Sustainable hydrogen production from oil palm derived wastes through autothermal operation of supercritical water gasification system

Hydrogen generation from empty fruit bunch and palm oil mill effluent through supercritical water gasification was studied on system level. The effect of alternative H2 separation process (Palladium Membrane or Pressure Swing Adsorption), H2S adsorption (zinc oxide or activated carbon) and inclusion of steam methane reformer on net H2 yield and system efficiency were examined under auto-thermal operation. Waste heat recovery by generating low pressure steam utilizable in palm oil mill were conducted to minimize exergy loss. At the lowest biomass concentration considered in this study (15 wt% empty fruit bunch), inclusion of steam methane reformer reduced the net H2 yield as product gas was mainly used as fuel. However, at high biomass concentration (25 wt% empty fruit bunch and palm oil mill effluent), the net H2 yield increased by up to 98%. Energy efficiency of 70% (without reformer) and 58.3% (with reformer) was achieved using high biomass concentration under optimal operating condition for H2 production. Exergy analysis revealed that 62.5–70.8% of total exergy loss was attributed to furnace and gasifier. Energy utilization diagram further revealed about 72–87% of the unit exergy loss was attributed to feed preheating. Waste heat recovery through steam generation raised the system efficiency by 5–18%.