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1 Design for Overpressure and Underpressure Protection Slide ShowExitSlides with Text

2 SLIDE PRESENTATION Design for Overpressure and Underpressure Protection HOME NEXT

3 Outline Introduction Causes of Overpressure and Underpressure Reliefs Effluent Handling Systems for Reliefs Runaway Reactions Overpressure Protection for Internal Fires and Explosions Introduction Causes of Overpressure and Underpressure Reliefs Effluent Handling Systems for Reliefs Runaway Reactions Overpressure Protection for Internal Fires and Explosions Introduction Reliefs Runaways Safeguards

4 For Further Information: Refer to the Appendix Supplied with this Presentation NEXT PREVIOUS TextHome

5 Causes of Overpressure Operating Problem Equipment Failure Process Upset External Fire Utility Failures Operating Problem Equipment Failure Process Upset External Fire Utility Failures Home NEXT PREVIOUS Text

6 Causes of Underpressures Operating Problem Equipment Failure Operating Problem Equipment Failure Home NEXT PREVIOUS Text

7 Presentation 1 of 3: Reliefs Causes of Overpressure/Underpressure Causes of Overpressure/Underpressure Presentation 1: Reliefs Presentation 1: Reliefs Presentation 2: Runaways Presentation 2: Runaways Presentation 3: Safeguards Presentation 3: Safeguards Home NEXT PREVIOUS Text

8 Pressure Relief Devices Spring-Loaded Pressure Relief Valve Rupture Disc Buckling Pin Miscellaneous Mechanical Spring-Loaded Pressure Relief Valve Rupture Disc Buckling Pin Miscellaneous Mechanical Home NEXT PREVIOUS Text

9 Spring-Loaded Pressure Relief Valve Home NEXT PREVIOUS Text

10 Rupture Disc Home NEXT PREVIOUS Text

11 Buckling Pin Relief Valve Closed Pressure Below Set Pressure Full Open Pressure at or Above Set Pressure (Buckles in Milliseconds at a Precise Set Pressure) Home NEXT PREVIOUS Text

12 Simple Mechanical Pressure Relief Home NEXT PREVIOUS Text

13 Types of Spring-Loaded Pressure Reliefs Safety Valves for Gases and Vapors Relief Valves for Liquids Safety Relief Valves for Liquids and/or Gases Safety Valves for Gases and Vapors Relief Valves for Liquids Safety Relief Valves for Liquids and/or Gases Home NEXT PREVIOUS Text

14 Types of Safety Valves Conventional Balanced Bellows, and Pilot-Operated Conventional Balanced Bellows, and Pilot-Operated Home NEXT PREVIOUS Text

15 Conventional Safety Valve Home NEXT PREVIOUS Text

16 Balanced Bellows Safety Valve Home NEXT PREVIOUS Text

17 Pilot-Operated Safety Valve Home NEXT PREVIOUS Text

18 Types of Relief Valves Conventional Balanced Bellows Conventional Balanced Bellows Home NEXT PREVIOUS Text

19 Types of Rupture Discs Metal Graphite Composite Others Metal Graphite Composite Others Home NEXT PREVIOUS Text

20 Rupture Disc and Pressure Relief Valve Combination Home NEXT PREVIOUS Text

21 Vacuum Relief Devices Vacuum Relief Valves Rupture Discs Conservation Vents Manhole Lids Pressure Control Vacuum Relief Valves Rupture Discs Conservation Vents Manhole Lids Pressure Control Home NEXT PREVIOUS Text

22 Conservation Vent Home NEXT PREVIOUS Text

23 Pressure or Vacuum Control Add Air or Nitrogen Maintain Appropriately Add Air or Nitrogen Maintain Appropriately Home NEXT PREVIOUS Text

24 Relief Servicing Inspection Testing Inspection Testing Home NEXT PREVIOUS Text

25 Relief Discharges To Atmosphere Prevented Effluent System To Atmosphere Prevented Effluent System Home NEXT PREVIOUS Text

26 Effluent Systems Knock-Out Drum Catch Tank Cyclone Separator Knock-Out Drum Catch Tank Cyclone Separator Home NEXT PREVIOUS Text

27 Effluent System (continued) Condenser Quench Tank Scrubber Flares/Incinerators Condenser Quench Tank Scrubber Flares/Incinerators Home NEXT PREVIOUS Text

28 Effluent Handling System Home NEXT PREVIOUS Text

29 Presentation 2 of 3: Runaways Home NEXT PREVIOUS Text Causes of Overpressure/Underpressure Causes of Overpressure/Underpressure Presentation 1: Reliefs Presentation 1: Reliefs Presentation 2: Runaways Presentation 2: Runaways Presentation 3: Safeguards Presentation 3: Safeguards

30 Runaway Reaction Temperature Increases Reaction Rate Increases Pressure Increases Temperature Increases Reaction Rate Increases Pressure Increases Home NEXT PREVIOUS Text

