Methodology for the optimal thermo-economic, multi-objective design of thermochemical fuel production from biomass

This paper addresses a methodology for the optimal conceptual design of thermochemical fuel production processes from biomass. A decomposed modelling approach with separate energy-flow, energy-integration and economic models is presented and coupled to multi-objective optimisation, which allows to generate a set of optimal process flowsheets that constitute a sound basis for the synthesis of a viable process

Process integration aspects in the design of biofuel processes

The design of biofuel processes is realised using a computer aided process system design methodology that aim at defining the type and the size of the technologies, the way they are interconnected and the way they are operated for a given socio-economical and environmental context. The method is using thermo-economic and environomic models of sub-systems that are structured in an equipment data base. In order to build the process, the equipment are assembled to build a flowsheet that represents the conversion of the raw materials (biomass) into products and by-products. Considering the different technological options to be used to build the flowsheet, a superstructure approach is used to systematically include all the possible combinations into a single process model from which the best flowsheet will be extracted using optimization techniques. In the process, energy is the driving force of the conversion. Therefore in the process design method, it is important to consider not only the mass flow interactions in the flowsheet but also the heat recovery and the combined heat and power production. The process integration is used to analyse, model and optimize the possible interactions between the equipments in the flowsheet. In the biofuel production processes, optimizing the process integration is of a major importance especially in thermo-chemical processes since the resource is also the energy source. Therefore increasing the efficiency of the energy conversion will at the sime time optimize the conversion efficiency of the raw material, maximizing the fuel production per unit of biomass. Several aspects of the process integration in biofuel production will be discussed and illustrated based on examples of synthetic natural gas and liquid fuels production from lignocellulosic biomass using thermo-chemical processes

Integration of LCA in a thermo-economic model for multi-objective process optimization of SNG production from woody biomass

This paper presents a methodology to integrate life cycle assessment (LCA) in models used to design energy conversion systems. It is illustrated by an application to a thermo-economic model for the multi-objective optimization of synthetic natural gas (SNG) production from woody biomass. The life cycle inventory (LCI) is written as a function of the parameters of the thermo-economic model. The obtained environmental indicators from the Life Cycle Impact Assessment (LCIA) are thus adapted to process design and scale. The conceived thermo-environomic model allows for taking into account the environmental impacts as a criterion in addition to economic and thermodynamic criteria in the process design and optimization

A Multi-Objective Optimization Method to integrate Heat Pumps in Industrial Processes

Aim of process integration methods is to increase the efficiency of industrial processes by using pinch analysis combined with process design methods. In this context, appropriate integrated utilities offer promising opportunities to reduce energy consumption, operating costs and pollutants emissions. Energy integration methods are able to integrate any type of predefined utility, but so far there is no systematic approach to generate potential utilities models based on their technology limits. This work focusses on the integration of industrial heat pumps and the development of a corresponding heat pump data base. This latter offers the possibility to integrate different heat pump types to any process, in a flexible and systematic way. A methodology, integrating the heat pump data base in an energy integration problem, and using multi objective optimization in order to identify optimal solutions, is presented. The results of a brewery process are presented and analyzed

Process design optimization strategy to develop energy and cost correlations of CO2 capture processes

In the context of CO2 emissions reduction from power plants, CO2 removal from flue gas by chemical absorption with monoethanolamine is analyzed in detail. By applying process integration and multi-objective optimization techniques the influence of the operating conditions on the thermo-economic performance and on the optimal thermal integration within a power plant is studied. With the aim of performing optimization of complex integrated energy systems, simpler parameterized models of the CO2 capture process are developed. These models predict the optimized thermo-economic performances with regard to the capture rate, flue gas flowrate and CO2 concentration. When applied to overall process optimization, the optimization time is considerably reduced without penalizing the overall power plant model quality. This approach is promising for the preliminary design and evaluation of process options including a CO2 capture unit

Process integration aspects of the design of a gas separation system for the upgrade of crude Synthetic Natural Gas (SNG) to grid quality in a wood to methane process

The present paper investigates the prospects of process integration of the biogenic production of crude synthetic natural gas (SNG) and its upgrade to grid quality. At the example of a separation by means of a membrane cascade, a holistic design approach targeting the overall process performances is presented. Compared to a design obtained from an isolated approach, it is shown that a considerable reduction of the size and cost of the separation system is possible if a tight process integration is considered in the system design

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

CO2 Mitigation in Thermo-Chemical Hydrogen Processes: Thermo-Environomic Comparison and Optimization

AbstractA systematic comparison and optimization of thermo-chemical hydrogen production processes with CO2 capture is performed. The process options include the resource type, the syngas production method and the hydrogen purification technology, including CO2 separation by ab- or adsorption or membrane processes. With regard to climate change mitigation, the removed CO2 can be compressed for storage. To analyze the competitiveness of different CO2 capture options and H2 process alternatives a consistent multi-objective optimization methodology combining energy-flow models with process integration techniques and economic and environmental evaluation is applied. The potential of efficient decarbonization in fossil and renewable H2 processes is highlighted

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

Thermo-chemical H2 production: Thermo-economic modeling and process integration

Within the global challenge of climate change and energy security, hydrogen is considered as a promising decarbonized energy vector to be used in electricity production and transportation. In this paper, the thermo-chemical production of hydrogen by natural gas reforming and by lignocellulosic biomass gasification are analyzed, compared and optimized by developing thermo-economic models. Combining flowsheeting with process integration techniques, thermo-economic analysis and life cycle assessment (LCA), a systematic comparison of different process options with regard to energy, economic and environmental considerations is made. The choice of the technologies is optimized together with the operating conditions using multi-objective optimization. In both natural gas and biomass based H2 pathways, a CO2 removal step is included during the H2 purification which allows for CO2 capture and further sequestration. The potential for greenhouse gas mitigation is assessed and compared with conventional plants without capture based on the CO2 avoidance cost and the overall CO2 equivalent emissions computed from the life cycle chain. The system’s performance is improved by introducing process integration valorizing the waste heat by the combined production of heat and power. The H2 application purpose and the corresponding required purity are key factors defining the process performance. The trade-offs between competing thermoenvironomic (i.e. energy, economic and environmental) objectives are finally assessed using a multi-objective optimization. For natural gas based H2 production overall energy efficiencies up to 80% and production cost of 22-110 USD/MWH2 are computed compared to around 60% efficiency and 75-263 USD/MWhH2 for biomass based processes having the advantage of using renewable resources. The CO2eq emissions are reduced by more than 6.4kgCO2eq/kgH2 for NG and 20kgCO2eq/kgH2 for BM processes compared to the cases without CO2 capture. The competitiveness on the energy market depends strongly on the resource price and on the imposed CO2 taxes. Our study shows that the thermo-chemical hydrogen production has to be analyzed as a polygeneration unit producing not only hydrogen but also captured CO2 and electricity