G.Odisharia, V.Safonov, A.YedigarovVNIIGAS, Russia

A.ShvyryaevMoscow State University, Russia

ABSTRACT

The problems of development of the Gas field in far North of Russia and expansion of LNG/LPG storage- transportation capacities are essentially associated with the limited choice of sites for terminalconstruction that would meet the recent requirements of safety for population and environment. The paperpresents base statements of the developed in Gas Research Institute Method of safety assessment ofliquefied gas installations and some results of its practical usage.

SAFETY AND RISK ANALYSIS OF HARASAVEY LNG/LPG PROJECT

ANALYSE RISQUE/SECURITE DU PROJET GNL/GPL DE HARASAVEY

RESUME

En Russie, Ies problemes de developpement du gisement gazier du Grand Nerd et I’extension descapacites de stockage et de transpoti” du GNL/GPL- sent essentiellement li6s au choix Iimite du site deconstruction d’un terminal qui remplirait Ies conditions de securite pour la population et I’environnement.Cet article presente Ies Iignes directrices de la methode devaluation de la securite des installations GNLdeveloppee a I’lnstitut de recherche sur Ie gaz (Gas Research Institute), ainsi que different resultats desa mise en pratique.

DISCLAIMER

Portions of this document may be illegibiein electronic image products. Images areproduced from the best available originaldocument.

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1. INTRODUCTION

It is well known that the problem of industrial safety cannot be solved only by means of technicalprotection components and demands detailed study of “inner mechanisms” of accidents as the inherentfeature of any technological system, possessing potential energy reserve. One of the modern tools forsolving the problem of industrial safety is the risk methodology. The main idea of the risk analysis is thecreation of hazard distribution maps in view of climatic-geographical peculiarities of a region where afacility is sited, which reflect a probabilistic nature of any accident and are based on graphicalinterpretation of consequences (hazardous zones and exposed population for instance) of all probableaccident scenarios at the industrial facility.

The developed Method of safety assessment is based on hazard sources identification, thedetermination of a probability of any accident in conjunction with the consequences predictions by meansof modelling of various accident scenarios. The Method assumes a calculation of potential dangerdistribution for each facility, based upon the adopted criteria of negative influence upon the variousgroups of risk, taking into account the technological specifics of the facility and reasomconsequencelogic of typical accidents occurrences, as well as the probable impact of environmental parameters uponthe scale of the initial danger in space and time. Transition to the quantitative estimation of the particulartypes of damage from the probable emergencies at the facility requires additional consideration ofdistribution over the territory (in the zone of negative influence) of risk affected objects. Note, that riskassessment is made for each dangerous installation and, on the base of comparative analysis, acontribution of each installation to integral risk of an industrial facility is determined.

One of the key steps of industrial safety and risk analysis procedure is the consequencesprediction of probable accidents. The successful solution of this problem is inseparably associated withthe creation and practical usage of the approved mathematical models and methods for computations ofunsteady hydrodynamics and heat-mass exchange processes that describe different stages of anaccident pass. The computer software, developed in Gas Research Institute Method for prediction ofhazardous zones and consequences resulting from accidental releases of liquefied gases from industrialfacilities, is based on representation of an accident as a set of the certain physical processes and onmathematical modelling of these processes. The algorithm is constructed in such a way that the results ofcomputations of one process are used as boundary conditions or input information for calculating theothers, bearing in mind their mutual time-space connections and thus providing continuity of the wholecomputation process. The introduction of the experimentally verified mathematical models of liquefied gasdischarge, evaporation, vapour dispersion and burning makes it possible to simulate close to realityaccident scenarios taking into account specific features of industrial facility operation and its siting.Special attention was paid to the correct simulation of heavy gas dispersion and the three-dimensionalhydrodynamic computer code was developed for the turbulent flow and vapour cloud propagationmodelling.

The results of mathematical modelling and maximum hazardous zones calculations are used as aninput information for the next stage of risk analysis - creation risk maps and determination of a number ofindividuals exposed to a certain level of risk round the facility under consideration

As an illustration of the developed Method and computer software practical. usage the results ofsafety analysis of such base facilities of Harasavey Gas Field as: LNG Terminal, Liquefaction Plant, LPGpressurised storage, LPG pipelines are presented in the paper.