31 Causes of Runaway Reactions Self-Heating Sleeper Tempered Gassy Hybrid Self-Heating Sleeper Tempered Gassy Hybrid Characteristics of Runaway Home NEXT PREVIOUS Text

32 Self-Heating Reaction Loss of Cooling Unexpected Addition of Heat Too Much Catalyst or Reactant Operator Mistakes Too Fast Addition of Catalyst or Reactant Loss of Cooling Unexpected Addition of Heat Too Much Catalyst or Reactant Operator Mistakes Too Fast Addition of Catalyst or Reactant Home NEXT PREVIOUS Text

33 Sleeper Reactions Reactants Added But Not Mixed (Error) Reactants Accumulate Agitation Started.. Too Late Reactants Added But Not Mixed (Error) Reactants Accumulate Agitation Started.. Too Late Home NEXT PREVIOUS Text

34 Tempered Reaction Heat Removed by Evaporation Heat Removal Maintains a Constant Temperature Heat Removed by Evaporation Heat Removal Maintains a Constant Temperature Home NEXT PREVIOUS Text

35 Gassy System No Volatile Solvents Gas is Reaction Product No Volatile Solvents Gas is Reaction Product Home NEXT PREVIOUS Text

36 Hybrid System Tempered Gassy Tempered Gassy Home NEXT PREVIOUS Text

37 Reliefs for Runaway Reactions Two Phase (or Three Phases: Liquid, Vapor, and Solid) Flow Relief Area: 2 to 10 Times the Area of a Single Gaseous Phase Two Phase (or Three Phases: Liquid, Vapor, and Solid) Flow Relief Area: 2 to 10 Times the Area of a Single Gaseous Phase Home NEXT PREVIOUS Text

38 Two Phase Flow Home NEXT PREVIOUS Text

39 Relief Valve Sizing Methodology Special Calorimeter Data Special Calculation Methods Special Calorimeter Data Special Calculation Methods Home NEXT PREVIOUS Text

40 Characterization of Runaway Reactions ARC VSP RSST ARC VSP RSST APTAC PHI-TEC Dewars Home NEXT PREVIOUS Text

41 Presentation 3 of 3: Safeguards Home NEXT PREVIOUS Text Causes of Overpressure/Underpressure Causes of Overpressure/Underpressure Presentation 1: Reliefs Presentation 1: Reliefs Presentation 2: Runaways Presentation 2: Runaways Presentation 3: Safeguards Presentation 3: Safeguards

42 Safety Interlocks Safeguard Maintenance System Short-Stopping Safety Interlocks Safeguard Maintenance System Short-Stopping Home NEXT PREVIOUS Text

43 Safety Interlocks Agitator Not Working: Stop Monomer Feed and Add Full Cooling Abnormal Temperature: Stop Monomer Feed and Add Full Cooling Agitator Not Working: Stop Monomer Feed and Add Full Cooling Abnormal Temperature: Stop Monomer Feed and Add Full Cooling Home NEXT PREVIOUS Text

44 Safety Interlocks (continued) Abnormal Pressure: Stop Monomer Feed and Add Full Cooling Abnormal Heat Balance: Stop Monomer Feed and Add Full Cooling Abnormal Conditions: Add Short-Stop Abnormal Pressure: Stop Monomer Feed and Add Full Cooling Abnormal Heat Balance: Stop Monomer Feed and Add Full Cooling Abnormal Conditions: Add Short-Stop Home NEXT PREVIOUS Text

45 Safeguard Maintenance System Routine Maintenance Management of Change Mechanical Integrity Checks Records Routine Maintenance Management of Change Mechanical Integrity Checks Records Home NEXT PREVIOUS Text

46 Short-Stops to Stop Reaction Add Reaction Stopper Add Agitation with No Electrical Power Add Reaction Stopper Add Agitation with No Electrical Power Home NEXT PREVIOUS Text

47 Protection for Internal Fires and Explosions Deflagrations Detonations Deflagrations Detonations Home NEXT PREVIOUS Text

48 Protection Methods for Internal Fires and Explosions Deflagration Venting Deflagration Suppression Containment Deflagration Venting Deflagration Suppression Containment Home NEXT PREVIOUS Text

49 Protection Methods for Internal Fires and Explosions (continued) Reduction of Oxidant Reduction of Combustible Flame Front Isolation Reduction of Oxidant Reduction of Combustible Flame Front Isolation Home NEXT PREVIOUS Text

50 Protection Methods for Internal Fires and Explosions (continued) Spark Detection and Extinguishing Flame Detection and Extinguishing Water Spray and Deluge Systems Spark Detection and Extinguishing Flame Detection and Extinguishing Water Spray and Deluge Systems Home NEXT PREVIOUS Text

51 Deflagration Venting Vent Area via NFPA 68 Vent Safely Vent Area via NFPA 68 Vent Safely Home NEXT PREVIOUS Text

52 Vent of Gas Deflagration Home NEXT PREVIOUS Text

53 Vent of Dust Deflagration Home NEXT PREVIOUS Text

54 Deflagration Suppression System Home NEXT PREVIOUS Text

55 Containment Prevent Rupture and Vessel Deformation Prevent Rupture but Deform Vessel Prevent Rupture and Vessel Deformation Prevent Rupture but Deform Vessel Home NEXT PREVIOUS Text

