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MOLTEN CARBONATE FUEL CELLS ANSALDO FUEL CELLS: Experience & Experimental results Filippo Parodi /Paolo Capobianco (Ansaldo Fuel Cells S.p.A.) Roma , 14th & 29th March 2007 MOLTEN CARBONATE FUEL CELLS ANSALDO FUEL CELLS EXPERIENCE MOLTEN CARBONATE FUEL CELLS Elements of Fuel Cell Theory ANSALDO FUEL CELLS EXPERIENCE Evaluation of the characteristic parameters Flow diagram of a typical MCFC plant ANSALDO Fuel Cells experience Experimental results Filippo Parodi (Ansaldo Fuel Cells S.p.A. - Italy) Roma , 14th March 2007 FUEL CELL IS A DEVICE ... Electrical Energy e- AFC H2 H2O PEFC H2 H+ DMFC CH 3OH CO2 H+ PAFC H2 H+ MCFC H2 H2 O H2 H2O SOFC OH - CO = 3 O= O2 100 °C O2 H2O O2 H2O O2 H2 O O2 CO2 O2 80 °C 80 °C 200 °C 650 °C 1000 °C Fuel Oxygen H2 Air Cathode Anode Electrolyte DIRECTLY TRANSFORMS THE CHEMICAL ENERGY OF THE FUEL INTO ELECTRICAL ENERGY BY ELECTROCHEMICAL REACTIONS FUEL CELLS BASED vs. CONVENTIONAL ENERGY PRODUCTION PROCESS CO2, NOx, SOx, particulate, ash FUEL Heat losses THERMAL TO MECHANIC CONVERSION COMBUSTION Mechanical losses MECHANIC TO ELECTRICAL CONVERSION ELECTRIC ENERGY OXYGEN Steam/Gas Turbine CO2 FUEL FUEL PROCESSING Alternator H2O H2 FUEL CELL ELECTRIC ENERGY OXYGEN HEAT Fuel Cells based vs. conventional power systems Direct energy conversion (no combustion) Less conversion steps / Lower energy losses Higher efficiency Environmental benefit No moving parts in the energy converter, Low maintenance , Low noise Low exhaust emissions, Modularity Size flexibility Good performance at off-design load operation Fuel flexibility Modular installations to match load and increase reliability hydrogen, Natural Gas, biogas, biomass gasification, landfill gas, reformed heavy fuels Possibility of remote/unattended operation Fuel Cells Technologies AFC PEMFC Potassium hydroxide Ion Exchange Membrane 100°C 80°C 205°C 650°C 800-1000°C OH- H+ H+ CO3= O= Ni, Ag, nobel metals Platinum Platinum Not required Not required Fuel H2 H2 H2 H2, CO H2, CO Oxidant O2 O2 / Air Air Air, CO2 Air Poisons CO, CO2, CH4, S CO, CO2, S CO, S S S Electrolyte Operating Temperature Charge Carrier Catalyst PAFC MCFC Immobilised Immobilised Liquid Liquid Phosphoric Molten Acid Carbonate SOFC Ceramic AFCo selects as most promising FC technology: MCFC Operating temperature about 650°C No noble metal catalysts are used into the stack Uses carbon monoxide as fuel and carbon dioxide as cathode reactant Allows much simpler reforming section Allows coupling to gas turbine hybrid cycles (higher efficiencies) Plants up to 1- 2 MW size, for stationary applications, demonstrated in USA & Japan Ansaldo Fuel Cells Labs MCFC single cells Electrochemical Reactions: CO2 + ½ O2 +2e- CO3- cathode H2 + CO3- H2O + CO2 + 2eanode ---------------------------------------------------H2 + ½ O 2 H2 O overall reaction Materials: anode: Ni / Cr cathode: Li x Ni 1-x O matrix: LiAlO2 electrolyte: K2CO3 e Li2CO3 MCFC STACKS single cell voltage = 0.6 - 1 V current = up to 1000A DC To obtain the required electrical voltage and power, many cells are connected in series to build the MCFC Stack MCFC stack components and manufacturing These aspects will be shown on the next lesson 29/03/07 Paolo Capobianco Ansaldo Fuel Cells S.p.A. Responsible for laboratories Working principles of Fuel Cells MCFC technology Key materials and components Technological development LAB level tests Elements of Fuel Cell theory Characteristic parameters Reversible cell potential cell voltage out of reversibility temperature effects operating pressure effects