Helium Liquefier Research Articles

Commissioning and operational results of helium refrigeration system at JLab for the 12GeV upgrade

The new 4.5 K refrigerator system at the Jefferson Lab (JLab) Central Helium Liquefier (CHL-2) for the 12 GeV upgrade was commissioned in late spring of 2013, following the commissioning of the new compressor system, and has been supporting 12 GeV LINAC commissioning since that time. Six design modes were tested during commissioning, consisting of a maximum capacity, nominal capacity, maximum liquefaction, maximum refrigeration, maximum fill and a stand-by/reduced load condition. The maximum capacity was designed to support a 238 g/s, 30 K and 1.16 bar cold compressor return flow, a 15 g/s, 4.5 K liquefaction load and a 12.6 kW, 35-55 K shield load. The other modes were selected to ensure proper component sizing and selection to allow the cold box to operate over a wide range of conditions and capacities. The cold box system is comprised of two physically independent cold boxes with interconnecting transfer-lines. The outside (upper) 300-60 K vertical cold box has no turbines and incorporates a liquid nitrogen pre-cooler and 80-K beds. The inside (lower) 60-4.5 K horizontal cold box houses seven turbines that are configured in four expansion stages including one Joule-Thompson expander and a 20-K bed. The helium compression system has five compressors to support three pressure levels in the cold box. This paper will summarize the analysis of the test data obtained over the wide range of operating conditions and capacities which were tested.

Automatic PID Control Loops Design for Performance Improvement of Cryogenic Turboexpander

Cryogenics field involves temperature below 123 K which is much less than ambient temperature. In addition, many industrially important physical processes—from fulfilling the needs of National Thermonuclear Fusion programs, superconducting magnets to treatment of cutting tools and preservation of blood cells, require extreme low temperature. The low temperature required for liquefaction of common gases can be obtained by several processes. Liquefaction is the process of cooling or refrigerating a gas to a temperature below its critical temperature so that liquid can be formed at some suitable pressure which is below the critical pressure. Helium liquefier is used for the liquefaction process of helium gas. In general, the Helium Refrigerator/Liquefier (HRL) needs turboexpander as expansion machine to produce cooling effect which is further used for the production of liquid helium.Turboexpanders, a high speed device that is supported on gas bearings, are the most critical component in many helium refrigeration systems. A very minor fault in the operation and manufacturing or impurities in the helium gas can destroy the turboexpander. However, since the performance of expanders is dependent on a number of operating parameters and the relations between them are quite complex, the instrumentation and control system design for turboexpander needs special attention. The inefficiency of manual control leads to the need of designing automatic control loops for turboexpander. Proper design and implementation of the control loops plays an important role in the successful operation of the cryogenic turboexpander. The PID control loops has to be implemented with accurate interlocks and logic to enhance the performance of the cryogenic turboexpander. For different normal and off-normal operations, speeds will be different and hence a proper control method for critical rotational speed avoidance is must. This paper presents the design of PID control loops needed for the efficient performance of cryogenic turboexpander (Radial Inflow type) to ensure that the control systems meet the technical conditions and constraints more accurately and ensure the equipment safety.

Experimental investigation and optimization of small-scale helium liquefaction with multi-cryocoolers

Small-scale helium liquefiers using regenerative cryocoolers with cooling power up to 1.5W at 4.2K could be used to re-liquefy evaporated helium gas of small- and medium-sized cryogenic devices such as MEG and PPMS. A serial–parallel-path helium liquefier with a liquefaction rate of 83Litres per day (L/d) using five 4K G-M cryocoolers is developed, and has been applied to the Wuhan National High Magnetic Field Center (WHMFC) in China. Different from parallel-path helium liquefier, the helium gas is effectively, stepwise precooled by heat exchangers on multi-cold flanges, and thus the additional purifier and precooling coil heat exchangers on the thinner part of the cold head cylinder containing the 2nd stage displacer could be removed to simplify the construction. Through theoretical calculation and conclusive analysis, an optimum configuration is proposed and makes a reference to the design of serial–parallel-path helium liquefier with multi-cryocoolers.

