In order to ensure self cleaning of all low pressure air separation unit, the temperature difference at the cold end of switching heat exchanger must be controlled within the allowable temperature range to ensure self cleaning. The self clearing temperature difference at the cold end is the difference between the temperature when the positive air passes through the cold end section and the temperature when the backflow gas passes through the section. In normal operation, the measured temperature difference at the cold end is the self clearing temperature difference.DEAR Cryogenic air separation unit.The sieve plate column is similar to the sieve plate column of distillation column, but the number of plates is small (generally about 5), and the diameter and spacing of sieve holes are large (about 5mm in diameter and 9mm in spacing). The cooling water is ejected from the top through the spray device and flows down the tray through the sieve hole layer by layer. The air flows counter current through the sieve hole from the bottom of the tower and bubbles up.
In general, the method of heating catalysis is used to pressurize the poor krypton or crude krypton to 0.5MPa. Under the condition of 500-550 ℃, the hydrocarbon reacts with oxygen to produce water and carbon dioxide in the contact furnace of silver and cobalt catalyst. Then the molecular sieve is used to absorb the dry water and carbon dioxide, or the silica gel is used to remove the water, and the caustic soda solution is used to absorb carbon dioxide.Generally, the temperature of air entering the tower is set at 30 ℃. When the tower inlet temperature is higher than the design index, the throttling cooling capacity of compressed air will be reduced, and the temperature difference and heat load at the hot end of the switching heat exchanger will be increased, resulting in the increase of cooling loss and energy consumption.DEAR Cryogenic air separation unit.If the pressure is reduced, the corresponding saturation temperature will also be reduced. Some saturated liquid will gasify and absorb heat, and become a mixture of saturated liquid and saturated steam at low pressure. The temperature is equal to the saturation temperature at this pressure. The throttling of liquid air and liquid nitrogen is in this case.
If the ratio of backflow to positive flow is smaller than the normal value, for example, if the annular flow is reduced or the pumping capacity is reduced, the positive flow air volume is more than the backflow air volume, and the cooling capacity absorbed by the positive flow air is more than that released by the backflow gas, that is, if the cooling capacity is insufficient, the temperature of the air out of the accumulator will rise, resulting in a larger temperature difference at the cold end.DEAR Cryogenic air separation unit.The energy of molecular motion is reduced to a certain extent and condensed into liquid due to mutual attraction. Therefore, as the temperature increases, the more water vapor can be contained in the air. The higher the temperature is, the higher the maximum content of water vapor (saturated content) is, and the higher the partial pressure (saturated vapor pressure) is.DEAR Cryogenic air separation unit.The temperature of expander can also be regulated by bypass air (low temperature air at the outlet of heat exchanger). In a word, as long as the temperature difference at the hot end is controlled and the intermediate extraction temperature is within a certain range, the working condition of the non switching plate fin heat exchanger is basically stable. Even if there are some changes, as long as the cooling capacity can be balanced, there is no need to make more adjustments.
