Answer: when the main cooling is seriously leaked, nitrogen with higher pressure will leak into the low pressure oxygen side in large quantities, then the pressure of the upper and lower towers and the purity of the product will change significantly until the normal production cannot be maintained and the product will be stopped.
When the main cooling slightly leaks, it often does not cause significant changes of the upper and lower tower pressure, nor does it cause significant reduction of liquid oxygen purity in the main cooling. The common phenomenon is that the purity difference between the main cold gas oxygen and the liquid oxygen is large, and the gas concentration is lower than the concentration value which is balanced with the liquid oxygen. For example, the test liquid oxygen concentration of a factory is 99%, and the gas oxygen concentration is 96%. As a result, there are 7 main cold tubes leaking during the overhaul.
The causes of the leakage are as follows:
1) the tube is grinded and leaked due to vibration. For the long-tube condensing evaporator, there are tens of thousands of copper tubes with a diameter of only 10mm and a length of 8 m, and the tube spacing is very small. In the process of operation, due to the impact and vibration of airflow, it is easy to twist and deform in the middle of the pipe and rub with each other, which may cause abrasion leakage over time.
2) the water in the pipe is frozen and cracked. When the heating is not complete, especially the blockage of the small tube brings opportunities to the accumulated water, which can not be blown off when heating, the water freezes into ice under low temperature, and the volume expands, which may break the small tube.
3) the main cooling slightly exploded locally. When the local scope of the main cooling is due to the accumulation of acetylene or hydrocarbon, explosion may occur under certain conditions. When this kind of slight explosion happened, there was no external response, and no sound was heard. At first, it was often unable to be perceived. Only when the purity of oxygen changes automatically but cannot be adjusted can this situation happen.
