Is a Belt Press or Plate and Frame Filter Press the Right ...

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Sludge dewatering is the process of separating the solid and liquid components that make up sludge waste. This is done to make the sludge easier and more cost-effective to transport and dispose of.

Many industries and municipalities turn to sludge dewatering as a way to meet waste minimization and sustainability objectives. There are many different technologies that can be used to remove water from sludge, including belt and plate and frame filter presses.

What is a Belt Press?

The belt press is most useful when a continuous operation is desirable. Typically a belt press produces between 18% and 25% solids by weight in the cake.

Belt presses work by removing sludge onto two different dewatering belts where freestanding water molecules are separated from the sludge by gravity and are collected by a trough. Next, the thickened sludge is pressed between two belt filters and squeezed under rollers to force excess water from the sludge. Finally, the sludge is scraped off the belt and collected in a bin while the water content is transferred back into a wastewater system for processing.

Since the belt press performs a continual action, it is most effective on high-volume waste streams. It is commonly used for the following applications:

• Paper mill sludge,
• River silt, and
• Municipal wastewater treatment plants.

What is a Plate and Frame Filter Press?

A plate and frame filter press uses pressure filtration to separate liquids from solids. Pressure is achieved through the use of a double diaphragm or in other cases, self-priming trash pumps.

There are two main types of filter presses that can be used:

1. High-pressure plate and frame filter presses that typically produce filter cakes that are between 40% - 70% solids by weight.
2. Low-pressure plate and frame filter presses that typically produce filter cakes that are between 25% - 50% solids by weight.

Plate and frame filter presses are useful when a high content of solid material are desirable in the filter cake. They operate by cycling so the batches they produce are referred to as 'drops.'

Plate and frame filter presses are most often used in applications that deal with:

• Biological sludge,
• API separator sludge, and
• Various sludge types where, for disposal, the cake needs to be as dry as possible and contain a high amount of solids.

About Handex

Handex is a provider of Pumping, Dredging, Sludge Dewatering and Treatment of industrial and process wastes and sediments. Our staff includes experienced Project Managers, Operators, Technicians, Fabricators, Mechanics and Health and Safety Professionals. Our objective is to meet and exceed client expectations while providing cost-effective services. In some cases, our clients find that the value of the raw materials returned to the process may pay for a portion of the sludge dewatering cost.

Today's separation and dewatering industries offer two basic dewatering technologies: belt filter presses and centrifuges.

Choosing between a belt press and a centrifuge for your sludge dewatering can be difficult if you are unaware of their different strengths and weaknesses. While both technologies will effectively produce a dry, solid cake, there are quite a few differences between the two.

The choice of using a belt press vs a centrifuge for sludge dewatering is often a difficult decision to make. Both technologies' design can produce a dewatered cake of approximately the same solids content, however, both technologies are quite different in a number of aspects.

What are belt filter press systems?

Belt filter press systems operate on the theory of incrementally increasing the stability of the sludge by increasing applied pressure.

In other words, belt filter press systems use pressure to compress and remove liquid. When it comes to performance, belt filter press usage is affected by the following factors:  sludge flow rate, polymer usage, belt speed, and belt tension.

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For instance, a situation where the sludge flow rate is high may result in a moist solid. Similarly, as belt tension increases, dryness increases. However, high belt tensions may lead to material spillovers and also can also contribute to a short belt service life.

What are centrifuges?

Centrifuges (both decanter and tricanter) operate on the theory of applying centrifugal force to flocculated solids in a bowl, conveyed out by a scroll- operating at slightly different speeds. As the materials are forced into rotation, denser substances are forced outward while the lighter particles are separated and move toward the center of the centrifuge.

Top 5 reasons why you would switch from a belt press to a centrifuge?

Let's dive into the reasons why you should switch from using a belt press to using a centrifuge for water treatment applications.

1- Centrifuges can handle large materials

Centrifuges can offer large solids handling capacity in very small spaces. This is advantageous in large plants where multiple centrifuges are needed.

2- Centrifuges easily handle greasy sludges

Centrifuges are good for greasy sludges. Centrifuges are a great selection for dewatering or separating fats, oils, and greases.

On the other hand, belt press systems have difficulty handling greasy sludges. These systems are not well suited to sludges containing high levels of oils, fats, and greases. These greases tend to blind the filter belt which normally degrades the performance of the belt press over time. Chemical cracking of emulsions is required to enable dewatering.

3- Centrifuges require less cleaning 

Centrifuge systems do not require belt wash water. This can come across as an advantage where an effluent reticulation system is not yet available.

Belt presses are continuously washed typically by recycled clarified plant effluent water. At some plants, this may not be a problem if they access to have effluent water systems for hose-down and clean-up. However, at some plants, recycled effluent water is not available and may require ways to flow water for clean-up.

Lastly, belt press systems are not externally as clean as centrifuges; therefore, they require more labor for cleanup.

4- Centrifuges can achieve higher cake solids

Centrifuges can sometimes achieve higher cake solids than the belt press filter with a low capture (or high polymer) dosage rate. This is due to the centrifuge's shearing ability as the sludge moves through the machine, while the temperature increase in the sludge from the power energy dissipated. 

5- Centrifuges generate negligible amounts of aerosols

When compared to belt presses, centrifuges generate negligible amounts of aerosols. 

Belt presses are known to produce large amounts of aerosols. This can be true for poor quality units, or badly maintained units.  Typically, high-quality machines generally include close-fitting filtrate trays, fully enclosed wash boxes, and piped discharges, so that aerosols are negligible.

Where do I get a centrifuge for wastewater treatment?

Are you interested in getting more information on Industrial Fluid Management 2-Phase or 3-Phase Centrifuge Packages?

Contact us today! Our company's continued success and rapid development are due to our ability to provide our clients with top-notch specialty service and excellent value on quality centrifuges.

Are you interested in renting a 2-phase or 3-phase centrifuge? Industrial Fluid Management has 2-phase and 3-phase centrifuge rental packages available for rent, as well as for sale.

References

Plate and Frame Filter Press vs. Centrifuge: Which One Do I Need to Use? - https://www.hcr-llc.com/blog/plate-and-frame-filter-press-vs.-centrifuge-which-one-do-i-need-to-use

THE CHOICE OF BELT PRESS vs CENTRIFUGE  - http://www.magytec.com/Magytec_International/Dewatering_Technology_files/beltpressvscentrifuge.pdf

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