Relieve system design problems and DIERS activity

1. Relieve system design problems and DIERS activity Experience of Simulis Thermodynamics usage for development of standards Leonid Korelstein

2. Russian standards on Safety Relieve Systems • GOST 12.2.085-2002 Vessels working under pressure. Safety valves. Safety requirements. • GOSR 24570-81 Safety valves of stream and hot-water boilers. Technical requirements. • UTB 06-90 Recommendations on safety relief valve selection, sizing and installation (in 3 parts). MinneftehimpromUSSR. 1991 • STP 12-07-01 (PSRE, part 1) • SA 03-005-07, PB 09-540-03, PB 03-576-03, PB 10-573-03, PB 10-574-03, RD 153-34.1-26.304-98, RD 51-0220570-2-93, IPMK-2005 and other documents for specific industries • GOST 31294-2005 Direct-acting safety valves. General specifications. • PB 03-583-03 Rupture disks design, manufacturing and usage rules

3. Russian standards are out of date! • Parameters of protected system and relieve systems are mixed • Set pressure is not necessary equal to MAWP ! • Relief valve sizing can be for accumulation pressure which is larger than overpressure • Allowable loss value for discharge piping is not defined • Backpressure influence (for backpressure >30%) on flow rate for balanced valves isn’t described • Rupture disks influence before and/or after relief valve isn’t taken into account • No temperature correction for spring selection (no such thing as “cold differential test pressure” defined) • Many common problems are not addressed

4. Russian standards are out of date! • Many algorithms or calculation method are missing or poorly described • Relieving requirements - capacity (except old UTBandits clones) • Valve sizing for two-phase gas-liquid relieve or flashing/condensing flow • Pressure and heat losses for discharge piping • Heat exchange model to use (Isothermic? Adiabatic –Fanno flow?) • Multiple choked flow (some misty tips inGOST 31294-2005) • Fluid temperature change calculation • Viscosity correction for valve capacity • Reactive force calculation • Noise and vibration estimation

5. International standards • ISO 23251:2006 (or ANSI/API STD 521 8 edition). Petroleum, petrochemical and natural gas industries. Pressure-relieving and depressuring systems • ISO 4126 Safety devices for protection against excessive pressure • Part 1: Safety valves • Part 2: Bursting disc safety devices • Part 3: Safety valves and bursting disc safety devices in combination • Part 4: Pilot-operated safety valves • Part 5: Controlled safety pressure relief systems (CSPRS) • Part 6: Application, selection and installation of bursting disc safety devices • Part 7: Common data • Part 9: Applicationandinstallationofsafetydevicesexcludingstand-aloneburstingdiscsafetydevices • Part 10 : Sizing of safety valves and connected inlet and outlet lines for gas/liquid two-phase flow

6. International standards • API RP 520. Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries. Part 1. Sizing and Selection. 7th edition, 2000. 8th edition, 2007 • API RP 520. Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries. Part 2. Installation. 5th edition. 2003 • API std 526. Flanged Steel Pressure Relief Valves. 5th edition. 2002. • API STD 2000. Venting Atmospheric and Low-Pressure Storage Tanks Nonrefrigerated and Refrigerated. 5th edition, 1998 • EN 764-7:2006. European standard. Pressure equipment – Part 7. Safety systems for unfired pressure equipment.

7. What isDIERS? • DesignInstituteforEmergencyReliefSystemsofTheAmericanInstituteofChemicalEngineers • Formed in 1976 asa consortium of 29 companies to develop methods for the design of emergency relief systems to handle runaway reactions • Became DIERS User Group – DUG - in 1985 • Presently, over 160 companies • European DIERS User Group (EDUG) is working • develop new techniques which will improve the design of emergency relief systems • Working in special Committees • Discuss problem on the meetings (spring and fall meetings each year) • Cross-testing of methods and software (Round-Robins) • Conferences, book publication • Participate in standard and RAGAGEP documents • training • PSRE Co is DUG member from 2009

8. International documents and methods from DIERS • DIERS (AIChE) methodology(DesignInstituteforEmergencyReliefSystemsofTheAmericanInstituteofChemicalEngineers) • Emergency Relief System Design Using DIERS Technology. The Design Institute for Emergency Relief Systems (DIERS). Project Manual. NY, 1992 • Workbook for Chemical Reactor Relief System Sizing. Contract Research Report 136/1998. HSE Books. 1998 • Guidelines for Pressure Relief and Enfluent Handling Systems (GPREH). American Institute of Chemical Engineers. 1998. • DUG members articles (Darby, Leung, Fisher, Melhem and others) • The most important DIERS methodology • Models and methods for Vessel Disengagement Dynamics and Prediction of Two-Phase Flow Onset and Flow pattern and parameters • Models and methods for relief system analysis and design for 2-phase, flashing and condensing flows • Models and methods for relief system analysis and design for systems with chemical reactions

