Filtration equipment has become a necessity for industries. They have been used to products manufacturing and clean products, types of filtration equipment based on the process.
(A) Filters are generally divided into major groups based on the function of filtration. Such types of filters are commonly used in the water treatment process.
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(i) Cake Filters
Filters that retain appreciable visible quantities of filtered solids on the surface of the filter medium are referred to as cake filters.
(ii) Clarifying filters
Filters that remove small amounts of solids to produce sparkling clear liquid are referred to as clarifying filters/Deep bed filters.Â
(B) Filters may be classified according to the method of operating or operating cycle.Â
(i) Batch Filters
Batch filters are used in the chemical industry to remove solids from liquid. They are also called filter presses, filter plates, filter cakes, or filtrate. The process of filtering is done by pressing the liquid through a porous surface with a certain pressure. A porous surface that is resistant to the passage of particles and liquids is called a filter medium.
Batch filters are used in many industries such as pharmaceuticals and food processing industries. They can remove impurities from water and wastewater, which reduces the number of chemicals needed for cleaning up the water supply.
(ii) Continuous Filters
Continuous filters are used for the separation of solids from liquid. The filter is divided into several cells, which are filled with a filtering medium. The filtering medium is usually made up of sand, crushed coal, or other solid particles.
The liquid to be filtered enters the cells and flows over the surface of the filtering medium, picking up and retaining any solid particles that might be present. The liquid then passes through the filter in a continuous flow, while any retained solids are left behind in their respective cells.
(C) Filters may be classified according to the driving force used for separation like gravity, pressure, vacuum, or centrifugal.Â
Filters used in the chemical industry
(i) Gravity FiltersÂ
Gravity filters are a type of filter that is used in the chemical industry. They are widely used in industries such as water treatment, oil refining, and wastewater treatment. The process involves the liquid passing through a series of filters which remove impurities by using gravity to move them through the system.Â
The first step is to create a preliminary separation between solids and liquids by using a coarse filter. This is done before the liquid enters the main filter for further purification. The liquid is then passed through a series of filters with progressively finer mesh sizes to remove any impurities that may have been missed during the first stage.
(ii) Pressure FiltersÂ
Pressure filters are often used in chemical industries to filter out unwanted materials from the process. Pressure filters have a wide variety of applications, such as wastewater treatment, oil, and gas production, and water filtration to name a few.
Pressure filters are mainly composed of three components: a filtering medium, an inlet for feeding material into the filter, and an outlet for filtered material.Â
(iii) Vacuum FiltersÂ
Vacuum filters are used in chemical industries to remove dust and impurities from the atmosphere.
Vacuum filters are used in chemical industries to remove dust and impurities from the atmosphere. This is done by using a vacuum pump that creates a difference of pressure on both sides of the filter. The air enters the filter, goes through it, and comes out clean on the other side.
(iv) Centrifugal FiltersÂ
Centrifugal filters are used in the chemical industry to remove solids and particulates from liquids. They are also used in the food, chemical, and pharmaceutical industries.
A centrifugal filter is a type of filter that can be used to separate mixtures of solid particles and liquid. The liquid is poured into a funnel-like container called a bowl, which has an outlet at the bottom.Â
Industrial cake filters are usually classified as followsÂ
1. Batch (discontinuous) pressure filters. For example, filter press - plate and frame press, pressure leaf filters.Â
2. Continuous pressure filters. For example, pressure filters - thickener, continuous pressure filters.
3. Batch vacuum filters. For example, vacuum notches, and vacuum leaf filters.
4. Continuous vacuum filters. For example, rotary drum filters, and vacuum precoat filters.Â
5. Centrifugal filters ( Batch and continuous). For example, suspended basket centrifugal - top driven or bottom driven, continuous filtering centrifugal.
The most important cake filters that will be referred to are plate and frame filter press, leaf filter, rotary drum filter, and basket centrifuge.
In many cases, in the chemical industry, it is the solids that are wanted.Â
The factors to be considered while selecting equipment for filtration and operating conditions
1. Properties of the fluid such as viscosity, density, and corrosiveness/chemical reactivity.
2. Nature of solids - particle size, size distribution, particle shape, and packing characteristics of solid particles.
3. Concentration of the solids slurry, i.e. feed slurry concentration.
4. Quantity of material to be handled and its value.Â
5. Whether the valuable product is solid, liquid, or both.
6. Necessary of washing the solids.
7. Necessary of heating the feed slurry.
8. Necessary of any form of pretreatment of the slurry for ease of infiltration.Â
9. Cost of labor and power, and initial investment.Â
Take these Notes is, Orginal Sources:Â Unit Operations-II, KA Gavhane