Mixed Refrigerant Research Articles

Pinch and exergy assessment of an innovative hydrogen and methane purification process configuration based on solar renewable energy

Energy recovery from waste sources and developing new high-performance systems are essential to minimize energy consumption. A novel purification structure is developed to produce hydrogen and liquid natural gas (LNG) using exhaust gases from various industries, mixed refrigeration system, organic Rankine cycle (ORC), and solar energy sources. Solar parabolic trough collectors are used to supply energy in the low-temperature ORC. The proposed system produces 1.922 kg/s hydrogen with purity of 94.25 mol% and 1.777 kg/s LNG as the main product by consuming 10.56 kg/s crude hydrogen feed gas. The LNG and pure hydrogen specific power consumption (SPC) are 0.4111 and 0.3803 kWh/kg, respectively. The SPC of the sum of both products is obtained at 0.1975 kWh/kg. The methane and hydrogen recovery factors are 94.80% and 98%, respectively, indicating maximum methane and hydrogen absorption of the crude hydrogen feed gas. The exergy analysis indicates that the total exergy destruction of the integrated system is calculated at 5561 kW, and its exergy efficiency is obtained as 28.56%. The heat exchanger networks for the HE1, HE2, HE3, HE4, and HE6 multi-stream heat exchangers are extracted through the pinch strategy. The multi-stream heat exchangers have 8, 13, 6, 8, and 2 simple heat exchangers. The outcome results obtained from the parametric study is a 25.88% increase in the production rate of the main products (LNG and pure hydrogen). In addition, when the ratio of LNG to fuel gas increases by 48.08%, the ratio of main product to by-product increases from 54 to 62 mol%. By performing parametric analysis, it can be concluded that increasing the hydrogen content of the crude feed improves the performance of the system.

An Innovative Approach for Natural Gas Liquefaction Using a Mixed-Multi-Component-Refrigerant

The natural gas liquefaction is the most expensive and energy-intensive phase in the natural gas-to-liquefied natural gas-to-natural gas chain. In addition, this region has the biggest development potential. As a result, numerous LNG production methods have been developed and are deployed at export facilities around the world. The goal of this study is to describe and assess an innovative approach for mixed-refrigerant (MR) LNG method. The authors have dubbed this technique the MR-X approach. The MR-X process was developed based on the globally proven liquefaction technology C3MR and its large-scale successor AP-X™ (which offers many benefits and flexibility), but with a novel precooling phase construct. In pre-cooling and liquefaction phases, the refrigerant is a combination of methane, nitrogen, propane, ethane, butane, and isobutane. The paper investigates the creation of the MR-X technology, as well as its modelling, energy, and exergy investigations.

Molecular dynamics investigation on the interaction of nitrile-based ionic liquids in the separation of azeotropic refrigerant R-513A

The reclamation of mixed refrigerants stands as a potent measure to substantially mitigate the emission of fluorinated gases (F-gases). In the separation of the azeotropic refrigerant R-513A (comprising 56 wt% R-1234yf, 2,3,3,3-Tetrafluoropropene, and 44 wt% R-134a, 1,1,1,2-Tetrafluoroethane), the extractive distillation process using ionic liquids (ILs) was employed. The molecular structure of nitrile-based ILs ([C4C1im][SCN], [C4C1im][N(CN)2], [C4C1im][C(CN)3], [C4C1im][B(CN)4]) exerts a regular impact on the solubility of refrigerants, thereby necessitating molecular dynamics simulation to ascertain the law of refrigerant solubility in ILs concurrent with the augmentation in the number of –CN in the anion. Additionally, an analysis was conducted to elucidate the mechanism underlying the high selectivity of nitrile-based ILs. The results revealed pronounced interactions between R-1234yf and R-134a, predominantly occurring between carbon atoms (-CF3 groups in R-134a and R-1234yf), and chiefly van der Waals interactions. An enhancement in the number of –CN in anion led to the fortification of the van der Waals interaction between R-134a/R-1234yf and the anion. The stronger nonbonding interaction energy between R-134a and the anion, as well as the higher radial distribution function (RDF) peak height between R-134a and the anion, signified a more robust interaction between R-134a and the anion compared to R-1234yf and the anion. Concurrently, the variance in the RDFs in the anion-C atom (-CH2F group in R-134a and -CF group in R-1234yf) revealed the selectivity of the four ILs to R-134a and R-1234yf. Among the four anions, [B(CN)4]− exhibited the most interaction sites with R-134a. This investigation contributes significantly to comprehending the interaction mechanism of azeotropic refrigerants and the interaction mechanism between refrigerants and nitrile-based ILs.

