Wastewater Treatment with Rotary Lobe Compressors

The Delta Hybrid range of blowers from AERZEN makes use of unmatched technical experience in the manufacture of positive displacement blowers and screw-type compressors to produce cutting-edge technology, in the form of the first rotary lobe compressor range in the world.

Image Credit: Aerzen

The Delta Hybrid range brings together blower and compressor technology in a blend of unique capabilities for producing both negative and positive pressures for air and other neutral gases, synchronizing the benefits of both in one intensively designed system.

The Delta Hybrid is at the leading edge of compressor development, as proved by its seven patents already granted or pending. The Roots principle based on isochoric compression is the technology of choice when it comes to lower pressure requirements, while the screw-type compressor which produces internal compression comes to the fore when the situation requires higher pressures.

Advantages

The Delta Hybrid range is based on the earlier Delta Blower and Delta Screw range from AERZEN, both deservedly famous and vastly successful, being a logical and innovative extension of these devices.

Versatility in Numbers

• The Delta Hybrid offers suction volume flow at rates between 110 m³/h to 9.000 m³/h
• Its control range is between 25% and 100%
• It can handle overpressures up to 1500 mbar
• It has nominal sizes from DN 100 to DN 300

Applications

The Delta Hybrid has found use in wastewater treatment, water treatment for potable use, and ventilation of lakes and rivers, among a host of other applications.

Benefits

The Delta Hybrid offers several advantages to the customer, such as:

• Low lifecycle costs
• Outstanding energy optimization
• Markedly higher range of uses and applicable pressures
• Extreme reliability and a very long service life
• Low maintenance needs
• Oil-free and absorbent-free processed air

The Delta Hybrid comes with the AERZEN guarantee, above all.

Technology

Two Profiles, One Packaged Unit

The Delta Hybrid brings together the advantages of innovative positive displacement blowers and screw-type compressors in a single synthesized unit. The new rotary lobe compressor actually contains two separate rotor profiles in one machine. The first is a twisted 3+3 blower system which operates for lower differential pressures up to 800 mbar. The other is a 3+4 compressor system which can handle much higher pressures all the way to 1500 mbar.

Specially designed 3+4 compressor profile with interior compression for lower pressure applications. Image Credit: Aerzen

Compression Principle of Twisted 3+3 Rotary Piston Profile (Delta Hybrid L)

The twisted profiles of the rotors operate on isochoric compression principles just as the positive displacement blowers with straight profiles do. However, the twist merges with the concept of twin stages to optimize the use of energy by taking advantage of the effects of this union on the physical properties of the machine. Since the medium flows in through a diagonal inlet port, and into the flow opening of the conveying chamber, the recoil is reduced and this results in a more efficient filling of the blower stage. Another effect called the gas-dynamic shock also comes into play to cause an initial compression of the medium within the conveying chamber. This leads to operation at higher volume flow efficiency.

The outcome of this design is compressed air available at unparalleled cost-efficiency due to the diagonal movement of air through the stage, unlike the flow in a positive displacement blower. The rotor movement itself creates the conveying chambers in conjunction with the housing walls. With different rotor profiles, internal compression occurs which pushes up the volumetric efficiency. This is the greatest difference between the positive displacement blower and the Delta Hybrid design.

3+3 Blower profile with twisted shafts and patented pulse charging as well as lower crushing losses. Image Credit: Aerzen

Once the blower stage fills with gas more efficiently, the usable volume flow will go up despite the conveying chamber retaining the same size, leading to increased volumetric efficiency.

Gas-Dynamic Shock

In a compressible medium which is passing freely through a space such as a pipeline, if an abrupt closure of flow is imposed such as a sudden valve closure, an impulse will be observed to move in the retrograde direction from the stop position to the inlet, at the speed of sound. The passage of the impulse will cause the compression of the medium behind it as well. At the inlet, the medium relaxes to the original state providing it is open. However, if this is closed before the inlet reaches it, internal compression occurs, the degree varying with the extent to which the impulse moved within this area before the closure of the inlet. If the twisted rotary piston generates isochoric compression, the following formula will give the effect of the coupling performance:

The pressure difference Δp directly affects the coupling performance P_k and can be determined by the equation

It is known that p₁ remains constant through the gas-dynamic shock, which leads to a smaller pressure difference and hence less coupling performance to maintain the same volume flow.

When a screw-type configuration is studied, the effect of using internal compression regarding power needs becomes apparent.

Image Credit: Aerzen

Compression Principle 3+4 Screw (Delta Hybrid S/H)

Screw compression of a medium leads to minimal isochoric compression with most of the compression being due to internal compression. This saves energy because of the use of a preset pressure ratio within the stage. If the internal pressure ratio and the downstream system pressure match, it is possible to avoid wasteful isochoric compression.

In this case too, the process air travels diagonally through the stage, with the conveying chamber consisting of the rotor blade and the stage housing.

The rotors mesh, creating a barrier to the backwash of air and thus directing the air in the right path. The screw rotation causes the medium to be carried from the intake port which is on the upper part to the discharge side which is on the opposite wall and at a lower point, as well as being of a specified size which results in precompression of the medium until it reaches the set pressure.

The advantage of using internal compression is that it carries the medium into the system at a preset intake pressure, which is created even before the medium reaches the system. Thus it uses up the energy which would ordinarily have been required to counteract the system pressure while the medium is in the compressor stage, either in part or under ideal conditions, in full, saving the amount of power used.

Image Credit: Aerzen

To understand this better, a p-V diagram is shown, in which the plane may be assumed to represent the power requirement. In such a case, isochoric compression when the system pressure is 1 bar (ü) in a positive displacement blower would need power corresponding to the plane shown as the dotted line (------). If the medium has already been precompressed within the stage to 0.8 bar (ü), less power is consumed as represented by the solid line showing the curve. It is thus transported into the system at 0.8 bar admission pressure (ü), which means the only power additionally consumed is for an isochoric compression of 0.2 bar (ü), represented as a violet rectangle (1). The difference in the power consumed when using internal and isochoric compression to achieve the same level of compression for the same volume of medium is shown by the distance between the planes.

Image Credit: Aerzen

Conclusion

The positive displacement blower uses energy to create compression, which accounts for about 90% of the costs incurred over its lifecycle. This design is therefore a crucial factor in achieving a better ecological balance and becoming a more competitive business, which depends upon utilizing resources appropriately. Aerzen Delta Hybrid units achieve energy efficiency with savings on energy consumption of up to 15%, which represents a significant return on investment. This can, in fact, lead to recovering the full investment in as little as two years, taking into account the volume and compression rate for each application. The Delta Hybrid unit thus stands for superb power economy and outstanding competitiveness for global businesses.

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.