Screw Press | Vincent Corp

March 10, 2013

Liquids are separated from solids in two common manners:  settling or squeezing.  The primary device used for the settling mechanism is the centrifuge, and the primary devise used for the squeezing mechanism is the screw press.

Settling results from the action of gravity.  Solids can be separated from liquids by letting the mixture sit in a settling pond, tank, Imhoff cone, etc.  The effect of gravity can be accelerated and multiplied by spinning the fluid in a centrifuge.  Centrifuges are used in a very wide range of industrial applications.  In fact, they are far more common than screw presses.

Materials can be squeezed by forcing them against a screen or other filter media.  Old fashioned wine presses, dating back to Roman times, are a familiar example:  grapes are put over a screen that is fastened at the bottom of a vertical cylinder.  A piston is forced down on the grapes, and the juice is expelled through the holes in the screen.

This mechanism has some disadvantages, the principal of which is that the pressing is done in batches, rather than in a continuous flow.  Another disadvantage is that a thick cake can form at the bottom, against the screen.  It is difficult for fluid at the top, next to the piston, to flow through this cake and through the screen.

(Incidentally, the fibrous solids separated by modern screw presses are referred to as press cake.  This term dates back to the cake-shaped plug formed in piston-type presses of the 18th century.)

The modern screw press overcomes these disadvantages by having the screw surrounded by a screened surface.  In other words, the cylinder walls are made into a screened surface.  And, instead of a piston, the material is conveyed toward the discharge by a helicoid screw.

The best known form of a helicoid screw is a screw conveyor.  Archimedes gets credit for having invented the screw conveyor.  It consists of a shaft about which is wound a spiral steel plate, much like a cork screw.  The screw conveyor is supported in a trough, and material is admitted to one end of the trough.  When the screw is turned, the material is moved to the other end of the trough.

This mechanism is used in a range of screw presses.  Some screw presses have no openings in the barrels that surround the screw.  Thus the mechanism does not separate liquids from solids.  The best known example is a plastic injection molding machine:  pellets of plastic are admitted at one end; the barrel surrounding the screw is heated; and molted plastic discharges at the other end and is pushed into the injection molding die.  Another such press is the cooker-extruder which is used to produce pretzels and other snack foods.  Flavored bakery dough is admitted at one end of the screw and cooked snack foods are extruded through the other end.

Other screw presses fall into two categories:  those which remove free water from fibrous material, and those known as Expellers®.  Oil Expellers® are screw presses which exert extremely high pressures.  They are used to squeeze the fat in soybeans, peanuts, sunflower seeds, canola (rape seed) and other oil seeds.  The internal pressure is so intense that the fat in these seeds is converted into liquid oil which flows through the openings in the screen cage which surrounds the screw.

The other screw presses, which remove free liquid from material, find an extremely wide range of applications.  They are used extensively in the pulp and paper industry to separate water from cellulose fiber.  They are also used in the production of food ingredients where an alcohol solution must be squeezed from foods such as soybean protein, pectin, and Xanthan gum.  More mundane applications call for separating water from waste streams at food processing factories.  In many cases these wastes are converted into animal feeds.  Examples include orange peel from orange juice production facilities; sugar beet pulp and trash from sugar beet mills; and spent brewer’s grain from breweries.  A growing use of screw presses in is dewatering dairy and hog manure as part of nutrient management programs.

The most widely used screw press of this type is the interrupted flight design.  Patented in the year 1900 by Valerius Anderson, the flights on the screws of these presses have interruptions which minimize co-rotation.   Compression is achieved by using graduated pitch compression stages, sometimes combined by tapering the diameter of the shaft of the screw so as to force material against the surrounding screen.

Final press cake moisture is controlled by a discharge cone (or door), which is actuated by an air cylinder.  This provides easy adjustment of the dewatering.  Options include both perforated and wedgewire (slotted) screens, a rotating cone, hard surfacing on the screw, and supplemental screen surface in the inlet hopper and on the face of the cone.  Standard construction is stainless steel, with a carbon steel bed frame on the larger machines.

In general, larger presses use a foot mounted gearbox, while smaller ones use a hollow-shaft gearbox.  Today almost all presses are driven by electric motors.  Hydraulic motor drives were popular in the past, but they have lost favor with the advent of reliable and low cost variable frequency drives (inverter VFD’s).

Dilute materials can be pumped directly into the screw press.  Sometimes pre-thickening improves performance.  Typically this is done with a static (sidehill) screen, rotating drum screen, gravity table or even a belt press.

Vapor-tight presses are a specialty.  These are used in the production of SPC (soybean protein concentrate), citrus and apple pectin, Xanthan gum, and bioresin.

