What is a Filter Press and How Does it Work?

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.

What are the Four Main Components of a Filter Press?

• Frame
• Filter Plates
• Manifold (piping and valves)
• Filter Cloth (This is key for optimizing filter press operations.

Basically, the 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.

 
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Filter Press History: From Across the Pond to Over It

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.

Common filter press applications include:

• Mining operations and aggregate
• “Ready-mix” concrete washout water recovery
• Food & beverage production
• Marble and stone cutting

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.

How does a Filter Press Work?

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.

What Is A Filter Press Used For?

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:

• Machine design
• Filtration capacity
• Plate size and number of chambers

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 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.

Many industries use filter presses for liquid and solid separation, including:

• Food and Beverage Processing
• Chemical Manufacturing
• Mining
• Power Generation
• Aggregates
• Asphalt and Cement Production
• Steel Mills
• Municipal Plants

Combining Clarifiers and Filter Presses

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 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.

Total Water Treatment with ChemREADY

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 filter press is right for you?

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