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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.
An example of a dewatering press is a wine press. Dating back to Roman times, these machines worked similarly to the modern screw press but possessed some disadvantages which have been corrected and improved within modern presses. The ancient wine press only allowed for grapes to be juiced in batches and often a thick cake would form against the screen, making it difficult for the juice to flow through the screen and be collected for wine. Most modern screw presses allow for a continuous flow of material by surrounding the screw with a screen, which also helps to avoid the build up of a layer of solid material on the screen. One modern approach even removes the screen in favor of a system of fixed and moving rings, which often eliminates solids buildup entirely. [1]
The most commonly known screw press of this design is said to have been invented by famous Greek mathematician Archimedes and is known as the screw conveyor. The screw conveyor consists of a shaft, which is surrounded by a spiral steel plate, similar in design and appearance to a corkscrew. This design is used in a multitude of screw presses. There are some machines of this and also of similar design that are not screw presses at all - they do not separate solids from liquids but are instead used to fuse them together. An example of this is a mold-filling machine. Plastic pellets are inserted at one end and heat is applied, melting the pellets and discharging them into a mold. Another example is known as a cooker-extruder and is used in the production of snack foods such as pretzels and more.
Most screw presses can have dilute materials pumped directly into the screw press, although pre-thickening sometimes improves the performance of the press. This is typically done with a static or sidehill screen, a rotating drum screen, belt press, or a gravity table.
Patented in 1900, Valerius Anderson's interrupted flight design is most commonly used as opposed to the continuous flight design. Anderson, upon studying the continuous flight design, noticed that it led to co-rotation and a less efficient job being done dewatering, especially with softer materials. He solved this by putting interruptions on the flights of the screw. The interruptions allowed for the materials to stop moving forward between interruptions along the shaft and also allows for an adequate buildup of the material before it is pushed through the screw press to container that catches the material. This allowed for a better job at the dewatering and a consistent cake material being released.
The interrupted flight design screw presses uses were broadened from just soft or mushy materials to include most materials screw presses were used for because unlike the continuous design screw presses the interrupted flight design did not require constant feed or consistency of material. If either were diminished in the continuous design so would production of the dewatered product, in order to avoid this while maintaining the continuous flight design a larger and heavier press with variable speed settings was a necessity; the press also entailed the need of an operator.
The interrupted flight design eliminated the need for consistency as the compression of the screw did not change as the material did not progress through the screw until a sufficient amount of the material had formed, as described above. This also eliminates the need for changing speed and an operator. The design allows for self-correction and efficiency that is unavailable with the continuous design. It allowed for a more economically effective screw press that has been used for more than just slimy or slippery materials.
After a period of time and its initial patent, resistor teeth were added to the presses where there was no flighting in order to increase the agitation of the materials adding to the limitation of the tendencies of co-rotation within the press
The buildup of press cake moisture is controlled by a discharge door or cone. Screw presses possess different options that include perforated/slotted screens, a rotating cone, hard surfacing on the screw, and supplemental screen surface in the inlet hopper on the face of the cone. The standard construction for screw presses is of stainless steel with a carbon steel frame on the larger presses.
The specific details of the design of a screw press depend on the material however. The configurations, screw speeds, screens for maximum outlet consistency, including an excellent capture rate vary per material. Most screw presses are designed to feed material that has a 40-60% water make up. The length and diameter ratio of the screw press also depends on the material. The range of the capacity of a screw press
Larger presses use a foot-mounted gearbox while smaller presses use a hollow-shaft gearbox. Currently, nearly all presses are driven by electric motors due to their reliable and low cost frequency drives. The electric motors replaced the previously popular hydraulic motor drives. A vertical design was popular in the 1800s through the 1950s but they are no longer made. Most screw presses are currently built with the screws in a horizontal configuration. One newer version uses an angled screw design to reduce floor footprint and press cake moisture. [2]
Compression is created within the screw press by increasing the inner shaft diameter of the screw. For example, if a 16" screw press has a 6" shaft at the start, the flights on the screw will be 5" tall. If this 6" shaft diameter is then increased to 12" at the discharge, the fights will be only 2" tall at this point. Thus compression is applied as the material is being pressed from a 5" opening through a 2" space.
This compression can also be achieved tightening the separation of the flights of the screw. If at the inlet, the pitch is 16", the material thus will move 16" with each revolution. If it is then decreased to 8" at the point of discharge, the material will move 8" per revolution. This results in there being more volume forced into the press than there is being forced out of the press at a time. This creates the desired compression and pushes the liquid through the screen.
Another way to achieve compression is to place a cone at the point of discharge. This can also be called a choke, stopper, or door. In many designs it is bolted into a fixed position, making a fixed, smaller opening which the material must pass through. More commonly found however, the screw press has the cone pushed into the point of discharge via a hydraulic or air cylinder.
Some other types of presses are vapor-tight presses, and twin-screw presses. Vapor-tight presses are used during the production of soybean protein concentrate (SPC), citrus and apple pectin, bioresin, and Xanthan gum. Twin-screw presses contain two overlapping compression screws. This is more complicated on a mechanical level because the screws must remain synchronized in order for them to work properly. These are often used for slippery materials and feature an internal shredding action.
