Steam reforming of biomass gasification gas for hydrogen production: From thermodynamic analysis to experimental validation

Biomass gasification produces syngas composed mainly of hydrogen, carbon monoxide, carbon dioxide, methane, water, and higher hydrocarbons, till C4, mainly ethane. The hydrocarbon content can be upgraded into richer hydrogen streams through the steam reforming reaction. This study assessed the steam reforming process at the thermodynamic equilibrium of five streams, with different compositions, from the gasification of three different biomass sources (Lignin, Miscanthus, and Eucalyptus). The simulations were performed on Aspen Plus V12 software using the Gibbs energy minimization method. The influence of the operating conditions on the hydrogen yield was assessed: temperature in the range of 200 to 1100 degrees C, pressures of 1 to 20 bar, and steam-to-carbon (S/C) molar ratios from 0 (only dry reforming) to 10. It was observed that operating conditions of 725 to 850 degrees C, 1 bar, and an S/C ratio of 3 enhanced the streams' hydrogen content and led to nearly complete hydrocarbon conversion (>99%). Regarding hydrogen purity, the stream obtained from the gasification of Lignin and followed by a conditioning phase (stream 5) has the highest hydrogen purity, 52.7%, and an hydrogen yield of 48.7%. In contrast, the stream obtained from the gasification of Lignin without any conditioning (stream 1) led to the greatest increase in hydrogen purity, from 19% to 51.2% and a hydrogen yield of 61.8%. Concerning coke formation, it can be mitigated for S/C molar ratios and temperatures >2 and 700 degrees C, respectively. Experimental tests with stream 1 were carried out, which show a similar trend to the simulation results, particularly at high temperatures (700-800 degrees C).

Automated summary

Biomass gasification produces syngas containing various components such as hydrogen, carbon monoxide, carbon dioxide, methane, water, and higher hydrocarbons like ethane. A study on the steam reforming process of five different streams, obtained from three biomass sources, was conducted using Aspen Plus V12 software and Gibbs energy minimization method. Various operating conditions were assessed, and it was found that temperature, pressure, and steam-to-carbon ratio significantly influenced the hydrogen content in the streams. The hydrogen purity and yield were highest for the stream obtained from the gasification of Lignin followed by conditioning, while coke formation could be mitigated by specific conditions.