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

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. U TB 06-90 Recommendations on safety relief valve selection, sizing and installation (in 3 parts). Minneftehimprom USSR. 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

Russian standards are out of date!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

Russian standards are out of date! Many algorithms or calculation method are missing or poorly described Relieving requirements - capacity (except old UTB and its 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 in GOST 31294-2005) Fluid temperature change calculation Viscosity correction for valve capacity Reactive force calculation Noise and vibration estimation

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: Application and installation of safety devices excluding stand-alone bursting disc safety devices Part 10 : Sizing of safety valves and connected inlet and outlet lines for gas/liquid two-phase flow

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.

What is DIERS? Design Institute for Emergency Relief Systems of The American Institute of Chemical Engineers Formed in 1976 as a 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

International documents and methods from DIERS DIERS (AIChE) methodology (Design Institute for Emergency Relief Systems of The American Institute of Chemical Engineers) 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

How PSRE Co participates in DIERS work? Studies DIERS methodology to use it in new Russian 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 GPREH document development

New edition of GPREH Work on 2nd Edition started at the end of 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 for valve sizing and piping analysis method examples

Basis of DIERS methodology Gas-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/or inlet/discharge piping Retrograde condensation in relief system

Basis of DIERS methodology Two-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 Vessels according DIERS 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

Basis of DIERS methodology Sizing 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-condensable gas) slip correlation should be applied For small valves (with nozzle length < 10 cm) and boiling liquid 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)

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

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

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

Discharge coefficients for two-phase flow Prof Darby proposal Use gas coefficient in case of choked flow Use liquid coefficient in case of non-choked flow

Two main 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!)

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…

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)