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ACHE LNG Plants

Text of Ache Lng Plants

  • Process Safety and Environmental Protection 9 1 ( 2 0 1 3 ) 351366

    Contents lists available at ScienceDirect

    Process Safety and Environmental Protection

    journa l h om ep age: www.elsev ier .co

    Force Coonsho

    M. Tanaa Engineerin Corpo220-6001, Jab Laboratory Univ

    a

    M olers

    of ach r

    for supporting the LNG process equipment and for allowing sea and land transportation. This results in additional

    congestion of the plant and large voids under module-deck, which are conned by large girders. Thus, in case of

    leaks, the proper ventilation to reduce the accumulation of gas is critical for the safety of the plant.

    This paper evaluates the Air-Fin-Cooler induced air ow in modularized LNG plants using Computational Fluid

    D

    pr

    sh

    pr

    of

    Ke

    1. Int

    Many base to remove hSince the rhuge in reclarge numband normaprocess traAnnual) capthose AFCsthe LNG pr

    Several modularizaimpact andfabricationconstructio

    CorrespoE-mail aReceived

    0957-5820/$http://dx.doynamics (CFD) analysis.

    The results of this evaluation show that the ventilation of the Air-Fin-Cooler induced air ow is inuenced by the

    ocess train orientation. Further, a moderate increase is observed in specic design conditions or areas, such as

    orter separation distances between modules. Based on the results of this evaluation, four design measures are

    oposed to optimize the use of Air-Fin-Cooler, such as train orientation against prevailing wind direction and use

    the grating deck material.

    2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

    ywords: Air-Fin-Cooler; Forced ventilation; Separation distance; LNG

    roduction

    load onshore LNG plants use Air-Fin-Coolers (AFC)eat for refrigeration cycle in liquefaction process.equired duty for cooling for refrigeration cycle isent large capacity base load onshore LNG plants,er of AFCs are applied for the required large dutylly mounted on the center pipe rack of the LNGin. For example, 45 MMTPA (Million Metric Ton Peracity LNG process train has over 250 AFC fans and

    are normally mounted on the center piperack ofocess train.ongoing LNG plant projects are planning to applytion concept in order to mitigate environmental

    difculty of remote site construction by using yard for plant construction as a substitute of siten. The modularized onshore LNG plant equipment

    nding author. Tel.: +81 45 682 8505; fax: +81 45 682 8850.ddresses: [email protected] (M. Tanabe), [email protected] (A. Miyake).

    23 September 2011; Received in revised form 11 July 2012; Accepted 4 September 2012

    has to be mounted on the module structure for supporting theLNG process equipment and for allowing sea and land trans-portation. The rst deck level is normally approximate 4 min height and large voids are left under the deck surroundedby 2 m deep module structure girders (Tanabe and Miyake,2010). To minimize gas accumulation in these spaces is theone of important safety aspects in the modularized onshoreLNG plant. Thus, the modularized LNG plant has higher explo-sion risk than normal stick-built LNG plant, and then the ACHmay become important indicator for safety.

    High wind velocity has been observed in actual LNG pro-cess train site using AFC air cooling process (measured in20092010). The high wind velocity increases especially in gapsfor safety separation and maintenance access, compared withthe process area, which is congested. The forced ventilationair ow by AFC in LNG process facilities layout is shown inFigs. 1 and 2.

    There are several ways to reduce risk by explosion,e.g., reducing possibility of ammable gas accumulation,

    see front matter 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.i.org/10.1016/j.psep.2012.09.001d ventilation effect by Air-Fin-re LNG plant

    bea,, A. Miyakeb

    g HSE Group, HSE Systems Department, Engineering Division, JGC pan

    for Safety Engineering and Risk Management, Yokohama National

    b s t r a c t

    any base load onshore LNG plants use large number of Air-Fin-Co

    the LNG process train. Further, the LNG plant modularized approm/locate /ps ep

    oler in modularized

    ration, 2-3-1, Minato Mirai, Nishi-ku, Yokohama

    ersity, Hodogaya-ku, Yokohama 240-8501, Japan

    normally mounted on the center pipe rack

    equires large, complex structures (modules)

  • 352 Process Safety and Environmental Protection 9 1 ( 2 0 1 3 ) 351366

    mitigating equipmentexpected bciple is appLNG plants

    Althougdesign are sion risk icongested Fig. 1 Air ow by AFC in LNG process tr

    explosion consequence (separation distance and layout) and making structures withstand thelast load (blast resistant design). This basic prin-lied for both onshore stick-built and modularized.h the equipment layout and the blast resistantcommonly applied as countermeasure for explo-n actual plant design, such as the gap betweenregions in view of minimization of explosion

    consequen(van den Bet al., 2009reducing thcommonlyof the vent

    The AFCtions, as thprocess eq

    Fig. 2 Air ow by AFC in LNG process train (plan view).

