Choosing the right thermal oil for bitumen heater oil: stability, viscosity and flash point
Compare brands/classes; lifetime and replacement; Pollution and coking
Definition of thermal oil and its importance in closed systems
- Stable heat transfer: Maintaining specific viscosity and heat capacity over time.
- Chemical resistance: No thermal decomposition and formation of unwanted materials such as coke and sediments.
Selection parameters: flash point, viscosity, resistance to coking
The selection of thermal oil should be based on the maximum operating temperature required (for example, 300°C for hot bitumen).
1. flash point
Flash point is the minimum temperature at which oil vapors ignite in contact with a flame or spark. For safe systems, the flash point of the oil should be at least 50°C higher than the maximum operating temperature of the system. For an oil heater that works up to 320 degrees, the oil must have a flash point above 370 degrees Celsius.
2. Viscosity
Viscosity determines the ease of pumping and the amount of heat transfer.
Suitable oils should have a kinematic viscosity between 10 and 20 centistokes at an operating temperature of 100 degrees Celsius.
3. Resistance to coking (Thermal Stability)
This is the most important parameter in oil bitumen heaters. High temperature causes molecular decomposition of oil and carbon solids (soot) are produced. These fleas:
- They cover the heat transfer surfaces and greatly reduce the efficiency.
- They block the oil circulation paths and increase the risk of pump or boiler failure.
Synthetic oils based on aromatic or diaromatic compounds (such as dophenyl and diphenyl oxide) have a much higher resistance to coking than base mineral oils.
Authentic brands and performance comparison
In the Iranian market, brands such as Mobil (Naphtalis), Shell (Termelan) and domestic products with a synthetic or semi-synthetic base are offered.
Oil type Common use Maximum operating temperature (recommended) Key advantage Modified mineral Old boilers, temperatures below 280°C 280°C Lower initial cost Aromatic/semi-synthetic Bitumen plants (high temperatures) 320°C Balance between price and stability Pure synthetics Very high temperatures or long life required 350°C up to max Durability and life
Power Steam Recommendation: For bitumen plants that operate continuously at temperatures above 300 degrees, the use of synthetic/aromatic base oils is essential to minimize fouling.
How to test the quality and oil change time
The useful life of thermal oil is usually between 3 and 7 years, but this time depends on the operating conditions. Periodic tests are necessary to monitor oil health:
- Viscosity and flash point test: If the flash point decreases by more than 50 degrees, the oil has become unstable.
- Acidity test (TAN): An increase in the acid number indicates the oxidation and decomposition of the oil.
- Check deposits: Check the amount of solids suspended in oil.
Replacement should be done when the heat capacity of the oil has reached less than 90% of its initial value or the safety parameters (flash point) are approaching a dangerous level.
Industrial storage and maintenance tips
Maintaining oil health during downtime and storage is also important:
- Closed system: The oil should always be covered with neutral gas (nitrogen) or at least protected from air with closed caps to reduce oxidation.
- Circulation during cooling: After the burner is turned off, the circulation pump should be kept on for a while so that the residual heat is distributed evenly and avoids the formation of hot spots. Spots) in the coils.
Thermal oil FAQ
- When should I replace the bitumen oil heater thermal oil?
It should be replaced when its flash point approaches the safety limit, or laboratory tests show that its heat transfer capacity has decreased significantly, usually between 3 and 7 years depending on how it is operated. - Can I use hydraulic or engine oil instead of thermal oil? Should I?
No. Engine or hydraulic oils are not designed for high operating temperatures and will quickly break down, produce coke, and cause serious damage to the boiler. - How can I minimize coking in my system?
By choosing high quality (synthetic) oil, maintaining operating temperatures within permissible limits (below the recommended maximum) and ensuring proper oil circulation after shutdown torch.