56 Reduction of Oxidant Vacuum Purging Pressure Purging Sweep-Through Purging Vacuum Purging Pressure Purging Sweep-Through Purging Home NEXT PREVIOUS Text

57 Reduction of Combustible Dilution with Air NFPA 69 Dilution with Air NFPA 69 Home NEXT PREVIOUS Text

58 Flame Front Isolation Home NEXT PREVIOUS Text

59 Spark/Flame Detection and Extinguishing Home NEXT PREVIOUS Text

60 Water Spray or Deluge Systems Home NEXT PREVIOUS Text

61 Deluge System Home NEXT PREVIOUS Text

62 Conclusion Home NEXT PREVIOUS Text

63 End of Slide Presentation Home NEXT PREVIOUS Causes of Overpressure/Underpressure Causes of Overpressure/Underpressure Presentation 1: Reliefs Presentation 1: Reliefs Presentation 2: Runaways Presentation 2: Runaways Presentation 3: Safeguards Presentation 3: Safeguards Text

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65 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home SLIDES WITH TEXT Design for Overpressure and Underpressure Protection This presentation includes technical information concerning the design for overpressure and underpressure protection. The presentation is designed to help students and engineers to: Slide

66 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Design for Overpressure and Underpressure Protection Understand the technologies, special engineering devices, and methods that are used for the protection against overpressure and underpressure (vacuum) incidents, Slide

67 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Design for Overpressure and Underpressure Protection Understand the root causes of overpressure and underpressure incidents, and Design plants with the appropriate features to protect against overpressure and underpressure incidents. Slide

68 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Six Sections 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions This presentation is divided into six sections: Slide

69 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Six Sections 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions The “Introduction” button on your left will lead you to this introduction and an explaination of the Causes of Overpressure and Underpressure SlideHome

70 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Six Sections 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions The “Reliefs” Button sends you to Sections 3 and 4, covering Reliefs and Effluent Handling Systems for Reliefs SlideHome

71 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Six Sections 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions The “Runaways” Button leads to a discussion on Runaway Reactions, and... SlideHome

72 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Six Sections 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions 1.Introduction 2.Causes of Overpressure and Underpressure 3.Reliefs 4.Effluent Handling Systems for Reliefs 5.Runaway Reactions, and 6.Overpressure Protection for Internal Fires and Explosions The “Safeguards” Button will take you to a section on Overpressure Protection fot Internal Fires and Explosions SlideHome

73 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Appendix Contains Detailed Information This design package includes an appendix with detailed information for each of the sections of this presentation. The appendix also includes an extensive list of relevant references. Slide

74 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Overpressure Operating Problem The major causes of overpressure include: Operating problems or mistakes such as an operator mistakenly opening or closing a valve to cause the vessel or system pressure to increase. An operator, for example, may adjust a steam regulator to give pressures exceeding the maximum allowable working pressure (MAWP) of a steam jacket. Slide

75 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Overpressure Operating Problem Although the set pressure is usually at the MAWP, the design safety factors should protect the vessel for higher pressures; a vessel fails when the pressure is typically several times the MAWP. Slide

76 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Overpressure Operating Problem Equipment Failure Operating Problem Equipment Failure Equipment failures; for example a heat exchanger tube rupture that increases the shell side pressure beyond the MAWP. Although the set pressure is usually the MAWP, the design safety factors should protect the vessel for higher pressures; a vessel fails when the pressure is typically several times the MAWP. Slide

77 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Overpressure Operating Problem Equipment Failure Process Upset External Fire Utility Failures Operating Problem Equipment Failure Process Upset External Fire Utility Failures Process upset; for example a runaway reaction causing high temperatures and pressures. External heating, such as, a fire that heats the contents of a vessel giving high vapor pressures, and Utility failures, such as the loss of cooling or the loss of agitation causing a runaway reaction. Slide

78 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Underpressures The causes of underpressure or the inadvertent creation of a vacuum are usually due to operating problems or equipment failures. Slide

79 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Underpressures Operating Problem Operating problems include mistakes such as pumping liquid out of a closed system, or cooling and condensing vapors in a closed system. Slide

80 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Underpressures Operating Problem Equipment Failure Operating Problem Equipment Failure Equipment failures include an instrument malfunction (e.g. vacuum gage) or the loss of the heat input of a system that contains a material with a low vapor pressure. Slide

81 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Part 1 of 3: Reliefs Slide

82 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Pressure Relief Devices Pressure relief devices are added to process equipment to prevent the pressures from significantly exceeding the MAWP (pressures are allowed to go slightly above the MAWP during emergency reliefs). Slide

83 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Pressure Relief Devices Spring-Loaded Pressure Relief Valve Rupture Disc Buckling Pin Miscellaneous Mechanical Spring-Loaded Pressure Relief Valve Rupture Disc Buckling Pin Miscellaneous Mechanical The pressure relief devices include spring-loaded pressure relief valves, rupture discs, buckling pins, and miscellaneous mechanical devices. Slide

