For safety, the impurities are removed in the purification device, such as molecular sieve adsorber. However, it can not be done for the self cleaning process of switching heat exchanger. Therefore, the following measures should be taken in the process design and operation: the volume fraction of acetylene and hydrocarbon in the raw material air should not exceed 0.5 × 10-6 and 30 × 10-5 respectively; liquid air adsorber should be installed to absorb harmful impurities;DEAR Biogas purification unit.With a large amount of oxygen condensing, the oxygen content in gas phase decreases, and the argon condensing relatively increases. Therefore, the argon content in gas phase gradually decreases, and it is only 0.0% after reaching the top of the tower. Because oxygen and argon are difficult to volatilize to nitrogen, they condense into liquid phase more than nitrogen, so the concentration of oxygen and argon in liquid phase is higher than that in gas phase.DEAR Biogas purification unit.The overall heating in cold state is the heating operation after parking. The main purpose is to remove the residual water, carbon dioxide, acetylene and other impurities, so as to prepare for the long-term operation or maintenance of the next cycle. Full heating in hot state is the heating operation before start-up. Its main purpose is to remove water and some solid debris.
The stage cooling method is one of the start-up operation force methods of air separation plant which uses switching heat exchanger to remove water and carbon dioxide. In the full low pressure air separation unit, the moisture has been basically frozen at - 40 ～ - 60 ℃ under the operating pressure of 0.5MPa (gauge pressure). However, carbon dioxide begins to precipitate and freeze below - 133 ℃ until the end of freezing at - 165 ～ - 170 ℃.The expansion heat exchanger is used to recover the cooling capacity to further reduce the temperature of expansion gas, and the liquid air subcooler is used to further reduce the temperature of liquid air flowing into the upper tower. Therefore, attention should be paid when the air separation unit with switching purification process is restarted after a short-term shutdown: before the recovery, the start-up circuit should be determined according to the temperature rise at the cold end.In argon production, part of liquid air and liquid nitrogen in the main tower need to be pumped as cold source. At the same time, due to the increase of equipment, the cold loss increases correspondingly. Therefore, more cooling capacity is required to keep the balance of cooling capacity. For medium pressure device, high pressure should be increased;
DEAR Biogas purification unit.The basic method of extracting rare gases is to use their different boiling points and molecular differences. But because their content is very small, they often need to be concentrated step by step and purified in stages, that is, after two stages of rough and refined, so the process is more complex.DEAR Biogas purification unit.Refrigeration is to remove the heat from the device which is lower than the ambient temperature, so as to balance the heat from the outside, keep the device at low temperature, or keep the internal temperature decreasing until the low temperature liquid is accumulated. Heat can only be transferred from high-temperature objects to low-temperature objects. To remove heat from low-temperature objects, we must first use artificial methods to create a lower temperature state, so that it has the ability to absorb and take away heat. Theoretically speaking, the cooling capacity is the capacity to take away heat.DEAR Biogas purification unit.If the resistance of the cold section increases, it is carbon dioxide freezing; if the resistance of the hot section increases, it is water freezing; if the resistance of the whole heat exchanger increases, it is both freezing, or molecular sieve powder is blocked; the abnormal operation of the refrigerator causes the temperature of the chilled water to rise, and the air cannot be cooled to the normal temperature.
