When the small oxygen generator uses liquid nitrogen throttle to adjust the purity of liquid nitrogen, it can be found that the valve is adjusted within a certain opening range, which has little effect on the purity of liquid nitrogen; while in a certain position, valve opening changes by 1 ° ~ 2 °, the purity of liquid nitrogen will change greatly. That is to say, the opening of liquid nitrogen throttle and the change of liquid nitrogen purity are not a simple proportional relationship, but the most sensitive position of adjustment.
This phenomenon has a lot to do with the structure of the top of the lower tower. As shown in figure 53a, the top of the lower tower is connected with the main cooling, nitrogen rises into the main cooling tube and condenses into the liquid nitrogen downstream, and the liquid nitrogen connection tank is set at the lower part of the main cooling. The liquid nitrogen in the liquid nitrogen tank flows to the top tower through the liquid nitrogen tube, and the condensate liquid nitrogen in the condensation tube in the inner circle of the liquid nitrogen tank will directly flow back to the bottom tower as the reflux liquid. When the opening of the liquid nitrogen throttle is too large and the liquid level in the liquid nitrogen tank is too low, the liquid nitrogen pipeline will be the mixture of vapor and liquid, as shown in figure 53b. At this time, the amount of liquid nitrogen condensing in the main cooling decreases correspondingly, and the reflux liquid of the lower tower also decreases, so the purity of liquid nitrogen is relatively low.
When the small liquid nitrogen throttle is closed, the amount of vapour through the throttle will gradually decrease, the recirculation of the lower tower will increase, and the purity of liquid nitrogen will gradually increase. When the liquid nitrogen throttle is closed so small that no vapour has passed through the pipe, and the liquid nitrogen in the liquid nitrogen tank is not full to the overflow degree (figure 53c ), even if the small liquid nitrogen throttle is closed, it will not change the amount of recirculation fluid of the lower tower. Therefore, the purity of liquid nitrogen basically remains unchanged. When the small throttle valve continues to be closed, so that all the liquid flowing into the liquid nitrogen tank cannot pass through the throttle valve, and the liquid level rises to some part overflows back to the lower tower, as shown in figure 53d, the recirculation fluid of the lower tower increases, the purity of liquid nitrogen will be greatly improved. Then turn off the small throttle, as the reflux fluid of the lower tower continues to increase, the purity of liquid nitrogen will continue to increase, but the change is slow, and there will be no mutation. In addition, if the amount of liquid nitrogen is too small and the purity of oxygen in liquid air is too low, it is also useless for rectification in the upper tower. It can be seen from the above that the situation in figure 53d is to adjust the sensitive position of liquid nitrogen. During operation, the purity of liquid nitrogen should be analyzed frequently to find out the corresponding opening degree of liquid nitrogen throttle at the sensitive point of Purity change of each equipment.
