Abstract
Nowadays LNG has become a common fuel for fuelling ship engines and similarly for the generation of power. Large gas engines are used for the propulsion of the ships and heating of the buildings. These engines are provided with big exhaust pipes which can be long and often contain a turbo charger or/and a silencer and/or a heat exchanger/boiler and a catalyser. In case of a release of an unburnt LNG-air mixture into the exhaust due to ignition failure subsequent ignition of the resulting cloud of natural gas, inert gases and air in the exhaust may occur. The resulting explosion may cause severe damage to the exhaust and the aforementioned equipment items installed in the exhaust pipe. Protection is possible by installing explosion vents. The paper addresses how to design this protection measure using the dedicated CFD-tool FLACS. Using the FLACS tool one can describe both the process of gas cloud-build-up after an ignition failure, the subsequent ignition of the cloud, the explosion development (strongly dependent on the presence of turbulence inducing elements such as a boiler, silencer, etc.) and the resulting loading of the exhaust pipe.
The paper addresses scenario choice, the effect of inerting gases (as present in fuel gas (mixtures of inert gases and methane)) on explosion development and how to optimalise explosion venting: number of bursting discs, their size and their location. A secondary hazard is the release of fuel gas (mixture of methane and nitrogen) may be released in a powerhouse. A powerhouse is an enclosed building, which contains the gas engines, potentially an alternator, the gas supply system and a fluid flow system all for power generation. In case of a release from the fuel gas system into the powerhouse, gas cloud build-up may result and upon ignition cause a damaging explosion. Using the FLACS CFD-tool the effect of several scenario parameters can be investigated such as the effect of different degrees of mechanical ventilation, release rate and direction, ignition source location and protection measures. The paper presents an example of such a study.
