STATUS OF SCO 2 POWER CYCLE STUDIES AT CEA

Transcription

1 STATUS OF SCO 2 POWER CYCLE STUDIES AT CEA 1

2 Na/SCO 2 chemical interaction Cycle thermodynamics: He/SCO 2 & Na/SCO 2 Cycle components: Intermediate heat exchanger Turbomachinery Cycle operation: Part load following Cold sink issue Conclusion OUTLINES 2

3 Na/CO 2 CHEMICAL INTERACTION : calorimetric experiments CONSTANT TEMPERATURE EXPOSURE (400 C- 673K) Molar ration Na/CO 2 =0.49 Heating until 400 C Sinclair & al., Reaction of carbon monoxide with sodium, The Alkali Metals Proc.Symp., Nottingham, July 19-22, Na/CO [1] Constant temperature exposure (400 C) INDUCTION TIME = f(t) COMPLEX MECHANISM : AUTO-COMBUSTION? GAS CHROMATOGRAPHY : CO FORMATION SEM : CONSISTENT WITH FORMATION OF Na 2 CO 3, Na 2 C 2 O 4 3

4 Na/CO 2 CHEMICAL INTERACTION : results & prospects PRESENT VIEW OF REACTION SCHEME (to be published*): T < C (773K) ; complex scenario ; kinetically controlled ; Carbonate & oxalate formation Na/oxalate & oxalate decomposition (CO release) Na/CO reaction (induction time) ; By-products : CO ; Na 2 CO 3 ; Na 2 C 2 O 4 ; C ; Na 2 O ; NaCO ; Na 2 C 6 O 6. T > 500 C (773K) ; no more induction, fast global reaction : 2Na + 1.5CO 2 Na 2 CO C UNDERTAKEN ACTIONS : Study the interaction in more representative conditions : direct injection P in dynamic Na knowledge of kinetics & ΔH reaction (assessment of of a "westage" scenario occurrence) Particles issue (carbonate): significant dissolution or trapping? Reaction detection systems : efficiency & reliability *N. Simon & al., Investigation of sodium-carbon dioxide interactions with calorimetric studies, ICAPP 07, Nice, May 13-18,

5 CYCLE THERMODYNAMICS : data & tools Cycle architecture: recompression ; {H, S, ρ,..} data: Span eq. of state By-pass compressor Main Compressor Density (kg/m3) T Flow Split SC Junction HT recuperator BT Récupérator Mass and energy balances: CYCLOP, CEA tool. Optimisation: genetic algorithms, adapted to multi-parameters problem Hypothesis for cycle efficiency calculations: Electrical and mechanical losses: 2% alternator, 1.3% shaft TM : η T = 93% & η C 88% HE : η recuperator = 90% ; η IHX SF Temperature ( C) ~ 88% (ΔT = 30 C) Cold cycle operating point = 21 C (294K) Pressure (bar) 5

6 CYCLE THERMODYNAMICS : Na/Brayton cycle η vs. gas type Na! Gaz? T out core = 550 C (823K) ; T in turb = 520 C ; P in turb = 50 bar (5MPa) Gas He He-N2 N2 T in core 395 C 395 C 395 C Pressure ratio x 1.7 x 2.0 x 2.1 Cycle η 35.2% 35.7% 36.4% CYCLOP Cycle efficiency 39% 38% 37% 36% 35% 34% 33% Turbine inlet pressure, bar % Na / steam Rankine cycle (18MPa) + 2% if Psec 120 b ; + 3% 250 b (25MPa) + 0.5% if η compressor +1% + 0.5% if η turbine +1% + 0.7% if η recuperator +1% 6

7 POWER core = 600 MWth P in turbine = 250 bar (25MPa) T in turbine = 520 C (793K) P = 76.9 bar (7.69 MPa) T out, cold sink = 32 C (305K) Cycle efficiency = 41.3% Psat = 59 bar (5.9 MPa) T out, cold sink = 21 C (294K) Cycle efficiency = 45.1% T in turbine = 620 C η Cycle = 49.1% P in turbine = 200 & 160 bar η Cycle = 44.4 & 41.7% CYCLE THERMODYNAMICS : Na/SCO 2 CYCLOP Ref - Na/N 2 : η < 40% T in turb 520 C & P 250 bar 7

8 CYCLE THERMODYNAMICS : optimal flow split analysis GFR simulation Split: T inlet SC T SC η cycle 10% from optimal fraction cycle efficiency of ~ 4 points. 8

9 CYCLE COMPONENTS : Na/SCO 2 & Na/N 2 -He heat exchanger 6 m For 1 bar of pressure drop 13 MW/m 3 11 MW/m MWth Plates & fins technology Preliminary sizing : 300 MWth, η IHX = 97% gas: d h ~ 2 mm, offset strip fins He-N 2 8 m S-CO 2 Na: d h = 4 mm, straight fins SCO 2 compactness : ρ = 10 ρ N2-He V ΔP/L Re Nu 10m Na 6 m Na λ = 1/3 λ N2-He h L = 3 m d h SCO 2 can be further reduced Sensitivity - basis : η IHX 88% ; ΔP 1 bar ; η cycle 45.1% C 28 MW/m 3 η IHX 95% η cycle 45.8% ; C 15 MW/m 3 ΔP 2 bar η cycle 45% ; C 40 MW/m 3 9

10 CYCLE COMPONENTS : recuperators,, pinch point INTERNAL PINCH POINT T evolution if Cp = Cp Transferred power Cp Power balance = Power balance Temperature Internal pinch-point issue Energy balance at inlets / outlets is not sufficient High power e.g. ~ 2 turbine power for He/SCO 2 (GT-MHR : about 1 ). significant impact of recuperator efficiency : + 5 % η recuperator + 2 % η cycle {ΔP = 0.4 b, η recup = 90%} MW/m 3 compactness for plates & fins techno. 10

