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Spaans Babcock
About

Surface Aerators

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In 1960 Spaans Babcock started with the production of different types of surface aerators. Modern Surface Aerators experienced a renaissance for some years. New developments make Surface Aerators to an economic solution and offer in addition advantages that hardly any other system can realize. Beside the fabrication, delivery and installation of the aerators, Spaans Babcock has also the knowledge to help you with advise about process and product design. Worldwide more than 1000 surface aerators, such as the O2Max aerator have been installed on municipal sewage treatment plants and industrial waste water plants. To learn more about the qualities and advantages of the Spaans Babcock Surface Aerators please select from the menu on the left or simply contact us!

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Surface aeration versus other aeration systems

Until the introduction of the fine bubble aeration, the alpha factor was hardly known, because this factor of 0.93 had always been neglected with surface aeration. Later on, this comparison factor between pure water and sewage water became an increasing problem for the fine bubble aeration process. Initially it was calculated with an alpha factor of 0.80 for bubble aeration, but a value of 0.65, which can dramatically fluctuate, quickly became a standard in the literature. Because most pressure elements lose 2 – 3 % per year of effectiveness, most offices calculate today using an alpha factor between 0.50 until 0.60. In the chart below a mathematical comparison illustrates the influence of aging and the alpha factor:

This comparison considers experienced values of a basin with a depth of approximately 4.5 metres. In more shallow basins, the economical advantage of the Surface Aerator in comparison with fine bubble aeration is becoming rapidly higher.
 

Advantages of O2Max vs. other aeration systems:
  • Extremely reliable
  • High aeration efficiency (>20% increased)
  • Non clogging
  • Low maintenance costs
  • Low vibrations
  • Low upthrust and radial force
  • Low investment costs
  • Long lifetime
  • No problems in adhesive or DS containing sludge (pulp and paper industry, breweries, dairies, sludge digestion/stabilization etc.)
 

High efficiency aerator

Spaans Babcock developed the third generation aerator: After a long period of testing, the ideal design was developed. A complete new design which ensures a high efficiency, a huge mixing effect and a very smooth running with less vibration to the bridge and drive unit. The new O2Max is designed on the basis of the latest know-how (knowledge) on surface aeration and beats the old problems with this kind of aerators.

The O2Max is approved for the Carrousel® system by DHV.

Water Depth: Because of the strong mixing power of the O2Max, in most cases a system without sludge settlement can be guaranteed up to 6 meter water depth.
Aerosols: Studies prove that the amount of aerosols is obviously lower than with fine bubble aeration. In addition protection systems are available.
Noise load: Simple covers are available for the drive unit. For the Aerator different covers and bridge systems are available.
Energy-efficiency: Until 4 meter water depth absolute the most economic aeration system. In larger water depths, it will be often an economical solution, but each single case must be proved.

 

Advantages:

  • Low investment costs
  • Low maintenance costs
  • Extreme reliable
  • High aeration efficiency (=20% increased)
  • Non clogging
  • Low vibrations
  • Long lifetime
  • No problems in adhesive or DS containing sludge (pulp and paper industry, breweries, dairies, sludge digestion / stabilization etc.)

Spaans Babcock constructs the largest and most high-performance surface aerators with achievements of up to 500 kg O2/h per machine.

 

Applications

The O2Max is especially suitable for Carousel® systems. Due to its high oxygen input and propulsion properties, it is often the most economical solution for this system. Extreme propellers are often not necessary, however, this will be required on a case-by-case basis.

 

O2Max floating

In cases where no bridge or platform construction are possible due to large water level changements, the installation with floaters is a possibility. Three floaters on a heavy load construction will allow the aerator to float itself.The aerator will be kept in its position by heavy steel cables. Installation is possible in all kind of square and round tanks.

O2Max circulator

The circulator is a construction of a floating aerator, connected in the middle of the tank and is moving self propelled on a circular path system through the tank. The system can be used for low load systems in all kinds of tanks. Installation is possible in relative large tanks.

The O2Max consist of:

  • aerator impeller
  • vertical shaft and coupling
  • foundation plate
  • gearbox
  • electric motor

The aerator impeller is a low speed, non-clogging and open type. The aerator is a heavy steel construction to withstand stresses created by mixed liquor motion and will be adequately anchored and supported to the bridge of the aeration tanks.The impeller consist of a flat plate with curved blades beneath the plate in order to obtain maximum efficiency and to suffer minimum friction losses between blades and water.

The O2Max design will comply to the following:

  • The maximum tip speed of the impeller will not exceed 6.5 m/sec so that the possibility of sludge floc break-up is kept to a minimum.
  • The entire weight of the impeller and shaft is suspended from and supported by the reducer drive shaft. No outboard support and steady necessary.
  • The maximum hydraulic up trust of the aerator at maximum performance will not exceed the total weight of the aerator impeller.
  • Each aerator is provided with lifting eyes on the upper side and has steel hooks cast into the platform, keeping the aerator in position when the gear unit is removed or is being serviced.

Properties

Standard oxygen transfer rate: The oxygen transfer rate under standard conditions (SOTR) of the O2Max® aerator depends on the aerator, the speed, the submergence of the aerator and the geometry of the aeration tank. In the table below the range of the SOTR can be found in relation to the motor power and tank dimensions.

 

Power regulation

The load on a sewage treatment plant is varying almost continuously. Therefore the oxygen transfer capacity required is not constant as well. To optimize energy consumption the oxygen input of the aerator should be adjusted accordingly. There are two possibilities to adjust the power input and oxygen transfer of the aerator: by changing submergence or by changing speed.

Changing submergence

The submergence range of a surface aerator is limited to a certain maximum and minimum value. Exceeding these values will cause reduction of efficiency. The variation of submergence can be created by changing the height of the aeration unit or by changing the water level. The last possibility is the cheapest but also the most time consuming.
 

Changing speed

At present the most popular way of regulating the power input of a surface aerator is by changing the speed. The speed of a surface aerator is limited to a certain maximum and minimum value. Exceeding these values will cause reduction of efficiency. The maximum and minimum speed for the O2Max® aerator is related to the diameter of the aerator and the peripherical speed. The peripherical speed is limited to about 6.5 m/s.
 
There are two methods of changing speed: application of a two speed motor or application of frequency control. With aid of a two speed motor the power input can be changed in steps from 100% at high speed to about 50% at low speed to zero when switched off. Applying a frequency control enables every power input in between 0% and 100%.

Changing the number of aerators in operation

When several aerators are applied in just one tank power adjustment can also be done by switching aerators on and off. The steps in the total power input depends on the number of aerators. The power input of the aerators should be adjusted to the real demand. All possibilities have been indicated previously. Spaans Babcock has all the knowledge to help you with advice about process and product design that will make your work easier.