DEAR Air separation plant.The main cooler is not cooled through in advance, which makes it impossible to transfer the cooling capacity to the tower in the liquid accumulation stage, while the switching heat exchanger appears to have excess cooling capacity and supercooling. At this stage, if the liquefaction amount of air is larger, it will be more conducive to the exertion of the cooling capacity of the expander, so as to accelerate the accumulation of liquid.1m3 air with pressure of 0.6MPa is compressed by air with pressure of 0.1MPa and volume of 6m3. The moisture content in 1m3 air also increased to 6 times, that is 6 × 30.3 (g / m3) = 181.8g/m3. If the temperature remains unchanged, the air can only hold 30.3g/m3 of water, then five sixths of the water will be released. With the increase of pressure, the more water is precipitated; the better the cooling effect is, the more water is precipitated.DEAR Air separation plant.It is of great economic significance to extend the operation cycle of air separation plant. It can reduce standby machine, reduce maintenance time, save money, and produce more oxygen and nitrogen products. Therefore, in the operation should be careful management, careful maintenance.
DEAR Air separation plant.It is not unlimited to increase the liquefaction temperature by increasing the pressure. For air. When the temperature is higher than - 140.6 ℃, no matter how high the pressure is, the air will not liquefy. In other words, - 140.6 ℃ is the highest temperature for air liquefaction, which is called "critical temperature". For each substance, there is a critical temperature of - 118.4 ℃ for oxygen and - 146.9 ℃ for nitrogen.When the process air enters the lower tower, there is a certain "moisture content", that is, a small part is liquid. Most of the air will liquefy in the main cooling. For the low pressure air separation unit, the air entering the lower tower is composed of the air coming out of the cold end of the main heat exchanger and the air passing through the liquefier.DEAR Air separation plant.Switching heat exchanger with water will also shorten the operation cycle. It is usually caused by improper operation of nitrogen water precooler. However, the slight water inflow is often due to the neglect of the blowing out of the water separator and the discharge of the condensed water in the air main pipe of the switching heat exchanger.
The outlet temperature of the hot fluid can be much lower than that of the cold fluid if the counter current arrangement is adopted. This is the case with the main heat exchanger. Therefore, in the design of heat exchanger, the flow direction of cold and hot fluid is mostly in the form of countercurrent arrangement.DEAR Air separation plant.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.When the forced valve is not tight, the upper tower pressure is usually reduced. When the automatic valve is not tight, the temperature of the positive flow air channel (or the cold accumulator) increases with the increase of air volume, and the temperature of the middle part of the polluted nitrogen channel (or the cold accumulator with nitrogen and oxygen) decreases with the increase of return flow.
