Air separation unit.The heat removed from the unit is (H ′ 4-h ′ 2), which is the cooling capacity of throttling effect at that time. This shows that the cooling capacity of throttling effect still exists in non isothermal compression, but it does not exist in the compression process. The compression process is to create conditions for throttling and cooling.Air separation unit.When l / di increases 5 times, the boiling heat transfer coefficient increases almost 2 times. Therefore, the condensing evaporators boiling in tubes are long tubes. However, the boiling heat transfer coefficient decreases with the increase of L / Di, and tends to be stable after L / di > 500, so it is generally taken as L / di < 500. Considering the manufacturing process, in fact, the pipe length is about 3M. At this time, the influence of static pressure of liquid oxygen column is still not great.Long tube and short tube condensing evaporators are tubular type. The copper tubes are arranged vertically according to concentric circles or equilateral triangles. Brass tube sheets are installed at the top and bottom. The tubes and tube sheets are soldered with tin. The long tube is for liquid oxygen evaporation, and the short tube is for gas nitrogen condensation. The length of long tube is about 3M.
Air separation unit.When the liquid is discharged, freezing occurs when the temperature drops. In order to prevent this situation, the valve should be continuously turned at the initial stage of discharging liquid, so as not to freeze the valve stem. If freezing has occurred, steam can be used to heat the stuffing box before closing it.Air separation unit.Reduce the temperature after expansion. The lower the temperature after expansion, the greater the temperature difference with the positive air, and the stronger the heat transfer. Therefore, at this stage, the temperature after the expander should be controlled as low as possible without liquefaction, such as - 180 ～ + 185 ℃.For the low pressure air separation unit, the absolute pressure of compressed air discharged from the air compressor is about 0.6MPa. After the air is compressed, the water content in the unit volume increases, making the water content reach the saturation content corresponding to the temperature at that time. When the air flows through the air cooling tower, with the decrease of temperature, the corresponding saturated moisture content decreases, and the excess part will be separated from the gas in liquid state.
Three krypton columns are set in the distillation process. After the first krypton column rectifies, the poor krypton is obtained; the second krypton column obtains the crude krypton. At the same time of concentration of krypton and xenon, the hydrocarbons contained in the oxygen are also concentrated in poor krypton or crude krypton, so the hydrocarbons must be removed after rectification in the first krypton tower and the second krypton tower.Air separation unit.The adjustment of the temperature condition of the accumulator (or switching heat exchanger) is based on the middle temperature. The "middle part" here does not refer to the median position in geometric dimension, but refers to the temperature on the cylinder (or switching channel) near the outlet of the middle suction or circulation.In order to avoid the increase of hydrocarbon concentration in liquid oxygen, according to the material balance, it is necessary to extract part of liquid oxygen from the main cooler and extract part of hydrocarbon from the main cooler. The minimum amount of liquid oxygen extracted is equal to 1% of the gas oxygen output, and then gasified separately.
