Selecting Between Plate and Shell-and-Tube Heat Exchangers

Types

1.Gasketed Plate Heat Exchangers: These consist of corrugated plates, elastomeric gaskets, and a frame with tightening bolts. They offer high thermal efficiency, permit adjustment of the heat transfer area by adding or removing plates, and are easily disassembled for cleaning. Their operating pressure and temperature are limited, typically not exceeding 2.5 MPa and 180°C. They are suitable for services with stringent hygiene standards and frequent cleaning needs, such as in the food, pharmaceutical, and HVAC industries.

2.Welded Plate Heat Exchangers: The plates in these units are joined by laser welding or brazing, eliminating the need for gaskets. They can withstand higher pressures and temperatures and offer greater corrosion resistance; however, they cannot be disassembled for mechanical cleaning. They are suitable for corrosive services, high-temperature and high-pressure applications, or where leak-tight integrity is critical.

3.Semi-Welded Plate Heat Exchangers: These feature a hybrid design where one fluid path is welded and the other is sealed with gaskets. This combines the benefits of both welded and gasketed types, making them suitable for applications where one fluid is highly corrosive and the other is less aggressive.

Selection Considerations:
1.Applicable Services: Suitable for clean fluids and applications requiring high heat transfer efficiency, such as cooling or heating purified streams. If the fluid contains solid particles or is prone to fouling, caution is advised, and a filter is recommended.

2.Pressure and Temperature: Pressure is generally limited to 2.5 MPa and temperature to 180°C. For more severe conditions, special materials or construction types are required.

3.Maintenance: Gasketed plate heat exchangers are easy to clean and are suitable for services prone to fouling or requiring regular maintenance. For welded and semi-welded types, the potential for chemical cleaning must be considered.

4.Installation Space: Plate exchangers have a compact footprint and are suitable for space-constrained locations. However, sufficient access for disassembly and maintenance must be ensured.

5.Material Selection: Materials such as stainless steel or titanium should be selected based on fluid corrosivity. Gasket materials must also be compatible with the operating temperature and chemical exposure.

Types

1.Fixed Tubesheet Heat Exchangers have a simple design and low cost. However, the tubes cannot be cleaned mechanically, and the temperature difference between the shell side and tube side must generally be controlled within 50°C. They are suitable for clean fluids, small temperature differences, and budget-conscious projects.

2.Floating Head Heat Exchangers allow for free thermal expansion, can handle large temperature differences, and the tube bundle can be removed entirely for cleaning. Their complex structure results in a higher cost. They are suitable for applications with temperature differences exceeding 50°C that require periodic cleaning.

3.U-Tube Heat Exchangers use U-shaped tubes, eliminating the need for floating head seals. They are suitable for high-temperature, high-pressure, and large-temperature-difference conditions with clean tube-side fluids, such as in high-pressure steam generators and high-temperature reactor circuits.

Selection Considerations

1.Applicable Services: Resistant to high temperatures and pressures, they are suitable for industries with high reliability requirements, such as petrochemicals, power, and nuclear energy. They are particularly well-suited for heat transfer involving viscous, particulate-laden, or corrosive fluids.

2.Pressure and Temperature: The design pressure can exceed 10 MPa, with a wide operating temperature range. The specific construction and materials must be selected according to the actual operating conditions.

3.Maintenance: The tube side typically has large flow passages that resist clogging, but the shell side is difficult to clean, often requiring a unit shutdown for maintenance. This makes them suitable for applications with low maintenance frequency.

4.Thermal Stress: For large temperature differences, floating head or U-tube designs should be prioritized to prevent equipment damage caused by thermal expansion.

5.Cost Control: The fixed tubesheet type has the lowest initial cost, but subsequent maintenance costs may be higher. A comprehensive assessment of the total lifecycle cost is necessary.

Plate Heat Exchangers are preferred when: The fluids are clean, high heat transfer efficiency is required, space is limited, frequent cleaning is needed, or high hygiene standards must be met, such as in food processing and air conditioning systems.

Shell-and-Tube Heat Exchangers are preferred when: Operating conditions involve high temperature and pressure, large temperature differences, corrosive fluids, or viscous/particulate-laden streams, such as in petrochemical, refining, and chemical production.

Comprehensive Evaluation: The final selection should be based on an evaluation of process conditions, fluid characteristics, operating pressure and temperature, maintenance costs, and footprint. Consultation with a professional engineer or equipment supplier is recommended.

In practice, gasketed plate heat exchangers require regular inspection of gaskets for aging to prevent internal leakage. Shell-and-tube heat exchangers require monitoring for fouling and periodic chemical or mechanical cleaning. Both types of equipment can be equipped with automatic control systems to enhance operational efficiency and safety.