When selecting a heat source for a reactor, industrial press, or dryer, process engineers often face the same question: steam or thermal oil?
The answer depends largely on the required process temperature.
The Pressure Penalty of High-Temperature Steam
Saturated steam transfers heat through latent heat, meaning its temperature is directly related to its pressure. As the required temperature increases, the saturation pressure rises sharply.
| Saturated Steam Temperature | Saturation Pressure |
|---|---|
| 180°C | 1.0 MPa (absolute) |
| 200°C | 1.55 MPa (absolute) |
| 250°C | 4.0 MPa (absolute) |
| 300°C | 8.59 MPa (absolute) |
| 350°C | 16.5 MPa (absolute) |
Above approximately 180–200°C, steam heating systems require thicker-walled pressure vessels, certified boiler operation, and heavier piping to accommodate the higher operating pressures.
By comparison, a thermal oil heating system transfers sensible heat through a circulating liquid.
Its operating pressure is determined primarily by pump head and static pressure rather than the required process temperature. At a process temperature of 300°C, a thermal oil system can operate at pressures below 0.8 MPa under the conditions described here.
Eliminating Water-Related Operating Issues
Steam boiler systems require continuous management of feedwater chemistry throughout their operation.
Common water-related issues include:
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Scale formation: Dissolved minerals can form deposits on heat transfer surfaces, reducing heat transfer efficiency and increasing the risk of localized overheating.
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Corrosion: Dissolved oxygen and carbon dioxide can cause corrosion in boilers and condensate return pipelines.
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Energy losses: Pressure relief and steam trap losses can result in additional fuel consumption.
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Freezing risks: Outdoor steam and condensate pipelines may be vulnerable to freezing during winter.
A closed-loop thermal oil system does not require boiler feedwater, blowdown, or condensate return. Consequently, these water-related operating and maintenance issues are eliminated.
However, when selecting thermal oil, engineers should still verify its pour point and viscosity at the lowest expected ambient temperature.
Temperature Uniformity and Multiple Heating Zones
A properly controlled thermal oil heater can maintain its outlet oil temperature within ±1°C of the target value.
The circulating liquid transfers heat through jackets, heated platens, or coils, providing stable heating surface temperatures.
A single thermal oil heater can also supply multiple heating points. Secondary circulation loops allow different process zones to operate at different temperatures while receiving heat from the same primary system.
This arrangement is commonly used in resin processing, laminate manufacturing, textile production, and chemical plants.
Thermal Oil Heater Design Considerations
Despite these advantages, thermal oil systems have several operating characteristics that must be considered during equipment selection and system design.
Lower Specific Heat Capacity
The specific heat capacity of thermal oil is approximately half that of water on a mass basis.
As a result, transferring the same amount of heat generally requires a higher circulation flow rate and greater pumping power.
Thermal Oil Degradation
Thermal oil can undergo oxidation and thermal cracking when exposed to excessive temperatures, particularly when the oil film temperature becomes too high.
Proper selection of the heat transfer fluid, heater configuration, and design flow velocity is therefore important.
Regular thermal oil analysis is also necessary to monitor fluid condition and identify degradation.
Flammability and Fire Protection
Thermal oil is combustible. System design must incorporate appropriate safety interlocks, ventilation, and fire protection measures.
Lower-Temperature Applications
For operating temperatures below approximately 150–180°C, steam may offer a simpler and more economical solution.
Steam is also preferable when the process requires direct contact with steam.
Quick Selection Guide: Steam or Thermal Oil?
| Process Requirement | More Suitable Heating Medium |
|---|---|
| Operating temperatures of 150–180°C or below | Steam |
| Direct steam contact required | Steam |
| Process temperatures of 200–350°C with relatively low system pressure | Thermal Oil |
| Multiple heating zones requiring different temperatures from one heat source | Thermal Oil |
| Outdoor installations exposed to freezing conditions | Thermal Oil, subject to fluid pour point verification |
| Operating temperatures above 380°C | Molten Salt |
CEEF Thermal Oil Heater Manufacturing and Standards
Changzhou Energy Engineering Co., Ltd. (CEEF) played a leading role in drafting China’s national standard for organic heat transfer fluid heaters, GB/T 17410.
CEEF’s thermal oil heater portfolio includes compact 24 kW skid-mounted units and large 46 MW (40,000,000 kcal/h) field-assembled heating systems.
The available heating equipment configurations accommodate multiple fuel and energy sources, including coal, biomass and biomass-derived gas, gas, fuel oil, and electricity.