THE TORE SUPRA CRYOGENIC SYSTEM. Design and operation

Transcription

1 THE CRYOGENIC SYSTEM Design and operation P.Reynaud 1

2 The Tore Supra Cryogenic system Outline Introduction : conception of the Tokamak Heat dissipations and constraints Design of the cryogenic system Operation of the cryogenic system Cryoplant availability Conclusion 2

3 Conception of the Tokamak Toroïdal field coil exploded view Average current density : 50A/mm², 4.5 T on the plasma axis, 9 T Peak field on the conductor. Tight envelop performed by the thin casing Thick casing acting as: - mechanical reinforcement, - magnetic shield, - thermal shield. Conductor (NbTi, Cu, CuNi) 1.8K Glass epoxy spacers Thin casing Polyamide alumina chocks Supercritical helium cooling channels 4.5K Thick casing 3

4 Conception of the Tokamak Torus cross section External vacuum vessel (20 C) External 80K thermal shield Thick casing and winding pack (4.4 K and 1.8 K) Internal 80K thermal shield Internal vacuum vessel and first wall ( C) Plasma All components are enclosed in a common vacuum vessel actively pumped 4

5 Conception of the Tokamak Torus assembly 80K thermal shields Module of magnet/ thermal shield/ vacuum vessel 5

6 Conception of the Tokamak Torus assembly Torus constituted by assembly of 6 modules of 3 coils Component Windings Casings Shields Mass 40 t 120t 20t 6

7 Insulating shocks Heat dissipation and constraints Winding pack heat loads Permanent losses windings Variable field losses Wc Hysteretic losses α (DB) Coupling losses α (db/dt) 2 Low Low energy thanks thanks to to efficient efficient magnetic magnetic shielding shielding Normal shot (5kJ) Plasma current disruption (15kJ) Fast discharge IT à 1250A (150kJ) 7

8 Heat dissipation and constraints Thick casing heat loads Permanent losses winding Thick casing variable field losses Wc Eddy currents = f (dip/dt) 2 Supporting legs During the plasma shots (< 150kJ) During the cleaning discharge (>= 1.MJ) During the plasma current disruption (>= 1.2MJ) 8

9 Heat dissipation and constraints 80 K thermal shields heat loads Wr External shield 1-Permanent losses Thermal radiation Thermal conduction (supports) Plasma Wc 300K Internal shield 80K shields Vacuum vessel Particular conditions :The :The baking baking The The Baking Baking of of the the vacuum vacuum vessel vessel is is one one of of the the techniques techniques used used to toobtain obtain very very low low impurity impurity release release conditions conditions Baking Baking is is effective effective in in removing removing water, water, volatile volatile hydrocarbons hydrocarbons and andhydrogen. Vacuum Vacuum vessel vessel temperature temperature is is led led and and maintained maintained to to around around 200 C 200 C (473K) (473K) during during several several days days Radiation Radiation heat heat loads loads on on thermal thermal shields shields of of vacuum vacuum vessel vessel increase increase about about 100% 100% 2-variable losses (negligible) 9

10 Heat dissipation and constraints Summary of the design heat dissipations 1.8 K 4.5K 80 K Transient load Heat load (kj) Recovery time Heat load (kj) Recovery time Heat load PF cycle 30 4 min min - Disruptions min min - Fast Safety Discharge min min - Cleaning Discharge 0.2 / cycle 2 s 1.5 / cycle 2 s - Static load (vessel at 120 C) 120 to 160 W 300 W 12kW Static load (baking at 200 C) kw The instantaneous power dissipated can be 10 times larger than average loads 10

