Public Appendix 13q

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WEAVER'S COVE ENERGYWEAVERS COVE OFFSHORE BERTH PROJECT

Resource Report 13

APPENDIX Q

THERMAL RADIATION AND VAPOR DISPERSIONREPORT

Q-1 CBI Document C01001, Vapor Dispersion, Thermal Radiationand Sump Sizing Calculations for Offshore J etty Spill

Q-2 Temperature Rise at an LNG Tankers Hull Resulting from aFire in the LNG Impoundment, by Pat Convery, PE, WeaversCove Energy, Offshore Berth Project

Q-3 LNG Release from an Underwater LNG Transfer Line, byPhani Raj, Technology & Management Systems, Inc.


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WEAVER'S COVE ENERGYWEAVERS COVE OFFSHORE BERTH PROJECT

Resource Report 13

Q-1 CBI Document C01001, Vapor Dispersion, Thermal Radiationand Sump Sizing Calculations for Offshore J etty Spill


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SW

AN

SE

A

SO

ME

RS

ET

Thermal Radiation10,000 BTU/hr-ft2 = 84.82 ft



Vapor Dispersion from DesignSpill Sump (1/2 LFL) = 300.4 ft

Scale 1:3,0001 inch = 250 feet

125 0 125 250

Feet Weaver's Cove Energy, LLC

Figure 11-1Design Spill - Vapor Dispersion and

Thermal Radiation Distances

G:\Projects\Fall_Riv\79001\alt_berth\Resource_Reports\RR11\Fig11-1_design_spill.mxd

Basemap: 2002-3 RIGIS2005 MassGIS Imagery

MAR

I

Location Within Bay


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CALCULATION

Weavers Cove Energy

Off-Shore Berth Project

Temperature Rise at an LNG Tankers HullResulting from a Fire in the LNG Impoundment.

Pat Convery, P.E.1/15/2009


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IntroductionThe purpose of this calculation is to demonstrate compliance to 33CFR Part 127paragraph 127.105 which requires that:

Impounding spaces must be located so that the heat fluxfrom a fire over the impounding spaces does not causestructural damage to an LNG vessel moored or berthed atthe waterfront facility handling LNG.

The Weavers Cove Energy Offshore Berth will have 2 impounding spaces located at theoffshore berth. One impoundment, the design spill impoundment, is provided and sizedto collect and contain any LNG spilled from a design spill as defined by NFPA 59A(1994) in paragraph 2-1.2. The spill volume is determined by the requirements set out inparagraphs 2-2.2.2 for a spill from an accidental leakage source. The accidental leakage

source chosen by WCE was the largest small diameter branch connection producing thelargest flow at operating conditions. (a 3 run-around valve on the unloading armisolation valves). This design spill impoundment is located in a segregated area within asecond, larger impounding space.

The large impounding space is designed to contain a spill from a full flow rupture of theLNG transfer system with the ship pumps running at maximum speed (115% of 12,000m3/hr) at the offshore berth plus additional space for draining of these lines. Thecalculations performed to demonstrate compliance to 33 CFR 127.105 assume a fire overboth impounding spaces.

This scenario was selected in consultation with the US Coast Guard office SectorSoutheast New England. The scenario assumes an LNG vessel, berthed at the Offshoreberth, is unloading normally when a failure occurs somewhere in the LNG transfersystem at the jetty resulting in a full flow spill (115% of 12,000 m3/) for 10 minutes,filling the impounding spaces. The spill is ignited by an unspecified ignition source and afire over the impounding spaces ensues. The tanker then takes 10 minutes to move offthe berth and head toward the navigation channel.

Weavers Cove Energy selected a temperature of 1000 degrees F as a limiting valueabove which steel structures may experience a significant loss of strength to causestructural damage. Damage to paint systems and coatings and localized plate

deformations can be expected to occur at temperatures below this level, however thislevel of damage has not been identified as a mechanism to impede the departure of anLNG vessel or to result in structural damage.


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depending on composition, surface conditions, etc. Weavers Cove has assumed aconservative figure of 0.8 for the purpose of these calculations.2 Using the worst-caseemissivity of 1.0, the failure temperature of the steel is not reached.

Other FactorsSeveral factors that could mitigate the effects of a fire in the large spill impoundment onan LNG tanker have not been accounted for in this analysis. These include:

The use of water curtain fire protection systems on the LNG tanker, The use of firewater cooling from remote controlled water monitors installed on

the jetty platform,

The use of firewater cooling from fire-fighting tugs that may be present at berth atthe time of the incident,

Reduction on thermal radiation due to the use of Foamglas FPS blocks in theimpoundment sumps,

Wind cooling of the tankers hull.

ResultsThe results of the simulation are included in Appendix A. A summary of the results isincluded in Table 1.

