Turbo Blowers – A Guide to the Next Generation of Machinery

The AERZEN turbo blower is Aerzen's latest machine technology and a particularly efficient, low-maintenance and compact turbo machine. The company’s expertise and experience in the turbo sector goes back to 1911, when Aerzener Maschinenfabrik was already constructing and then distributing the first turbo blowers.

Image Credit: Aerzen

The blower stage concept used all that time ago, based on the principle of a radial compressor, was basically identical to today's modern turbo blowers, except that the blower size and drive technology have changed considerably over time. In view of these developments, existing speed-regulated units are considerably more efficient, more compact and virtually maintenance-free.

The new Generation 5 AT turbo blower range from Aerzener Maschinenfabrik has been specifically developed to meet the needs of communal and industrial biological wastewater treatment plants. Operated with high speed, permanent-magnetic motors, the AERZEN turbo blowers can be easily adjusted to fluctuating process air demands of between 40 and 100%, with no need for mechanical adjusters.

Versatility in Numbers

• Intake volume flows from 110 m³/h to 9,000 m³/h
• Overpressures up to 1,000 mbar
• Nominal sizes DN 100 to DN 300
• Regulation range from 40 to 100%

Applications

• Ventilation of rivers, lakes and much more
• Wastewater cleaning

Your Advantages

• High reliability and longevity
• Minimal maintenance
• Exceptional energy efficiency
• Reduced life cycle costs

A line reactor and frequency converters are combined into the systems ready for connection. Compared to standard motors, this high-speed motor is significantly more efficient. The air-cooled, compact motor is speed-regulated and driven through a completely oil-free, contact and vibration-free air-foil bearing. The effect: exceptional efficiency, reduced wear and minimal maintenance effort.

Technology

Compression Principle and Specific Work of a Radial Compressor Stage

The AERZEN turbo blower is a radial compressor. Radial compressors are considered to be turbo machines, and here differ fundamentally from displacement units such as screw compressors and positive displacement blowers. In turbo machines, compression is pulsation-free as it is constant. Generally, ambient air is sucked into the impeller in the axial direction and redirected via the impeller and the housing construction at an angle of 90°. This is reflected in the name “radial compressor” since the air exits in the radial direction. The impeller rotates at high speed and charges the suctioned air with kinetic energy via its speed. This is because of the rotation of the impeller.

Here, the air is continuously moved outwards. The air escaping from the impeller at high speed is slowed down by the downstream diffusor and then collected in the spiral housing surrounding the impeller. Slowing down the air converts the high kinetic energy levels into potential energy, thus generating pressure. When slowing down the accelerated air in the diffusor, congestion takes place and the subsequent air molecules collide at great speed with those that have slowed down. This compresses the air and produces static pressure in the system. When air has been collected in the spiral housing, the air in the downstream cone diffusor is slowed down again to guarantee that the remainder of the still remaining “kinetic energy“ is converted into potential pressure energy without major losses.

Pressure is generated by expansion and delay of the fluid in the spiral housing and the diffuser. Image Credit: Aerzen

Pressure and flow velocity throughout the compressor. Image Credit: Aerzen

The operating principle is explained primarily by Bernoulli's Law and the equation P + 0.5 pv² = P0. This explains that the total energy of a system continues to be constant when the mass flow via a system is constant. Thus, if the flow speed of the air in the system increases, the static pressure of the air flow decreases simultaneously. This dynamic also applies in reverse, in that the overall energy of the system continues to be the same. This principle applies chiefly to the diffusors of the turbo blower stage.

Energy is only brought into the system of the radial compressor through the impeller in the form of kinetic energy.

Image Credit: Aerzen

This principle becomes clear when one considers the basic formula of an impeller. Here, the torque acting on the shaft is considered to be equal to the mass flow multiplied by the ratio of the speed of the inlet impeller to the outlet impeller, that is, the air quantity/mass and the isentropic conveyor height quantified by the system, or the pressure increase. These fundamental parameters define the optimal basic geometry of the impeller and the housing.

That is the reason why the impeller plays the most vital role in this process. Its geometry can take a number of forms and can be decisive for the flow pattern in the whole blower stage. As the turbo blower is a turbo machine with extremely high flow speeds within the stage, a flow that is free of turbulence, and thus losses, becomes a vital parameter for attaining high insentropic stage efficiency levels. The specific work of a radial compressor stage is established by its enforced conveyed-air mass flow and the contribution of the supplied energy, that is, the supplemental effect that is responsible for increasing speed.

Torque= m(r₂V₀₂-r₁V₀₁). Image Credit: Aerzen

Characteristic Diagram of a Turbo Machine

Image Credit: Aerzen

Characteristics of the Turbo Blower

Each turbo blower is recognized by a special characteristic map which illustrates the operating range outside and within the operating limits. In most cases, the different efficiency fields are also incorporated. Illustrating the blower's operating point within its characteristic map allows it to be instantly obvious whether the blower is operated at an economically advantageous point and within its physical limits. The limits of the physical blower are determined by the following four parameters: the choke limit defined by the maximum throughput, the maximum possible drive performance, the pump limit defined by the minimal possible throughput, and the maximum speed. Within this characteristic map, the turbo blower reaches a high isentropic efficiency level mainly in the center of the characteristic map when compared to other blower technologies.

Efficiency levels differ and are directly related to the given conveyed volume flow and the pressure increase. Based on the operating range of the system, the correct layout of the turbo blower is considered to be a deciding factor for profitability and reliability. Operating the blower outside the characteristic map is not possible, and can result in the destruction of the machine. If the turbo blower is correctly designed, it will be able to reach very high levels of efficiency, mainly for high and medium volume flows and, based on the pressure increase, a comparatively broad control range between the pump limit and the maximum drive performance and/or choke limit.

The components inside the AERZEN turbo blower are all exclusively constructed for turbo applications and have no application range outside of them. The result is a turbo blower with the highest current power density and very good profitability. These characteristics can only be attained by employing directly-driven radial blower stages without loss-generating drives and regulation devices, and with field-based regulation of the synchronous motor. That is the reason why every blower unit is available with a drive motor, control system, frequency converter and the unit components essential for operation, as standard. The constant conveying and compression of the process air without pulsation explains that noise levels and the strain on vibration-sensitive locations and components are reduced.

W2P Wire to Process = Total Efficiency Level

Due to the increased number of integrated components, the user's only key concern refers to the overall efficiency level. The overall efficiency level contains all partial efficiency levels of the unit such as the motor, motor cooling, control system, frequency converter and other potential partial efficiency levels of integrated components. It is essential to consider the complete scope of the employed air generators, particularly in comparison with other technologies that do not integrate all components essential for the preferred operating type. This happens because subsequent, additional losses can take place by using add-on components, such as frequency converters, fans, gears, coolant pumps etc.

Image Credit: Aerzen

This information has been sourced, reviewed and adapted from materials provided by Aerzen Machines Ltd.

For more information on this source, please visit Aerzen Machines Ltd.