Simulative and experimental research on the heat exchanger for cold energy recovery of liquefied natural gas

Abstract

Natural gas, a widely used energy source, is transported as liquefied natural gas (LNG). During the gasification of LNG, a large amount of cold energy is released, which can be recycled to achieve energy savings. An LNG cold energy heat-exchanger (shell-and-tube type) was designed to recover cold energy for application in 0 ℃ ammonia cold storage. To conduct a more intuitive and detailed study of the effects of the tube space and flow rate on each heat-exchange tube in a shell-and-tube heat exchanger, a double-pipe heat exchanger was designed and manufactured. Liquid nitrogen and a secondary refrigerant (antifreeze) was used as the cold and heat source, respectively. Owing to the effects of the tube space and refrigerant flow velocity on the heat transfer coefficient, simulations and experiments were conducted on the antifreeze velocity and tube space. The results showed that increasing the antifreeze flow velocity and reducing the tube space increased the amount of cold energy recovered. Based on the physical parameters of liquid nitrogen and LNG, the cold energy recovery ratio was 1.3. The predicted amount of cold energy recovered from LNG in double-pipe and shell-and-tube heat exchangers were determined by the cold energy recovery coefficient, cold energy recovery ratio, and number of heat-exchange tubes. The recovery of cold energy from LNG in a shell-and-tube heat exchanger was applied to cold storage, which can improve the cold storage performance by 36.8 %.