Table 1, Summary of Results

CaseNumber Radiant Fluxat Hull(BTU/ft2-hr)

AmbientTemperature HullTemperatureAfter 10 Minutes

MaximumHullTemperature

Time toMaximumHull Temperature

1 8694 12 F 360 F 711 F 42.3 minutes2 7427 100 F 393 F 689 F 39.6 minutes

ConclusionA fire over the impounding spaces at the offshore berth is described in these calculationsdoes not give rise to structural failure of the LNG vessel or be of significant magnitude to

prevent the vessel from departing the berth in the event of a fire in the impoundingspaces for a fire of 10 minutes duration or longer. The calculations show that themaximum temperature reached at the vessel at berth is 711 degrees F, well below theidentified failure temperature of 1000 degrees F.

2 Using the theoretical worst-case value for emissivity of the steel outer hull, the maximum temperatureoccurs after 34 minutes and is 734 degrees F, well below the temperature of concern for structural damage.


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Appendix B

Formulas Used in BREEZE Model3

3 BREEZE LFG Fire/Risk Users Guide. Version 5.0 Rev 1.0, Copyright 2004 Trinity Consultants. Usedby permission.


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LNG release from an

Underwater LNG transfer line

A technical report

Submitted to

Mr. Leon Bowdoin

Vice President, Weavers Cove Energy

Fall River, MA 02720

by

Phani Raj

Technology & Management Systems, Inc

Burlington, MA 01803

8th January, 2009


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Page (i)

Table of ContentsPage #

Executive Summary (iii)

Chapter 1 Introduction

1.1 Background 11.2 Objective 2

Chapter 2 Findings from the literature

2.1 Underwater LNG release tests 42.1.1 Test by the US Bureau of Mines 4

2.1.2 Maplin Sands tests by Shell 5

2.2 Mixing of hot and cold liquids 52.3 Droplet & Bubble formation and Heat Transfer 11

2.4 Summary of findings from the literature 15

Chapter 3 Modeling LNG jet release froma transfer-pipe underwater

3.1 General description of LNG Jet Behavior in Water 17

3.2 Modeling LNG Jet Release, Liquid Droplet Formation and 20

Vapor Bubble Heating3.2.1 Jet release rate 20

3.2.2 Homogeneous nucleation of a superheated liquid 21

3.2.3 Potential vapor explosion yield 223.2.4 Liquid droplet size and vapor bubble size 243.2.5 Vapor bubble rise and heating 27

3.3 Example Results 30

Chapter 4 Discussions and Conclusions

4.1 Discussions 334.2 Conclusions 37

Nomenclature 38

References 41

Appendix A: Assessment of the results from the U.S. Bureau of Mines 1970 43underwater LNG release experiment


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Page (v)

Figure E-1A: LNG release at 40 ft depth of water

Figure E-1B: LNG release at 30 ft depth of water

Figure E-1C: LNG release at 20 ft depth of water

Figure E-1: Results for vapor bubble rise and heating distances for differentrelease depths and sizes of holes on the pipe wall


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Page 5 of 55

1 The entire mass of LNG released evaporated underwater.

2 No white vapor cloud was observed on the surface of water. It is surmised that thevapor released was warm and buoyant.

3 The pressure pick ups located under water registered some overpressure. Using thisdata the Bureau estimated that the total energy yield by the explosion wasequivalent to that from approximately 0.4536 kg (1 lb) high explosive TNT charge.

4 Measurement made by noting the time stamp in the film indicates that the first signof vapor coming out of the water surface is about 8 2 s after the detonator was

charged. The entire vapor is released from the surface in a big bubble within about2 seconds after the first hiss of vapor emerging from the water surface. It has to be

noted, however, that the time at which the detonator was charged is not indicated

(or commented on) in the film but is guessed by watching the film many times. That

is, the entire 7.7 kg of LNG seems to be evaporated in a matter of about 10 s ( 2 s).

A model has been developed to interpret the results from the US Bureau of Mines test.The details of this model and the conclusions from it are discussed in Chapter 3.

2.1.2 Maplin Sands tests by Shell

Only one test of releasing LNG continuously underwater is reported by Blackmore, et al.,

[1984]. The test involved the continuous release of LNG (at the rate of 4.1 m 3/min for

230 seconds in a 4.7 m/s wind speed) from an 8 inch diameter pipe whose end was justbelow the surface of water. The authors do not provide any data on the depth of pipe-end

below the water surface; it may be assumed that the pipe-end was less than 0.5 m below

the water surface. The vapor produced was found to be buoyant. No other quantitative

data are provided. It is, however, significant to note that even when LNG was releasedunderwater from a relatively shallow depth the vapors produced were buoyant.