84 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Spring-Loaded Pressure Relief Valve This is a sketch of a spring-loaded pressure relief valve. As the pressure in the vessel or pipeline at point A exceeds the pressure created by the spring, the valve opens. The relief begins to open at the set pressure which is usually at or below the MAWP; this pressure is usually set at the MAWP. Slide

85 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc This is a sketch of a rupture disc. In this case the disc ruptures when the pressure at A exceeds the set pressure. Recognize, however, that it is actually the differential pressure (A-B), that ruptures the disc. Slide

86 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Buckling Pin Relief Valve Closed Pressure Below Set Pressure Full Open Pressure at or Above Set Pressure (Buckles in Milliseconds at a Precise Set Pressure) This sketch shows a buckling pin pressure relief valve. As shown, when the pressure exceeds the set pressure, the pin buckles and the vessel contents exit through the open valve. The rupture disc and the buckling pin relief valves stay open after they are opened. Slide

87 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Buckling Pin Relief Valve Closed Pressure Below Set Pressure Full Open Pressure at or Above Set Pressure (Buckles in Milliseconds at a Precise Set Pressure) The spring operated valves close as the pressure decreases below the “blowdown” pressure. The blowdown pressure is the difference between the set pressure and closing pressure. Slide

88 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Simple Mechanical Pressure Relief A simple mechanical pressure relief is a weighted man-way cover as shown in this sketch. Another mechanical relief is a U- tube filled with water (or equivalent). Slide

89 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Types of Spring-Loaded Pressure Reliefs Safety Valves for Gases and Vapors Relief Valves for Liquids Safety Relief Valves for Liquids and/or Gases Safety Valves for Gases and Vapors Relief Valves for Liquids Safety Relief Valves for Liquids and/or Gases There are three types of spring-loaded pressure relief valves: Safety valves are specifically designed for gases. Relief valves are designed for liquids, and Safety relief valves are designed for liquids and/or gases. Slide

90 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Types of Safety Valves Conventional Balanced Bellows, and Pilot-Operated Conventional Balanced Bellows, and Pilot-Operated There are three types of safety valves; that is: Conventional, Balanced bellows, and Pilot-operated. Slide

91 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Conventional Safety Valve A conventional safety valve is designed to provide full opening with minimum overpressure. The disc is specially shaped to give a “pop” action as the valve begins to open. Slide

92 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Balanced Bellows Safety Valve A balanced bellows safety valve is specially designed to reduce the effect of the back pressure on the opening pressure. As illustrated in this sketch the differential pressure that is required to open the valve is the pressure inside the vessel minus the atmospheric pressure. Slide

93 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Balanced Bellows Safety Valve The bellows design allows the outside air and pressure to be on the downstream side of the valve seal. Once the relief is open, then the flow is a function of the differential pressure A-B. Slide

94 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Pilot-Operated Safety Valve A pilot-operated safety valve is a spring-loaded valve. As illustrated, the vessel pressure helps to keep the valve closed. When the pressure exceeds the set pressure (or the spring pressure), the pressure on top of the valve is vented and the valve opens. Slide

95 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Pilot-Operated Safety Valve The set pressure of this type of valve can be closer to the operating pressure compared to conventional and balanced bellows valves. The disadvantages, however, are (a) the process fluid needs to be clean, (b) the seals must be resistant to the fluids, and (c) the seals and valves must be appropriately maintained. Slide

96 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Pilot-Operated Safety Valve These disadvantages are also true for spring operated reliefs. Pilot-operated valves are not used in liquid service; they are normally used in very clean and low pressure applications. Slide

97 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Types of Relief Valves Conventional Balanced Bellows Conventional Balanced Bellows Relief valves (for liquid service) are either the conventional or the balanced bellows types. Slide

98 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Types of Rupture Discs Metal Graphite Composite Others Metal Graphite Composite Others As illustrated, there are many different types of rupture discs. They are especially applicable for very corrosive environments; for example: discs made of carbon or Teflon coating are used for corrosive service. Slide

99 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Types of Rupture Discs Metal Graphite Composite Others Metal Graphite Composite Others A rupture disc that is used for pressure reliefs may need a specially designed mechanical support if it is also used in vacuum service. Slide

100 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc and Pressure Relief Valve Combination Rupture discs, as illustrated, are sometimes used in combination with a spring operated relief device. In this case the disc gives a positive seal compared to the disc-to-seal design of a spring operated valve. Slide

101 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc and Pressure Relief Valve Combination This is useful when handling very toxic materials where even a very small release (through the seal) may be hazardous, or when handling materials that polymerize. The spring operated relief following the rupture disc reseats when the pressure drops below the blow-down pressure. Slide

102 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc and Pressure Relief Valve Combination This design, therefore, stops the discharge from the vessel. The discharge is not stopped if only a rupture disc is used. This design (rupture disc followed by a spring-operated relief) is discouraged by some practitioners. Slide

