Flow field simulation of agitating tank and fine coal conditioning

•The relationships between flow field parameters,impeller size,and agitating speed were studied.•The effects of flow field parameters on flotation indices were analyzed.•Maximum shear rate plays a more important role than fluid velocity and average shear rate for fine coal conditioning.•The values of impeller power consumption were calculated and their influences on flotation indices were studied.•An effective conditioning mode of small diameter with high agitating speed for − 0.074 mm coal was proposed.

Numerical simulation was performed to predict the flow field parameters in an agitating tank. The relationship between characteristic parameters, impeller size, and agitating speed was studied. The conditioning and flotation tests were conducted by using fine coal from Henan province in China. Based on the simulation results, the effects of velocity, shear rate, and power consumption on conditioning and flotation processes were discussed. Maximum shear rate had more notable influence on fine coal flotation indices than fluid velocity and average shear rate. The agitating mode of smaller diameter with higher speed had better performance and lower power consumption than larger diameter with lower speed for fine coal conditioning. Particle size analysis indicated that the combustible recovery and flotation efficiency of the − 0.074 mm fraction significantly increased with the increase of maximum shear rate.