Numerical and Experimental Study on the Colliding Flow Pulp Conditioning for the Separation Intensification of Unburned Carbon from Coal Gasification Slag

As a byproduct of the coal gasification process, a large amount of coal gasification slag is generated. The failure to fully dispose of it has caused the occupation of land resources and environmental pollution. Before its comprehensive utilization, the carbon and ash constituents must be separated, for which flotation is an effective method. However, the small difference in surface hydrophobicity of them cannot result in a high-efficiency separation. Therefore, a colliding flow pulp conditioning device (CFPCD) was proposed in this work to improve the interaction between the collector droplets and fine particles, and strengthen the modification of collector on the particle surface by generating a properly constructed turbulent flow field. Computational fluid dynamics (CFD) was employed to simulate the internal flow field of CFPCD to obtain the critical flow field parameters, such as the velocity, strain rate, turbulent kinetic energy, turbulent dissipation rate, and turbulent eddy scale. Additionally, particle wrap angle measurements and flotation tests were conducted to verify the performance of pulp conditioning. The results showed that a velocity gradient was obvious in the inner cylinder colliding flow area, thereby inducing the large strain rate and the intense turbulence, which were responsible for the pulp homogenization and the enhanced particle-collector interaction. With the feeding velocity increased, the fluid shear was larger and the improved performance was more obvious. According to the flotation results, the maximum recovery of unburned carbon was obtained with the feeding velocity equal to 2.5 m/s, which was consistent with the tendency of wrap angle. Meanwhile, the loss on ignition of the tailings reached the optimal value, corresponding to 9.94%.