Twin screw presses feature two overlapping compression screws.  These are more complicated mechanically because the screws must remain synchronized.  Such presses feature very positive displacement, so they are used on slippery materials such as shrimp waste.  At the same time they feature internal shredding action, so they are used on fibrous material such as corn husk.

All screw presses today are built with the screws in a horizontal configuration.   Through the 1800’s up until the 1950’s vertical designs were popular; however, these are no longer being manufactured.

Laboratory and pilot plant models are popular.

For more information, please visit oil seeds crushing machine.

SMALL PRESS, NO SCREEN COVER

PRESS LIQUOR FROM SCREEN

ALFALFA PRESS, SCREEN REMOVED

PRESS WITH SCREENS REMOVED

FOOT MOUNTED GEARBOX DESIGN

PRESS CAKE DISCHARGE

Photos and drawings provided by Vincent Corporation.

Issue 254

In today’s rapidly evolving industrial landscape, businesses are continually seeking innovative solutions to optimize their processes, reduce waste, and enhance sustainability. At French Oil, we take pride in our commitment to delivering cutting-edge technologies that meet our clients’ diverse needs. One such area where our expertise shines, specifically, is in custom screw press dewatering systems.

The Design

At French, our engineers have developed screw press and fiber press designs renowned for their long-lasting durability and decades of exceptional performance. Featuring advanced technology that ensures accurate regulation of discharge moisture, our range includes custom-designed dewatering presses for both virgin and recycled wood pulp. Moreover, you can select from a variety of drive and control systems to find the perfect fit for your specific needs, and our team of skilled French engineers is readily available to guide you in making the optimal choice.

Pulp Dewatering Systems

The French series of LP (low-pressure) pulp dewatering presses are also meticulously designed to deliver unparalleled control over discharge moisture to excel in efficiently separating liquids and solids from moisture-laden fibrous materials. Furthermore, by operating with a feed consistency ranging from 2% to 4% and discharging at 25% to 35%, these presses are available in four primary models: LP-1890, LP-18120, LP-28150, and LP-28200, offering a daily capacity range from 50 to 300 bone-dry metric tons. Select the perfect model that aligns with your application requirements and experience the remarkable engineering prowess of French technology in action.

Screw Press Applications:

Here is a compilation of the most prevalent applications where our premium, tailor-made screw press dewatering systems excel:

Pulp Washing and Bleaching:

The paper industry relies heavily on efficient pulp washing and bleaching processes to produce high-quality paper products. That’s why our custom screw press designs are adept at extracting water and chemicals from pulp, resulting in a cleaner and more refined material. This not only improves the quality of the final paper but also helps in reducing chemical usage and water consumption, making your paper production process more sustainable.

Paper Recycling and De-Inking Operations:

As the world embraces sustainability and environmental consciousness, the demand for recycled paper is on the rise. Our screw presses, for instance, play a crucial role in paper recycling and de-inking operations, as they effectively remove ink, contaminants, and excess water from the recycled paper pulp. By partnering with French Oil for these processes, your paper recycling plant can significantly reduce water usage and energy consumption, contributing to a greener future.

High Consistency Refining of Primary Pulp and Rejects:

Optimizing paper production relies heavily on efficiently refining primary pulp and rejects. That’s why our team of experts engineers our custom screw press designs to handle high-consistency refining effortlessly. By precisely extracting water and fiber from the material, our presses improve the refining process’s efficiency, leading to higher-quality paper products and reduced waste.

Liquid Removal before Pulp Storage and Transport:

To ensure smooth storage and transportation of pulp, it is essential to remove excess liquids effectively. So, our screw press applications excel at precisely this task, reducing the moisture content in pulp to the desired level before storage or transport. This not only improves the handling of pulp but also minimizes the environmental impact of the entire process.

Concentration of Waste Treatment Sludges:

Waste treatment sludges can pose significant challenges to industries, both economically and environmentally. Fortunately, our screw press designs offer an effective solution for concentrating waste treatment sludges. By reducing the moisture content, the volume of waste is minimized, which leads to easier disposal and potential resource recovery.

Excess Water Removal from Various Materials:

Apart from paper-related applications, our screw press designs are versatile enough to handle excess water removal from various materials like corn fiber, corn germ, alfalfa, and more. Furthermore, the ability to efficiently extract moisture from these materials opens up opportunities for multiple industries, including agriculture and biofuel production.

Request A Quote Today

At French Oil, we understand that every industry has unique processing requirements. Our commitment to customization ensures that our screw press dewatering systems can seamlessly integrate into your existing operations, enhancing efficiency, reducing waste, and promoting sustainability. Whether it’s paper manufacturing, recycling, or diverse applications like agricultural materials, we are your trusted partner in processing. Contact our team of experienced engineers to discover how our custom screw press designs can elevate your business to new heights of success!

If you want to learn more, please visit our website automatic screw press machine product.