A solid bowl centrifuge is a type of centrifuge that uses the principle of sedimentation. A centrifuge is used to separate a mixture that consists of two substances with different densities by using the centrifugal force resulting from continuous rotation. It is normally used to separate solid-liquid, liquid-liquid, and solid-solid mixtures. Solid bowl centrifuges are widely used in various industrial applications, such as wastewater treatment, coal manufacturing, and polymer manufacturing. One advantage of solid bowl centrifuges for industrial uses is the simplicity of installation compared to other types of centrifuge. There are three design types of solid bowl centrifuge, which are conical, cylindrical, and conical-cylindrical.
During the industrial process of wastewater treatment, huge quantity of sludge is produced. The sludge needs to be disposed of or having further treatment. One of the treatment methods available is thickening the sludge by using solid bowl centrifuges. While prior sludge have the concentration around 0.5-1 % of dry solid, after the thickening process, it will contain up to 5-6% of dry solids. This process reduces the waste of active sludge volume by more than 80% as well as minimizing the sludge amount for digestion by 30-40%. Furthermore, less disposal sludge also lowers the cost of polymer and improves the characteristics of dewatering.
Coal slurry, which contains around 6% solids by weight and nearly 60% of 10 mm material, is thickened using solid bowl centrifuges. By using this centrifuge technique, the concentration of the end product could reach up to 55-60% solids without extra chemical added. Additionally, solid bowl centrifuge is also used in the water removal process from waste slurry obtained from coal-cleaning facility.
Solid bowl centrifuge is used in the manufacture of polymer to recover acetates from polymer slurry. The conical beach is used for internal washing for acetates recovery improvement. Previously, the centrifuge only consists of single lead conveyor, and then improved using double lead conveyor in order to increase the capacity. Furthermore, the extra double lead conveyor with minimized pitch is used to improve the acetate yield.
Solid bowl centrifuge designs are divided into three different types based on the solid bowl shapes, which are conical, cylindrical, and cylindrical-conical. The choice of the centrifuge design in a particular industry is determined by the characteristics of the slurry and solids. [5]
Among the three designs, initially conical bowl was the most preferable design due to its maximum allowance of water removal and its excellent classifying ability. However, this design is less effective in achieving a high centrate quality, which makes it a poor clarifier.
Unlike conical bowl design, cylindrical bowl design does not allow maximum water removal, and thus mainly produces wet cakes. In addition, it is also a less effective classifier. However, cylindrical bowl design is more effective in achieving a high centrate quality compared to the conical bowl design, which makes it a better dewatering device compared to the conical bowl design.
Conical-cylindrical bowl design was developed based on the conical and cylindrical bowl designs. This design is basically a combination of the best individual characteristics of the previous two designs, and therefore is a more advanced design. This particular design allows efficient dewatering ability, effective clarification, and fairly good classification within one unit. It has the ability to change and control the balance between the water removal and the centrate quality by the adjustment of its pool length, depending on the required product. Thus, conical-cylindrical bowl design is the most widely used in the industry today.
A typical conical-cylindrical solid bowl centrifuge design contains a rotating bowl unit connected to a conveyor with a gear system. The gear system allows the rotating bowl and the conveyor to rotate at different speeds but in the same direction. Commonly, the conveyor operates at the speed between 1900 and 2400 rotation per minute, while the bowl unit operates at 100 rotation per minute higher. [6]
The performances of the shape designed centrifuge types can be seen in the table as follows:
Based on the exit stream of the solid cake and liquid centrate, there are two types of solid bowl centrifuge designs, which are: [6]
For this design, the solid cake and the liquid centrate leave the centrifuge bowl at the same end.
This design allows the solid cake and the liquid centrate to leave the centrifuge bowl at opposite ends. For this design, the conveyor pushes the sludge towards the end streams and the supernatant liquid is allowed to exit over the weirs.
With the help of helical screw conveyor, solid bowl centrifuges separate two substances with different densities by the centrifugal force formed under fast rotation. Feed slurry enters the conveyor and is delivered into the rotating bowl through discharge ports. There is a slight speed difference between the rotation of conveyor and bowl, causing the solids to convey from the stationary zone where the wastewater is introduced to the bowl wall. By centrifugal force, the collected solids moves along the bowl wall, out of the pool and up the dewatering beach located at the tapered end of the bowl. At last the solids separated go to solid discharge while the liquids go to liquid discharge. The clarified liquid flows through the conveyor in the opposite direction through adjustable overflow parts.
