The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units at 1.8 K, each of them coupled to a 4.5 K refrigerator. Taking into account the cryogenic architecture of the LHC and corresponding process design constraints, a reference solution based on a combination of cold centrifugal and warm volumetric compressors was established in 1997. The process and technical requirements expressed in the specification issued in 1998 and the procurement scenario based on pre-series acceptance prior to final series delivery between 2002 and 2004 are presented in this paper

Claudet, S

Gayet, P

Jäger, B

Millet, F

Roussel, P

Tavian, L

Wagner, U

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsSPECIFICATION OF EIGHT 2400 W @ 1.8K REFRIGERATION UNITSFOR THE LHCS. Claudet, Ph. Gayet, B. Jager*, F. Millet*, P. Roussel*, L. Tavian and U. WagnerThe cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC),at CERN, will be provided by eight refrigeration units at 1.8 K, each of them coupled to a 4.5 Krefrigerator. Taking into account the cryogenic architecture of the LHC and corresponding processdesign constraints, a reference solution based on a combination of cold centrifugal and warm volumetriccompressors was established in 1997. The process and technical requirements expressed in thespecification issued in 1998 and the procurement scenario based on pre-series acceptance prior to finalseries delivery between 2002 and 2004 are presented in this paper.LHC Division*SBT, DRFMC, CEA, 17 avenue des martyrs, 38054 Grenoble Cedex, FrancePresented at the Eighteenth International Cryogenic Engineering Conference (ICEC 18)21-25 February 2000, Bombay Mumbai, IndiaGeneva, Large Hadron Collider ProjectAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandLHC Project Report 392Abstract26 July 20001Specification of Eight 2400 W @ 1.8K Refrigeration Units for the LHCSerge Claudet, Philippe Gayet, Bernard Jager*, François Millet*, Pascal Roussel*, Laurent Tavian andUdo WagnerLHC Division, CERN, 1211 Geneva 23, Switzerland*SBT, DRFMC, CEA, 17 avenue des martyrs, 38054 Grenoble Cedex, FranceThe cooling capacity below 2 K for the superconducting magnets in the LargeHadron Collider (LHC), at CERN, will be provided by eight refrigeration units at1.8 K, each of them coupled to a 4.5 K refrigerator. Taking into account thecryogenic architecture of the LHC and corresponding process design constraints, areference solution based on a combination of cold centrifugal and warmvolumetric compressors was established in 1997. The process and technicalrequirements expressed in the specification issued in 1998 and the procurementscenario based on pre-series acceptance prior to final series delivery between 2002and 2004 are presented in this paper.1 INTRODUCTIONTo complete the cryogenic refrigeration installations for the Large Hadron Collider [1], eight 1.8 Krefrigeration units producing the cooling capacity for superconducting magnets, have been specified.Each of these units will be coupled to a 4.5 K refrigerator. In order to validate the process andcomponents, a first unit called “pre-series unit” will be validated by extensive testing at CERN beforelaunching the series unit production. Depending on the technical risk of the proposed solutions, it wasenvisaged to eventually order and test two pre-series units of two different suppliers. Figure 1 shows thegeneral architecture of the cryogenic installation.Warm CompressorStationUpper Cold BoxInterconnection BoxCold BoxWarm CompressorStationLower Cold BoxDistribution Line Distribution LineMagnet Cryostats Magnet CryostatsCold CompressorboxWarm CompressorStationCold CompressorboxWarm CompressorStationShaftSurfaceCavernTunnelLHC Sector (3.3 km) LHC Sector (3.3 km)1.8 K Refrigeration Unit New 4.5 K Refrigerator Existing 4.5 K refrigerator 1.8 K Refrigeration UnitFigure 1  General architecture of a typical cryogenic installation in an even point of LHC22 INTERFACE CONSTRAINTS AND STEADY STATE OPERATIONA preliminary study on possible upgrades of the existing 4.5 K refrigerators has established two maindesign constraints. The first constraint concerns the limited entropic load available for the unit; the secondone concerns the limited available cold return connection in the low-pressure side of the heat exchangerblocks. These two constraints impose that the capacity induced by the units must be seen by the 4.5 Krefrigerators as non-isothermal refrigeration between 4.5 and 20 K. Integral cold compression with directreturn to the low-pressure side is no more possible. As a direct consequence, warm compressor (WC), oilremoval system (ORS), counter-flow heat exchangers as well as switchable 80 K adsorbers (ADS) areneeded. Depending also on the load produced by the cold compressors, active