# Equipment used in the filtration process

Filtration equipment or apparatus is used to filter, thicken, or clarify a mixture of different elements. There are several different ways to classify equipment.

## Types of Equipments or apparatus used in the filtration

The following is a list of different types of filtering equipment:

### (i) Sedimentation equipment

This equipment uses a gravitational force or chemical process to cause particles to settle to the bottom. Equipment that uses flocculation and gravity sedimentation is included in this category.

Flocculation: Flocculation is the formation of a cake or aggregate, usually through a chemical process, although a magnetic field may be used for particles containing iron. Flocculation is an important process in the treatment of wastewater.

Gravity sedimentation: Gravity sedimentation is used to reduce the solids concentration of the material to be processed. It can be either a clarification or a thickening process. In gravity sedimentation, the heavier particles sink to the bottom under the force of gravity. The rate of settling varies depending on the difference in density between the liquid phase and the solids and the size of the solid particles.

### (ii) Gravity filtration equipment

Gravity filtration equipment uses the hydrostatic pressure of a pre-filter column above the filter surface to generate the flow of the filtrate. Common products include bag filters, gravity nutsches, and sand filters. Bag filters are used mainly as collection equipment. They use bag-shaped woven-fabric or felt filters. Bag filters are not recommended for process filtration. A gravity nutsche is a tank with a perforated or porous false bottom. They may or may not have a separate filter medium. The hydrostatic head of the slurry in the tank provides the filtration driving force. The sand filter is the most common type of gravity filters used. It is constructed of a tank containing layers of gravel and sand or pulverized anthracite. The size of the bed particle decreases from bottom to top of the bed. This granular bed forms the filter media. Sand filters are clarifying equipment that forms a cake on the surface. They are used almost exclusively for water conditioning.

### (iii) Vacuum filtration equipment

Vacuum filtration is a category of liquid-solid separation equipment and this type of filtration equipment has many different types. Vacuum filters are available in batch (vacuum nutsches and vacuum leaf filters) and continuous (drum filters, disk filters and horizontal filters) operating cycles. Continuous vacuum filters are widely used in the process industry. The three main classes of continuous vacuum filters are drum, disk, and horizontal filters. All of these vacuum filters have the following common features:

(i) A filtering surface that moves from a point where a cake is deposited under a vacuum to a point of solids removal, where the cake is discharged through mechanical or pneumatic means, and then back to the point of slurry application.
(ii) A valve to regulate pressure below the surface.
(iii) An apparently continuous operating cycle that is actually a series of closely spaced batch cycles.

For example, disc filters, horizontal belt filters, rotary drum filters, rotary drum pre-coat filters, table filters, tilting pan filters, tray filters, and vacuum nutsches.

### (iv) Pressure filtration equipment

Pressure filters operate at super atmospheric pressures at the filtering surface. The media is fed to the machine by diaphragm, plunger, screw and centrifugal pumps, blow cases and streams from pressure reactors. Most pressure filters are batch or semi-continuous machines. Rotary drum pressure filters have continuous operating cycles and are more expensive and less flexible than batch machines. For example, automatic pressure filters, candle filters, filter presses, horizontal plate pressure filters, polishing filters, and vertical pressure leaf filters.

### (v) Thickening equipment

Thickening equipments (Thickeners) are used to separate solids from liquids by means of gravity sedimentation. Most thickeners are larger, continuous operation pieces of equipment. They are used for heavy duty applications such as coal, iron ore taconites, copper pyrite, phosphates, and other beneficiation processes. Thickeners are a category of industrial filtration equipment that includes conventional thickeners, high-rate thickeners, lamella thickeners, and tray thickeners.

### (vi) Clarifying equipment

Clarifying equipments (Clarifiers) encompass conventional clarifiers, sludge-basket clarifiers, suction clarifiers, and reverse osmosis (RO) clarifiers. The primary end product of clarifiers is a clarified liquid. They are virtually identical in design to thickeners, but have a lighter duty drive mechanism. They are generally used for industrial and residential waste. For example, conventional clarifiers, reverse osmosis equipment, sludge-blanket, suction, and other clarifiers.

### (vii) Centrifugal separators

Centrifugal separators uses centrifugal force to separate solid particles from a liquid solution. They include both centrifuges and hydrocyclones. A centrifuge is a device for separating particles from a solution according to their size, shape, density, viscosity of the medium and rotor speed. A hydrocyclone uses centrifugal force to separate particulate elements of different sizes, shapes, and densities.

Factors influencing filtration