The table below shows the percentage of solid separation that has been achieved within different solids and cake solid formed while considering the effect of adding polymer: [12]
The post-treatment of the waste stream produced by the solid bowl centrifuge diverse depending on the industrial application. Since different industries have different feed for the centrifuge system, the waste stream will be different as well, and thus require different post treatments. Below are some examples of the waste stream production and its necessary post treatment in various applications in the industry.
In water treatment, the wanted product is the clean water, while the waste is the sludge containing dissolved organic and inorganic materials, fibrous matter, and extracellular polymer (ECP). The sludge is commonly discarded down the sewer or to landfill. Occasionally, the sludge is used in the production of bricks and concrete, in agriculture as a soil additive, or for land reclamation. In this application, solid bowl centrifuge is used as the final step of the water treatment sludge before disposal in order to reduce landfill charges and transport costs.
Solid-bowl centrifuge is used for dewatering the coal waste slurry along with plate-and-frame filter press in coal manufacturing to dewater the slurry before being disposed of. The slurry feed was attained from the underflow of a functioning bituminous coal-cleaning thickener device. As for the waste stream, it is usually disposed of into slurry cells or deserted underground mine site if available, or more commonly in slurry impoundments.
In this industry, acetate is recovered during the manufacturing of polymers. In this case, the wanted product is actually the polymer; however, the acetate is not a waste either since it is recovered. While the polymer solids are discharged through the solid exit port and further processed, the acetate that is recovered through the liquid exit port and further separated from the washing liquid to recover pure acetate.
There are various aspects that can be improved from the current solid bowl centrifuges in order to increase its performance and reliability. To allow more control and simpler operation, support systems such as feed equipment, chemical dosing facility and better transfer pumps were designed and added. Moreover, the operating parameters can be adjusted to optimize the sludge dewatering process. It relies on rotational force in order to throw the solids out and for the sludge to stick to the outer all surfaces. The use of a metal screen or some suitable filtering material can also be added to achieve better solids dryness. [15]
A centrifuge is a device that uses centrifugal force to subject a specimen to a specified constant force, for example to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities or liquids from solids. It works by causing denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense are displaced and moved to the centre. In a laboratory centrifuge that uses sample tubes, the radial acceleration causes denser particles to settle to the bottom of the tube, while low-density substances rise to the top. A centrifuge can be a very effective filter that separates contaminants from the main body of fluid.
Hydrocyclones are a type of cyclonic separators that separate product phases mainly on basis of differences in gravity with aqueous solutions as the primary feed fluid.
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.
A coal preparation plant is a facility that washes coal of soil and rock, crushes it into graded sized chunks (sorting), stockpiles grades preparing it for transport to market, and more often than not, also loads coal into rail cars, barges, or ships.
Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting, or incineration. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options. Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas.
A Rotary Vacuum Filter Drum consists of a cylindrical filter membrane that is partly sub-merged in a slurry to be filtered. The inside of the drum is held lower than the ambient pressure. As the drum rotates through the slurry, the liquid is sucked through the membrane, leaving solids to cake on the membrane surface while the drum is submerged. A knife or blade is positioned to scrape the product from the surface.
Powdered Activated Carbon Treatment (PACT) is a wastewater technology in which powdered activated carbon is added to an anaerobic or aerobic treatment system. The carbon in the biological treatment process adsorbs recalcitrant compounds that are not readily biodegradable, thereby reducing the chemical oxygen demand of the wastewater and removing toxins. The carbon also acts as a "buffer" against the effects of toxic organics in the wastewater.
An industrial filter press is a tool used in separation processes, specifically to separate solids and liquids. The machine stacks many filter elements and allows the filter to be easily opened to remove the filtered solids, and allows easy cleaning or replacement of the filter media.