2.2 Mixing of hot and cold liquids

Other industries where the mixing of a hot liquid and cold liquid are of concern include

metal casting (especially steel and aluminum), nuclear fission, nuclear fusion, and

alternative motor fuel technology. All of these industries are concerned with accidental

mixing of the hot liquid with a cold liquid leading to superheat explosion (of the coldliquid). It should however be noted that most of the research investigations in these

industries involve laboratory scale tests (of sizes of the order of magnitude of 1 meterdepth or smaller).

The concern in the nuclear fission industry is with the potential meltdown of the uranium

core rods due to loss of coolant followed by the hot molten metal plunging into theemergency water deluge system. In the case of the nuclear fusion industry the concern is

with water circulating in the jacket to extract heat from the reactor coming in contact

with the liquid helium coolant (at 4 K or -443oF) used to cool the super-conducting

magnets. In these situations the sudden and substantial production of superheated vapor


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Page 8 of 55

maximum depth of jet penetration is limited by the buoyancy and the onset bulk boiling of

water which collects in a cavity created during the initial phases of water jet penetrationof the molten metal. Figure 2-2 shows, at different times after the water jet plunges into the

molten metal. The formation of the cavity in the hot metal and its filling with water, rapid

evaporation of water and the subsequent shattering explosion, are shown. The bulk

boiling starts as the sub-cooled water supply to the cavity becomes limited due to pinchinginstabilities in the upper region of the cavity.

These authors provide a graph of the so called Thermal Interaction Zone (TIZ), s a plot in

which the jet liquid temperature is on the Y-axis and the bulk liquid (in this case the molten

metal) temperature is on the X-axis. The graph indicates the regions in which the vaporexplosion is possible. The variables used in the graph include TMFB, the minimum film

boiling temperature and THN, the homogeneous nucleation temperature of the jet liquid.

The principal findings from the tests of Sibamoto, et al., [2002] are summarized as follows:

1 As the water jet penetrates into the molten metal, a cavity is formed very quickly andthe cavity expands both vertically and laterally. The

2 The cavity penetration velocity into the molten metal remains constant until it breaks upat about ten (10) jet diameters. The cavity penetration velocity is dependent upon the

water to metal density ratio. The actual velocity is about 0.69 to 0.77 of the theoretical

velocity given by /[1 ]mC Jw

u u

= + where uC and uJ are respectively, the cavity

penetration velocity and jet injection velocity. the densities of molten metal and water,

are, respectively, m and w.

3 The maximum penetration depth (HC) to jet diameter (dJ) ratio is a function of thedensimetric Froude number (Fr), defined by Jwith R=J J wFr u Rgd = . The

penetration depth is given by 1.45CJ

HFr

d

=

. It is noted that the water into the molten

metal represents the case of positive buoyancy of the jet and hence this may limit the

penetration depth.


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Page 10 of 55

Source: Sibamoto, et al., (2002), Copyright 2002, Nuclear Technology.

Reproduced with permission (2008) from the American Nuclear Society.

Figure 2-2: Cavity formation, water accumulation, rapid evaporation and liquid

shattering in a water jet plunging into a molten metal

4 In the case of entry of jet at high Froude number into another liquid of comparabledensity (i.e., the density ratio of the ambient fluid to jet fluid not greater than, say 2) the

jet penetration depth is limited by the dynamic break up of the jet rather than due to

thermal effects discussed above.

5 The maximum volume of cavity formed (VC) before shattering occurs is a function of

the Froude number and is given by 3 25 / 6C J

V d Fr = .

6 During the formation and growth of the cavity, a part of the injected water is emitted

out of the cavity as water, a part is vaporized and a part accumulates in the cavity. Thecavity contains evaporating water and part of the vapor formed. The mass of water

accumulated in the cavity is about 94% (at high molten metal temperature) to about

86% (at low molten metal temperature) of the theoretical mass injected up to the time

the cavity vanishes due to super heat explosion.

7 The bulk boiling time (or the time for the superheat explosion) is a function of the ratioof the temperature of the molten metal to that of water. The higher this ratio the longer

is the super heat explosion time for a given jet velocity. The non dimensional time (t*),

defined by * / where [ =( / ) Characteristic time]ch ch J J

t t t t d u= = , to super heat

ranges from 180 (at a low bath temperature) to 240 (a high bath temperature).

2.2.4 Perets, et al., [2005] have also experimentally studied the vapor explosion

phenomenon that occurs when a cold liquid (water) jet is injected into a hot liquid surface

(tin). The experiments involved using 1 kg of molten tin (at temperatures ranging from

230oC to 700

oC) in an open geometry and directing a jet of sub cooled water at

temperatures ranging from near 0oC to 99

oC and velocity of 11.3 m/s released from

about 30 cm above the surface of the molten tin. High water velocities were needed for

the water jet to penetrate the molten tin surface. The influence of the injection mass flow


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Page 15 of 55

distance of 0.12 m. The tests range in Reynolds numbers (based on liquid kinematic

viscosity and bubble rise velocity) between 100 and 3000.

