Mixing in Biogas Digesters and Development of an Artificial Substrate for Laboratory‐Scale Mixing Optimization

Abstract

The current state of the art in mixing of biogas digesters is described and the areas where future research needs to be concentrated are outlined. Since mixing is the biggest contributor to energy consumption in digesters, it is important to optimize it in order to improve the overall cost-effectiveness of biodigestion. This optimization problem is a large-scale nonlinear mixed-integer problem with many decision variables. Also, an artificial substrate for lab-scale experimental studies on digester mixing is introduced. This artificial substrate has several properties crucial for the task like rheological behavior which allows for transferring the results of the labscale experiments to full scale, transparency to observe flow patterns, and thus, quantify the degree of mixing, stability preventing the substrate to change its rheological properties over time, and lack of any health hazards

CFD Modelling of Biomass Mixing in Anaerobic Digesters of Biogas Plants

“…spatial and operational arrangements of agitators) is required [5]. Laboratory scale experiments and computational simulations emerge as convenient and appropriate approaches to investigate the mixing in term of fluid dynamics [6], [7].…”

Operational Parameters of Biogas Plants: A Review and Evaluation Study

“…Enhance the metabolism of the microorganisms and enhance the anaerobic process stability. Moreover, the mixing assists the gas-bubbles to flow upwards from the biodegradable feedstock at high total solids values [26,91,92].…”

Numeric Simulation‐Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants

“…Several models describe the flow of non‐Newtonian fluids. In the present study, the power‐law model of Oswald‐de Waele was selected because it is relatively simple and empirically valid for Newtonian and non‐Newtonian fluids . In the model, the shear stress τ and applied shear rate S are related by a consistency factor K and a dimensionless power‐law index m : …”

“…According to the dimensions at the reference plant (UTS in Dorfen) (see Figs. 1d, e), in the CFD model was D (R1) = 0.94 m and D (R2) = 1.5 m. The dynamic viscosity of digester substrates was measured experimentally using a three‐bladed rotational viscometer at the plant; results have been reported in a previous study of the authors . For a substrate with DMC = 12 wt % and ρ = 1090 kg m −3 , the dynamic viscosity was 5 Pa s. Tab.…”

“…Testing the different design concepts in anaerobic digesters, which are filled with biomass, is not only cost‐ and time‐intensive but also challenging, due to the insufficient optical access and chemistry of the atmosphere , . Therefore, many research laboratories are equipped with scaled‐down digester prototypes and safe and easy‐to‐handle artificial substrates to simplify the understanding of the physical systems . Instead of monitoring biogas production, fluid flow patterns are investigated and velocity distributions are analyzed .…”