11 Heat dissipation and constraints Other constraints : the cool down Major requirements are led by the differential contractions between materials function of temperature. Mechanical constraints during transients cooling down or warming up must be contained to avoid any plastic deformation of structures or between thick casing supports and thermal shields The contraction of materials is significant between 300K and 80K, therefore, between these values, the temperature gradient between any part of the system must be kept under 40K. 300K 1000 mm 997 mm DL/L=3mm/m 1000mm negligible 80K 80K 4.5K 999.9mm DL/L=0.1 mm/m Contraction of SS function of temperature To respect the previous requirement and to optimize the duration of the cool-down, the maximum speed rate of cooling down has been fixed at 2K/h to limit the temperature gradient between the thick casing and the centre of the windings In practice, the cool-down of the whole system from 300k to 1.8K takes around 15 days 11

12 Design of the cryogenic system Summary of the design requirements - Providing the cold power to : The Toroidal Superconducting Magnet at 1.8K (HeII bath) with comfortable margin, The thick casings at 4.5K (supercritical helium), The thermal shields at 80K (GHe), - Using thermal storages, allowing the installed cold power to be lower than instantaneous heat loads, - Ensuring a safe cool-down of the system following requirements on temperature gradients, with a reasonable duration, - Including redundancies, to preserve the cold parts from fast divergences of temperatures in case of any failure of the system - Liquefying helium and distributing LHe for the batch users : Diagnostics, Neutral Beam test beds, Gyrotrons, Magnet Group test beds.. - Adopting operational modes depending on plasma operation, for energy savings purpose. 12

13 T H=cst H3 6 6 Design of the cryogenic system W Helium réfrigération : «Cycle de Claude» H H1 HP Cold power = m H = m(h8-h7) BP 13 S Isenthalpic E1 12 E E3 E4 E5 C W W JT valve 7 The architecture of the refrigeration box is based on this thermo dynamical cycle The system sets to work a warm compression station, heat exchangers, turbo expanders, and expansion devices for the liquefaction. 13

14 P installed = 300W Permanent losses = 120W Design of the cryogenic system He II refrigeration at 1.8K Warm ring pumps P1-P2 C Compression cycle Available power 180W PF Heat exchanger Cold pumps 2 circuits: saturated He II pressurized He II 14g/s 1.75K - 13 mb HeII sat Cold source windings LHe W from 7 up to 17W / coil He II 1.25b The windings are located in a static pressurized superfluid helium bath The refrigerating power is obtained by the means of evaporation by pumping 14

15 Design of the cryogenic system He II pressurized for coils No risk of air leakage Easy helium transfer Improvement of the coil stability Increase of the critical current margin High limiting flux, independent of immersion depth All open and even recessed cavities are completely filled with liquid Vapour can only appear with a high T P (MPa) 0.1 He II T=1.8K He I Helium phase diagram Tλ=2.172 K T= 4.2 K P= 0.1MPa T (K) 15

16 Design of the cryogenic system The pumping on the He II bathes The pumping on saturated bathes is performed in 2 parts: A cold part compresses in 2 stages 14g/s of helium gas from 12mbar at 4.3K up to 80mbar near 15K. At this pressure the helium is warmed to room temperature by standard heat exchangers. At room temperature the final compression from 70mbar could be performed by an oil ring pump. The cold centrifugal compressors developed by L AIR LIQUIDE run on magnetic bearings and are driven by variable speed drives developed by the S2M company. At the moment of the design of the cryogenic system, the use of this technology for this particular purpose for the first time in the world was a major breakthrough for the helium refrigeration and opened the way of larger refrigeration plants at 1.8K. The choice of oil ring pump for the warm part of compression was also the result of comparatives studies both on technical aspects and economic costs. 16

17 P P Association 18 MPa 4.5 K Design of the cryogenic system The 4.5 K thick casing refrigeration Refrigerator 17 bar 4.5K Super critical He Circulation at Te = 4.5 K P,T Thermal ballast 3000 LHe P C pump Refrigeration box LHe Dedicated power to cold source : P= 600W Principle Casings connected in series Supplied with SHe coming from cold box Fixed inlet temperature of casings Thermal ballasts filled with LHe Operation at V=cst Absorption and smoothing of the loads Refrigeration box with evaporation Compensation of liquid from external tank W 18 thick casings W Practically constant operation Lhe restocking in off-peak hours Optimization of the cold box size 17