The heat transfer coefficient data indicated by Komaro and Sano [1999] can be expressed

as

[ ]0.5

31.8 10L LNu x Pe

= (2-10)

where,

NuL = Nusselt number based on the bulk liquid property;b

L

L

h dNu

K= (2-11)

PeL = Peclet number based on bulk liquid properties; see equation 2-7).

It is noticed that the exponent on the PeL in the equations of Iguchi, et al, and that of

Komaro and Sano do not agree, one being 0.5 and the other being 0.7, respectively. Furthermore, it appears that the Nusselt numbers themselves (compared in consistent

units using the vapor thermal conductivity in the definition of the Nusselt number) do not

agree in magnitudes. In order to demonstrate this discrepancy, we have used the thermalproperties of water (for bulk liquid) and that of saturated LNG vapor at ambient pressure.We have in addition used ReL = 3000 and PrL = 7 (for water). When these values are used

equations 2-5 and 2-11 provide the following results.

From equation 2-5 1,156vNu =

and, from equation 2-11 6.5vNu =

In fact, further examination of the results from Iguchi, et al indicates that their correlation

above does not predict the experimentally measured value (of 100 W/m2 K) for the heat

transfer coefficient. Their correlation for the condition of the tests gives a result that is atleast 50 times higher than their own measured value. Therefore, it is concluded that thecorrelation (in equation 2-10) of Komaro and Sano is a better representation of the heat

transfer process between vapor bubbles and bulk liquid.

2.4 Summary of findings from the literature

The following are the summary findings from the review of the relevant literature relatedto the release of a cold, almost saturated liquid as a jet at some depth below the surface of

a bulk liquid (such as water) at normal ambient temperature.

1 In the case of LNG release at a depth of about 4.5 m below the water level in a lake,all of the released LNG ( 7 kg) evaporated completely within the water column

resulting in no LNG pool formation on the water surface. In addition, the vapor

released from the surface of water was above the dew point temperature of water (and

perhaps at the temperature of water). The latter finding is based on an interpretationof the observation that no white LNG vapor cloud was observed on the water surface.

2 Even in small scale experiments with liquid nitrogen releases in the form of a jet fromunder water, all of the released LN2 is seen to evaporate in a very short distance (of


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the order of centimeters to less than a meter) and that the vapor emanating from the

water surface is at the temperature of water. This occurs not withstanding the fact thatthe jet velocity is of the order of 10 to 30 m/s.

3 Results from test conducted with liquid metals jetted into water and water jetted intoliquid metals indicate that the shattering of the jet within very short time of jet

penetration into the bulk fluid (within distances of the order of 10 to 15 jet diameters).The shattering of the jet into droplets is primarily caused by the superheating of the

volatile fluid, followed by a localized vapor explosion. This explosion leads to the

shattering of the jet.

4 In the case of release of a cold or hot vapor bubbles into a bulk liquid at a differenttemperature, the vapor bubbles are heated by the surrounding bulk liquid to

essentially the temperature of the bulk liquid within a distance less than one meter,

and many times within 0.3 m. The bubbles, even when released as a stream from anozzle at high velocities (of 20 to 50 m/s) slow down to the respective terminal

velocities (consistent with the diameter of the bubbles) in about 15 nozzle diameters.

The rise velocity of bubbles of 5 mm bubbles is in the 0.6 to 0.75 m/s range.

5 The effective heat transfer coefficient correlations for heating vapor or gas bubbles ina column of water show values close to 100 W/m2 K.

6 There exist no experimental or theoretical correlations to predict the mean size ofdroplets formed or the distribution of droplet sizes when a cold, saturated liquid is

jetted into a warm bulk liquid. The only correlation that exists is for the maximumdiameter of liquid droplets formed when a liquid jet is injected into another liquid at

the same temperature and no evaporation of either of the liquids takes place.

In chapter 3, the above results from the literature are used to develop a model for

describing the processes that occur and determining, quantitatively, the resulting effects

when LNG is released in the form of a jet from a hole in the transfer pipe located at thebottom of a river at a depth of 10 to 15 m.


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To the extent possible, and based on the available data & correlations from the literature,

a model is developed to determine the temperature of the vapor emanating from the watersurface when a LNG jet is released from a specified size hole (in both walls of the

transfer system). This model is formulated and discussed in the next section.