103 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc and Pressure Relief Valve Combination In this design, as illustrated, a pressure detection device (per ASME Code), e.g., a pressure indicator, needs to be placed between the disc and the spring-operated valve. This pressure reading is checked periodically to be sure the rupture disc has its mechanical integrity. Slide

104 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc and Pressure Relief Valve Combination A pin-hole leak in the rupture disc could increase the pressure on the discharge side of the disc. This is a major problem because it increases the relief pressure, that is: the differential pressure across the disc is the rupturing mechanism. Slide

105 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Rupture Disc and Pressure Relief Valve Combination Another major problem with this design is the possibility that a piece of the rupture disc could plug the discharge orifice of the spring operated relief. This problem is prevented by specifying a rupture disc that will maintain its integrity when it is ruptured; that is, non-fragmenting. Slide

106 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Vacuum Relief Devices Vacuum Relief Valves Rupture Discs Conservation Vents Manhole Lids Pressure Control Vacuum Relief Valves Rupture Discs Conservation Vents Manhole Lids Pressure Control Vacuum relief devices are: vacuum relief valves, rupture discs, conservation vents, manhole lids designed for vacuum relief, and pressure control. Slide

107 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Conservation Vent A conservation vent is illustrated in this sketch. As shown, it is designed to relieve a pressure usually for pressures in the region of 6 inches of water. It is also designed to let air into the vessel to prevent a vacuum, usually a vacuum no more than 4 inches of water. Slide

108 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Pressure or Vacuum Control Add Air or Nitrogen Maintain Appropriately Add Air or Nitrogen Maintain Appropriately Sometimes pressure or vacuum control systems are used to add air or nitrogen to the vessel to maintain a slight pressure. In this case, the system needs to be appropriately maintained because a malfunction could result in an overpressure or underpressure. In either case the consequence could be a ruptured vessel. Slide

109 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Relief Servicing Inspection Testing Inspection Testing Every relief device needs to be inspected and tested before installation and then at predetermined intervals during its lifetime. The interval depends on the service history, vendor recommendations, and regulatory requirements, but it is usually once a year. Slide

110 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Relief Servicing Inspection Testing Inspection Testing Operating results and experience may indicate shorter or longer intervals. Records must be carefully maintained for every inspection and test, and for the entire life of the plant. Slide

111 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Relief Discharges To Atmosphere Discharges from pressure relief devices may be sent directly to the atmosphere if they are innocuous, discharged in a safe manner, and regulations permit it. Slide

112 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Relief Discharges To Atmosphere Prevented To Atmosphere Prevented An additional option is to prevent releases by (a) designing vessels with high MAWPs to contain all overpressure scenarios, or (b) add a sufficient number of safeguards and/or controls to make overpressure scenarios essentially impossible. Slide

113 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Relief Discharges To Atmosphere Prevented Effluent System To Atmosphere Prevented Effluent System The third option is to design an effluent system to capture all nocuous liquids and gases. Slide

114 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Effluent Systems Knock-Out Drum Catch Tank Cyclone Separator Knock-Out Drum Catch Tank Cyclone Separator An effluent system may contain a Knock-out drum Catch tank Cyclone separator Slide

115 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Effluent System (continued) Condenser Quench Tank Scrubber Flares/Incinerators Condenser Quench Tank Scrubber Flares/Incinerators Condenser Quench tank Scrubber, and/or Flares or incinerators An effluent handling system may have any combination of the above unit operations. Slide

116 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Effluent Handling System One effluent handling system is illustrated in this sketch. Every element of an effluent system needs to be designed very carefully. The design requires detailed physical and chemical properties, and the correct design methodology for each unit operation. Slide

117 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Effluent Handling System It should also be recognized that it is important to size the relief appropriately, because the size of the entire effluent system is based on this discharge rate. The design methodology is in the references noted in the Appendix of this package. Slide

118 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Part 2 of 3: Runaways Slide

119 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Runaway Reaction Temperature Increases Reaction Rate Increases Pressure Increases Temperature Increases Reaction Rate Increases Pressure Increases A runaway reaction is an especially important overpressure scenario. A runaway reaction has an accelerating rate of temperature increase, rate of reaction increase, and usually rate of pressure increase. The pressure, of course, increases if the reaction mass has a volatile substance, such as, a solvent or a monomer; or if one of the reaction products is a gas. Slide

120 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Runaway Reactions Self-Heating Sleeper Tempered Gassy Hybrid Self-Heating Sleeper Tempered Gassy Hybrid Characteristics of Runaway In general, there are two causes of runaway reactions (self- heating and sleeper) and three characteristics of runaways (tempered, gassy, and hybrid). Slide

121 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Causes of Runaway Reactions Self-Heating Sleeper Tempered Gassy Hybrid Self-Heating Sleeper Tempered Gassy Hybrid Characteristics of Runaway When protecting a system for overpressures due to runaway reactions the engineer needs to know the type of runaway and needs to characterize the behavior of the specific runaway with a special calorimeter. This specific methodology is described in this section of this presentation. Slide

