Efficient Blower Selection at WWTP’s

In general, the term blower is a machine used for moving gas with a moderate increase of pressure, but it is easier to answer the question if we compare the fan, blower, and compressor. An air compressor has a high pressure-to-volume ratio, whereas an air blower has a low pressure-to-volume ratio. The following statement can be found on many web pages: As per the American Society of Mechanical Engineers (ASME) the specific ratio (i.e. the ratio of the discharge pressure over the suction pressure) is used for defining the fans, blowers, and compressors.

EquipmentPressure Ratio
FanUp to 1.11
Blower1.11-1.2
CompresserAbove 1.2

However, the blower pressure ratio limit goes up to 3.0 in the ASME PTC-13:2018.

In wastewater, all aeration devices are known as blowers but in the case of a typical 5m water depth, the required pressure ratio is over 1.2. ((101.325Pa + 50.000 Pa) /101.325Pa = 1.49)

What industries do blowers play a role in?

Almost every industry such as agricultural, automotive, chemical, food processing, oil and gas, medical, and mining, or water /wastewater use blowers for their specific purpose. These blowers are used for different purposes so there are big variety of the parameters.

Where are blowers used in the wastewater treatment process?

Blowers are important pieces of equipment in the wastewater sector since they consume the most energy in the facility. Blowers consume around 60% of the total plant usage, as a rule of thumb.

Blowers are used in different positions in the wastewater treatment process in different technologies. One of the key positions is the reactor where aeration is required. The reactor, which requires aeration, is one of the critical places. Root blowers and centrifugal blowers are employed in this application. Blowers are frequently used in conjunction with VFDs to provide as wide of a range in flow as possible.

What kind of information is required to select an air blower in a preliminary design?

In process point of view the followings are required:

  • Media (density, relative humidity)
  • Capacity range
  • Rated Operating Pressure

In Mechanical point of view:

  • Blower type
  • Operating temperature range

In electrical point of view:

  • Voltage
  • Frequency
  • VFD requirement

Type of the blowers used in the wastewater industry:

  • Positive displacement /Rotary lobe
  • Dry screw
  • Multistage centrifugal
  • Single-stage integrally geared centrifugal
  • High-speed turbo gearles

The efficiency of the blower depends on the blower type, in our tool (Transcend Design Generator) you can find suggestions to set the efficiency value.

How can we estimate the power consumption of a blower?

The power consumption of a blower can be estimated based on different theories. It is very important to underline it as an estimate because the real values will be provided by the Vendors. Although, these estimations are still very useful in preliminary design to be able to estimate the OPEX of the equipment and the whole technology. In the power consumption estimation, the process requirements and mechanical requirements are also considered.

Adiabatic compression

In thermodynamics, an adiabatic process is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work.

Polytropic compression

In the case of a polytropic compression, the gas being compressed is not at constant entropy as in the adiabatic process, or at a constant temperature as in the isothermal processes.

In our tool, adiabatic compression is considered in the average power consumption calculation and also in the electrical motor selection. The tool contains the equations to be transparent to our users on how the tool works.

The importance of the temperature rise!

According to the thermodynamic behavior of gases, as the pressure of the gas increases, so will the temperature. This fact may be significant in terms of safety, as well as in terms of supporting the downstream pipe and material choices. In case the temperature of the downstream pipe is above 50 C (it could be different based on the local regulation), there shall be some personnel protection insulation applied for the parts which can be touched.

The relevance of material selection is highlighted by the instrument selection and when the system has certain polymer components or pipelines composed partially of polymer. This might happen due to the diffusers plumbing under the water; however, the material modification must be done cautiously here.

We’ve built a blower size tool to assist you in deciding the best option for your blower choices and to ensure your blower’s performance is efficient. The blower sizing tool is available here.

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