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by Sissel Eng

DNV Technology Services

Dynamic depressurisation calculations

LNG regasification unit

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Agenda

Project background Presentation of results

HYSYS dynamic depressuring unit

Service provided by DNV TS

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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 forShips 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

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Background

Compare API methodology with Scandpower Guideline

in general

Investigate thermal effects during depressuring of LNG

processes

Investigate dynamic depressuring utility available inHYSYS version 3.4

Establish a procedure for performing depressuring

calculations in accordance with NORSOK, ISO 13702,

API RP 520, PED

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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

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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 =

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Agenda

Project background Presentation of results

HYSYS dynamic depressuring unit

Service provided by DNV TS

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Comparison API and Stephan-Boltzman

Pressure profile

0

2000

4000

6000

8000

10000

12000

14000

16000

0 200 400 600 800

Time [s]

P

re

s

s

ur

e

k

P

a

API

Stephan-Boltzman

Pressure profile versustime plotted

Initial pressure 60 bara,and 60 0C

Initially 50% liquid filled

Depressuring orificeconstant throughoutsimulations

Graph shows larger

evaporation rate withStephan-Boltzman firemode

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Comparison API and Stephan-Boltzman

Vapor temperatureversus time plotted

S-B fire mode shows

higher temperatures

Which model is correct?

Bulk vapour temperature

-100

0

100

200

300

400

500

600

700

0 200 400 600 800

Time [s]

APIStephan-Boltzman

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S-B compared with experimental values: vapour wall temperature

0

200

400

600

800

1000

1200

0 200 400 600 800 1000

Time (sec)

Walltemperature(degC)

Calculated

Experimental

Experimental values presented by NH/Sintef at FABIG 2003

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Results: Thermal effects

Fire mode selected: StephanBoltzman

Heat input according toNORSOK fire

Orifice sized for colddepressuring. Down to 6.9barg in 15 minutes. Orificesize kept constant throughsimulations

Initial pressure 60 bara, initialtemperature -60 0C

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

0

5000

10000

15000

20000

0 200 400 600 800

Time [s]

Pressure[kPa]

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

@ 100% init liq vol

0

100

200

300

400

500

600

0 200 400 600 800

Time [s]

WallTemperature[degC]

Vap Wall T @ 0% init liq vol

Vap Wall T @ 50% init liq vol

Vap Wall T @ 100% init liq vol

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Results: other parameters reported by Hysys

Remaining mass in vessel

0

100

200

300

400

500

600

700

800

900

0 200 400 600 800

Time [s]

Rem

aining

m

ass[kg]

Vapour mass

Liquid mass

Mass flow out of valveSB Fire Mode

0

500

1000

1500

2000

2500

3000

3500

0 200 400 600 800

Time [s]

MassFlowrate[kg/h]

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

@ 100% init liq vol

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Agenda

Project background Presentation of results

HYSYS dynamic depressuring unit

Service provided by DNV TS

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HYSYS dynamic depressuring utility

Commercially available

Rigorous thermodynamic

Dynamic depressuringsimulation

Often used for steady

state process simulations

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Services provided by DNV TS

Procedure developed for detailed depressuring

calculations

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