Hydrodynamic Constraints and Safety Implications of a 100% Hydrogen Fuel-Supply Train Retrofit for a Gas-Engine Power Plant: An Integrated Assessment

Retrofitting existing natural-gas power plants for hydrogen operation may reduce asset replacement, but energy-equivalent fuel substitution can substantially alter hydraulic loading and accident consequences. This study evaluates a 100% hydrogen fuel-supply train retrofit for an 8.11 MW gas-engine power plant by integrating hydraulic calculations, computational fluid dynamics (CFD), screening-level consequence analysis, hazard and operability analysis (HAZOP), and layer of protection analysis (LOPA). Under a hypothetical constant-energy-input scenario, the required normalized volumetric fuel flow increased from 1842.6 Nm3/h for natural gas to 6115.6 Nm3/h for hydrogen. In the existing 80A piping, the calculated velocity increased from 26.9 to 89.3 m/s; enlargement to 150A reduced hydrogen velocity to 22.8 m/s and the straight-pipe frictional pressure loss from 3.41 to 0.11 kPa per 10 m. CFD mean velocities were within approximately 3% of the analytical values and were interpreted as a numerical consistency check rather than independent validation. Screening-level ALOHA simulations produced slightly shorter hydrogen jet-fire radiation distances but substantially larger vapor-cloud-explosion (VCE) overpressure distances, including an 8.0 psi distance of 216 m under the documented scenario assumptions. HAZOP and LOPA identified residual scenarios and evaluated protection layers, with calculated mitigated frequencies below the project-specific 1.0 × 10−5 yr−1 screening target under the adopted assumptions. These results indicate that a hydrogen fuel-supply train retrofit requires integrated evaluation of fuel demand, piping hydrodynamics, consequence characteristics, and risk-control measures rather than simple fuel substitution.