Mixed Refrigerant Research Articles

A simulation of R32 refrigerant mixing with R1270 to reduce GWP R410A on wall mounted air conditioning

Refrigerant R410A is a cooling barrier that is still widely used for air conditioning. This R410A contains the Fluoro element which can increase the value of GWP. In this research simulation, we used an AC unit using R410A with the aim of reducing GWP (Global Warming Potential) by mixing synthetic refrigerant with hydrocarbons. R410A still has content GWP: Mixing using R32 / R1270 refrigerant is predicted to reduce the GWP value because R1270 is one of the hydrocarbon refrigerants that has a GWP value of only: 3. By using Refprop software it can be simulated a mixture composition starting from 50/50, 40/60, 30/70, 20/80 and 10/90. From the results of the mixture simulation conducted, obtained a mixture approaching the characteristics of R410A, namely in the mixture: 20/80 with COP: 5.17 while R410A: 4.12. Compression ratio: R410A: 2.0 and for mixed refrigerants 20/80: 1.9. The refrigerant effect of mixed refrigerants is 20/80: 254,51, R410A: 162,77. Using this refrigerant mixture can reduce the GWP value and improve the performance of the AC cooling system. This refrigerant has considerable potential to replace the R410A.

Research on burning velocity of R152a and its binary mixture

The burning velocity plays an important role in determining the safety level of new refrigerants. Based on the self-designed test system for burning velocity characteristics of flammable refrigerants, the burning velocities of R152a with different concentration were studied by vertical glass tube method. And the maximum burning velocity of R152a was analyzed, which was close to the standard recommended value. R1234yf with environmental advantages and lower flammability may form a new alternative refrigerant mixture with R152a. Therefore, the flame propagation and burning velocity characteristics of R152a+R1234yf were studied under the conditions of different component ratio and different concentration. Based on the theoretical analysis, three calculation methods for predicting the burning velocity of binary mixed flammable refrigerant were proposed for the first time. Then, three groups of predicted burning velocity of R152a+R1234yf under different composition or concentrations were calculated. Compared with the experimental data, it was found that the prediction accuracy of the component equivalent simplified method is the highest among the three methods. It was of great significance for the prediction of burning velocity and the assessment of safety level of new mixed refrigerant or flammable gas.

Improvement of offshore adaptability of main cryogenic heat exchanger in FLNG dual mixed refrigerant liquefaction process

The dual mixed refrigerant liquefaction process and its key equipment applied in FLNG (floating liquefied natural gas) suffer performance deterioration due to the offshore conditions. In order to improve the offshore adaptability of FLNG dual mixed refrigerant liquefaction process, the experimental device of FLNG dual mixed refrigerant liquefaction process, the numerical simulation model and the visualization experimental device of falling film flow are developed. Multi-scale marine adaptability is studied from the aspects of the liquefaction process and its key equipment (meter scale) and liquid film thickness distribution (micron to millimeter scale). The results show that the effect of offshore conditions is more obvious on the spiral wound heat exchanger (SWHE) than the plate-fin heat exchanger (PFHE) of precooling circuit and the low temperature throttle valve of natural gas. It is recommended to use the corrugated tube with the diameter difference of 2 mm in the FLNG spiral wound heat exchanger to improve the offshore adaptability of dual mixed refrigerant liquefaction process.

Simulation of Mixing Synthetic with hydrocarbons Refrigerant to Reduce the Value of Global Warming Potential with Refprop Software

The problem of global warming or called GWP (Global Warming Potential) that occurs in the earth’s atmosphere, one of which comes from synthetic refrigerants used in household air-conditioning refrigeration machines. R410A is a refrigerant that still contains GWP: 1942. Hydrocarbon refrigerant is a refrigerant that does not contain ODP (Ozone Depleting Potential) and a very small GWP. By using ref prop software, the mixing process can be simulated to obtain refrigerants that have characteristics similar to R410A. Mixing using R32 / R290 ingredients varied with percentage compositions ranging from 50/50, 40/60, 30/70, 20/80, and 10/90. From the simulation results, a mixture approaching R410A with 10/90 composition with COP: 3.85 for R410A and 5.76 for 10/90 mixture was obtained. Compression ratio: R410A: 2.8 and for mixed refrigerants 10/90: 1.8. The refrigerant effect of mixed refrigerants is 10/90: 264,13, R410A: 161,68. By using this refrigerant mixture can reduce the GWP and improve the performance of the Air Conditioning cooling system so that it has a reduced GWP value that can be obtained significantly and has a large enough potential to replace the R410A.

