Noriyuki Yamada

Coating mass distributions of seed particles in a tumbling fluidized bed coater. Part II. A Monte Carlo simulation of particle coating

Abstract In the preparation of coated particles, a homogeneous distribution of the coating mass is often desired and much effort is made to obtain this. If it is possible to predict the effect of operating conditions on coating mass distributions by computer simulations, some of the experimental difficulties will be reduced. Therefore, in this study, Monte Carlo simulations of coating mass distribution of particles were performed to reproduce a series of experimental results obtained using a tumbling fluidized bed. This method was found to be applicable for reproducing the effect of the operating conditions on the coating mass distributions showing that a more homogeneous distribution was achieved under the following conditions; long coating time; small hold up of core particles; high rate of mixing of the particles, etc. Furthermore, some predictions of the effect of operating conditions on coating mass distributions using this simulation method were performed.

Coating mass distributions of seed particles in a tumbling fluidized bed coater

In order to control the extent of particle coating, it is necessary to clarify how the amount of coating material of each individual seed particle varies with operating condition. The influence of these conditions on the distribution of the mass of coating material, deposited on each single seed particle treated in a tumbling fluidized bed, was experimentally examined in this work. As a result, the coating mass per unit surface area of a single seed particle was proven to obey a normal distribution by number. Moreover, it also became clear that the coefficient of variation of the coating mass distribution, cv, decreased with increasing coating time and size of the seed particle, and with decreasing their holdup. However, the rotational speed of the disk, which forces the aggregative coated particles apart, hardly affected the cv value in the experiment.

Coagulation and dispersion of red mud suspensions

Abstract Red mud is a waste stream the Bayer process for alumina production. This paper deals mainly with the influence of pH on the coagulation and dispersion of red mud suspensions. For the purpose of understanding the coagulation and dispersion phenomena of dilute red mud suspensions, the relationship between zeta potential of red mud and pH is measured, and the phenomena in the case of basic suspensions are analyzed by using the experimental data of zeta potential and the DLVO theory. It is shown that the theory agrees fairly well with the experimental results. Furthermore, measurements of the specific volume of sediment, the zeta potential, the mass fraction of less than 2 μm in red mud and the apparent viscosity of some kinds of slurries, show that in order to entirely disperse red mud suspensions, the addition of a dispersing agent to the suspensions is necessary.

Coagulation of red mud suspensions with an inorganic coagulant

Abstract This paper deals with the coagulation of red mud (a waste product from the Bayer process to produce alumina) in water with an inorganic coagulant (FeCl 3 ·6H 2 O). The coagulative state is evaluated by measuring the transmittance of supernatant liquid and/ or the specific volume of the sediment in suspensions after standing for 24 h. It is found that the most important factor in coagulating red mud is maintaining the pH of solutions in suspensions within the range of 7 to 8 regardless of red mud concentration, because the zeta potential of red mud in this pH range is less than approximately |13| mV, which is already known as the potential range necessary to coagulate fine particles in general.

Change in density distribution with time caused by segregation in a continuous fluidized bed nuder unsteaby state.

偏析を伴う矩形の連続式流動層について, スタートアップ時における層の高さ方向の密度分布が時間とともに変化する様子を理論および実験により検討した.物質収支に基づくシミュレーションのためのモデルにおいて層内に投入された試料は平均滞留時間に比較し, 無視しうる時間内に層の上下方向の偏析を完了し, 軽質粒子は層上部排出部から薄層状で, 重質粒子は層下部排出部から実験的に決定される分配関数にしたがって排出されると仮定している.実験は, 未燃炭の含有のため連続的な密度分布をしめす石炭灰を用いて行った.層内の密度分布は供給速度に対する下部からの粒子の排出速度の割合により変化した.定常状態は平均滞留時間のおよそ5倍の時間の後に達成された.シミュレーションと実験結果とはよい傾向の一致を示した.