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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.

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.