Thermal fluid systems for calender rolls heating and paper drying

When designing a thermal fluid boiler for the paper industry, it’s essential to consider factors contributing to ensuring efficiency, reliability, productivity, and safety. Correct design and installation are crucial to ensuring the thermal fluid system meets the specified requirements for each application.

Here are some key factors to consider:

• Determine the boiler’s production capacity, i.e., the thermal power required to efficiently transfer to the drying process. This should align with the paper manufacturing plant’s production requirements.
• Define the required temperature of the thermal fluid for the drying process. This depends on the type of paper and the required quality standards. The boiler must be capable of reaching and maintaining the desired temperature precisely and consistently.
• Energy efficiency is a critical factor to consider, as an efficient boiler helps minimize operational costs and reduce environmental impact. Aspects such as heat exchanger design, thermal insulation, and residual heat recovery should be evaluated to maximize efficiency.
• Safety is fundamental in boiler design. Proper safety measures, such as over-temperature protection devices, pressure relief systems, flame controls, and monitoring systems, must be implemented to ensure safe and reliable operation.
• Select suitable construction materials, commonly carbon steel or stainless steel, to ensure corrosion resistance and withstand high temperatures. Additionally, the boiler design should consider ease of maintenance and cleaning, as well as accessibility to key components.
• Ensure the boiler complies with all applicable local and international regulations. This includes design codes, emission requirements, safety standards, and any other relevant legal requirements.
• Design the thermal fluid boiler with integration and control of the entire drying system in the paper manufacturing plant in mind. Effective coordination with other equipment, such as drying cylinders, and a control system allowing easy monitoring and adjustment of thermal fluid temperature and pressure are crucial.

While these are the main factors to consider, each paper manufacturing plant may have specific additional requirements based on its processes and unique needs.

An industrial heating system using thermal fluid boilers consists of several key components.

Firstly, there is the boiler itself, the main equipment responsible for heating the thermal fluid. The boiler uses an energy source, which can be gaseous fuel, liquid fuel, or electricity, to heat the thermal fluid inside.

The thermal fluid used in these boilers is a specialized thermal oil with properties suitable for efficient heat transfer. Often, a high-temperature mineral or synthetic oil is used, capable of reaching temperatures above 300 °C without degrading.

Once the thermal fluid has been heated in the boiler, it is pumped through a closed piping system to the drying cylinders of the paper machine. These drying cylinders are arranged in a series of sections where the paper drying process takes place.

Each drying cylinder is equipped with coils or heat exchangers designed to allow hot thermal fluid to circulate around them, transferring heat to the paper in contact with the cylinder.

As the paper moves through the drying cylinders, the heat transferred from the thermal fluid causes the water in the sheet to evaporate. The generated water vapor is extracted from the system, while the paper gradually dries.

It is important to note that a thermal fluid system provides precise temperature control, and operators can adjust the thermal fluid temperature according to the specific requirements of the drying process, ensuring optimal drying.
In summary, the thermal fluid boiler system for the paper drying process uses specialized thermal fluid heated in a boiler and pumped through coils in the drying cylinders. The heat transferred from the thermal fluid to the paper facilitates efficient drying during the manufacturing process.

Advantages and Benefits

Thermal fluid boilers offer several significant advantages compared to other solutions for drying operations in paper manufacturing. Some of these advantages include:

• Thermal fluid boilers are known for their high energy efficiency. Because the thermal fluid circulates in a closed system, heat losses are minimized, and thermal energy is maximally utilized. This results in efficient energy use and lower operating costs.
• Thermal fluid boilers allow precise temperature control during the paper drying process. Operators can adjust and maintain the thermal fluid temperature within a specific range to suit the needs of the paper in process. This ensures consistent and high-quality productivity.
• The thermal fluid used in boilers has a high heat transfer capacity. This enables rapid heat exchange between the thermal fluid and the paper, speeding up the drying process and increasing plant productivity.
• Thermal fluid boilers can operate at relatively high temperatures, exceeding 300 °C. This is especially beneficial in applications where quick drying is required or in the production of special papers that need elevated temperatures for efficient water removal.
• The thermal fluid is evenly distributed through coils or heat exchangers on drying cylinders. This ensures uniform heat distribution across the paper, avoiding cold or hot spots and improving process quality.
• Low maintenance.

Alternative Solutions to Thermal Fluid Boilers

While thermal fluid boilers are the most commonly used solution in the paper industry due to their high productivity and performance, there are other solutions that offer lower efficiency but can still be used in paper and cardboard production plants where specific needs or characteristics of the produced paper justify the use of these alternative technologies.

Apart from thermal fluid boilers, the most recommended paper drying technologies are as follows: air drying, vacuum drying, and microwave drying.

The choice of the drying system depends on various factors, such as the type of paper, production capacity, energy efficiency, and quality requirements of the final product. In many cases, combinations of different drying methods are used at different stages of the paper manufacturing process to optimize results.

A thermal oil heating system to provide heat to calender rolls uses a controlled flow of thermal oil heated in a boiler and distributed to the rolls to maintain a constant and uniform temperature in the calendering process. This system ensures that the paper or material passing through the rolls receives the necessary heat to achieve desired effects on its surface.

Key elements of this system include:

• Thermal Oil Boiler, where the oil is heated to the desired temperature through the combustion of fuel, electricity, or another heat source.
• Distribution Circuit, which pumps the thermal oil through a closed circuit of pipes. This circuit connects the boiler with the calender rolls and is designed to ensure a continuous and controlled flow of thermal oil.
• Calender Rolls, which receive the heat transferred by the thermal oil, are designed to allow efficient and uniform heat transfer to the paper or material passing through them.
• Temperature Control System, including temperature sensors located at different points, such as the boiler outlet, pipes, and rolls, continuously monitoring the temperature. These sensors send signals to the controller, which adjusts the pump speed and boiler power to maintain the desired temperature precisely.
• Return and Recirculation of the oil, which returns to the boiler to be heated again once it has cooled after transferring heat to the calender rolls.

Advantages and Benefits

Thermal fluid boilers offer high performance in key aspects crucial for the proper functioning and productivity of calender rolls:

• Precise and controlled temperatures are applied, allowing the rolls to maintain a constant and uniform temperature throughout the calendering process.
• Temperature stability, without abrupt fluctuations, is essential for achieving consistent results in calendering.
• Operators can adjust and regulate the temperature according to the specific needs of the paper and the desired effect on the surface. This allows for precise and repeatable results.
• The risk of paper burning is reduced, as heat is transferred more uniformly and gradually through the rolls.

These advantages position thermal fluid systems as the preferred option in the paper and board manufacturing industry, where maintaining reliable and efficient production processes is essential.