HOME

TheInfoList



OR:

A dewatering screw press is a
screw press A screw press is a type of machine press in which the ram is driven up and down by a screw. The screw shaft can be driven by a handle or a wheel. It works by using a coarse screw to convert the rotation of the handle or drive-wheel into a small d ...
that separates
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, an ...
s from
solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structura ...
s. A screw press can be used in place of a belt press,
centrifuge A centrifuge is a device that uses centrifugal force 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 (e.g. cream from milk) or ...
, or
filter paper Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solid particles from liquids or gases. The raw materials are different Pulp (paper), paper pulps. The pulp may be made from soft ...
. 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 Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...
and the liquid is collected through the screen for collection and use.


History

An example of a dewatering press is a
wine press A winepress is a device used to extract juice from crushed grapes during wine making. There are a number of different styles of presses that are used by wine makers but their overall functionality is the same. Each style of press exerts contro ...
. Dating back to
Roman times In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 BC ...
, 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
grape A grape is a fruit, botanically a berry (botany), berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non-Climacteric (botany), climacteric type of fruit, generally occurring in clusters. The cultivation of ...
s 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. The most commonly known screw press of this design is said to have been invented by famous Greek mathematician
Archimedes Archimedes of Syracuse (;; ) was a Greek mathematician, physicist, engineer, astronomer, and inventor from the ancient city of Syracuse in Sicily. Although few details of his life are known, he is regarded as one of the leading scienti ...
and is known as the
screw conveyor 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 conveyo ...
. The screw conveyor consists of a shaft, which is surrounded by a spiral steel plate, similar in design and appearance to a
corkscrew A corkscrew is a tool for drawing corks from wine bottles and other household bottles that may be sealed with corks. In its traditional form, a corkscrew simply consists of a pointed metallic helix (often called the "worm") attached to a hand ...
. 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 A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
-filling machine.
Plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
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.


Design

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


Options

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 Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, coba ...
frame on the larger presses.


Capacity

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


Drive

Larger presses use a foot-mounted
gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), diffe ...
while smaller presses use a hollow-shaft gearbox. Currently, nearly all presses are driven by
electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate forc ...
s due to their reliable and low cost frequency drives. The electric motors replaced the previously popular
hydraulic motor A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement ( rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadl ...
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.


Compressive Mechanisms

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.


Specialized types

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 ''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is nati ...
and
apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ances ...
pectin Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component o ...
, bioresin, and
Xanthan gum Xanthan gum () is a polysaccharide with many industrial uses, including as a common food additive. It is an effective thickening agent, emulsifier, and stabilizer that prevents ingredients from separating. It can be produced from simple sug ...
. 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.


Classification

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.


Expellers

Oil expellers are used to squeeze the
fat In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple es ...
out of
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...
s,
peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible Seed, seeds. It is widely grown in the tropics and subtropics, important to both small ...
s,
sunflower seed The sunflower seed is the seed of the sunflower (''Helianthus annuus''). There are three types of commonly used sunflower seeds: linoleic (most common), high oleic, and sunflower oil seeds. Each variety has its own unique levels of monounsatu ...
s, canola (rape seeds), and other
oil seed Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fats ...
s. 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.


Removal of free liquid

Screw presses that are used to free liquid from material are commonly used in the
pulp Pulp may refer to: * Pulp (fruit), the inner flesh of fruit Engineering * Dissolving pulp, highly purified cellulose used in fibre and film manufacture * Pulp (paper), the fibrous material used to make paper * Molded pulp, a packaging material ...
and
paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre e ...
industries,
municipal A municipality is usually a single administrative division having corporate status and powers of self-government or jurisdiction as granted by national and regional laws to which it is subordinate. The term ''municipality'' may also mean the ...
biosolids Biosolids are solid organic matter recovered from a sewage treatment process and used as fertilizer. In the past, it was common for farmers to use animal manure to improve their soil fertility. In the 1920s, the farming community began also to use ...
,
septage Fecal sludge management (FSM) (or faecal sludge management in British English) 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 slud ...
and grease trap sludge,
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ...
production,
food waste Food loss and waste is food that is not eaten. The causes of food waste or loss are numerous and occur throughout the food system, during production, processing, distribution, retail and food service sales, and consumption. Overall, abou ...
,
manure Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the fertility of soil by adding organic matter and nut ...
, and also within the
chemical industry The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials ( oil, natural gas, air, water, metals, and minerals) into more than 70,000 different products. T ...
.


Applications


Pulp and paper industries

Pulp and paper industries remove water within
cellulose fiber Cellulose fibers () are fibers made with ethers or esters of cellulose, which can be obtained from the bark, wood or leaves of plants, or from other plant-based material. In addition to cellulose, the fibers may also contain hemicellulose an ...
.


Sewage disposal

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 Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...
manure for sale and commercial use.


Food processing

Alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
solutions are squeezed from foods with screw presses (such as
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...
s,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
,
pectin Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component o ...
, and
xanthan gum Xanthan gum () is a polysaccharide with many industrial uses, including as a common food additive. It is an effective thickening agent, emulsifier, and stabilizer that prevents ingredients from separating. It can be produced from simple sug ...
.) Food processing factories use screw presses to separate water from waste streams and convert the solid into animal feeds. For example,
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet ('' Beta vulgaris''). Together ...
pulp,
orange Orange most often refers to: *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower * Orange (colour), from the color of an orange, occurs between red and yellow in the visible spectrum ...
peel Peel or Peeling may refer to: Places Australia * Peel (Western Australia) * Peel Island, Queensland *Peel, New South Wales * Peel River (New South Wales) Canada * Peel Parish, New Brunswick * Peel, New Brunswick, an unincorporated communi ...
, and
spent grain Brewer's spent grain (BSG) or draff is a food waste that is a byproduct of the brewing industry that makes up 85 percent of brewing waste. BSG is obtained as a mostly solid residue after wort production in the brewing process. The product is i ...
. 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 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. Dairies destroy returned goods such as yogurt and other dairy products with expired date and faulty manufacture.


Chemical industry

Within the chemical industry screw presses are used for "ABS,
sodium alginate Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colour ...
and
carrageenan Carrageenans or carrageenins ( ; ) are a family of natural linear sulfated polysaccharides that are extracted from red edible seaweeds. Carrageenans are widely used in the food industry, for their gelling, thickening, and stabilizing properties. ...
,
synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubbe ...
,
synthetic resin Synthetic resins are industrially produced resins, typically viscous substances that convert into rigid polymers by the process of curing. In order to undergo curing, resins typically contain reactive end groups, such as acrylates or epoxides. ...
, hydrated
polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...
,
naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08  ppm by mass. As an aromat ...
,
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic ...
ic adhesive,
color film Color photography is photography that uses media capable of capturing and reproducing colors. By contrast, black-and-white or gray-monochrome photography records only a single channel of luminance (brightness) and uses media capable only of ...
emulsion, CmC,
pharmaceuticals A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and ...
" and more. 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.


References

{{Reflist


External links

Liquid-solid separation