Edition 03/2017

Dust-air mixtures are explosive when the dust consists of combustible material. This includes besides timber, flour and cellulose cocoa, coffee, starch and inorganic substances such as the elements magnesium, aluminium and iron. These raw materials are typical when pneumatic conveying systems are used for which blowers or compressors made by AERZEN ensure the continuous supply of the production by the silo.

Potential risks in Ex-protection areas cannot be excluded even with a blower. If it comes to an input of sparks into the pressure pipe, as a rule, this results from a defect of the compressor stage. A too high bearing clearance, for example due to lack of maintenance, may be the reason why inside the rotary pistons do not rotate any longer with the defined air gap but hit together and generate sparks. In application ranges coming under the ATEX regulations, the spark arrester within the discharge silencers represents an effective measure to safely prevent the entry of activation energy into the material conveying flow. Thus, the silencer is among the reactive ATEX measures, as it is used when a damage has already occurred.While the above measures aim to guarantee the Ex-protection, particularly for pressure pipes, AERZEN considers also for vacuum conveying the ATEX requirements as integral part of a blower solution from one single source. Concerning vacuum conveying the penetration of the material into the blower must be excluded safely. For this, mainly filter inserts are used, creating a barrier between the material to be transported and the assembly, in this case providing the negative pressure. Furthermore, AERZEN developed their own zone separation filters, representing as so-called sentinel filter a further decoupling between the upstream process and the assembly. “If it comes to a filter fracture we can react accordingly quickly and shut down the assembly, before an explosive atmosphere can generate inside the compressor stage,” explains Fabian Pasimeni, product manager for blowers and rotary lobe compressors at AERZEN. If, however, as a result of a chain of unfortunate circumstances it comes to an explosion the effects on the environment can be reduced effectively by using special material for the construction of the compressor stage. Pasimeni: “If the ATEX requirements and the explosion risk are high, for the housing of the compressor stage we no longer use normal grey cast iron, but special spheroidal graphite cast iron.” Mainly in ATEX relevant application ranges AERZEN uses early warning systems to prevent serious and safety relevant damage from the start. Here, this concerns the active mechanisms of Condition Monitoring, with which potential damage can be detected reliably - mainly by means of vibrational monitoring. “We offer an expansion stage covering three levels,” says Pasimeni. The easiest way to monitor vibrations of a compressor stage are special measurement points installed near the bearing positions. With sensors as second expansion stage AERZEN takes a step towards continuous monitoring. The sensors installed at the sides of the compressor stage measure continuously and emit corresponding 4-20 mA signals which can be monitored and evaluated by the control system. If the AERZEN blower itself is installed in an ATEX zone, the sensors are supplied with a corresponding approval. “Meanwhile, our modular system of blower solutions is so nuanced that we are able to quote for different applications with varying ATEX requirements as standard,” states Pasimeni. Based on this extensive know-how AERZEN developed the third stage of real-time monitoring. With up to four sensors per compressor stage “we can look precisely into the inside and find out the condition of the corresponding bearing,” explains the product manager. This includes condition monitoring of internal rings, Pitting (local material damage) and touching of the rotor against the internal housing wall as a consequence of thermal deformations. If the assemblies themselves are installed in an ATEX zone, AERZEN serves this application with motors of different rating and further components with ATEX approval.