Plate-Fin Heat Exchangers of LNG system - Working Principle

Plate-fin heat exchangers (PFHEs) in LNG systems act as compact, high-efficiency cryogenic heat exchangers, using stacked aluminum plates and corrugated fins to create alternating channels for hot natural gas and cold refrigerants. They enable multiple streams to exchange heat, cooling natural gas to ≈ -161°C within cold boxes.

Key Working Principles

• Structure: Composed of thin aluminum plates (parting sheets) stacked with corrugated fins, sealed at the edges with bars to create small flow channels.
• Heat Transfer Enhancement: Fins increase the surface area for heat transfer while acting as structural supports, allowing them to handle high pressures (e.g., in MR—Mixed Refrigerant—cycles).
• Multistream Operation: A single PFHE can handle several fluid streams simultaneously (e.g., natural gas and multiple refrigerant cycles).
• Counter-Current Flow: Fluids flow in opposite directions through alternating layers to achieve maximum efficiency in heat recovery and cooling.
• Cryogenic Cooling: They cool high-pressure natural gas from ambient temperatures down to < -160°C by transferring its heat to evaporating cold refrigerant.

Advantages in LNG Applications

• High Compactness: Extremely high surface area to volume ratio ( > 1000 m²/m³), making them ideal for space-constrained applications like offshore platforms.
• Multiphase Capability: Capable of handling gas, liquid, and two-phase flows simultaneously.
• Flexibility: Different fin types (plain, serrated, perforated) can be selected for specific heat transfer vs. pressure drop requirements.

• Fouling: Small channels are prone to fouling, making them unsuitable for dirty fluids.
• Cleaning: Cannot be mechanically cleaned; require stringent filtration, often requiring downtime.
• Thermal Shock: Require careful, gradual cooling down to prevent thermal stress/structural damage.