Analysis of lower GWP and flammable alternative refrigerants

High global warming potential (GWP) refrigerants for refrigeration and heat pump systems or organic Rankine cycle systems are being phased out because of their impact on climate change, such as R134a, R410A and R404A. So it is urgent to find the refrigerants with excellent environmental protection performance. Firstly, nearly 40 alternative refrigerants, including pure refrigerants and mixed refrigerants, are classified according to their environmental and safety characteristics. Secondly, the performance parameters of some typical alternatives, such as refrigerating capacity, COP, safety and environmental protection, are comprehensively compared. It can be concluded that R513a and R466A have good comprehensive performance as alternative refrigerants of R134a and R410A respectively, while those alternatives to R404A have both advantages and disadvantages. The application and technical characteristics of R32, some typical HFOs, natural refrigerants and mixtures are summarized and analyzed. In addition, our group has carried out experimental and theoretical research on the flammability of low GWP and flammable refrigerants such as R1234yf, R161, R290, R600a and R1150, and found that hydrocarbons are more difficult to be inhibited than halogenated hydrocarbons. Finally, a new research idea on the risk of refrigerant explosion is put forward, which can cover the refrigerant leakage, combustion and risk aversion.

Thermodynamic performance of ammonia in liquefied natural gas precooling cycle

The selection of proper refrigerants for natural gas liquefaction processes play a key role in cycle?s efficiency. Mixed refrigerants have been proven to improve cycle?s exergy efficiency over single pure refrigerant. However, the future of some of these refrigerants with higher global warming potential index are unknown due to the continuous restriction being enforced by the energy and environmental agencies over the past few decades. This study examines the benefits and drawbacks of mixing ammonia, a refrigerant with zero global warming potential index and a high occupational safety characteristic, with lighter hydrocarbon refrigerants such as methane and ethane as a mixed refrigerant in a natural gas liquefaction?s precooling cycle. Results showed, presence of ammonia in mixed refrigerant not only saved in capital cost due to the smaller footprint of plant and smaller cold box, it also lowers the plants precooling operation expense by reducing the required compression power needed for the precooling cycle up to 16.2%. The results of exergy analyses showed that by reducing the molar concentration of more pollutant refrigerant methane and replacing it with ammonia enhanced the cycle?s efficiency by 4.3% and lowered the heat exchanger total exergy loss up to 47.9 kW.

Thermo-Economic Assessment and Uncertainty Quantification of Hydrofluoroolefin-Based Single Mixed Refrigerant Process for Natural Gas Liquefaction

Among Floating liquefied natural gas (FLNG) operations, natural gas liquefaction is the most energy intensive. Hence, to achieve energy-efficient and eco-friendly FLNG operations that can meet offshore environment requirements, a hydrofluoroolefin-based single mixed refrigerant (SMR) natural gas (NG) liquefaction process is proposed. The proposed process is optimized using a sine cosine paradigm to reduce the overall energy consumption. Then, the economic performance of the proposed process is performed and analyzed against that of the conventional LNG process. Finally, uncertainty quantification is performed to analyze the process outputs under the effects of uncertain key decision variables to guarantee operational reliability. The optimization yields an energy consumption of 0.2317 kW, resulting in a 41.73% energy saving compared to the conventional SMR process. Moreover, the total annualized cost is reduced to 26.02% owing to the appropriate mixed refrigerant selection and process design. The results of the uncertainty quantification analysis indicate that the flow rates of methane and butane, the evaporation pressure, and the condensation pressure are the most influential factors when processing energy consumption and utilizing the minimum internal temperature approach. This study highlights the importance of introducing eco-friendly refrigerants to replace conventional refrigerants used in NG liquefaction processes.

