Application of a Fluid-Structure Interaction Model for Analysis of the Thermodynamic Process and Performance of Boil-Off Gas Compressors.

Bin Zhao,Jianmei Feng,Xueyuan Peng,Shuangmei Zhou,Xiaohan Jia

doi:10.3390/e21040341

Abstract

Boil-off gas (BOG) compressors are among the most critical devices in transportation and receiving systems for liquid natural gas (LNG) because they are used to pump out excess BOG from LNG storage tanks to ensure safety. Because of the ultralow suction temperature, the influence of heat transfer between the cold gas and the compressor parts on the in-cylinder thermodynamic process cannot be ignored. This paper reports the effects of suction temperature on the thermodynamic process and performance of a BOG compressor with consideration of gas pulsation. A computational fluid dynamics (CFD) model with dynamic and sliding meshes was established, in which user-defined functions (UDFs) were used to calculate the real-time valve lift to realize coupling between the thermodynamic process and the gas pulsation, and a performance test rig was constructed to verify the proposed numerical model. The simulated results agreed well with the experimental ones. The results show that as the suction temperature decreased from 30 °C to −150 °C, the first-stage volumetric efficiency decreased to 0.69, and the preheating increased to 45.8 °C. These results should provide academic guidance and an experimental basis for the design and optimization of BOG compressors.

Highlights

Natural gas (NG) is playing an increasingly important role in the world’s energy structure because of its abundance, high efficiency, high calorific value, and low emission and price
The data acquisition system (DAS) used in this study mainly included a signal-conditioning device—NI SCXI-1125—and an acquisition card—PCI-6220—with 16 analog inputs and a 250 kHz sampling frequency
The results indicated that the in-cylinder temperature still increased during the suction process, even without heat the in-cylinder temperature still increased during the suction process, even considering heat in-cylinder temperature still increased during the suction process, even without heat transfer,because becausethe theworking workingchamber chamberof ofthe theshift shiftside sidewas wascompressing compressing when when that that of of the thehead head side side transfer, transfer, because the working chamber of the shift side was compressing when was in in the thesuction suctionprocess

Summary

Introduction

Natural gas (NG) is playing an increasingly important role in the world’s energy structure because of its abundance, high efficiency, high calorific value, and low emission and price. One cubic meter of LNG generally contains 625 cubic meters of NG in the gaseous state, which makes storage and transportation economical and convenient [1,2,3,4]. LNG terminals and related projects have developed rapidly in recent years to meet the substantial increase in global demand for NG. Owing to heat leakage from the surrounding environment, LNG boils and evaporates into BOG during transportation, storage, and especially unloading of LNG, and the pressure in the container increases as the amount of BOG increases. If the pressure in the container exceeds the designed value, it will pose a severe threat to LNG transportation and the receiving terminals. The excess BOG must be handled to maintain a relatively stable pressure within the container

Methods

Results

Conclusion