refrigeration usingexpansion turbine (T) must be added to the cold compressor box (CCB) [2]. Figure 2 shows a typical flowscheme of a 1.8 K refrigeration unit as well as the interface conditions of the different operation modes.The installed refrigeration capacity is 2400 W at 1.8 K. Due to the high level of dynamic load [3], aratio of 3 is required for the turndown capability. In steady-state operation, for efficiency considerationand except for the in-situ capacity check mode, no extra heating is allowed in the phase separator (PS).Interface conditionsModes Bm[g/s]BT[K]BP[kPa]Cm[g/s]DT[K]Installed 124 4.0 ≤ 1.5 ≤ 2 ≤ 20Normal 83 4.0 ≤ 1.5 ≤ 2 ≤ 25Low beam intensity 62 4.2 ≤ 1.5 ≤ 2 ≤ 28Injection standby 42 4.8 ≤ 1.5 ≤ 2 ≤ 30Cold standby 37 5.6 ≤ 24 ≤ 2 ≤ 30Capacity check 0 \ ≤ 1.5 126 ≤ 200.3 MPa4.6 K0.13 MPa,20 -30 KCCCCWCS1.8 K Refrigeration UnitLHe 1.8 K Q1.8KORSCCB4.5 KRefrigeratorADSPSTBDCWCBCD mmm  +=Cm  limited to 2 g/s for process optimisationFigure 2  Generic scheme of a 1.8 K refrigeration unit and interface conditions for different steady-state modes3 TRANSIENT OPERATION MODESFor the transient modes encountered during LHC operation, extra heating is provided for in the phaseseparator. The corresponding gas production can be used to facilitate the cold compressor adaptationduring fast flow variation. This is however not applicable for liquid filling and cooldown of the magnets(see 3.3). Limited magnet quenches should not be seen by the unit whereas full-sector quench should leadto valving off of header B.3.1. Cooldown and Warmup of the Cold Compressor BoxThe cooldown and warmup of the cold compressor box must be possible with the 4.5 K refrigerator innormal operation. The cooldown and warmup must be completed in less than 5 hours. The CCB turbineas well as 40 g/s of helium at 4.5 K coming from interface C could be used for cooldown.3.2. Pump-down and Specific Cooldown of the Pumping LineAfter a unit stop, the cold compressor box must be reconnected to the pumping line (3.3 km, 60 tons)which has a relatively high temperature (up to 40 K) but still a low pressure. The cold compressors arenot well adapted to these interface conditions and cold gas produced in the phase separator can be mixedto recover acceptable conditions at the cold compressor inlet. The pump-down time must be less than2 hours without pumping line coupling (in capacity check) and less than 4 hours with coupling.33.3. Liquid Filling and Cooldown of Magnets to 1.9 KThe 1.8 K refrigeration unit must also be used to complete the filling of the magnets by condensing thevapour remaining in their helium vessels. During this operation, the pressure at interface B must be keptbelow 24 kPa. The cooldown of the magnets to 1.9 K must follow and the interface B pressure has to begradually reduced down to 1.5 kPa. During this transient mode, the 4.5 K refrigerator has no capacitymargin and no extra heating is allowed to compensate for pumping flow variation less than 2 g/sper minute.3.4. Beam Dump and InjectionBeam dump and injection are accompanied by slow current deramping and ramping which give pumpingflow variations of ± 6 g/s per minute. The pressure at interface B must remain below 1.7 kPa.4 SPECIFIC REQUIREMENTSConcerning standard refrigeration components (valves, instrumentation, expansion turbines, 80 Kadsorbers, provision for dryers and process control) the same specification as for the 4.5 Krefrigerators [4] is applied. Only specific components and requirements are developed hereafter.4.1. Cold CompressorsTechnology referenced for operation with helium is mandatory [5]. The guaranteed mean time betweenmaintenance of cold compressors must be at least 8000 hours. With respect to the maximum foreseenrotational speed, a margin of 20 % must be possible. A cold compressor cartridge must be exchangedwithout a complete CCB warmup within 4 hours. The electrical circuits in contact with very-low-pressurehelium must have adapted low-voltage power supplies.4.2. Sub-atmospheric Warm CompressorsTechnology based on screw compressors or liquid ring pumps, referenced for operation with helium ismandatory. If several compressors have to be connected in parallel, each one must have the same size andthe same suction and discharge pressures. The discharge pressure must remain above the atmosphericpressure in all operation modes.4.3. Helium GuardsSome components operating below atmospheric pressure and not housed in a vacuum enclosure have tobe protected from air inleak by a guard with helium at a pressure above atmospheric. For the warmcompressor station, it concerns the instrumentation if not equipped with ISO-KF vacuum flanges, thedynamic seals of valves and compressors if not equipped with bellows or double-garniture with oilinjection