Pinch point analysis of heat exchange for liquid nature gas (LNG) cryogenic energy using in air separation unit. (June 2018)

• Record Type: Journal Article
• Authors: Chen, Shiqing; Xu, Jian; Dong, Xuezhi; Zhang, Hualiang; Gao, Qin; Tan, Chunqing
• Is Part Of: International journal of refrigeration. Volume 90(2018)
• Page Start: 264
• Page End: 276
• Publication Date: 2018-06
• Subjects: Pinch point -- LNG -- Air separation unit -- The cryogenic energy utilization rate; Analyse Pinch -- GNL -- Unité de séparation d'air -- Taux d'utilisation de l'énergie cryogénique; ASU air separation unit -- CEASU cryogenic energy used in air separation unit -- HiPPSS high performance energy supply system -- LC lower column -- LNG liquefied natural gas -- NG natural gas -- MESH Material balance, phase-Equilibrium relation, mole-fraction Summations, energy balance -- UC upper column; Refrigeration and refrigerating machinery -- Periodicals; 621.56
• DOI: 10.1016/j.ijrefrig.2017.12.015
• Languages: English
• ISSNs: 0140-7007

Abstract

Highlights: The pinch point occurs in the design and calculation of the CEASU. Performance of heat exchange process is mainly affected by the outlet state of N2 . Performance of the CEASU declines as the increasing of temperature difference of E3. Performance of the CEASU has an optimal value as the increasing of pressure of N2 . Energy consumption of the CEASU is less than that of convectional processes. Abstract: Due to strong nonlinear variation of supercritical liquid nature gas (LNG) and nitrogen (N2 ) isobaric heat capacity with temperature and pressure, pinch point analysis is conducted for heat exchange process between LNG and N2 and its effect on the air separation unit cooled by LNG cryogenic energy (CEASU) is studied in the present study. The effect of pinch point value, temperature difference at the cold end and pressure of N2 on mass flow ratio (N2 to LNG), approach temperature difference, energy consumption of CEASU and cryogenic energy utilization rate are analyzed in detail. For the heat exchanger process between LNG and N2, the different value of pinch point have little effect on its location, and increasing the temperature difference at the cold end effectively increases the mass flow ratio and decreases the approach temperature difference, while rising the pressure of N2 leads to a valley value of the mass flow ratio, in contrast to a peak value in the approach temperature difference. For the energy consumption of CEASU, choosing the lower temperature difference at the cold end is good for the energy consumption and equivalent energy consumption per kilogram liquid production, but a large amount of LNG is needed and cryogenic energy could not be fully used; while the influence of pressure of N2 on the energy consumption presents different variation trend. The result shows the energy consumption per kilogram liquid production of proposed CEASU is roughly 5–12% lower than that of convectional processes which the cryogenic energy is only used for cooling the nitrogen or the feed air.