The Effect of Heat Exchanger Tube Structure on the Condensation Heat Transfer of R1234ze(E)/R152a Inside Smooth Tubes

Abstract In this paper, the flow condensation heat transfer characteristics of the environmentally friendly nearly-azeotropic refrigerant R1234ze(E)/R152a (mass ratio of 40:60) in smooth tubes with varying structures were numerically investigated. Under the operating conditions of mass flux of 400 kg/m2/s, heat flux of 12 kW/m2, and saturation temperature of 308.15 K, this study investigated the influence of circular tube inner diameter, elliptical tube aspect ratio, and installation orientation on condensation heat transfer, while the influence on pressure drop has not been taken into account in the present study. The results indicate that the condensation heat transfer coefficient in the tube increases as the inner diameter of the circular tube decreases. The condensation heat transfer coefficient increases by 1.086 times when the circular tube inner diameter is reduced from 10.7 mm to 5 mm. Under identical operating conditions, the condensation heat transfer coefficient of the mixed refrigerant in elliptical tubes increases with an increase in the aspect ratio. The average condensation heat transfer coefficient increases by 18.21% as the aspect ratio of the elliptical tube increases from 1 to 2. Compared to a vertical elliptical tube, a horizontal elliptical tube is more favorable for condensation heat transfer within the tube.

Research on shell-side heat and mass transfer with multi-component in LNG spiral-wound heat exchanger under sloshing conditions

The spiral-wound heat exchanger (SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop. These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.

Energy and Exergy Analysis of Cascade Mixed Refrigerant Joule–Thomson System with the Application of a Precooler

This study proposes the application of a precooler to the cascade mixed refrigerant Joule–Thomson (CMR J–T) cycle, herein referred to as the precooled CMR J–T (PCMR J–T) system. The purpose of the precooler is to utilize the temperature gradient characteristics within the two-phase region exhibited by the non-azeotropic mixed refrigerant. The precooler reduces the temperature of the high-temperature gas exiting the compressor by using cooling water from the condenser, thereby decreasing the capacity requirements of the high-temperature cycle (HTC). The working fluid comprises a nonflammable mixed refrigerant (R218, R23, R14, and Ar), and simulations were conducted by varying the HTC evaporation temperature and cooling water temperature for energy and exergy analysis. Under the analysis conditions, the capacity of each component in the HTC can be reduced by over 45%, leading to a maximum increase of 21.6% in the system’s coefficient of performance. Furthermore, the exergy destruction in the PCMR J–T system decreases along with the reduction in component capacity, with the most significant reduction occurring at the HTC expansion valve. The exergy efficiency of the system increases by up to 47.4%.

Enhancing Energy Efficiency and Reliability in Floating LNG Operation: A Hydrofluoroolefin-Based SMR Cycle with Thermo-Economic Assessment and Uncertainty Analysis

Natural gas liquefaction is the most energy-intensive technique in floating liquefied natural gas (FLNG) operations. Hence, a hydrofluoroolefin-based single mixed refrigerant (SMR) technology was proposed to achieve energy-efficient and eco-friendly operations. The study was perfomed to enhance the SMR process by substituting expansion valves with hydraulic turbines to improve process reversibility and enhance energy efficiency. The proposed process was optimized using a sine–cosine concept-based algorithm that tuned the design variables which yielded an overall compression energy consumption of 0.2501 (kWh/kg-LNG), resulting in a 21.43% saving as compared to the conventionally used mixed refrigerant-based process. This resulted in a reduction of about 38.81% in overall exergy destruction. The economic analysis results draw curtains that the process saves about 26.02% of total annualized cost as compared to conventional study. Owing to the appropriate mixed refrigerant component mixture ratio and process design improvement. To determine the process reliability under uncertain conditions the optimal compression power and minimum approach temperature were determined. Further, uncertainty analysis reveals that the methane and butane refrigerant flow rates along with evaporation, and condensation pressure, were among the most influential parameters that influence the process most that may affect the whole operation in uncertain process inlet conditions. In summary, our approach presents immense promise for achieving energy efficiency, environmental responsibility, and economic viability in FLNG operations, offering a robust solution for the challenges of offshore plants.

