Thanks to the reduced sewage duty resulting from basic changes to the aeration basins in 2008, modification costs of € 1.3 million were amortised after only three years. Replacement of the two existing turbo compressors with two new Aerzen rotary lobe compressors of series Delta Hybrid, led to an additional energy saving of approximately 13 % of process air generation. Since then, the entire energy consumption per month has been reduced from approximately 250,000 kWh to only 140,000 kWh (see also COM. PRESS 3/2011). This shows that the energy efficiency of process air generation can be improved still further by the replacement of other old turbo compressors – however, this time with turbo blowers of the new AERZEN series ‘AT Turbo Generation 5’ provided with air bearings.
An intensive examination of the frequencies of required quantities in basins 1 and 2 had shown that replacement of the large turbo compressors used (delivery volume 10,000 Nm³/h) with a new unit which can meet these demands, will lead to further energy savings.
At the end of 2012 they decided for the new turbo blowers made by AERZEN. This unit (delivery volume 6,000 Nm³/h) covered the most frequent operational range of between 5,000 and 6,000 Nm³/h on its own. For lowload operation below 4,100 Nm³/h they used the Aerzen rotary lobe compressor series Delta Hybrid which had already been installed in 2010. In case of a requirement of more than 6,000 Nm³/h, both units work simultaneously.
With the new ‘AT-turbo Generation 5’ blowers AERZEN has realised the production of process air for biologically working sewage plants, offering the highest possible energy efficiency and security of supply. As a rule, the process air requirement of a sewage plant can only be satisfied using a combination of various machine types with various capacities, which can be defined as ideal base and peak load units due to their construction features and performance ranges. The physical advantages of turbo machinery – high energy efficiency of the design – can be perfectly combined with the advantages of rotary piston machines – high controllability and good efficiency in part load operation.
Here, the units of the new controllable turbo blowers prove to be the ideal base load generators. As optimal generators of peak and low load requirement AERZEN supplies the controllable positive displacement blowers series Delta Blower and the controllable rotary lobe compressors series Delta Hybrid.
“It is a fact that the energy efficiency of the process air generation is continuously optimised”, explained sewage plant manager Thorsten Jung in January 2014, referring to the data already available from the field test and to calculations on the basis of the data from the combination of AERZEN units presently used for basins 1 and 2. The two Aerzen Delta Hybrid rotary lobe compressors, which have been available since 2010, and which, according to Thorsten Jung, have proved successful up to now, are kept available for all three basins as concurrently working redundancy units. But they are also planning to use an additional Delta Hybrid unit in basins 1 and 2 for covering low load requirements.
Previous experience has shown that the planned concept will lead to an annual saving in energy costs of around € 60,000. In addition, due to operating only new units, maintenance costs will reduce by about € 15,000. The operators therefore expect a payback period of at most five years. Meanwhile, other sewage treatment plant operators are interested in the new concept operating in Kaiserslautern and the relevant positive experiences.
