Moisture transfer of wet coal and its effect on fluidization behavior in a gas–solid separation bed

Abstract

The characteristics of gas–solid fluidized beds, which are often applied for the separation of minerals, are affected by the moisture carried by wet coal. 3D X-Ray Microanalyser (3D-XRM) and electrical capacitance tomography (ECT) were used to monitor the moisture transfer process of wet coal, as well as the structure and distribution of agglomerates formed in the bed. The fluidization performance of the bed was then studied by a high-speed camera system and pressure drop measurement. The moisture in the wet coal was found to be mainly in the form of free moisture or external moisture on the coal surface. The free moisture mainly formed agglomerates of magnetite, whereas the external moisture caused magnetite to adhere to the surface of raw coal. The agglutinating value of wet coal is mainly affected by external moisture and size fraction, but has little correlation with coal density. The tendency of the formed agglomerate content can be divided into three stages: (i) When the external moisture is 1%, no agglomerates appear in the bed; (ii) When the external moisture reaches 2%, agglomerates are present in the form of magnetite adhering to the coal surface; (iii) When the external moisture exceeds 3%, magnetite adhered to the coal surface is dominant for the agglomerates. Excess moisture will cause the magnetite itself to agglomerate and participate in the internal particle circulation in the bed. At the same time, the moisture content plays a crucial role in the fluidization behavior of the bed. As the moisture content increases, the fluidization behavior of the bed begins to transition from group B to An under low moisture content (<0.25%), and eventually to group C for high moisture (>0.75%).