Thermodynamic performance assessment of three biomass-based hydrogen production systems

Abstract

Hydrogen is likely to be an important energy carrier in the future. It can be produced by the steam reforming of natural gas, coal gasification and water electrolysis among other processes. However current processes are not sustainable because they use fossil fuels or electricity from non-renewable resources. In this context, this thesis focuses on biomass based-hydrogen production and considers three plants intended for sustainable producing hydrogen using. These three systems are analyzed thermodynamically using Aspen Plus and their performances are examined and compared in regards to hydrogen yield. Therefore, comparisons of the systems are made based on several factors, including energy and exergy efficiencies. In addition, an economic analysis is performed in order to determine the minimum hydrogen production cost for these three systems. The results are expected to be useful to efforts for the design, optimization and modification of hydrogen production and other related processes. In the three system considered, the gasifiers are modelled using the Gibbs free energy minimization approach and chemical equilibrium considerations. Gasification, which is characterized by partial oxidation, is a vital component of several clean energy technologies including the ones considered here. Parametric analyses are carried out of several factors influencing the thermodynamic efficiency of biomass gasification. The energy efficiencies were found to be between 22-33% for all systems. However the exergy efficiencies range from around 22 to 25%. It was also found that gasifier produces the greatest quantity of entropy, due to its high irreversibility, and merits attention from those seeking to improve efficiencies. It was found that the hydrogen production cost range varies between 1.28 and 1.84 $/kg for the three systems; this is higher than the cost for that produced from conventional oil.