Thermodynamic analysis of sorption enhanced steam reforming of the volatile stream from biomass fast pyrolysis
Pablo Comendador, Jon Álvarez, Laura Santamaria, Maider Amutio, Martı́n Olazar, Gartzen López
Abstract
Biomass fast pyrolysis and in line Steam Reforming (SR) is a potential alternative to produce hydrogen. The addition of a sorbent such as CaO in the reforming process allows capturing in situ the CO 2 produced and shifting the equilibrium of the reactions involved towards the products, thus leading to higher H 2 production and purity. A thermodynamic equilibrium analysis by means of Gibbs free energy minimization method was performed to delimit the range of best operating conditions and assess the impact of Sorption Enhanced Steam Reforming (SESR) strategy on hydrogen production and purity, as well as on reaction enthalpy. A wide range of reforming operating conditions were studied with respect to temperature (300–800 °C) and Steam/Biomass (S/B) ratio (0–4), and the conventional SR was compared with the SESR processes. The SESR simulations were developed by adding the stoichiometric amount of calcium oxide (sorbent) required to capture all the CO 2 produced when full conversion of the volatile stream was attained in the SR process. In the SESR, a H 2 production of around 12.4 wt % (by mass unit of the biomass in the feed) and a H 2 purity higher than 98 vol % were obtained at temperatures in the 400–600 °C range and S/B ratios in the 1.5–3 range. In the SR, a H 2 production close to 11.8 wt % and a purity of 67.3 vol % was attained in the 550–650 °C range with a S/B ratio of 4. The SESR allows operating at lower temperatures and S/B ratios, thereby reducing energy requirements and, at the same time, attaining better performance than the conventional SR in terms of H 2 production and purity. • Gibbs free energy minimization method was used for SESR and SR simulation. • SESR obtains higher H2 yield and purity at lower temperatures and S/B ratios. • In SESR, H2 yield (12.4 wt%) is maximum within 400–600 °C and 1.5–3 S/B ratios. • SESR requires less energy than SR as CO2 capture makes the process more exothermic. • The results obtained evidence the interest of in line pyrolysis-SESR strategy.