    ce for both stick-built and modularized plantserg and Versloot, 2003; Mores et al., 1996; Huser; Paterson et al., 2000; Pitblado et al., 2006), thee possibility of ammable gas accumulation is not

    taken as a reliable safeguard since quanticationilation effect in open area is complex.

    fans are normally stopped in emergency condi-e AFC is not considered safeguard, but only as

    uipment (i.e., heat exchangers). Process design of

    ain (side view).

  • Process Safety and Environmental Protection 9 1 ( 2 0 1 3 ) 351366 353

    Table 1

    CFD mode ge

    Detailed CFuantiirlationule

    Simplied lts du

    ry da

    uantilationd henompaoptioutat

    cost

    a Target vo

    AFC speciand AFC isthe duty acwhich is anvolume andthe currentis not effecreduce posular with m

    The stution by AC(2) to checktion). This pventilationAFC inducelarized LNGtraditional Dynamics (for evaluatimodifying

    1. The incrwind co

    2. The imp modu deck m

    Based oncover gas dgeometries

    1. Geomet wind modu deck m

    2. Leak par leak r buoya

    Me

    Str

    mplitry, fantagh dpings sigovidetionrisonCFD model strategy.

    ling Purpose Modeling Advanta

    D model To evaluatedetailed air owfor each case

    Actual geometryfor all equipmentAir ow based onAFC fanperformancecurve

    Canprovide/qdetailed aow/ventieach mod

    CFD model To determinetrends of in/outows (targetvolumea)consideringhigh/low packingdensity

    Actual geometryonly for largeequipmentPorosity used forcongested area(wherecalculatedporosity is lessthan 0.9)Constant AFC airow

    Early resuthe use ofpreliminaCanprovide/qarea ventitrends, anbasis for cof design Save comptime and

    lumes in this study are above deck area, below deck area and gap.

    es the required duty for the process uid cooling designed to provide the required air ow rate forcordingly. However, the Air Change per Hour (ACH),

    indicator of ventilation and the function of area air ow rate, is not normally calculated. Thus, in

    standard design practice, the AFC forced air owtively used for enhancing the ventilation (i.e., tosibility of ammable gas accumulation), in partic-odular design, during emergencies.

    dy is planned in two steps (1) to quantify ventila-H as general indication for ventilation effect and

    gas dispersion trend (e.g., buoyancy, release direc-aper covers the rst step and estimates the forced

    2.

    2.1.

    The sigeomedisadvAlthouand pirequirecan prventilacompa effect of AFC (i.e., the increase of ACH due to thed air ow over natural ventilation) inside modu-

    process trains which have higher congestion thanonshore stick built LNG plant. Computational FluidCFD) analysis has been used for the estimates andng the design measures for increasing ACH withoutAFC process design, such as

    ease of ventilation in the modules and gaps due tonditions and orientation of the trainsact on AFC induced air ventilation ofles separation distancesaterial

    the ndings from this paper, the second step willispersion study using CFD for the following model

    and leak parameters

    riesconditions and orientation of the trainsles separation distancesaterial

    ameterselease direction (downward and horizontal)ncy (methane gas, LNG, propane).

    ventilation

    2.2. Stu

    The basic d(recent typthe study a

    Plant cap AFC mou Total ind Size of LN Size of m

    deck) inc Size of A

    (H) Number

    2.3. Air

    The increaevaluated bcompared tDisadvantage Remarks

    fy

    for

    Require detailed vendordata (later phase)Difculties in deningdetailed model for largescale geometrySignicantcomputational time andcost dictates that fewsimulations are able tobe run in a practicaltimescale

    Not used in thisstudy

    e to

    ta

    fy

    ce arison

    nsional

    Sensitivity not based ondetailed geometryFlow patterns arisingfrom small scalegeometry might not beaccurately capturedThe effect of variationsof incoming air ow onfan performance is notcaptured

    Used in thisstudy

    thodology

    ategy

    ed geometry is structured, rather than accurateor the CFD model in this study. The advantage andge of the both models are summarized in Table 1.etailed air ow behavior around small equipment

    can be identied by the detailed CFD model, itnicant computational cost. The simplied model

    area (i.e., above module, below module and gap), which is sufcient indicator for ventilation, and

    among desi

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