface Condensers and Refinery Vacuum Towers (1118290348) cover image

Vacuum systems are in wide spread use in the petrochemical plants, petroleum refineries and power generation plants. The existing texts on this subject are theoretical in nature and only deal with how the equipment functions when in good mechanical conditions, from the viewpoint of the equipment vendor.  In this much-anticipated volume, one of the most well-respected and prolific process engineers in the world takes on troubleshooting vacuum systems, and especially steam ejectors, an extremely complex and difficult subject that greatly effects the profitability of the majority of the world's refineries.

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Preface xiii

Introduction xv

Definition of Terms xix

Other Books by Author xxiii

1 How Jets Work 1

1.1 The Converging-Diverging Ejector 1

1.2 Interaction of Steam Nozzle with Converging-Diverging Diffuser 5

1.3 Compression Ratio 6

1.4 Converging-Diverging Ejector 7

1.5 Velocity Boost 9

1.6 Surging 10

1.7 Critical Discharge Pressure 11

1.8 Observing the Conversion of Heat to Velocity 12

1.9 Jet Discharge Pressure 13

1.10 Reducing Primary-Jet Discharge Pressure 14

1.11 Bypassing First Stage Ejectors 15

2 Making Field Measurements 17

2.1 Getting Started 17

2.2 How to Unscrew Steel Plugs 23

2.3 Effect of Barometric Pressure on Indicated Vacuum 24

2.4 Use of Piccolo 25

2.5 Measuring Deep Vacuums using an Hg Manometer 27

2.6 Measurement of a Deep Vacuum without Mercury 28

2.7 Measuring Condensibles in Feed to First Stage Ejector 30

2.8 Identifying Loss of Sonic Boost by Sound 31

2.9 Identifying Air Leaks 32

2.10 Air Leaks in Flanges 34

2.11 Vacuum Measurement Units 35

3 Tabulation of Vacuum System Malfunctions 39

3.1 Tidal Flop in Delaware 40

3.2 Critical Discharge Pressure 43

3.3 Fouling in Final Condenser 43

3.4 Reduction in Back Pressure 45

3.5 Loss of LVGO Pan Level 45

3.6 Variations in Cooling Water Temperature 47

3.7 Multi-Component Malfunctions 50

3.8 Partial Tabulation of Vacuum System Malfunctions 51

4 Effect of Water Partial Pressure on Jet Efficiency 55

4.1 Vapor Pressure of Water Limits Vacuum 56

4.2 Reminder about Water Partial Pressure 59

4.3 Air Leaks in Steam Turbine Surface Condensers 59

4.4 Variable Cooling Water Temperature 60

4.5 Loss of Sonic Boost 60

4.6 Relative Jet Efficiency 62

4.7 Definition of "Vacuum Breaking" 63

4.8 Critical Discharge Pressure Exceeded 64

5 Air Leaks 67

5.1 Upper Explosive Limits 67

5.2 How to Find Air Leaks 68

5.3 Diffuser Air Leaks 69

5.4 Air Leaks on Vacuum Towers 70

5.5 Air Leaks in Heater Transfer Lines 71

5.6 Air Leaks - Turbine Mechanical Seal 72

6 Sources and Disposal of Hydrocarbon Off-Gas 75

6.1 Evolution of Cracked Gas 75

6.2 Sources of Cracked Gas 78

6.3 Cracked Gas Evolution from Boot 80

6.4 Air Equivalent 81

6.5 Overloading Vacuum Jets 84

6.6 Excess Cracked Gas Flow 85

6.7 Field Checking Gas Flow Meter in Vacuum Service 85

6.8 Surging 3rd Stage Jet Bogs Down Primary Jet 89

6.9 Exchanger Leaks Overloads Jets 90

6.10 Poor Vacuum Tower Feed Stripping 92

6.11 Level Connection Purges and Pump Mechanical Seal Gas 94

6.12 Effect of Heater Outlet Temperature 95

6.13 Extracting H2S from Vacuum Tower Off-Gas Upstream of Ejectors 97

6.14 Disposal of Seal Drum Off-Gas 99

6.15 Fouling of Waste Gas Burner 100

7 Motive Steam Conditions 101

7.1 Effect of Wet Steam 102

7.2 Water in Motive Steam 103

7.3 The Tale of Weak Steam 104

7.4 Internal Freezing of Steam Nozzle 105

7.5 High Pressure, Superheated Motive Steam 108

7.6 Effect of Moisture Content of Saturated Steam on Temperature 108

7.7 Steam Pressure Affects Vacuum 109

7.8 Effect of Superheated Steam 111

