Optimization of an Externally Mixed Biogas Plant Using a Robust CFD Method

Biogas plants have to be continuously or periodically mixed to ensure the homogenization of fermenting and fresh substrate. Externally installed mixers provide easier access than submerged mixers but concerns of insufficient mixing deter many operators from using this technology. In this paper, a new approach to improve homogenization of the substrate mixture is proposed by optimizing external mixer configurations across a wide range of rheological properties. Robust optimization of a biogas reactor is coupled with CFD simulations to improve parameters for the angles of inflow and the position of the substrate outlet in a large-scale fermenter. The optimization objective is to minimize the area in the tank which is poorly mixed. We propose to define this “dead volume zone” as the region in which the velocity magnitude during mixing falls below a certain threshold. Different dry substance contents are being investigated to account for the varying rheological properties of different substrate compositions. The velocity thresholds are calculated for each dry substance content from the mixer-tank configuration of a real biogas reactor in Brandenburg, Germany (BGA Warsow GmbH & Co.KG). The robust optimization results comprising the whole range of rheological properties are compared to simulations of the original configuration and to optimization results for each individual dry substance content. The robust CFD-based optimized configurations reduce the dead volume zones significantly across all dry substance contents compared to the original configuration. The outcomes of this paper can be particularly useful for plant manufacturers and operators for optimal mixer placement in industrial size biogas fermenters.BMBF - ROENOBIO project with contract number 05M2013UTA (Germany), DFG - RTG 2126 Algorithmic Optimization (Germany

A Practical Approach for Biochemical Modeling in the CFD Evaluation of Novel Anaerobic Digester Concepts for Biogas Production

The detailed physics-based description of anaerobic digesters is characterized by their multiscale and multiphysics nature, with Computational Fluid Dynamics (CFD) simulations being the most comprehensive approach. In practice, difficulties in obtaining a detailed characterization of the involved biochemical reactions hinder its application in the design of novel reactor concepts, where all physics interplays in the reactor must be considered. To solve this limitation, a practical approach is introduced where a calibration step using actual process data was applied for the simplified biochemical reactions involved, allowing us to efficiently manage uncertainties arising when characterizing biochemical reactions with lab scale facilities. A complete CFD modeling approach is proposed for the anaerobic digestion of wastewater, including heat transfer and multiphasic flow. The proposed multiphase model was verified using reference data and, jointly with the biochemical modeling approach, applied to a lab-scale non-conventional anaerobic digester for winery wastewater treatment. The results showed qualitative improvement in predicting methane production when the diameter of the particles was reduced, since larger particles tend to move downwards. The biochemistry of the process could be simplified introducing a preexponential factor of 380 (kmol/m3)(1 – n)/s for each considered chemical reaction. In general, the proposed approach can be used to overcome limitations when using CFD to scale-up optimization of non-conventional reactors involving biochemical reactions

Multi-scale modeling and optimization for industries with formulated products

[ES] La tesis titulada "Multi-scale Modeling and optimization for Industries with Formulated Products" se centra en el desarrollo de modelos matemáticos y técnicas de optimización para este tipo de productos. Por un lado la tesis se focaliza en modelado de secadores con diferentes metodologías. Primero, se desarrolla un modelo cinético de secado de una una única gota. Luego, se desarrolla un modelo basado en mecánica de fluidos computacional (CFD) para los secadores y el cuál se ha validado a escala industrial. Finalmente, se desarrollan modelos basados en "data-driven" y modelos subrogados para reducir el coste computacional del modelo en CFD sin perder su nivel de detalle. Por otro lado, la tesis tiene una segunda parte donde se focaliza en el desarrollo de modelos de optimización matemática para el tratamiento de residuos y la revalorización del biogás

Selected Papers from SDEWES 2017: The 12th Conference on Sustainable Development of Energy, Water and Environment Systems

EU energy policy is more and more promoting a resilient, efficient and sustainable energy system. Several agreements have been signed in the last few months that set ambitious goals in terms of energy efficiency and emission reductions and to reduce the energy consumption in buildings. These actions are expected to fulfill the goals negotiated at the Paris Agreement in 2015. The successful development of this ambitious energy policy needs to be supported by scientific knowledge: a huge effort must be made in order to develop more efficient energy conversion technologies based both on renewables and fossil fuels. Similarly, researchers are also expected to work on the integration of conventional and novel systems, also taking into account the needs for the management of the novel energy systems in terms of energy storage and devices management. Therefore, a multi-disciplinary approach is required in order to achieve these goals. To ensure that the scientists belonging to the different disciplines are aware of the scientific progress in the other research areas, specific Conferences are periodically organized. One of the most popular conferences in this area is the Sustainable Development of Energy, Water and Environment Systems (SDEWES) Series Conference. The 12th Sustainable Development of Energy, Water and Environment Systems Conference was recently held in Dubrovnik, Croatia. The present Special Issue of Energies, specifically dedicated to the 12th SDEWES Conference, is focused on five main fields: energy policy and energy efficiency in smart energy systems, polygeneration and district heating, advanced combustion techniques and fuels, biomass and building efficiency

Generation of (synthetic) influent data for performing wastewater treatment modelling studies

The success of many modelling studies strongly depends on the availability of sufficiently long influent time series - the main disturbance of a typical wastewater treatment plant (WWTP) - representing the inherent natural variability at the plant inlet as accurately as possible. This is an important point since most modelling projects suffer from a lack of realistic data representing the influent wastewater dynamics. The objective of this paper is to show the advantages of creating synthetic data when performing modelling studies for WWTPs. This study reviews the different principles that influent generators can be based on, in order to create realistic influent time series. In addition, the paper summarizes the variables that those models can describe: influent flow rate, temperature and traditional/emerging pollution compounds, weather conditions (dry/wet) as well as their temporal resolution (from minutes to years). The importance of calibration/validation is addressed and the authors critically analyse the pros and cons of manual versus automatic and frequentistic vs Bayesian methods. The presentation will focus on potential engineering applications of influent generators, illustrating the different model concepts with case studies. The authors have significant experience using these types of tools and have worked on interesting case studies that they will share with the audience. Discussion with experts at the WWTmod seminar shall facilitate identifying critical knowledge gaps in current WWTP influent disturbance models. Finally, the outcome of these discussions will be used to define specific tasks that should be tackled in the near future to achieve more general acceptance and use of WWTP influent generators

Biomass Wastes for Energy Production

Environmental problems are forcing a rethinking of the world’s energy supply system. In parallel, there is an increasing amount of global solid waste production. A fundamental shift toward greater reliance on biomass wastes in the world’s energy system is plausible because of ongoing major technological advances that hold the promise of making the conversion of biomass into high-quality energy carriers, like electricity and gaseous or liquid fuels, economically competitive with fossil fuels. Therefore, waste-to-energy systems have become a paramount topic for both industry and researchers due to interest in energy production from waste and improved chemical and thermal efficiencies with more cost-effective designs. This biomass shift is also important for industries to become more efficient by using their own wastes to produce their own energy in the light of the circular economy concept. This book on “Biomass Wastes for Energy Production” brings novel advances on waste-to-energy technologies, life cycle assessment, and computational models, and contributes to promoting rethinking of the world’s energy supply systems