11 CYCLE COMPONENTS : SCO 2 axial turbomachinery VERY PRELIMINARY SIZING, ΔH MAX / STAGE STAGE COUNT : Compressor : Haller criterion for diffusion losses, qualitative, V 2 / V Turbine : Craig & Cox abacus, ΔH/U 2 = function (Va/U, η) 600 MW th cycle, T in-turb 550 C, 200/76.9 bars, T out-cold sink = 32 C. P h /P b Stages count max Minimum blades height COMPRESSOR GT-MHR (He) CO 2 SC- BYPASS BP+HP : 40 ~ m < 0.9 m 5 cm < 3 cm TURBINE GT-MHR (He) CO 2 SC ~ m 1.2 m - - IMPRESSIVE COMPACTNESS FOR AXIAL TECHNOLOGY 11

12 CYCLE COMPONENTS : Na/SCO 2 bypass compressor sizing AXIAL SIZING: mean line analysis ; diffusion, secondary & annular losses Haller criterion Friction >> ~ 0.7 m, L ~ 1.4 m Poor deflexion control Blades count (solidity) : balance of blades flexion stress η compressor optim. η = 88% applying correlations from opened literature ; results reliability? diffusion losses: should be ok, high reynolds number (10 7 ). annular & secondary losses for such small blades height? tip clearance losses (not modelised). RADIAL - ΔH = 99 kj/kg 1 stage U ~ 330 m/s ; ~ 2 / 1 m at 3000 / 6000 rpm η? = 1 m at 3000 rpm 5 stages 12

13 CYCLE OPERATION : part load control, nitrogen case Na/N 2 PART LOAD CONTROL : Na/N 2 CORE & TURBINE BYPASS OR INVENTORY INVENTORY CONTROL PRINCIPLE : MAINTAIN OF VOLUMETRIC FLOWS AT TM INLETS Turbine & Comp. velocity Δ remain constant i.e. at design incidence. ΔH/kg remain constant (Euler) so does pressure ratio (perfect gas law) η cycle AT DESIGN STATIONARY : Mass flow balance (dρ & dp sym. variation, perfect gas law) Pressure equilibrium IN FACT, INVENTORY CONTROL η cycle : Turbine power proportionaly to pressure whereas head losses pumping power has a slower with pressure. Turbomachinery efficiency because : Reynolds number operating point is slightly modified (due to head losses) blades incidence 13

14 CYCLE OPERATION : part load control, SCO 2 case INVENTORY CONTROL STUDY : GFR ; η design = 44.8% ; 76.9 bar / 32 C Main compressor Bypass compressor Turbine Pressure decrease -4% -4% -50% ASYMMETRY : Turbine & bypass compressor : close to perfect gas behaviour W = ΔH = f(p out /P in, Te), Main compressor, real gas behaviour dh = f(p,t) Simulation = maintain of volumetric flow at both compressor inlets (ΔH/kg): Change of turbine volumetric flow Additional valves at turbine & bypass compressor outlets for pressure equilibrium ( losses) Flow split modification to adjust % nominal pressure ratio 74% ~ 100 % ~ 100% flow rate (asym. density change) VERY COMPLEX : valves + weak pressure variation % nominal density -47% -5.5% -48.5% 14

15 CYCLE OPERATION : cold sink issue ISSUE : IMPACT OF SEASONAL VARIATION OF COLD SINK TEMPERATURE ON CYCLE OPERATION AND EFFICIENCY. NITROGEN H2O CO2 T ( C) P (bar) Density (kg/m3) T ( C) Psat (bar) Density (kg/m3) T ( C) Psat (bar) Density (kg/m3) 21 23,3 26,8 21 0, , ,8 762, ,3 25,9 31 0, , ,5 711, ,3 23,4 61 0, , ,5 SCO 2 cycle designed for condensation (η: + 4 pts) implies significant change of low pressure to meet saturation. Process? Cycle efficiency? CO2_SC T ( C) P (bar) Density (kg/m3)! H COMP. (kj/kg) P out (bar) 32 76,9 598,1 18, ,9 739,4 15, ,9 273,7 32,4 200 Vol. flow rate = 2.2 ; W = 1.8 Even when designed for 76.9 b & 32 C, SCO 2 cycle implies significant change of density as well as power required to maintain pressure ratio. What is the new operating point and associated cycle efficiency in case of single shaft for compressors and turbine? May possibility of compressor speed change simplify and optimise cycle process and efficiency? Need of turbomachinery performance maps (off-design). 15

16 CONCLUSION Na / SCO 2 CHEMICAL INTERACTION : key point for sodium fast reactors! CYCLE THERMODYNAMICS : attractive efficiency at design, but : reduced gain / nitrogen depending on part load conditions occurrence (i.e. other part load following mode to be found). adaptation to cold sink temperature change to be studied : relevance of condensation cycle & speed change requirement? CYCLE COMPONENTS : compactness. main concern is for compressor efficiency due to its very small blades. relevance of a radial compressor instead of an axial: efficiency of a such a component? CYCLE OPERATION : CYCLE OPERATION : stability concern due to significant variations of physical properties close to critical point need of a dynamic code to study this point (with a good description of components running!) 16

17 CYCLE THERMODYNAMICS : He/SCO 2 POWER core = 2400 Wth P in turbine = 250 bar (25MPa) T in turbine = 650 C (923 K) P = 76.9 bar (7.69MPa) T out, cold sink = 32 C (305 K) Cycle efficiency = 44.8% Psat = 59 bar (5.9MPa) T out, cold sink = 21 C (294 K) Cycle efficiency = 48.7% ref - GTMHR : η ~ 47% T in turb 850 C He direct cycle CYCLOP 17