Liquid Nitrogen Precooling Research Articles

Nitrogen precooling heat exchanger replacement and control system upgrade in superfluid cryoplant at CMTF

Liquid nitrogen precooling is used in most cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF superfluid cryoplant, where the helium supply directly exchanges heat with liquid nitrogen, freezing of nitrogen occurred inside the heat exchanger due to heat exchanger flow imbalance during a cryoplant trip. Trapped vapor pockets of nitrogen within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold helium gas from cold end during abrupt cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of nitrogen which can damage the heat exchanger.

Parametric design optimization and thermodynamic analysis of plate fin heat exchanger for helium liquefaction system

The plate-fin heat exchanger is one of the most important components of helium liquefaction system as it recovers cold energy from helium gas in the cold box. Because of larger heat transfer surface area and compact geometrical configuration, plate-fin heat exchangers are widely used. The design of heat exchanger using helium as a cryogenic fluid needs high thermodynamic performance with minimum pressure drop which particularly requires the optimization of dimensional array and its geometrical configurations. In this regard, a parametric investigation was performed to compute the effective geometrical parameters and its effect on thermodynamic (effectiveness and log-mean temperature difference) performance has been discussed in detail. The present study aims to design optimization and thermodynamic performance evaluation of plate-fin type heat exchangers used in helium liquefaction systems. The developed helium liquefaction model has been simulated for the most critical liquefier with and without liquid nitrogen precooling, mixed mode, and refrigeration mode. Each component of the liquefaction model has been technically and thermodynamically analyzed and, in particular, four plate-fin heat exchangers have been considered and designed accurately using Aspen EDR®. Initially, the sensitivity analysis was carried out to characterize the most significant geometrical parameters (fin thickness, height, number and arrangement of layers, frequency, and fin type) and their effect on thermodynamic performance and pressure drop. After that, the artificial intelligence model was used to determine the optimal range of such geometrical variables in which the heat exchanger has maximum effectiveness and log mean temperature difference. Finally, the operating conditions obtained from cycle modeling and optimized geometrical datasets have been applied in commercial simulation software Aspen EDR® for plate-fin heat exchangers design. Finally, a comparative thermodynamic analysis has been carried out to determine the performance of all the designed heat exchangers operating at four different modes (boundary conditions).

Constrained multi-objective optimization of helium liquefaction cycle

The helium cryo-plant is an indispensable subsystem for the application of low temperature superconductors in large-scale scientific facilities. However, it is important to note that the cryo-plant requires stable operation and consumes a substantial amount of electrical power for its operation. Additionally, the construction of the cryo-plant incurs significant economic costs. To achieve the necessary cooling capacity while reducing power consumption and ensuring stability and economic feasibility, constrained multi-objective optimization is performed using the interior point method in this work. The Collins cycle, which uses liquid nitrogen precooling, is selected as the representative helium liquefaction cycle for optimization. The discharge pressure of the compressor, flow ratio of turbines, and effectiveness of heat exchangers are taken as decision parameters. Two objective parameters, cycle exergy efficiency, ?ex,cycle, and liquefaction rate, ?L , are chosen, and the wheel tip speed of turbines and UA of heat exchangers are selected as stability and economic cost constraints, respectively. The technique for order of preference by similarity to the ideal solution (TOPSIS) is utilized to select the final optimal solution from the Pareto frontier of constrained multi-objective optimization. Compared to the constrained optimization of ?ex,cycle, the TOPSIS result increases the ?L by 23.674%, but there is an 8.162% reduction in ?ex,cycle. Similarly, compared to the constrained optimization of ?L, the TOPSIS result increases the ?ex,cycle by 57.333%, but a 10.821% reduction in ?L is observed. This approach enables the design of helium cryo-plants with considerations for cooling capacity, exergy efficiency, economic cost, and stability. Furthermore, the wheel tip speed and UA of heat exchangers of the solutions in the Pareto frontier are also studied.