Experimental results and analysis of throttling refrigeration with ternary mixed refrigerant

In-depth analysis of the influence of mixed working fluids on the thermodynamic performance of a throttling refrigeration cycle through experimental research. After optimizing the calculation of two ternary mixed working fluids with different compositions, the charging test is carried out, and the throttle characteristic curve of the mixed working fluid the law of temperature and pressure changes in the experiment was analyzed. The results show that: a mixed working fluid with a mixing ratio of 30.39mol% R14, 10.73mol% R170 and 58.87mol% R600A, at a pressure ratio of 2.5/0.1, a low temperature of -67.7°C is obtained, and the cooling time is 113.42min. The refrigeration system COP is 0.076; the mixing ratio is 30.39mol%R14, 15.73mol%R23 and 53.87mol%R600A mixed working fluid, in the case of a pressure ratio of 2.14/0.1, a low temperature of -76.4°C is obtained, and the cooling time is 160min, the refrigeration system COP is 0.106.

Weed colonization‐based performance improvement opportunities in dual‐mixed refrigerant natural gas liquefaction process

AbstractDual‐mixed refrigerant (DMR) process is a promising candidate for liquefying the natural gas (LNG) at onshore as well as offshore sites, thanks to its higher liquefaction capacity and flexibility in using full gas turbines. DMR involves two mixed refrigerant cycles to perform precooling and subcooling of natural gas (NG), and these refrigerant compositions need constant tweaking to match the ever‐changing NG cooling curve, as it is obtained from different gas fields. Mismatching of cooling curves often results in suboptimal operation, which ultimately leads to an increase in the overall energy consumption. Thus, this study is aimed at making DMR liquefaction operation close to optimal using the invasive‐weed paradigm. At first, the decision variables for performance improvement were determined using degrees of freedom analysis then through invasive‐weed paradigm the best set of parameters that results in minimal overall energy consumption were obtained. For the given set of conditions, it was found that after optimization, the DMR process can produce LNG using 16.2% less compression power compared to the published optimized DMR process. Taking into account the higher sensitivity of the DMR process against NG feed conditions, the IWO approach was also examined to find the multiple optimal solutions corresponding to different sets of feed conditions. The thermodynamic evaluation revealed that the mixed refrigerant involves in NG subcooling and interstage coolers have the highest level of exergy destruction. After successful performance improvement of the DMR process, it is also found that still, 62% improvement potential (based on avoidable/unavoidable exergy destruction analysis) is available in the DMR process that can be attained through either sole optimization or optimal retrofitting/revamping.

Performance of wire finned coiled tube heat exchanger in a small J-T refrigerator

Non-azeotropic, mixed refrigerant of hydrocarbons nitrogen takes place in heat exchangers while boiling and condensation simultaneously at various cryogenic temperature and pressure. It is very difficult to design a heat exchanger in order to undergo boiling and condensation simultaneously. In the present paper, heat exchanger is designed numerically by applying the steady state conditions. Heat transfer coefficients are calculated numerically by applying homogenous model, which is developed by writing a computer programme. This model is validated with the experimental data. This study is carried out with three different refrigerant mixtures. Also, observed that a significant increase in percentage of heat transfer coefficient values in all the three mixtures considered in this study. It is found that 50% increase in tube side and 33% in shell side in the mixture 1 whereas in the mixture 2 it is 31% and 18% and similarly in the mixture 3 the increase is 40% in tube side and 20% in shell side. So the refrigerant with mixture 1 will perform better. Further the study is extended to heat exchanger with wire fin wound around the inner tube. It is observed that there is a significant improvement in heat transfer coefficient when wire fin is used.

