Dr. Emeka Okafor Department of Petroleum and Gas Engineering

1. INSTITUTE OF CONSIDERATIONS OF SOME ENVIRONMENTAL SAFETY ASPECTS OF LNG OPERATIONS IN VIEW OF NIGERIA’S “EMERGING” GAS MARKET Dr. Emeka Okafor Department of Petroleum and Gas Engineering University of Port Harcourt (UNIPORT), NIGERIA 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.

2. 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

3. 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.

4. The Nigerian Gas Master Plan (NGMP) Three planned Gas Pipeline Transmission System… • 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.

5. 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!

6. Safety implications of increased LNG activity A look at the general problem of LNG spillages/leakages… Immediate ignition leads to pool fire (no vapour cloud formed) Release location affects spill dynamics Delayed ignition leads to vapour- cloud fire or explosion Vapour Cloud Spill Wind Vaporization Spreading of pool Pool Spreading of pool Spreading of pool Substrate heat flux CONTACT WITH NON-PENETRABLE SUBSTRATES LEADS TO CRYOGENIC DAMAGE SUBSTRATE Penetration of pool

7. LNG-steel contact model and solution Why is the current problem important? Spherical (MOSS) Type LNG Ships …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 Membrane Type LNG Ships DESIGN FEATURES OF A GTT MARK III TYPE INSULATION SYSTEM

8. LNG inlet 4 mm 170 mm IBS Inlet (Nitrogen, 153 K) IBS IBS Opening (1 atm + 5 mbar) 4 mm 100 mm Leakage Area 170 mm 30 mm 2.5 mm IS Inlet (Nitrogen, 253 K) IS Opening (1 atm + 8 mbar) IS STEEL INNER HULL OF SHIP 18 mm Porous Region Conjugate Heat Transfer Air (273 K) LNG-steel contact model and solution Considering a worst case LNG leakage scenario…

9. 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-Kuttamethod, respectively. The model was validated using experimental data from literature.

10. Summary of example simulation results Inner Hull Surface Cooling Temperature History… • 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. • 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.

11. Summary of example simulation results LNG contact fraction during transition boiling regime… • LNG contact • fraction predicted • from Kalinin’s • correlation shows • a rapid rise in the • fraction of the inner • hull steel plate in • contact with LNG. • Increasing LNG • contact fraction • during transition • boiling will affect • the coefficient of • heat transfer.

12. 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.

13. 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.

14. THANK YOU