Comparative design evaluation of plate fin heat exchanger and coiled finned tube heat exchanger for helium liquefier in the temperature range of 300-80 K

Present Indigenous Helium Liquefaction system at RRCAT uses the cross-counter flow coiled-finned tube heat exchangers developed completely from Indian resources. These coiled-finned tube heat exchangers are mainly suitable up to medium capacity helium liquefiers. For large capacity helium liquefier, plate fin heat exchangers are more suitable options. This paper presents the comparative evaluation of the design of both types of heat exchangers in the temperature range of 300-80 K for helium liquefier.

Development of a Measurement and Control System for a 40l/h Helium Liquefier based on Siemens PLC S7-300

A 40l/h Helium Liquefier has been commissioned by the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. A measurement and control system based on Siemens PLC S7-300 for this Helium Liquefier is developed. Proper sensors are selected, for example, three types of transmitters are adopted respectively according to detailed temperature measurement requirements. Siemens S7-300 PLC CPU315-2PN/DP operates as a master station and three sets of ET200M DP remote expand I/O operate asslave stations. Profibus-DP field communication is used between the master station and the slave stations. The upper computer HMI(Human Machine Interface) is compiled using Siemens configuration software WinCC V7.0. The upper computer communicates with PLC by means of industrial Ethernet. A specific control logic for this Helium Liquefier is developed. The control of the suction and discharge pressures of the compressor and the control of the turbo-expanders loop are being discussed in this paper. Following the commissioning phase, the outlet temperature of the second stage turbine has reached 8.6K and the temperature before the throttle valve has reached 13.1K.

Improvement of the Operational Settings of a Helium Purifier, Leading to a Higher Purity of the Recovered Gas

The internal purifier operating conditions of commercially available helium liquefiers are determined by adjusting the cold end temperature, the cold flow, the regeneration completion temperature and the heater temperature. By changing the cold end temperature of the internal purifier from 32.5 K to 22 K, it was possible to improve the purity of the helium gas recovered from the purifier from 33.5 to 99%. The current internal purifier regeneration operation settings are as follows: cold end temperature 22 K, cold flow rate 180 ℓ/min, and regeneration completion temperature 145 K. This paper describes how the internal purifier system of a helium liquefier was improved.

Observation and Data Archiving System of a Superconducting Gravimeter at Syowa Station, Antarctica

A superconducting gravimeter (SG, model TT70#016, GWR Instruments) was deployed for the first time in Antarctica in 1992 at Syowa Station. Observations began in April 1993. Although the SG was equipped with a 10 K cryocooler, its liquid helium (LHe) required refilling twice a year to maintain its superconducting state. The LHe was produced by a separate helium liquefier. After continuous gravity measurement with the SG for 11 years, it was replaced by a second SG (CT#043) with a 4 K cryocooler in December 2003 in order to reduce loads of person in charge for LHe production. Because the manufacturer could not supply a replacement 4 K cryocooler, this SG ceased measurement in November 2009. In January 2010, a new superconducting gravimeter (OSG#058) was installed and had recorded high-quality gravity time series with data acquired every second for more than five years without interruption. Because the personal computer (PC) controlling the observation and data acquisition is connected with PCs in Japan through an Intelsat satellite communication link, we can check the status of observations in real time. It is also possible to fix remotely certain problems with the gravimeter. The observed gravity data are transferred daily to a data server in Japan. Also included in the upload are diagnostic data of the gravimeter such as the temperature of the coldhead and environmental data such as atmospheric pressure. Plots of the daily data are publicly available. The raw data with a 1 s sampling interval are also released to registered researchers. The released gravity time series along with the environmental data are greatly useful for investigating solid earth dynamics especially in the long period bands. We provide necessary information to use these long-range data sets.