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2. LNG TERMINAL

The problem is faced due to the plans of the construction of the LNG liquefaction plant, port andexport loading terminal in Yamal Peninsula of Russia. The design of the Harasavey Cape Terminal (30109 m3 per year capacity) supposed an assessment of different alternatives of placing liquefaction plant,storage tanks, port facilities with due account of high intensity of ship traffic and using the port as a basefor the Yamal region pioneering (Fig.1 ).

As it is well known, the formation and evolution of dense vapour clouds accompany the mostdangerous accidents at LPG/LNG facilities. The explosive cloud could spread over a long distanceproducing large hazardous zone and severe consequences. That is why special attention was paid to thenumerical modelling of heavy gas propagation in the atmospheric boundary layer. Different accidentscenarios were examined including emergency discharge of LNG from the 100000 m3 tank (Fig.2),loading facilities, tankers on soil and water within the wide range of spillage amounts and atmosphericparameters changing and corresponding hazards estimated. Numerical simulation of instantaneousrelease of LNG from the tank showed that the explosive cloud first gradually increased to its maximumextent, then smoothly decreased and contracted toward the source that is caused by sharp reductionof the evaporation rate.

Different variants of hazardous facilities siting were considered while predicting accident affectedareas as well as the distribution of probable ignition sources. In order to determine territorial riskdistribution, the real personnel deposition was also taken into account bearing in mind the actual time oftheir presence at the facility. It allowed to range the personnel affected by risk levels. The results ofranging are presented at Fig.3. As integral parameters of risk there were used the following ones: numberof persons to be under risk from the different technology installations and the whole facility, collective tiskdefined as the sum of risks for all people at the facility, average individual risk of personal groupcharacterizing an average level of hazard for persons in the group. The analysis allowed to understandthat the layout of technology installations has great influence on the territorial distribution of risk and theintegral risk values. There was a great difference (twice) in integral risk values for both variants of siting.

Comparative analysis of input of different LNG installations to integral risk value of LNG Terminaloperation made it clear that the main contribution to the risk is caused by liquefaction plant and isothermaltanks (Fig.3). The risk contribution caused by possible accidents during loading and manoeuvring tankersin the port harbour was varied from 10- 15 % depending on different alternatives.

3. LPG PIPELINE

According to the Harasavey project natural gas and unstable condensate willl be delivered to theliquefaction plant by the pipelines. In view of increased danger of LPG pipelines the corresponding safetyanalysis was made and its results are also presented in the paper.

The following accident scenarios at LPG pipelines were examined: complete or partial rupture ofthe pipeline without pumping shut-down, stop pumping in a certain period of time (after leakageidentification) and isolation of the pipeline damaged section by means of shut-off valves. The main dangerfrom the LPG pipeline rupture is caused by vapour cloud propagation. The performed numerical modellingof LPG accidental discharges from the pipeline made it clear that the maximum hazardous zone andprobable consequences depend to a great extent not only on the atmospheric stability class and windspeed but also on the time required for the accident identification and decision making. For instance, thecomputations of complete rupture of the pipeline of 0.5 m in diameter showed that if no actions wereundertaken by operators, than hazardous zone downwind extent could be more than 6 km since 5 hoursthe leakage had occurred. Simulation of the same accident scenario but bearing in mind that shut-off

valves would be put in operation was evidence that the explosive cloud maximum extent was reducedconsiderably (Fig.4)

The dependence of LPG discharge rate, time of stop pumping, distance between valves on thehazardous zones were also investigated by means of numerical experiments.

In further risk calculations the regional specifics was taken into account that influences thepipeline failure rate in different regions. The risk analysis allowed to determine integral risk for thesettlements along the pipeline route being under probable negative exposure (Fig.5) and to study of anumber of engineering and technological measures for reducing risk to tolerable level. In particular theanalysis has shown the integral risk for the environment and population located within 3 km zone alongthe pipeline. Ranging localities by mean individual risk levels has revealed that 95% of overall risk relatesto localities being closest to the pipeline. It has been shown there are a number of engineering andtechnological measures related to the pipeline construction stage to allow reducing risk to tolerablelevels. These are changing the pipeline route,, increasing the pipeline wall thickness and metal toughness.

4. LPG STORAGE

One of the purposes of the study was to understand hazards associated with the operation of LPGpressurised storage tanks as a constituent part of technology of Harasavey Gas Field exploration.Different accident scenarios were examined at standard horizontal tanks of 200 m3capacity including ahypothetical one – instantaneous release of a content of a single tank.