Design and optimization of a high-density cryogenic supercritical hydrogen storage system based on helium expansion cycle

Cryogenic supercritical hydrogen storage technology is a high-density physical hydrogen storage method, which is a highly promising hydrogen storage approach. However, existing research has mainly focused on the development of storage devices for cryogenic supercritical hydrogen, with limited research on the cooling process of supercritical hydrogen. Therefore, a novel cooling process for cryogenic supercritical hydrogen production based on helium expansion cycle with liquid nitrogen (LN2) pre-cooling is proposed in this paper. In this process, after being compressed and cooled in multiple stages, the feed hydrogen is pre-cooled by LN2. Then, cryogenic supercritical hydrogen (10 MPa, −235.15 °C, 63.36 g/L) is obtained by helium multi-stage expansion refrigeration. The process is simulated by Aspen HYSYS and optimized by genetic algorithm (GA) to obtain lower specific energy consumption (SEC). Thermodynamic analyses are conducted to evaluate the process. And compared with the conventional hydrogen liquefaction process, the results show that the proposed process is reasonable and superior. The SEC0, figure of merit (FOM), and the total exergy loss of the system are 5.432 kWh/kgH2, 43.88%, and 289.69 kW respectively. This study indicates that the proposed process has significant implications for the hydrogen industry and provides valuable information for cryogenic supercritical hydrogen storage systems.

Geothermal assisted hydrogen liquefaction systems integrated with liquid nitrogen precooling; Thermoeconomic comparison of Claude and reverse Brayton cycle for liquid nitrogen supply

Hydrogen liquefaction systems are of paramount importance in achieving a low liquid hydrogen price in developing the hydrogen supply chain. In these systems, reduction of compression work and efficient supply of liquid nitrogen for precooling purposes is essential. In this respect the present research proposes an investigation of two efficient configurations comprised of a Claude cycle for hydrogen liquefaction integrated with geothermal driven organic Rankine cycle to compensate some of the consumed power. In the proposed schemes, either the Claude or reverse Brayton cycles are employed and modeled for liquid nitrogen supply, while in most of previous research a fixed value was considered for compression work to supply the liquid nitrogen, reducing the accuracy of their reported outcomes. A comprehensive thermoeconomic assessment was implemented to determine a better scheme under various operating conditions using a parametric study. The results revealed the vital importance of integrated modeling of the liquid nitrogen supply unit with that of the hydrogen liquefaction system.

Research on building cryo-compressed test condition on large CcH2 vessel for heavy-duty fuel cell trucks

To test the performance of cryo-compressed hydrogen vessels for heavy-duty fuel cell trucks, a novel inconstant filling method was proposed by applying liquid nitrogen and compressed helium to create the target cryo-compressed environment. The computational fluid dynamics method was used to simulate the loading process of generating suitable conditions in a large cryo-compressed vessel. The element-based finite volume method and the k – ω based shear stress transport model were applied to simulate the thermal flow of filled gas. Temperature distribution and loading performance were carefully analyzed under different filling cases. In a bid to compare the loading performance, five key factors (gas consumption, temperature rise of aluminum layer and carbon fiber, average filling rate, and time consumption) were put in a radar map for discussing the optimized strategy of each application. The simulation results revealed that the cryo-compressed test condition can be well established by using liquid nitrogen precooling and gas helium pressurization. Nevertheless, the mass flow should be maintained at a low rate before the construction of high-pressure. These findings help design and operate the cryo-compressed test by enhancing its safety and improving efficiency.

A turnkey gaseous helium-cooled superconducting CORC® dc power cable with integrated current leads

High-temperature superconducting (HTS) direct current (dc) power cable systems, capable of delivering power exceeding 10 MW while being cooled with cryogenic helium gas, have been developed for applications on naval electric ships, electric aircraft and in data centers. Current injection from room temperature into the superconducting power cable causes by far the greatest heat load to the cryogenic system. Efficient current leads with integrated helium gas heat exchangers were developed to inject a current exceeding 1 kA from room temperature into a superconducting Conductor on Round Core (CORC®) power cable, without the need for liquid nitrogen pre-cooling. A 2 m long single-pole CORC® power cable system that included current leads was cooled using a Stirling cryocooler with a closed-loop helium gas circulation system. The turnkey power cable system allowed cool down from room temperature to its operating temperature of 60 K–70 K within 5 h, after which continuous operation at 1.2 kA was demonstrated. The successful development and demonstration of a CORC® power cable with current leads containing integrated helium gas heat exchangers enables widespread implementation of HTS MW-class, high current density superconducting dc power cables in many applications with constrained space that require a power dense solution.