Experimental and simulation study on R134a/RE170/R152a mixture as R134a replacement in a moderately-high temperature heat pump

A novel ternary mixed refrigerant was proposed in this study, and its optimal ratio was determined. The newly proposed refrigerant was termed RDR-a. Experiments were performed to compare the system performance of RDR-a and R134a for applications in the moderately high-temperature heat pump (MHTHP) system. As indicated by the results of this study, RDR-a achieved a lower cost, and it exhibited the capability of applying to the system of R134a directly. Besides, RDR-a achieved a GWP of 61.79% lower than R134a. Moreover, the coefficient of performance (COP) of RDR-a and R134a was elevated by 0.071/℃ and 0.037/℃, respectively, with the inlet temperature of chilled water. Moreover, the COP of RDR-a and R134a declined by 0.09/℃ and 0.037/℃, respectively, with the outlet temperature of cooling water. The COP of RDR-a and R134a tended to be first increased and then decreased with the rise of the charge amount, and RDR-a achieved an optimal charge amount that only accounted for 80.95% of that of R134a. Furthermore, RDR-a achieved a COP of 4.94%, 10.01% and 20.52% higher than that of R134a, respectively, as the inlet temperature of chilled water, the outlet temperature of cooling water and the charge amount of the refrigerant varied. The heating capacity of RDR-a was examined to be 13.61%, 19.14%, and 29.47% higher than that of R134a, respectively.

Evaluation of flammability characteristics of mixed refrigerants R134a/R1270, R134a/R170, and R170/R1270

Hydrocarbons (HCs) are considered promising alternative refrigerants due to their excellent thermodynamics, transport properties, and environmental friendliness. However, hydrocarbons are flammable. Conversely, R134a is a widely used non-flammable refrigerant but was listed in the Montreal Protocol-Kigali Amendment due to its relatively high global warming potential (GWP). Therefore, in order to reduce the GWP of R134a and inhibit the flammability of hydrocarbon refrigerants, this study investigated the flammability characteristics of mixed refrigerants R134a/R1270, R134a/R170, and R170/R1270. The flammability limits of different concentrations of R170/R1270, R134a/R1270, and R134a/R170 were measured under standard conditions, and the inhibition mechanism of R134a was briefly analyzed. Additionally, the flammability limits of R170/R1270, R134a/R1270, and R134a/R170 were predicted using the polynomial fitting method. Subsequently, the flame propagation speed and the flame color of R1270 and R170, with and without R134a, were compared and analyzed. Furthermore, the cycle performance of R134a/HCs was calculated. The research results are expected to provide guidance for the safe and effective utilization of R1270, R170, and their mixtures in refrigeration systems.

Optimization researches on the cooling-down process of the linde-hampson refrigeration system for a high-low temperature test chamber

This paper focus on the cooling-down performance of the LHRS for a high-low temperature test chamber, and proposed a new method to optimize the cooling-down process of the LHRS based on a quasi-steady-state simulation model to investigated the optimal MR concentration and the shifting strategy of suction pressure during the cooling-down process. Targeted on the maximum cooling capacity, the optimal suction pressure-evaporating temperature curve at a specified mixed refrigerant concentration can be obtained, which can be matched by the sectional suction pressure adjustment in the practical cooling-down process to reduce the overall cooling-down time. As an example, the fastest overall cooling-down time is achieved using the R50/R1150/R290/R600a mixed refrigerant (0.3/0.4/0.05/0.25 b y mole) and corresponding shifting parameters (including two shifting temperatures and three shifting pressures) for the sectional suction pressure adjustment, when the air temperature in the test chamber is dropped from 20 °C to −80 °C. The investigation results can provide good references for the industrial design of a high-low temperature test chamber. The optimization method used in this paper can also provide references for researches on cooling-down processes of other refrigeration systems using multi-component mixed refrigerants.

