Silicone based HTF in parabolic trough applications – from lab to loop

Abstract

HELISOL® 5A has been subject to continuous research since 2012. This paper presents at selection of the most relevant test and measurement results gained along the parabolic trough collector application related qualification of this new HTF. HELISOL® 5A successfully demonstrated its loop scale functionality achieving the proof of concept at Plataforma Solar de Almería (PSA) after 480 hours of operation at 425 °C. The degradation processes induced formation of low boiling and gaseous products is shown for the aging tests in lab environment and for the loop scale application. In terms of operational safety five key investigations are presented. Three of which include the direct comparison with the commonly used mixture of diphenyl oxide and biphenyl (DPO/BP) the wick flame persistence test, the reaction of HELISOL® 5A and DPO/BP with molten salt and the spray ignition test. The other two tests cover the flammability of HELISOL® 5A in contact with hot (475 °C) surfaces and the worst case scenario of a tube rupture at collector level at 420 °C / 17 bar which both don’t lead to ignition of the HTF.