Cryogenic Refrigeration System Research Articles

Hazard, risk, reliability assessment and improvement of Darlington Tritium Removal Facility (DTRF) cryogenic refrigeration system

Tritium is a radioactive isotope of hydrogen, produced in heavy water, during CANDU reactor operations by neutron absorption. The tritium removal facility at Darlington (DTRF) is used to extract tritium from the heavy water on a continuous basis and concentrates it in preparation for immobilization and storage. There are several internal and external hazards associated with the operation of DTRF, such as fires, onsite transportation accidents, exposure to radioactive materials, explosion due to Hydrogen (H2) and the release of radioactive substances from the Tritium Immobilization System. This paper conducts a risk analysis for the DTRF Cryogenic Refrigeration System, associated with both Low and High Tritium Distillation columns. This study includes hazard identification, consequence analysis and risk estimation. Fault Tree and Event Tree Analysis conducted, system reliability, availability and human reliability was considered. Consequently, methods for risk reduction and integration with improvement to CRS design is discussed.

Cryogenic system of the high performance 1.3 GHz 9-cell superconducting radio frequency prototype cryomodule

High quality factor 1.3 GHz 9-cell superconducting radio frequency (SRF) cavity cryomodule is the core technology of the international advanced accelerator. China’s first high-quality factor 1.3 GHz 9-cell SRF cavity cryomodule was developed, assembled and tested at the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences for the Dalian Advanced Light Source (DALS) and Circular Electron Positron Collider (CEPC) R&D. The 9-cell cavities in the cryomodule achieved a high average intrinsic quality factor (Q0) of 3.8 × 1010 at 16 MV/m and 3.6 × 1010 at 21 MV/m in the horizontal test. With such high specifications, the SRF cavity system has corresponding requirements for the cryogenic system. Key criteria for stable and reliable operation include a dependable cryogenic refrigeration system and process design, good thermal insulation, pressure control, temperature uniformity, and quench protection, etc. IHEP has successfully completed cryogenic testing development of the first 1.3 GHz 9-cell SRF prototype cryomodule. The whole cooldown period was 74 h, and the automatic cooldown was completed. The successful development and implementation of the 1.3 GHz superconducting cryomodule cryogenic system will provide a stable and reliable test environment for advanced superconducting cavity cryogenic testing, which will be critical in promoting the further development of the Free Electron Laser (FEL) and CEPC projects.

Mechanical and process design of the interface to a 20,000 liter liquid helium dewar

A new 20,000-liter (20 kL) liquid helium dewar is being integrated in to the existing cryogenic system at the Facility for Rare Isotope Beams at Michigan State University (MSU-FRIB). This dewar will mainly be used for the helium inventory management at FRIB (preserving helium inventory during unplanned / planned maintenance of the cryogenic system) and also in sharing the capacity to support the various cryogenic refrigeration systems to increase the operational efficiency and availability. It is also designed to interface to future cryogenic system upgrades (i.e., new 4.5 K refrigerators). This dewar has a single large penetration, or ‘neck’, that all the process lines and instrumentation pass through. On top of the ‘neck’ is a vacuum insulated interface box, or ‘neck can’, which houses all the connections between the dewar and the connecting distribution system. Though not generally common, this design approach has been successfully implemented on 5 to 10 kL liquid helium dewars at the Spallation Neutron Source (SNS), Jefferson Lab (JLab), and also at FRIB. It has been found that this approach greatly simplifies the mechanical design, while allowing for multiple process and instrumentation interfaces and still permitting a low heat in-leak. This paper presents an overview of the mechanical and process design of this neck can.

