Oxygen and nitrogen discharge valve is used to control the purity of oxygen and nitrogen and low pressure. When the purity of oxygen is lower than the use requirement, the oxygen discharge valve should be shut down to reduce the oxygen flow by several grids; meanwhile, open the nitrogen discharge valve and open the nitrogen flow by several grids to maintain the low pressure. On the contrary, when the purity of oxygen is too high and the purity of nitrogen is lower than the application requirements, the method of "turning off nitrogen and turning off oxygen" should be used to improve the purity of nitrogen. The methods of improving the purity of oxygen and nitrogen are opposite. They restrict each other, but they are also the unity of contradiction, so the adjustment should be slow. The range of each adjustment should be about 1 grid of the indication reading of the flow meter, and at the same time, the lag effect should be paid attention to. It should be predictable and both sides should be taken into consideration.
The low pressure is related to the stability of the rectification working condition of the upper tower. Simply from the point of rectification, the lower the pressure of the upper tower is, the more favorable it is. However, the regeneration need of the purifier must be taken into account, so it is generally controlled around 0.05MPa (surface pressure. When the low pressure needs to be increased, turn off the oxygen and nitrogen discharge valve at the same time to reduce the flow rate; on the contrary, when the pressure needs to be reduced, turn on the flow rate at the same time to ensure the purity and stability of oxygen and nitrogen.
The operating principle of oxygen and nitrogen discharge valve is: The air rectification process in the distillation column must have a certain amount of rising steam and a certain proportion of recirculation liquid to achieve. The condensing evaporator provides the upper tower with the amount of rising steam, and extracts a small part from it as oxygen products. When the oxygen discharge valve is closed small or the nitrogen outlet valve is opened large, the amount of oxygen extracted will decrease, and the amount of steam rising from the upper tower will increase, and the condensation amount of oxygen molecules in the vapor in the liquid layer of the tower plate will increase. The corresponding condensation heat also increases, the nitrogen molecules in the liquid layer are fully evaporated, the oxygen molecules in the liquid phase of the upper tower plate increase correspondingly, and the purity of the liquid oxygen flowing into the condensing evaporator increases. At the same time, in the evaporation process of liquid nitrogen molecules on the tower plate, the oxygen molecules taken away also increase correspondingly, and the oxygen content of nitrogen in the tower also increases.
Therefore, the result of "turning off oxygen and removing nitrogen" is to improve the purity of oxygen, reduce the purity of nitrogen and reduce the output of oxygen. On the contrary, when "Oxygen is on and nitrogen is off" (if there is no distillation working condition or the distillation extraction quantity remains unchanged), the reduction of the nitrogen extraction quantity will inevitably increase the oxygen extraction quantity. The amount of steam rising from the upper tower will decrease, and the relative reflux ratio will increase. The total condensation amount of oxygen molecules in the vapor in the liquid phase will decrease, and the condensation heat released relatively will also decrease, nitrogen molecules in liquid cannot be fully evaporated. Therefore, the result of "turn on oxygen and turn off nitrogen" improves the purity of nitrogen in the output Tower, decreases the purity of oxygen and increases the output of oxygen.