9. How PSRE Co participates inDIERS work? Studies DIERS methodology to use it in newRussian standards and RAGAGEP documents and in “Safety Valve” software Participates in discussions on the meetings Reports own experience (implemented in Hydrosystem software) Participates in new edition of GPREHdocument development

10. New edition of GPREH • Work on 2ndEditionstarted at the endof 2006 • New edition is going to include the most modern methods • Currently most part of the book is written • Book structure • Chapter 1 – Introduction • Chapter 2 – Relief Design Criteria and Strategy (Review) • Chapter 3 – Relief System Design and Rating Computations. The most difficult chapter, describes methods for different computations: • Venting requirements (including chemical reaction cases) • Relief valve sizing • Inlet and Discharge Piping Analysis • Reactive force and Vibration • Chapter 4 – Handling Emergency Relief Effluents (Review) • Chapter 5 – Design Methods for Handling Effluent from Emergency Relief Systems • We are participating in the work on chapter 3 and are responsible forvalve sizing and piping analysis method examples

11. Basis of DIERS methodologyGas-liquid flow in relief system • What cases to consider • Two-phase fluid discharge from protected system • As the result of boiling in protected system • Liquid with non-condensable gases • Liquid flashing in the valve and/orinlet/discharge piping • Retrograde condensation in relief system

12. Basis of DIERS methodologyTwo-phase fluid flow discharge • When possible • Foam product • High viscosity liquid boiling • Volume boiling • Chemical reactions • When boiling at the vessel walls is about the same as volume boiling (large surface vs volume ratio) • heating jackets • narrow zones, channels or tubes • Swelling of the liquid due to boiling and two-phase discharge as the result • Flow patterns in the VesselsaccordingDIERS • Homogenious • Bubble • Churn – turbulent • DIERS elaborated methods and equations for two phase discharge, flow parttern, void fraction prediction • For reactive systems DIERS proposed analysis methods on the base of chemical kinetics equations using the lab data from adiabatic calorimeter tests

13. Basis of DIERS methodologySizing of relief valve • In most cases relief valve discharge rate can be calculated on the base of combination of the following models: • Ideal nozzle at isentropic flow • Homogeneous equilibrium flow model (HEM)for two-phase flow • Appropriate discharge coefficient correcting from ideal to real case • For frozen two-phase flow (liquid + non-condensablegas) slip correlation should be applied • For small valves (with nozzle length < 10 cm) and boilingliquid with quality < 0.1 there is not enough time to establish thermodynamic equilibrium. HEM model underestimates valve discharge capacity (sometimes in several times). More precise calculation demands taking into account boiling delay (superheated liquid)

14. Valve discharge capacity • From momentum or energy equation • By integration on pressure and assuming zero velocity at the enter to the valve • Choked and non-choked flow • From this equation analytical equations can be developed for given state equation – for example for ideal liquid or ideal gas

15. Homogeneous Direct Integration Method (HDI - Darby) Direct numerical calculation of the integral Density is calculated as Temperature and quality is calculated as result of isentropic flash calculation at given pressure (thermodynamic library is necessary) This method is the most general, covers all cases including subcooled liquid, 2-phase mixture, retrograde condensation etc

16. Omega-method (Leung) For one-component fluid far from critical point, when thermodynamic library isn’t available Density vs pressure is described as This allows to get analytical expressions from the basis equation This approach works for subcooled case as well

17. Discharge coefficients for two-phase flow • ProfDarby proposal • Use gas coefficient in case of choked flow • Use liquid coefficient in case of non-choked flow

18. Twomain problems currently DIERS is working on How to take into account thermodynamics non-equilibrium Methods of predicting relief valve instability to escape chatter (replacement of 3% rule!)

19. Thermodynamics non-equilibrium models Darby - HNDI (Homogenious Non-Equillibrium Direct Integration) method Leung – Омеga HNE method Diener-Schmidt omega – method More complex relaxation methods All above methods deal only with one-component fluid…

20. Relief system stability models 3% rule is empirical engineering practice rule not based on firm facts or theory More correct empirical rule (for example in terms of blowdown) Fisher-Melhem model Darby model (API)