Tube-Fin Heat Exchanger for Large Industrial Oxygen Generator

Tube-Fin Heat Exchanger for Large Industrial Oxygen Generator

In large industrial oxygen generators (typically referring to equipment with oxygen production ≥1000 Nm³/h based on cryogenic air separation technology), heat exchangers serve as the core heat transfer equipment for air pre-cooling, impurity separation, and cold recovery. They primarily function as “main heat exchangers” and “subcoolers,” and in some scenarios, they are also used in medium to large-scale condensing evaporators. Their structural design is highly optimized for cryogenic operating conditions (-196°C to 30°C), requiring a balance among four core requirements: high-efficiency heat transfer, resistance to low-temperature embrittlement, anti-clogging properties, and low pressure drop.

Fin tube heat exchangers are primarily employed in two critical processes: air pre-cooling and purification, and product subcooling. Their operating principle relies on “counterflow/crossflow heat exchange,” utilizing the cold energy from low-temperature product gases (oxygen, nitrogen) to cool ambient-temperature feed air while simultaneously recovering cold energy to reduce system energy consumption.

1. As the “Main Heat Exchanger”: Air Pre-cooling and Preliminary Impurity Separation

Input Fluid:

Hot side: Compressed, dust-removed ambient-temperature feed air (approx. 30°C, 0.5–1.2 MPa pressure, containing trace moisture and CO₂);

Cold side: Low-temperature oxygen (-180°C to -190°C) and nitrogen (-190°C to -196°C) from air separation columns (upper/lower towers).

Process:

Ambient air enters the “air flow channel” of the heat exchanger. As it flows through the channel, it exchanges heat with the cryogenic fluids in the adjacent “oxygen/nitrogen flow channel” via the partition + fins;

The air temperature gradually decreases to -170°C to -175°C (approaching the liquefaction temperature), causing the moisture and carbon dioxide within to freeze into solids (adhering to the fin surfaces);

The cryogenic oxygen/nitrogen absorbs heat, raising its temperature to -10°C to 5°C, and is discharged as “reheated product gas” (oxygen supplied to users, nitrogen partially recycled to the air separation tower and partially vented);

Frozen moisture and carbon dioxide are removed via “periodic thermal purging” (backwashing with ambient dry air) to prevent channel blockage.

Core Objective: Cool air to cryogenic temperatures while partially separating impurities, preparing for subsequent “oxygen-nitrogen separation in the distillation column,” and recovering cooling energy (preventing cold loss from venting cryogenic gases directly).

2. As a “Subcooler”: Enhancing Liquid Oxygen/Nitrogen Recovery

Input Fluids:

Hot side: Saturated liquid oxygen (-183°C, near boiling point) and saturated liquid nitrogen (-196°C) from the top of the upper air separation tower;

Cold side: Cryogenic nitrogen gas (-190°C to -195°C) from the bottom of the lower tower.

Process:

Saturated liquid oxygen/nitrogen flows through the “liquid flow channel,” exchanging heat with cryogenic nitrogen in the “nitrogen flow channel.” This further lowers its temperature to -188°C to -198°C (5–10°C below boiling point, achieving a “subcooled state”).

Core objective: Prevent “flash vaporization” during subsequent throttling and pressure reduction, where liquid near boiling point partially evaporates into gas, causing product loss. This enhances liquid oxygen/nitrogen recovery rates (large oxygen generators can achieve over 98% recovery).