The transfer and utilization of heat is crucial in many aspects of industrial production. Thermal Fluid Heating Systems are used in a wide variety of applications as an efficient and stable heating method. So what exactly is a thermal fluid heating system?
A thermal fluid heating system is a device that combines a heater with a thermal fluid such as thermal oil, water, or glycol. The core operating principle is that the heater first heats the selected thermal fluid, which is then continuously circulated within the system to transfer heat to the appropriate process systems, mechanical equipment and materials by indirect heat transfer. This centralized indirect heating mode eliminates the need for direct contact between the heater and the object to be heated, which is one of its significant advantages over direct-fired heating systems.
The thermal fluid system utilizes a dual circuit design to precisely control the needs of each heat user.
Main circuit: This consists mainly of the heater, the drain and expansion tanks, and single or multiple circulation pumps. The primary loop ensures a constant supply of thermal fluid to one or more users at a constant flow and temperature, regardless of the return temperature, ensuring a consistent supply of heat.
Secondary circuits: the system can be equipped with single or multiple secondary circuits. The secondary circuits usually contain heat exchangers, thermal fluid control valves and, in some cases, secondary circuit pumps. These circuits meet the individual needs of different users by extracting heat from the thermal fluid at the desired flow rate and temperature.
Globally, thermal fluid heating systems are referred to by different names, commonly thermal oil heaters, thermal fluid systems, thermal oil boilers, thermal fluid heaters, thermal oil heaters, etc. . Despite the variety of names, they all refer to the same type of closed-loop fluid-phase heat transfer system. It is important to note that many people are accustomed to using the designation”thermal oil boiler” or”thermal fluid boiler”, however in reality, most of these systems do not involve any vaporization process , which is an area that needs to be clarified in the conceptual understanding.
The fuel is first fed into the fuel storage hopper in front of the combustion chamber. A chain feeder then feeds the fuel into the combustion chamber while an air supply fan is activated to supply air into the combustion chamber to fully combust the fuel. The hot flue gases from the combustion are transported to the oil furnace. Inside the oil furnace, the heat exchange pipeline is arranged, the heat transfer oil flows inside the pipeline, and the hot flue gas is outside the pipeline, through which the heat transfer oil inside the pipeline is heated. After the heating is completed, the heat of the hot flue gas is gradually dissipated and subsequently sucked out by a fan and sent to an air preheater at the rear of the furnace. In the air preheater, the hot flue gases preheat the air entering the combustion chamber. The preheated air enters the combustion chamber, which helps the fuel to burn more fully, thus increasing the efficiency of the system. Finally, the hot flue gas from the air preheater enters the exhaust gas treatment system and is discharged into the atmosphere through a chimney after reaching the standard.
The cold thermal oil returned from the heat-using equipment is pumped back by the circulating oil pump and sent to the heating furnace for heating and warming, and the warmed thermal oil is then sent back to the heat-using equipment to complete a cycle. In the heat transfer oil pipeline, there is an automatic gas separation line, whose function is to separate the gas in the system, especially when the system is just started and the heat transfer oil is not yet filled, it needs to run for a period of time to completely separate the gas. In addition, there is a filling line in the system, which is responsible for replenishing heat transfer oil to the system to ensure that the heat transfer oil in the system is always sufficient to maintain stable operation of the system.
The design of the ash collection system is adjusted according to the type of fuel and the amount of ash expected to be collected. The combustion of the fuel produces ash, the larger ash is collected at the rear of the boiler; the lighter ash is carried out of the air preheater with the flue gases and is captured and collected in the exhaust gas treatment system.
Burner selection is highly specific, and the system designer will pick the right burner based on the dimensions of the heater's combustion chamber. At the same time, the burners are selected for their heating capacity to ensure that the heat load of the combustion chamber can be met.
Many thermal fluid heating systems today are equipped with Programmable Logic Controller (PLC) control packages, and some older systems have been upgraded with them. PLC control packages automate the system, making it safer to operate and easier to adjust. The operator can control the heating system intelligently without direct intervention and at a safe distance from the heating components, reducing the risk of injury or accident.The PLC control package can also be integrated into the plant's distributed control system (DCS) for quick application. The control panel offers a wide range of functions:
Continuous flow monitoring: Real-time monitoring of heat circulation by installing differential pressure switches and orifice plates in each heater coil.