122 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Self-Heating Reaction Loss of Cooling Unexpected Addition of Heat Too Much Catalyst or Reactant Operator Mistakes Too Fast Addition of Catalyst or Reactant Loss of Cooling Unexpected Addition of Heat Too Much Catalyst or Reactant Operator Mistakes Too Fast Addition of Catalyst or Reactant One self-heating scenario occurs when the reaction is exothermic and a loss of cooling gives an uncontrolled temperature rise. A few causes of self-heating scenarios are shown. Slide

123 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Sleeper Reactions Reactants Added But Not Mixed (Error) Reactants Accumulate Agitation Started.. Too Late Reactants Added But Not Mixed (Error) Reactants Accumulate Agitation Started.. Too Late Sleeper reactions are usually the result of an operator error. Two examples include: (a) the addition of two immiscible reactants when the agitator is mistakenly in the off position, and (b) the addition of a reactant to the reaction mass when the temperature is mistakenly lower than that required to initiate the reaction. Slide

124 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Sleeper Reactions Reactants Added But Not Mixed (Error) Reactants Accumulate Agitation Started.. Too Late Reactants Added But Not Mixed (Error) Reactants Accumulate Agitation Started.. Too Late In these cases the runaway is initiated by starting the agitator and adding heat respectively. Slide

125 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Tempered Reaction Heat Removed by Evaporation Heat Removal Maintains a Constant Temperature Heat Removed by Evaporation Heat Removal Maintains a Constant Temperature Tempered runaway reactions maintain their temperature when the energy exiting the relief device is equal to the energy generated in the reactor due to the exothermic reaction. The reaction heat is absorbed by the evaporation of the volatile components. The vapor pressure in a tempered system can typically be characterized by an Antoine type equation. Slide

126 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Gassy System No Volatile Solvents Gas is Reaction Product No Volatile Solvents Gas is Reaction Product A system that is characterized as “gassy” has no volatile solvents or reactants. The pressure build-up is due to the generation of noncondensible gas such as N 2 or CO 2. Slide

127 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Hybrid System Tempered Gassy Tempered Gassy A hybrid system is the combination of a tempered and a gassy system. Under runaway conditions, the pressure increases due to the vapor pressure of the volatile components as well as from the generation of noncondensible gaseous reaction products. Slide

128 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Reliefs for Runaway Reactions Two Phase (or Three Phases: Liquid, Vapor, and Solid) Flow Under runaway conditions, when the relief device opens, the relief discharge is a foam; that is, the gases are entrained with the liquid. Slide

129 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Reliefs for Runaway Reactions Two Phase (or Three Phases: Liquid, Vapor, and Solid) Flow To maintain a constant temperature in the reactor (i.e. control the runaway reaction), the relief valve is sized to remove all the heat generated from the exothermic reaction via the heat removed with the discharged mass, which is typically a foam. Detailed information on runaway reactions is found in the appendix. Slide

130 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Reliefs for Runaway Reactions Two Phase (or Three Phases: Liquid, Vapor, and Solid) Flow Relief Area: 2 to 10 Times the Area of a Single Gaseous Phase Two Phase (or Three Phases: Liquid, Vapor, and Solid) Flow Relief Area: 2 to 10 Times the Area of a Single Gaseous Phase The required relief area to remove this heat with the foam is two to ten times the area that would be required by releasing a single gaseous phase. Slide

131 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Two Phase Flow This is a picture that illustrates the two-phase flow characteristics of a relief discharge due to a runaway reaction. As illustrated, the discharge is similar to the release of foam from a freshly opened bottle of pop after being shakened. If the relief is not designed for two-phase flow, the pressures would increase rapidly and the vessel could rupture. Slide

132 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Relief Valve Sizing Methodology Special Calorimeter Data Special Calculation Methods Special Calorimeter Data Special Calculation Methods The relief valve sizing methodology for runaway reactions is very complex. It requires the characterization of the runaway reaction using a specially designed calorimeter. Relief valve sizing, additionally, requires special calculation methods that are described in the Appendix of this package. Slide

133 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Characterization of Runaway Reactions The characterization of runaway reactions includes the determination of the rates of rise of the temperature and pressure under adiabatic conditions. The test results also characterize the reaction type, that is, tempered, gassy, and/or a hybrid system. Slide

134 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Characterization of Runaway Reactions ARC VSP RSST ARC VSP RSST Various calorimeters are used for this characterization: The accelerating rate calorimeter (ARC) The vent sizing package (VSP) The reactive system screening tool (RSST) Slide

135 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Characterization of Runaway Reactions ARC VSP RSST ARC VSP RSST APTAC PHI-TEC Dewars The automated pressure-tracking adiabatic calorimeter (APTAC) The Phi-Tec, and Dewars. Each of these calorimeters have advantages and disadvantages that need to be understood when studying a specific system. Slide

136 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Part 3 of 3: Safeguards Slide

