Thermal heat transfer fluid problems following a system flush with caustic and water

Heat transfer fluid (HTF) ageing is a complicated chemical process. Laboratory techniques can provide rapid insights into the status of a HTF and a HTF system.In the current case, a potential client had requested their newly charged HTF be analysed. Prior to filling, however, the system had been flushed with caustic and water. The client reported reduced flow rates, high sludge formation in filters and regular HTF top-ups.Laboratory testing indicated that the HTF was showing signs of serious thermal cracking (high carbon levels and low flash point temperatures) and significant thermal oxidation (a high total acid number). The recommendation was to drain the HTF from the system and flush the system to remove carbon, acids and flammable by-products. This action would work to reduce the risks associated with coke depositing on the internal pipework of the system and eliminate any fire risk presented by the formation of flammable by-products within the system.The case highlights the detrimental effects of HTF decomposition on a system as well as the need to flush a system with a fluid intended to be used as a flush and to washout any residual cleaner prior to filling with a new HTF.