Mixed Refrigerant Research Articles

Design and optimization of large-scale natural gas liquefaction process based on triple refrigeration cycles

In large-scale natural gas liquefaction, minimizing specific energy consumption has consistently been a primary objective. This study aims to develop a large-scale natural gas liquefaction process that balances energy efficiency and cost-effectiveness, presenting a viable option for industrial production. By employing a refrigerant strategy of “propane + mixed refrigerant + mixed refrigerant”, a novel large-scale natural gas liquefaction process based on triple refrigeration cycles (TRC) is proposed. To address the challenge of boil-off gas (BOG) re-liquefaction, the TRC process is further refined to integrate BOG re-liquefaction (TRC-BR). Thermodynamic models are built for the proposed TRC and TRC-BR processes, as well as the propane pre-cooled mixed refrigerant (C3MR) and AP-X processes as baseline cases. Global optimization is conducted using the Particle Swarm Optimization (PSO) algorithm, with the specific power consumption (SPC) serves as the objective function. The results reveal that the SPC of the TRC and TRC-BR processes are 0.2726 and 0.2704 kWh/kg-LNG respectively. Compared with the C3MR and AP-X processes, the SPC of the TRC decrease by 1.54% and 4.84%, respectively. The total investments for the TRC and TRC-BR processes are estimated at a similar level compared to the baseline cases, demonstrating their significant potential for industrial application.

Advanced Dual Mixed Refrigerant (DMR) Natural Gas Liquefaction Plant with Liquid Air: Focus on Configuration and Optimization

This study introduces a novel approach to integrating LNG cold energy into the dual mixed refrigerant (DMR) process, employing liquid air as a cold energy carrier. The DMR process is chosen for natural gas liquefaction due to its flexibility in adjusting mixed refrigerant compositions when external cold sources are utilized. Two configurations are investigated: the low-pressure liquid air (LPLA) process, which relies solely on heat exchange, and the high-pressure liquid air (HPLA) process, which involves the pressurization and expansion of liquid air. Additionally, two optimization strategies are explored: 'With Composition' (WC) optimization, which includes refrigerant composition as a variable, and 'Without Composition' (WOC) optimization, which does not. Utilizing liquid air reduces the load on the refrigeration cycle, leading to improved performance compared to the conventional DMR process. The air expansion generates additional power and cold energy, while WC optimization further reduces the flow rate of low-boiling-point components, significantly lowering compression energy consumption. As a result, the DMR-HPLA-WC process achieves a 44.17% reduction in energy consumption, an 8.7% improvement in exergy efficiency, and a 37.63% decrease in specific costs.

Optimization of BOG Reliquefaction Process of Carbon Dioxide Considering Nitrogen Content

<i>As the importance of carbon capture and storage (CCS) technology increases for greenhouse gas reduction, CO<sub>2</sub> transportation technology is also becoming crucial. Efficiently handling boil-off gas (BOG) generated during voyages is particularly important. This paper proposes a process incorporating two-stage separation and mixed refrigerants to reliquefy CO<sub>2</sub> BOG containing nitrogen efficiently. This process was optimized based on specific power consumption (SPC) criteria and compared with the conventional single-stage separation using an ammonia refrigerant. The two-stage separation allows the removal of non-condensable gases, such as nitrogen, before expansion, and the use of mixed refrigerants enables more efficient heat exchange than ammonia refrigerants, improving the reliquefaction rate. As a result, the proposed process reduced SPC by up to 8.8 % with a nitrogen content of 5 mol% and up to 74.7 % with a nitrogen content of 15 mol%. In addition, the proposed process achieved a reliquefaction rate of over 74.2 % across all nitrogen content ranges of 5–15 mol%.</i>

Enhancing Semiconductor Chiller Performance: Investigating the Performance Characteristics of Ultra-Low-Temperature Chillers Applying a Liquid Receiver