Single mixed refrigerant LNG process: Investigation of improvement potential, operational optimization, and real potential for further improvements

The single mixed refrigerant (SMR) process is categorized as one of the most promising candidates for LNG-FPSO (floating production storage and offloading) projects as well as small-scale applications, owing to its simple and compact design. Nevertheless, high energy consumption is one of the major issues associated with the SMR processes. This study presents a systematic approach that includes identifying the improvement potentials in the existing SMR process, operational optimization of the system according to those potentials, and uncovering the real potential for further enhancements in the optimized process. To this end, the sources of irreversibilities are identified using an advanced exergy analysis in order to identify further potential of an improvement. The results reveal that 43% of the overall exergy destruction associated with the Base Case (Case I) of the SMR process can be avoided by either optimization or process retrofitting/revamping. Considering this improvement potential, the multivariate Coggins optimization (MCO) approach is applied and specific energy consumption value of 0.35 kWh/kg-NG is achieved leading to 18% energy savings with 77% overall exergy efficiency. The large difference between the exogenous and endogenous exergy destructions indicates that the interconnection between the process equipment is extremely weak, and that the performance of the equipment involved does not have a significant effect on the efficiency of the other equipment. Composite curves analysis is performed to analyze the performance of the LNG cryogenic heat exchanger before and after the application of the MCO approach. To determine economic feasibility and savings, economic analysis is executed that determine the 18% and 16.4% savings for operating cost and total annualized cost, respectively.

Simulation study of deep eutectic solvent-based biogas upgrading process integrated with single mixed refrigerant biomethane liquefaction

Deep eutectic solvents (DESs) comprise ChCl/urea, in combination with water, have been considered in removing acid gases (CO2 and H2S) from biogas. The evaluation of DES for biogas upgrading at relatively high pressure (i.e., >8.0 bar) has not been reported before. The aqueous DES performance has also not been analyzed compared to conventional amines-based solvent (MEA) and ionic liquid (IL). To the best of our knowledge, this is the first study that presents the integration of DES-based biogas upgrading with a mixed refrigerant liquefaction process to facilitate the safe and economical transportation of biomethane over long distances. The biogas considered in this study consisted of 60% CH4, 39% CO2, and 1% H2S. The aqueous ChCl/urea (70 wt%) results in biomethane with ≥99.0 wt% purity and ≥97.0 wt% recovery. Then, this biomethane was liquefied with ≥90% liquefaction rate. Based on the results obtained herein, overall capital, operating, and total annualized cost savings of 2.8%, 25.82%, and 14.26% were achieved using the 70% DES-based integrated process in comparison with the MEA-based integrated process. Whereas 1.41%, 16.85%, and 8.71% capital, operating, and total annualized costs could be saved in comparison with the IL (i.e., [Bmim][PF6])-based integrated process. It could be deduced that the overall cost of the biomethane value chain can be reduced using the proposed approach.

Тепловые диаграммы для расчета циклов холодильных машин, работающих на смесевом хладагенте

The article represents the advantages and disadvantages of refrigeration machines operating on non-azeotropic refrigerant mixtures. There has been illustrated their specific feature in comparison with pure substances: they are non-isothermal during phase transitions. It can be effective when cooling or heating flows that significantly change the temperature, and ineffective when working with volumes, where it is necessary to maintain a constant temperature. In the first case there takes place a decrease in the internal irreversibility of heat transfer processes in evaporators and condensers; in the second case - an increase. When using mixed refrigerants, it is possible to simultaneously obtain several temperature levels in a single-stage machine at the same pressure in the evaporators, they can obtain low boiling points of the refrigerant without vacuum in the evaporator and regulate the refrigeration capacity of the machine by changing the composition of the mixture. The prospects of using mixtures of working bodies of refrigerating machines have been proved. The diagrams T-S, T-ξ, i-ξ are presented allowing to calculate the cycle of the machine, to determine its operating parameters and to calculate the technical and energy characteristics. The developed thermal diagrams make it possible to accurately examine the dynamics of the boiling and condensation processes of a binary mixture, show the change in the concentration of the mixture in the vapor and liquid phases and make it possible to construct and calculate the cycle of a refrigeration machine operating on a mixed refrigerant. Examples of constructing cycles of two schemes of refrigeration machines operating on a mixed refrigerant are considered: with separation of the working substance flow and without separation. Methods for calculating the cycle are provided