and all the connection not completely welded nor equipped with O-ring joints. For the coldcompressor box, it concerns the safety valves, instrumentation and all the connections and assemblies notcompletely welded.5. INTEGRATED COST ESTIMATE FOR ADJUDICATIONFor adjudication purpose, CERN has evaluated the bid prices using a formula that takes into account thecost of electricity during ten years of operation. The bidders must provide guaranteed data for theelectrical input power of the 3.3 kV supply in the “low intensity” mode (Pg_low), in the “normal” mode(Pg_norm) as well as in “Installed” mode (Pg_inst). In 1998, it was envisaged to adjudicate a firstcontract for the pre-series to one or two suppliers at a price Ip quoted by the bidder followed, afteracceptance of the pre-series, by a second contract for seven series units to only one supplier at a price I7quoted by the bidder. For the assessment, the total cost C8 for eight units is considered using theformula (1) in which, C and I are in CHF and Pg in kW. The factor 1584 and 792 result from the expected26400 hours, respectively 13200 hours of operation at a electricity cost of 0.06 CHF per kWh [6].Pg_inst)792Pg_norm1584Pg_low(15848IIC 7p8 ⋅+⋅+⋅⋅++= (1)4For the three operating modes, the 3.3 kV power consumption measured during the reception tests will becompared to the guaranteed values of the bids. The difference will result in a compensation payment byCERN (half of the difference) in case of lower consumption than guaranteed, or by the supplier (fulldifference) if the power consumption exceeds the guaranteed value.6 TIME SCHEDULEThe time schedule specified for the eight units is as given in Table 1. After the reception test of the pre-series in a surface building, this unit will be used for testing of series cold compressor cartridges and bere-installed in the dedicated cavern after.Pre-series Series 1 Series 2 Series 3 Series 4 Series 5 Series 6 Series 7Location Point 1.8 Point 4 Point 8 Point 6 Point 4 Point 8 Point 6 Point 2Ready for reception 30-Jun200131-Mar200330-Jun200330-Sep200315-Dec200331-Mar200430-Jun200430-Sep2004Re-installation date 30-Apr2005/ / / / / / /Table 1  Time schedule for the 1.8 K refrigeration units7 CONCLUSIONFollowing the specification for the 1.8 K refrigeration units, CERN received two offers in October 1998.After the evaluation of the offers which completely fulfilled the technical requirements, it was decided tosplit the supply in two. Consequently two contracts for the supply of one pre-series unit each followedafter successful reception by a contract for the supply of three series units, were signed with Air Liquide(France) [7] and a consortium between IHI (Japan) and Linde Kryotechnik AG (Switzerland) [8]. Thecontract with the consortium will be funded by the Japanese contribution to the LHC project. In case offailure during the pre-series phase of one of the suppliers, option for four additional series units have beennegotiated. Despite this split, the overall requirements of the technical specification are preserved andboth firms are motivated and engaged to supply efficient and reliable equipment.REFERENCES1. Benda, V. et al, Conceptual design of the cryogenic system of the Large Hadron Collider (LHC), 5th European ParticleAccelerator Conference EPAC’96, Sitges Barcelona, Spain, (10-14 June 1996)2. Millet, F., Roussel, P., Tavian, L. and Wagner, U. A Possible 1.8 K Refrigeration Cycle for the Large Hadron Collider,paper presented at CEC’97, Portland, USA.3. Tavian, L. and Wagner, U. LHC sector heat loads and their conversion to LHC refrigerator capacities,LHC Project Note 140 (1998)4. Claudet, S., Gayet, Ph. and Wagner, U. Specification of four new large 4.5 K helium refrigerator for the LHC, paperpresented at CEC’99, Montréal, Canada5. Bézaguet A., Lebrun, Ph. and Tavian, L. Performance assessment of industrial prototype cryogenic helium compressorsfor the Large Hadron Collider, In: Proc. ICEC17, Bournemouth, D. Dew-Hugues, R.G. Scurlock & J.H.P. Watson, eds.,IoP, Bristol & Philadelphia (1998), 1456. Claudet, S., Gayet, Ph., Lebrun, Ph, Tavian, L. and Wagner, U. Economics of large helium cryogenic system: experiencefrom recent projects at CERN, paper presented at CEC’99, Montréal, Canada7. Hilbert, B., Gistau-Baguer, G. and Dagut, F. 2.4 kW at 1.8 K refrigeration units for CERN LHC project supplied by AirLiquide, paper presented at this conference.8. Asakura, H., Honda, T., Mori, M., Yoshinaga, S., Bosel, J., Kündig, A., Kurtcuoglu, K., Meier, A. and Senn, A.E., Four2400 W / 1.8 K refrigeration units for CERN-LHC: the IHI/Linde system, paper presented at this conference.

Specification of Eight 2400 W @ 1.8 K Refrigeration Units for the LHC

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