Introduction

Liquid ammonia (NH₃) is widely used in the chemical, refrigeration, and fertilizer industries due to its excellent thermodynamic properties. In many processes, controlling the temperature of liquid ammonia is crucial for safety, efficiency, and process optimization. This is where liquid ammonia heat exchangers come into play. They are specialized heat transfer devices designed to manage the thermal energy of ammonia under various process conditions, such as condensation, evaporation, or subcooling.

Why Liquid Ammonia Requires Specialized Heat Exchangers

Ammonia is a volatile, highly reactive compound that requires careful handling. Key considerations for its heat exchangers include:

• Corrosion Resistance: Ammonia is incompatible with copper and copper alloys, so materials such as carbon steel, stainless steel, or nickel alloys are often used.

• Pressure & Temperature Control: Ammonia systems often operate at moderate to high pressures (commonly 10–25 bar) and require precise control during phase changes.

• Safety: Ammonia is toxic and can cause severe damage to human tissue and the environment in case of leakage. Thus, robust design and strict compliance with codes like ASME or API are essential.

Types of Liquid Ammonia Heat Exchangers

1. Shell and Tube Heat Exchanger

   • Structure: Comprises a cylindrical shell and a bundle of tubes.

   • Application: Commonly used for subcooling liquid ammonia or heating it before vaporization.

   • Advantages: High durability, suitable for high pressure.

2. Plate Heat Exchanger

   • Structure: Series of corrugated plates clamped together.

   • Application: Ideal for compact installations and lower ammonia charge.

   • Advantages: High heat transfer efficiency and small footprint.

3. Coil-in-Tank Heat Exchanger

   • Structure: Tubing coils immersed in a liquid bath.

   • Application: Used in refrigeration systems where liquid ammonia acts as the refrigerant.

Design Considerations

• Material Selection: Carbon steel or stainless steel to prevent ammonia-induced stress corrosion cracking.

• Pressure Rating: Must comply with pressure vessel codes (e.g., ASME Section VIII).

• Heat Transfer Efficiency: Depends on flow arrangement (counterflow or crossflow), surface area, and turbulence.

• Maintenance & Inspection: Non-destructive examination (NDE) methods such as RT or UT are recommended for weld integrity verification.

Common Applications

• Ammonia Refrigeration Systems: Used in cold storage, food processing, and ice plants for condensing and evaporating ammonia.

• Chemical Processing: For temperature control in ammonia-based synthesis (e.g., urea, nitric acid).

• Energy Industry: Utilized in heat recovery and absorption refrigeration systems.

Safety and Compliance

Design and fabrication of liquid ammonia heat exchangers should adhere to:

• ASME Boiler and Pressure Vessel Code

• API 660 (for shell and tube exchangers)

• Local Safety Regulations for Handling Toxic Substances

Regular inspection and preventive maintenance are critical to avoid leaks, corrosion, and catastrophic failures.

Conclusion

Liquid ammonia heat exchangers are indispensable in industries that rely on ammonia for refrigeration or chemical processes. Proper material selection, robust design, and compliance with international standards ensure safety and efficiency. As industries continue to focus on energy optimization and environmental safety, the demand for advanced ammonia heat exchanger designs will only grow.