18 Design of the cryogenic system Thermal behavior during plasma operation 11,5 Pressure (mbar) 11 10,5 10 Toroidal field ramp up Plasma disruption and conditioning discharges Long plasma pulse 1 GJ 9, , time (h) HeII saturated bathes pressure W Toroidal field ramp up Plasma disruption and conditioning discharges Heat loads extracted from thick casings Long plasma pulse 1 GJ time (h) 18

19 Design of the cryogenic system 300K Cool down of the toroidal magnet from SC6 at 300K 1st Triple exchanger 80K from SC2 at 300K T out = ( )/3 T out = 227K A first division by 3 is performed at the refrigerator exit in order to divide the power between the «3 satellites 19

20 Design of the cryogenic system Cool down of the toroidal magnet 300K from SC6 at 300K 2nd triple exchanger 227K from SC2 at 300K T sortie = ( )/3 T sortie = 276K Within each satellite, a further division by 3 is operated 20

21 Design of the cryogenic system Cool down of the toroidal magnet Double exchanger 300K from casing at 300K 276K T sortie = ( )/2 T sortie = 288K 300K Casing N X 288K T BEp= =12K Finally, divisions by 2 are accomplished T global refrigerator / 18 (300-80)/18= 12 21

22 Design of the cryogenic system 80 K thermal shields cooling loop 4.6 b 18.6 b Oil removal system CB First heat exchanger 2 cold sources LN2 T1 water GHe circulation at T = 80K Available cold power from 2 sources 80K LN2 sat4 sat6 V1 T1 turbine sat4 sat6 with T1 during normal operation P = 10kW Thermal shields 18b sat2 with T1+LN2 evaporation during baking P = 30kW Increasing mass flow rate P windings 22

23 Design of the cryogenic system Functional layout Warm machine room Gathering warm compressors and pumps Including Oil removal system Providing the high pressure levels Collecting low pressure levels Cold box Providing the 80K and the 4.5K levels Liquefying helium Performing the cold pumping Liquid helium storage Cryogenic satellites Connecting the different circuits Performing the 1.8K source Smoothing the heat loads Part of the T division Cold Box Warm Machines room Torus Hall Torus Hall 23

24 Design of the cryogenic system Overview of the components and utilities Compressor House He screw compressors Oil removal systems He/H 2 O exchangers Oil/H 2 O exchangers Oil ring pumps He Balloons HP storage 200 bar compressors Coalescers Driers Analysers He buffer tank Safety systems Control & instrumentation systems Cryogenic Area Cold box He/He Exchangers Gas bearing turbines Expander engines Cold compressors 80 K GHe purifier Charcoal adsorbers Analysers LN2 tanks LHe tank Cryolines Vacuum systems Safety systems Control & instrumentation systems Utilities Vacuum system Water cooling systems Compressed air supply Power supply 24

25 Design of the cryogenic system Redundancies Mainly aim to maintain the whole system under 80K, A single cycle compressor is sufficient : 100g/s Rescue cold box Including a single heat exchanger with a LN2 evaporator Included set of valves, Linked to the thermal shields by distinct circuits Utilities Vacuum system Water cooling systems : switchable on raw water circuits Compressed air supply from different sources Power supply from different sources Rescue Programmable Logic Controller 25

26 Design of the cryogenic system System layout Within the Torus hall - 3 colds boxes acting as cryogenic relays called cryogenic satellites, - Each satellites contain a 1.8K source and a 4.5K thermal ballast, - Each of satellites feeds 6 toroidal field coils, - Each satellite is connected to the refrigerator by cryogenic lines Within the cryogenic hall - The cold box - A primary cryogenic line connected to the main cold box Adjoining the cryogenic hall - 1 storage of 20m 3 for LHe - 2 storages of 50m 3 each for LN2 Within the warm machine hall( 70m from the cryogenic hall) - The compressors and the warm pumps included in the system - The recovery compressors - Temporary helium storages: 200m 3 and 400m 3 gas bags Adjoining the warm machine hall A high pressure storage (18MPa) of gaseous helium : total volume 70m 3 26

