Filtration is a process used to separate particles from a liquid or gas. It is an essential part of many industrial processes, and there are a variety of filtration techniques available. In this article, we will explore the different types of filtration and their applications. Gravity filtration is the simplest form of filtration and is widely used in chemical laboratories.
This technique relies on the force of gravity to separate particles from a liquid or gas. Cold filtration is another common technique that makes use of very low temperatures, often through the use of an ice bath. This method works by suspending certain substances, such as fatty acid particles, in the mixture as they cool, allowing them to be filtered more easily. Particle filtration requires the use of filters to separate particles from a liquid or gas.
There are several different filters that can be used for this purpose, as certain aspects of the wastewater to be treated can vary greatly depending on the system in which the water is used. Characteristics that most commonly affect filter choice include particle density, particle size, shape, quantity and texture, as well as any other substances present in the water. The three main types of filters used for particle filtration are bag, cartridge and self-cleaning filters. Bag filters are an excellent choice for smaller applications and systems where minimizing waste is important.
As the name suggests, bag filters have the shape of an elongated bag. Waste water enters the bag, where solid particles in the water are trapped, allowing only clean water to flow through the pores of the bag to the other side. Bag filters are an ideal choice for those looking for cost-effective filtration, such as those in industries where the cost associated with self-cleaning filtration systems would not be appropriate. This design also accumulates less total debris than other filter systems. Cartridge filters are another type of filter used for particle filtration.
These filters consist of a central section of thick metal mesh that holds the filter media and allows the filtrate to escape. This center section is covered on both sides with the filter medium, which is usually a woven wire screen with the appropriate mesh size. The sheets can be circular or rectangular and are assembled into a frame with holes for filtering removal. The assembly is generally enclosed in a pressure vessel that also contains the suspension. After sufficient filter cake is deposited on the sheets, the pressure is removed, the container is opened and the sheet assembly with the filter cake is removed.
The cake is removed by spraying water or by applying air pressure to the filter line. Cartridge filters offer more versatility than baghouse filters but have less filtrate handling capacity. Leaf filters are also used for batch pressure filtration. These filters involve the use of tanks that are generally constructed of concrete. At the bottom of the tank there is a grate or false bottom; above it is coarse-grained gravel or crushed rock of gradual size; on top there are layers of quartz sand of uniform size.
In industrial filtrations, step-sized crushed coke is used in lead-lined boxes to filter sulfuric acid, step-sized crushed limestone is used for alkaline liquors, and coal beds are used to purify organic liquids by both filtration and adsorption. The rotary drum vacuum filter is widely used in industry for continuous filtration of large quantities of slurries containing a high content of suspended solids. The filter consists of a cylindrical drum with internal divisions, ports and valves for vacuum application and removal of filtrate. The drum is covered with the filter medium, usually a woven wire screen or cloth, and partially immersed in a slurry channel. The partial vacuum inside the drum causes the filtrate to flow into the drum and out the ports, depositing a filter cake on the surface of the drum. As the drum rotates, the cake can be sprayed with wash water and then removed with scrapers. In another design for continuous vacuum filters, a blade assembly similar to those of the discontinuous blade pressure filter is used instead of the drum.
Blades provide a larger filter area but have less filtrate handling capacity. In another design of rotating drum vacuum filter, the drum is surrounded by a hood fed with hot air that dries out the filter cake. In this design, slurry is generally fed to the top of the drum and scraped off from bottom in a hopper. Filtration involves a variety of fluids and solids such that in many cases special techniques are required. If the filter cake is extremely compressible, gelatinous or viscous and tends to blind out filter then a filter aid made up porous and easily filtered solids such as diatomaceous earth or bone black can be added to suspension to improve filtration. Air and other gases are generally continuously filtered by causing gas to pass through thick filter medium by application of pressure or vacuum. In household air filters, pressure is used and medium in filter units may be several inches glass fibers impregnated with oil to retain removed dust particles. These filter units are replaced when covered with dust. When using pleated cloth or another type screen cartridge filters are type modular filter (Figure, intended trap particles even chemicals through filtration process).
Types pressure filtration equipment include automatic pressure filters candle filters press filters horizontal plate pressure filters polishing filters vertical pressure leaf filters. Second required purity water reused after filtering plays role type filter needed. Depending type filter used most industrial filtration operations employ pressure or vacuum speed up filtration reduce amount equipment needed.
