Annular or U-shaped condensing isolation pipe must be added to the pipeline used for the detection of steam or other condensing gas near mounted instruments to prevent overheating of measuring elements; for the positive and negative pressure detection pipelines of flow and liquid level, the length and number of elbows shall be consistent as far as possible, so as to make the resistance of positive and negative pressure pipelines the same and eliminate the instrument error caused by local resistance of pipelines;DEAR Air separation unit.The liquefying temperature of gas is not only related to the type of gas, but also related to the pressure. The higher the pressure. The closer the molecules are, the easier they are to attract each other and turn into liquid. Therefore, the liquefaction temperature decreases with the increase of pressure. For air, the liquefying temperature is - 149 ℃ when the pressure is 2.45mpa;The start-up of an air separation unit consists of three stages: cooling, liquid accumulation and purification. For a certain device, the time needed to start is about certain. For low-pressure air separation plant, there is no room to adjust the pressure of air compressor. Generally, two expanders are equipped to work at the same time to increase the cooling capacity in the start-up stage and shorten the start-up time.
The middle pumping volume should be small at the beginning. For the 6000m3 / h oxygen generator, 200m3 / h can be pumped first. With the continuous decrease of the temperature of the intermediate extraction, the gas extraction volume is gradually increased. Increase 500m3 / h each time, so that the temperature at the bottom of the accumulator does not rise sharply and the outlet temperature of the expander is not lower than - 180 ℃.In order to condense the required amount of nitrogen, it is necessary to increase the pressure of the lower tower to increase the heat transfer temperature difference, which will increase the energy consumption of the air separation unit. Neon and helium purge pipes are installed on the top of condensing evaporator. During operation, it is necessary to open neon and helium purge valves regularly to discharge them. When air liquefies in the liquefier, there will also be accumulation of neon and helium non condensable gases, so neon and helium purging pipes are installed on the upper part of the liquefier for regular discharge.
DEAR Air separation unit.The throttling effect can reduce the refrigerating capacity, and the air with higher pressure entering the air separation unit will expand in the unit due to the pressure reduction of throttling valve, pipeline and equipment. Usually, the throttling process will cause the temperature to decrease, and the ability of the gas to take away the heat is the heat that the low-pressure gas can take away when it returns to the same inlet temperature when it leaves the device. This shows that at the same temperature, the energy (enthalpy) of the gas with high pressure is smaller than that of the gas with low pressure, and the difference between the two energy (enthalpy) is the heat absorbed, which is called throttling effect cooling capacity.It is possible to obtain lower temperature than the environment by artificial means. However, it needs to cost a certain amount of energy (work, electric energy, etc.) to achieve. This process of artificially obtaining low temperature is called "refrigeration".
DEAR Air separation unit.When the packing is not uniform or tight, or the valve stem is not straight or round, the cryogenic liquid or gas will leak out along the gap of the packing. As the cooling capacity is transmitted, the moisture in the air will freeze on the packing and freeze the valve stem. In this case, only steam or hot water can be used to heat the packing to open and close the valve. However, after the valve is opened and closed, the water accumulated in the packing will freeze again.DEAR Air separation unit.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.
