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How to choose heat transfer oil reasonably? The reasons of heat transfer oil deterioration?

2019-02-21 来源:亚科官网

As an excellent heat transfer medium, heat transfer oil has high temperature and low pressure heat transfer performance, it has high thermal efficiency, uniform heat transfer, accurate temperature control and low operating cost. It has now become the most widely used and used heat carrier. .

Composition of heat transfer oil

The ideal component of the base oil is a cycloalkane, an isoparaffin, and a refined intermediate aromatic hydrocarbon component. The base oil should have good thermal stability and a suitable range of distillation range, which plays a decisive role in the heat transfer oil. The heat transfer oil is operated in a high temperature environment for a long time. In order to improve the thermal stability and oxidation stability of the heat transfer oil, it is necessary to add additives to the base oil, mainly high temperature antioxidants, composite focus agents, pour point depressants, Viscosity reducing agent, etc.

Selection of heat transfer oil

The choice of heat transfer oil should be based on the application temperature and heating energy requirements of the heating process.

Users should pay attention to the following issues before purchasing:

(1) In actual purchase, oil should be selected at least 20°C higher than the average temperature of the main fluid at the heater outlet.

(2) Inspect the evaporability and safety of the product in strict accordance with the provisions of the quality index——the flash point meets the requirements of the standard index, the initial boiling point is not lower than its maximum use temperature, the distillation range is relatively narrow, and the spontaneous ignition point is relatively high.

(3) Investigate the low-temperature fluidity of the product, and select the appropriate low-temperature performance according to the environment in which the user is located and the ambient temperature of the equipment. QB and QC pour point ≤ 9°C, low temperature kinematic viscosity (0°C or lower) is relatively low.

(4) The heat transfer performance of the product should have a lower viscosity, a higher density, a higher specific heat capacity and a thermal conductivity.

(5) Select products produced by regular enterprises. There are conditions to investigate the improvement of its production equipment and testing methods.

(6) Consider the price factor under the condition that the technical requirements are met.

Analysis of causes of heat transfer oil degradation

High-temperature thermal deterioration: When the heat-conducting oil is in a high-temperature environment for a long time, inter-atomic and inter-molecular chain bond rupture occurs, and the compound is decomposed. The decomposition products mainly include gases, low molecular substances and free radical molecules, and active groups of polymers are formed, and the reaction is chained. As the time elapses, the molecular weight and amount of the produced polymer tend to increase. Thermal polymerization produces macromolecular high-boiling substances such as fused aromatic hydrocarbons, colloids and asphaltenes, which are gradually deposited on the surfaces of heaters and pipes to form coke. At this time, the viscosity, flash point, initial boiling point, and residual carbon of the heat transfer oil change.

Oxidative degradation: The high temperature heat transfer oil is easily oxidized by air, the degree of easy oxidation is: alkane <cycloalkane < aromatic hydrocarbon. That is to say, alkanes are less susceptible to oxidation and aromatic hydrocarbons are relatively easy to oxidize. The organic acid is formed after oxidation, and the pyrolysis polymerization of the heat carrier is further promoted. When the high-temperature heat-conducting oil contacts the oxygen in the air, it will oxidize to form an organic acid, and the organic acid can further promote the polymerization of the heat-conducting oil, and the reaction speed increases as the temperature increases, and the result is an increase in viscosity and total acid value, and the generated organic acid will cause some corrosion to the equipment after it encounters water. Therefore, the design of the process should consider that the heat carrier cannot be in direct contact with the air.

Edited by Suzhou Yacoo Science Co., Ltd.