Use of an air fluidized bed separator in a dry coal cleaning process

Abstract

Experimental investigations into the effects of coal particle size and process variables (fluidized bed depth, superficial gas velocity, coal to magnetite feed weight ratio and processing time) on coal cleaning efficiency in a bubbling, fluidized bed dry coal purifier indicate that particles smaller than 30 mesh and larger than 140 mesh can be cleaned with high efficiency. Particles smaller than 140 mesh are subject to high interparticle cohesive forces, resulting in a relatively poor cleaning performance. The coal cleaning experiments were conducted on various size fractions of one of Pennsylvania's bituminous coals, Rushton coal. Magnetite was used to enhance the segregation rate. Estimates of the segregation behavior of the bed under different process variables were obtained by using a theoretical bubbling air-fluidized bed model. The results indicate that the fluidized bed should be operated using shallow bed depths and processing times of 30 seconds or more. In addition, the values of superficial air velocity and feed weight ratio of coal to magnetite should be selected in certain ranges to achieve improved efficiency. The performance of the coal cleaning process is measured with the aid of sulfur and ash removal efficiencies as well as generalized distribution curves. Theoretical model predictions agree with the results from coal cleaning experiments. Thus, the cleaning efficiency is a strong function of operating conditions, bed configuration and coal particle size.