Today's separation and dewatering industries offer two basic dewatering technologies: belt filter presses and centrifuges.
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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.
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?
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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
Belt filter presses are industrial machines, used for solid/liquid separation processes, particularly the dewatering of sludge's in the chemical, mining, and water treatment industries.
A costly burden on many companies, belt filter presses require continuous staffing and excessive maintenance costs that often surpass the expenses needed to replace and upgrade the current equipment.
Until recently, belt filter presses have been the default bio-solid dewatering method. However, an improved alternative method such as the decanter centrifuge is currently available.
Decanter centrifuges separates solids and liquids, and has become an essential component of water waste facilities and the chemical, oil, and food processing industries.
When To Consider a Centrifuge over a Belt Press?
Comparing belt presses and centrifuges really comes down to the needs of the facility. In order to develop a true cost analysis, operation size and ancillary odor abatement concerns all are factors in the equation.
Centrifuges are proven to meet needs and exceed expectations in the refinery industry.
A few questions come to mind for many companies when considering the switch from a belt press to a centrifuge:
1. Why hasn’t this been done before?
Well until 5-10 years ago, there weren’t too many decanter centrifuges large enough to compete with belt presses as far as throughput goes. A 2-meter belt press (common size used) can process bio sludge in the range of 150-200 gpm. With a 21" centrifuge, you can produce this same throughput if not greater.
2. What is the economic impact of going with a centrifuge as opposed to a belt press?
The economic impact can be large. Using a centrifuge, it is possible to get the solids content up significantly. This is accomplished by reducing the water content of the solids by reducing the weight of the product to be disposed.
Switching from a belt press to a centrifuge also dramatically reduces the man-hours needed for solids handling. Many case studies show that switching out belt filter presses for centrifuges can reduce the hours worked per week without sacrificing production.
The main economic impact is the disposal of less solids. With a centrifuge producing dryer solids, the weight by volume is less which in turn reduces the disposal cost.
3. What are the advantages and disadvantages?
Centrifuge Advantages:
- Gets the same, if not better, throughput than a belt press
- Captures more solids than a belt press with better efficiency and dryer solids
- Easier to operate than a belt press with more efficient technology
- Greater range of mobility
- Could see up to a 40% reduction in operations costs
Belt Press Disadvantages
- Facilities often receive products with high oil content, causing the belts to clog and decreasing operating efficiency. Belt change out costs can be expensive.
- Belt presses are notoriously difficult to operate, requiring extensive training for the operators and decreasing workforce efficiency.
- Belt presses require a significant amount of water to operate (due to the cleaning mechanism used to attempt to clean the belts) this water is a resource for other parts of the operation but is now turned into a waste which will have to be treated.
- A belt presses solid capture efficiency is less than a centrifuge, which allow more solids to get through the process.
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