Predicting the syngas hydrogen composition by using a dual stage equilibrium model

This paper presents an analysis of hydrogen syngas composition obtained by biomass gasification when simulated by a dual stage equilibrium model. The numerical model takes advantage of the carbon boundary point (CBP) concept to study the hydrogen production at maximum energetic and exergetic efficiencies. The numerical simulation was carried out using three large biomass residues available in Portugal: coffee husks, pine residues and vine pruning wastes. It was concluded that the three biomass substrates showed similar trends at different operating conditions and the vine pruning wastes showed the best hydrogen outputs. The computed results were also compared with pilot scale experimental data obtained for coffee husk residues. The numerical results differ from experimental data, but in both cases the hydrogen composition has similar changes taking into consideration the effect of different operating conditions. It was concluded that the hydrogen molar composition increases steeply with a steam to biomass ratio (SBR) below the CBP and with a slow rate above the CBP, up to an asymptotic value. Similar behavior was found considering the temperature effect on hydrogen production. It was also found that energy efficiency first increases with the SBR up to a maximum value and then decreases.