This study investigates the implementation of a cryogenic chiller utilizing a mixed-refrigerant cascade refrigeration cycle (MRCRC). In this setup, R-404A is employed in the high-temperature circuit (HTC), while a mixture of refrigerants is utilized in the low-temperature circuit (LTC). Unlike a conventional MRCRC that operates without a receiver to maintain the composition ratio, this research explores the impact of receiver installation on system performance. Experiments were conducted with and without a receiver to assess performance improvements and device behavior. With a fixed refrigerant charge of 4 kg, the suction and discharge pressures of the LTC compressor remained low and stable after the receiver’s installation. The addition of a receiver significantly reduced the cooling time, with further reductions observed as the refrigerant charge increased. The system achieved evaporative heat capacities of 0.59, 1.76, and 2 kW for refrigerant charges of 4, 7, and 9 kg, respectively. Notably, at the maximum refrigerant charge of 11 kg, the evaporative heat capacity peaked at 3.3 kW. These findings indicate that incorporating a receiver is crucial for enhancing the cooling performance of cryogenic coolers using mixed refrigerants and stabilizing device operation. This contrasts with previous studies that omitted receivers due to concerns over potential alterations in the composition ratio of the mixed refrigerant.

Proposals for Next-Generation Eco-Friendly Non-Flammable Refrigerants for a −100 °C Semiconductor Etching Chiller Based on 4E (Energy, Exergy, Environmental, and Exergoeconomic) Analysis

Recent advancements in cryogenic etching, characterized by high aspect ratios and etching rates, address the growing demand for enhanced performance and reduced power consumption in electronics. To precisely maintain the temperature under high loads, the cascade mixed-refrigerant cycle (CMRC) is predominantly used. However, most refrigerants currently used in semiconductor cryogenic etching have high global warming potential (GWP). This study introduces a −100 °C chiller using a mixed refrigerant (MR) with a GWP of 150 or less, aiming to comply with stricter environmental standards and contribute to environmental preservation. The optimal configuration for the CMRC was determined based on a previously established methodology for selecting the best MR configuration. Comprehensive analyses—energy, exergy, environmental, and exergoeconomic—were conducted on the data obtained using Matlab simulations to evaluate the feasibility of replacing conventional refrigerants. The results reveal that using eco-friendly MRs increases the coefficient of performance by 52%, enabling a reduction in compressor size due to significantly decreased discharge volumes. The exergy analysis indicated a 16.41% improvement in efficiency and a substantial decrease in exergy destruction. The environmental analysis demonstrated that eco-friendly MRs could reduce carbon emissions by 60%. Economically, the evaporator and condenser accounted for over 70% of the total exergy costs in all cases, with a 52.44% reduction in exergy costs when using eco-friendly MRs. This study highlights the potential for eco-friendly refrigerants to be integrated into semiconductor cryogenic etching processes, responding effectively to environmental regulations in the cryogenic sector.

Experimental investigation on flow boiling heat transfer of R290, R600a and their mixtures in a horizontal minichannel

The flow boiling heat transfer characteristics of R290, R600a and their mixtures were experimentally investigated in a horizontal minichannel with an inner diameter of 1.54 mm. In order to investigate the effects of mass flux and vapor quality, heat flux, saturation temperature, and component concentration on the flow boiling heat transfer coefficients, experiments were conducted with mass fluxes ranging from 200 to 400 kg/(m2·s), heat fluxes ranging from 20 to 30 kW/m2, saturation temperatures of 22 °C, 24 °C, and 26 °C, vapor qualities ranging from 0 to 1, and mass ratios of 70/30, 50/50, and 30/70 for R290/R600a. The experimental results indicate that with the increase of vapor quality, the mass flux promotes the heat transfer coefficient more obviously, and the heat transfer coefficient tends to increase first and then decrease. The heat transfer coefficients of both pure and mixed refrigerants increase with increasing the heat flux. The effect of saturation temperature on the heat transfer coefficients of pure and mixed refrigerants is not significant in this study. In the low vapor quality region, the heat transfer coefficients of R290/R600a mixtures are between those of R290 and R600a. As vapor quality increases, the heat transfer coefficients of the mixtures increase more slowly than those of pure refrigerants. In addition, experimental data were compared with the predictions of the empirical correlations. Among all the correlations, the Tran et al. correlation predicts the heat transfer coefficients for R290 and R600a best. The Lim and Kim correlation gives the best predictions of the heat transfer coefficients for R290/R600a mixtures.