Comprehensive comparison of small-scale natural gas liquefaction processes using brazed plate heat exchangers

The brazed plate heat exchanger (BPHE) has some advantages over the plate-fin heat exchanger (PFHE) when used in natural gas liquefaction processes, such as the convenient installation and transportation, as well as the high tolerance of carbon dioxide (CO2) impurities. However, the BPHEs with only two channels cannot be applied directly in the conventional liquefaction processes which are designed for multi-stream heat exchangers. Therefore, the liquefaction processes using BPHEs are different from the conventional PFHE processes. In this paper, four different liquefaction processes using BPHEs are optimized and comprehensively compared under respective optimal conditions. The processes are compared with respect to energy consumption, economic performance, and robustness. The genetic algorithm (GA) is applied as the optimization method and the total revenue requirement (TRR) method is adopted in the economic analysis. The results show that the modified single mixed refrigerant (MSMR) process with part of the refrigerant flowing back to the compressor at low temperatures has the lowest specific energy consumption but the worst robustness of the four processes. The MSMR with fully utilization of cold capacity of the refrigerant shows a satisfying robustness and the best economic performance. The research in this paper is helpful for the application of BPHEs in natural gas liquefaction processes.

Liquefied natural gas supply chain using liquid air as a cold carrier: Novel method for energy recovery

A novel concept for energy integration across the liquefied natural gas (LNG) supply chain is proposed by using liquid air as a medium for recycling cold energy. This allows the natural gas liquefaction and LNG regasification stages to be integrated despite the long distance between the two sites. LNG carrier ship is used to convey liquid air on its return journey when it would otherwise be empty. On its return to the liquefaction site, the cold energy stored in the liquid air can then be harnessed to liquefy natural gas for transportation. At the regasification site, LNG cold energy is used to regenerate liquid air for the ship’s return journey. In this way, LNG cold energy, which is generally wasted, is used in the proposed LNG supply chain. As a result, the energy requirement for liquefying natural gas can be reduced significantly, and the waste LNG cold energy recovered. The proposed mixed refrigerant with liquid air (MRLA) process design has an energy requirement of 865.82–917.20 kJ/kg-LNG, which is 26.1–30.2% lower than that for a single mixed refrigerant (SMR) process. The proposed process exhibits even lower energy requirements with a much lower capital cost when compared to the propane precooled mixed refrigerant (C3MR) process (974.0–992.0 kJ/kg-LNG), known as one of the most efficient natural gas liquefaction processes. The results of exergy analysis for the proposed processes show that the cold energy supply from liquid air achieves a reduction in the energy requirement. Furthermore, a techno-economic study reveals that an 18.6–22.6% reduction in total costs for LNG liquefaction can be achieved and economically attractive to be implemented in commercial natural gas liquefaction plants, given the minimal infrastructural changes necessary. Overall using this novel approach, the liquefaction and regasification stages are integrated despite the physical separation of the individual processes over long distances. This significantly enhances the LNG supply chain by not only improving its energy performance but also contributes to the utilization of cold energy by using the empty LNG ship on the return journey.

Environment friendly refrigerant options for automobile air conditioners: a review

In this paper, the environment friendly refrigerant options suitable for automobile air conditioners are reviewed. Initially, the thermophysical, thermodynamic and chemical characteristics of the environment friendly refrigerant options are presented. Then, the reviews of research investigations reported on environment friendly refrigerant options (such as hydrofluorocarbons, hydrofluoroolefins, hydrocarbons, carbon dioxide, composite mixed refrigerants and nanorefrigerants) are presented. The limitations and further research needs with environment friendly refrigerant options are identified and listed. The paper concludes that the hydrocarbon refrigerants will dominate the automobile air conditioning sector due to their good thermodynamic, thermophysical and environmental properties. Secondary loop configurations are recommended for the use of hydrocarbon refrigerants to reduce the flammable risk. The carbon dioxide is identified as a good option for electrical vehicles operating at low ambient conditions. The hydrofluoroolefins have short atmospheric life and get decomposed in the atmosphere and form tri-fluoro-acetic acid, which is harmful to the aquatic environment. Hence, hydro-fluoro-olefins are identified as an interim option. The outcome of this review is more helpful to the manufacturers and researchers working in the field of automobile air conditioners.

