Multi-Objective Sustainability Optimization of Biomass Residues to Ethanol via Gasification and Syngas Fermentation: Trade-Offs between Profitability, Energy Efficiency, and Carbon Emissions

Elisa M De Medeiros,Rubens Maciel Filho,Henk Noorman,John A Posada

doi:10.3390/fermentation7040201

Elisa M De Medeiros, Rubens Maciel Filho + Show 2 more

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https://doi.org/10.3390/fermentation7040201

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Abstract

This work presents a strategy for optimizing the production process of ethanol via integrated gasification and syngas fermentation, a conversion platform of growing interest for its contribution to carbon recycling. The objective functions (minimum ethanol selling price (MESP), energy efficiency, and carbon footprint) were evaluated for the combinations of different input variables in models of biomass gasification, energy production from syngas, fermentation, and ethanol distillation, and a multi-objective genetic algorithm was employed for the optimization of the integrated process. Two types of waste feedstocks were considered, wood residues and sugarcane bagasse, with the former leading to lower MESP and a carbon footprint of 0.93 USD/L and 3 g CO2eq/MJ compared to 1.00 USD/L and 10 g CO2eq/MJ for sugarcane bagasse. The energy efficiency was found to be 32% in both cases. An uncertainty analysis was conducted to determine critical decision variables, which were found to be the gasification zone temperature, the split fraction of the unreformed syngas sent to the combustion chamber, the dilution rate, and the gas residence time in the bioreactor. Apart from the abovementioned objectives, other aspects such as water footprint, ethanol yield, and energy self-sufficiency were also discussed.

Highlights

In recent years, significant progress has been achieved in the field of biobased production, especially regarding ethanol production from lignocellulosic materials such as sugarcane bagasse, corn stover, and wood residues—the so-called 2nd-generation (2G)ethanol [1]
Gasification has a long history of applications with different purposes, but most large-scale gasifiers operate with coal, while biomass gasification has been applied on a far more limited scale and has mostly been used for heat and power generation as an alternative to natural gas and biomass combustion [5]
The main goals of this work are (i) the development of a framework for modeling and optimizing the integrated process for ethanol production from biomass via the thermo-biochemical route by considering two types of feedstock; (ii) the holistic impact analysis of the operating conditions and design parameters; (iii) the analysis of the optimal trade-offs between economic, energy, and environmental performance; and (iv) the analysis of the Pareto-optimal conditions of the multiple units involved in the process by taking into account their interactions

Summary

Introduction

Significant progress has been achieved in the field of biobased production, especially regarding ethanol production from lignocellulosic materials such as sugarcane bagasse, corn stover, and wood residues—the so-called 2nd-generation (2G)ethanol [1]. Fermentation 2021, 7, 201 with five of them targeting ethanol production (two operational) and only one at a commercial scale: the Enerkem plant in Alberta, Canada, which converts municipal solid waste (MSW) to syngas, with further chemical conversion to ethanol and other chemicals [6]. Only one (by LanzaTech/Aemetis) is projected for use in a gasification–fermentation route. This plant, which is still expected to begin construction, will first convert agricultural waste to syngas via plasma gasification [6], a relatively new technology with the ability to convert nearly any type of carbonaceous material yet at still high costs and limited process understanding [7]

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