A techno-economic analysis (TEA) of a combined process of torrefaction and gasification of lignocellulose biomass (bagasse) for methanol and electricity production

This study investigates a comprehensive process for the production of methanol and electricity from bagasse. A total of four main scenarios (S1–S4) were considered in this study, they are bagasse gasification for methanol and electricity co-production with torrefaction (S1), and bagasse gasification for the production of electricity only with torrefaction (S2) while the other two (S3 and S4) are without torrefaction process respectively. The gasification process was modelled in Aspen Plus using a kinetic-free equilibrium model using steam and pure oxygen as the gasification agent. For the syngas cleaning, the Rectisol process was employed while for the methanol synthesis, hydrogenation reactions of CO₂ and CO coupled with the water gas shift reaction were employed. From the result obtained, the process involving torrefaction has more syngas yield; hence, more methanol was synthesized (0.48kg_MeOH/kg_Bagasse) when compared to the process without torrefaction (0.41kg_MeOH/kg_Bagasse). The syngas from the torrefaction processes also has higher lower heating values (LHV) of 9.25 MJ/Nm³ and 8.71 MJ/Nm³ for S1 and S2, when compared to that without torrefaction (S3 and S4) with LHV of 9.00 MJ/Nm³ and 8.49 MJ/Nm³ respectively. In addition, the economics involved in the production process of the four scenarios were investigated in terms of the key economic parameters which include the net present value (NPV), the rate of return on investment (ROROI), and the discounted payback period (DPBP). The result showed that S1 is the most economically viable production route. The sensitivity analysis also shows that revenue from the sales of the main products (methanol and electricity), as well as the cost of raw material materials, was the most sensitive. These two will incur the highest risk on the total investments from the four scenarios.