Thermodynamic, Economic and Environmental Analyses of Ammonia-Based Mixed Refrigerant for Liquefied Natural Gas Pre-Cooling Cycle

Abstract

Analyzing the entire liquefaction cycle, using a large temperature span with many degrees of freedom, may not always result in a practical solution. The objective of this paper is to investigate the feasibility of using an environmentally friendly refrigerant compound, ammonia, in the mixed refrigerant (MR) for the liquefied natural gas (LNG) pre-cooling cycle through thermodynamic performance, economic analyses and environmental impact. Fifteen cases studies within three major mixed refrigerants groups of MR-1, MR-2 and MR-3 were developed by adding ammonia to various molar compositions of lighter and heavier hydrocarbons. The thermodynamic analysis shows increasing ammonia’s concentrations in the mixed refrigerant by 10% had the largest enhancement on coefficient of performance (COP) of MR-1 by 0.67 and decreased the specific energy consumption of the pre-cooling cycle by 128 kJ/kg compared to the base case. Economic analyses revealed that the mixed refrigerant MR-1, with ammonia, methane, ethane and propane, benefited the most from higher concentration of ammonia in the mixed refrigerant, which resulted in both lower annual capital and operational costs by $2.52 MM and $3.67 MM, respectively. Lastly, reducing the methane concentration in MR and replacing it with ammonia, decreased the amount of refrigerant leakage through compressor’s seals and reduced the global warming potential index (GWPI) of mixed refrigerant up to 24.3%.

Energy and economic comparison of five mixed-refrigerant natural gas liquefaction processes

“…Then, it is possible to verify that the applied methodology is valid and does not present great disparities when the main parameters in the economic analysis have their values modified. [11,28,36] Electricity cost (𝒄 𝒆𝒏𝒆 ) 0.0667 $/kWh [30] 0.0681 $/kWh 0.0692 $/kWh [30] Lifetime (n) 15 years 20 years 25 years [14,37]…”

A Comprehensive Review of Stratification and Rollover Behavior of Liquefied Natural Gas in Storage Tanks

“…Liquefied natural gas (LNG) refers to the low-temperature liquid mixture of hydrocarbon and non-hydrocarbon by the cryogenic freezing process at −162 • C after pre-treating NG and removing impurities, which has a volume around 1/600 that of the natural gas at room temperature [9][10][11]. The liquefaction of natural gas is not only conducive to the efficient storage of natural gas but also provides a safer and more economical way for natural gas transportation [12][13][14]. As a consequence, the industry is accelerating to meet the global utilization of LNG, and global LNG demand is expected to grow by 45% by 2040 [15].…”