Abstract
This research work unfolds a simple, safe, and environment-friendly energy efficient novel vortex tube-based natural gas liquefaction process (LNG). A vortex tube was introduced to the popular N 2 -expander liquefaction process to enhance the liquefaction efficiency. The process structure and condition were modified and optimized to take a potential advantage of the vortex tube on the natural gas liquefaction cycle. Two commercial simulators ANSYS® and Aspen HYSYS® were used to investigate the application of vortex tube in the refrigeration cycle of LNG process. The Computational fluid dynamics (CFD) model was used to simulate the vortex tube with nitrogen (N 2 ) as a working fluid. Subsequently, the results of the CFD model were embedded in the Aspen HYSYS® to validate the proposed LNG liquefaction process. The proposed natural gas liquefaction process was optimized using the knowledge-based optimization (KBO) approach. The overall energy consumption was chosen as an objective function for optimization. The performance of the proposed liquefaction process was compared with the conventional N 2 -expander liquefaction process. The vortex tube-based LNG process showed a significant improvement of energy efficiency by 20% in comparison with the conventional N 2 -expander liquefaction process. This high energy efficiency was mainly due to the isentropic expansion of the vortex tube. It turned out that the high energy efficiency of vortex tube-based process is totally dependent on the refrigerant cold fraction, operating conditions as well as refrigerant cycle configurations.
Highlights
The refrigeration and liquefaction in LNG plant demands the high capital investment and consumes a tremendous amount of energy
This study addressed the potential benefits of vortex tube coupled with turbo expander to enhance the energy efficiency of N2 expansion LNG process
The results showed the specific compression energy can be saved significantly up to 20% in comparison with the commercial N2-expander LNG process
Summary
The refrigeration and liquefaction in LNG plant demands the high capital investment and consumes a tremendous amount of energy. In terms of energy consumption, liquefaction of 1 kg natural gas consumes 1,188 kJ of energy [2], which is equivalent to the 30–35% of the total required energy for the LNG production. Various optimization techniques have been reported to enhance the energy efficiency of the N2 refrigeration process [3,4,5,6] Another alternative to improve the energy efficiency of the LNG plant is to enhance the refrigeration cycle units like compressors, cryogenic heat exchangers, and expansion devices. By improving the refrigeration cycle units like compressors, cryogenic heat exchangers, and expansion devices is another main alternative approach to improve the energy efficiency of LNG plant [7]. The structure and design parameters of the proposed process were optimized to achieve the maximum benefits of proposed vortex tube-based configuration corresponding to the minimum required compression power. The modified knowledge-based optimization method was proposed and successfully applied to optimize the proposed LNG process
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