What is a Filter Press and How Does it Work?

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A filter press is one of the oldest and most trusted pieces of dewatering equipment. It’s used for wastewater treatment across a variety of industries and applications. A filter press works by separating out solids from liquids, removing impurities, and suspended solids from industrial wastewater. This allows plant managers to easily handle and dispose of waste while returning clean water to their systems.

Filter presses separate liquids and solids. Specifically, the filter press separates the liquids and solids using pressure filtration across a filter media. Afterward, the slurry is pumped into the filter press and then dewaters under pressure.

Basically, the concentrate filter press design is based on the dewatering volume and type of slurry. ChemREADY is an expert in liquid and solid separation and offers a wide range of filter press types and capacities to suit specific application needs for trouble-free, economical dewatering.

The origin of the filter press dates to around the mid-19th century in the United Kingdom, where a rudimentary form of the press was used to obtain vegetable oil from seeds. However, it wasn’t until major developments in the mid-20th century that engineers were able to develop the world’s first automatic horizontal-type filter press.

It’s this long history of advancements that’s allowed the filter presses of today to achieve significantly lower energy and maintenance costs compared to their belt press and centrifuge counterparts. In fact, the total operating filtration cost for a filter press can easily be 1/6 the cost of what it would be for a belt press or centrifuge.

While there are many different styles of modern filter presses, the plate and frame filter press are one of the oldest and most tested types of dewatering equipment available. You can read more on this type of filter press, along with a more detailed comparison between different types of dewatering equipment, in our Water Facts blog on How Industrial Wastewater Pretreatment Works.

Filter presses are especially useful as the leftover solids are cheaper and easier to move than the entire slurry. With the clean water that filter presses return, plant managers can discharge that to their local municipalities, watersheds or use the water in their own closed-loop systems, creating highly efficient processes.

Without a filter press or similar pieces of dewatering equipment, a settling pond is often the first option for water treatment. Not only do ponds require a large amount of real estate to use, but they also lose their ability to clean water over time as the solids that you remove build up in the pond water. This gives ponds an unfavorable long-term ROI as dirty water will eventually start coming back into your process unless you dredge the pond or make a new pond. At ChemREADY, we advise the use of a filter press and other dewatering equipment over a pond in most applications.

During the fill cycle, the slurry pumps into the filter press and distributes evenly during the fill cycle. Solids build up on the filter cloth, forming the filter cake in the void volume of the plate. The filtrate, or clean water, exits the filter plates through the ports and discharges clean water out the side of the plates.

Filter presses are a pressure filtration method. As the filter press feed pump builds pressure, the solids build within the chambers until they are completely full of solids. This forms the cake. The filter cakes release when the plates are full, and the cycle is complete. Also, many higher capacity filter presses use fast action automatic plate shifters which speeding cycle time. Matec specifically designs their filter presses for fully automatic, 24-hour operation in a harsh environment such as mines or chemical manufacturing plants for wastewater treatment.

While the various styles of filter presses work differently, they all operate under similar principles. Slurries of water mixed with solids are pumped into the press by using a feeding pump. Once inside the press, pressure – often from a centrifugal pump or similar device – pushes the slurry through chambers made of filter plates. This removes impurities from the water as “filter cakes” of solids build up on the machine’s filters.

Once the chambers of a filter press are full, its filtration cycle is complete, and the machine releases the filter cakes. These cakes are easily removed, allowing you to filter your water at high efficiencies. In filter presses, fast action automatic plate shifters may be used to help speed up cake removal and cycle time. In harsher environments where continuous operation is required – like in mining processes or chemical manufacturing plants – a fully automatic filter press design is needed to handle the 24-hour workloads.

To get the best performance out of your filter press, the cloth of the filter should be specifically designed for your application and the types of solids that you are filtering.

The following can also be customized to fit your individual needs:

In addition to these, you can use additional systems such as cloth washing systems, drip trays, and cake shields to further increase filter press performance and functionality. Ultimately, each filter press should be designed based on the expected volume and type of slurry that it will be handling.

Since filter presses work using pressure, equipment that increase pressure through the means of high-pressure technology are great for optimizing your dry tailings filter press system. That’s the secret to success for Matec® filter presses, which use pressures of 21 to 30 bar to handle even the most difficult and hard to treat slurries, no matter the sector or application.

Filter presses can be built in a wide range of sizes, from small, lab-scale presses, to those with much larger capacities, such as those with 2000×2000 mm plates.

While filter presses are great pieces of dewatering equipment, they are best used on a slurry made up of about 50-60 percent solids. Lower solids concentration requires running the water through a clarifier first.

Clarifiers are best described as large settling tanks, preferably used in the initial dewatering phase. Here, water can enter at a much lower solids concentration, typically around 5-10 percent solids. Using gravity and polymers, clarifiers cause solids to build up at the bottom of the tank, where they can be discharged as sludge.