Design and analysis of dual mixed refrigerant processes for high-ethane content natural gas liquefaction

Recovery and purification of ethane has a significant impact on economic benefit improvement of the high-ethane content natural gas. However, current LNG-NGL integrated processes mainly focus on conventional natural gas, which are not applicable to natural gas with high ethane content. To fill this gap, three dual mixed refrigerant processes are proposed for simulation study of high-ethane content natural gas liquefaction. The proposed processes are optimized by a combination method of sequence optimization and genetic algorithm. Comparatively analysis is conducted to evaluate the three processes from the energetic and exergetic points of view. The results show that the power consumption of Process 3 which compressing natural gas after distillation is the lowest. For safety or other considerations, some common compositions of the mixed refrigerant may need to be removed under certain circumstances. Considering this, case studies of mixed refrigerant involving six composition combinations are carried out to investigate the effects of refrigerant selection on the process performance.

Energy saving research of natural gas liquefaction plant based on waste heat utilization of gas turbine exhaust

In this study, a series of novel natural gas liquefaction systems integrated with waste heat utilization of gas turbine exhaust are proposed to reduce the energy consumption of the liquefaction plants. The most widely used propane precooled mixed refrigerant (C3MR) and cascade natural gas liquefaction processes, are integrated with the waste heat utilization methods of adsorption refrigeration and organic Rankle cycle (ORC). The integrated systems are simulated and optimized with HYSYS software and genetic algorithm. The results show that, with ammonia water absorption refrigeration, the power consumption of C3MR process and cascade process is reduced by 16.23% and 14.62%, respectively, and the waste heat utilization exergy efficiency of the two integrated processes reaches 56.96% and 48.73%, respectively; With ORC, the power consumption is reduced by 20.59%, and the waste heat utilization exergy efficiency reaches 75.61%. In addition, for a liquefaction plant with an annual processing capacity of about 1.4 million tons, the waste heat utilization achieves CO2 emission reduction of about 4000–6000 t/a.

Constructal design of a shell-and-tube condenser with ammonia-water working fluid

A shell-and-tube condenser with ammonia-water as the working fluid is studied in this paper. Based on constructal theory, constructal design of the condenser is conducted. A complex function (CF) formed by entropy generation rate (EGR) and total pumping power (TPP) is minimized, and the tube diameter is optimized. The parameter influences on the optimal results are researched. The result reveals that the EGR, TPP and CF are respectively diminished by 0.92%, 20.60% and 1.18% in the comparative calculation example. Therefore, the CF reflects a trade-off between EGR and TPP. The gained results have certain guiding significances for the condenser designs with mixed refrigerants.

Investigation of the Efficiency of Autocascade and Cascade Heat Pumps in Cold Climate

The efficiency of an autocascade heat pump at low ambient temperatures in comparison with a cascade heat pump is investigated. The operation principle of an autocascade heat pump is based on the zeotropic property of mixed refrigerants, the components of which have different boiling points. A mixture of R32/R134a/R365mfc refrigerants was selected as a working fluid for the autocascade heat pump. R410a and R134a were selected as refrigerants for the cascade cycle. The simulation of heat pump cycles was carried out and graphs of the dependence of the coefficient of performance on the ambient temperature were plotted. It is shown that at ambient temperatures below – 20°С the autocascade heat pump is more efficient than a cascade heat pump. At ambient temperatures below – 35°C, the coefficient of performance of the autocascade heat pump is more than 7% higher than the coefficient of performance of the cascade heat pump.