3.2 Modeling LNG Jet Release, Liquid Droplet Formation and VaporBubble Heating

3.2.1 Jet release rate

The velocity of liquid (LNG) release from the jet is given by following equation

( )2 a W W PJ D

L

P gS PU C

+ = (3-1)

and the volume flow rate by

2

4J J JV d U

=

(3-2)

where,

CD = Coefficient of discharge of the jet orifice (generally 0.6 to 0.7)

dJ = diameter of the orifice of the jet (or initial jet diameter) (m)

g = Acceleration due to gravity (9.8) (m/s2)

Pa = Atmospheric pressure (N/m2)

PJ = Absolute pressure inside the pipe (N/m2)

SW = Depth under water of the jet orifice (m)

UJ = Velocity of liquid at jet exit from the orifice (m/s)

JV = Volumetric flow rate of liquid (LNG) our of the orifice (m3/s)

Table 3-1 shows the results of flow rate calculations for an assumed 1 diameter for the

hole-size on the pipe wall, and different depths of pipe below the water level. It shouldbe noted that in modeling the LNG release from the PiP transfer system, it is assumed

that size of punctures in both the inner and outer wall of the transfer system is assumed to

be the same. This is tantamount to assuming that the outer pipe and the insulationbetween the inner and outer pipe have no influence on the puncture size. It is further

assumed that the corrosion coating and the approximately 2.5 inch concrete weight

coating on the lines have no influence on the puncture formation or its size. Theseassumptions are very conservative.


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3.2.3 Potential vapor explosion yield

In an underwater LNG release test conducted by the US Bureau of Mines (Burgess, et al.,

[1972]), it is reported that an energy equivalent of less than 1 lb (0.45 kg) of TNT release

was realized from the superheat explosion: underwater. A comparison of this data andthat calculated using the above calculations is indicated in Appendix A. It is seen that if

the entire mass of LNG released underwater, 7.71 kg (17 lbs), participated in thesuperheat energy release then the equivalent energy released is equal to that from 0.33 kg

(0.73 lbs) of LNG. This comparative result seems to indicate that all of the LNG released

participates in the superheat energy release. The fact that the entire mass of LNG released

participated in the superheat energy release in the test by Burgess, et al., could beattributed to the relatively small mass of LNG that was used.

According to the findings of laboratory scale experiments of Sibamoto, et al. [2002],when a cold liquid is injected into a hot liquid, the penetrating liquid jet initially forms avapor cavity in which the liquid accumulates until the vapor cavity collapses leading tothe sudden evaporation (of the superheated liquid in the cavity). This release of superheatenergy can be considered as a local explosion. It is uncertain whether such aphenomenon occurs when a LNG jet enters water, especially from the bottom of thewater body. In the case of Sibamoto, et al., tests colder water was introduced at the top ofa molten metal, thus the jet velocity vector and the upward buoyancy force were inopposite directions. In the case of LNG entering water at its bottom, the buoyancy forceis in the same direction as the jet velocity vector leading, perhaps to a differentmechanism than the formation of a vapor cavity holding superheated jet liquid.

The following analysis is indicated for the sake of completeness, without being certainthat the results of this analysis will hold for the case of a LNG jet entering a water body.

The volume of superheated liquid formed and held in a vapor cavity is given by

'3JSL ch

V V Fr = (3-3)

where,

VSL = Volume of superheated liquid in the vapor cavity (m3)

Vch = A characteristic volume equal to that of a sphere (m3)

with diameter the same as that of the jet = 3

6ch J

V d

= (3-4)

FrJ = Modified jet Froude number defined by,

( )

' JJ

J LNG W

UFr

d = (3-5)

In Table 3-2 are shown the results from an example calculation for the case of LNGrelease from a 1 inch diameter hole in the transfer system pipe walls (at 40 ft underwater) and the resulting LNG jet release characteristics. Also indicated in Table 3-2 arethe results of application of the analysis in this section (3.2.3) for the superheatexplosion yield. It is seen that the TNT equivalence of the superheat energy released is


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3.2.4 Liquid droplet size and vapor bubble size

As discussed in chapter 2, there are no experimental data which indicate the magnitude or

the distribution of sizes of liquid droplets formed when LNG is released underwater. It

can be anticipated that the sizes of droplets of LNG formed by the dynamic forces of jet

flow in water as well as the thermal interaction will be smaller than that due to justdynamic effects. Hence, if one models the effects of large size droplets on the formation

and heating of LNG vapor bubbles underwater, the results will be conservative (in thatsmaller liquid droplets and vapor bubbles will heat faster).

