1. Principle of expansion mechanism refrigeration: High pressure gas expands adiabatically inside the expansion machine, and while doing work externally, the temperature decreases (isentropic expansion), which is the core means of refrigeration in the low-temperature section of air separation equipment. Features: High refrigeration efficiency, capable of producing temperatures below -150 ℃. It needs to be used in conjunction with a compressor to form a closed cycle. Application scenario: Deep low-temperature separation (such as liquid oxygen and liquid nitrogen production).
2. Principle of throttle valve refrigeration (isentropic expansion): High pressure gas is rapidly reduced in pressure through a throttle valve (such as a capillary tube), and the temperature is lowered due to the Joule Thomson effect. Features: Simple structure, no need for mechanical moving parts. The refrigeration efficiency is lower than that of the expander, and it is suitable for the medium and low temperature range (such as -100 ℃ or above). Application scenarios: Pre cooling systems or small air separation equipment.
3. Principle of reverse Brayton cycle refrigeration (gas bearing expander): High speed gas bearing expander is used to achieve efficient refrigeration through turbine expansion, commonly used in large-scale air separation equipment. Advantage: Efficiency is 10% -20% higher than traditional piston expanders. Low vibration, long lifespan, suitable for continuous operation.
4. The purpose of the pre cooling system (water cooling/ammonia cooling) is to initially cool the air to a temperature close to the dew point (usually below 10 ℃), reducing the load on the subsequent expansion machine. Method: Water cooling: Cooling through a cooling tower or plate heat exchanger. Ammonia cooling: using ammonia evaporation to absorb heat for further pre cooling.
