Absolutely oil free, absolutely dry


The German Aerospace Centre (DLR) imposes very stringent requirements on the quality of the compressed air it uses. In order to satisfy these, a customised solution is essential – and that’s where Aerzen Systems comes into play…


At the DLR site in Cologne, a maximum pressure of 10 bar is required to operate test facilities. Two gigantic storage vessels containing a combined total of 1,200 m³ are used to store compressed air. The quality requirements for compressed air are very stringent. For example, the air must be absolutely free of oil. Previously, the air was compressed using a pair of two-stage, oil-free piston compressors. Following the total failure of one system, and continuously rising maintenance costs on the other one, the decision was taken in 2010 to install a new screw compressor.

Short amortisation periods

“At the outset, we were not convinced we would need an oil-free compressor system,” recalls graduate engineer Levin Lübke, Director of Building & Operational Matters at the DLR. One argument in favour of an oil-free screw compressor was that all the existing turbo and piston compressors were already able, without exception, to compress air in an oil-free manner. Furthermore, the wish was to avoid the potential residual risks of subsequent oil-free processing operation. Finally, the higher temperatures of an oil-free compressor system can be utilised in an energy-neutral manner for the regeneration of the absorption agent for a heat-of-compression absorption drier, a key component in the generation of absolutely dry compressed air. Moreover, this dispensed with the need for condensate processing.

Following careful and extended consideration, and talks with four providers, the decision was taken to acquire a Delta Twin DTS 11/10 WB, a two-stage, oil-free screw compressor, manufactured by Aerzener Maschinenfabrik. This unit operates at a fixed speed, is water-cooled, has an intake volume of max. 752 m³/h and an ultimate pressure rating of 10 bar. Levin Lübke: “The decisive factor, alongside the convincing technical concept, was the solution proposed by Aerzen for generating absolutely dry compressed air with a unit known as an HOC drier. This absorption drier operates without any loss of compressed air and without using additional energy, which means that the entire concept convinced us with its short amortisation periods.”

Wear recognised at an early stage

As an interim solution, until the time of delivery, a two-stage, oil-free, air-cooled rental compressor was provided by AERZEN Rental Division (ARD). Aerzen Systems GmbH then supplied the new compressor unit. This company in the Aerzen Group designs optimum customer-specific solutions and turnkey pneumatic stations to operate alongside the full range of tried-and-tested Aerzen screw compressors.

During the commissioning process, a reference oscillation test was conducted on the system while still in brand new condition. Thereafter, through continuous comparison against this reference value, it was possible at all times to establish the current status of the system, i.e. to detect in a timely fashion any wear on bearings and on other machine components that have an influence on vibration characteristics. This reduces the risk of damage, improves operational reliability and cuts the costs of maintenance and of spare parts.

  • Rental Unit AIR
  • Screw Compressors
  • Aerzener Maschinenfabrik GmbH
  • Aerzen Group