Superstructure-based Rigorous Simulation for Synthesis and Evaluation of Lignocellulosic Biofuels Processes

In the present work, a process synthesis framework for the conversion of softwood biomass to liquid (BtL) transportation fuels was developed. We defined processing blocks out of promising thermochemical and upgrading technologies, and performed individual blocks rigorous simulations in Aspen Plus® V8.8. The simulations and experimental data taken from the literature were used to predict conversions, recovery factors, capital and energy costs of the processing blocks. From the simulations, it was found that Gasification-Low Temperature Fischer-Tropsch (LTFT) followed by fractional upgrading and fractionating units (BC-GLTUF), was the most cost-effective, in terms of total annual cost (TAC) and liquid fuels production. Then, given the preliminary results, the possibility of combining blocks between the thermochemical routes, as well as mass and energy integration were explored. A superstructure was proposed and defined as a Mixed Integer Non-Linear Programming (MINLP) problem coded in GAMS 24.5.6, which sets the objective to minimize the TAC’s of BtL fuels under different cases and integration scenarios. The results showed that a combined alternative of Gasification followed by simultaneous high and low temperature FT reactions (CA-GLTHT) could increase the liquids fuels production and product distribution from 87 % to 90 % (wt) and reduce the TAC in around 26 % if mass and energy integration are considered.