8 Mechanical Defects of Ejectors 113

8.1 Steam Nozzle Testing 113

8.2 Other Mechanical Defects of Jets 114

8.3 Fouled Steam Nozzles 117

8.4 Diffuser Erosion 118

8.5 Repair of Ejector Body 119

8.6 Changing Worn Steam Nozzles 119

8.7 Restoring Critical Flow 120

9 Condenser Fouling and Cleaning 123

9.1 Fouling Mechanism in Condensers for Refinery Vacuum Towers 123

9.2 Fouling Due to Chemical Additives 124

9.3 Minimizing Condenser Fouling in Vacuum Towers 125

9.4 Fouled Pre-condenser 126

9.5 Fixed Tube Sheet Condensers 128

9.6 Cleaning Condensers On-Stream 129

9.7 Optimum Condenser Bundle Configuration 130

9.8 Chemically Cleaning Condensers 130

9.9 Ball Cleaning Condenser Tubes 131

9.10 Corrosion Control by Better Desalting 132

10 Pressure Control of Vacuum Towers 135

10.1 Positive Feedback Loop 141

11 Condenser Cooling Water Flow 143

11.1 Cooling Water Flow Configuration 143

11.2 Air Evolving from Cooling Water Reduces Cooling Water Flow 145

11.3 Cooling Water Pressure to Surface Condensers 148

11.4 Tube Leaks 149

12 Condensate Back-Up in Condensers 151

12.1 Undersized Condenser Drain Nozzle 153

12.2 Seal Drum Level Indication 155

12.3 Leaking Gauge Glass on Surface Condenser Boot 157

12.4 Condensate Pump Cavitation Due to Air Leaks 161

12.5 Condensate Back-Up in Surface Condenser Boot 162

12.6 Experiment with Condensate Back-Up 165

12.7 Condensate Back-Up 166

13 Seal Leg Drainage 169

13.1 Sludge Accumulation in Seal Drum 169

13.2 Seal Leg Leak Inside Seal Drum 171

13.3 Seal Leg Flange Leak Outside Seal Drum 174

13.4 Seal Leg Design 177

13.5 Inadequate Seal Leg Length for Hydrocarbons 180

13.6 Inadequate Seal Leg Capacity 182

13.7 High Back-Pressure from Seal Drum 183

13.8 Detecting Condensate Back-Up in Seal Legs 184

13.9 Condensate Back-Up Due to Air Leak in Barometric Drain Line 186

13.10 Seal Drum Design 188

13.11 Seal Drum Fills with Corrosive Deposits 189

13.12 Seal Drum Design Tips 193

13.13 An Unfortunate Incident 194

14 Other Types of Vacuum Equipment 197

14.1 Hogging Jets 197

14.2 Use of Hogging Jet on Surface Condenser 198

14.3 Liquid Seal Ring Compressors 200

14.4 Gas Ejectors 202

14.5 Liquid Ejectors 203

14.6 Ejector Compression Efficiency 204

15 Air Baffle and Impingement Plate in Surface Condensers 205

15.1 Mechanical Configuration of Seal Strips 206

15.2 Corroded Brass Seal Strips 208

15.3 Air or Vapor Baffle Leak 208

15.4 Identifying Defective Seal Strips 209

15.5 Air Baffle Clearance 211

15.6 Fouling Mechanism in Vacuum Tower Surface Condensers 212

15.7 Surface Condenser Impingement Plate 212

15.8 Oversized Impingement Plate 214

15.9 Impingement Plates as Vapor Distributors 215

16 Optimizing Vacuum Tower Operation 217

16.1 Steam to Heater Passes 218

16.2 LVGO Pan Level Loss Causes a Loss in Vacuum 220

16.3 Carry-Over of LVGO Pumparound Spray 226

16.4 Optimizing Vacuum Tower Top Temperature 227

16.5 Plugged Vacuum Tower Top Demister 229

16.6 Bypassing Primary Ejector 232

17 Frequently Asked Questions 233

17.1 Vacuum Systems 233

The Norm Lieberman DVD/Video Library 243

Index 247

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Norm Lieberman is one of the most well-known and respected process engineers in history. With over 47 years of experience and eight often-quoted and often-used books to his credit, he has left and continues to leave a lasting impression on the energy industry. His contribution to the industry is considerable, and troubleshooting vacuum systems is the single biggest part of his business. With a writing style that is unique to technical books, he brings a no-nonsense and practical approach to his subjects.
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