Bespoke noise protection: AERZEN relies on the advantages of reactive silencers

21/04/2017

With reactive silencers, AERZEN reduces the noise emissions on the discharge side of its screw compressors, positive displacement blowers, and rotary lobe compressors. The innovative concept of these reactive silencers is superior to classic dissipative silencers in many respects.

The sound waves developing on the discharge side of a Delta Screw compressor made by AERZEN can reach 170 to 190 dB. Therefore, a downstream silencer is obligatory, same as with all customary compressors. The high frequencies of the sound waves lead to considerable vibration forces which have a damaging effect on the piping and the insulating material in conventional dissipative silencers. This so-called micro friction wears out the filter material over time and can damage even stainless steel in the long run. This leads to a reduction of the effectiveness of the silencer and to the erosion of finest particles. These contaminate the process air and can lead to hygiene risks for example in the foodstuff production or can clog the fine-pored aeration elements in the aeration basin of a wastewater treatment plant. Downstream filters have to be used, which lead to pressure losses, reduced efficiency levels, reduced energy efficiency and increased maintenance expenditure.

The other way: neutralising instead of absorbing
With the patented reactive silencers (EP1857682) AERZEN not only neutralised the noise, but also the above mentioned problems. A special piping system generates a defined counter-noise, which superimposes the sound waves with a certain delay and thus neutralises them. The sound conduction must be designed exactly for the corresponding sound source by means of varying pipe lengths and pipe diameters. AERZEN has mastered this feat perfectly, particularly as for conveying systems for process gases (Process Gas Division) the assemblies are designed especially for the corresponding application and the silencer is always an individual item. The concept is so convincing that AERZEN now also equips the directly driven screw compressors with reactive silencers. The perfectly tuned modules do not wear, are maintenance-free and correspond to international standards PED and ASME.
The proactive ATEX concept already provides a TÜV certified solution. An integrated spark arrester avoids sparking over in the hazardous zone in a case of emergency. The installation of spark arresters on site can completely be omitted - a decisive advantage for the customer. These important components are manufactured by the subsidiary Emmerthaler Apparatebau. So, AERZEN achieves a high level of flexibility and quality, in particular for special customer requirements.

AERZEN reactive silencers - durable, quiet, and ATEX certified

The Aerzener Maschinenfabrik uses specially developed reactive silencers in screw compressors and positive displacement blowers. Compared to conventional silencers, these offer several advantages.

Positive displacement blowers, screw compressors, and rotary compressors from AERZEN are used in a variety of industries for compressing and conveying air or gases. Depending on the industry, the processed air generated in the assemblies is used quite differently: in the wastewater industry for the enrichment of oxygen in settling tanks, in the food industry for the conveyance of groceries (e.g. flour), or in the cement production for the transport of fuels (such as carbon dust or fluff).

The rotary pistons resp. rotors in the machines are driven by a motor and can reach very high speeds. The medium (process air or gas) is conveyed through the rotary pistons, or is compressed by the rotors and guided into the piping system. This results in high noise emissions of up to 170 or up to 190 dB. The attenuation is based on a downstream silencer which is installed on the discharge side of the machines. The sound waves generate high pulsations as well as high temperatures which, in addition to the noise emission, can also lead to material fatigue on the insulating material of conventional absorption silencers.

To counteract this problem, AERZEN uses so-called “reactive silencers” on the discharge side of its standard products. These, in contrast to conventional silencers, manage without insulating material. The noise is neutralised in the silencers developed by AERZEN. This technology is a new development, for which the mechanical engineers from AERZEN even have a patent.

Absorption silencers - contamination of the process or conveying air by abrasion

Conventional silencers are lined with insulating material. Due to the high material stress from the sound development, as well as the prevalently high temperatures in the long term, the insulating material is dissolved. This can contaminate the airflow in the machines, since the high frequencies cause micro-friction, resulting in the erosion of very fine particles from the absorption layer.

This removal of absorption material is also problematic for several reasons:

If machines are used in the food, pharmaceutical or chemical industries, there is a risk of contamination if the product encounters the process air.
When used in wastewater treatment plants, the fine-pored aeration elements can be clogged in the aeration tanks.
The discharge of fine particles also leads to a higher noise emission over time and to a higher maintenance expenditure in the long term.

In addition, a pulsation chamber for smoothing the sound waves is installed in the absorption silencer between the blower and the silencer, resulting in additional energy loss.

Reactive silencers - AERZEN sets new standards with innovative technology

With the patented reactive silencers (EP1857682), AERZEN has succeeded in finding a solution to these problems. For the so-called “absorption-free” or “reactive silencer”, the use of absorption material can be omitted. Contamination of the process air by abrasion of the insulating material is avoided. The occurring sound waves are erased by the destructive interference method instead of damping materials. The sound waves are neutralised by counter-waves. This anti-noise method is also successfully used in other areas as noise protection - for example: high-tech headphones from aircraft pilots are equipped with this system.

The AERZEN technology for sound waves leveling in reactive silencers works as follows:
the sound waves are measured first. Based on the measured frequency, a precise balanced sound is produced in an inner piping system, which superimposes the original sound waves in a time-offset manner, thus eliminating them. The AERZEN development team makes it possible to adapt these controls very delicately and individually to every application – thus, the right solution is achieved for every customer-specific application.

With the AERZEN silencers, the resulting pressure losses are additionally reduced by corresponding inflow ducts. The downstream piping system is less stressed, resulting in a longer service life.

Process safety, work safety, energy efficiency, and explosion protection

For the silencers and machines, this primarily means high process reliability in the respective application. By avoiding abrasion, the process air remains pure, downstream processes are not affected by polluted process air. As opposed to absorption silencers, the duct pressure is not increased. The reactive silencers can be completely omitted with the pulsation chamber installed in absorption silencers, for smoother sound waves, which also means additional energy losses. The AERZEN silencers also increase energy efficiency.

While conventional silencers are becoming increasingly louder and more time consuming due to the increasing effectiveness of the insulating material, the acoustic level in the reactive silencers does not change. The efficiency remains constant. This sustained noise reduction not only extends the life of the machines and reduces maintenance, but also guarantees long-term safety by constant noise protection. The noise emissions remain constant and the noise protection measures do not need to be adjusted.

Many applications of the positive displacement blowers and compressors require special explosion protection. Thus, (e.g. in the food industry when conveying flour with process air) the material being conveyed is precisely atomised and can ignite on contact with sparks flying. Often, Ex-protection is also required in the chemical industry (e.g. usages in which the direct transport medium is not air, but a gas mixture which requires an ATEX environment, due to its chemical properties). Here, AERZEN proposes the design of its reactive silencers with one flap, thus bringing a third decisive advantage: the innovative construction inside the silencers not only ensures that the sound waves are extinguished here - the discharge silencer also acts as spark arrester and is certified by the TÜV Nord according to ATEX directive 2014/34/EU.

For certain - ready for international use

AERZEN screw compressors, rotary piston compressors, and positive displacement blowers are distributed and used worldwide. Since strict safety requirements apply to European machine manufacturing and marketing, the assemblies must meet international safety standards. The silencer modules of Aerzener Maschinenfabrik therefore comply with the international Pressure Equipment Directive (PED) 2014/68/EU and the Pressure Equipment Directive (PED). In addition, they are compliant with the regulations of the association for pressure vessels of the American Society of Mechanical Engineers (ASME).