137 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Safeguards This section of the presentation covers safeguards. Safeguards include the methods and controls used to prevent runaways. As illustrated previously, a containment system (a safeguard), can be very complex and expensive. Alternatively, a series of safeguards may be justified. Slide

138 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Safeguards Safety Interlocks Safeguard Maintenance System Short-Stopping Safety Interlocks Safeguard Maintenance System Short-Stopping Safeguards include safety interlocks, safeguard maintenance system, and/or short-stopping. Slide

139 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Safety Interlocks Agitator Not Working: Stop Monomer Feed and Add Full Cooling Abnormal Temperature: Stop Monomer Feed and Add Full Cooling Agitator Not Working: Stop Monomer Feed and Add Full Cooling Abnormal Temperature: Stop Monomer Feed and Add Full Cooling The list of alternative interlocks is fairly extensive. Usually more than one interlock and some redundancy and diversity is required for each runaway scenario. As the number of interlocks increases, the reliability of the system increases. These are examples of safety interlocks for a semibatch polymerization reactor. Slide

140 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Safety Interlocks (continued) Abnormal Pressure: Stop Monomer Feed and Add Full Cooling Abnormal Heat Balance: Stop Monomer Feed and Add Full Cooling Abnormal Conditions: Add Short-Stop Abnormal Pressure: Stop Monomer Feed and Add Full Cooling Abnormal Heat Balance: Stop Monomer Feed and Add Full Cooling Abnormal Conditions: Add Short-Stop This is a list of additional interlocks. Other interlocks (manual) that are not on this list include: gages with manual shutdowns, and alarms with manual shutdowns. Slide

141 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Safeguard Maintenance System Routine Maintenance Management of Change Mechanical Integrity Checks Records Routine Maintenance Management of Change Mechanical Integrity Checks Records A safeguard maintenance system includes routine maintenance, management of change, mechanical integrity checks, and the appropriate records. These are the steps that are required to be sure the safeguards and interlocks perform appropriately under emergency conditions and/or potential runaway reaction scenarios. Slide

142 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Safeguard Maintenance System Routine Maintenance Management of Change Mechanical Integrity Checks Records Routine Maintenance Management of Change Mechanical Integrity Checks Records The maintenance of safeguard systems is especially important, because: Safeguards and interlocks do not operate on a day-to-day basis, but When they are required to operate (emergency conditions) they need to operate flawlessly. See ISA SP for details for the design of safety instrumented systems. Slide

143 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Short-Stops to Stop Reaction Add Reaction Stopper Add Agitation with No Electrical Power Add Reaction Stopper Add Agitation with No Electrical Power A short-stopping system, stops a runaway reaction by adding a reaction stopper solution to the reacting mass. The reaction-stopper stops the reaction in time to short-circuit the progress of the reaction. A reaction stopper needs to be added when the reaction mass is relatively cold. If the mass is too hot, a short-stopper will not work. Slide

144 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Short-Stops to Stop Reaction Add Reaction Stopper Add Agitation with No Electrical Power Add Reaction Stopper Add Agitation with No Electrical Power Good agitation, of course, is required to adequately mix the reaction mass with the inhibitor. Since a power failure is often the initiating event of a runaway, an alternative method of agitation needs to be included in the design. A compressed nitrogen system together with a sparge ring is one alternative. Slide

145 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Protection for Internal Fires and Explosions Deflagrations Detonations Deflagrations Detonations This section of the presentation covers protection methods for internal fires and explosions. Overpressure protection is needed for process equipment that can potentially explode due to an internal deflagration or detonation. Slide

146 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Protection for Internal Fires and Explosions Deflagrations Detonations Deflagrations Detonations A deflagration is defined as the propagation of a combustion zone at a velocity in the unreacted medium that is less than the speed of sound. A detonation has a velocity greater than the speed of sound in the unreacted medium. Slide

147 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Protection for Internal Fires and Explosions Deflagrations Detonations Deflagrations Detonations The burning material can be a combustible gas, a combustible dust, a combustible mist, or a hybrid mixture (a mixture of a combustible gas with either a combustible dust or combustible mist). The reaction actually occurs in the vapor phase between the fuel and the air or some other oxidant. Slide

148 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Protection Methods for Internal Fires and Explosions Deflagration Venting Deflagration Suppression Containment Deflagration Venting Deflagration Suppression Containment The protection methods used for fires or explosions include Deflagration venting Deflagration suppression Containment Slide

149 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Protection Methods for Internal Fires and Explosions (continued) Reduction of Oxidant Reduction of Combustible Flame Front Isolation Reduction of Oxidant Reduction of Combustible Flame Front Isolation Reduction of the oxidant Reduction of the combustible Flame front isolation Slide

150 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Protection Methods for Internal Fires and Explosions (continued) Spark Detection and Extinguishing Flame Detection and Extinguishing Water Spray and Deluge Systems Spark Detection and Extinguishing Flame Detection and Extinguishing Water Spray and Deluge Systems Spark detection and extinguishing Flame detection and extinguishing Water or foam spray deluge systems Slide

