Waste-heat-assisted ammonia cracking for onboard hydrogen production: An energy and exergy assessment
Kubilay Bayramoglu, Tolga Bayramoglu, Kerim Deniz Kaya, Semih Yilmaz
article (Uluslararası, Hakemli) | Yazar(lar): Kubilay Bayramoglu, Tolga Bayramoglu, Kerim Deniz Kaya, Semih Yilmaz — Özet: Hydrogen is a promising carbon-free marine fuel, although its onboard storage remains challenging. This study investigates waste-heat-assisted onboard hydrogen production through catalytic ammonia
Hydrogen is a promising carbon-free marine fuel, although its onboard storage remains challenging. This study investigates waste-heat-assisted onboard hydrogen production through catalytic ammonia cracking. A steadystate MATLAB packed-bed reactor model incorporating Ru/gamma-Al2O3 kinetics and thermodynamic equilibrium constraints was integrated with a CoolProp-based waste-heat-recovery model. Marine exhaust heat at approximately 250 degrees C was utilized for ammonia vaporization and feed preheating, while reactor temperatures of 300-650 degrees C, pressures of 1-10 bar, and gas hourly space velocities of 2000-4000 h- 1 were investigated. Nearly complete ammonia conversion and a hydrogen mole fraction approaching 0.75 were achieved above 600 degrees C. Waste-heat integration reduced auxiliary specific energy consumption by 88.1% at 300 degrees C and 57.1% at 450 degrees C, while the minimum value decreased to approximately 5.87 kWh/kg H2 at 550 degrees C. The maximum external thermal utilization efficiency increased from approximately 47% without waste-heat recovery to 74% with integration. Component-wise exergy analysis revealed strong temperature dependence, with specific exergy destruction decreasing sharply through the kinetically controlled regime and approaching stable values at high conversion. These findings demonstrate the potential of low-grade marine exhaust heat to substantially reduce external thermal demand for onboard ammonia-to-hydrogen conversion.