Sedimentacion FUNDAMENTO TEORICO

FUNDAMENTO TEORICO

SEDIMENTATION

Sedimentation is the unitary operation consisting of separating by gravity a solid finally divided from the liquid in which it is suspended, as a result of this process a clear liquid is obtained, and a suspension with a higher concentration of solids.

1. SIMPLE SEDIMENTATION

By simple sedimentation, the operation of removing solid particles contained in a fluid by gravity is generally part of the primary treatments and is intended to charge sedimentable solids whose particle sizes are relatively large.

2. INDUCED SEDIMENTATION

Also called decantation, it refers to the sedimentation of colloidal particles, whose coagulation or agglomeration has previously been included by chemical agents such as alum or ferric hydroxide, among others.

THE SETTLERS

Are tanks of large diameter and shallow with a rake in the bottom that rotating slowly, force the mud to the exit hole located in the deepest part. The clarified liquid overflows the edges of the tank being collected in an open channel that is arranged peripherally, the food is introduced through the center of the tank.

Industrial settlers can perform:

Discontinuous sedimentation operations.

Continuous sedimentation operations.

1. Sedimentation operation continues.

It consists in feeding a constant diluted suspension to a device from which clarified liquid and concentrated suspension or sedimentation sludge are extracted, with constant flow.
Continuous settlers or thickeners are tanks of large diameter and shallow with a rake in the bottom that rotates slowly, forcing the sludge towards the exit hole located in the deepest part. The clarified liquid overflows the edges of the tank being collected in an open channel that is arranged peripherally, the food is introduced through the center of the tank.

2. Stages of discontinuous sedimentation.

A description of a discontinuous sedimentation experiment on a glass cylinder or specimen will be used to explain how this operation will take place in order to be able to observe through the walls of the vessel the changes taking place within the suspension.

DISPLACEMENT OF SOLIDS THROUGH A FLUID

The direction of movement of the particles of a solid within a fluid will be from top to bottom, or vice versa, depending on the relative density of the solid with respect to the fluid. Those particles whose density is lower than that of the fluid, will rise and float, while the denser ones will submerge and descend into the same.

THE PRESSURE GAUGE METHOD

The technique is based on the measurement of the pressure increase on the tank bottom owing to the suspension of solid particles. In order to understand how pressure measurements can give information on the amount of suspended solids, one may consider that when solid particles lie on the vessel bottom their apparent weight is borne by the bottom it self by direct mechanical interaction with the particles. On the other hand, when particles are lifted into suspension, their apparent weight is borne by the liquid, which eventually discharges it on the vessel bottom as a pressure increase with respect to the case where no particles are suspended. Another way of looking at the same phenomenon, is by considering that when particlesare suspended, the apparent density of the agitated fluid phase increases, resultingin a greater hydrostatic pressure gradient and hence again in a greater hydrostatic head on the tank bottom. In the following, the relation ship between the pressure increase and the mass of suspended  particles will be derived by simply performing an macroscopic force balance on the system, which is defined as the volume occupied by the liquid and particles introduced in the vessel.

HYDROSTATIC PRESSURE

Is the force per unit area that exerts a liquid at rest on the walls of the container that contains it and on any body that is submerged, as this pressure is due to the weight of the liquid, this pressure depends on the density (p), The gravity (g) and the depth (h) of the place where we measure the pressure.

SEDIMENTACION

La sedimentación es la operación unitaria que consiste en separar, por acción de la gravedad un sólido finalmente dividido del líquido en el que está suspendido, como resultado de este proceso se obtiene un líquido claro, y una suspensión con mayor concentración de sólidos.

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