A novel hydrogen liquefaction process using dual mixed cryogenic refrigeration system: Energy, exergy, and economic analysis

In conventional hydrogen liquefaction plants, the liquefaction process consumes high portion of about 30 % of the liquid hydrogen (LH2) energy content. In addition, existing LH2 technology uses pure or single mixed refrigerants, which are susceptible to freezing problems. To address these challenges, this study introduces an innovative hydrogen liquefaction process utilizing dual mixed refrigeration (DMR) system. This process incorporates two interactive mixed refrigerants in two integrated refrigeration loops, offering flexible capability to handle large-scale capacities with minimal energy consumption and free of freezing problems. The proposed process achieved extremely low specific energy consumption (SEC) of 3.732 kWh/kgLH2, 48 % lower than the average SEC of the large-scale single mixed refrigerant (SMR) systems (7.128 kWh/kgLH2). Also, its exergy efficiency (59.65 %) is 33 % higher than the average exergy efficiency of the SMR-based systems (44.89 %). Furthermore, the proposed DMR-based process reduces the levelized cost of liquid hydrogen production to 1.89 $/kgLH2, which is 70 % lower than the small-scale processes and 21 % lower than the average cost of the large-scale SMR-based systems. This study of the dual mixed cryogenic refrigeration approach provides new methodology and guidelines for future research to significantly improve the technical and economic feasibility of LH2 production, making it competitive with other energy storage and transportation options.

Modeling and exergy analysis of an integrated cryogenic refrigeration system and superconducting magnetic energy storage

Superconducting magnetic energy storage (SMES) systems widely used in various fields of power grids over the last two decades. In this study, a thyristor-based power conditioning system (PCS) that utilizes a six-pulse converter is modeled for an SMES system. The main subject of this research is the generation of required helium for an SMES because for the coil to be at superconducting temperature, it needs to always be immersed in liquid helium. In the conducted simulation, the helium production system provided, in which primarily the gaseous helium temperature was reduced by heat transfer in LNG heat exchangers, and then after the sudden pressure drop, it turned into a liquid. The effect of the various firing angles is investigated, and it is found that at angles lower than 90°, at a specific angle, the output current enhances with time. In the 90°, this current remains constant, and at degrees greater than 90°, the output current reduces with time. The percentage of input flows to the expanders is investigated to find the rate of the maximum liquid helium production amount to the inlet gaseous helium. The diverted ratio of mass flow via expander 1 and expander 2 was 0.46 and 0.35, respectively. The system's work utilization of network, and liquid helium production is 67.18 MW and 12.7 kg/h. Also, the exergy analysis is done and the results show 35.7 % exergy efficiency. The efficiency of helium production has a direct relation to liquid nitrogen mass flow. However, due to the required high power for producing liquid nitrogen, with mass flow rate increment, the total system's efficiency is reduced. The results are evaluated with Aspen HYSYS, Aspen Energy Analyzer, and MATLAB. Specific work obtained from the analysis is 290,097 kW.s/kg which indicates that uses lower power in comparison with the other helium production methods which saves power and electrical costs.

Thermal Loss Analysis, Design, and Test of a Novel HTS Magnet System for the Double-Stator Field-Modulation HTS Electrical Machine

A novel double-stator field-modulation high temperature superconducting electrical machine (DSFM-HTSM) has been proposed, in which the armature windings and the HTS magnets are mounted on the outer and inner stator respectively, realizing stationary seal of the coolant and brushless transfer of the excitation current. The HTS magnet system is the core component of the DSFM-HTSM, consisting of the HTS magnets and the cryogenic refrigeration system, the design and safe operation of which are a key issue. Therefore, this paper focuses on the thermal loss analysis, design and test methods of the new HTS magnet system for the DSFM-HTSM. An atypical HTS magnet with small dimensions is proposed to suit the topology of the DSFM-HTSM. The different thermal loss sources are carefully analyzed and theoretically calculated, considering the characteristics of each source. The detailed design process of the HTS magnet system is presented. Moreover, an experimental platform is built and tested to verify the validity of the thermal loss analysis and design method. The corresponding research results can lay the foundation for the development and application of the large scale DSFM-HTSM, and can provide some reference for the analysis and design of similar HTS magnet systems.

Energy and exergy analysis of a modified three-stage auto-cascade refrigeration cycle using low-GWP refrigerants for sustainable development.

