Characteristics of liquid hold-ups in a soaked and unsoaked fixed bed

Abstract

In most previous works, liquid hold-ups were studied by using a cold model of a fixed bed soaked prior to experiments. However, they did not consider that the dripping zone of a blast furnace is saturated with liquids or with evenly distributed droplets. In the present study, the characteristics of liquid hold-ups and liquid flow were investigated by using a one-dimensional cold model of a fixed bed soaked and unsoaked prior to experiments (initially soaked and unsoaked beds). Packed balls were five kinds, the diameters (DP) of which ranged from 5.4 to 30 mm. Tap water was used as liquid. Contact angles (θ) for these particle/liquid systems were about 70° and 10° for fluorine-coated particles and non-coated particles, respectively. Although, under bad wettability condition (θ ≒ 70°), total and static hold-ups for initially unsoaked bed packed with small balls arc remarkably smaller than those for initially soaked bed, the difference in their hold-ups between initially unsoaked and soaked beds decreases with increasing ball size in the bed. In initially soaked bed, total and static hold-ups increase monotonically as ball size decreases, which means the specific surface area increases. On the other hand, in initially unsoaked bed, total and static hold-ups under bad wettability condition indicate maximum values at about D P =10mm and decrease abruptly in proportion to a decrease in particle size, despite an increase in the specific surface area. Only restricted liquid droplets and/or liquid rivulets are formed within the packed bed with good wettability condition (θ=10°) for initially unsoaked bed, nevertheless liquid is easy to spread out on the solid surface. The influence of the initial bed condition, soaked or unsoaked bed, on liquid hold-ups is great under bad wettability condition.