reversible cell potential calculation polarisation effects: activation, ohmic, concentration experimental data on MCFC thermal management and operating ranges MCFC based power plants fuel reforming + MCFC mass balance performance experimental results reversible cell potential The Fuel Cell is a device that directly transforms chemical energy of the fuel into electric energy by mean of electrochemical reactions. From the thermodynamic point of view: From the thermodynamic point of view: at constant pressure: 1st Principle of Thermodynamics: RL H U P V H P e- U P V - U Q L A for electro-chemical reactions Q T S W P V Wel C H+ H2 for reversible transformations: + O2 reversibie cell potential definition Wel is related to anode and cathode voltages: Wel n F VC ,rev VA,rev with: n F VC, rev VA, rev Number of exchanged electrons in the unit reaction Faraday’s constant reversible cathode potential reversible anode potential From thermodynamics the Gibbs potential is G P H P T S n F VC ,rev VA,rev defining the reversible cell potential as: Erev VC ,rev V A,rev we have the direct relationship between available chermical energy G and the electric potential Erev G P n F Erev Temperature effects on Erev Erev S T nF Erev 0 T S T T [K] [°C] 298 25 54583 57973 -11.4 600 327 51147 58342 -12.0 800 527 48610 58757 -12.7 1000 727 46005 59034 -13.0 1250 977 42615 59633 -13.6 1500 1227 39202 59702 -13.7 -G -H [cal/gmole] [cal/gmole] [cal/gmole K] H2 1 2 O2 H 2O 70000 1.4 60000 1.2 50000 1.0 40000 0.8 30000 -DG -DH E = -3E-08T2 - 0,0002T + 1,2551 20000 DG = -0,0012T2 - 10,621T + 57895 10000 0.6 0.4 E (T, pi=1ata) 0.2 DH = -0,0002T2 + 1,886T + 57371 0 0.0 0 100 200 300 400 500 600 700 800 T [K] 900 1000 1100 1200 1300 1400 1500 1600 E (T, 1ata) [V] - DG [cal/g mole] - DH [cal/g mole] Temperature effects on Erev Operating pressure effects on Erev Erev V P T nF H2 1 2 Erev 0 P T O2 H 2O p products products G G R T ln reactan ts preact . 0 A B C D Erev 0 Erev 0 R T 0 nF p products products ln react preact * p products R T products * Erev Erev (T * ) ln react nF preact Operating pressure effects on Erev anodo H 2 CO32 H 2O CO2 2 e catodo CO2 1 H 2, A CO2,C 1 Erev 2 O2 2 e CO32 650C 2 O2,C H 2OA CO2, A p p R T H 2O , A CO2 , A * Erev (T ) ln 1 2 2F p p p H 2 , A CO2 ,C O2 ,C Erev 1 R T xH 2O , A xCO2 , A P 2 * Erev (T ) ln 1 2 2F x x x H 2 , A CO2 ,C O2 ,C Erev : study case calculation for MCFC T [K] P [ata] 923 3.5 CATODO O2 CO2 H2 O N2 Erev 10.2 6.2 21.0 62.6 ANODO H2 CO2 CO H2 O N2 CH4 51.0 6.6 8.2 33.4 0.0 0.8 1 xH 2O , A xCO2 , A P 2 R T * Erev (T ) ln 1 2 2F x x x H 2 , A CO2 ,C O2 ,C E*rev (923K) = 1045 mV Erev (923K) = 1039 mV %mol %mol %mol %mol %mol %mol 1.060 20.0 1.055 18.0 1.050 16.0 1.045 14.0 1.040 12.0 1.035 10.0 E* 1.030 8.0 Erev(P) a 650°C 1.025 6.0 dErev/dP 1.020 4.0 1.015 2.0 1.010 0.0 1 2 3 4 5 6 P [ata] 7 8 9 10 dErev/dP [mV/atm] Erev [V] Erev: pressure effects on MCFC Elements of Fuel Cell theory Characteristic parameters Reversible cell potential cell voltage out of reversibility temperature effects operating pressure effects reversible cell potential calculation polarisation effects: activation, ohmic, concentration experimental data on MCFC thermal management and operating ranges MCFC based power plants fuel reforming + MCFC mass balance performance experimental results cell voltage on load RL ne- I - + A C H+ combustibile fuel ossidante oxidant I V RL V Erev out of reversibility conditions cell voltage on load 1.5 1.4 Erev-OCV: parasitical reactions 1.3 Erev 1.2 OCV-A: OCV 1.1 polarization for activation A-B: linear voltage drop - ohmic