The correlations of Okhotskii [1988] indicated in equations 2-1 to 2-3 together with the

parameter definitions indicated in equations 2.3a through 2-4d are used to calculate thesize of the maximum diameter of the droplet formed in the LNG jet released underwater,

subject to the assumptions indicated above. The results of these calculations are shown in

Table 3-3. It is seen that for the conditions of release and jet diameter assumed, thelargest diameter of the liquid droplet formed is about 1.6 mm. The laminar rise terminal

velocity of this size droplet is given by

2(1 / ); Laminar terminal velocity

18

L W Pd

W

g dU

= (3-6a)

And the turbulent rise velocity by

(1 / )4;Turbulent flow terminal velocity

3

L W p

d

D

g dU

C

=

(3-6b)

Where, CD is the drag coefficient on a spherical drop (generally assumed to be about0.44). For the above conditions the droplet terminal velocity is calculated to be 0.7 m/s.Assuming a water to droplet film boiling heat transfer coefficient (hFB) it can be shown

that the rate of decrease of diameter is given by,

( )FB P W sat P

L

h A T T dV

dt

= (3-7)

Where,

AP = Surface area of the droplet for heat transfer = dP2

(m2)

hFB = Film boiling heat transfer coefficient (W/m2

K)

VP = Volume of the droplet at any time = (/6) dp3 (m3)

L = Density of LNG (kg/m3)

= Heat of vaporization of LNG (J/kg)

Equation 3-6 implies that the droplet diameter decreases linearly with time and all of thedroplet is evaporated in a time (tevap) given by


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Table 3-3: LNG droplet and its characteristics

Parameter Symbol Value UnitEquation #

orReference

Assumed jet diameter at release (diameter of the

hole on the outer and inner walls of the pipe) =1inch

dJ 2.54E-02 m

Assumed water temperature TW 293 K

Assumed film boiling heat transfer coefficientbetween water and liquid droplet surface

hd 200 W/m2

K ABS [2004]

CALCULATED VALUES

Jet Reynolds number ReJ 4.11E+07 Table 3-2

Characteristic diameter dch 0.00486769 m 2-3a

Effective jet diameter for droplet size calculations d'J 0.00486769 m 2-3b

Bond number Bo 9.8696044 2-4a

Weber number WeJ 2.65E+05 2-4dLp number (Okhotskii [1988]) Lp 1.55E+02 2-4b

Beta (a constant introduced by Okhotskii [1988]) 0.3

Ratio of diameter of the droplet to characteristicdiameter of the jet

dP/d'J 3.23E-01 2-1

Hence, the maximum size of liquid droplet formed dP 1.573E-03 m

Mass of the largest droplet formed mP 9.166E-07 kg

Diameter of the saturated vapor bubble formedby the above droplet

dVap 9.871E-03 m

Total heat to vaporize mP droplet mass atsaturation conditions.

Ed 4.67E-01 J

Rate of heat input into the droplet of diameter dPdue to temperature difference between water andLNG

E 7.048E-02 W

Time to evaporate the largest droplet tevap 5.0 s 3-8

Laminar (Stokian) terminal velocity of dP dropletsize

Ud 0.7 m/s

Reynolds number based on Ud Red 1164.9 Laminar

Vertical distance travelled by the droplet by thetime of complete evaporation [Note: Diameter ischanging with time & terminal velocity is diameterdependent]

Sd 1.2 m 3-9


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With the above assumptions, the following equations are written3.

1.74 Turbulent flow terminal velocitydS

U g ddt

= = = (3-10)

1 "Effective gravity"g

W

g g

= = (3-11)

The total pressure at any depth S is given by

( )a W

P S P g S = + (3-12)

The equation of state of the vapor inside the rising gas bubble is

gPP V m RT or RT = = (3-13)

The mass of vapor in the bubble is

3

6

i i ii i

i i

P V Pm d

R T R T

= = (3-14)

The rate of heat transfer to the bubble is represented by

( )P W

dT

m C h A T T dt=

(3-15)

The definitions of the parameters in the above equations are as follows:

A = Surface area of the equivalent spherical vapor bubble (m2)

CP = Specific heat of vapor at constant pressure (J/kg k)

d = Equivalent diameter of the spherical vapor bubble (m)

di = Vapor bubble diameter at the point of generation at depth Si (m)g = Acceleration due to gravity (m/s2)

g = Reduced effective gravity due to buoyancy (m/s2)

h = Water to vapor bubble overall heat transfer coefficient (W/m2 K)

m = Mass of vapor in the bubble = Initial mass (kg)

mi = Initial mass of vapor in the bubble = (kg)P = Total pressure at any depth S (N/m2)

Pa = Atmospheric pressure (1.01325E5) (N/m2)

Pi = Total pressure at the initial depth of bubble release (N/m2)

R = Gas constant for the vapor (for LNG it is 519.63) (J/kg K)S = Depth below the water surface. S is positive as depth increases (m)

3All symbols are defined in the Nomenclature section.


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3

i i

p p

p p = =

(3-22)

And ( )2 Wd

d

= (3-23)

The above set of equations (3-20 through 3-23) has the following initial conditions

At 0; 1, 1, 1, 1, 1u = = = = = = (3-24)

It should be noted that = 0 represents the water surface.