Thermodynamic performance analysis of the fractionation and flash separation auto-cascade refrigeration cycle using low GWP refrigerant

The auto-cascade refrigeration is a critical technical approach to achieve below −40 °C. The separation efficiency of mixed refrigerant is a main factor affecting the performance. Fractionation purifies low-boiling composition but reduces refrigerant flow rate within the evaporator, which may decline the performance. This paper proposes two novel cycles combining fractionation and flash separation. The novel configurations purify the composition and increase the mass flow rate of refrigerant within the evaporator. The thermodynamic analysis results indicate that the presented cycles outperform the fractionation cycle and the basic cycle in terms of energy and exergy efficiency. Under the design condition, the mass fraction of low-boiling composition in the fractionation-enhanced cycle and the fractionation-modified cycle increased by 4.21 % and 2.97 % compared to the basic cycle. The mass flow rate within the evaporator of novel cycles increased by 25.87 % and 34.78 %. The COP and exergy efficiency of the fractionation-enhanced cycle and the fractionation-modified cycle is 42.57 % and 45.44 %, 46.61 % and 55.15 % higher than those of the basic cycle. Generally, the combination of fractionation and flash separation addresses the issues of low composition separation efficiency in the basic cycle and low flow rate of the fractionation cycle, enhancing the performance of the auto-cascade cycle.

Optimizing the refrigerants in ultra-low temperature Semiconductor processing chiller with mixed Refrigerant

Mixed refrigerant (MR) Cascade Refrigeration Systems are widely employed in industries requiring both extremely low temperatures and large cooling capacity, such as semiconductors and displays. The composition of the MR has a significant impact on the performance of the cascade refrigeration systems, so optimizing the MR composition is essential. The current studies mainly focus on optimization that changes only the composition ratio with a limited number of refrigerants. Therefore, there may be a configuration and composition ratio that can improve the performance of the system more than existing methods. This study presents the need to find the optimal combination and number of MRs before determining the performance of MRs according to changes in composition. The proposed method selects five types of refrigerants that meet the conditions, then classifies cases according to the number of refrigerants in MR and analyzes the performance of each MR at various HTC evaporation temperatures based on energy and exergy through cycle simulation for each case. The proposed method showed COP up to 14.85 % higher than the conventional method, so it is expected to contribute to improving system performance by finding the optimal refrigerant combination and number before optimizing the composition of the MR.

Operation optimization of propane pre-cooled mixed refrigerant LNG Process: A novel integration of knowledge-based and constrained Bayesian optimization approaches

Liquefied natural gas (LNG) technology, particularly the propane precooled mixed refrigerant (C3MR) process, has demonstrated efficiency and emerged as a distinctive dual-refrigerant technology widely used in LNG production. However, the liquefaction process is the highest energy-intensive stage within its supply chain as it consumes about 8 % of the LNG energy content. Thus, for the first time, this study proposes systematic knowledge-based and constrained Bayesian optimization approaches to identify the optimal operation of the C3MR process. These approaches optimize both the operational parameters (pressures and flow rates) and the composition of the mixed refrigerant with practical equipment specifications and rigorous constraints. The results show that the specific energy consumption (SEC) is reduced to 0.264 kWh/kgLNG, which is 14.6 %, and 26 % lower than the basic C3MR process (unoptimized case) and typical industrial C3MR processes, respectively. In addition, the optimized SEC in this study is 14.5 % to 38.6 % lower than those reported in the literature. At large-scale LNG production (10,000 tons per day), the reduction in the SEC is translated into an 18 MW decrease in compression power, saving approximately 4.7 million $ per year for each C3MR train. Moreover, the coefficient of performance (COP) of the C3MR process was improved by about 15 %, and the CO2 emissions were reduced by 17 % (7 tons per year) compared to the basic C3MR process, indicating potential advancements in large-scale LNG liquefaction processes.