Alarm functions: Equipped with high stack temperature alarms and redundant fluid outlet temperature alarms to monitor temperature anomalies; liquid level alarms, high and low fuel pressure alarms can also be set.
Automatic interlock: Prevents sudden increase in burner fire during system startup, protecting the heating system.
Burner Monitoring: Utilizes UV flame scanner and electronic flame programmer to monitor burner operating status.
Ordinary hot water pumps and boiler feed pumps are not suitable for thermal fluid systems, which require specially designed high-temperature pumps that are able to withstand the pressure drop of the fluid and the effects of gravity. In a well-designed system, each pump is customized based on its intended function and the characteristics of the thermal fluid being transported. Common pumps for thermal fluid systems include:
Centrifugal pumps: their overflow parts are required to be made of ductile or cast iron.
Positive displacement pumps: better performance when made of alloy steel.
Air-cooled, mechanically sealed pumps: specific selection is based on system and usage. In addition, water-cooled, magnetically coupled or API-compliant pumps are available and should be equipped with bellows seals.
Valves are also indispensable in the thermal fluid system, which is responsible for controlling the flow direction, flow rate and pressure of the thermal fluid, and the common types are globe valves, regulating valves, safety valves, etc. Different valves play their own roles to ensure the stable operation of the system.
Thermal fluid heaters are designed to optimize energy use, reducing fuel consumption while maintaining high thermal efficiency, effectively cutting operating costs. This energy-efficient design also helps reduce the carbon footprint of the heating process and promotes environmental sustainability, making it an excellent choice for companies seeking to improve energy efficiency and reduce costs.
Precise temperature control is one of the highlights of the Thermal Fluid Heating System, which is critical for industrial processes where temperature stability is critical. With the ability to maintain a stable temperature range of 100°F to 750°F (38°C to 400°C), the system meets the needs of many industrial scenarios.
Compared to steam heating systems, thermal fluid systems can operate at lower pressures at higher temperatures for greater safety. In the event of a hazardous situation, electrically heated thermal fluid systems can quickly shut off the heat source, further enhancing safety. In addition, the system's circuitry is designed to include controls such as primary and secondary interlocks to protect operators and equipment.
Compared to steam systems, thermal fluid systems are less susceptible to corrosion and scaling problems and therefore require less maintenance. This means that there is no need for constant manning, which reduces equipment downtime, improves productivity and makes the entire production process more efficient and economical.
Thermal fluid heating systems are used in a wide range of applications, covering almost all areas of industrial production:
Food and beverage industry: play an important role in baking, frying, drying and other food processing links.
Chemical industry: for continuous processing operations in chemical production, as well as batch reactor heating.
Petrochemical industry: in distillation, synthesis, catalysis and other processes, relying on thermal fluid systems for efficient heat transfer.
Asphalt industry: Thermal fluid systems help to achieve optimal thermal mixing in the production of asphalt for roofing and road paving.
Plastics and Composites: Providing a stable heat source for heating operations such as extrusion, molding and laminating.
In addition, electrically heated thermal fluid systems have a promising future in many more applications due to their environmental benefits of zero harmful emissions (e.g., carbon dioxide, nitrous oxide, and other common byproducts of coal combustion).
When selecting a thermal fluid heater, the following key factors need to be considered:
Operating temperature: Ensure that the heater is capable of reaching the temperature required for the application.
Heat load: Calculate the heat load accurately and select a heater with sufficient heating capacity.
Thermal fluid compatibility: Ensure that the heater is compatible with the thermal fluid being used.
Efficiency: Prioritize heaters with high thermal efficiency to reduce long-term operating costs.
Safety features: Make sure that the heater is equipped with necessary safety devices such as overheat protection and pressure relief valves.
Thermal fluid heating systems have become an indispensable heating solution in modern industrial production due to their unique working principle, reliable system components, significant performance advantages and wide range of applications. Whether in the pursuit of high energy efficiency or in scenarios with stringent requirements for temperature control, safety and maintenance, thermal fluid heating systems show great adaptability and competitiveness.
