High Temperature Tubular Heat Exchanger for Heating Drying Air

High Temperature Tubular Heat Exchanger for Heating Drying Air

A high - temperature tubular heat exchanger used for heating drying air is a crucial component in many industrial drying processes. It enables the transfer of heat from a high - temperature heat source to the drying air, increasing the air's temperature and thus its drying capacity.

Structure and Components

Tubes:

The tubes are the core part of the heat exchanger. They are usually made of materials with high - temperature resistance and good thermal conductivity, such as stainless steel or alloy steel. The diameter and wall thickness of the tubes are designed according to the heat transfer requirements and the pressure of the working fluids. For example, in a high - temperature application, the tube wall may be thicker to withstand the high - temperature gradient and pressure difference.

The arrangement of the tubes can be in - line, staggered, or in other configurations. Staggered tube arrangements generally provide better heat transfer performance because they induce more turbulence in the fluid flow around the tubes.

Shell:

The shell encloses the tube bundle and provides a passage for one of the fluids (usually the fluid to be heated, i.e., the drying air). It is also made of materials that can withstand the operating temperature and pressure. The shell's shape is usually cylindrical to evenly distribute the pressure and provide a compact structure.

There are inlet and outlet ports on the shell for the fluid to enter and exit. Baffles are often installed inside the shell to direct the flow of the fluid across the tube bundle, increasing the contact time and heat transfer efficiency between the fluid and the tubes.

Working Principle

Heat is supplied from a high - temperature source (such as steam, hot oil, or hot gas) to the inside of the tubes. The drying air, which is the cold fluid in this context, flows over the outside of the tubes through the shell.

The temperature difference between the hot fluid inside the tubes and the cold drying air outside the tubes drives the heat transfer process. Heat is conducted through the tube walls and then convected to the drying air. The heat transfer rate is affected by factors such as the temperature difference, the heat transfer area (which is related to the number and size of the tubes), and the heat transfer coefficients of the fluids.

For example, if steam at a temperature of 150°C is passed through the tubes and the inlet temperature of the drying air is 20°C, the temperature of the drying air will increase as it absorbs heat from the steam - filled tubes. The heat transfer equation  can be used to calculate the heat transfer rate, where  is the heat transfer rate,  is the overall heat transfer coefficient,  is the heat transfer area, and  is the log - mean temperature difference.

Design Considerations for High - Temperature Applications

Material Selection:

Given the high - temperature environment, the materials must have excellent high - temperature strength and resistance to thermal fatigue. As mentioned earlier, stainless steel or alloy steel is often used. For example, in applications where the temperature exceeds 500°C, special high - chromium - nickel alloys may be required to prevent material degradation and ensure the long - term stability of the heat exchanger.

The compatibility of the materials with the working fluids is also crucial. If the heat exchanger is used with a corrosive heat source (such as some industrial waste gases), the materials need to have good corrosion - resistance properties.

Thermal Expansion:

At high temperatures, the materials of the tubes and the shell will expand. To accommodate this thermal expansion, expansion joints or flexible connections may be incorporated into the design. Failure to account for thermal expansion can lead to structural damage, such as tube - shell misalignment, tube bending, or even tube rupture.

The design should also consider the differential thermal expansion between different components. For example, the coefficient of thermal expansion of the tubes and the shell may be different, and proper design measures (such as using materials with similar expansion coefficients or providing appropriate compensation mechanisms) need to be taken to avoid stress concentrations.

Advantages

High - Temperature Resistance: It can efficiently operate at high temperatures, enabling the heating of drying air to the required high - temperature levels for effective drying processes. This is essential for industries such as food drying, where high - temperature air can quickly remove moisture from products.

Efficient Heat Transfer: The tubular design provides a large heat transfer area, and with proper baffling and fluid flow arrangements, it can achieve high heat transfer efficiencies. This means that less energy is wasted in the heat transfer process, resulting in energy - savings and cost - effectiveness.

Reliability: When properly designed and maintained, high - temperature tubular heat exchangers can have a long service life and reliable performance. Their robust structure can withstand the harsh conditions of high - temperature and high - pressure operations, reducing the frequency of equipment replacement and maintenance.

Applications

Food Industry: In food drying processes, such as drying fruits, vegetables, or grains. The high - temperature tubular heat exchanger heats the drying air to a suitable temperature (usually between 60 - 120°C), which helps to remove moisture from the food products while maintaining their quality and nutritional value.

Chemical Industry: For drying chemicals and chemical intermediates. For example, in the production of polymers, the drying air heated by the heat exchanger is used to remove solvents or water from the polymer products to achieve the desired product specifications.

Pharmaceutical Industry: In pharmaceutical drying applications, such as drying active pharmaceutical ingredients (APIs) or pharmaceutical granules. The high - temperature and precise control of the drying air temperature provided by the tubular heat exchanger are crucial for ensuring the quality and stability of the pharmaceutical products.