29 Sep Criteria of HTF Maturing and Scraping
Heat transfer fluid (HTF) experiences thermal cracking and polymerization reaction because of high operating temperature during long term operation. Also, when it contacts with air, there will be reaction generating low and high boiling substance, and changes HTF chemical property.
The standards for scraping HTF depend on the change of several indicators, such as flashing point, viscosity, acid value and carbon residue.
1. Flashing Point: Flashing point is the minimum temperature when the mixture of HTF vapor and air touches open fire during operation and causes flash burn. It is an indicator about HTF volatility and safety, so if flashing point is not up to standard, there could be unsafe factors.
2. Viscosity: Viscosity is used to measure the thickness and fluidity of HTF, which has direct relationship with HTF heat transfer efficiency. The higher the viscosity the lower the fluidity, and the bigger the power of circulating pump is required, which decreases the heat transfer efficiency and increases energy consumption.
3. Acid Value: Acid value is the organic acid content in HTF, that is, the amount of KOH (potassium hydroxide) consumed by the free acid in per gram of HTF. It relates to the corrosion of equipments, and corrosivity will increase as temperature goes up. When the acid value of operating HTF is over 1.5mgKOH/g, that HTF should be scrapped.
4. Carbon Residue: Carbon residue contains the colloid, asphaltene, polycyclic aromatic hydrocarbon generated by HTF thermal cracking and polymerization, and also carbon substance produced under high temperature. The content of carbon residue has direct impact on the heating system and HTF service life. The large amount of carbon residue will cause coking on the oil pipes, and there is a big difference between the heat transfer coefficients of coking and metal. Coking, to certain extent, will overheat the oil pipes leading to tube burst. If carbon residue is beyond 1.5%, HTF should be replaced.
The criteria presented above should be comprehensively analyzed to make the correct decision. To minimize economic loss is to avoid scrapping HTF too soon. Also, avoiding the use of scrapped HTF is to protect system from being damaged.
Schultz has rich experience from many years’ HTF technical study, and professional technical support teams to regularly provide clients with online liquid analysis and suggestions on HTF quality.