Experimental study on performance characteristics of a −70 °C ultra-low temperature medical freezer with mixed hydrocarbon refrigerant

It is well-known that the −70 °C ultra-low temperature freezers have been widely concerned for vaccine and biomedical products storage due to the outbreak of COVID-19. This paper carries out the experimental investigation on performance characteristics of a −70 °C ultra-low temperature medical freezer with single-stage Joule-Thomson refrigeration system by using binary hydrocarbon mixture R601a/R1150 and ternary mixture R601a/R290/R1150. The aim is to explore and verify hydrocarbon refrigerants that can achieve lower energy consumption, thereby providing a scientific basis for the optimization of ultra-low temperature medical freezers. The experimental results show that both R601a/R1150 and R601a/R290/R1150 with a charge of 250 g could achieve the refrigeration temperature below −70 °C in a 568 L large volume vertical freezer. Comparing binary with ternary refrigerants, it is found that the addition of medium-boiling component R290 is beneficial to reduce the daily energy consumption. When the mass fraction of R601a/R1150 is 0.70/0.30, the lowest daily energy consumption for −70 °C is 9.06 kW h·24 h−1. When the mass fraction of the R601a/R290/R1150 is 0.70/0.10/0.20, the daily energy consumption is 8.42 kW h·24 h−1, which is 7.06 % lower than that when using the R601a/R1150. This indicates that careful selection of refrigerant components and composition optimization can lead to substantial energy savings. Furthermore, it is also observed that among these three components, the low-boiling component R1150 has the most significant influence on the system pressures and operating power, followed by R601a and R290.

Integration of the single-effect mixed refrigerant cycle with liquified air energy storage and cold energy of LNG regasification: Energy, exergy, and efficiency prospectives

The escalating global energy demand has prompted increased focus on the industry of liquefied natural gas (LNG), emphasizing the need for optimizing liquefaction processes to minimize capital costs. Thus, the integration between liquified natural gas LNG regasification and liquid air energy storage (LAES) to produce electricity and utilize the cold energy of LNG regasification has several interests to maximize the benefits of the process to generate power and face the challenges such as energy saving and reducing the total operations costs … etc. Fortunately, this study introduces a novel approach that combines a single-effect mixed refrigerant (SMR) cycle with air liquefaction, incorporating regenerative Rankine cycles for enhanced efficiency. The effectiveness of the LNG-SMR-LAES process was evaluated using comprehensive energy, exergy, and economic analyses to ascertain its viability. The results showed a notable improvement in the overall net power energy by 6 % and an increase in exergy efficiency by 11.7 % compared to the base case. Energy savings of 31.6 % (470.10 kW) contributed to the process's environmental and economic feasibility. The net present value was estimated at 11,230.4 US dollars, affirming the industrial-feasible design and economic viability of the LNG-SMR-LAES process.

4E analysis for a novel cryogenic hydrogen liquefaction process using various refrigerants: Energy, exergy, economic, and environment

Hydrogen liquefaction process (HLP) is a principal technology to overcome energy storage and transportation problems and to meet the demand for an eco-friendly energy source. This study proposes three conceptual designs of HLPs with various refrigerant cycles. The specific energy consumption (SEC) of HLP could be reduced by various refrigerants. Three different refrigerants (liquid air (LA)), liquified natural gas (LNG), and mixed refrigerants (MR)) were compared to the conventional LN2-based HLP to verify 4E (efficiency, exergy, economics, and environmental) of each process based on their thermodynamic properties. From the results, we found that the process performance, economics, and environmental effects of the LNG-based hydrogen liquefaction process (LNG-HLP) were the best. In particular, the LNG-HLP, which uses the cold energy of LNG, required less refrigerant than LN2, thereby reducing the energy consumed by major compressors. It had an SEC of 11.04 KWh/kg-LH2 and capital, operating cost, and CO2 emissions of the LNG-HLP process were considerably lower by 5.5 %, 6.2 %, and 12.2 % (unit kg CO2eq/kg LH2), respectively, compared to the conventional process. To propose better economic or environmental scenarios to stakeholders and governments, in this study, the HLP and hydrogen production processes were expanded to include CO2 emission calculation and carried out analysis for levelized cost of hydrogen contribution rate to electricity production types by country.