Integration and Commissioning of the ARIEL e-linac Cryogenic System at TRIUMF

The Advanced Rare IsotopE Laboratory (ARIEL) is a major expansion of the Isotope Separation and Acceleration (ISAC) facility at TRIUMF. The key part of the ARIEL project is a superconducting radiofrequency (SRF) linear electron accelerator (e-linac). The e-linac helium cryogenic system was designed to meet the ARIEL specifications. The HELIAL LL helium liquefier byAir Liquide Advanced Technologiessupplies 4 K liquid helium (LHe) to cryomodules via aLHe distribution system. The cryomodules have a top-loaded-coldmass design. The 4 K–2 K temperature conversion is achieved by a counter flow heat exchanger and a JT-valve installed onboard each cryomodule[1]. The temperature in the 2 K volume of the cryomodules is controlled by pressure control in the sub-atmospheric line. Sub-atmospheric helium is warmed up in a custom-designed heat exchanger and after passing sub-atmospheric pumps goes to the helium compressor suction line. The LN2 system supplies liquid nitrogen to the liquefier, 80 K shielding of the cryomodules and LHe distribution system, as well as to the freeze-out helium purifier. The installation of the e-linac cryogenic system components started in February 2013 while the corresponding subsystems tests started in November 2013.This paper describes the e-linac cryogenic system components integration and presents the results of the acceptance tests and commissioning activities performed at TRIUMF since November 2013.

Liquid Helium Technologies at the Cryogenic Complex of the Heavy Ion Collider NICA

Since 1992, the largest Russian cryogenic helium complex of the superconducting accelerator Nuclotron with the cooling capacity of 4000 W at 4.5 K has been operating at the Joint Institute for Nuclear Research in Dubna. The construction of this high-efficient cryogenic system included a large number of technical ideas that had never been applied before in the world. The helium complex of the Nuclotron has become the most advanced and largest Russian liquid helium plant consisting of two KGU–1600/4.5 units, which are capable to operate for a common collector of the liquid helium delivery to the consumer and provide the total capacity of 1000 l/h. In 1992 its use allowed one to begin for the first time the export of liquid helium by means of 40 m3 auto transport containers. The annual level of export deliveries reached 1 million liters. In the near future it is planned to construct a new accelerator complex comprising beside the Nuclotron a superconducting booster and collider to provide collisions of high-intensity beams of heavy ions up to gold Au+79. The cryogenic system of this megaproject includes the latest Russian developments: helium liquefiers with the capacity of 1100 l/h and screw helium compressor aggregates with the outlet pressure of 3 MPa and capacity of 6600 Nm3/h. The assembling and tests of pilot units are being carried out at present. This equipment being commissioned to mass production may lay the foundation for the technology of industrial liquefaction of helium for the development of new deposits in Eastern Siberia.

Ultracold neutron source at the PULSTAR reactor: Engineering design and cryogenic testing

Construction is completed and commissioning is in progress for an ultracold neutron (UCN) source at the PULSTAR reactor on the campus of North Carolina State University. The source utilizes two stages of neutron moderation, one in heavy water at room temperature and the other in solid methane at ~40K, followed by a converter stage, solid deuterium at 5K, that allows a single down scattering of cold neutrons to provide UCN. The UCN source rolls into the thermal column enclosure of the PULSTAR reactor, where neutrons will be delivered from a bare face of the reactor core by streaming through a graphite-lined assembly. The source infrastructure, i.e., graphite-lined assembly, heavy-water system, gas handling system, and helium liquefier cooling system, has been tested and all systems operate as predicted. The research program being considered for the PULSTAR UCN source includes the physics of UCN production, fundamental particle physics, and material surface studies of nanolayers containing hydrogen. In the present paper we report details of the engineering and cryogenic design of the facility as well as results of critical commissioning tests without neutrons.

Cryogenics for the future accelerator complex NICA at JINR

The NICA cryogenics will be based on the modernized liquid helium plant that was b uilt in the early 90’s for the superconducting synchrotron known as the Nuclotron. The main goals of the modernization are: increasing of the total refrigerator capacity from 4000 W to 8000 W at 4.5 K, making a new distribution system of liquid helium, and ensuring the shortest possible cool down time. These goals will be achieved by means of an additional 1000 l/hour helium liquefier and “satellite” refrigerators located near the accelerator rings. This report describes the design choices of the NICA, demonstrates helium flow diagrams with major new components and briefly informs of the liquid nitrogen system that will be used for shield cooling at 77 K and at the first stage of cooling down of three accelerator rings with the total length of about 1 km and “cold” mass of 290 tons.

