Biomass To Liquids | EPFL Graph Search

Biomass is the major source of renewable carbon which can be used to substitute fossil carbon in fuels and chemical products. This thesis addresses the modelling, design and thermoeconomic evaluation and optimisation of processes converting Biomass to Liquids (BtL) for the effective exploitation of a renewable, yet limited, resource. The focus is on thermochemical conversion, through gasification and Fischer-Tropsch (F-T) synthesis, producing drop-in fuels which could be used in the current infrastructure. Given the number of potential technological options and process configurations, a methodology is developed for a systematic comparison in terms of several performance indicators. The analysis is carried out through a framework combining thermochemical modelling, economic evaluation, process integration and multi-objective optimisation. Particular attention is given to the representation of biomass and its coherent modelling in terms of its elemental composition. Experimental data from previous studies is used to develop new thermochemical models for torrefaction and for fluidized bed gasification. Other technologies included in this study are air and steam drying, entrained flow gasification, tar reforming, high temperature tar cracking, water and gas quench and radiant panels, hot and cold gas cleaning, water gas shift, high temperature steam and steam/carbon dioxide electrolysis and F-T synthesis and upgrading. The final comparison, through the multi-objective optimisation, provides a better understanding of the trade-offs of different technological options and process variables in terms of competing economic and thermodynamic objectives. For 200MWth biomass input plant capacities, production costs are in the range of 1.0-1.4 euro/l for technologies producing up to about 0.5 kJFT /kJth and close to being neutral in terms of electricity balance. For technologies using electrolysis the conversion can increase to 0.8 kJFT /kJth with production costs of 1.8 euro/l. The electricity storage capacity, in this case, is of 0.5 kJe/kJFT , corresponding to a net electricity requirement of about 0.4 kJe/kJth. This work stems from the collaboration between LTB (Biomass Technology Laboratory) of CEA/Liten in Grenoble, France, and IPESE (Industrial Process and Energy Systems Engineering) of EPFL in Lausanne, Switzerland.

Thermo-economic analysis and multi-objective optimisation of lignocellulosic biomass conversion to Fischer-Tropsch fuels

Guillaume Boissonnet, François Maréchal, Emanuela Peduzzi

This paper addresses the techno-economic evaluation and optimisation of processes converting lignocellulosic biomass into liquid fuels, through the development of a suitable framework and the modelling and design of Biomass to Liquids (BTL) processes. In particular, the focus is on the production of drop-in fuels through gasification and Fischer-Tropsch (FT) synthesis. Several conversion technologies are presented and evaluated in the literature, but the comparison of different options is hazardous because of the different assumptions and methodologies adopted in each study. A systematic and consistent approach is therefore developed to explore the trade-offs of alternative process configurations and of the operating conditions. The comparison presented in this study explores the trade-offs of different technological options in terms of competing economic and thermodynamic objectives. Results show that for 200 MWth biomass input plant capacities, production costs are in the range of 1.0-1.4 €/l for technologies producing up to about 0.5 kJFT/kJth and close to being neutral in terms of electricity balance. For technologies using electrolysis the conversion can increase to 0.8 kJFT/kJth with production costs of 1.8 €/l. The electricity storage capacity, in this case, is of 0.5 kJe/kJFT, corresponding to a net electricity requirement of about 0.4 kJ e/kJth.

2018

Scenario modelling and optimisation of renewable energy integration for the energy transition

Victor Codina Gironès

A large number of countries have engaged themselves in an energy transition towards more re- newable energy in their energy systems. Motivations stem mainly from the need to reduce CO2 emissions, and from a desire of their population to phase out technologies such as nuclear. Most of these countries promote biomass, wind and solar energy sources, among other possibilities. How- ever the current rate of deployment of renewable energy systems globally is not sufficient to reach the CO2 emissions reduction that would allow to maintain the global average temperature increase below the 2°C threshold. The main barriers to a wider integration of renewable energy systems are i) their limited realisable potential, ii) their still limited competitiveness, iii) their intermittence; iv) public acceptance often related to poor level of energy literacy amongst citizens. Citizens are key decision-makers. They must decide on energy policies and on the energy technologies they use, hence they have the power to foster or halt the energy transition. This thesis presents two different strategies for addressing the problem of the integration of re- newable energy sources for energy transitions. The first one (Chapter 1) consists in developing an energy modelling tool to help decision-makers understand the energy system and find their own answers. The modelling approach also includes a new methodology for the calculation of the total cost of a national energy system. A model of the Swiss energy system has been created following this approach, which serves as basis to develop the Swiss-Energyscope online calculator. This calculator and its model present an optimal trade-off between scientific rigour and user-friendliness, which allows the reproduction of the energy transition scenarios conceived by the Swiss Government, and consequently its use for energy policy making. The second strategy (chapters 2 and 3) profits from the possibilities offered by mathematical mod- elling and optimisation to analyse national energy systems, and derive insights for policy and decision-makers. First, a methodology using a mix-integer linear programming (MILP) model analyses biomass usage pathways to determine its optimal use in Switzeland in 2035. Second, in order to study the role of biomass, non-linear optimisation is applied to create future scenarios. (Chapter 3) focuses on the solutions to deal with the variability of renewable electricity. To this end, a MILP model with hourly time resolution is conceived to study the use of flexible electricity supply and demand options for the integration of renewable electricity. The optimisation methodologies are validated on case studies for the Swiss energy system. Regarding biomass, the results reveal that woody biomass chemical conversion technologies can allow for an overall better performance in terms of CO2 avoided emissions compared to direct combustion, as long as the produced biofuels are used in efficient technologies. Results also show that the combination of the gasification-methanation process of woody biomass with the production of H2 produced from excess electricity would allow to reduce the Swiss natural gas imports to zero by 2050. Concerning the integration of variable renewable electricity, the cost difference between using flexible electricity supply- and demand-options or electricity imports to deal with variable renewable electricity is below 2.5% of the total cost of the energy system.

EPFL2018

Integration of deep geothermal energy and woody biomass conversion pathways in urban systems

Léda Gerber, François Maréchal, Stefano Moret, Emanuela Peduzzi

Urban systems account for about two-thirds of global primary energy consumption and energy-related greenhouse gas emissions, with a projected increasing trend. Deep geothermal energy and woody biomass can be used for the production of heat, electricity and biofuels, thus constituting a renewable alternative to fossil fuels for all end-uses in cities: heating, cooling, electricity and mobility. This paper presents a methodology to assess the potential for integrating deep geothermal energy and woody biomass in an urban energy system. The city is modeled in its entirety as a multiperiod optimization problem with the total annual cost as an objective, assessing as well the environmental impact with a Life Cycle Assessment approach. For geothermal energy, deep aquifers and Enhanced Geothermal Systems are considered for stand-alone production of heat and electricity, and for cogeneration. For biomass, besides direct combustion and cogeneration, conversion to biofuels by a set of alternative processes (pyrolysis, Fischer-Tropsch synthesis and synthetic natural gas production) is studied. With a scenario-based approach, all pathways are first individually evaluated. Secondly, all possible combinations between geothermal and biomass options are systematically compared, taking into account the possibility of hybrid systems. Results show that integrating these two resources generates configurations featuring both lower costs and environmental impacts. In particular, synergies are found in innovative hybrid systems using excess geothermal heat to increase the efficiency of biomass conversion processes. The application to a case study demonstrates the advantages of using a system approach for the analysis over a stand-alone comparison between options.

2016

Scenario modelling and optimisation of renewable energy integration for the energy transition

Victor Codina Gironès

EPFL2018