This study proposed a modified three-stage auto-cascade refrigeration cycle (MTARC) operating with environmentally benign zeotropic mixture of R1234yf/R170/R14 at the refrigeration temperature level of - 80°C. Compared with the conventional three-stage auto-cascade refrigeration cycle (CTARC), MTARC incorporates an additional pressure regulator between the condenser and separator to realize phase separation at a lower pressure and temperature. A comprehensive evaluation of energy and exergy performance of the two cycles was conducted theoretically. Under a typical working condition, the cooling capacity, COP and exergy efficiency of the MTARC are improved by 15.85%, 11.69% and 7.65% in comparison with the CTARC, respectively. In addition, a lower evaporating temperature was also obtained by the MTARC under the same operating condition. When the intermediate pressure drops from 2 to 1MPa, the cooling capacity, COP and exergy efficiency are improved by 35.43%, 25.25% and 16.74%, respectively, for the MTARC, meanwhile the compressor outlet temperature increases 19.93°C from 92.27 to 112.20°C. Therefore, the selection of the intermediate pressure should be comprehensively considered to ensure a desirable cycle performance and a proper working condition for the compressor. The proposed modified cycle offers new pathways for designing innovative cryogenic refrigeration systems, thereby potentially improving the energy economy in a myriad of modern energy applications for sustainability concerns.

An efficient optimization of an irreversible Ericsson refrigeration cycle based on thermo-ecological criteria

• Thermo-ecological problem of Ericsson refrigeration cycle is developed and solved. • Multi-objective optimization of Ericsson refrigerating cycle is investigated. • Investigation of the effect of operating parameters on the system performance. • Investigation of the sensitivity of design variables on the thermo-ecological objective. In the present work, a multi-objective optimization study of an irreversible Ericsson cycle is carried out to evaluate a cryogenic refrigerator system based on thermal and ecological performance. The coefficient of performance, cooling load and input power are considered as objective functions along with an ecological objective function and the effect of variables like the effectiveness of the heat sink heat exchanger, the effectiveness of the heat source heat exchanger, the temperature ratio of heat sink and heat source and the capacitance rate of the heat sink and heat source. Objective functions are optimized using a heat transfer search optimization algorithm for two different scenarios, and the Pareto front is obtained. The decision making method namely TOPSIS is adopted to identify the best solution among numerous optimal solutions for each scenario. The effect of design variables on thermo-ecological objective functions is explored and presented. A maximum cooling load of 3.27 kW at heat sink temperature of 172 K is obtained for a cryogenic refrigerator operating on an irreversible Ericsson cycle at an input power of 3.91 kW with a COP of the system as 0.84. Finally, the distribution of the design variables during the optimization is identified and presented.

극저온 냉각시스템용 스크롤 압축기 성능실험

This paper describes the performance test of a helium scroll compressor originally used for Gifford-McMahon (GM) cryocooler. This compressor can also be used for the reverse Brayton cryogenic refrigeration system. In this paper, the performance characteristics of a scroll compressor is experimentally investigated with helium and neon gas to obtain reference data for designing thermodynamic cycle of cryogenic refrigeration system. To maintain constant suction pressure during experiments, an experimental setup contains pressure regulation system which consists of three control valves and gas buffer. Pressures, mass flow rate and power consumption are measured for 400, 450, 500, 550 kPa of suction pressure condition. With experimental measurements, performance characteristics of a helium scroll compressor is investigated. The tested scroll compressor shows the higher isentropic efficiency with helium as a working gas than neon.

Structural and Thermal Design of Cryogenic Heater

Cryogenic testing heat load is the key equipment for testing the cooling capacity of large helium cryogenic refrigeration system, and the heater is the core component of it. Through the heat transfer analysis in the heating process, the specific mechanical structure and heat transfer law under cryogenic conditions are explored. The mechanical structure and thermal design of the heater are carried out, and the optimized mechanical structure is given to meet the experimental needs.