Substituting equations 3-20 and 3-22 in equation 3-23 we get the following differential

equation

( )*

1

i

W

pd

d P

= +

(3-25)

The above non linear equation in is solved numerically with the initial condition

indicated in 3-24. Once q is known as a function of, can be obtained easily from

equations 3-22 and hence the bubble volume ( 3 = ).

3.3 Example Results

Calculations were performed for different conditions of LNG release from the PiP LNG

transfer system. The two principal parameters varied in the calculations were the depth of

the transfer system underwater and the size of the puncture hole. The calculations

involved the evaluation of the LNG jet characteristics, the length of the jet when it breaksdown into liquid droplets, the maximum size of liquid droplet formed and duration of

time over which the droplet evaporates to produce a vapor bubble. The vapor produced isassumed to be at a saturated condition corresponding to the pressure at the depth at which

the vapor is generated. The final result of calculations is the depth at which the

temperature of the largest size vapor bubble is close to (within 1%) the temperature of

water in the river. LNG vapor at normal river temperature is positively buoyant in theatmosphere. The results of these calculations are indicated below. Discussion on these

results and the conclusions therefrom are indicated in Chapter 4.

To illustrate the calculation procedure, a test case involving the release of LNG from a 1

(2.54 x 10-2 m) diameter hole on the wall of the line located at 40 ft (12.2 m) depth underwater is assumed. Table 3-1, Table 3-2 and Table 3-3 indicate the results on LNG jetcharacteristics, the maximum size of LNG droplets formed, the rise velocity of the

droplets and the size of the saturated vapor bubble formed by the evaporation of the

largest size liquid droplet. Table 3-4 below provides the results related to the rise of thevapor bubble, its heating by water and the depth at which the vapor bubble temperature is

essentially equal to that of the surrounding water.


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same temperature, there are no correlations to predict the jet penetration length when

there is significant thermal interaction between the liquids, especially when suchinteraction leads to superheat caused, spontaneous shattering of the jet liquid. It is

however, known, empirically from laboratory scale tests that this distance of

penetration is about 10 jet nozzle diameters for the case of a colder liquid jet of

density lower than that of the bulk liquid entering from the top of the bulk liquid. Inthis case the buoyancy of the jet liquid, perhaps, assists in limiting the penetration

depth. Unfortunately, no direct photographic evidence is available for determining thejet penetration distance before completely shattering when a buoyant, vaporizable

liquid is introduced at the bottom of a heavier and hotter bulk liquid.

This empirical result above has been used in the model presented in Chapter 3 toestimate the LNG jet penetration (vertically up) distance. It is not possible to state

whether this simple factor formula is sufficient for different release rates, jet

diameters and release depth underwater. Proper scaling laws may have to bedeveloped in the future, based on physics and carefully conducted experiments with

LNG releases underwater. In any such future tests the values of the independentvariables (such as the depth of release, the rate of release, the initial diameter of theLNG jet and water temperature) should be varied over realistic range of values and

the jet break down phenomenon should be carefully measured. Until such detailed

data or correlations therefrom are developed, it is reasonable to assume that the jet

breakup distance is 10 times the jet diameter, since there is experimental evidence forsuch a factor from other liquid jet-bulk liquid situations.

2 Sizes of liquid droplets: The conclusion from the literature findings indicated inChapter 2 is that no data or correlations are available for the maximum droplet size or

the distribution of liquid droplets formed when a LNG jet penetrates a warm water

body and their dependence on the release conditions. In the model described inChapter 3 the correlation developed by Okhotskii [1988] was used to calculate the

maximum liquid droplet size formed. Okhotskiis correlations are based on

theoretical analyses and experimental results applicable to the penetration of a liquidjet into another bulk liquid when there are no thermal or chemical interactions

between the liquids. That is the breakup of the jet liquid is solely due to mechanical

effects and the development of shear stress induced waves in the liquids and

turbulence caused tearing.

It can be argued that using Okhotskii correlation results in a very conservative

calculation. This is because, in the case of the thermal interaction of LNG with water,the superheat induced rapid boiling and the generation of shock waves will result in

the formation of the largest droplet size which will be smaller than that obtained from

Okhotskii correlation based purely on mechanical shattering of a jet. Assuming alarger droplet size leads to larger size of vapor bubbles formed and less efficient

heating of the bubbles by water. However, as we see from the results in Figure 3-4a,

3-4b and 3-4c, even with this large droplet assumption, the vapor is heated to water

temperature at considerable depth below the water surface.