A vacuum ceramic filter is designed to separate liquids from solids for dewatering of ore concentrates purposes. The device consists of a rotator, slurry tank, ceramic filter plate, distributor, discharge scraper, cleaning device, frame, agitating device, pipe system, vacuum system, automatic acid dosing system, automatic lubricating system, valve and discharge chute. The operation and construction principle of vacuum ceramic filter resemble those of a conventional disc filter, but the filter medium is replaced by a finely porous ceramic disc. The disc material is inert, has a long operational life and is resistant to almost all chemicals. Performance can be optimized by taking into account all those factors which affect the overall efficiency of the separation process. Some of the variables affecting the performance of a vacuum ceramic filter include the solid concentration, speed rotation of the disc, slurry level in the feed basin, temperature of the feed slurry, and the pressure during dewatering stages and filter cake formation.
Dewatering is the removal of water from a location. This may be done by wet classification, centrifugation, filtration, or similar solid-liquid separation processes, such as removal of residual liquid from a filter cake by a filter press as part of various industrial processes.
The belt filter is an industrial machine, used for solid/liquid separation processes, particularly the dewatering of sludges in the chemical industry, mining and water treatment. Belt filter presses are also used in the production of apple juice, cider and winemaking. The process of filtration is primarily obtained by passing a pair of filtering cloths and belts through a system of rollers. The system takes a sludge or slurry as a feed, and separates it into a filtrate and a solid cake.
A dewatering screw press is a screw press that separates liquids from solids. A screw press can be used in place of a belt press, centrifuge, or filter paper. It is a simple, slow moving device that accomplishes dewatering by continuous gravitational drainage. Screw presses are often used for materials that are difficult to press, for example those that tend to pack together. The screw press squeezes the material against a screen or filter and the liquid is collected through the screen for collection and use.
A pusher centrifuge is a type of filtration technique that offers continuous operation to de-water and wash materials such as relatively in-compressible feed solids, free-draining crystalline, polymers and fibrous substances. It consists of a constant speed rotor and is fixed to one of several baskets. This assembly is applied with centrifugal force that is generated mechanically for smaller units and hydraulically for larger units to enable separation.
The peeler centrifuge is a device that performs by rotating filtration basket in an axis. A centrifuge follows on the principle of centrifugal force to separate solids from liquids by density difference. High rotation speed provides high centrifugal force that allows the suspended solid in feed to settle on the inner surface of basket. There are three kinds of centrifuge, horizontal, vertical peeler centrifuge and siphon peeler centrifuge. These classes of instrument apply to various areas such as fertilisers, pharmaceutical, plastics and food including artificial sweetener and modified starch.
A centrifuge is a device that employs a high rotational speed to separate components of different densities. This becomes relevant in the majority of industrial jobs where solids, liquids and gases are merged into a single mixture and the separation of these different phases is necessary. A decanter centrifuge separates continuously solid materials from liquids in the slurry, and therefore plays an important role in the wastewater treatment, chemical, oil, and food processing industries. There are several factors that affect the performance of a decanter centrifuge, and some design heuristics are to be followed which are dependent upon given applications.
A conical plate centrifuge is a type of centrifuge that has a series of conical discs which provides a parallel configuration of centrifugation spaces.
Screen/Scroll centrifuge is a filtering or screen centrifuge which is also known as worm screen or conveyor discharge centrifuge. This centrifuge was first introduced in the midst of 19th century. After developing new technologies over the decades, it is now one of the widely used processes in many industries for the separation of crystalline, granular or fibrous materials from a solid-liquid mixture. Also, this process is considered to dry the solid material. This process has been some of the most frequently seen within, especially, coal preparation industry. Moreover, it can be found in other industries such as chemical, environmental, food and other mining fields.
Fecal sludge management (FSM) is the storage, collection, transport, treatment and safe end use or disposal of fecal sludge. Together, the collection, transport, treatment and end use of fecal sludge constitute the "value chain" or "service chain" of fecal sludge management. Fecal sludge is defined very broadly as what accumulates in onsite sanitation systems and specifically is not transported through a sewer. It is composed of human excreta, but also anything else that may go into an onsite containment technology, such as flushwater, cleansing materials, menstrual hygiene products, grey water, and solid waste. Fecal sludge that is removed from septic tanks is called septage.
Bellmer GmbH is a company founded in 1842 in Niefern-Öschelbronn, Germany by Carl Bellmer. It is still family-owned with over 600 employees globally. Bellmer operates 16 sites around the world but the products are manufactured in Germany and Finland.
A centrifuge is a device that uses centrifugal force to separate its components.
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