Developed hydrogen liquefaction process using liquefied natural gas cold energy: Design, energy optimization, and techno‐economic feasibility

This study focuses primarily on improving large-scale hydrogen liquefaction process by integrating liquefied natural gas (LNG) stream to utilize LNG cold energy. For the hydrogen liquefaction process, a large amount of energy is required for the compression and the cryogenic refrigeration system. LNG is one of the main sources for producing hydrogen, and it can be an opportunity to save energy because LNG cold energy is normally discarded into seawater during regasification. The objective of this study is to reduce the specific energy consumption and specific liquefaction cost. The proposed design which produces 300 ton/day of liquid hydrogen is compared with a base case design comprising two-stage mixed refrigerant refrigeration cycles. To minimize the specific energy consumption, multiparameter optimization is conducted by connecting simulation results to a genetic algorithm. Through the optimization, the flow rates of LNG and MR in the precooling cycle decrease by 1.08 and 21.00 kg/s, respectively. The specific energy consumption is reduced from 4.36 to 4.07 kWh/kg-LH2. Particularly, in the precooling cycle where the LNG stream is integrated, it decreases by more than 26.40%. Regarding the specific liquefaction cost of hydrogen liquefaction, the capital expenses are reduced by 15.16%, and annual operating expenses are diminished by 9.05%. Therefore, the total specific cost liquefaction shows a reduction of approximately 7.7%. Overall, an efficient hydrogen liquefaction process will provide a guideline for LNG-dependent countries by reducing the specific energy consumption and the specific liquefaction cost by recovering the waste cold energy.

Development and experimental study of a high-efficiency helium twin-screw compressor

Large-scale cryogenic refrigeration equipment is the sole way to realize the cryogenic environment for scientific facilities such as space technology, quantum computer and magnetic levitation. As one of the key moving components in cryogenic system, the helium compressor determines the reliability and performance of the whole cryogenic system. The twin screw compressor is a promising choice to be used in large-scale cryogenic refrigeration system due to its high efficiency and reliability. It can also be used in helium refrigeration cycle to produce liquid hydrogen for hydrogen fuel cells which are paid much attention recently. This paper presents the development of a high-efficiency oil-injected helium twin-screw compressor. In order to realize its high efficiency and reliability, several methods were adopted to overcome some intractable problems about leakage and high temperature rise. The profile was designed specially for this application. Optimized design and control of clearances were planned to compensate the thermal deformation due to the heat of compression. In addition, a special layout of two-stage mechanical seal was established to prevent helium from leaking into outside environment. To keep the purity of helium, the combined oil separator was selected to separate oil from discharge helium. Moreover, a performance test of the compressor has been carried out. The results demonstrate that the developed oil-injected helium twin-screw compressor has excellent performance.

Realistic nonlocal refrigeration engine based on Coulomb-coupled systems.

We investigate, in detail, a triple quantum dot system that exploits Coulomb coupling to achieve nonlocal refrigeration. The system under investigation is a derivative of the nonlocal thermodynamic engine, originally proposed by Sánchez and Büttiker [Phys. Rev. B 83, 085428 (2011)PRBMDO1098-012110.1103/PhysRevB.83.085428], that employs quadruple quantum dots to attain efficient nonlocal heat harvesting. Investigating the cooling performance and operating regime using the quantum master equation approach, we point out some crucial aspects of the refrigeration engine. In particular, we demonstrate that the maximum cooling power for the setup is limited to about 70% of the optimal design. Proceeding further, we point out that to achieve a target reservoir temperature lower than the average temperature of the current path, the applied voltage must be greater than a given threshold voltage V_{TH} that increases with the decrease in the target reservoir temperature. In addition, we demonstrate that the maximum cooling power, as well as the coefficient of performance, deteriorates as one approaches a lower target reservoir temperature. The triple quantum dot system, investigated in this paper, combines fabrication simplicity along with descent cooling power and may pave the way towards the practical realization of efficient nonlocal cryogenic refrigeration systems.

