Process design and economic evaluation for methane and electricity production from Agave bagasse using different pretreatments

Abstract

Agave bagasse is an agricultural residue that has the potential to be used as feedstock biorefineries. However, its complex structure requires a pretreatment step to facilitate the accessibility to carbohydrates for its subsequent conversion. In this study, the capital and operative expenses (CAPEX and OPEX) were simulated for industrial plants processing 500 ton/d of Agave bagasse using different pretreatment platforms for methane production and power generation on experimental data. The scenarios consisted of i) biological, ii) enzymatic, iii) dilute acid, and iv) steam explosion pretreatments and a case-based scenario without pretreatment. All these scenarios included milling, pretreatment, anaerobic digestion, and cogeneration stages. The results showed that those pretreatments carried out under soft conditions (biological and enzymatic) decreased between 2.1 and 2.8 times CAPEX compared to the highest value obtained in the diluted acid and case-based scenarios. The steam explosion, a pretreatment carried out under severe conditions, was less effective reducing CAPEX by only 1.2 times compared to the highest value. Furthermore, compared to the case-base scenario, only the biological pretreatment reduced the OPEX by a factor of 2, whereas the other pretreatments resulted in OPEX that were 2.0 to 3.5 times higher. Among the utilities (cooling water, steam generation, and energy) the steam generation contributed 47% to 76% of the total OPEX. The energy produced (kW⋅h/yr) was approximately twice the energy consumed for all scenarios. A sensitivity analysis demonstrated the robustness of the platforms since fluctuations in the prices of feedstock and raw materials did not impact the total production cost of methane, except for biological and enzymatic pretreatments. For all platforms, the solid loading was the process parameter with the highest impact on the production cost of methane. Overall, the study showed that biological and enzymatic pretreatments had the best economic performance. However, low substrate conversion and the high cost of enzymes and equipment, respectively, remained the main challenges to address in future research.