Development and modification of large-scale hydrogen liquefaction process empowered by LNG cold energy: A feasibility study

Hydrogen (H2) is considered a promising fuel and an energy carrier for carbon neutrality, but H2 has an issue in transportation and storage due to its low volumetric density. H2 liquefaction is an important technology in H2 supply that can overcome the low density issues, but the system has a serious challenge of high energy consumption. Thus, an improved energy efficient 50 ton day−1 of H2 liquefaction system comprising 4 mixed refrigeration cycles is proposed in this study. Especially, liquefied natural gas (LNG) was mainly used in the replacement of the precooling cycle, and the energy was saved by using the cold energy of LNG and generating electricity through vaporization. The specific energy consumption (SEC) of the proposed system was obtained as 3.996 kWh kg−1, however, particle swarm optimization (PSO) was implemented to increase energy efficiency of proposed process. As a result, the SEC of the optimized process was reduced to 2.917 kWh kg−1 where the LNG-cold energy control during the optimization was crucial to improve the energy efficiency. In addition, the economic and environmental feasibility were investigated. For the optimized process, the cost of the liquefied H2 (LH2) model was calculated as 1.37 $ kg-1, and 1.14 kgCO2 kg−1LH2 emissions were recorded as a result of environmental assessment. Moreover, the uncertainty analysis was implemented to assess the degree of the cost variance and the possibility of H2 production from water electrolysis was quantified. Unfortunately, electrolysis-based LH2 was hard to be economically better than steam methane reforming-based H2, however, alkaline water electrolysis-based LH2 showed the potential to overcome that of steam methane reforming in the future through technological advancement and reduction in production cost. The proposed H2 liquefaction process has a highly improved energy consumption rate, and this process can contribute to developing the H2 economy and become the potential candidate to overcome storage and transportation issues.

Performance comparison of pure, binary and ternary refrigerants considering different systems

Mixed refrigerants are widely used in heat pumps; thus, it is necessary to analyze the performance advantages of pure, binary and ternary refrigerants. In this paper, 14 kinds of pure refrigerants were selected, and 24,024 kinds of pure, binary and ternary refrigerants were obtained and analyzed. The refrigerant performance in terms of the COP and volumetric heating capacity were compared in normal, vapor injection with internal heat exchanger and with flash tank systems. In this paper, 40 °C was used as the temperature lift, and four cases with heating production temperatures of 70, 80, 90 and 100°C were analyzed. The Pareto fronts for the different refrigerant types and compositions were obtained by using exhaustive method. The COP and volumetric heating capacity exhibited contradictory trends in all cases. The results showed that mixed refrigerants had significant advantages over pure refrigerants in achieving the Pareto fronts. However, in all cases, when the COP was higher than 5, the binary refrigerants had similar advantages to ternary refrigerants; thus, ternary refrigerants were not necessary. When the COP was lower than 5, it was difficult to further increase the volumetric heating capacity by sacrificing the COP.

Performance Analysis of Using Hydrocarbon Mixed Refrigerant R32-R290 as an Alternative to R410A in Reducing the GWP Value of Household Split Air Conditioners

An experiment conducted on the mixed refrigerant R32-R290, which is used in household air conditioners, is aimed at reducing the global warming potential and improving the environmental CO2 quality. This mixed refrigerant has a lower GWP and density than the refrigerant R410A. This research was conducted to determine the effect of the increased mass charge of R290 as a mixed refrigerant on the performance of split air conditioner. Three percentage compositions of 20%/80%, 25%/75%, and 30%/70% were applied as a change to R410A in household air conditioners. For the testing equipment condition, the air inlet evaporator and condenser temperatures were 17°C (300 K) and 35°C (308 K), respectively. In the first performance test, refrigerant mass charge of 100% (340 g) was employed. In the second test, mass charge of 40% (136 g), 50% (170 g), and 60% (204 g) were utilized for mixed refrigerant R32-R290. Compared to the performance of R410A, the experimental results for the mixed refrigerant indicated a 0.5% increase in the air outlet evaporator temperature, a 1% decrease in the air condenser outlet, a 29.7% increase in the average COP, a 12.9% decrease in the electrical power consumption from 545.12 W to 474.7 W, a 9.1% increase in the average exergy destruction average from 401.5 W to 441.6 W, and a 19.7% increase in the average exergy efficiency from 24.2 W to 30.1 W.