27 200b Ghe storage Design of the cryogenic system General overview balloon GHe Compressors and pumps station 2*50 000l LN2 tank l Lhe tank Refrigerator cold box Cryogenic lines Satellites Cases and windings 27

28 Design of the cryogenic system The main figures First machine using a large quantity of superfluid helium 1m3 of saturated superfluid He, 4m3 of pressurized superfluid He Cold Power at 3 levels of temperature 10 to 30 kw at 80 K 1000 W at 4.0K 300 W at 1.75K Electric consumed power in nominal operation : 1.2MW Mass at low temperature kg at 80K shields kg at 4.5 K thick casings kg at 1.75 K conductors Cooling down duration 15 days to cool the magnet from 300 K to 1.75 K Fully automatic system with several operating modes for energy savings during short plasma shut down, 500 measurement loops, 300 cryogenic valves, 250 safety valves, 600 manual valves, 8 vacuum pumping systems, 7 Programmable Logic Controllers 28

29 1000 standby at 300 K Operation of the cryogenic system Typical Plasma experimental campaign (2006) WINTER SHUTDOWN COMMISSIONING Temperature of the TF magnet EXPLOITATION PERIOD SUMMER CENTRE CLOSURE IN-VESSEL WATER LEAK EXPLOITATION PERIOD WINTER SHUTDOWN Temperature (K) standby at 4 K Heavy maintenance of the cryogenic systems (4 weeks available per year) Annual test of the auxiliary cold box operation at 1.8 K Plasma Operation rhythm : ~ 40 hours a week 4 days a week : TF magnet at 1.8K 3 days at 4.2K week-end and maintenance day (Monday) Annual Shutdown : ~ 3 months a year Heavy maintenances: Warm Compression Station for example, Regulatory controls for pressure equipments, power supplies,etc Tore Supra configuration changes, etc. week (year 2006) weeks 29

30 Operation of the cryogenic system The cryoplant operational modes Warm stop Liquefaction only Idle at 80 K Liquefaction at 80 K Liquefaction at 4 K Nominal operation Liquefaction at 2 K The more usual operational modes of the cryoplant 30

31 Cryoplant availability Time spent in the different operating modes trough years Operating mode hours totals hours Totals hours totals hours totals Warm stop confirmed 1732 h 20 % 1311 h 15 % 543 h 6 % 1342 h 15% Idle at 80 K confirmed 476 h 5 % 853 h 10 % 338 h 4 % 421 h 5 % Liquefaction at 300K confirmed 222 h 3 % 577 h 7 % 192 h 2 % 192 h 2% Liquefaction at 80 K confirmed 501 h 6 % 558 h 6 % 89 h 1 % 399 h 5 % Liquefaction at 4 K confirmed 1841 h 21 % 1893 h 22 % 3645 h 43% 1512 h 17 % Liquefaction at 2 K confirmed 177 h 2 % 0 h 0 % 0 h 0 % 0 h 0 % Nominal operation confirmed 1770 h 20% 2036 h 23 % 2495 h 28 % 2445 h 28 % Total time spent in transitions 2013 h 23 % 1518 h 17 % 1394 h 16 % 2440 h 28 % TOTAL 8784 h 100 % 8760 h 100 % 8760 h 100 % 8760 h 100 % 31

32 Cryoplant availability Relative availability to the plasma experimental campaign Operating mode hours total hours total hours total hours total Nominal operation confirmed 1770 h 20% 2036 h 23 % 2495 h 28 % 2445 h 28 % Availability of the cryogenic system** 76.2 % 92.9 % 100 % 97.3 % Availability of the whole Tore Supra installation 53 % 54 % 76 % 80 % ** Relatively to experimental campaign 32