Engineering the Big Chill: The Story of JLab’s Central Helium Liquefier

This article tells the story of the Central Helium Liquefier (CHL) at the Thomas Jefferson National Accelerator Facility (JLab), one of the US National Laboratories. JLab’s successful superconducting radio frequency accelerator was only possible because a group of JLab engineers successfully tackled a complex of difficulties to build a cryogenic system that included the CHL, a task that required advancing the frontier of cryogenic technology. Ultimately, these cryogenic advances were applied far beyond JLab to the benefit of cutting-edge programs at other US national laboratories (Oak Ridge, Brookhaven, and the Facility for Rare Isotope Beams at MSU) as well as NASA. This innovation story dramatizes the sort of engineer-driven technological problem solving that allows the successful launch and operation of experimental projects. Along the way, the CHL story also provides an important addition to our understanding of the role played by engineers and industry in creating knowledge at physics laboratories.

Speech alarm and cycle helium gas monitoring of helium refrigerator

Two helium liquefiers are running round-the-clock in parallel. One of them is always connected to the Superconducting Cyclotron in refrigeration mode. EPICS based alarm system is running with alert sound in computer speaker. But the fault cannot be located without opening the fault screen. An audible English speech alarm system was envisaged and implemented in EPICS platform. Voice message are now being played in relation to faults or alarms. In continuously operating refrigeration system pure helium gas inventory is an important parameter to log. We need to calculate total pure equivalent helium cycle inventory. Now, we have put these calculations together in EPICS controller. This continuously calculates displays and archives the pure equivalent cycle helium gas. If any leak develops in the process, this trend gives a quick indication.

Recent trials with the experimental helium liquefier developed by BARC

An experimental helium liquefier has been designed and fabricated by Cryo-Technology Division and installed at Bhabha Atomic Research Centre, Mumbai. The helium liquefaction process is based on a modified Collin's cycle consisting of one pre-cooler turboexpander, a pair of by-pass turboexpanders (warm and cold) and a series of 7 compact brazed plate fin high effectiveness heat exchangers. Liquid nitrogen pre-cooling facility along with another heat exchanger to recover cold of gaseous nitrogenhas also been provided in the system. After the full installation of the process compressor and its integration with the helium liquefier cold box, trial runs were started. A lowest temperature of about 7.8 K was registered in a temperature sensor located downstream of the JT valve.

Design of a triaxial bayonet for connecting a helium liquefier cold box and receiver Dewar vessel

A transferline with a triaxial bayonet for connecting a helium liquefier cold box and Dewar has been conceived. Liquid helium (LHe) settles in the Dewar vessel and the remaining cold gaseous helium (GHe) returns to the cold-box as a part of the liquefier cycle. The two coaxial lines are enclosed in an outermost vacuum line. These three coaxial lines come out of the liquefier through a triaxial bayonet joint which facilitates assembly/disassembly of the system due to the absence of welded joints. The present paper discusses schematic, design, and working of such a triaxial bayonet. It is conceived such that reduction in overall length, ease of fabrication, reduction of thermal stresses due to flexibility of bellows and reduction in fabrication cost are achieved.

Optimum number of stages and intermediate pressure level for highest exergy efficiency in large helium liquefiers

In this paper, an attempt has been made to study the influence of different design and operating parameters on the performance of large scale helium liquefiers through the concept of pre-cooling stages. Through exergy analysis and simulation with Aspen HYSYS® 7.0, it has been demonstrated that four refrigeration stages is the best option for large helium liquefiers when all expanders operate between the entire available pressure differences. However, when some of the expanders are operated at intermediate pressure, a more number of stages gives a higher thermodynamic efficiency. Relationship between the number of stages, effective heat exchanger area and operating pressure levels of expanders, which could optimally be employed for least specific power consumption has been established through exergy analysis. Optimum number of stages, intermediate pressure and corresponding plant efficiency are, however to a large extent, dictated by the prevailing compressor efficiency. The intermediate pressure that gives the maximum exergy efficiency for the plant increases from 0.2 MPa with constant compressor efficiency to 0.35 MPa when considering two-staged compressor where pressure ratio influences compressor efficiency. Results presented may be useful in designing energy-efficient helium liquefiers of large capacity.

