The so-called saturated liquid refers to the liquid whose temperature has reached the gasification temperature under the pressure at that time but has not yet been gasified. If the saturated liquid continues to be heated, saturated vapor will be generated and the temperature will remain unchanged.The cooling capacity is required by the cooling capacity balance of the whole air separation unit. When the cooling capacity is greater than the demand, the liquid level of the condensing evaporator will rise, so the cooling capacity should be reduced accordingly. When the liquid level drops to a suitable height, a little more cooling capacity is needed to make it balanced and stable.DEAR Air separation plant.The control of temperature difference at the hot end is also relatively simple. If multiple parallel large plate fin heat exchanger groups are used, it is only necessary to control the air quantity distributed to oxygen, pure nitrogen and sewage nitrogen by the large group (composed of several groups in parallel), and no regulating valve is set in each group.
In design, the linear expansion coefficient is different due to the different materials of valve stem and valve sleeve. Generally, the valve stem is made of stainless steel with a coefficient of linear expansion of 1.73 × 10-6 ℃ - 1; the valve sleeve is made of brass with a coefficient of linear expansion of 19.9 × 10-6 ℃ - 1, which means that the shrinkage of brass is larger than that of stainless steel, and the thread may be seized at low temperature. Especially when the structure of concealed rod and fine thread are used, the temperature range of the thread is large, the thread gap is small, and the phenomenon of biting is more likely to occur.DEAR Air separation plant.The gas in the channel does not switch, so a higher flow rate can be adopted in the design to improve the heat transfer coefficient, and the heat transfer temperature difference of the cross section is not limited by the self cleaning condition. In order to reduce the loss of incomplete recovery of cooling capacity at the hot end, the temperature difference at the hot end is still small (2 ~ 3 ℃).
DEAR Air separation plant.There is a limit to the amount of water vapor that can be contained in the air. When it reaches a certain value, the content can not continue to increase, and the excess will precipitate in the state of liquid water. This maximum allowable content is called saturation content. In our daily life, we can see that in the sealed container, the water evaporates to a certain extent and will not continue to evaporate.DEAR Air separation plant.As a convenient cold source, liquid nitrogen is widely used in food industry, medical treatment, animal husbandry and scientific research.DEAR Air separation plant.In order to avoid the local accumulation of acetylene and other hydrocarbon impurities, porous fins are often used in condensing evaporators, which is also conducive to the formation of vaporization core; on the condensing side, holes can destroy the boundary layer of the condensing film to enhance heat release.DEAR Air separation plant.The process of accumulating the necessary cryogenic liquid in the distillation column is actually a process of "storing the cold capacity". In this process, the balance relationship of cooling capacity is: total cooling capacity = total cooling loss + cooling capacity required by liquid accumulation.