Study on Characteristics of the Helium Refrigeration System of HL-2M Tokamak

HL-2M, a new generation of tokamak, has been built continuously in 2020 in Southwestern Institute of Physics, China National Nuclear Corporation, and the first plasma discharge was successfully achieved in 12th, Dec. This tokamak experiment device has high design parameters, and its maximum operating current reaches 3 MA. As a satellite device of ITER, it aims to explore and solve the severe physical and engineering problems. Cryogenic system is an auxiliary system of HL-2M, which mainly meets the stable operation of cryopumps and superconducting magnets. The refrigeration capacity under the condition of Liquid Nitrogen Precooling will up to 500W@4.5K, the liquefaction rate is 160L/h. In this report, we present the main characteristic parameters of the refrigeration system. At present, the system has completed the field assembly, and is expected to start commissioning in June 2021.

Matlab Simulations of the Helium Liquefier in the FREIA Laboratory

We describe simulations that track a state vector with pressure, temperature, and gas flow through the helium liquefier in the FREIA laboratory. Most components, including threeway heat exchangers, are represented by matrices that allow us to track the state through the system. The only non-linear element is the Joule-Thomson valve, which is represented by a non-linear map for the state variables. Realistic properties for the enthalpy and other thermodynamic quantities are taken into account with the help of the CoolProp library. The resulting system of equations is rapidly solved by iteration and shows good agreement with the observed LHe yield with and without liquid nitrogen pre-cooling.

Loading procedure for testing the cryogenic performance of cryo-compressed vessel for fuel cell vehicles

To overcome the disadvantages of high cost and hazards in the cryo-compressed vessel test with liquid hydrogen, a combined process with liquid nitrogen and compressed helium was carried out. A computational fluid dynamics (CFD) model was introduced to simulate the loading procedures required to generate suitable conditions in a cryo-compressed vessel with a Carbon Fiber wrapped Aluminum liner. Element-based finite volume method (FVM) and a k – ω based shear stress transport (SST) model have been used to simulate the thermal flow of helium. The simulation model was validated by a similar experiment result and the data from the U.S. National Institute of Standards and Technology reference database. To investigate the thermal characteristics of the vessel, temperature distribution, loading performance, and helium consumption were analyzed at various filling mass flow rates. The simulation results confirmed that cryo-compressed test conditions could be achieved by liquid nitrogen precooling followed by pressurization with compressed helium. The cryogenic conditions were highly depended on the inlet mass flow rate and the corresponding loading time. Lower inlet mass flow rates (longer loading times) leaded to a high temperature increase of 84.04 K in Carbon Fiber during the loading, which was minimized to only 1.65 K when using the highest mass flow rate. Considering both final condition and loading efficiency, high filling speed is optimal for single tests, while lower filling speeds were more appropriate for cyclic fatigue testing of vessels because of lower helium consumption and equipment costs. Not only thermal fluid was simulated to investigate the loading parameters to generate cryo-compressed conditions, but also the thermal transfer result of composite materials. Our findings are expected to assist in the design and operation of this challenging experiment in a safe and efficient way.

Process optimization and analysis of a novel hydrogen liquefaction cycle

The preliminary designed hydrogen liquefaction plant process based on liquid nitrogen precooling and helium gas turbine expansion refrigeration is firstly modified, simulated and analyzed by Aspen HYSYS. In addition, the multi-parameter optimization of the system is carried out by genetic algorithm (GA) by considering the specific energy consumption (SEC) of the system as the objective function. After optimization, it can be found that the SEC of the system is 7.1329 kWh kgLH2−1, which is 19.65% lower than that of base case and the coefficient of performance (COP) and figure of merit (FOM) are 0.1704 and 0.4941, which are higher than that prior to the process optimization. In addition, sensitivity analysis is conducted to present the effects of different operation conditions of the designed process on the features of the hydrogen liquefaction process. Compared with the other two systems of hydrogen liquefaction, the process in this paper shows the best performance.

