Liquefaction is the physical conversion of a gas into a liquid state. Natural gas is steadily peaking pace as a greener alternative source of energy. Transportation of natural gas is best in liquefied form as its volume reduces to almost 600 times. Recent technological advances have led to the development of a supersonic separator that combines expansion cooling and centrifugal separation in a single compact device with no chemical requirement. This devise has been introduced to treat natural gas for condensing and separating water and heavy hydrocarbons due to its advantages of being smaller, lighter, and less expensive as well as having fewer emissions than the conventional dehydration technology. As such, a great deal of scientific research has focused on the structural design and the separation performance of the supersonic separator.
Recent studies have revealed that the Laval nozzle is a significant part of a supersonic separator that leads to the condensation of the target components. Moreover, it has been established that phase characteristics and the calculation of the liquefaction efficiency are the most effective methods to evaluate the condensation of the natural gas in a supersonic nozzle. Unfortunately, the phase characteristics coupled with liquefaction efficiency, and supersonic liquefaction properties of natural gas in the Laval nozzle are still not clear.
Recently, China University of Petroleum scientists: Jiang Bian (PhD candidate), Mawugbe Ayivi Edem, Pengbo Yin, Professor Wenming Jiang and led by Professor Xuewen Cao together with Dr. Wen Yang from South China Branch, Sinopec Sales Co., Ltd developed a novel type of natural gas liquefaction process using the Laval nozzle . To be precise, the researchers analyzed the supersonic flow characteristics and the liquefaction process of the methane-ethane binary system in a Laval nozzle by combining the theories of phase equilibrium, gas dynamics and thermodynamics. Their work is currently published in the research journal, Energy.
The research team evaluated the effects of the inlet temperature, inlet pressure, back pressure and inlet composition on the liquefaction process using computational fluid dynamics (CFD). To sum it up, they assessed the liquefaction efficiencies of the nozzle and the throttle under different conditions by calculating and contrasting using the MATLAB and HYSYS software packages.
The authors observed that the critical liquefaction temperature and pressure of the methane-ethane binary system decreased under low inlet temperature or high inlet pressure conditions and the range of the liquid phase region increased, which in turn promoted the liquefaction process. In addition, they reported that with the increase of the back pressure of the nozzle, the position of the shock wave moved forward and the liquefaction environment became completely destroyed.
In summary, the study by China University of Petroleum successfully presented a novel approach to liquefy natural gas by the use of the Laval nozzle. Generally, it was seen that the multi-component natural gas, in which the heavy hydrocarbon content is high, natural gas was quite easily liquefied using the Laval nozzle system. Altogether, the nozzle more easily achieves liquefaction when compared with a throttle under the same conditions.
Jiang Bian, Xuewen Cao, Wen Yang, Mawugbe Ayivi Edem, Pengbo Yin, Wenming Jiang. Supersonic liquefaction properties of natural gas in the Laval nozzle. Energy, volume 159 (2018) page 706-715.Go To Energy