Comparative energy and exergy analysis of ortho-para hydrogen and non-ortho-para hydrogen conversion in hydrogen liquefaction

This study reports the comparative energy and exergy analysis of ortho-para hydrogen and non-ortho-para hydrogen conversion in hydrogen liquefaction process. Two cases were simulated, case A – hydrogen liquefaction with ortho-parahydrogen conversion and case B – hydrogen liquefaction without ortho-parahydrogen conversion. This is the first study that presents a comparative energy and exergy analysis between such two cases. In this research, a hydrogen liquefaction process was designed adopting cascaded five-stage Brayton refrigeration cycle. The process was simulated in Aspen PLUS. The process used a mixed refrigerant (of liquefied natural gas) refrigeration cycle to precool the gaseous hydrogen feed from 26 °C temperature to −192 °C temperature, and mixed refrigerant (of nelium) was subsequently used to further deep-cool the the hydrogen stream from −192 °C temperature to −245.99 °C temperature in the cryogenic section of the process. Liquefaction was achieved by expanding the hydrogen through Joule-Thomson valve at −248.37 °C and 1 bar. The simulated results of the two cases showed the specific energy consumption of case A to be 8.45 kWhr/kgLH, and that of case B to be 15.65 kWhr/kgLH respectively. The results also indicated a total exergy efficiency of 92.42% in case A and 87.18% in case B. The research results showed that the hydrogen liquefaction designed with configuration of ortho-parahydrogen conversion has better performance indicators than the liquefaction without ortho-parahydrogen conversion. Therefore, hydrogen liquefaction with ortho-parahydrogen conversion can be considered in the design and development of new hydrogen liquefaction plants. Process optimization is recommended to further enhance the specific energy consumption and exergy efficiency of both processes.

Surrogate-assisted constrained hybrid particle swarm optimization algorithm for propane pre-cooled mixed refrigerant LNG process optimization

The propane pre-cooled mixed refrigerant (C3MR) process is one of the most widely used and efficient natural gas liquefaction processes. However, optimization of this process involves various design and operational constraints, complex thermodynamics, and hence nonconvex in nature. Therefore, it's computationally expensive, often involving trial and error approaches. Existing optimization algorithms often possess flaws such as insufficient accuracy and premature convergence, leading to suboptimal solutions that may violate essential process constraints. This article proposes a novel method to optimize the C3MR process that handles the computational complexity, meets the constraints, and achieves feasible solutions quickly. The proposed method includes modified feasibility-based constraint handling and radial basis function network-assisted surrogate modeling and optimization, where the power consumption is optimized using a hybrid of the particle swarm optimization (PSO) and social learning PSO algorithm. The proposed algorithm achieves the optimum power consumption (121109.31 kW), which is 21.5 % less than the base case (154200 kW). The optimization results are compared with similar optimization algorithms, where the proposed algorithm outperformed the other algorithm regarding optimal solution, convergence, and speed. The results from this study are compared to previous studies from the literature, which validate the accuracy and applicability of the proposed method.

Efficient enhancement of cryogenic processes: Extracting valuable insights with minimal effort

Cryogenic systems are widely used in industries but are known for their high energy consumption. Designing these systems involves numerous variables, objectives, and constraints. This study introduces an optimization approach applied to three cryogenic processes: Natural Gas Liquids (NGLs) recovery, Air Separation Unit (ASU), and propane mixed refrigerant (C3MR) liquefaction, focusing on minimizing energy input to enhance efficiency and LNG output in a mega LNG plant. Exergy analyses identified energy losses in compressors (47 %), columns (37 %), heat exchangers (10 %), and valves/mixers (5 %), highlighting the need for improved compressor design. Optimization showed that inefficiencies could be reduced by adding inter-cooled compression stages and isentropic/isothermal compression routes. The ASU optimization involved five independent variables with optimized conditions demanding 30 MW of compression power while achieving 51 % separation efficiency. Heat exchangers are the main source of exergy loss in the standalone C3MR cycle, accounting for 61.82 % of 69.0 MW followed by compressors ∼29.27 %. When simulated with utilities, total exergy loss increases to 249.0 MW, with compressors accounting for 78.34 %, exergy loss from heat exchangers drops to 17.94 %. Results affirm the practicality of the proposed method for optimizing complex cryogenic systems, providing valuable engineering insights and potential for significant energy savings.