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tch,T = Characteristic heating time (See equation 3-17) (s)

, 2

i

Initial bubble sensible heat

Heat transfer rate to initial bubble at a temp diff T

i P ich T

i i

m C Tt

d hT= =

T = Temperature of the vapor inside the bubble at any time (K)

Ti = Initial temperature at release of the vapor in the bubble (K)

i

UuU

= = Dimensionless terminal velocity with respect to initial velocity

U = Terminal velocity of rise of bubble at any location (m/s)

Ub = Rise velocity of the gas bubble (m/s)Ui = Initial terminal velocity of rise (m/s)

V = Volume of the droplet or vapor bubble (m3)

i

VV

= = Dimensionless vapor bubble volume

WeJ = Jet Weber number;2 '

J JJ

J

U dWe

=

Greek letters

L = Thermal diffusivity of the liquid (m2/s)

= A constant of value 0.3

i

dd

= = Dimensionless bubble diameter

i

SS

= = Dimensionless depth

,

Characteristic rise time

Characteristic heating time

ch

ch T

t

t = =

= Ratio of viscosity of gas to viscosity of bulk liquid v

L

=

L = Dynamic viscosity of the bulk liquid (N s/m2)

v = Dynamic viscosity of the vapor inside the bubble (N s/m2)

L = Kinematic viscosity of the liquid (m2/s)

v = Kinematic viscosity of the vapor inside the bubble (m2/s)

g = Density of gas (vapor) in the bubble at any time (kg/m3)

J = Density of jet liquid (kg/m3

)

W = Density of water (medium into which the jet is injected) (kg/m3)

= Density deviation = (W J) (kg/m3)

J = Surface tension of the jet liquid (N/m)

i

TT

= = Dimensionless temperature with respect to initial temperature


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WW

i

TT

= = Dimensionless water temperature

ch

tt

= = Dimensionless time

Subscripts

b = Property of the bulk liquid

i = Initial conditionJ = Jet properties

L = Liquid injected into the bulk liquid (LNG)

v = Property of vapor

W = Property of water


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APPENDIX A

Assessment of the results from theU.S. Bureau of Mines 1970 underwater LNG release experiment

In 1970 the U.S. Bureau of Mines conducted a test in which LNG held in a bottle was

released en masse underwater in a lake near Pittsburg, PA. The details of the tests areindicated in a video of vintage 1970.

Total mass of LNG released = 17 lbs = 7.71 kgDepth of water at which release occurred = 15 ft = 4.57 m

The commentary in the film indicates that

5 All of the LNG release seemed to have evaporated underwater.

6 No white vapor was found on the surface of water. It is surmised that the vaporreleased was warm and buoyant.

7 The pressure pick ups located under water registered some overpressure. Using thisdata the Bureau estimated that the total energy yield by the explosion was

equivalent to that from a 1 lb (0.4536 kg) high explosive charge (or TNT).

A.1 Some calculations

The heating value of TNT = 4.69 MJ/kg

Bureaus estimate the energy yield from the superheat explosion = 0.4536 kg of TNT

= 2.13 MJ

The superheat explosion yield is the same as the total sensible heat stored in the liquid

(due to superheating up to the superheat limit temperature) and released when the liquidattains the saturated temperature corresponding to the pressure at the given location.

A.2 Simple heat transfer model

Consider the situation shown schematically in Figure A-1. It is assumed that the

instantaneously released LNG (of mass 7.7 kg) has initially a form of a sphere of volume

equal to the released volume.

Released volume of LNG VLNG = (7.71/450) = 17.13 x 10-3

m3

The equivalent diameter of this sphere is D = [(6/) VLNG](1/3)

= 0.3209 m.


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Figure A-1: Schematic representation of the heating of LNG by water

It is assumed that this liquid is initially at the saturation temperature corresponding to thelocal pressure (assumed for the purposes of calculation to be the normal atmospheric

pressure). This spherical blob of liquid is heated by the surrounding water. When the

surface temperature of the blob reaches the super heat critical temperature, we assumethat there will be spontaneous boiling (super heat explosion) resulting in the shattering

of the spherical liquid into a spectrum of droplets. The energy released in this

explosion will be the excess sensible heat above the saturation enthalpy stored in the

liquid blob at the time of the explosion. This excess energy is calculated below.

A.2.1 Assumptions.

1 The heat transfer analysis is conducted with a 1-D model for heat penetration fromthe surface of the blob.

2 The temperature distribution radially is linear

3 The convective heat transfer coefficient is equal to the film boiling heat transfercoefficient

4 Quasi steady state is assumed.

5 There are circulations within the blob and the heat transfer into the body of the blob isonly through a conduction mechanism.

The sensible excess energy over the saturated liquid state, stored in the blob, at any time t

is given by

2 ( )( ) ( )2

S Sat LNG Sat

T TE D b t C T

+ =

(1a)


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Documents

Public Appendix 13q