Disintegration of lime mud particles - influence of type of impeller

The disintegration of lime mud particles during slaking and causticizing ha s been studied. This work was focused on the influence of the type of impel ler: a high-flow impeller a pitched-blade turbine and a Rushton turbine wer e investigated. Tests were made in a batch reactor having a capacity of 65 kg suspension. A model describing the disintegration was developed. The experimental study showed that, for residence times longer than 10 minu tes, the particle size was influenced by the mechanical energy input from t he impeller as well as its design. It was found that the bulk flow (kinetic energy in macro-scale) has a major impact on the disintegration of the lim e mud agglomerates. Nevertheless, it was possible to characterise this phen omenon by introducing the average turbulence fluctuation (kinetic energy in micro-scale). This was possible since the kinetic energy generated by the impeller roughly can be divided in micro-scale and macro-scale kinetic ener gy. The model developed describes the average particle size as a function o f the energy input, the turbulence fluctuation and the initial particle siz e. The model has two material-specific parameters which were determined by fitting the model to the experimental data. It was found that, at constant impeller speed and constant residence time, the influence on the particles increased in the order: high flow impeller < pitched blade turbine < Rushto n turbine. At constant energy input the order is reversed.