Extractive distillation process using organic and ionic liquids for the separation of high-GWP refrigerant R410A: A thermodynamic and techno-economic assessment

Reclamation of mixed refrigerants can effectively reduce high global warming potential (GWP) fluorinated gases (F-gases) emissions. Two organic liquids (OLs), Dimethylformamide (DMF) and N, N-Dimethylacetamide (DMAC), were proposed to explore the possibility of separating high GWP and near-azeotropic mixture R410A (50 wt% R32 (difluoromethane) + 50 wt% R125 (pentafluoroethane)) by absorption. Solubilities of R125 in DMF and DMAC were measured from 283.15 to 333.15 K and well correlated with the five-parameter non-random two-liquid (NRTL) activity coefficient model. Ideal selectivity for R32 + R125 of DMAC were higher than that of DMF. Five ionic liquids (ILs) and DMAC on the Pareto front showed good overall performance (integration of capacity and selectivity) for separating R410A, and in the area below the Pareto front, the overall performances of the other solvents were not as good as those from the Pareto front. Subsequently, based on DMAC, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][Tf2N]) and 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]), the extractive distillation processes for R410A separation were simulated and evaluated in Aspen Plus. Results showed DMAC was a suitable choice of extractant nowadays due to the lower viscosity and consumption than ILs and the mature corresponding R410A separation process. ILs may be the mainstream extractant for R410A separation in the future, once the price of some ILs such as [BMIM][PF6] can be reduced to $30/kg, the separation process using ILs as extractants will cost less than that of DMAC. Heat pump technology can be further applied for energy integration in the corresponding process of ILs with high ideal selectivity such as [EMIM][SCN]. Thermodynamic and economic analysis of OLs and ILs could provide the key information for the separation of commercial refrigerant R410A, which can also be used as a benchmark to screen more efficient extractants.

Compositions optimization method based on the effective refrigeration effect for Mixed-refrigerant Joule-Thomson refrigerators cooling distributed-temperature heat loads

Mixed-refrigerant Joule-Thomson refrigeration (MJTR) is the dominant technology for cooling distributed-temperature heat loads, such as natural gas liquefaction. The mixed refrigerant determines the refrigeration cycle's performance (cooling temperature and efficiency, etc.). However, the current mathematical methods for mixed refrigerants’ optimization are time-consuming. In this paper, a mixed refrigerant optimization method based on the effective refrigeration effect is proposed. The equivalent enthalpy (EH˙) of temperature difference is proposed to predict the temperature difference distribution in the recuperator without cycle simulation. The optimization objective is to optimizeEH˙much closer to zero. In each step, only one component is adjusted, which is determined through its’ effective refrigeration effect, i.e., the partial molar enthalpy difference, in the optimization process. This method is applied to natural gas liquefaction (LNG), nitrogen liquefaction (LN2) and Cryo-compressed hydrogen storage (CcH2) systems. The exergy efficiencies in LNG, LN2 and CcH2 systems are 0.462, 0.390 and 0.421, which increase about 23.9%, 22.4% and 23.5% compared to references, respectively. The optimization time is less than 10 min per case in this study. This method can optimize mixed refrigerants in MJTR cooling various distributed-temperature heat loads.

Experimental investigation of the using graphene oxide and titanium dioxide nanolubricant for a refrigeration system operated by mixed refrigerant

Experimental investigation of the using graphene oxide and titanium dioxide nanolubricant for a refrigeration system operated by mixed refrigerant

Theoretical and experimental study on the selection of pure and mixed refrigerants for a power-cooling system driven by ultra-low-grade heat

This study theoretically and experimentally evaluates the performance of a system that combines an organic Rankine cycle (ORC) and a vapor compression cycle (VCC) driven by ultra-low-grade heat (ULGH). A systematic method is developed for the selection of pure refrigerants for the efficient performance of ORC over a temperature range between 50°C to 100°C. Binary and ternary mixtures are developed followed by sensitivity analyses and composition optimization to determine the optimal performance of these mixtures. Several experimental tests are conducted to ensure the operability of the system with the developed refrigerants. The results show that the use of ternary and binary mixtures enhances the performance of the system with lower GWP and ODP compared to pure refrigerants. Several mixtures are developed with energy efficiencies higher than 9% at a heat source temperature of 75°C. A mixture of R142b/R152a/R600 improves the energy efficiency of the system by 22.80%, reduces the back work ratio by 19.40% with an increase in the evaporation capacity by 13.25%. The methodology and results presented herein will be useful in the development, design, and optimization of power and cooling systems driven by ULGH with pure and mixed refrigerants.