Application of Refrigerant Cooling in a Battery Thermal Management System under High Temperature Conditions: A Review.

Battery thermal management (BTM) is crucial for the lifespan and safety of batteries. Refrigerant cooling is a novel cooling technique that is being used gradually. As the core fluid of refrigerant cooling, refrigerants need to possess excellent properties while meeting environmental requirements. This paper elucidates the current state of refrigerants (single refrigerants and mixed refrigerants), synchronously summarizing them from the perspectives of refrigerant properties and refrigerant cooling (immersion and cold plate indirect). It outlines the advantages and disadvantages of single and mixed refrigerants as well as the research and development in the vehicle thermal management system (TMS). The choice of refrigerant directly affects cooling performance, and research on vehicle air conditioning (AC) systems can indirectly guide the BTM. R1234yf and R152a can directly replace R134a, while although R744 has a strong heating capacity, it cannot directly replace R134a. Specific mixed refrigerants reduce the global warming potential (GWP) and flammability issues, thereby improving system efficiency. Additionally, immersion cooling controls the temperature through container pressure. Coordinated control strategies are crucial for indirect cold plate cooling, offering broad prospects for optimizing the cold plate design and intelligent control. The selection of refrigerant and the optimal design of the cooling method greatly improve the thermal performance of the battery. This may promote the good development of BTM.

High ethane content enables efficient CO2 capture from natural gas by cryogenic distillation

Cryogenic CO2 capture technique is superior to other CO2 capture methods in terms of potential environmental protection, because it uses no chemical solvent or membrane materials that need regular replacement. However, the freezing problem of CO2 makes it difficult to achieve CO2 capture through simple gas–liquid separation, and the existing cryogenic CO2 capture techniques often require a specially designed separation equipment. In addition, cryogenic CO2 capture is generally considered a method with high energy consumption due to the need for refrigeration. This study proposes a cryogenic distillation-based CO2 capture method for natural gas with high ethane content, such as shale gas and oilfield associated gas. This method utilizes the azeotropic characteristics of CO2 and ethane to avoid CO2 freeze-out and the energy consumption for CO2 capture is minimized through process integration with natural gas liquefaction and ethane recovery. The proposed system uses the propane precooled mixed refrigerant process to provide the required refrigeration, and it is simulated in Aspen HYSYS and optimized by a combined method of a genetic algorithm and sequential optimization. The results show that the proposed process can remove up to 17 mol% of CO2 to less than 50 ppm. With extractive distillation, 99.50 % of the ethane in the feed gas is recovered with a purity of 99.50 mol%. The optimal results corresponding to the maximum allowable CO2 content to avoid its freeze-out (with a solubility margin of 500 ppm) show that when ethane content is 2–20 mol%, the specific power consumption of the system is about 0.43 kWh/Nm3(NG) with an exergy efficiency higher than 50 %. The proposed process achieves energy-saving and efficient CO2 capture method for natural gas with high ethane content.

Design and analysis of steam methane reforming hydrogen liquefaction and waste heat recovery system based on liquefied natural gas cold energy

To improve the utilization rate of liquefied natural gas (LNG) cold energy, reduce hydrogen (H2) liquefaction cost, recover waste heat and reduce carbon dioxide (CO2) emission, this study designs a steam methane reforming (SMR) H2 liquefaction and waste heat recovery system based on LNG cold energy for the production of 10 tons of liquid hydrogen (LH2) per day. Parameters analyses and optimization, exergy analyses and economic analyses of the system are carried out and compared with other H2 liquefaction systems. The results show that: under the optimal conditions, the values of specific energy consumption (SEC), coefficient of performance (COP) and exergy efficiency (ƞex) were 5.93 kWh/kg LH2, 0.2225 and 53.24%, respectively. Exergy losses of system is mainly distributed in heat exchange equipment and compressors. Decreasing the heat exchange equipment cold and heat sources inlet temperature difference and reducing the compressors compression ratio were beneficial to reduce equipment exergy losses. The pre-cooling performance of LNG is better than that of liquid nitrogen (LN2) and mixed refrigerant (MR). Compared with the pre-cooling H2 liquefaction system without waste heat recovery, the SEC decreased by 0.26 kWh/kg LH2 and ƞex increased by 2.28%. Research results are conducive to resource conservation and environmental protection.

