Nitrogen Precooling Research Articles

Design and performance comparison of large-scale hydrogen liquefaction processes based on mixed refrigerant cycle

Design and performance comparison of large-scale hydrogen liquefaction processes based on mixed refrigerant cycle

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.

Research on the Temperature Variation Law during the Nitrogen Pre-Cooling Process in LNG Unloading Pipelines

In order to study the temperature change law of a nitrogen pre-cooling LNG unloading pipeline, a three-dimensional numerical simulation of an LNG pipeline with a bellow expansion bend was conducted using Fluent software (2020 R2). This simulation involved progressively controlling the nitrogen injection temperature and flow rate. The results show that increasing the nitrogen flow rate can improve the pre-cooling rate and reduce the top–bottom temperature difference of the pipeline, but there is an optimal value. Under the same nitrogen injection velocity conditions, it was found that smaller pipe diameters result in smaller temperature differences between the top and bottom of the pipeline. However, due to the reduced cooling capacity of the nitrogen injection, this leads to a decrease in the pre-cooling rate. The top–bottom temperature difference of the pipeline is mainly related to the strength of the natural convection in the pipeline. The stronger the natural convection, the greater the temperature difference between the top and bottom. Gr and Gr/Re2 reflect the relative magnitude of the natural convection intensity and forced convection intensity in the pipe. The larger the Gr and Gr/Re2, the stronger the natural convection. Therefore, Gr and Gr/Re2 are positively correlated with the top–bottom temperature difference, and the variation trend of the top–bottom temperature difference can be judged by the values of Gr and Gr/Re2.

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

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

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

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

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

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

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.

Study on the energy efficiency of bioethanol-based liquid hydrogen production process

A hydrogen liquefaction process combined with bioethanol producing hydrogen process and multistage compressor process is designed, simulated and analyzed. Its specific energy consumption (SEC) and coefficient of performance (COP) are 5.41 kWh/kgLH2 and 22.38%, respectively, and the functional exergy efficiency is 71.13% for entire process and 53.61% for the hydrogen liquefaction process. The systematic relationship among hydrogen liquefaction ratio, SEC, COP and functional exergy efficiency of nitrogen precooling cycle, helium cryogenic cycle and whole process are deduced and analyzed. The results show that the process's performance improves with the hydrogen liquefaction ratio, and the variation trends of SEC, COP and functional exergy efficiency change significantly. The optimal hydrogen liquefaction ratio is 0.89, and the corresponding SEC is 4.71 kWh/kgLH2, reduced by 12.94%, the COP and functional exergy efficiency are 25.70% and 81.70%, and the general exergy efficiency is 43.60%.

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.

Research on systems for producing liquid hydrogen and LNG from hydrogen-methane mixtures with hydrogen expansion refrigeration

In industrial production processes, gas mixtures with hydrogen and methane as main useful components are often obtained as by-products, which are often not well utilized. In this paper, an innovative approach is proposed to produce both liquid hydrogen and LNG from industrial by-products with H2 and CH4 as main components. Taking the purified hydrogen-methane mixtures as the research object, four different separation-liquefaction processes (namely Open Loop-N2, Open Loop-H2, Closed Loop-N2, Closed Loop-H2) are constructed and optimized, with refrigeration supplied with hydrogen expansion at the cryogenic section and nitrogen or hydrogen expansion at the precooling section. A distillation column is set up before the mixture enters the cryogenic section to facilitate the production of high purity methane and hydrogen products. Every system achieves excellent energy integration, and the load of condenser and reboiler in the column is borne by the hydrogen expansion cycle in the cryogenic section. For each process, the influence of hydrogen mole proportion in feed gas between 10% and 90% on the process performance is analyzed. The results show that the purities of LNG and liquid hydrogen products obtained by the system are higher than 99.99%, and the specific energy consumption of the systems is within 18.01–41.72 kWh·kmol−1 for different situations. At the same time, an open loop and a closed loop are constructed, respectively, to investigate the necessity of recovering cold energy of boil-off gas. The results suggest recommendation of open loop system with nitrogen precooling.

Development of a clean power plant integrated with a solar farm for a sustainable community

Renewable energy sources are attracting attention as a replacement of fossil fuel-based sources. This paper presents a new renewable combined cycle power plant to deliver smart services for a sustainable community. A case study is undertaken for the Kedron Community in the city of Oshawa in Canada. The integrated power plant depends on solar radiation and seawater. The services produced are electric power, heating load, fresh water, and liquified hydrogen as a clean fuel. The combined plant consists of six subsystems: solar farm, Gas turbine cycle, Rankine cycle, multi-effect desalination, electrolyzer, and hydrogen liquefaction subsystem. The integrated system has been studied thermodynamically to investigate the thermal and exergy performance. The solar farm uses HITEC with a mass flow rate of 2000 kg/s to produce an overall heat of 201.3 MW to the combined cycle. The combined cycle delivers 133.1 MW of electric power, a heating load of 284 MW for desalination, and a heating load of 98.2 MW for residential applications. The multistage flash desalination system provides 684 kg/s of fresh water, where 32.09 kg/s is used for electrolysis to produce hydrogen gas. The hydrogen liquefaction system consists of nitrogen precooling refrigeration system, hydrogen Claude refrigeration system, and hydrogen liquefying stream. This liquefaction system produces 355 ton/day of liquefied hydrogen with SFC of 5.24 kWh/kg-LH2. The overall thermal efficiency of the integrated system is 88.12%, while the exergetic efficiency is 23.05%.

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

• Loading of a cryo-compressed vessel studied using computational fluid dynamics. • The filling time is the key parameter determining vessel thermal performance. • Higher mass flow rates reduce temperature increase during loading. • Higher mass flow rates are better for single tests to ensure thermal performance. • Intermediate mass flow rates can reduce helium consumption and investment costs. 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

Abstract 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.

Analysis of a clean hydrogen liquefaction plant integrated with a geothermal system

Abstract Hydrogen is attracting a lot of attention because of its high-energy content and lower weight and volume, making it a promising replacement of fossil fuels. Hydrogen liquefaction is an energy-intensive process that requires high electrical power. This paper presents a novel approach of a large-scale hydrogen liquefaction system combined with geothermal and isobutene power plant. The hydrogen liquefaction system uses a hydrogen Claude refrigeration system and a nitrogen precooling system to produce 335 ton/day of liquefied hydrogen. The mass flow rate of hydrogen in the refrigeration system and nitrogen precooling system were 14 kg/s and 52 kg/s, respectively, to produce specific energy consumption of 6.41 kWh/kg-LH2. The overall power consumption of the liquefaction system was 107 MW. This requires constructing three geothermal and isobutene power plants to produce 130 MW of electrical power. Some parametric studies were conducted to reduce the specific energy consumption (SEC). It is found that reducing the hydrogen mass flow rate to 9 kg/s and the high pressure to 20 bar results in the reduction of the SEC to 4.7 kWh/kg-LH2. However, increasing the steam and isobutene mass flow and high pressure in the system results in an increase in the electric power delivered to 225 MW from 130 MW.

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.

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.

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.