Thermal control of solid oxide electrolyser cells / fuel cells with high temperature heat pipes

Transkript

1 Hydrogen Days 2015, Prague March 2015 Thermal control of solid oxide electrolyser cells / fuel cells with high temperature heat pipes Planar Heat Pipe Tensioning nterconnector Ni-contact Cell (ESC) sealing Marius Dillig, Jürgen Karl Lehrstuhl für Energieverfahrenstechnik Friedrich-Alexander-Universität Erlangen- Nürnberg Gas supply

2 Outline 1. Motivation SOFC /SOEC & Heat Pipes mproved thermal management Dynamic operation 2. Planar Heat Pipe development Heat Pipe Design Experimental results 3. Short stack design & Experiments Stack design and Heat Pipe integration First experimental results 4. Conclusions Folie 2

3 1. Motivation SOFC & Heat Pipes mproved thermal management Dynamic operation Folie 3

4 Concept planar Heat Pipe nterconnector no HP Cell temperature Cell temperature with HP Heatpipe temperature evaporation HT heat SOEC SOEC condensation wick Folie 4 heat SOEC metal interconnector SOEC High air supply Steam supply 2 main goals of integrated planar heat pipe: - nternal temperature gradient reduction dynamic operation of stacks reduction of cooling air - sothermal heat extraction from SOFC stack high temperature heat supply to secondary processes SOEC metal interconnector SOEC no air supply Steam supply planar heat pipe

5 Load flexible SOFC / SOEC Stack Thermal Balance: Heat production depending on operation mode: Electrolysis exothermal endothermal thermoneutral point Fuel Cell Operation exothermal U ΔH =U op - Exothermal - Endothermal - Thermoneutral operation ΔU rev ΔU irr U ocv =U ΔG U op ΔU rev ΔUirr 800 C Current Voltage Diagram of Solid Oxide Cell Folie 5

6 Hydrogen Days 2015, , Praha Load flexible SOCs Thermal gradients in stacks in cell layer Dynamic stress Cell degradation: Microcracking Delamination Sealing degradation Heat Pipe integration: nternal thermal balancing in cell layer Heat supply / removal geometry endothermal SOEC 1.16 V, 0,27 A/cm², SU=0.13 T fuel = 800 C, no inlet air cell V, 0,96 A/cm², SU=0.78 T fuel = 800 C, no inlet air no HP 1000 K cell K 1.16 V, 0,43 A/cm², SU=0.28 T fuel = 800 C, no inlet air cell5 steam supply cell1 exothermal SOEC 1.34 V, 0,82 A/cm², SU=0.78 T fuel = 800 C, no inlet air with HP 1051 K 1083 K no HP with HP planar HP, 1073 K Folie 6

7 Evaporation Process integration Direct thermal integration of SOFC stacks and endothermal fuel preparation: - CH 4 (pre-) Reforming - H 2 release from H 2 storage media Casing ( LOHC*) SOFC / SOEC system (0,75V,AR=2) *Liquid organic hydrogen carriers: D. Teichmann, W. Arlt, P. Wasserscheid, nt. J. Hydrogen Energy 2012, 37, Fluid backflow Vapor transport in capillaries Wick Condensation Cavity Heat from SOFC stack [W/cm²] Heat demand [W/cm²] 100% pre SR** CH Almost 4 0,30 0,19 (SR CH4) isothermal operation 25% pre SR CH 4 0,14 0,05 (SR CH4) Folie 7 H 2 from LOHC 0,29 0,28 (LOHC) **Steam Reforming.

8 2. Planar Heat Pipe development Heat Pipe Design Experimental results Folie 8

9 HP nterconnector: Design and production heat pipe housing wick mesh spacer heat pipe housing heat pipe housing wick mesh coarse mesh a) Screen mesh layers as wick structure separated by spacing elements b) Rectangular axial grooves with vapour space separators c) Sandwich design with fine screen mesh layers as wick and coarse mesh as vapour space separator Mesh sizes Grooves size µm Mesh size: 10; heat pipe housing spacer heat pipe housing porous structure Capillary for Na-transport d) Small flat housing gap as planar capillary structure Capillary height µm e) Porous medium as wick structure and vapour space separator Pore sizes: ca µm Folie 9

10 HP nterconnector: Design and production 2 Vapour pressure [bar] 1,5 1 0,5 Hg Na p max p min NaK eut Li Temperature [ C] K Folie 10 Filling and degassing procedure Approaches: Planar high temp. Heat Pipes: Heat transfer fluid (max p sat =1 bar): Sodium (Na), Potassium (K) or NaK Wick material: Casing: Crofer 22H

11 Heat Pipe performance - results Folie 11 almost isothermal operation (only few K of dt in casing) for horizontal operation axial heat transfer rates up to 1000 W per planar HP (to 100 W/cm² HP cross section) grooved structures and pourous media still under evaluation screen meshed heat pipes with best results (mesh: ) planar Heat Pipe heater thermocouples cooler

12 3. Short stack design & Experiments Stack design and Heat Pipe integration First experimental results Folie 12

13 Stack Design: Cell: ESC 10Sc1CeSZ 100 x 100 mm nterconnector: Crofer 22H milled flow field, crossflow Heatpipe - nterconnector: 270 x 130 mm, t = 4 mm, Sandwich Design (Mesh 80, 8), Sealing: Thermiculite 866, 0,2-0,4 MPa Planar Heat Pipe Tensioning nterconnector Ni-contact Cell (ESC) sealing Gas supply Folie 13

14 Shortstack test set up 2-cell shortstack set up with integrated HP Placing of thermocouples within stack structure thermocouples mechanical load planar heat pipe gas supply Folie 14 voltage probes current connectors

15 SOFC / SOEC shortstack tests Results: Approaches: Dynamic operation possible: 300 SOFC / SOEC cycles SOFC: 0,20 A/cm²; 0,70 V SOEC: 0,32 A/cm²; 1,10 V differences in cell contacting due to planarity problems of planar heat pipe Sealing, Contacting to be improved SOEC operation: 850 C, 90 g/h H2O, 1.8 Nl/min H2, 3.0 Nl/min Air SOFC operation: 850 C, 1.5 Nl/min H2, 1.5 Nl/min N2, 3.0 Nl/min Air Folie 15

16 SOFC / SOEC 2 - cell shortstack tests with HP Results: Approaches: ncrease in heat pipe temperature shows thermal heat pipe integration Anode temperature is kept very close to heat pipe temperature Folie 16 SOEC operation: 850 C, 90 g/h H2O, 1.8 Nl/min H2, 3.0 Nl/min Air SOFC operation: 850 C, 1.5 Nl/min H2, 1.5 Nl/min N2, 3.0 Nl/min Air

17 Shortstack tests with HP without HP with HP Results: Folie 17 Thermal integration of heat pipe sothermal temperature profiles for SOFC and SOEC operation

18 4. Conclusions Folie 18

19 Conclusions Summary Development of planar heat pipe interconnectors, stack integration Up to 1000 W at isothermal operation, (t=4mm) - inert gas buffers, H 2 buffers - capillary limit for horizontal operation sothermal stack operation in SOFC /SOEC Outlook Temperature distributions in HP stacks under dynamic operation (start up bahviour) full scale stack layout & process integration Folie 19