| 1. |
Simple : |
More complex : |
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A single drive driving a single rotor. |
Two (2) drives - A main drive and a back drive driving two (2) rotors, the bowl and the scroll. |
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Low maintenance. |
High maintenance. |
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| 2. |
Low speed: 0,5 to 2,5 RPM max. |
High speed: 1500 to 3500 RPM |
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No (or very low) live floor loads. Nothing special is required. |
High live floor loads. Building needs to be designed especially to deal with these loads. |
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Reduced noise: Nothing special is required. Acoustic protection is not required. |
High noise: Noise attenuation is required as part of the building construction. |
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Vibration and temperature: Monitoring is not required for the Rotary Press. |
Vibration and temperature: Monitoring of the electric motor, bowl and scroll is very critical. |
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| 3. |
Low Power Consumption : |
High Power Consumption : |
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Low installed HP and reduced power consumption: 10 kW-hr/dry ton. |
High installed HP and high power consumption estimated at 171 kW?hr/dry ton* . The additional power cost over the life of equipment is very significant. |
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No consideration for power factor. |
Consideration for power factor. |
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Reduced installation costs for the electrical connection. |
High installation costs for the electrical connection. |
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| 4. |
Simple and short start-up and shut down procedures. |
More complex and lengthy start-up and shut down procedures. Bowl may continue to rotate for a while after shut down. |
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Frequent stops and starts are possible. |
Frequent starts and stops are not possible. |
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| 5. |
In the event of an eventual shut down, repairs can be completed at the waste water treatment plant by regular mechanics. |
In the event of a shut down, the centrifuge may have to be shipped to the manufacturing plant for specialized repairs. The centrifuge may require visits from specialty mechanics. |
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| 6. |
For a multi-channel machine, one or more channel(s) may be removed for maintenance purposes, while the machine with the remaining channel(s) may still be operated. |
The whole machine is in operation or it is shut down. |
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| 7. |
Vibration analysis and preventative maintenance are not critical. |
Vibration analysis and preventative maintenance are very critical. Additional training of plant personnel may be required. |
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| 8. |
The Rotary Press includes a flocculator with a variable speed agitator to optimize flocculation and polymer dosage, which most likely results in a reduced polymer consumption. |
Flocculation takes place inside the centrifuge and cannot easily be controlled, and may result in a higher polymer consumption and higher annual expenditures. |
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| 9. |
More reliable: |
Less reliable: |
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Very few components of the Rotary Press may cause catastrophic shut down of the equipment due to its low speed and simple design. |
Many more components may cause a shut down due to the high speed and high power. |
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| 10. |
A high capture rate is intrinsic in the Rotary Press design giving a reasonable flocculation. |
The centrifuge will operate at a lower capture rate, which will reduce further if left unattended. |
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| 11. |
The effects of grit are greatly reduced in the slow-moving Rotary Press. |
The centrifuge may be affected by the presence of grit in the sludge in the form of unpredictable premature abrasion wear. |
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| 12. |
With the Rotary Press, it is possible to obtain very high cake dryness at reduced flow. |
The same cake dryness may not be possible with the centrifuge. |
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| 13. |
No external lube system is required. |
External lubrication system is usually required. |
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| 14. |
Low maintenance cost. |
High maintenance cost. |
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| 15. |
Generally, no shredder is required upstream. |
May require a shredder upstream. |
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| * According to an article written by Mr. Chuzo Nishizaki in the "The Proceedings of the Management of Water and Waste Water Solids for the 21st Century June 19-22, 1994" published by the Water Environment Federation, U.S.A. (p 7?35). |