Increasing Conversion Efficiency in Fuel Ethanol Production from Lignocellulosic Biomass by Polygeneration - and a Paradoxon between Energy and Exergy in Process Integration

In the public and scientific debate on biofuels, ethanol from lignocellulosic biomass is generally the most popular alternative that may allow for a sustainable production. Compared to thermochemical processing of biomass which assures a complete conversion of the feedstock, it yet suffers from an inherently lower fuel yield due to the resistance of lignin to biological degradation. Based on a recently developed process model for fuel ethanol production from lignocellulosic biomass, this paper discussed the cogeneration alternatives for the conversion of the residual lignin. Whereas an integrated gasification combined cycle (IGCC) increase the power cogeneration efficiency compared to the conventional combustion and power generation in a steam Rankine cycle, it is shown that alternative gasification and methanation to Synthetic Natural Gas (SNG) allows for roughly doubling the fuel yield from biomass. The paper further demonstrates the paradox situation that conventional energy recovery is limited by the available energy, and not, as usually, the available exergy from the waste heat. In order to overcome this limitation, a more general energy integration approach that allows for increasing the cogeneration efficiency in this kind of situations is proposed.

Integration of Supercritical Water Gasification in Combined 1G/2G Ethanol Production

François Maréchal, Alberto Mian, Adriano Viana Ensinas

The present study investigates the potential conversion of sugarcane into ethanol and synthetic natural gas. The considered conversion path consists in combining ethanol first and second generation ethanol production plant with a catalytic supercritical water gasification system. The main steps of the ethanol conversion consider fermentation of sugars (1G) and enzymatic hydrolysis of bagasse (2G). Enzymatic hydrolysis is selected since it represents a promising alternative for 2nd generation biofuels due to its high conversion efficiency. Among streams that are leaving the ethanol production plant are some high watered streams, whose carbon/energy content is not negligible. These streams should be valorised in an efficient way in order to improve the energy conversion efficiency. In this context supercritical gasification process allows to valorise these flows leaving the ethanol plant. Using supercritical water gasification it is in fact possible to avoid the drying the ethanol production leftovers, thus performing a direct gasification. The conversion of ligno-cellulosic residues into synthetic natural gas is modelled considering a catalytic supercritical gasification plant. Since the goal is to achieve high energy and exergy conversion efficiencies, the potential use of an additional set of utilities, such as burners, steam injected gas turbines or steam networks, is added to the sizing problem. The mathematical nature of the optimal utility selection problem deals with mixed integer linear programming (MILP) model, in which the type and size of utilities represent the independent variables, having fixed the process size. The results of the integration are showed in terms of Composite and Grand Composite Curves, economic indicators and local CO2 balance. Finally, having identified the ratio of sugarcane that goes to second generation ethanol plant as key dependent variables, the results of a sensitivity analysis are presented. The sensitivity analysis results are shown accounting economics for the Brazilian market, energy conversion performance indicators and considering local carbon dioxide balance.

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Next generation cogeneration system for industry - Combined heat and fuel plant using biomass resources

Ayse Dilan Celebi, François Maréchal, Adriano Viana Ensinas

The requirement for sustainable development has prompted the researchers to explore solutions for better utilization of renewable energy resources in the future. Biomass is a promising resource and it can be converted to multiple products and services including fuels, chemicals, heat and electricity via different conversion routes. Hence, replacement of fossil-based services with biomass-based services is critical to mitigate fossil CO2 emissions, and innovative design of new and efficient energy conversion systems is necessary. Different industries need heat for their operations at different temperature levels. Today, these demands are satisfied using conventional natural gas boilers by imposing a CO2 tax to account for their emissions. In this study, we discuss the potential of replacing conventional boilers with a combined heat and fuel (CHF) plant design which utilizes lignocellulosic biomass in thermochemical conversion to generate heat for different industrial sectors together with biofuels cogeneration. Heat is generated due to the exothermic nature of the thermochemical conversion processes that operate at high temperatures. Gasification process produces syngas which is converted into fuels such as synthetic natural gas, Fischer-Tropsch crude, methanol and dimethyl ether and electricity. Different scenarios are evaluated considering the CO2 produced via this system is either released, sequestrated, or stored and used in a co-electrolysis unit in which surplus renewable electricity available during summer is converted into additional syngas. A parametric analysis has been performed considering type and size of plants, CO2 tax, and purchase and transportation costs of wood to compare the price of heat for the industrial sectors. Natural gas and wood boilers are used as the basis to calculate the breakeven CO2 tax values for the same heat prices for the proposed CHF systems. The results of this study present a state-of-the-art renewable energy system as an alternative to conventional boilers. (C) 2019 Elsevier Ltd. All rights reserved.

2019

Optimal process design for thermochemical production of fuels from biomass

Martin Gassner, François Maréchal

Transport applications are a major global source of greenhouse gas emissions and the production of fuels that are renewable and neutral in CO2 is an important issue in chemical process research and development. Contrary to the biological routes that produce bioethanol and -diesel on industrial scale through fermentation or esterification, 2nd generation biofuels obtained through thermochemical processing of lignocellulosic and waste biomass by means of gasification and fuel reforming are expected to be truly sustainable since high conversion efficiencies and a decidedly positive environmental balance are achieved. The poster addresses the optimal design of such thermochemical fuel production processes with respect to its environomic (energetic, economic and environmental) performance. Thereby, the challenge is to develop design methodologies that allow the identification of the most promising conversion routes in a specific environmental and economical context. Thermo-economic process modelling and integration techniques are coupled with a multi-objective optimisation algorithm to target the best process technology and operating conditions for the trigeneration of fuels, heat and power. The approach is demonstrated on the production of synthetic natural gas from wood considering different gasification technologies and the possibility to increase the fuel yield from biomass and electrical power by integrating an electrolyser in the system.