DEAR Air separation plant.After several stages of air compressor cooler leakage, in operation will not occur water accident (because the air pressure is higher than the cooling water pressure). When the air compressor stops, the cooling water may still enter the air passage. If not drained, once the air compressor is restarted, water will flow into the air separation unit. In addition to the above two large-scale water inflow conditions, if the heating gas is not dry, the water will also be brought into the regenerator (or switching heat exchanger) during thawing and heating.During the start-up of the low-pressure oxygen generator, liquid air first appears in the lower tower, and then liquid oxygen appears in the upper tower. The cooling capacity needed for liquid accumulation in the tower mainly comes from the expander, and part of the air is liquefied in the liquefier by using the low temperature gas after expansion.DEAR Air separation plant.In our daily life, we can see that a cup of hot water will naturally cool to the ambient temperature, and a piece of ice will naturally melt into water in the environment above 0 ℃. But water doesn't spontaneously drop to a lower temperature than the surrounding air and freeze. These phenomena show a basic law of nature: heat can only be transferred spontaneously from high-temperature objects to low-temperature objects, but the opposite process cannot be carried out spontaneously.
If the expansion amount is within the allowable range of the minimum reflux ratio (less than 20% - 25% of the process air volume) required by the upper column distillation, it can all enter the column. Otherwise, it can't enter the tower completely, and part of the expanded air only produces cold air and doesn't participate in distillation. These three quantities restrict each other. The expansion capacity is composed of two parts: the circulating flow and the bypass flow from the lower tower. Therefore, the temperature and gas flow of the circulating flow will directly affect the inlet state of the expander.DEAR Air separation plant.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.
DEAR Air separation plant.In order to avoid the air at the cold end being liquefied, it is necessary to pay attention to the loop flow in the operation. The size of the circulating flow should be adjusted according to the temperature difference between the hot end, the cold end and the middle part of the accumulator. It can not be fixed mechanically because the air volume and the tower working condition are constantly changing. In addition, we should pay attention to the working condition of subcooler and liquefier, and deal with the problems in time. When the liquid is accumulated during the start-up process, if the expansion is too large, it should be reduced appropriately.After grouting for 7 days, tighten the screws and recheck the verticality of the tower again. Then, the pad iron and the bottom plate shall be welded firmly, and the slurry shall be sealed around; the connecting pipeline shall be installed, and the air tightness of the connecting pipe flange and welded joint shall be inspected. Generally, it is qualified if there is no bubble in soapy water;
The separation process of poor krypton and crude krypton is mainly the separation of oxygen, krypton and xenon. The preparation of pure krypton and xenon can be carried out by batch distillation repeatedly according to the boiling point difference of krypton and xenon. There are three methods for extracting krypton and xenon in air separation column: 1) distillation; 2) adsorption; 3) large scale chromatography.Then, the following steps can be followed: turn the switching mechanism from automatic to manual, close the forced valve and equalizing switching valve of the air into the tower. Open the waste nitrogen vent valve. Cut off the expander solenoid valve, close the expander inlet control valve and the expander inlet and outlet valves.The most likely leakage place of the switching heat exchanger is the weld, especially the joint between the head and the pipe. The causes of leakage are mostly manufacturing and installation quality problems, and also related to maintenance. The working condition of the switching heat exchanger is poor. It is not only impacted by the alternating air flow, but also the air temperature changes greatly. In the long-term operation, the weak part is easy to leak.