The two main types of clarifiers are the horizontal rake style clarifier and the vertical deep cone clarifier. Vertical deep cone clarifiers use the principle of static decantation for a natural precipitation of solid material, while horizontal rake style clarifiers use a rake mechanism that stirs the sludge through rotation. Determining which type of clarifier is best for you depends on your clarifying needs, driven by maintenance costs, material types and solids requirements. You can read more on the two different types of clarifiers in our Water Facts blog, Deep Cone vs. Rake Style Clarifiers.

When used in combination with each other, a clarifier and chemical filter press can recover 90-95 percent of your water as clean water. The remaining water will discharge with the solids from the filter press.

Here at ChemREADY, our team of water treatment experts can help bring your dewatering efforts together with a total water treatment that optimizes your systems. We can analyze your water from a chemical perspective to find the right flocculants, coagulants, and pH balancers that we can used to treat your water before it goes through mechanical separation. This helps to optimize the performance of your clarifiers and filter presses, giving you a better and more efficient total water treatment.

Apart from our chemical products, we also can help get you setup with the best dewatering devices, including the Matec filter press.

Compared to standard filter presses, the Matec filter press offers:

• Complete treatment with real automatic washing
  
  
• Fully automated systems
  
  
• Remote monitoring and assistance
  
  
• High-pressure technology (HPT) that works at 30 bar
  
  
• Open filtrate design, which allows for the simple and rapid identification of bad filter cloths
  
  
• Perfect cake discharge with gasser shakers
  

Are you running a smaller business and wondering if a high efficiency filter press is right for you?

Read our useful Water Facts blog Can my Small Operation Afford a Filter Press? to learn more.

The Filter Press is one of the oldest filtration technologies still in use today. It was first developed in the mid 1800’s. Unlike vacuum filters, which operate continually, the Filter Press and many other pressure filters run in batches. After a batch of slurry has run through the filter, and the filtrate drained out, it must shut down, open the filter pack, and discharge the solid cake.

The components of a featured filter press include the frame or skeleton and the filter pack. The filter pack consists of plates, sometimes frames, and filter media.

Stationary Head- The side of the frame without the closure system has a head that aligns with the filter pack. It is also known as the fixed head. It has a feed hole for the slurry to enter and drain hole for filtrate to exit.

Follower Head- The hydraulic ram pushes the follower head, or thrust head against the filter pack. There are no feed or drain holes on this head.

Closure System- A hydraulic ram is used to press the plates together and hold the filter together during operation. It creates a positive seal and prevents leaks.

Sidebars- The smelting washing filter press plates rest on sidebars to keep alignment and bear weight.

Pump- Necessary to create the pressure which drives the process, it is usually a positive displacement pump or a centrifugal feed pump.

Extra Features- Newer models can include additional components like plate shifters, spray bars, and automatic cake dischargers.

While cotton was the main filter media, in the 1960’s synthetic fibers created better performing and longer lasting press cloths. National Filter Media has a wide variety of fibers, and weave types. Please contact Shane in the link on the Navbar if you would like to ensure that the cloth your filter uses is the best one for your application.

Here is a list of configurations for Media.

Drape over cloth- Twice the length of a plate, a Drape Over Cloth sits on top of the plate and lays down each side. It can be held in place by small nubs, or “dog ears”.

Drape over paper- If cake has a tendency to blind filter media after one batch, a filter paper can be draped on top of the cloth. When the Filter Press opens to discharge, the paper is thrown out with the cake.

Duplex cloth- Two separate cloths, each the size of a plate’s single face, are sewn to a gusset that covers the feed hole that runs through a plate. The top and side edges of the cloth either have grommets or Velcro to secure both side of the cloth to the plate.

CGR Cloth- This duplex cloth is shaped to fit in the groove of a CGR Plate. There is a rope sewn into the cloth’s border that gets caulked into each side of the plate.

As filtrate passes through the filter cloth it collects on the plate panel and drains into outlet holes on the corner(s) of the panel. The outlet holes have a channel that goes into the adjacent corner eye. The channel runs between the packing surfaces. Another function of the system is to allow the cake to be dried “blown down” by compressed air. The manifold piping at the end of the press can be valved to let air into the even numbered plates pushing the liquid thru the cloth/cake/cloth out the odd numbered plates. Sometimes particles of precoat and bodyfeed pass through the filter cloth and become trapped within the drainage channels plugging or partially blocking them. It can be easy to overlook, since you can’t see into the channels unaided.

The plug likely occurs after a filter cloth tear or if the filter media is too permeable for the precoat and body feed used. The best time to check is when you notice a chamber has not formed a dry, firm cake as it usually does. If some chambers in the filter pack form great cakes and others form wet partial cakes, this could indicate which plates are plugged.