DEAR Biogas purification unit.The centralized cooling method, also known as the complete cooling method, is also one of the start-up operation methods of the air separation unit with the freezing self cleaning process. This method is to use the cold capacity of the expander to cool the accumulator to the operating temperature, that is, the temperature of the cold end reaches - 170 ～ - 172 ℃, so that it can completely pass through the freezing stage of water and carbon dioxide, and then cool other equipment, accumulate liquid and adjust the distillation condition.Under the design condition, the positive and return flow rates of the hot section of the switched heat exchanger (or cool storage) are basically equal. In the cold section, the amount of backflow air must be greater than that of positive flow air, and a certain proportion should be maintained, so that the temperature difference at the cold end is within the range required by the self removal of water and carbon dioxide, and the temperature difference at the hot end should be more appropriate.
DEAR Biogas purification unit.For the same oxygen generator, the amount of accumulated liquid required is the same, so the cooling capacity required is the same. However, the total cooling capacity and total cooling loss of an oxygen generator are related to the specific conditions, and sometimes there is a big difference. It is related to the installation, maintenance quality and start-up operation of the oxygen generator.The moisture content of the air into the tower is determined by the distillation system according to the heat balance of the tower. Because the heat transfer temperature difference of the main heat exchanger is larger than that of the switching heat exchanger, the heat transfer area needed to transfer the same heat can be reduced, so the length of the non switching plate fin heat exchanger is generally shorter than that of the switching heat exchanger.For carbon dioxide, the cold end temperature should be below - 133.5 ℃ before some carbon dioxide begins to precipitate in the heat exchanger. The carbon dioxide content at the cold end is the saturation content corresponding to the temperature at that time. According to the above method, the minimum allowable temperature of carbon dioxide in the expander can also be determined.
DEAR Biogas purification unit.The process of extracting neon and helium from air separation unit is generally divided into three steps: the first step is to prepare crude neon and helium; the second step is to prepare pure neon and helium mixture; the third step is to separate neon and helium to obtain pure neon and helium products. The purpose of the preparation of crude neon and helium is to remove nitrogen from the raw material and concentrate it.DEAR Biogas purification unit.When the adsorber does not clean up the moisture and carbon dioxide in the air and enters the heat exchanger, it will freeze on the heat transfer surface, which will reduce the heat transfer coefficient and heat transfer capacity. In this case, the resistance of heat exchanger will increase. For example, the temperature difference at the hot end of a 6000m3 / h oxygen generator increased from 3 ℃ to 6 ℃, and the resistance of the main heat exchanger also increased from 10KPA to 22kpa. At this time, it is necessary to warm and purge the main heat exchanger to make it return to normal.
DEAR Biogas purification 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.When the air volume is reduced or the product throughput is increased, the temperature difference at the cold end will be reduced, the temperature difference at the hot end will be enlarged, and the temperature at the outlet of the circulation (or the middle extraction) will be reduced. Therefore, when increasing the air throughput or reducing the product throughput, we should pay attention to the expansion of the temperature difference between the cold end and the middle; when reducing the air throughput or increasing the product throughput, we should pay attention to the cold loss at the hot end. If necessary, it should be supplemented by circulation regulation.
