Characterisation and analysis on the agitation of downward pitched blade turbine in the Stirred Tank Reactor

In anaerobic digestion biogas plant industry, high-efficiency agitation system in the Continuously Stirred Tank Reactor (CSTR) is vital for encouraging mixing between substrates and bioliquids with low energy consumption. This study numerically investigated the downward pumping agitation system in an industrial CSTR test site to explore the dynamic characteristics of flow patterns with varied pitched blade turbine (PBT) design. A novel approach was developed to visually distinguish the agitation zone in the CSTR tank, which could be utilised to quantitatively assess the agitation performance and to assist the design of impeller spacing. The numerical approach would vastly improve the cost-efficiency to investigate the close connections among impeller spacing, pitched angle, and agitation intensity The pitched angle was found having more prominent effects on the shape and size of formed circulation loops in the tank. The 45-degree would be the critical pitched angle for PBT since the agitation zone would be rapidly shrunk once the configuration goes beyond this value.