THERMAL FLUIDS. Sfera II Net working activity 7 th SFERA Summer School

THERMAL FLUIDS Sfera II Net working activity 7 th SFERA Summer School Francisco Sanz Pérez, PhD Laboratorio de Combustibles y Petroquímica Fundación Gómez Pardo (UPM) 1

What s a Heat Transfer Fluids? In Parabolic Trough power plants, HTF is a mixture of biphenyl and biphenyl oxide. Composition 73,5 % 26,5 % 2

What s a Heat Transfer Fluids? THE MIXTURE EVAPORATES AZEOTROPICALLY, i.e. WITH THE SAME COMPOSITION OF LIQUIDS AND VAPOURS FORMING New BP of mixture New FP of mixture 3

What s a Heat Transfer Fluids? How many types of HTF there are? Glycol Mineral Aromatic Aromatic mixture Ionic liquids Molten salts Temperatura Range (ºC) -70 to 150 100 to 300 Up to 350 398 460 600 Better thermal stability 4

Required properties of heat transfer fluids When you have to choose a good HTF, your fluid must have the next properties: High thermal stability Good heat transfer properties Low energy transportation losses Low vapor presure Low freezing point Low hazard properties No corrosion tendency Good material compatibility Economical product and maintenance costs 5

Specifications of heat tranfer fluids Properties Standard Value Kinematic viscosity @ 40 ºC ASTM D 445 2,45 cst Density @ 25 ºC ASTM D 4052 1063-1068 kg/m 3 Flash point ASTM D 93 110 ºC Freezing point ISO 3016 12 ºC Water content ISO 12937 <250 mg/kg (ppm) Total acid number ASTM D 664 < 0,2 mg KOH/g Specific heat @ 20 ºC ASTM D 2766 1,573 kj/kg.k Pentane insolubles ASTM D 4055 < 1 % High and low boilers Crhomatography method < 10 % wt. 6

Degradation of heat transfer fluids Typically, heat transfer fluids are specific blends of chemical compounds. The chemical composition of a fluid determines thermal stability. When the temperature becomes high enough, the molecular bonds within the chemical structure break to form two main types of degradation products. One class of products produced from this thermal cracking are lower in molecular weight and are commonly known as low boilers. Because of their volatility, low boilers can be detrimental to system operations. High boilers can also be generated by thermal degradation The fluid degradation kinetics are following the Arrhenius law, that means the degradation is not a linear function it is an exponential one. 7

Degradation of heat transfer fluids 8

Degradation of heat transfer fluids: mechanims 9

Degradation of heat transfer fluids: mechanims Mechanims of terphenyl formation is: 10

Degradation of heat transfer fluids: mechanims Mechanims of dibenzofuran formation: Catalytic conversion Surface of a solid metal oxide 11

Degradation of heat transfer fluids: mechanims Aromatic compounds formed during thermal breakdown of HTF are: 12

Degradation products analysis in the laboratory Low and high boilers analysis by vacuum distillation 13

Degradation products analysis in the laboratory Low and high boilers analysis by vacuum distillation: Real sample 260,0 HTF s distillation profile 255,0 Temperature ºC 250,0 245,0 240,0 Nuevo Usado 235,0 230,0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % Weight 14

Degradation products analysis in the laboratory New method to analyze degradation products of HTF aged: Gas chromatography with mass spectrometry detector 17

Degradation products analysis in the laboratory Example: HTF with 25 % wt. of high boilers Chemical compound Bifenilo Óxido de bifenilo Dibenzofurano 1-fenilnaftaleno o-terfenilo 1-fenoxinaftaleno 2-fenilnaftaleno 2-fenoxinaftaleno 2-fenoxi-1,1`-bifenilo 4-fenoxi-1,1`-bifenilo 9-fenil-9-H-carbazol 1,2,4-trifenilbenceno 7,12-dihidro-α-antraceno 2,2 -difenoxi-1,1 -bifenilo 4-fenil-m-terfenilo 8-difenilmetil-1-naftilmetanol 2,2 -difenoxibifenilo Moléc. Con 5 y6 anillos 18

Disolved Gases Analysis In the degradation mechanims of biphenyl oxide, one molecule of hydrogen is formed. A few ppm, if we work at high temperature of hydrogen are soluble in HTF. Is very important to know the hydrogen concentration in HTF because high concentration of this gas can damage the pumps (i.e. cavitation). In the lab, we can analyze hydrogen concentration using shake test and micro gas chromatography. 19

HTF- Preventive maintenance analysis (I) Acid number and aqueous phase extraction with ph determination, shows current oxidation level of the fluid. This is a prediction of sludge formation and fouling problems. Viscosity, determines whether fluid has become too viscous for efficient heat transfer by thermal stress or oxidation degradation. Distillation range, analyzes fluid boiling profile for alteration caused by overheating or contamination. Moisture, indicates that either there is a system leak on the process side or wet fluid has been added to the system. 20

HTF- Preventive maintenance analysis (II) Acetone insolubles, warns about contamination from dirt, corrosion products, severe oxidation, or thermal stressing. Low and high boiling components, measured by gas chromatograpic analysis generally indicate contamination, oxidation or thermal stressing of fluid. Other standard methods like: Infrarred spectroscopy (FTIR), metals content by spectrometry (ICP-OES), density, flash and fire points, cupper corrosion, Conradson carbon residue (CCR), etc. An effective preventive maintenance program of industrial plants or processes should always include regularly scheduled analysis of heat transfer fluids and lubricants 21

Fuel and petrochemical laboratory For any questions about heat transfer fluid analysis or preventive maintenance program, please, write me to alub.lpp.minasyenergia@upm.es Thank you so much!!! 22