What is a Frame Filter Press Used For?

Filter presses may sound niche, but they play a vital role across industries like mining, wastewater treatment, and food and beverage production. Broadly speaking, a filter press is a piece of dewatering equipment used to separate liquids and solids. But they come in different configurations for different applications.

In this post, as a professional plate and frame filter press manufacturer, I’ll dig into what exactly a frame filter press is used for, who uses them, and why they are designed the way they are. My goal is to write an in-depth guide so you can learn everything you need to know about frame filter presses.

What Is a Frame Filter Press?

Let’s start with the basics – what is a frame filter press?

A frame filter press is a type of filter press used to dewater slurries and separate liquids and solids. It consists of a series of vertical plates covered in filter cloths, with hollow frames placed between each plate. When closed together under pressure, the plates and frames create a series of chambers to collect filter cake.

The key components of a frame filter press include:

• Filter plate – Flat plates covered in a filter cloth, typically made of polypropylene or metal. Liquid seeps through the permeable cloth while filter cake accumulates on the surface.
• Hollow frames – Spacer frames placed between each filter plate to create chambers where filter cake accumulates. Frames come in varying thicknesses.
• Filter cloth – Fabric such as polypropylene installed onto the filter plates to collect solids while allowing liquid to pass through tiny pores.
• Feed inlet – Corner ports where slurry enters the system. Typically, multiple corners are used alternately for feed and discharge.
• Filtrate outlet – Corner ports on the opposite side where filtered liquid exits the press.

Now you know what the physical components are. But how do these parts come together to work as a dewatering filter press?

How Does a Frame Filter Press Work?

The frame filter press process relies on pressure filtration to efficiently separate solid and liquid components. Here are the basic steps:

1. Filling: Slurry is pumped into the feed inlet ports under pressure, entering the chambers created between each frame. Suspended particles accumulate on the filter cloths.
2. Filtering: Liquid migrates across the filter plates while solids build up layer upon layer to form filter cake within the frames.
3. Dewatering: Increasing pressure squeezes additional liquid out of the compacted filter cake to improve its dryness.
4. Unloading: Once chambers are filled with cake, the press opens. Frames discharge cake for removal and recovery.

I’ll break the process down further below. But first, let’s look at why someone would choose a frame filter press over other separation methods.

Key Benefits of a Frame Filter Press

Frame filter presses have remained popular over the years thanks to advantages that set them apart from other approaches like centrifuges and belt presses. Some of the key perks include:

Adjustable cake thickness – Frames come in different depths. Switching out frames enables optimization of cake thickness and drying for a given application.

Handles fragile particles – The low pressure drop prevents damage to fragile compressed solids like crystals or carbon fines.

Less maintenance – Frame filter presses have simple designs with relatively few moving parts compared to something like a belt press.

Higher throughput – The large filter area enables processing higher volumes than a smaller centrifugal separator.

Now let’s see how these benefits come into play as the press operates.

Steps in the Frame Filter Press Process

Understanding how frame filter presses work helps clarify why they excel in certain dewatering applications. Here’s a closer play-by-play of what’s happening inside the press during each phase:

1. Filling

The process begins by pumping a stream of slurry into the feed inlet ports under pressure – typically between 100-200 psi. The slurry fills the chambers created between each frame, covering the entire surface of the filter cloths.

The slurry itself is usually 1-4% solids by weight, with particles ranging from diameters of 5 microns up to a couple centimeters. But frame filter presses can process higher solids concentrations as well.

2. Filtration

After initially coating the cloths, the suspended particles continue migrating across the permeable fabric as liquid passes through the tiny pores of the filter cloth. This liquid – known as the filtrate or the filtrate stream – travels across the plates to exit through the filtrate outlet ports.

Meanwhile, as more liquid gets pressed through the medium, particles accumulate on the surface and compact together to form a mat. This mat becomes the filter cake.

The filter cake itself acts like a depth filter during this process. Even fine particles unable to pass through the initial cloth get trapped in the thicker filter cake layers, improving separation efficiency.

3. Dewatering

As filtration progresses, pressure keeps building inside the chambers. This pressure squeezes additional liquid out of the damp filter cakes, increasing the cake dryness.

The optimal pressure level and time for this dewatering step depends on the characteristics of the slurry itself – factors like particle size distribution, compressibility, and permeability through the formed cakes.