33 Cryoplant availability Tore Supra Cryoplant events 30% 25% 20% 15% 10% 5% 0% Cold component Instrumentation Process control Utilities Operation Warm component Distribution of faults during the cryoplant operation over the last 3 years Cold components: expanders, cold compressors, valves, exchangers. Instrumentation: Probe and signal conditioning. Process control: Hardware and software, process application Utilities: Water cooling, compressed air, power supplies, vacuum. Operation: He analysis and purification, the other faults. Warm components: compressors, pumps, valves, driers,. 33

34 Cryoplant availability Main troubles encountered through years Cryogenics Clogging of 80K stage exchanger of the cold box : addition of an external purifier Tightness breaking of Al/SS junction of thick casing circuit inside a cryoline, Many gaseous helium leaks : installation of a recorded helium leak detector, Water in oil circuits of the warm compressors in 2005, Pollution of the coils circuits during the cool-down in 2008, Utilities Very short life span of the compressor motors bearings at the beginning, Inappropriate system of command-control replaced by industrial PLC later Corrosion on water cooled black steel exchangers in the warm machine room, Corrosion and water leaks on vacuum diffusion pumps circuits, 2 total electric shutdown in the 4 last years : rescue by Electrical Mobile Groups 34

35 Conclusion The conception of the Tore Supra cryogenic system at the end of the 70 s was the result of studies lead by CEA about design and sizing of 1.8K refrigeration circuits. More than 20 years after its commissioning, and without any large updating, the cryogenic system is operated in quasi-industrial conditions with a satisfying level of performance and availability. Keeping a human presence on the site, performing daily inspections of the critical components and a reliable and ergonomic control-command system make possible an increase of availability during the 4 last years. Total operating time at low temperature h including h at T = 1.8K 35

36 Extra-slide Technical specifications of cold components Turbine T1 AL C5-500 In/out Temperature 110/80K Power 16kW Flow rate 110g/s Turbine T2 AL C3-500 In/out Temperature 50/30K Power 2.8kW Flow rate 24g/s Turbine T3 AL C4-500 In/out Temperature 19/10K Power 2.2kW Flow rate 50g/s Wet reciprocating engine AL/KPS model 1400 In/out Temperature 6/4.5K In/out Pressure 18/1.2bar Flow rate 10g/s Cold compressor PF1 AL/S2M Cold compressor PF2 AL/S2M Liquid storages Suction conditions 10mb/4.5K Suction conditions 34mb/10K Compression ratio 3 Compression ratio l of LHe + 2 x 50000l of LN2 Flow rate 14g/s Flow rate 14g/s 36

37 Extra-slide Technical specifications of warm components Compressor C1 STAL S7 Compressor C2 STAL S73 Compressor C3 STAL S51 Compressor C4 STAL S57 Oil ring pump P1 Alstom Hydro PL 160 Oil ring pump P2 Alstom Hydro PL 50 Recovery compressor C7 Sulzer type C5U Recovery compressor C8 Sulzer type C5U Gas bags HP storage In/out Pressure 1/4.5bar In/out Pressure 1/4.5bar In/out Pressure 4.5/18bar In/out Pressure 4.5/18bar In/out Pressure 70/600mbar In/out Pressure 0.6/1bar Pressure max 200 bar Pressure max 200bar Pressure max 200bars Flow rate 101g/s Flow rate 101g/s Flow rate 144g/s Flow rate 218g/s Flow rate 14 g/s Flow rate 60g/s Flow rate 10g/s Flow rate 10g/s 160m m3 Whole capacity : 1500kg Electrical power of motor 200kW Electrical power of motor 200kW Electrical power of motor 250kW Electrical power of motor 400kW Electrical power of motor 315kW Electrical power of motor 132kW Electrical power of motor 90kW Electrical power of motor 75kW 37