Sustainability evaluation of C3MR natural gas liquefaction process: Integrating life cycle analysis with Energy, Exergy, and economic aspects

In a transition towards a clean energy future, natural gas serves as an interim fuel due to its lower emissions whereas the C3MR (propane pre-cooled mixed refrigerant process) is widely recognized for high efficiency and commercial scale application converting natural gas to LNG. Previously, numerous studies have been conducted to optimize the energy efficiency and performance of C3MR process but very little contribution has been made towards its sustainability analysis. To address this, a life cycle analysis approach is established to evaluate the carbon footprint of C3MR process. In order to showcase its link with energy consumption and put forward the groundwork of analyses, the research focuses on using simulation – assisted optimization to reduce the specific energy consumption (SEC) of C3MR process by optimizing design variables. The study highlights the use of mixed refrigerant (MR) as a process variable and validates that its optimal implementation has decreased SEC to 0.2195 kWh/kg LNG, while achieving a minimum inlet temperature approach (MITA) of main cryogenic heat exchanger (MCHX), less than 3 °C. The knowledge − based optimization approach applied in this research, developed comparative case studies on which multiple analyses are performed to verify scientific findings. Energy and exergy analyses are conducted to determine thermal efficiency of the process where the optimized case exhibits a reduced difference in its composite curves and an 8.65 % improvement in exergetic performance compared to the base case. The economic indicators assessment reveals that optimized case demonstrates lower capital and operating costs, establishing economic viability. Furthermore, the energy consumption parameters are utilized for evaluation of ecological impact ofLNGsupply chain through life cycle assessment (LCA) which reflects reduced greenhouse gas (GHG) emissions for optimized case. Hence, the current study fills existing research knowledge gaps in terms of providing a comprehensive process system engineering by evaluating energy synergistic point, thermodynamic irreversibility, process viability and sustainability using life cycle assessment.

Design of nonflammable mixed refrigerants based on the partial molar enthalpy difference in mixed-refrigerant Joule-Thomson refrigerators with/no pre-cooling stage

Mixed-refrigerant Joule-Thomson refrigeration (MJTR) is an important cooling method at temperatures from 80 to 230 K. It can be used in cryosurgery, high-temperature superconductivity and sensor cooling etc. However, most of the studies are on nitrogen-hydrocarbon refrigerants, which are not allowed in applications where there is a special need to avoid flammability risks. Therefore, non-flammable mixed refrigerants were investigated in this study.The composition of the mixed refrigerant is a key factor in the system performance (refrigeration temperature, refrigeration capacity, etc). However, the purely mathematical optimization methods lack system knowledge in the optimization of the process, and may have the disadvantages of being a time-consuming process. In this study, the isothermal throttling effect of mixed refrigerants is optimized, and the optimization process is based on the partial molar enthalpy difference of each component. The method is based on thermodynamic properties and is time-saving relative to purely mathematical optimization techniques.Non-flammable mixed refrigerants (NFMR) with refrigeration temperatures from 100 K to 140 K were designed in this study. The results show that the designed mixed refrigerant has a higher COP compared to the reference. Argon has an advantage at refrigeration temperatures from 120 K to 140 K, while nitrogen has an advantage from 100 K to 120 K. In addition, mixed refrigerants for systems with pre-cooling stage were optimized and the results showed that the highest exergy efficiency is achieved at a pre-cooling temperature of 250 K. The exergy efficiencies with pre-cooling stage are nearly twice as high as those without that. Therefore, a pre-cooling stage for nonflammable mixed refrigerants is necessary where there is no requirement for system size.