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