Specification of the 2nd cryogenic plant for RAON

RAON is a rare isotope beam facility being built at Daejeon, South Korea. The RAON consists of three linear accelerators, SCL1 (1st SuperConducting LINAC), SCL2, and SCL3. Each LINAC has its own cryogenic plant. The cryogenic plant for SCL2 will provide the cooling for cryomodules, low temperature SC magnets, high temperature SC magnets, and a cryogenic distribution system. This paper describes the specification of the plant including cooling capacity, steady state and transient operation modes, and cooling strategies. In order to reduce CAPEX with the specification, two suppliers will consider no liquid nitrogen pre-cooling, one integrated cold box, and one back-up HP compressor. The detail design of the plant will be started at the end of this year.

Thermodynamic analysis and economical evaluation of two 310-80 K pre-cooling stage configurations for helium refrigeration and liquefaction cycle

In 310-80 K pre-cooling stage, the temperature of the HP helium stream reduces to about 80 K where nearly 73% of the enthalpy drop from room temperature to 4.5 K occurs. Apart from the most common liquid nitrogen pre-cooling, another 310-80 K pre-cooling configuration with turbine is employed in some helium cryoplants. In this paper, thermodynamic and economical performance of these two kinds of 310-80 K pre-cooling stage configurations has been studied at different operating conditions taking discharge pressure, isentropic efficiency of turbines and liquefaction rate as independent parameters. The exergy efficiency, total UA of heat exchangers and operating cost of two configurations are computed. This work will provide a reference for choosing 310-80 K pre-cooling stage configuration during design.

Multi-objective Optimization on Helium Liquefier Using Genetic Algorithm

Research on optimization of helium liquefier is limited at home and abroad, and most of the optimization is single-objective based on Collins cycle. In this paper, a multi-objective optimization is conducted using genetic algorithm (GA) on the 40 L/h helium liquefier developed by Technical Institute of Physics and Chemistry of the Chinese Academy of Science (TIPC, CAS), steady solutions are obtained in the end. In addition, the exergy loss of the optimized system is studied in the case of with and without liquid nitrogen pre-cooling. The results have guiding significance for the future design of large helium liquefier.

Numerical studies on sizing/ rating of plate fin heat exchangers for a modified Claude cycle based helium liquefier/ refrigerator

Performance of modern helium refrigeration/ liquefaction systems depends significantly on the effectiveness of heat exchangers. Generally, compact plate fin heat exchangers (PFHE) having very high effectiveness (>0.95) are used in such systems. Apart from basic fluid film resistances, various secondary parameters influence the sizing/ rating of these heat exchangers. In the present paper, sizing calculations are performed, using in-house developed numerical models/ codes, for a set of high effectiveness PFHE for a modified Claude cycle based helium liquefier/ refrigerator operating in the refrigeration mode without liquid nitrogen (LN2) pre-cooling. The combined effects of secondary parameters like axial heat conduction through the heat exchanger metal matrix, parasitic heat in-leak from surroundings and variation in the fluid/ metal properties are taken care of in the sizing calculation. Numerical studies are carried out to predict the off-design performance of the PFHEs in the refrigeration mode with LN2 pre-cooling. Iterative process cycle calculations are also carried out to obtain the inlet/ exit state points of the heat exchangers.

A new cryogenic test facility for large superconducting devices at CERN

To expand CERN testing capability to superconducting devices that cannot be installed in existing test facilities because of their size and/or mass, CERN is building a new cryogenic test facility for large and heavy devices. The first devices to be tested in the facility will be the S-FRS superconducting magnets for the FAIR project that is currently under construction at the GSI Research Center in Darmstadt, Germany. The facility will include a renovated cold box with 1.2 kW at 4.5 K equivalent power with its compression system, two independent 15 kW liquid nitrogen precooling and warm-up units, as well as a dedicated cryogenic distribution system providing cooling power to three independent test benches. The article presents the main input parameters and constraints used to define the cryogenic system and its infrastructure. The chosen layout and configuration of the facility is presented and the characteristics of the main components are described.

