In the condensation evaporator, the liquid oxygen from the bottom of the upper tower is heated and evaporated by the gas nitrogen from the top of the lower tower, some of which is extracted as oxygen products, and some of which is used as rising gas to participate in the rectification of the upper tower; The gas nitrogen emits heat and condenses into liquid nitrogen. Part of it is used as a reflux liquid to participate in the distillation of the lower tower, and part of it is throttled to the top of the upper tower to participate in the distillation of the upper tower. This indicates that the temperature of gas nitrogen in the condensing evaporator is higher than that of liquid oxygen.
At the same pressure, the saturation temperature of nitrogen is lower than that of oxygen. Under standard atmospheric pressure (0.1013MPa), the liquefaction (gasification) temperature of nitrogen is - 195.8 ℃, and the liquefaction (gasification) temperature of oxygen is - 183 ℃. However, this saturation temperature is pressure dependent and increases as the pressure increases. Due to the absolute pressure at the top of the lower tower being around 0.58 MPa, the corresponding gas nitrogen condensation temperature is - 177 ℃; The absolute pressure of liquid oxygen in the upper tower is about 0.149MPa, and the corresponding gasification temperature is - 179 ℃. Therefore, there is a temperature difference of about 2 ℃ between gas nitrogen and liquid oxygen in the condensing evaporator. Heat is transferred from gaseous nitrogen to liquid oxygen.
The latent heat of evaporation of 1kg of liquid oxygen is not equal to the latent heat of condensation of 1kg of gaseous nitrogen. At the above temperature, the gasification latent heat of oxygen is 207 kJ/kg, and the condensation latent heat of nitrogen is 168 kJ/kg. Therefore, after heat is transferred from gaseous nitrogen to liquid oxygen, the condensation amount of nitrogen is about 1.23 times the evaporation amount of oxygen.
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