(391d) Modeling and Simulations of the Liquefaction and Separation Process Via 3S Separator in Cryogenic Conditions

Supersonic swirling separator, which is also called 3S separator, has been successfully applied in natural gas industry for water removing and heavy hydrocarbons removing. It could also been employed in the liquefaction of natural gas with proper pre-cooling of the feed natural gas. It has advantages such as high efficiency, simply process, low investment and no moving device, which means 3S separator will be appropriate for utilization in many fields.

The flow, liquefying and separation process of natural gas via 3S separator at cryogenic condition has different characteristics with that in the temperature range of the separation process of water and heavies. The modeling and simulation of the process is significant for understanding the liquefaction and separation process via 3S separator. It is also essential for the prediction the performance of liquefaction plant with a 3S separator.

Based on aerodynamics, thermal dynamics and nucleation theory, a theoretical model of the flow, liquefaction and separation process via 3S separator is established. The total process via 3S separator is divided into subsonic section, nozzle section, nucleation section, separation section and diffuse section. The assumption in each section is made based on the feature in this section and the theoretical model for the process in each section is set up. The natural gas at cryogenic condition should be retreated as real gas and its property is calculated using PR equations of stat. A modified CNT model is employed to describe the nucleation process of liquid droplet of natural gas when its temperature is below the saturate temperature. The Gyamathy model is used to describe the growing process of liquid droplet of natural gas when it expands further through the nozzle. The nucleation and growth of liquid droplet is rather important for the separation of LNG and gas. The numerical simulation is carried out by programming using MATLAB on the basis of the model.

A cryogenic experimental device with pre-cooling using liquid nitrogen is designed and set up. Experiments at different pre-cooling temperature are carried out and the experimental results confirm the practicability of the liquefaction of gas by proper pre-cooling. The pre-cooling temperature is an important factor which affects the liquefaction performance. The comparison between experimental data and prediction results of the model is done and the comparison results prove the validity of the model. The results also indicate the nucleation and separation is essential for the liquefaction of natural gas. The modeling is valuable to predict the performance of 3S separator at cryogenic condition and be useful for the development of LNG plant using 3S separator.