Operation of Cryogenic Facility in e-way at Tata Institute of Fundamental Research, Mumbai, India.

In an attempt towards the development of modern, model and paperless cryogenic facility, the Low Temperature Facility of Tata Institute of Fundamental Research, at Mumbai, India; carried out many automation works using programmable logic controller (PLC) and other modern electronic tools, with the objective of bringing the entire plant operation to your palm whenever and wherever you are. Efficiency in the plant operation by keeping a watch on the plant healthiness, advance indication about the possible plant problem by means of pre-warning alarms, so that the remedial action can be taken well prior to the actual failure affects the plant operation, reduction in plant down time were achieved by the automation works. Large size in our cryogen production, controlling the complicated helium liquefier, meeting the uninterrupted supply of cryogen to the users on “any time availability basis,” safety in handling cryogens and high pressure gas, effective usage of limited skilled manpower etc., all these requirements call for the definite need of modern electronic gears and gadgets. This paper will describe in details about the automation works carried out at our cryogenic facility at TIFR.

Exergy Analysis of Different Cold End Configurations for Helium Liquefiers

Cold end in helium liquefiers, where finally the gas is converted to liquid, may have different alternatives in configuration to achieve maximum exergy efficiency. Apart from high exergy efficiency, which also means low specific power consumption, reliability of operation and complexity of equipment design are also some of the concerns for designers. In this work, various cold end configurations are compared at different operating conditions to help arrive at appropriate choices during design and operation. When single Joule–Thomson valve is replaced by more efficient cold ends with expanders, it allows reduction of the number of Brayton stages in precooling section as well as the total heat exchanger size. Cold end with expander and Joule–Thomson valve combination has been found to be a good compromise between reliability, liquid production, specific power consumption, and exergy efficiency. However, for such a configuration, it is important to fix the intermediate pressure at appropriate level so as to avoid liquid formation at the exit of the expander.

Application of exergy analysis in designing helium liquefiers

Exergy has proved to be a useful tool to analyze and optimize the design and operation of many systems. Some studies on helium refrigerators and liquefiers based on exergy are available in literature. In this paper, systematic evaluation of important operating and geometric parameters has been done to determine the exergy destructions in components as well as in the entire cycle of Collins helium liquefiers. Grassmann diagram of exergy flow has been shown to be of immense help in understanding relative importance of different components used in the system. Compressor pressure, expander flow rates, heat exchanger surface area are some of the parameters optimized considering both presence and absence of pressure drop in the heat exchangers. Non-dimensionalization of parameters makes the results applicable to plants of any capacity. Exergy-analysis based on Second Law proves to be far superior to the First Law based energy analysis in designing of the helium plant as the former is holistic in approach and capable of deriving some additional conclusions. Results derived on Collins cycle may be applicable in large-scale helium liquefiers by providing basic understanding of the influence of components on the plant performance and reasonable initial guess values in their design and simulation.

Exergy based analysis on different expander arrangements in helium liquefiers

In helium liquefiers, refrigeration stages have expanders connected in parallel (reverse Brayton stage) and also in series with heat exchangers between them (modified Brayton stages). Options of splitting and combining Brayton stages into modified Brayton stages are evaluated and compared by exergy analysis. Results show that as two Brayton stages are combined to make two modified Brayton stages, the performance deteriorates. When one Brayton stage is split into two modified Brayton stages, the performance shows improvement with the total heat exchanger surface area remaining unchanged. When the stage operates at lower temperatures, such splitting has led to more improvement. Each stage, whether it is Brayton or modified Brayton, has been found to behave as an independent refrigeration stage allowing more additions of heat exchanger area. In a one-to-one comparison, a Brayton stage has been found to be superior to a modified Brayton stage at any temperature of operation. The impact of replacing Brayton stage with modified Brayton stage has been found to be more pronounced when heat exchangers in the configuration are less balanced in mass flow.