The liquid nitrogen subcooler of the air separation unit uses the low temperature gas nitrogen from the upper tower to cool the liquid nitrogen from the lower tower to reduce the gasification rate when the liquid nitrogen enters the upper tower through throttling.
Why is the temperature of gas nitrogen lower than that of liquid nitrogen? This is because for the same material, the phase change temperature (saturation temperature) is related to the pressure. The lower the pressure, the lower the corresponding saturation temperature. At the top of the upper tower, the gas nitrogen and liquid nitrogen coexist in a saturated state, and both have the same saturation temperature. The absolute pressure of nitrogen leaving the upper tower is about 0.13MPa, the corresponding saturation temperature is - 193 ℃, and the temperature of nitrogen saturated steam leaving the tower is also this temperature. The absolute pressure at the top of the lower tower is about 0.55MPa, and the corresponding nitrogen saturation temperature is about - 177 ℃. The extracted saturated liquid nitrogen is also at this temperature. The temperature of the liquid nitrogen is about 16 ℃ higher than the temperature of the gas nitrogen in the upper tower. Therefore, when the two streams of liquid nitrogen flow through the liquid nitrogen subcooler, the liquid nitrogen releases heat and is cooled into supercooled liquid, and the gas nitrogen becomes superheated steam due to heat absorption.
DEAR Air Separation is a service provider specializing in the research, development, manufacture and installation of various complete sets of air separation equipment. It emphasizes technical expertise and provides customers with high-quality air separation project design solutions to meet customer needs.