The results of numerical modelling showed that the instantaneous discharge of a large quantity ofheavy gas into the atmosphere leads to an appreciable change in the initial velocity field, as well as in thenature of atmospheric turbulence (Fig.6). Radial gravitational spreading of heavy gas at rates of 3-4 m/swas observed near the source. The analysis of cloud propagation showed that hazardous zone maximumextent is determined by the evolution of the “primary” cloud that forms as a result of the instantaneousdischarge and evaporation due to flashing of a large quantity of LPG. After a certain period of time (- 30rein) the vapours are dispersed in the atmosphere to safe concentrations. It should be noted, that themaximum extent of the hazardous cloud for this scenario is less than for an accidental discharge of LPGfrom a filling pipeline, as a consequence of strengthening of vapour flow in a cross-wind direction coupledwith an intensification of the turbulent mixing process.

Further risk analysis allowed to find out all the factors influencing negatively on technical personnelof LPG storage and estimate risk associated with the operation of such liquefied gas facility. In result ofthe statistic analysis of LPG leaks at analogous facilities it has been established that sum probability ofoccurring large leaks (with rates of 10 kg/s and more) at the LPG tank farm is 1*10-2 events per year.Incidentally the maximum probability of an explosive vapor cloud formation at level of 0.0018 per year ispredicted only in vicinity of the LPG tanks. The consequences of the cloud explosions are greatlyinfluenced by the presence and distribution of ignition sources at the facility territory. The special analysishas established that the conditional probability of occurring the cloud explosion is about 0.03 -0.04. Inview of this the maximum risk values are focused at the LPG tank location (Fig. 7). The contribution of thefire ball and pool fire scenarios to the facility personnel risk is 50-60% . It has been established thataccidents at the LPG tank farm are not present great hazard to the facility personnel.

5. CONCLUSION

In conclusion, it should be noted that the application of risk methodology grounded on accidentnumerical modelling makes it feasible to assess the safety level of a facility and to elaborate rationalmeasures to reduce risk.

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Fig.1 Risk distribution map for Harasavey LNG TERMINAL

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28 rlwl

4%m

Fig.2 Vapor cloud evolution resulting from theaccidental discharge of100.000m3 LNGlsosurfaces:C=15% (UFL), C=5%(LFL), C=2.5%(halfofLFL)

Atmosphere conditions: stabiIityclass -’’F”, windspeed-2m/s

.*

Isothermal tank farm

h ~.sz.

4 -5 -6 -7 -8 .9 -10 -11 -12Risk level, log(R)

a ‘T Cryogen piping

h-s -6

dA->-11 -12Risk level, log(R)

;s

% I Tankers on LNG loading~S E

Risk level, log(R)

I I D E

c

7

LNG plant

Risk level, log(R)

i :~.4 -5 -6 -7 .X .0 -10 -11 -12

Risk level, log(R)

g:. T Whole facility

Risk level, log(R)

Fig.3 The facility personnel distribution by risk

levels both for different elements of the facility

(A, B, C, D, E) and the whole facility (F). G - the

contribution of different elements of the facility

to integral risk.

M mm4C!min

W min

Fig.4 Explosive cloud evolution as a result of the Main LPG pipeline rupture (d= 500 mm)if pumping stopped in 30 minutes after the rupture Isosutiace :C=l% (half of LFL)

Atmosphere conditions: stability class - “F”, wind speed -2 m/s

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‘Density of the population N(L) pipeline

D)

.. ..,:

..>.-

----

/’

village ~

Distance from pipeline, L (m) Number of persons, N(R)

&l.. ,I

w

40

ZQ

o [ 1■

1 1

—,Risk value, loglO(R)

Fig. 5 Sharlama and Suleevo villages in Tatarstan: population of 310 persons.

Rz = 0.51’10 + per year, Rind= 1.7 * 10-7 per year. There are 293 affected.

.,,

Fig.6 Evolution of the explosive vapor cloud resulting from the LPG accidentaldischarge from the tank. Isosurface C=l% VOL (half of LFL)

Atmosphere conditions: stability class - “F”, wind speed -2 mls

17A Im!wll

Ml!4,4I

1

‘“ H+tPd—H1 I t,

w’ klflII.,, In

i’i , , , , ,s , I , ,

I II I I I II I m t

6

L

d!!!KJ

I/yearRisk levels

Fig. 7 Integral risk distribution map (including explosions, tires, fire balls accident scenarios)

for LPG storage