CONSIDERATIONS OF SOME ENVIRONMENTAL SAFETY ASPECTS OF LNG OPERATIONS IN VIEW OF NIGERIA’S “EMERGING” GAS MARKET

Paper presented at the 3rd International Downstream Conference/Exhibition on Petroleum Refining, Petrochemicals and Fertilizers holding at the Presidential Hotel, Port Harcourt, 27 August, 2014.

Dr. Emeka Okafor

Department of Petroleum and Gas Engineering

University of Port Harcourt (UNIPORT), NIGERIA

INSTITUTEOF

Outline

Introduction The Nigerian Gas Master Plan (NGMP) Safety implications of increased LNG activity LNG-steel contact model and solution Summary of example simulation results Concluding remarks

The Nigerian Gas Master Plan (NGMP)

The NGMP is a guidance document that detailed a strategy that could help harness Nigeria’s 187 TCF proven gas reserves.

Three key elements which are: (i) Domestic Supply Obligation (DSO); (ii) Gas Infrastructure Blueprint (GIB); and (iii) Gas Pricing Policy (GPP).

Under the GIB, a network of gas gathering and central processing facilities (CPFs) will be situated in three FRANCHISE AREAS.

The Nigerian Gas Master Plan (NGMP)

The South-North Gas Transmission Pipeline System originating from the Calabar Region CPF;

The Western Gas Transmission Pipeline System cutting across the existing Escravos-Lagos Pipeline System (ELPS) and a planned offshore bypass; and

The Interconnector Gas Transmission Pipeline System.

Three planned Gas Pipeline Transmission System…

The Nigerian Gas Master Plan (NGMP)

Success of the GIB can lead to increased LNG activity…

Gas moves from fields to CPFs via designated nodes, where it is processed and distributed for domestic use and for export;

Planned developments under the GIB will not only position Nigeria as a regional hub for gas based industries, but can increase the country’s global market share in LNG Business;

However, we must not lose sight of the safety implications of increased LNG activity!

Safety implications of increased LNG activity

A look at the general problem of LNG spillages/leakages…

Spreading of pool

Vaporization

Spill Vapour Cloud

Immediate ignition leads to pool fire(no vapour cloud formed)Release location

affects spill dynamicsDelayed ignitionleads to vapour-cloud fire orexplosion

Wind

Penetration of pool

Substrate heat flux

Pool Spreading of pool

SUBSTRATE

CONTACT WITH NON-PENETRABLE

SUBSTRATES LEADS TO CRYOGENIC DAMAGE

Spreading of pool

LNG-steel contact model and solution

Why is the current problem important?

Distribution of historic LNG accidents (Vanem et al (2007)

Accident Category Accidents

Collisions 19

Grounding 8

Contact 8

Fire and explosion 10

Failure of Cargo tank 27

…because LNG can leak into insulation walls thereby increasing the potential for cargo tank failure as a result of cryogenic damage to

the ship’s structural members

DESIGN FEATURESOF A GTT MARK III TYPE INSULATIONSYSTEM

Spherical (MOSS) Type LNG Ships

Membrane Type LNG Ships

LNG-steel contact model and solution

Considering a worst case LNG leakage scenario…

170 mm4 mm

4 mm

30 mm 170 mm

100 mm

18 mm

2.5 mm

Porous Region

Air(273 K)

IS Inlet(Nitrogen,

253 K)

IBS Inlet(Nitrogen,

153 K)

IBS Opening(1 atm + 5 mbar)

IS Opening(1 atm + 8 mbar)

IBS

IS

LNG inlet

LeakageArea

STEEL INNER HULL OF SHIP

ConjugateHeat Transfer

LNG-steel contact model and solution

The following partial differential equation (PDE) describing the temperature distribution within the inner hull steel substrate was solved:

where the symbol T is the temperature, α is thermal diffusivity, and x, y, and z are the three coordinate directions of heat conduction. The equation used for the calculation of the substrate heat flux, q, and the ordinary differential equation (ODE) solved for the liquid vaporization rate, V, are respectively given by:

where the symbol h is the heat transfer coefficient, TLNG is the boiling temperature of LNG, R is the pool radius and L is the latent heat of vaporization.

The above equations were solved numerically by making use of the finite difference method and the fourth-order Runge-Kutta method, respectively. The model was validated using experimental data from literature.

2

2

2

2

2

2

z

T

y

T

x

T

t

T

)/(

)(2 LqRV

TThq LNG

Summary of example simulation results

Inner Hull Surface Cooling Temperature History…

The decreasing surface temperature during

film boiling leads to a collapse of the vapour

film and a change in the boiling regime.Transition boiling started within 7-8

minutes after the onset of film boiling.

Time-dependent cooling of steel

plate in boiling LNG indicates that a three-regime

cooling process (i.e. film, transition

and nucleate boiling) occurred.

Approx. three minutes is sufficient to reach the brittle fracture regime.

Summary of example simulation results

LNG contact fraction during transition boiling regime…

LNG contact fraction predictedfrom Kalinin’scorrelation showsa rapid rise in the fraction of the innerhull steel plate in contact with LNG.

Increasing LNG contact fraction during transitionboiling will affect the coefficient of heat transfer.

Summary of example simulation results

Cooling Rate vs. Initial Temperature Cooling Rate vs. Plate Thickness

Inner hull cooling rate affected by the magnitude of substrate’s initial temperature and thickness, respectively.

Concluding remarks

Successful implementation of the NGMP has the potential to harness Nigeria’s enormous gas potential and drive economic growth;

However, issues of safety and security must be continuously addressed in order to maintain the industry’s enviable safety record;

An LNG-steel contact model has been proposed and used to evaluate the safety of a large LNG ship under barrier leakages;

Findings indicate that there is a potential for cryogenic damage of the inner hull steel plate within few minutes following a secondary barrier rupture. Furthermore, cooling rate of the steel plate is affected by boiling regime, substrate thickness and substrate’s initial temperature, respectively.

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