In industrial heating systems, water is typically used as the working fluid and the medium for heat transfer. However, at high temperatures, the use of this fluid requires extremely high operating pressures, which can be costly and challenging in terms of safety. Therefore, thermal oil boilers are used in applications that require high temperatures. Reaching high temperatures with thermal oil is possible at pressures close to atmospheric pressure, whereas achieving similar temperatures with water and steam requires much higher pressures.
Thermal oil boiler
One type of industrial boilers in the water-tube category is the thermal oil boiler, where thermal oil flows through the pipes, heating the water surrounding them within the boiler shell. The thermal oil boiler is an advanced type of boiler that is widely used in various industries to provide the necessary heat for systems. Unlike steam or hot water boilers that use water as the heat transfer fluid, thermal oil boilers use thermal oil to transfer heat. These oils are capable of withstanding high temperatures (up to about 300 degrees Celsius or more) without boiling or requiring an increase in system pressure.
Advantages of using thermal oil boilers
Thermal oil boilers have numerous advantages due to their unique features, making them a suitable choice for industrial applications. Below are some of these advantages:
Operation at high temperatures
One of the main advantages of thermal oil boilers is their ability to raise the thermal oil to temperatures of up to 300 degrees Celsius or higher, without the need for high pressure in the system. In steam systems, reaching such temperatures requires a significant increase in pressure, whereas in thermal oil systems, this issue does not occur.
Enhanced safety
Thermal oil boilers, due to the absence of high pressure requirements, carry fewer risks compared to water and steam boilers. The risk of explosion in these systems is significantly lower.
Prevention of scale formation and corrosion
In steam boilers, scale usually form in the tubes and equipment, which can lead to reduced efficiency, increased maintenance needs, and higher costs. However, in thermal oil boilers, due to the use of thermal oil, the system does not require frequent cleaning.
Longer system lifespan
Due to reduced corrosion and no scale formation, thermal oil boilers generally have a longer service life compared to steam or hot water boiler.
Lower maintenance costs
Thermal oil boilers have lower maintenance and operating costs compared to other types of boilers, as thermal oil does not need frequent replacement, and there is no requirement for regular cleaning and repairs.
Disadvantages of thermal oil boilers
While thermal oil boilers offer several advantages, they also have some disadvantages:
High flammability
Thermal oil is flammable at high temperatures. If the pipes, fittings, or tanks of the system are damaged and the oil leaks out, it can come into contact with hot surfaces or flames, potentially causing a fire.
Higher cost of thermal oil
The cost of acquiring thermal oil is higher compared to water and requires careful management.
Environmental impacts
In case of leakage, thermal oil may damage the environment and demands proper safety precautions.
Use of high-temperature pumps
For circulating thermal oil in a thermal oil boiler, specific pumps are necessary. These pumps must be capable of tolerating high temperatures, as thermal oil in these systems can reach up to 300 degrees Celsius or beyond.
Thermal oil boiler components
The main components of a thermal oil boiler include the furnace, heat coil, and burner, each of which is described in detail. Additionally, other essential parts such as the expansion tank, oil circulation pump, control valves, and more are also discussed, as they play a critical role in the boiler’s operation.
Furnace
This is the heart of the boiler, where the combustion process takes place. In the combustion chamber, fuels such as natural gas, diesel, or heavy oil are burned, releasing thermal energy. This thermal energy is then transferred to the heating coils, which carry the thermal oil.
Heating coil
These are a network of tubes located inside the combustion chamber. The tubes are coiled around the flame to provide a larger surface area for contact with the hot gases produced by combustion. The thermal oil flows through these coils, absorbing the heat produced by the combustion. The number and arrangement of the coils vary depending on the boiler’s capacity and design.
Burner
In a thermal oil boiler, the burner is responsible for producing the necessary heat by burning fuels like natural gas or oil, and then transfer this heat to the thermal oil within the heating coils.
Control system
This system consists of electronic components and sensors which monitor the boiler’s performance. It measures the pressure, temperature, and oil flow rate, ensuring the boiler operates safely and optimally. Advanced control systems have the ability to adjust automatically and provide alerts.
Oil pump
The oil pump is responsible for circulating the thermal oil throughout the system. It must be capable of directing the oil into the coils at the correct flow rate and pressure. Given the high temperature of the oil, these pumps are built to endure and function properly at high temperatures.
Control valves
These valves are used to regulate the pressure and flow rate of the oil in the system, controlling the oil’s inlet and outlet flow.
Expansion tank
The expansion tank serves to compensate for the volume changes of the oil caused by thermal expansion. As the oil heats up, its volume increases, and if there isn’t enough space for this expansion, the pressure within the system rises significantly. The expansion tank allows the oil to expand without causing excessive pressure buildup. Typically, the expansion tank is located at a higher elevation than the boiler and other equipment, which creates a static pressure in the oil circuit, keeping the oil in its liquid phase and preventing it from vaporizing.
A key function of the expansion tank is to provide make-up oil. It serves as a storage for thermal oil, ensuring that when oil levels decrease due to leakage or evaporation, extra oil is injected into the system.
Since oil is highly flammable at high temperatures, one way to prevent explosions is inert the space above the tank. This is done through a process called blanketing, where an inert gas like nitrogen fills the upper space of the tank, preventing oxygen and air from entering.
