In the cryogenic separation process of air separation equipment, gaseous nitrogen can cool liquid nitrogen. The core is to use the phase change characteristics and energy exchange principle of nitrogen. Essentially, it is a two-way heat exchange process of gaseous nitrogen releasing latent heat and liquid nitrogen absorbing latent heat. It is also a key link for air separation equipment to realize continuous output and stable storage of liquid nitrogen.
In the air separation equipment, the air enters the rectifying column after being compressed, purified and cooled, and the gas nitrogen and liquid nitrogen with qualified purity are separated through rectification. As the product at the top of the rectifying column, gaseous nitrogen is in the gas state at normal temperature or low temperature, while liquid nitrogen is the liquid product at the bottom of the rectifying column or in the condensing evaporator, both of which have obvious energy difference and phase change potential.
The core carrier of gaseous nitrogen cooling liquid nitrogen is the condensing evaporator. The gaseous nitrogen flows on one side of the condensing evaporator and the liquid nitrogen flows on the other side. Heat transfer is completed through the heat exchange wall. Under the action of pressure, the gas nitrogen will release its own sensible heat and latent heat of condensation when contacting with the low-temperature heat exchange surface, and the temperature will gradually decrease and finally condense into liquid nitrogen; Correspondingly, the liquid nitrogen on the other side absorbs the heat released by the gas nitrogen, maintains the low temperature state, and supplements the liquid nitrogen lost due to evaporation to ensure the stable supply of liquid nitrogen.
In addition, the condensation process of gaseous nitrogen will maintain the pressure balance and temperature gradient in the rectifying column, providing guarantee for continuous rectification and separation of air. This heat exchange realized by the phase change of the medium itself, without additional cooling medium, is efficient and energy-saving. It is an indispensable core step in the cryogenic process of the air separation equipment, and directly supports the stable demand for liquid nitrogen and gaseous nitrogen in the steel, chemical and other industries.
