Troubleshooting Vacuum Systems Scrivener Publishing 100 Cummings Center, Suite 541J Beverly, MA 01915-6106 Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected]) Troubleshooting Vacuum Systems Steam Turbine Surface Condensers and Refinery Vacuum Towers Authored by Norman P. Lieberman Φ SSccrrii vener Publishing )WILEY Copyright © 2012 by Scrivener Publishing LLC. All rights reserved. Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts. Published simultaneously in Canada. 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Infrared temperature sens- ing gun in hand, Liz has provided innumerable surveys for steam ejector and inter-stage condenser surface temperatures for vacuum systems at the most remote corners and hostile environments of our little home planet. Contents 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 vn viii CONTENTS 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 CONTENTS ix 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 H S from Vacuum Tower 2 Off-Gas Upstream of Ejectors 97 6.14 Disposal of Seal Drum Off-Gas 99 6.15 Fouling of Waste Gas Burner 100 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 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 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 x CONTENTS 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 CONTENTS xi 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