Fluidization and separation characteristics of gas–solid separation fluidized bed with wet coal

Abstract

Raw coal is usually sorted using a gas–solid separation fluidized bed in a dry environment. However, when wet coal is sorted, the moisture carried by the coal causes the fluidized environment in the gas–solid separation fluidized bed to become extremely complex. In the present study, the mechanism whereby moisture is transferred to the medium particles was examined, the phenomenon that the coal and medium particles were subject to an agglomeration mechanism was found. The surface bonding properties of coal are affected by the particle size, moisture content, and the relative motion of the coal and medium particles, which is determined by the formula for calculating the bridging force. The effect of the moisture content on the fluidization characteristics is such that an increase in the water content exacerbates the agglomeration of the media particles, especially once the water content exceeds 1%, with channel flow and local collapse occurring in the fluidized bed (e.g. Sp = 0.33 in the axial direction), which adversely affects the sorting. Through a study of the coal surface adhesion and sorting, it was revealed that the critical amount of external moisture for the effective separation of coal falls with the particle size. For medium- and fine-grained coal, the critical moisture content can be as low as 2% and 1%, while the value can be as high as 4% for the coarse-grained coal.