Combined Bio-Hydrogen, Heat, and Power Production Based on Residual Biomass Gasification: Energy, Exergy, and Renewability Assessment of an Alternative Process Configuration

Bio-hydrogen from residual biomass may involve energy-intensive pre-treatments for drying and size management, as in the case of wet agro-industrial residues. This work assesses the performance of an alternative process layout for bio-hydrogen production from citrus peel gasification, with the aim of cogenerating heat and power along with hydrogen, using minimal external energy sources. The process consists of an air-steam fluidized bed reactor, a hydrogen separation unit, a hydrogen compression unit, and a combined heat and power unit fed by the off-gas of the separation unit. Process simulations were carried out to perform sensitivity analyses to understand the variation in bio-hydrogen production’s thermodynamic and environmental performance when the steam to biomass ratios (S/B) vary from 0 to 1.25 at 850 °C. In addition, energy and exergy efficiencies and the integrated renewability (IR) of bio-hydrogen production are evaluated. As main results, the analysis showed that the highest hydrogen yield is 40.1 kgH2 per mass of dry biomass at S/B = 1.25. Under these conditions, the exergy efficiency of the polygeneration system is 33%, the IR is 0.99, and the carbon footprint is −1.9 kgCO2-eq/kgH2. Negative carbon emissions and high values of the IR are observed due to the substitution of non-renewable resources operated by the cogenerated streams. The proposed system demonstrated for the first time the potential of bio-hydrogen production from citrus peel and the effects of steam flow variation on thermodynamic performance. Furthermore, the authors demonstrated how bio-hydrogen could be produced with minimal external energy input while cogenerating net heat and power by exploiting the off-gas in a cogeneration unit.