Sediment Tank Ventilation and Wastewater Treatment Technology - The Developments

The AERZEN turbo blower is Aerzen’s latest offering, and boasts of extreme efficiency, a small footprint and reduced maintenance, backed by the company’s long experience in this field, dating back to its first turbo blower design and marketing in 1911

At the time, a blower stage was designed upon the basis of a radial compressor, and not much has changed since then. However, the turbo blowers of today have a great advantage in terms of small size and advanced technology in machine drive. This has made them capable of easy speed changes, capable of being fitted into small spaces, energy-efficient and requiring very little maintenance.

Aerzener Maschinenfabrik has now come out with the brand-new Generation 5 AT turbo blowers, which are meant especially to deal with plants that deal with community or industrial biological wastewater treatment. They have stunning technical specifications such as the high-speed motors comprising permanent magnets, simple adaptation to changing air demands between 40% and 100% during the process, without having to use mechanical adjusters.

Features

Versatility in numbers

  • The AERZEN turbo blower can regulate the air supply at between 40% and 100% of its maximum capacity
  • It can have intake flows of medium ranging from a volume of 110 m³/h to 9,000 m³/h
  • It can handle overpressures of up to 1000 mbar
  • It can have nominal sizes DN 100 to DN 300

Applications

  • Treatment of wastewater
  • Providing ventilation for rivers, lakes and other water bodies

Benefits

  • The AERZEN turbo blower is designed to reduce energy consumption to the optimum level
  • Its life cycle costs are extremely low
  • It is highly dependable and robustly built
  • It requires little service or maintenance

This machine has inbuilt frequency converters as well as a line reactor which are ready to connect. Additionally, this motor runs at high speed yet requires little energy. It is air-cooled and occupies little space, is regulated by speed and runs on the basis of a specialized air-foil bearing which requires neither oil nor contact, and produces no vibrations. As a result of this design, the turbo blower is highly efficient, needs little maintenance and has a very long time because the wear on its parts is lower compared to conventional blowers.

Technology: Compression Principle and Specific Work of a Radial Compression Stage

The AERZEN turbo blower operates on the principle of radial compression, which yields constant rather than pulsatile compression. Ambient air is taken into the impeller along the axis and sent out again through the housing construction and impeller after its direction is changed to the perpendicular of the intake stream – the radial direction, from which its name is derived. This redirection is the primary difference between radial compressors and positive displacement blowers or screw compressors. The high speed of rotation of the impeller leads to the generation of kinetic energy and its transfer to the air sucked in.

The impeller movement pushes air outwards in a continuous fashion, and this escaping air is channeled to a lower velocity by the cone diffusor located downstream, and piled up in the spiral impeller housing. The kinetic energy is changed into potential energy which leads to the increase in air pressure. In other words, the accelerated air molecules undergo sudden slowing of motion within the diffusor which causes them to move in random motions, colliding at high speed with the slower air molecules already within the housing. The latter thus imparts energy to the slower air molecules, causing the compression of the air and increased static pressure. The interaction of air in the cone diffusor and the spiral impeller housing continues until all the kinetic energy of the air has been converted to potential energy in the form of air pressure with low losses.

The principle on which a turbo blower runs is given by Bernoulli’s Law in the form of the equation:

     P + 0.5 pv² = P0

This principle ensures that a system remains at constant total energy if its mass flow remains the same. If the air flow speed within the system increases, the static pressure of the flowing air must go down, and vice versa. This is studied here mainly in the background of the turbo blower diffusers.

The entry of energy into this system is only via the impeller as kinetic energy. For this reason the impeller is the decisive factor in the use of energy. Its blade pattern may be varied but it is key to setting the blower stage air flow pattern. The turbo blower achieves very high flow speeds, and if this can be done without turbulence and the resultant energy losses, this high-speed flow is important in deciding how efficiently the insentotropic stage operates. In short, the amount of work performed by a radial compressor stage depends upon the enforced mass flow of the conveyed air and how much energy is contributed by the supplied air in the form of the speed increase caused by the supplemented effect.

The torque acting on the shaft is the product of the mass flow and the ratio of inlet impeller speed to outlet impeller speed. In other words, the air or mass quantity multiplied by the isentropic conveyor height of the specific system, or the pressure increase, are the determinants of the geometry that enables the impeller and housing to function at optimal level.

Characteristic diagram of a turbo machine

Characteristics of a Turbo Blower

Turbo blowers are represented by special maps that show the operating range of the machine when the parameters are within or beyond the appointed operating parameters. These maps typically also depict the efficiency fields as well. The operating point can be identified within the characteristic map of each blower, thus making it apparent when the operation is being performed at a point that is within these limits and thus is cost effective. The physical blower limits are defined in terms of the four parameters given below:

  1. The pump limit as shown by the lowest possible throughput
  2. The choke limit or maximum throughput
  3. The maximum possible drive performance
  4. The maximum speed

Within the map, each device has a point of high isentropic efficiency, which is in the center of the map for turbo blowers. The isentropic efficiency is directly proportional to the specified conveyed volume flow and the increase in pressure achieved. Within the operating range, the design of the turbo blower is thus critical in determining how well it will fit the system to achieve cost reduction and how reliable its operation will be. Outside this range, it is not possible to run the blower and may harm it. On the other hand, the design may be optimized to achieve very high energy efficiencies especially in the medium and high volume medium flows. It is also possible to design a wide control range between the first three operating parameters, namely, the pump limit, the choke limit and the maximum drive performance.

The AERZEN turbo blower is constructed of specialized components which are designed for turbo applications alone, which ensures the highest possible current power density and very high profits within the operating range. They include direct-drive radial blower stages without intervening drive or regulation components which increase energy losses, and field-based regulators which control the synchronous motor. Every blower unit comes equipped with standard components such as a drive motor, a frequency converter, a regulator or control system, and other unit parts required for its operation. Constant air conveying and compression in a non-pulsatile manner results in reduced noise as well as minimal strain upon locations and components which could be vulnerable to vibration.

W2P Wire to Process

Since the AERZEN turbo blower comes as a single integrated unit containing all necessary components, a glance at the total efficiency level is the only thing necessary to make a choice. The total efficiency level includes the partial efficiencies at all levels, such as that of the motor, the frequency converter, the motor cooling, the control system and other components. When a turbo blower is compared with other non-integrated machines in particular, the full range of accessories and fittings such as fans, gears and frequency converters must be considered when looking at the total efficiency level of the latter, because such add-ons are bound to increase the total energy loss in the system.

This information has been sourced, reviewed and adapted from materials provided by Aerzener Maschinenfabrik GmbH.

For more information on this source, please visit Aerzener Maschinenfabrik GmbH.

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