At DLR in Cologne, the highest pressure for the operation of the pilot plants is 10 bar. There are two reservoirs with a total volume of 1.200 m³ of compressed air. The air quality required is high and it must be completely oil-free. In the past it was produced by two double-stage oil-free piston compressors. After the breakdown of one of the units and continuously increasing maintenance expenditure concerning the other one it was decided in 2010 to install a new screw compressor.
”First of all, it had to be decided if it should be an oil-free compressor”, recalls Dipl.-Ing. Levin Lübke, Manager of constructional and operational skills at DLR. An oil-free screw compressor was recommended as all the existing turbo and piston compressors are oil-free. Subsequently, this would eliminate the risks to continue with an oil-free operation. And finally the higher temperatures of an oil-free compressing unit enables the regeneration of the absorption from the air drier giving completely dry compressed air. Also condensate treatment is not required.After careful consideration and conversations with four suppliers a double-stage oil-free screw compressor model Delta Twin DTS 11/10 WB from Aerzener Maschinenfabrik was chosen with fixed speed and water cooling with an intake volume of max. 752 m³ and a discharge pressure of 10 bar. Levin Lübke stated: “Also the solution recommended by Aerzen was a decisive point apart from the convincing technical concept for the generation of absolutely dry compressed air with a so-called HOC-drier. This absorption drier works without loss of compressed air and without the needs of additional energy so that the total concept convinced by shorter cost recovery.”
As an interim solution up to delivery a double-stage oil-free compressing, aircooled rental unit of Aerzen International Rental (AIR) was provided. Aerzen Systems GmbH supplied the new compressor unit. The company is a part of the Aerzen Group specialised in solutions for compressed air units designed for operation with the Aerzen Screw Compressors. During commissioning of the new units its reliability was determined by a reference vibration.By comparison with this reference value the current condition of the unit can be determined so that the wear of the bearings and other vibration-relevant machine components is detected on time. That reduces the damage risk and increases the operating safety and the need for the maintenance and spare part costs is lower.
