Impressive long-term balance

In December 2008, a MicroTurbine plant with two units (CR30 and CR65) started operation at the treatment plant in the municipality of Going, situated in front of the wonderful panorama of the Kaiser Mountains. It’s a date that the VTA case technicians vividly remember, and they can still hear the words of the treatment plant manager: ‘No matter what happens’, Erich Wallner told them at the time, and in no uncertain terms, ‘the turbines must be running on December 18: that’s when the holidaymakers get here, and the digester produces oodles of gas!’ The deadline was met, as were all other expectations of the MicroTurbines.

The team at the treatment plant had originally been rather reserved about a technology that was then still quite young. So a meticulous investigation of its suitability was undertaken, including visits to treatment plants in Bad Goisern in Upper Austria and Piding in Bavaria, which at that time already had several years of experience with MicroTurbines. The information exchange between colleagues and other positive references convinced the decision-makers, and so the Reither Ache wastewater association decided in favour of the VTA technology.

Permanently under full load

The project received an additional boost from 2010 onwards: since then, the Reither Ache wastewater association – which includes the municipalities of Going, Reith, Kirchberg and Kitzbühel – has been fulfilling all official requirements for the addition of co-substrates to the digestion. The seasonal fluctuations in gas production have been balanced and both turbines permanently operated at full load. With the increased volume of sewage gas, the association managers soon asked themselves whether a switch to two CR65 turbines would be possible and whether it would also make economic sense. Long-term records and purely economic considerations were in favour. On top of that, both MicroTurbines reached 50,000 operating hours in autumn 2014, the point in their service life at which various components of the turbine need to be replaced.

Now with two CR65 turbines

So the decision was taken not to re-invest in the existing CR30 machine and instead replace it with a larger CR65. Replacement of the turbine including the heat exchanger, as well as a number of manageable replacements of the original machinery (gas compressor), were completed in the shortest possible time. The plant was up and running again at the end of November 2014, and the results achieved since then confirm that the Reither Ache wastewater association had made the right decision.

Since they have been back in operation, each of the two MicroTurbines has achieved a performance of almost 20,000 operating hours, equivalent to more than 8,600 operating hours per year. The Going treatment plant now generates around 90% of its own electricity, and when the electricity generated by the photovoltaic system on the roof of a building at the plant is added, energy self-sufficiency has been achieved.

In terms of emissions too, the MicroTurbines are also in a class of their own. At the end of 2016, in accordance with the decision of the Kitzbühel district authority, TÜV SÜD Landesgesellschaft Österreich GmbH carried out recurring exhaust gas emission measurements at the turbine plant in Going. The exhaust gas flow for both turbines was measured individually in several measuring cycles, the concentrations of carbon monoxide (CO), nitrogen oxides (NOX) and non-methane hydrocarbons (NMHC) were determined, as were the oxygen and exhaust gas temperatures. The result is quite impressive, as the graphic shows!

Field report from the VTA Group’s scientific journal “Laubfrosch”, issue 75