behaviour 1 B-C: V 0.9 polarization for concentration A 0.8 0.7 B 0.6 0.5 C 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 i V Erev Ri I att conc V Erev 0.9 1 Elements of Fuel Cell theory Characteristic parameters Reversible cell potential cell voltage out of reversibility temperature effects operating pressure effects reversible cell potential calculation polarisation effects: activation, ohmic, concentration experimental data on MCFC thermal management and operating ranges MCFC based power plants fuel reforming + MCFC mass balance performance experimental results Experimental results on a MCFC stack 1400 1,40 design condition 1100 1000 900 800 700 600 500 400 300 200 100 1,00 [KW/m²] 1,20 0,80 0,60 0,40 Power Density Cell Average Voltage [mV] 1300 1200 0,20 0 0 200 400 600 800 1000 1200 Current Density [A/m²] Voltage vs current characteristic curve is linear: V = Erev - Rpol • I Negligible activation and parasitic voltage loss High current density design condition is possible 1400 1600 1800 0,00 2000 By courtesy of Ansaldo Fuel Cells SpA Concentration effects experimental results on MCFC single cell 1.6 Experimental Simulation 1.4 can be measured only for gas compositions very poor in H2 Cell Voltage [V] 1.2 or H2 Concentration 1.0 at very high current densities 0.8 good agreement with simulated values 0.6 0.4 0.2 0.0 0 500 1000 1500 2000 2 Current density [A/m ] 2500 3000 By courtesy of Ansaldo Fuel Cells SpA Elements of Fuel Cell theory Characteristic parameters Reversible cell potential cell voltage out of reversibility temperature effects operating pressure effects reversible cell potential calculation polarisation effects: activation, ohmic, concentration experimental data on MCFC thermal management and operating ranges MCFC based power plants fuel reforming + MCFC mass balance performance experimental results Thermal management on MCFC results from detailed simulation code (*) exothermal electrochemical reaction power generation produces heat excess in the cell thermal management need to avoid high temperature damaging of components high gas flow rate is used to cool down the stack (*) By courtesy of Ansaldo Fuel Cells SpA and PERT group of Genoa University Thermal management on real MCFC STACK MCFC - experimental data temperature distribution on the cell plane 700-710 690-700 680-690 670-680 660-670 650-660 640-650 630-640 620-630 610-620 600-610 By courtesy of Ansaldo Fuel Cells SpA typical operating ranges operating parameter typical values management 580 < T < 700°C cooling system: cathode gas high flow rates exhaust gas recirculation pressure and pressure drops 1 5 atm P anode/cathode < 20 mbar pressurised sytems allows higher performance, higher flow rates and lower pressure drop fuel utilisation oxidant utilisation 75% 56% prevent concentration effects on V vs. I curve temperature necessary for cathode reaction CO2 5% available by recirculation of anode exhaust to cathode (catalytic burner) Oxygen concentration 10% necessary for cathode reaction and catalytic burner combustion pollutants H2S, HCl, NH3, trace metals proper clean up systems Fuel Cells Plant Concept CONTROL SYSTEM FUEL FUEL processor Steam + heat H2 Steam + heat COGENERATION FUEL CELLS O2 to accomplish with proper AIR AIR TREATEMENT operating ranges the fuel cell DC / AC (DC / DC) need of a Balance of Plant tailored on the application MOLTEN CARBONATE FUEL CELLS ANSALDO FUEL CELLS EXPERIENCE Elements of Fuel Cell Theory Evaluation of the characteristic parameters Flow diagram of a typical MCFC plant ANSALDO Fuel Cells experience Experimental results