DEAR Air separation plant.After positioning the vessel and valve, prepare the pipeline according to the actual situation. Don't force to install when the welding joint of valve and pipeline is too large; according to the field experience, generally, each welding joint shrinks about 1.5mm after cooling. For this reason, according to the specific situation of the installation welding joint at the flange connecting with the valve and vessel, the flange bolts shall be tightened without gasket before welding, and then the gasket shall be added after welding, so as to reduce the bolt pre tightening force and pipeline stress;It should be noted that the latent heat of evaporation of 1 kg liquid oxygen is not equal to that of condensation of 1 kg 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 the heat is transferred from gas nitrogen to liquid oxygen, the condensation amount of nitrogen is about 1.23 times of the evaporation amount of oxygen.
DEAR Air separation plant.The internal reason for the phase transition is that when the temperature changes, the motion of the molecules that make up the material changes. When the temperature decreases, the molecular motion slows down, the distance between the molecules decreases, and the force between the molecules increases until the attraction increases to the liquid state. The temperature at this point is the liquefaction temperature. Since the liquefaction temperature of air under atmospheric pressure ranges from - 191.3 ℃ to - 194.3 ℃, it exists in the form of gas at room temperature. However, as long as the temperature is low enough, air can not only turn into liquid, but also into solid.DEAR Air separation plant.The throttling temperature drop plays an important role in the refrigeration of small high and medium pressure oxygen generators. In the start-up stage, in order to speed up the cooling rate, the method of increasing the pressure is often used to increase the cooling capacity of throttling effect. After the normal operation of the equipment, the required cooling capacity is reduced, and then the working pressure is reduced.
After all valves are in place, they shall be opened and closed again, and it is qualified if they are flexible and free from jamming; after large air separation tower is exposed to cold, the flange of connecting valve shall be pre tightened once in cold state to prevent leakage at room temperature but at low temperature; it is strictly forbidden to climb the valve stem as scaffold during installation.Most of the liquid flows down as reflux, and a small part is drawn out from the top as semi-finished product. The liquid with high oxygen content at the bottom of the crude argon column returns to the same tray at the distillation outlet of the main column, or 1-2 trays below the distillation outlet.DEAR Air separation plant.If you want to increase the output of liquid products and open one more expander in normal production, it is OK only from the perspective of cold balance, but too much expansion air into the upper tower will destroy the distillation condition of the upper tower and reduce the extraction rate of low oxygen. At the same time, taking more liquid will also affect the working condition of the heat exchanger in the tower and the reflux ratio of the distillation tower, so it is also limited.
DEAR Air separation plant.Air pressure test on site is mainly to check the air tightness of the equipment. Attention should be paid to the following problems during pressure test: it is strictly forbidden to use oxygen as the pressure test gas source; clean and oil-free pressure test gas source should be used for the oil-free equipment which is no longer degreased after pressure test; the pressure gauge used for pressure test should be calibrated and lead sealed before use.In the process of liquid accumulation, the pressure of upper tower should be increased. When the equipment is cooled to liquefying temperature, liquid begins to appear. As the liquefaction temperature increases with the increase of pressure, the corresponding condensation latent heat decreases. Therefore, in the stage of liquid accumulation, when the pressure of upper tower is increased from 0.04MPa to 0.065mpa, the liquefaction temperature of oxygen can be increased from - 180 ℃ to - 178.3 ℃. It can accelerate the liquefaction speed.
