Conventional and Advanced Exergy Analyses of an Integrated LNG Regasification–Air Separation Process

Abstract

Liquefied natural gas (LNG) is being imported in Pakistan to bridge the gap between the indigenous production and demand for natural gas. The calorific value of imported LNG must be lowered to meet the design requirements of the existing gas-fired power plants. This reduction in calorific value requires mixing with high-purity nitrogen, which can be obtained from the cryogenic distillation of air. Because imported LNG has a significant amount of cold energy and must be regasified/vaporized before injecting into the gas pipeline network, there is potential for recovering this cold energy by integrating the LNG regasification process with the cryogenic air separation process. To achieve these objectives, we developed an integrated LNG regasification–air separation process and compared it with the standalone air separation process. Conventional exergy analysis shows that the integrated process is better than the standalone air separation process both in terms of total power consumption and total exergy destruction ratio. The integrated process was further analyzed using advanced exergy analysis to identify the origin and nature of exergy destruction in the process. The results show that 44.3% of total exergy destruction in the process can be classified as avoidable. Moreover, 91.7% of the avoidable exergy destruction is of endogenous nature, showing that improving the efficiency of individual pieces of equipment should be the topmost priority for process improvement.

Thermodynamic and Economic Analysis of an Ammonia Synthesis Process Integrating Liquified Natural Gas Cold Energy with Carbon Capture and Storage

“…In addition, the yield of hydrogen is inversely proportional to the amount of methane in the SMR reaction. Second, in the WGS reaction, the ratio of hydrogen to carbon dioxide is increased to improve the conversion rate of the reaction and reduce the destruction of exergy . For the CCS unit, the exergy of refined syngas is 134.33 MW, the exergy of CO 2 storage stream is 57.12 MW, the exergy destruction of the unit is 389 MW, and the exergy efficiency is 63.7%.…”

“…The physical exergy and chemical exergy can be calculated by eqs – E ph = m [ false( h i − h 0 false) − T 0 false( s i − s 0 false) ] E ch = R T 0 ∑ z i ln ⁡ z i + prefix∑ z i E 0 , i ch where R represents the constant of the equation of state of the gas, R = 8.314 kJ/(kmol·K), x i is the mole fraction, and the information of standard chemical exergy E 0 ,i ch can be seen from Table S3. , …”

“…Air separation processes mainly include cryogenic air separation, membrane separation, and pressure swing adsorption. , Among them, cryogenic air separation technology can not only obtain high-purity liquid nitrogen but also store liquid oxygen and liquid argon or sell them as byproducts . The cryogenic air separation process requires a large amount of cold energy, − and the LNG regasification process will release a large amount of cold energy. To save energy consumption, the cold energy released from LNG regasification is applied to the ASU, and the energy consumption in the subsequent hydrogen production process from natural gas can be reduced .…”

Термодинамічний Цикл Регазифікации Зріджених Газів З Одержанням Механічної Енергії

“…they are liquefied, consuming a lot of thermal and mechanical energy, which accumulates in the liquefied gases, i.e. a negative potential is created between the liquefied gas and the environment [8][9][10][11][12].…”

Performance Analysis and Simulation of the Gas Condensate Stabilization Process: Energy and Exergy Aspects

“…Using an optimization technique, they reduced the total exergy destruction of the process by 27.3%, leading to a 14% reduction in operating costs and 2893.6 t/y decrease in CO 2 emissions. Hamayun et al 26 evaluated the integration of the LNG regasification process with the cryogenic air separation process and compared it to the standalone air separation process. Exergy analysis revealed an improvement potential in the total power consumption and the exergy destruction ratio when integrating LNG regasification and the air separation process.…”