The upper tower pressure of the two-stage distillation tower of small air separation unit  

Regulation of liquid nitrogen throttle valveThe opening of the liquid nitrogen throttle valve not only affects the reflux ratio of the upper tower, but also affects the reflux ratio of the lower tower. When the opening is increased, the reflux ratio of the upper tower increases, while the reflux ratio of the lower tower decreases, the purity of the nitrogen in the upper tower increases, and the purity of the oxygen enriched night sky in the lower tower increases. However, after the opening is over, the purity of the liquid nitrogen decreases, and the reduction of the reflux ratio of the upper tower is also detrimental to the improvement of the purity of the liquid oxygen. Therefore, an equilibrium point should be found for the opening of the liquid nitrogen throttle valve. We can generally use the purity difference between liquid nitrogen and gas nitrogen to judge whether the opening is appropriate. Generally, the purity of the sprayed liquid nitrogen is equal to that of the upper towe

In the field of air separation, entropy is the core thermodynamic parameter to measure the energy quality and irreversibility of the system, which directly determines the energy consumption level and operation efficiency of the unit. Entropy, with the symbol s, is essentially a measure of the degree of chaos and energy unavailability of a system, in kj/(kg ・ K). The second law of thermodynamics clearly states that the total entropy of an isolated system only increases but does not decrease, that is, the principle of entropy increase. The higher the entropy, the lower the energy quality, and the more difficult it is to convert into cold energy or useful work; The smaller the entropy, the more orderly the energy, and the more sufficient the available energy. The essence of air separation unit is the combination of cryogenic refrigeration and distillation separation, and the whole process is closely related to entropy. The ideal reversible process is an isentropic process, and the entropy