Thermal oil used in thermal oil boilers
These oils must have a high heat capacity to transfer heat effectively. Thermal oils need to be stable at high temperatures and retain their properties. Resistance to oxidation is crucial to prevent the formation of deposits in the system. The oils should have a high boiling point to avoid vaporization at elevated temperatures. Additionally, they should not cause corrosion in the system components and must be environmentally safe.
Classification of thermal oils
Thermal oils are divided into two main categories: mineral oils and synthetic oils. More details about them are explained below:
Mineral oils
The largest group of thermal oils consists of mineral oils. These oils are obtained through the distillation of crude oil in refineries. The operational temperature range for mineral oils is from -10°C to 300°C, which is why they are used for temperatures below 300°C. Mineral oils are more economical than synthetic oils and have less environmental impact. Paraffinic and naphthenic oils are examples of mineral oils.
Synthetic oils
These oils are produced through chemical synthesis processes. Synthetic oils, also referred to as aromatic oils, are based on a benzene structure. The operational temperature range for these oils is from -20°C to 400°C. Their aromatic structure makes them thermally more stable than mineral oils, which is why synthetic oils are used for temperatures higher than 300°C. Synthetic oils offer higher efficiency and greater heat transfer at elevated temperatures. Poly glycol fluids, ester and diester compounds, and silicone-based oils are types of synthetic oils.
Commonly used thermal oils include:
- Behran thermal oil (Behran Hararat 32)
- Shell thermal oil S2
- Total Seriola eta thermal oil 32
- Theminol thermal oil 66
Operation of a thermal oil boiler
Thermal oil boiler functions by circulating thermal oil through a closed system. The heating process is carried out by a burner that uses either gas or liquid fuel. The process of heating the oil is carried out by a burner that uses either gaseous or liquid fuel. The burner ignites the fuel, generating thermal energy, which is transferred to the oil. The thermal oil then flows through a series of heating coils situated inside the boiler furnace. These coils are usually spiral-shaped to maximize contact with the hot gases produced during combustion.
In this way, the oil inside the coils is heated by absorbing heat from the hot gases. The thermal oil is then transferred through piping to heat exchangers or other industrial systems. After transferring its heat, the thermal oil cools down and the cooled oil returns to the boiler to be reheated. This cycle continues continuously, supplying the necessary heat for the processes without interruption.
Types of thermal oil boilers
Thermal oil boilers are classified into two categories based on their installation method and overall structure: horizontal thermal oil boilers and vertical thermal oil boilers. They are also categorized according to the type of fuel used: gas-fired thermal oil boilers and electric thermal oil boilers.
Vertical thermal oil boiler
This type of thermal oil boiler is typically produced in smaller capacities and is commonly used in locations with space limitations. Due to gravity, the discharge of hot oil in these boilers occurs more quickly.
Horizontal thermal oil boiler
Thermal oil boilers of the horizontal type are manufactured in larger capacities than their vertical counterparts and offer higher efficiency. In horizontal thermal oil boilers, accessing different parts of the boiler, as well as performing maintenance and inspections, is more convenient.
Electric thermal oil boiler
This type uses electrical energy to heat the thermal oil instead of fossil fuels (such as gas or oil). In these boilers, heating elements generate the required heat to warm the oil. The heated oil is then transferred in a closed-loop system to different sections of the system to supply the necessary heat for processes. The non-use of fossil fuels in electric thermal oil boilers reduces environmental pollutants. Due to the high flammability of thermal oil at high temperatures, electric thermal oil boilers are recommended for lower capacities instead of gas-fired thermal oil boilers.
Applications of thermal oil boilers
Thermal oil boilers are used in a wide range of industries. One of the most important applications of thermal oil boilers is in industries where heat transfer is done indirectly. This makes them highly effective for heating flammable materials like crude oil and natural gas. Some of the uses of thermal oil boilers are as follows:
Wood industry
Thermal oil boilers play a crucial role in the processes related to the production of wood products in the wood industry. By utilizing these boilers, the moisture within the wood is gradually evaporated in a controlled manner, which improves the wood’s longevity and stability.
Textile industry
Thermal oil boilers are used as the primary heat source in dryers and dyeing machines for fabric and fiber processing. These boilers, by providing a uniform and precise temperature, help improve color absorption and facilitate the rapid drying of fibers.
Chemical industry
Thermal oil boilers are used in the chemical industry due to the high temperature and heat requirements for producing solvents, adhesives, and resins. They are also employed in the production of bitumen, waterproofing membranes, asphalt, and the heating of heavy petroleum materials.
Thermal oil boilers: Efficiency, Safety, and Lower Costs
These boilers are considered as one of the most effective and efficient heating systems across different industries. By providing indirect heat, these boilers not only contribute to improving product quality but also play a crucial role in boosting productivity through energy savings and process optimization. From food and chemical industries to textiles and petrochemicals, thermal oil boilers are an ideal choice for meeting thermal needs due to their flexibility and high efficiency. Raadman intelligent burners, using advanced controllers, play a significant role in optimizing fuel consumption and increasing the efficiency of thermal oil boilers.
