Structural optimization and performance evaluation of high-solid anaerobic digestion reactors by CFD simulation at various scales

High-solid anaerobic digestion (AD) is an effective method for treating organic solid waste. However, high solid concentrations can hinder mass transfer, leading to uneven mixing and reduced gas production efficiency. This study employs computational fluid dynamics (CFD) to simulate the multiphase (solid-liquid-gas) flow in a horizontal reactor, providing insights into its rheological properties, which can be used to optimize the structural and operating conditions of the reactor. The key factors, such as blade type, inclination angle, blade spacing, rotational speed, and solid content, are comprehensively investigated. The results suggest that an optimized combination of parameters significantly increases the area of high flow velocity within the reactor, enhancing the uniformity of solid distribution and reduces the standard deviation of concentration. However, higher solid content in the reactor expands the regions of high-solid-concentration and increases viscosity, resulting in greater energy consumption. Therefore, it is recommended to use C- or Z-type blade in reactor design. The inclination angle should be set between 10 degrees and 20 degrees, and the blade spacing should be adjusted between 250 mm and 447 mm depending on the gradient scale. Additionally, the rotational speed should be maintained between 3 and 5 rpm. These findings offer valuable guidance for designing high-solid AD reactors with good performance.