The results in this work show the influence of long-term operation on the decomposition of working fluidsin eight different power plants (both heat-led and electricity-led) in a range of 900 kWel to 2 MWel. Allcase study plants are using Octamethyltrisiloxane (MDM) as a working fluid. The case study plants arebetween six to 12 years old. On one system detailed analyses, including the fluid distribution throughoutthe cycle, have been conducted. All fluid samples have been analysed via Head Space Gas ChromatographyMass Spectrometry (HS-GC-MS). Besides the siloxane composition, the influence of contaminantssuch as mineral oil based lubricants (and its components) has been examined. In most cases the originalmain working fluid has degraded to fractions of siloxanes with a lower boiling point (low-boilers)and fractions with a higher boiling point (high-boilers). As a consequence of the analyses, a new fluidmanagement system has been designed and tested in one case study plant (case study number 8). Themeasures include fluid separation, cleansing and recycling.Pre-post comparisons of fluid samples have proved the effectiveness of the methods. The results showthat the recovery of used working fluid offers an alternative to the purchase of fresh fluid, since operatingcosts can be significantly reduced. For large facilities the prices for new fluid range from e15 perlitre (in 2006) to e22 per litre (in 2013), which is a large reinvestment, especially in the light of fillingvolumes of 4000 litres to 7000 litres per cycle. With the above mentioned method a price of e8 per litreof recovered MDM can be achieved.
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