151 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Deflagration Venting Vent Area via NFPA 68 The technology required for venting deflagrations is given in NFPA 68. Deflagration venting is usually the simplest and least costly means of protecting process equipment against damage due to the internal pressure rise from deflagrations. Slide

152 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Deflagration Venting Vent Area via NFPA 68 Vent Safely Vent Area via NFPA 68 Vent Safely If equipment is located inside a building, the vents must be discharged through a vent duct system to a safe location outside of the building. The design of the vent duct system is critical to avoid excessive pressures developed during the venting process. See NFPA 68 for details. Slide

153 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Deflagration Venting Vent Area via NFPA 68 Vent Safely Vent Area via NFPA 68 Vent Safely A safe location will avoid injury to personnel and minimize damage to equipment outside of the building. The next two pictures illustrate that the “safe venting” may not be trivial. Slide

154 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Vent of Gas Deflagration This is a picture of the venting of a gas deflagration. As illustrated, the flame propagates a significant distance from the vessel. The length of the flame is estimated using an equation found in NFPA 68. The main purpose of venting is to protect the mechanical integrity of the equipment. As illustrated, even when it is vented safely, this is a major event. Slide

155 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Vent of Dust Deflagration This is a picture of the venting of a dust deflagration. As illustrated, the burning dust continues to burn at great distances from the vent. With dusts, this burning zone is larger because the container has a larger fuel-to-air ratio compared to the gas deflagration scenario. These pictures clearly illustrate the problems with venting deflagrations. Slide

156 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Deflagration Suppression System One alternative to venting a deflagration is suppression. This sketch illustrates a deflagration suppression system that includes (a) a flame or pressure detector, (b) a quick opening valve, and (c) the addition of a flame suppressant. Slide

157 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Deflagration Suppression System The commonly used suppression agents include water, potassium acid phosphate, sodium bicarbonate, and Halon substitutes. The technology for deflagration suppression is described in NFPA 69. Slide

158 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Containment Prevent Rupture and Vessel Deformation Prevent Rupture but Deform Vessel Prevent Rupture and Vessel Deformation Prevent Rupture but Deform Vessel The thickness of vessel walls may be increased to contain the pressure of a deflagration. The wall thickness can be large enough to prevent the deformation of the vessel, or The wall thickness may be large enough to prevent a rupture, but allow the vessel to deform. Slide

159 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Reduction of Oxidant Vacuum Purging Pressure Purging Sweep-Through Purging Vacuum Purging Pressure Purging Sweep-Through Purging Protection for overpressures is also provided with an inert gas blanket to prevent the occurrence of a deflagration. Before introducing a flammable substance to a vessel, the vessel must also be purged with an inert gas to reduce the oxidant concentration sufficiently so that the gas mixture cannot burn. Slide

160 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Reduction of Oxidant Vacuum Purging Pressure Purging Sweep-Through Purging Vacuum Purging Pressure Purging Sweep-Through Purging The purging methods include vacuum purging, pressure purging, and sweep-through purging. See NFPA 69 and the book by Crowl and Louvar for more details. Slide

161 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Reduction of Combustible Dilution with Air NFPA 69 Dilution with Air NFPA 69 A deflagration can also be prevented by reducing the concentration of the combustible material so that the concentration is below the lower flammability limit (LFL). This is usually accomplished by dilution with nitrogen. The specifications for this type system are given in NFPA 69. Slide

162 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Flame Front Isolation As illustrated, isolation devices are used in piping systems to prevent the propagation of a flame front. The method illustrated has a fast-acting block valve. This isolation system prevents the propagation of the flame front; more importantly it prevents deflagration transitions to detonations. Slide

163 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Spark/Flame Detection and Extinguishing Another method of preventing the propagation of deflagrations in pipelines is the early detection and extinguishment of sparks or flames. In this type system, a detector activates an automatic extinguishing system that sprays water or other extinguishing agents into the fire. This system is similar to the deflagration suppression system discussed previously. Slide

164 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Water Spray or Deluge Systems Process equipment and structures are very effectively protected against fire by water spray or deluge systems. They can be activated manually or automatically. They are designed to cool the equipment or structural members so that the heat from a fire will not weaken them. Slide

165 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Deluge System This picture shows a typical deluge system in operation. In this example, the deluge system is automatically activated when the concentration of the flammable gas below the vessel is detected to be at or over 25% of the lower flammability limit. Slide

166 NEXT PREVIOUS Introduction Reliefs Runaways Safeguards Home Conclusion This concludes our technology package covering overpressure and underpressure protection. The appendix of this package contains more detailed information. The enclosed references contain the state-of-the-art technology to assist engineers and students with their detailed designs. Slide

167 End of Slide Presentation (with text) HOME PREVIOUS Causes of Overpressure/Underpressure Causes of Overpressure/Underpressure Presentation 1: Reliefs Presentation 1: Reliefs Presentation 2: Runaways Presentation 2: Runaways Presentation 3: Safeguards Presentation 3: Safeguards SlideExit

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