An environmental optimization model for bioenergy plant sizes and locations for the case of wood-derived SNG in Switzerland

Bioenergy from woodfuel has a considerable potential to substitute fossil fuels and alleviate global warming. One issue so far not systematically addressed is the question of the optimal size of bioenergy plants with regards to environmental and economic performance. The aim of this work is to fill this gap by modeling the entire production chain of wood and its conversion to bioenergy in a synthetic natural gas plant both with respect to economic and environmental performance. Several spatially explicit submodels for the availability, harvest, transportation and conversion of wood were built and joined in a multi-objective optimization model to determine optimal plant sizes for any desired weighting of environmental impacts and profits. We find a trade-off between environmental and economic optimal plant sizes. While the economic optima range between 75 – 200 MW, the environmental optima are with 10 – 40 MW significantly smaller. Moreover, the economic optima are highly location specific and tend to be smaller if the biomass resource in the geographic region of the plant is scarcer. The results are robust with regards to the effect on global warming as well as with respect to the aggregated environmental impact assessment methods Ecoindicator ’99 and Ecological Scarcity 2006.

Systematic integration of LCA in process systems design: Application to combined fuel and electricity production from lignocellulosic biomass

Martin Gassner, Léda Gerber, François Maréchal

This paper presents a methodology to integrate life cycle assessment (LCA)in thermo-economic models used for the optimal conceptual design of energy conversion systems. It is illustrated by an application to a thermo-economic model developed for the multi-objective optimization of combined synthetic natural gas (SNG) and electricity production from lignocellulosic biomass. The life cycle inventory (LCI) is written as a function of the parameters of the thermo-economic model. In this way, the obtained environmental indicators from the life cycle impact assessment (LCIA) are calculated as a function of the decision variables of process design. The LCIA results obtained with the developed methodology are compared with the results obtained by a conventional LCA of the same process. Then, a multi-objective environomic (i.e. thermodynamic, economic, environmental) optimization of the process superstructure is performed. The results highlight the important effects of process configuration, integration, efficiency and scale on the environmental impacts.

Elsevier2011

Identifying environmentally and economically optimal bioenergy plant sizes and locations: A spatial model of wood-based SNG value chains

Martin Gassner, Léda Gerber, Luca Pampuri, Bernhard Steubing

The optimal size and location of bioenergy plants with regards to environmental and economic performance are assessed with a spatially explicit value chain model of the production of synthetic natural gas (SNG) from wood. It consists of several individual models for the availability, harvest, transportation, conversion of wood to SNG, electricity and heat, and the use of these products to substitute non-renewable energy services. An optimization strategy is used to choose the optimal technology configuration for plant sizes from 5 to 200 MW and different locations for any desired weighting between the environmental performance based on life cycle assessment (LCA) and the economic performance. While the economic optima are found at plant sizes between 100 and 200 MW, the environmental optima are found in the range of 5e40 MW. This trade-off can be minimized at plant sizes above 25 MW according to the presented model. The most important driver of the environmental performance is the efficient substitution of non-renewable energy, which is a site-specific factor. In comparison to this, spatial factors such as wood availability, harvest, and transportation, have a smaller influence on the environmental performance, at least for a country of the size of Switzerland. The main drivers of the economic performance are the revenues from the sale of the SNG plant’s products and the SNG production costs, but transportation and wood costs also play a role.

Pergamon-Elsevier Science Ltd2014

Integration of Life Cycle Assessment in the conceptual design of renewable energy conversion systems

Léda Gerber

Life Cycle Assessment (LCA) is a well-established methodology that has been extensively used for the environmental evaluation of emerging technologies in the field of renewable energy conversion systems. In order to identify effective solutions for impact mitigation already at the conceptual process design stage, it is necessary to take into account the environmental aspects in the process design procedure, in consistency with economic and thermodynamic criteria. This thesis presents a systematic methodology for the integration of LCA in the conceptual design of renewable energy systems, using process design, process integration and multi-objective optimization techniques. The developed methodology is illustrated by three application case studies. The first one concerns the evaluation of different candidate technologies for the combined production of Synthetic Natural Gas and electricity from lignocellulosic biomass by thermochemical conversion. The second case study treats of the environomic optimal configurations of Enhanced Geothermal Systems for combined heat and power production, considering different potential conversion technologies. The third case study deals with the design and the synthesis of an urban energy system, accounting for the different energy services to be supplied, the different potential resources, the candidate conversion technologies, and the waste to be treated. In this last case study, the overall supply chains from resources or wastes to services are synthesized, accounting for the industrial ecology possibilities. A first major outcome of these application case studies is that accounting for the process integration in the evaluation of the environmental impacts leads to an important impact reduction. Secondly, the developed methodology allows for calculating the trade-offs between the environmental criteria and the thermo-economic ones. Therefore, the optimal promising configurations of an emerging technology or of a system considering its environmental performances can be identified. Finally, it is demonstrated that integrating the environmental impacts in the process design procedure leads to a different decision-making than if only thermo-economic criteria are considered.

EPFL2012

Integration of Life Cycle Assessment in the conceptual design of renewable energy conversion systems

Léda Gerber

EPFL2012