2 nd Swiss Symposium Thermal Energy Storage Lucerne, January 16 th 2015 Aqueous sodium lye seasonal thermal energy storage development and measurements on the heat and mass transfer units P. Gantenbein 1, X. Daguenet-Frick 1, E. Frank 1, M. Rommel 1, B. Fumey 2, R. Weber 2 and K. Goonesekera 3, T. Williamson 3 1 Institute for Solar Technologies SPF, University of Applied Sciences Rapperswil (CH) 2 EMPA Swiss Federal Laboratories for Materials Science &Technology (CH) 3 Kingspan Renewables Ltd. (Northern Ireland)
EU financed project COMTES in the seventh framework programme (FP7 / 2007-2013 FP7: COMTES Combined development of compact thermal energy storage technologies Research partner: Industry partner: EMPA Kingspan Renewables Ltd. experimental steps with the NaOH-H 2 O at EMPA in a technical pre-project COMTES development lines: A (adsorption), B (absorption), C (super-cooling of PCM) 2
Liquid sodium lye sorption energy storage concept: Seasonal storage with low thermal losses and high volumetric energy density Thermochemical storage based on water absorption/desorption in sodium hydroxide (NaOH) High renewable energy fraction by using solar collectors and environment heat Thermal heat pump principle: - charging: 3
Liquid sorption energy storage concept: Seasonal storage with low thermal losses and high volumetric energy density Thermochemical storage based on water absorption/desorption in sodium hydroxide (NaOH) High renewable energy fraction by using solar collectors and environment heat Thermal heat pump principle: - discharging: 4
design and construction: Absorption process combined heat and mass transfer Components description simulation & design Photo: Liquid Sodium Lye & Solid Sodium Hydroxide Thermo-physical properties of the materials - Mass flow rates dm/dt - Concentration c i ; i=1, 2 (1=Water, 2=NaOH) - Temperature T - Pressure p(c, T), boiling and condensing curves - Surface tension - Viscosity etc. 5
Thermo-physical properties of aqueous sodium lye: Vapour pressure curve process cycle H 2 O Summer (vapour) E C D Winter (vapour) A NaOH H 2 O 6
Absorption process combined heat and mass transfer Components description combination of A&D to 1 unit and E&C to 1 unit Absorption (A) / Desorption (D) Sodium lye flow (NaOH-H 2 O) m Solutionin, h in (c in, T in ) Evaporation (E) / Condensation (C) Water flow m Liquid, in h in (c in, T in ) D: Heating Fluid A: Cooling Fluid A/D A & D unit m Solutionout, h out (c out, T out ) m Vapour, in m Vapour, out E: Heating Fluid E/C C: Cooling Fluid m Liquid, out h out (c out, T out ) E & C unit 7
Tube bundle falling film heat and mass transfer concept: Successful application in absorption chillers (but fixed operation point) verdünnte Lauge diluted lye T (low) High heat transfer rates - mass transfer(?) Process steps combination (seasonal sequential running, costs reduction, compact) Tube bundle technology for the two heat an mass exchangers (A&D and E&C) Simple design & low costs Wasserdampf Water vapour Recirculation (?) Recirkulation 18kg/h, 61% wetting (15mm spacing, brushed) 720kg/h, 94% wetting (groove, brushed) T (high) temperature konzentrierte Lauge concentrated lye Schematic of the charging process step 8
Heat and mass overview: Vacuum tight containers (no non-condensing gasses at P & T, no leakages) Process stages/steps combination (sequential operation, low costs, compact) Choice of tube bundle technology for the two heat an mass exchangers (simple and compact) A/D unit (chamber 1) vapour feed through E/C unit (chamber 2) sight glass NaOH-H 2 O inlet water inlets tube bundle flanges heat transfer medium collectors NaOH-H 2 O outlet discharging charging level measurement cell water outlet 9
Combined E/C components description Vapour feed through A/D E/C: low pressure loss, IR shield Fluid manifold: designed to ensure an homogeneous liquid distribution Tube bundle unit: - A/D sized without fluid recirculation, E/C with the lower rate possible - most of the connections/sensors placed on the flange Level measurement cell: limitation of the parasitical energy consumption feeding tube manifold plate with nozzles (fluid distribution) tube bundle hair pin (simples handling) vacuum flange E/C unit level measurement cell 10
Wetting measurements: A/D tube bundle characterization Acquisition of the pictures dark area = presence of droplets Statistics: Achieved on 1000 pictures, at each pixel minimal light intensity value of the field retained Post-processing: - Light intensity in function of position - Threshold; wetting fraction ratio calculation Nozzle manifold Distance 2m Tube bundle (3 x 6) CCD camera Pump Back lamp Light diffusor Front lamp 11
A/D tube bundle characterization: Wet surface fraction development in function of the mass flow rate at different positions Modelling with logarithmic trend lines at the top of the tube bundle possible Highest values of the wet surface fraction at the top of tube bundle implementation of temperature sensors => light wet surface fraction enhancement (max 8 % of relative increase at the tube bundle bottom) 12
experiments with tube bundle falling film absorber: Power & temperature lift Absorber flow rate: 0.95 l(naoh-h 2 O)/min Power: Range P=(0.4 1.2)kW Temperature: Range DT=(2 4) C 13
experiments with tube bundle falling film absorber / evaporator: Tube bundle surface wetting flow modes - from literature - Absorber flow rate: 0.6 l(naoh-h 2 O)/min Absorber flow rate: 1.2 l(naoh-h 2 O)/min Evaporator maximum flow rate: 6.0 l(h 2 O)/min 14
experiments with tube bundle falling film absorber: Absorber flow rate: 0.95 l(naoh-h 2 O)/min Absorber: 0.4 l(naoh-h2o)/min Non-condensable gas! Power: Range P=(0.4 1.2)kW Temperature: Range DT=(2 4) C 15
Conclusion: Reaction zone construction philosophy: Easy access to the tube bundles and their accessories ( easy maintenance) Good sight on the process ( fluid distribution / surface wetting & control) Reduced number of gaskets ( low air leakage rate) measurements / assessments: System (containers) is vacuum tight Experimental results reached E & C unit functioning as expected Manifold concept validated Tube bundles instrumentation do not severely disturb the fluid flow A/D Photo: A/D and E/C units. E/C 16
Outlook further work: Desorption experiments planned Assessment of the concept unified components A/D & E/C Increasing mass transfer coefficient (Nu=Nu(Re, Pr); Sh=Sh(Re, Sc)) Increasing surface area tube number Increasing surface wetting fraction modified manifold, surfactants etc. Example 1: Deionised water droplet on the surface. Example 2: Acetone on surface structured copper tube. 17
COMTES: Combined development of compact thermal energy storage technologies Development Line B: Thermal energy storage in a aqueous sodium lye. Thermal energy storage is essential (in all time scales). Thank you for your attention! Financial support by the European Union in the seventh framework programme (FP7 / 2007-2013) under the grant agreement No295568 is gratefully acknowledged. We gratefully acknowledge financial support of our research institutions EMPA Swiss Federal Laboratories for Materials Science and Technology, the HSR University of Applied Sciences of Rapperswil and the Swiss Commission for Technology CTI. 18