The temperature difference of heat transfer rises, but it is impossible to return to the temperature difference of heat transfer before the change of working conditions, which is larger than the original, so the cooling capacity of backflow gas will still increase. However, due to the increase of air volume, the amount of cold absorbed per 1 kg air is reduced, otherwise it is impossible to reach a new heat balance. This will inevitably lead to the expansion of the temperature difference at the cold end and the decrease of the temperature difference at the hot end.DEAR Air separation unit.The method of extending the switching time is often used for the accumulator, that is, when the temperature in the middle of the accumulator is high and the temperature in the middle of the accumulator is low, the switching time should be extended appropriately. When the temperature condition of one group of accumulators is abnormal and that of the other group is normal, in order not to affect the other group of accumulators, the extended time is divided into two equal parts and added before and after the switching of the other group of accumulators, which is commonly known as 1 / 2 delay method.
Although the chemical properties of N2O are inactive, neither corrosion nor explosion will occur, its physical properties are harmful to air separation. Its critical temperature is 309.7k, critical pressure is 7.27mpa, and its three-phase point is 182.3k and 0.088mpa. Under the condition of pressure and temperature of air separation device, it has sublimation property. At atmospheric pressure, its boiling point is 185K, which is higher than that of N2, O2 and ar. therefore, it will be concentrated in liquid oxygen during the separation of oxygen and nitrogen.The increase of temperature difference at hot end is not necessarily due to the freezing of heat exchanger. Because the opening of cam and throttle-1 valve is not suitable, the distribution of high-pressure air into oxygen, nitrogen and distillate compartment is unreasonable, too much processing air or poor heat exchanger manufacturing will cause the increase of temperature difference at the hot end.DEAR Air separation unit.In order to avoid the local accumulation of acetylene and other hydrocarbon impurities, porous fins are often used in condensing evaporators, which is also conducive to the formation of vaporization core; on the condensing side, holes can destroy the boundary layer of the condensing film to enhance heat release.
For the detection pipeline with wet gas as the measured medium, a condensing device should be set at the lowest point of the pipeline to prevent the liquid from accumulating in the pipeline; for the detection pipeline with liquid as the measured medium, when the pipeline and instrument are higher than the measuring point, a vent valve should be installed at the highest point of the pipeline to prevent the gas from accumulating in the pipeline;DEAR Air separation unit.According to the cold end temperature (which determines the water content brought into the expander) and the ratio of the cold end pressure to the pressure after expansion (which determines the multiple of volume expansion, that is, the multiple of water content reduction in every 1m3 of air), the minimum temperature allowed for no precipitation of water behind the expander can be determined, as shown in table 48. The data in the table are given according to the absolute pressure of 0.6MPa at the cold end and 0.135mpa after expansion.
DEAR Air separation unit.The cross-sectional area of plate fin heat exchanger is smaller than that of switching heat exchanger due to the increase of flow velocity. Therefore, for the same equipment, the non switching plate fin heat exchanger has the advantages of light weight, simple piping, convenient operation and quick start-up, so it is widely used.Only by increasing the oxygen concentration in the liquid and air and reducing the burden of distillation on the upper tower, can the oxygen yield be increased. It should be noted that liquid nitrogen control valve should be used to regulate the purity of liquid nitrogen, not the liquid nitrogen reflux valve of lower tower. The return valve should be fully open under normal conditions.DEAR Air separation unit.The liquid oxygen absorbs the latent heat of condensation released by the gas nitrogen with higher temperature and evaporates. So it is called "condensing evaporator". Condensing evaporator is an important heat exchange equipment in distillation system. Its working quality is related to the power consumption and normal production of the whole air separation unit. Therefore, it is necessary to correctly operate and maintain the condensing evaporator.
