by Sissel EngDNV Technology Services

Dynamic depressurisation calculations LNG regasification unit

Agenda

Project background Presentation of results HYSYS dynamic depressuring unit Service provided by DNV TS

Standards and Codes evaluated for LNG regasifications systems

NFPA 59A: Standard for the Production, Storage and Handling of Liquefied Natural Gas

EN 1473: Installation and equipment for liquefied natural gas design of onshore installations

IGC: International Code for the Construction and Equipment for Ships Carrying Liquefied Gases in bulk Code (Gas Code)

API RP 520/521/14C NORSOK Relevant ISO standards DNV rules and offshore standards Other class societies: ABS, Lloyds SIGGTO LNG Operation in Port Areas IP Guideline/Scandpower guideline

Background

Compare API methodology with Scandpower Guideline in general

Investigate thermal effects during depressuring of LNG processes

Investigate dynamic depressuring utility available in HYSYS version 3.4

Establish a procedure for performing depressuringcalculations in accordance with NORSOK, ISO 13702, API RP 520, PED

Typical regasification unit

Two stage heating system Capacity of one skid: 50-210 tons LNG per hour Length, width, height: 11 x 4 x 8 meters Operating pressure: 40 to 130 bara Locked-in volume approximately 1 ton Initial liquid inventory, varied from 0 to 100% No insulation

Comparison heat absorption models

API heat absorption equation per area (API fire mode)

Heat transfer per area, taken into account radiation, convection (Stephan-Boltzman fire mode)

4,,

4 )())(( tTtTThTq OSSOSfrfS +=

82,0000,34 AFq =

Agenda

Project background Presentation of results HYSYS dynamic depressuring unit Service provided by DNV TS

Comparison API and Stephan-Boltzman

Pressure profile

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0 200 400 600 800Time [s]

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APIStephan-Boltzman

Pressure profile versus time plotted

Initial pressure 60 bara, and 60 0C

Initially 50% liquid filled Depressuring orifice

constant throughout simulations

Graph shows larger evaporation rate with Stephan-Boltzman fire mode

Comparison API and Stephan-Boltzman

Vapor temperature versus time plotted

S-B fire mode shows higher temperatures

Which model is correct?

Bulk vapour temperature

-1000

100200300400500600700

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Time [s]T

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APIStephan-Boltzman

S-B compared with experimental values: vapour wall temperature

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CalculatedExperimental

Experimental values presented by NH/Sintef at FABIG 2003

Results: Thermal effects

Fire mode selected: Stephan Boltzman

Heat input according to NORSOK fire

Orifice sized for cold depressuring. Down to 6.9 barg in 15 minutes. Orifice size kept constant through simulations

Initial pressure 60 bara, initial temperature -60 0C

Liquid level varied from 0, 25, 50, 75 and to 100% initially liquid filled

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0 200 400 600 800Time [s]

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@ 0% init liq vol@ 50% init liq vol@ 100% init liq vol

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Vap Wall T @ 0% init liq volVap Wall T @ 50% init liq volVap Wall T @ 100% init liq vol

Results: other parameters reported by Hysys

Remaining mass in vessel

0100200300400500600700800900

0 200 400 600 800Time [s]

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Vapour mass Liquid mass

Mass flow out of valveSB Fire Mode

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@ 0% init liq vol@ 50% init liq vol@ 100% init liq vol

Agenda

Project background Presentation of results HYSYS dynamic depressuring unit Service provided by DNV TS

HYSYS dynamic depressuring utility

Commercially available Rigorous thermodynamic Dynamic depressuring

simulation Often used for steady

state process simulations

Services provided by DNV TS

Procedure developed for detailed depressuringcalculations Utilizing a well established simulation tool Competence within material data (UTS) Competence within piping stress

Evaluation of results: risk analysis and consequences of possible rupture

Evaluation of results: ESD S/D logic and sectioning philosophy