A swirl static mixer with diluent for reducing the flammable extent of venting gases in a low-flashpoint fueled vessel

Analyses on the gas dispersion from a vent mast have been conducted using fire dynamics simulator (FDS) for a 50000 dead weight tonnage (DWT) gas-fueled bulk carrier, under the assumption that methane and propane gases are discharged through a pressure relief valve in the vent system of the fuel storage tank. To assess the transient flammable extents for representative vent scenarios, the initial conditions of venting gases were selected as propane at–30 °C and methane at–150 °C, when wind velocity was set to 2 m/s in the ship exterior. The same ship layout was applied in each of these scenarios with different configurations of the inner components of the vent mast outlet. As a result, the cases with a plate head in the current vent mast outlet did not satisfy international code requirements for the safety distance of the vent mast location in ships powered by low-flashpoint fuels. However, the flammable extents of the venting gases could be significantly reduced by a novel vent system in which a swirl head and nitrogen diluent at 20 °C were adopted. Therefore, a safety design procedure considering gas dispersion characteristics was required to determine the location of the vent mast outlet in the gas-fueled vessel to satisfy the minimum requirements of the international code.