Analysis on feasibility of a novel cryogenic heat exchange network with liquid nitrogen regeneration process for onboard liquefied natural gas reliquefaction

Flexibility and compact multi-stream heat exchange process with cryogenic heat exchange network (CHEN) and liquid nitrogen regeneration refrigeration system (LN2 ReS) was proposed for onboard liquefied natural gas (LNG) reliquefaction. LNG circulates heat exchange with liquid nitrogen through recuperator, precooler, and subcooler successively in the CHEN to become supercooled LNG. Then it sprayed from the upper part into the storage tank to cool its boil off gas (BOG). To achieve the purpose of BOG reliquefaction in the tank. Based on the reverse Brayton nitrogen cycle, the nitrogen is regenerated into liquid nitrogen by an economizer, compressor, cooler, and expander in turn for storage and the next heat exchange. Measured the heat transfer result of 20 kW cold capacity, and found that the proposal has the characteristics of compact structure, no freezing, simple control logic, efficient pre-cooling liquefaction, etc. It only needs to control the design freedom of the flow rate of the LN2 ReS, which can be adapted to the LNG reliquefaction process. Besides, the exergy loss of the proposed CHEN accounts for 30.3% of the total, which is less than the proportion of the LN2 ReS. After process calculation, experimental case study, and exergy loss analysis, it proves the feasibility of the proposal and is particularly suitable for new energy ships.

Thermal and Mechanical Design for Refrigeration System of 10 MW Class HTS Wind Power Generator

A 10 MW class high temperature superconducting (HTS) wind power generator is being developed using REBCO wires for offshore installations. The REBCO coil operates at 35 K and is cooled via forced circulation of helium gas cooled though a heat exchanger in a rotating neon reservoir. Thermal and structural designs should be conducted to ensure that the structure can withstand mechanical stress created by the large torque from the 10 MW power, before building a cryogenic refrigeration system. This paper describes the design of supporting structures and the corresponding thermal characteristics of the HTS magnet. The supporting structure considers Lorentz force in the HTS magnet, fully coupled with an electromagnetic design result of the 10 MW class generator, under full load conditions. To estimate total heat loss, thermal radiation and heat loss at current leads are considered. A thermal analysis combined with cooling channels where the cold helium gas flows is performed to verify if the maximum temperature of the coil meets the design criteria. The analysis and design results are applied to develop a novel “neon-helium hybrid refrigeration system” for the 10 MW HTS wind power generator.

Choice and justification of the optimum cooling temperature for HTS cable

At the first stage of designing a high-temperature superconducting (HTS) cable and its cryogenic refrigeration system (CRS), it is necessary to choose the optimum cooling temperature. The operating temperature is selected not only according to the critical parameters of the HTS conductor, but also taking into account other design and operational characteristics - geometry, length, operating current and the need to have subcooled nitrogen to prevent the occurrence of steam inclusions. Normally the range of cooling temperatures is limited by the critical temperature of the HTS conductor (THTS≤ 104К) and the triple point temperature of nitrogen (TLN≥ 63.15K). The choice of a certain temperature value will enable us to approximately evaluate the parameters of the CRS and overall characteristics of the cable. The article presents an analysis of the dependence of the electric power magnitude consumed by the CRS on the choice of the cooling temperature value and cable geometry. The analysis may be useful for determining the characteristics of the HTS cable operating at different temperature levels.

Design and experimental research of superconducting magnetic bearing for helium cold compressor

In the large-scale superfluid helium cryogenic refrigeration system, the helium cold compressor faces the complex operating conditions of low temperature, high speed and sub-atmospheric pressure. The radial type high temperature superconducting (HTS) bearing of inner rotor and outer superconducting stator has the advantages and characteristics that they are suitable for being used in the helium cold compressor. Combining with the structure and operating parameters of a successful application of centrifugal active magnetic bearings in helium cold compressor, the design of radial HTS magnetic bearings considering bearing levitation performance and rotor dynamic performance was carried out. In order to ensure the accurate measurement of the rotor load and the rotor offset displacement, a performance measurement platform for the HTS magnetic bearing is built, and accurately weighed load rings and differential measurement method are used. The measured axial levitation force is 77 N when the offset displacement is 0.1 mm. And the axial stiffness is 771 N/mm and radial stiffness is about 385.5 N/mm in the measuring range. The first bending mode critical speed of the rotor system can reach 74,108 rpm. The designed HTS magnetic bearing system can provide sufficient levitation force and support stiffness for the practical application of helium cold compressor system. The research work provides a guiding for the application of HTS magnetic bearings in helium cold compressor.