But by precisely controlling pressure, frame filter presses can achieve extremely effective moisture reduction across a range of compressed solids.

4. Unloading

Once the chambers fill completely with filter cake, the feed pump shuts off. The press then opens up, allowing the plates to separate and discharge the cake.

At this point the cake typically contains upwards of 30% solids by weight. In some cases the dryness reaches as high as 50-60% solids. But anything from 15-50% counts as successful dewatering depending on how the recovered material gets processed downstream.

After discharge, filter cloths get cleaned or replaced. Changing out dirty cloths prevents them from getting blinded off by fine particles – a common cause of declining performance over long-running operations. The press then resets, closes, and repeats the cycle.

What is a Frame Filter Press Used For?

Now that you know the basic processes and advantages of a frame filter press, let’s discuss some of the most common applications.

Mining & Mineral Processing

Frame filter presses dewater mineral slurries during ore processing, coal washing, and tailings management.

Industrial Wastewater

Many factories use frame filter presses to treat oily process water or remove dyes from textile facility discharge streams.

Food & Beverage

Wineries, breweries, and juice companies use frame filter presses to clarify liquids via cold sterilization of beverages.

Pharmaceutical

Frame filter presses help recover expensive pharmaceutical ingredients as plants streamline waste and improve sustainability.

Chemical

Specialty chemical producers use corrosion-resistant frame filter presses to separate high value products.

Power

Frame filter presses dewater fly ash and gypsum byproducts from coal-fired power plants.

Pulp & Paper

Pulp and paper mills use frame filter presses to recycle whitewater and reduce freshwater usage.

No matter the industry, companies select frame filter presses when adjustable chamber depth and easy flow distribution help optimize separation efficiency for their application.

Real-World Examples of Frame Filter Presses in Action

To give you a better idea of how frame filter presses get utilized, let’s look at two real-world examples:

Coal Slurry Dewatering

A coal preparation plant processes raw run-of-mine coal to remove impurities like ash and sulfur. The beneficiation process uses water to separate good coal from unwanted rock through sinks and floats separation. This water suspension is called a coal slurry.

After washing, the clean coal goes on to get dried, stored, and shipped. Meanwhile, the separated rock and coal fines discharge as waste tailings in the form of a slurry. This aqueous mixture contains about 10-20% solids along with chemicals added during coal washing.

Before the plant can safely dispose the tailings, this slurry gets dewatered to recover water and avoid environmental contamination. Frame filter presses perform this solid-liquid separation extremely well.

The press can handle the occasional larger rock fragments without damaging the filter cloth. It can also process the huge volumes of coal tailings waste. And adjustable frames account for daily changes in particle size distribution and cake moisture targets.

Fruit Juice Clarification

Another common application is using frame filter presses to clarify fruit juices and beverages. Companies need to remove haze, particulates, and debris that make juice appear blemished to meet purity standards and customer expectations.

A frame filter press first receives the unclarified fruit juice slurry. This feedstock enters the press frames under pressure, where particles accumulate on the filter cloth to form cake. The crystal clear juice passes through the medium as filtrate.

What makes frame filter presses ideal for juice clarification? Mainly the simplicity of the process combined with excellent results.

Frame filter presses operate as an efficient, sanitary, cold-sterilization method. The juice never gets heated, retaining more flavor and nutrients. The press also prevents oxygen pickup compared to other filtration methods.

Minimal oxidation maximizes product quality and shelf life. Lastly, producers can easily fine tune pressure settings and frame depth to achieve targeted clarity and extract purity.

Key Takeaways on Frame Filter Presses

Filter presses might seem complex at first glance. But once you understand the basic mechanics and benefits of a frame filter press, it becomes clear why industries like mining, wastewater, food and beverage rely on this technology.

To recap the key points:

• Frame filter presses utilize pressure filtration to dewater slurries and recover solids, making them a versatile waste and water treatment option.
• Adjustable frame depth gives users flexibility to optimize cake dryness and tailor filtration to feed conditions.
• Simple, low-maintenance construction handles large throughputs across young and mature operations alike.
• Applications range from metal recovery to beverage clarification, but always involve separating two-phase mixtures into liquid filtrate and solid filter cake.

I hope this guide gave you a helpful introduction to frame filter press fundamentals. Let me know in the comments if you have any other questions! I’m always happy to help readers better understand industrial liquid/solid separation.