Effect of Tank Diameter on Solid Suspension in Industrial Reactor Vessels

Abstract

Present research study analyses the suitability of baffled reactor vessels with large diameter agitated using the Rushton Turbine (RT) impeller maintained at standard clearance condition for the solid-liquid suspension process. The mean and turbulent flow fields associated with reactor vessels of various diameter were simulated using Computational Fluid Dynamics (CFD) approach. The impeller rotation was modelled using Multiple Reference Frame (MRF) technique and entrainment of air was simulated using Volume of Fluid (VOF) method respectively. The increase in the diameter of reactor vessel keeping impeller at standard clearance condition lead to the transition from double to single loop pattern with considerable decrease in the power number. In large reactor vessels, a low pressure zone is developed below the impeller which deflects the discharge streams and trailing vortices towards bottom surface of the reactor vessel causing the formation of single loop down-pumping pattern. The downward propagation of trailing vortices weaken the flow separation region behind the impeller blades which in turn decreases the form drag and power number of the impeller. The development of single loop down-pumping pattern, high magnitudes of axial velocity, vortex and turbulence fields near vessel bottom and inferior entrainment of air makes the large reactor vessels suitable for the solid-liquid suspension process. The high magnitudes of axial velocity developed below the impeller of large reactor vessel with same power consumption as compared to low clearance vessel makes the former vessel configuration more suitable for the solid-liquid suspension process.

Keywords

• stirred tank
• mixing
• flow pattern transition
• power number
• trailing vortices
• gas hold-up