Study on Conceptual Designs of Superconducting Coil for Energy Storage in SMES

Superconducting Magnetic Energy Storage (SMES) is an exceedingly promising energy storage device for its cycle efficiency and fast response. Though the ubiquitous utilization of SMES device is restricted because of the immense cost of cryogenic refrigeration system to sustain the superconducting state but with the continuous evolution of high Tc superconductors, SMES is turning into a major contender to the existing energy storage devices in the future. Among its several parts, the superconducting coil is considered to be the most crucial segment of this technology and the inductance generated in the coil determines the quantity of stored energy. In this paper, the possible geometrical configurations of SMES coil have been demonstrated. High Tc superconducting tapes are usually employed to form these configurations worldwide. BSCCO (Bismuth strontium calcium copper oxide)-2223 tape superconductor has been considered for studying the conceptual designs of superconducting coil of SMES. Before estimating the results, the value of critical current at different magnetic field densities and temperatures have been addressed through the study of superconducting tape characterization. Numerical results and the relationship among the several parameters for both the solenoid and toroid configurations in different specifications have been presented. Based on the results, the size ratio in solenoid and the mean toroid diameter in toroid arrangement is found to play the vigorous roles in the generation of inductance and hence the energy storage. The results also match the propensity of other studies. Suggestions for maximum energy gain from a specific solenoid configuration have been provided. Future research scopes with alternative superconducting tapes and limitations of this study have been briefly conferred.

Design and thermoeconomic analysis of a multi-effect desalination unit equipped with a cryogenic refrigeration system

In this paper, a hybrid tri-generation system is designed to produce LNG and freshwater simultaneously based on a multi-effect desalination system and analyzed using energy and exergy analyses. For natural gas liquefaction, the initially required cooling of the cycle is supplied by ammonia-water absorption system, and the required intermediate cooling load and liquefaction process are provided by a refrigeration system with mixed fluid. Two alternatives for providing power generation to the system and the required heat for driving the absorption cycle have been considered and compared. The first alternative relies on a natural-gas-fired power plant, while the second is based on steam-solar power plant with dish collectors. The former results in the total energy efficiency of 85.8% (LHV). The highest thermodynamic irreversibilities occur in the heat exchangers (61%), even if they have the highest exergy efficiency compared to the other plant equipment. On the other hand, using solar dish collectors enables to decrease carbon dioxide emissions by 40%, and increases freshwater and LNG production by 95% and 4.7% respectively. The power obtained per kg of LNG produced is about 0.19 kWh, which is less than or equal to the other similar patents. The results of the economic analysis with the annualized cost method of the system show that the products prime cost of both structures 1 and 2 are equal to 0.2580 and 0.1784 US$ per kg of LNG, respectively. A suitable strategy for modelling enhancement of system’s parameters is suggested by expanding of sensitivity analysis on the important parameters of the developed system.

Operating Thermal Characteristics of REBCO Magnet for Maglev Train Using Detachable Cooling System

Recently, high speed trains over 1000 km/h have been proposed in an evacuated tunnel and a Maglev train using REBCO magnets can be considered as a feasible option due to their excellent mechanical and electromagnetic characteristics. A cryogenic cooling system for REBCO magnet occupies an installation space and burdens system weight. For a Maglev train with a limited space, it is important to minimize the installation space and reduce the system weight. The electric power is also limited while the magnet is running. This paper describes thermal characteristics of a prototype REBCO magnet with a solid nitrogen vessel as a thermal battery, a detachable cryocooler, and a quasi–persistent current switch to reduce the installation space and system weight. Solid nitrogen vessel, attached on the magnet bobbin, is designed to maintain the magnet temperature below an operation limit without an on-board cryocooler, which simulates an external cryogenic refrigeration system that periodically cools the magnet at stations. Heat capacity of the solid nitrogen, which includes a solid phase change at 35.6 K, is used to maintain the magnet temperature. The experimental results with solid nitrogen are compared with a design and simulation results. The result shows the possible application of external cooling system and the quasi-persistent current mode of the REBCO magnet for a high-speed maglev train <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</b>