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Multi-AD 4 AgroSMEs Project was born from the anaerobic multiphase reactor patented by AEMA. This technology was experimentally tested at a 0.1 m3 pilot scale prototype giving promising results regarding efficiency, environmental impact and costs. One of the objectives of the project is the development of a new design based on AEMAs prototype and adequate for its operation at the industrial scale. This upscaling process was supported by Computational Fluid Dynamic (CFD) modeling, a technique that provides information about the performance of a new design prior to its construction.

Computational Fluid Dynamics (CFD) makes use of numerical methods and algorithms to solve problems regarding fluid mechanics that is the physics branch studying the liquid and gaseous movement and the forces causing them. ITAINNOVA has wide experience on CFD modeling and simulation and its application on industry for virtual sensoring, model based control, process optimization and product design.

Anaerobic reactors for wastewater hydrolysis, acidogenesis, acetogenesis and methanogenesis. The organic matter contained in the water (liquid) is put into contact with the biomass (solid particles) to degrade it and generate biogas (gas). An adequate mixing of liquid and solid particles is essential to achieve high reaction yields. Multi-AD reactor takes advantage of the turbulence created by geometry to provide mixing avoiding the use of mechanical stirring.

The upscaling of the process made it necessary the modification of the pilot plant design to adapt it to industrial plants characteristic requirements. Structural limitations, safety and economical efficiency goal were the main challenges tackled in the reactor redesign process. It was accomplished in three steps: i) the acquisition of knowledge about pilot plant performance (specially the mixing level), ii) the proposal of design modifications meeting the industrial size requirements and iii) the evaluation of the new design mixing level. CFD models and simulations were key tools in all these steps.

A complete Multi-AD reactor model comprises a multiphase (solid particles, liquid and gas) model, a turbulence model, and solving biochemical reactions together with energy and species transport equations. This complexity makes the model computationally demanding and, thus, the simulation becomes time consuming. During the upscaling, several geometries had to be tested. This kind of complex model was therefore incompatible with a quick design procedure.

A methodology was developed to address this issue. Different models were implemented to adapt their features, mainly accuracy and computation demand, to the agility required in each part of the process. The model was modified into three levels of simplification concerning the mesh, the number of phases involved, and the phenomena studied. The complex pilot plant model was used to determine the accuracy of each simplification and the parameters indicating good mixing and adequate performance.

The simplest model permitted fast geometry modification and real time simulation. It was used in an initial screening of multiple different designs. Results provided no accurate values but trends indicating the most promising geometries. This selection was simulated and analyzed using the subsequent level of simplification models to obtain quantitative results and determine the most adequate design.

The selected reactor represents a balance among performance, construction viability and costs. It is already installed in the demonstration plant and will be tested within the Multi-AD 4 AgroSMEs project during the next months.