There are two major kinds of screw presses of this design. One type, known as Expellers ®, removes water from fibrous material, while the other removes free liquid from a material.
Oil expellers are used to squeeze the fat out of soybeans, peanuts, sunflower seeds, canola (rape seeds), and other oil seeds. The expeller works by exerting extremely high pressures which convert the fat in seeds into a liquid oil. Once the oil is liquefied the oil flows through the screen and is collected.
Screw presses that are used to free liquid from material are commonly used in the pulp and paper industries, municipal biosolids, septage and grease trap sludge, food production, food waste, manure, and also within the chemical industry.
Pulp and paper industries remove water within cellulose fiber.
Biosolids are dewatered and heated through a specific process which includes raising the pH to a level of 12. Septage and grease trap sludge is dewatered with a simple screw press of the above stated design. Nutrient management programs dewater hog and cow manure for sale and commercial use.
Alcohol solutions are squeezed from foods with screw presses (such as soybeans, protein, pectin, and xanthan gum.) Food processing factories use screw presses to separate water from waste streams and convert the solid into animal feeds. For example, sugar beet pulp, orange peel, and spent grain.
Fish and orange peel dewatering often provide maximum yield when dewatered within a press of the interrupted flight design and with the addition of steam begin injected into the material. Commonly steam injection holes are drilled into the resistor teeth of the press close to the screw's shaft.
PET bottles "polyethylene terephthalate" is the preferred packaging for soft drinks, fizzy drinks, juice and water. This results in large waste problems. For breweries, large volumes of discharged products need to be destroyed regularly in order to eliminate the risks of the bottles being resold again. For waste collectors handling and transport is difficult and expensive, as there is a large discrepancy between weight and volume [3]
Manufacturers of ice-cream have a need to destroy returned goods with expired date and faulty manufacture to prevent the products being sold by mistake. [4]
Dairies destroy returned goods such as yogurt and other dairy products with expired date and faulty manufacture. [5]
Within the chemical industry screw presses are used for "ABS, sodium alginate and carrageenan, synthetic rubber, synthetic resin, hydrated polymer, naphthalene, elastomeric adhesive, color film emulsion, CmC, pharmaceuticals" and more. [6]
Cosmetics: To many manufacturers and brands the challenge is often that they have large amounts of discarded products, that needs 100% destruction to ensure no reselling on the black market. [7]
Expeller pressing is a mechanical method for extracting oil from raw materials. The raw materials are squeezed under high pressure in a single step. When used for the extraction of food oils, typical raw materials are nuts, seeds and algae, which are supplied to the press in a continuous feed. As the raw material is pressed, friction causes it to heat. In the case of harder nuts the material can exceed temperatures of 120 °F (49 °C).
A lobe pump, or rotary lobe pump, is a type of positive displacement pump. It is similar to a gear pump except the lobes are designed to almost meet, rather than touch and turn each other. An early example of a lobe pump is the Roots Blower, patented in 1860 to blow combustion air to melt iron in blast furnaces, but now more commonly used as an engine supercharger.
Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weatherstripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation.
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.
A screw conveyor or auger conveyor is a mechanism that uses a rotating helical screw blade, called a "flighting", usually within a tube, to move liquid or granular materials. They are used in many bulk handling industries. Screw conveyors in modern industry are often used horizontally or at a slight incline as an efficient way to move semi-solid materials, including food waste, wood chips, aggregates, cereal grains, animal feed, boiler ash, meat, bone meal, municipal solid waste, and many others. The first type of screw conveyor was the Archimedes' screw, used since ancient times to pump irrigation water.
For environmental remediation, Low-temperature thermal desorption (LTTD), also known as low-temperature thermal volatilization, thermal stripping, and soil roasting, is an ex-situ remedial technology that uses heat to physically separate petroleum hydrocarbons from excavated soils. Thermal desorbers are designed to heat soils to temperatures sufficient to cause constituents to volatilize and desorb from the soil. Although they are not designed to decompose organic constituents, thermal desorbers can, depending upon the specific organics present and the temperature of the desorber system, cause some organic constituents to completely or partially decompose. The vaporized hydrocarbons are generally treated in a secondary treatment unit prior to discharge to the atmosphere. Afterburners and oxidizers destroy the organic constituents. Condensers and carbon adsorption units trap organic compounds for subsequent treatment or disposal.
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.
In winemaking, pressing is the process where juice is extracted from the grapes with the aid of a wine-press, by hand, or even by the weight of the grape berries and clusters. Historically, intact grape clusters were trodden by feet but in most wineries today the grapes are sent through a crusher/destemmer, which removes the individual grape berries from the stems and breaks the skins, releasing some juice, prior to being pressed. There are exceptions, such as the case of sparkling wine production in regions such as Champagne where grapes are traditionally whole-cluster pressed with stems included to produce a lighter must that is low in phenolics.
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.
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.
Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical and pharmaceutical industries. Typically, granulation involves agglomeration of fine particles into larger granules, typically of size range between 0.2 and 4.0 mm depending on their subsequent use. Less commonly, it involves shredding or grinding solid material into finer granules or pellets.
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 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.
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.