Importance of Solid-Liquid Separation

In many processes, solid-liquid separation is an essential and important procedure. Basically, the aim, starting from a suspension, is to separate the liquid and the solid phases. The task here determines both the correct selection of the filtration process and also the technical configuration of the installation.

Liquid-solid separation involves the separation of two phases, solid and liquid, from a suspension. It is used in many processes and is divided into 4 stages based on the necessity of the  component, these 4 stages are as follows:

  1. Recovery of valuable solid components, here the liquid is being discarded.
  2. For the recovery of liquid, here the solid is being discarded.
  3. Recovery of both the components that are solid and liquid.
  4. Recovery of neither of the two components, solid or liquid. (e.g., when a liquid is being cleaned prior to discharge, as in the prevention of water pollution).

Solid/liquid separation is all too often designed as a ‘stands alone’ unit in a plant flowsheet. The performance of a solid/liquid separation device is sensitive to the history of the feed solution and, in particular, to the properties imparted to the suspension by its method of manufacture, e.g., on the shape, size, and size distribution of the particles, which result from the operating conditions in the precipitator or crystallizer. A change in particle production conditions can affect the best choice of filter for a particular purpose. The economics and viability of producing the product are often affected by the amount of liquid removed in the post-treatment processes. For example, if the cake is to be transported, briquette,d or pelletized, cake moisture content will need to be within a specified range; or if a bone dry product is required the thermal load on the dryers can be reduced by correct choice and operation of the filter.

It is important, therefore, to consider simultaneously and in some detail those processes which are to feed suspension to the solid/liquid separations plant, and the subsequent processing of the solid or liquid products.

Primary properties:- Primary properties are those which can be measured independently of the other components of the system; specifically, they are the solid and liquid physical properties, the size, size distribution, and shape of the particles, and the surface properties of the particles in their solution environment.

State of the system: The description of the state of the system (porosity or concentration, and the homogeneity and extent of dispersion of the particles) combines with primary properties to control the macroscopic properties, which are measured to investigate the application of a particular separation method. Such measurements may be the permeability or specific resistance of the filter bed or filter cake, the terminal settling velocity of the particles or the bulk settling rate of the suspension.

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