Thermodynamic advantages of flash intercooling in natural gas liquefaction’s precooling cycle

This paper evaluates flash intercooling (FIC) in the precooling cycle to enhance the liquefaction process efficiency. Utilizing FIC reduces the precooling refrigerant temperature at the compressors inlet from a superheated to saturated vapor state. Both propane and ammonia are examined as precooling refrigerants. Energy and exergy analyses are adopted to evaluate the propane pre-cooled mixed refrigerant (C3MR) and the ammonia pre-cooled mixed refrigerant (NH3MR) process efficiency of eight case studies at two different ambient temperatures of 25 °C and 40 °C. The liquefaction process was modeled to minimize the specific energy consumption (SEC) and determine optimal operating pressure for compressors. The results obtained using FIC show that at the nominal ambient temperature of 25 °C, the SEC of C3MR and NH3MR is reduced by 12.6% and 4.0%, respectively. On a hotter day with an ambient temperature of 40 °C, the FIC enhances the process efficiency at a greater rate in which the NH3MR process SEC reduces by 5.7%, while C3MR process SEC reduces by 5.0%. Moreover, the findings from the exergy analysis reveal that compressors and heat exchangers are two major contributors to exergy destruction which are responsible for 76% of the cycle exergy destruction. Moreover, employing FIC shows that the largest impact in exergy destruction saving occurs for the C3MR at 25 °C by reducing the exergy destruction by 19%, in which combination of compressors and heat exchangers exergy destruction reduces by 121 kJ/kg.LNG.

Condensation heat transfer and correlation analysis in helical tube of mixed carbon-hydro refrigerant

The heat transfer coefficient of the mixed carbon-hydrogen refrigerant (hmix) in a helically tube has been confirmed as the core parameter related to natural gas liquefaction. Moreover, an experimental system of the two-phase flow in the helical pipe was designed, and a simulation model was built to analyze the changing law of hmix. The effects of operating parameters (operating pressure (2–4 MP), mass flux (200–600 kg/(m2·s), and vapor quality (0–1)) and structural parameters (spiral diameter (1–3 m), helix angle (4–14°), and inner diameter (8–12 mm)) on hmix of methane/ethane/propane in the spiral tube were examined. Subsequently, 11 heat transfer correlations were analyzed and then compared. As indicated by the comparison results, the correlations of Boyko were the most accurate among the above-mentioned correlations, laying a basis for this type of hmix. Furthermore, the mean absolute relative deviation and determination coefficient of Boyko's correlation were obtained as 20.30% and 0.48, respectively.

Optimization method for mixed refrigerants in Joule–Thomson refrigerators with fixed-temperature heat loads

Mixed-refrigerant Joule–Thomson refrigeration is a widely used and effective method for refrigeration in the temperature range of 80–230 K. The demand for cooling heat loads at fixed temperatures, such as biological storage and cryogenic treatment of materials, is significant. The mixed refrigerant determines the refrigeration temperature and capacity in many cases; therefore, optimizing the mixed refrigerant composition is essential. The current mathematical approach for optimizing mixed refrigerants is not well-defined, owing to the challenge of determining how to adjust the concentrations of the components in the optimization process. Therefore, the current approach may exhibit poor robustness or a longer optimization time. This study proposes an alternative optimization method based on the effective refrigeration effect. The method aims to overcome the challenges associated with complex algorithms typically used in optimizing mixed refrigerants. The maximum refrigeration capacity was achieved by optimizing the isothermal throttling effect in the full-temperature zone without cycle simulations. Only one component with a significant refrigeration effect was changed at each optimization step. The proposed method was applied to a cryogenic refrigerator at 120 K, achieving a higher coefficient of performance than a genetic algorithm and other references. The study determined that varying the initial concentrations of the refrigerant components changed the performance coefficient to less than 0.002, indicating good robustness of the proposed optimization approach. Thus, our proposal is reliable for optimizing the composition of mixed refrigerants and can be extended to all mixed-refrigerant Joule–Thomson refrigeration systems with fixed-temperature heat loads.