Analysis of various liquid nitrogen pre-cooling schemes for large-scale helium liquefiers/refrigerators

Liquid nitrogen precooling is widely used in helium liquefier/refrigerator for increased liquefaction as well as providing initial cool-down up to 80 K. The advantages are reduction in plant size and in number of equipment. There are several configurations of liquid nitrogen precooling for helium plants have been proposed in literature and are being used in practice. The configurations mainly differ in number of equipment like heat exchangers, valves, dewars and the arrangement of helium and nitrogen streams. In this paper, through parametric analysis of some reported configurations using Aspen HYSYS® V7.3, design decisions for adopting a precooling scheme for given helium plant has been presented. Results have been analyzed for the adopted plant configuration to arrive at conclusion regarding optimum configuration for precooling in the helium plant.

Specification of the ESS Accelerator Cryoplant

The European Spallation Source (ESS) is a neutron-scattering facility being built with extensive international collaboration at Lund, Sweden. The ESS accelerator will deliver protons with 5 MW of power to the target at 2.0GeV, with a nominal current of 62.5mA. The superconducting part of the accelerator is about 300 meters long and contains 43 cryomodules. The ESS accelerator cryoplant will provide the cooling for the cryomodules and the cryogenic distribution systeminterconnecting cryoplant and cryomodules. The cryoplant will cover three cryogenic circuits: bath cooling for the cavities at 2K, the thermal shields at around 40-50K and 4.5K forced helium cooling for the power couplers. This paper describes project stages,the cryogenic architecture andthe design basis including cooling capacity, operation modes and interfaces. The important design choices comprising no liquid nitrogen pre-cooling,one integrated cold box, waste heat recovery and process control system strategy as well as the principles of evaluation are presented. All the topics above are implemented and addressed in the technical specification, which has been finished and issued in June 2014. That is a very important step in the development of the ESS cryogenics system.

Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

In this paper we present the development of a new hybrid energy transfer line with 30m length. The line is essentially a flexible 30m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26K, hydrogen flow from 70 to 450g/s and pressure from 0.25 to 0.5MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ∼10m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB2 cable passed high voltage DC test up to 50kV DC. Critical current of the cable at ∼21K was 3500 A. It means that the 30m hybrid energy system developed is able to deliver ∼50–60MW of chemical power and ∼50–75MW of electrical power, i.e. up to ∼135MW in total.

COMMISSIONING RESULT OF THE KSTAR HELIUM REFRIGERATION SYSTEM

To keep the superconducting (SC) magnet coils of KSTAR at proper operating conditions, not only the coils but also other cold components, such as thermal shields (TS), magnet structures, SC bus-lines (BL), and current leads (CL) must be maintained at their respective cryogenic temperatures. A helium refrigeration system (RRS) with an exergetic equivalent cooling power of 9 kW at 4.5 K without liquid nitrogen () pre-cooling has been manufactured and installed. The main components of the KST AR helium refrigeration system (HRS) can be classified into the warm compression system (WCS) and the cryogenic devices according to the operating temperature levels. The process helium is compressed from 1 bar to 22 bar passing through the WCS and is supplied to cryogenic devices. The main components of cryogenic devices are consist of cold box (C/B) and distribution box (D/B). The C/B cool-down and make the various cryogenic helium for the KSTAR Tokamak and the various cryogenic helium is distributed by the D/B as per the KSTAR requirement. In this proceeding, we will present the commissioning results of the KSTAR HRS. Circuits which can simulate the thermal loads and pressure drops corresponding to the cooling channels of each cold component of KSTAR have been integrated into the helium distribution system of the HRS. Using those circuits, the performance and the capability of the HRS, to fulfill the mission of establishing the appropriate operating condition for the KSTAR SC magnet coils, have been successfully demonstrated.