For the irreversible adiabatic process, the entropy increases. In other words, the physical quantity entropy can express the direction of the process. The spontaneous process in nature always goes in the direction of the increase of the total entropy, and the total entropy of the ideal reversible process remains unchanged. For the above two irreversible processes, the entropy of the final state must be greater than that of the initial state. The common cases of water inflow into the accumulator (or switching heat exchanger) are as follows: the automatic water level regulation system of the air cooling tower of the nitrogen water precooling system fails, which makes the water level too high. Or improper operation, such as unreasonable start-up of air cooling tower or sudden drop of air separation tower pressure, resulting in a large number of water inflow accidents.
Under the condition of 3 ℃ temperature difference at the hot end of a large capacity air separation plant, the incomplete heat exchange loss accounts for about half of the total cooling loss. If the temperature difference increases by 1 ℃, the total cooling loss will increase by about 16%. In order to make up for the increased cold loss, it is required to increase the expansion capacity of the expander, which will affect the work of the whole device. In the process of operation, pay attention to the change of temperature difference at the hot end, and take corresponding measures to prevent the expansion of temperature difference and avoid exceeding the design value. When the manufacturer of air separation unit measures the temperature, take the thermometer out of the casing and read it again. The correct installation and use method is: first, the air inlet pipe and the return air pipe are respectively opened at about 1.6m above the ground, and the thermometer joint with 45 ° to the main pipe is welded. If a platinum resistance thermometer or a glass rod thermometer with a metal shell is used, the temperature measuring element point should be inserted into the inner diameter of the main pipe 1 / 3 ~ 1 / 2, so that the temperature measuring element is aligned with the fluid.
During the shutdown of air compressor, the outlet and inlet valves of cooling water shall be closed. After start-up, the accumulated water in the pipeline should be blown away. In case of serious leakage, the cooler shall be shut down for maintenance or replacement; Third, the heating gas must be dry. Generally, the nitrogen content in the distillate of the air separation plant manufacturer shall not exceed 0.01%. In a word, the operation of the crude argon column should gradually increase the load of the crude argon condenser, too fast operation will be counterproductive, making the whole system fluctuate. When the air cooling tower of air separation plant manufacturer is put into use, the pilot gas is required, and then the water pump is started. This is a measure to prevent air from carrying water. Because the pressure of the air in the tower before charging is atmospheric pressure, when the high-pressure air with a pressure of about 0.5MPa (gauge pressure) is introduced into the tower, due to the expansion of the volume, the pressure will suddenly decrease and the air flow speed will increase sharply, which has a strong impact and entrainment effect.
Under the condition that the steam content of the air separation plant manufacturer remains unchanged, due to the decrease of temperature, the original unsaturated steam in the air can become saturated steam, and the excess water will be separated out. The temperature at which water vapor reaches saturation is called the dew point. When the liquid air throttling in the lower tower reaches the upper tower, the temperature will decrease from - 173 ℃ to - 191 ℃; When the liquid nitrogen is throttled to the upper tower, the temperature decreases from - 177 ℃ to - 193 ℃. However, when the tap water flows out from the valve, the phenomenon of temperature drop can not be seen. This is mainly because the liquid throttled in the air separation column is "saturated liquid"; Tap water is a supercooled liquid.
