Fluidization Characteristics and Separation Performance of an Air Dense Medium Gas-Solid Fluidized Bed Based on the Secondary Air Distribution Layer

The secondary air distribution layer was introduced to improve the air distribution stability of the conventional air dense medium gas-solid fluidized bed. With the 0.074-0.3 mm magnetite powder as the dense medium, the apparent fluidization characteristics of the fluidized bed were investigated with various-sized quartz sand as the filling of secondary air distribution layer. The results showed that the optimum fluidization numbers were 1.6, 1.7 and 1.5 for achieving the stability of the bed density with the quartz sand of 0-0.15, 0.15-0.3 and 0.3-0.5mm as the filling of secondary air distribution layer, respectively. The separation efficiency of 10-15 and 15-20 mm lignite using the dense medium gas-solid fluidized bed were investigated through the orthogonal separation experiments based on the variables of various-sized quartz sand, static bed height, fluidization number, and height of the secondary air distribution layer. The results indicated that the appropriate size fractions of the quartz sand were 0-0.15 and 0.15-0.3 mm for the efficient separation of 10-15 and 15-20 mm lignite. Under the conditions, the ash segregation degree reached the maximum of 0.70 and 0.78, respectively. The ash contents of 10-15 and 15-20 mm lignite were decreased from 15.32% and 14.35% to 8.25% and 9.49% with the clean coal yields of 28.26% and 50.57%, respectively. This technique provides an alternative approach for the cleaning of low-rank coal in the arid and water-deficient countries.