Production of Synthesis Gas by High-Temperature Electrolysis of H 2 O and CO 2 (Coelectrolysis)

Transcription

1 Production of Synthesis Gas by High-Temperature Electrolysis of H 2 O and CO 2 (Coelectrolysis) Carl Stoots Idaho National Laboratory Sustainable Fuels from CO 2, H 2 O, and Carbon-Free Energy Columbia University, New York, May 4, 2010

2 Why High Temperature Electrolysis (HTE) at INL? INL is US lead nuclear energy laboratory Nuclear power has significant excess generating capacity But, nuclear power is only used for electrical power generation Water splitting / hydrogen production via nuclear power could: Utilize excess generating capacity via load leveling Relieve the pressure on natural gas for hydrogen production Provide raw materials and GHGfriendly energy for synthetic fuels production Diversify uses for nuclear power Extension to coelectrolysis leverages our much larger program studying high temperature H 2 O electrolysis Energy Information Administration / Annual Energy Review 2008 However, as will be discussed later, high temperature electrolysis is also synergistic with intermittent renewables such as wind or solar.

3 History of INL HTE Program DOE Nuclear Hydrogen Initiative (NHI) founded 6 years ago Goal -- demonstrate commercial-scale production of hydrogen using: Advanced nuclear energy (non-carbon emitting) Water splitting technology (sustainable) High temperature (energy efficient) Three processes developed in parallel SI Process Hybrid Sulfur Process HTE Process INL lead lab for HTE

4 Program Status NHI program conducted a down-selection last summer HTE identified as most promising technology Considered most robust Reversible (produce H 2 or electricity) Steam and Steam/CO 2 electrolysis DOE-NE should focus on the continued development of HTE INL HTE now funded through Next Generation Nuclear Plant (NGNP) program Historically we have concentrated on designs from Ceramatec Inc. NASA BSC Stack With increasing interest in H 2 production, we have tested more designs from other vendors Rolls Royce Fuel Cell Systems Typical Ceramatec SOEC Stack St. Gobain MSRI

5 INL HTE Program Description Bench Scale Experiments CFD Simulation Scale-Up System Modeling 720 cells, 15 kw

6 Coelectrolysis electricity, heat H 2 O + CO 2 H 2 + CO + O 2 Coelectrolysis reduces H 2 O and CO 2 simultaneously Motivation: Syngas can be feedstock for methane or synthetic liquid fuel production Coelectrolysis syngas production to synfuel utilization can be carbon-neutral if: non-co 2 emitting energy source is used (nuclear, wind, etc.) CO 2 source is from biomass Actively being studied by INL, Risoe, and Ceramatec INL coelectrolysis funding << steam electrolysis

7 Coelectrolysis Coelectrolysis is not well understood - Multiple reactions Steam electrolysis Reverse Shift Reaction (RSR) CO 2 + H 2 CO + H 2 O CO 2 electrolysis? Our Area Specific Resistance (ASR) measurements indicate: ASR coelectrolysis ~ ASR H2O ASR dry CO2 > ASR H2O - Seems that: H 2 O consumed in electrochemical reaction CO 2 consumed in RSR Figure of merit representing net effect of all loss mechanisms in cell / stack - While it is possible to produce syngas by separately electrolyzing steam and CO 2, there are significant advantages to electrolyzing steam and CO 2 simultaneously Lower cell resistance (lower ASR) Reduced possibility of further reduction of CO to C

8 Coelectrolysis Testing Apparatus

9 Stack Performance: Electrolysis vs. Coelectrolysis CO 2 Electrolysis ASR CO2 ~ 3.84!cm 2 Stack Operating Voltage (V) H O Electrolysis 2 ASR ~ 1.36!cm 2 H2O H O/CO Coelectrolysis 2 2 ASR ~ 1.38!cm 2 H2O/CO2 Tests #20, 21, 22 (sequential tests) Same stack 800 C operating temperature Stack Current (A) Dry CO 2 ASR significantly higher than steam ASR Stack performance same for steam electrolysis or coelectrolysis Explanation (as stated earlier): H 2 O consumed in electrochemical reaction CO 2 consumed in RSR

10 Typical Coelectrolysis Stack Results 20 Inlet CO 2 15 H 2 Experimental Results Mole % (Dry Basis) 10 CO 2 Inlet H 5 2 CO Inlet CO Electrolysis Current (A) Model Results Stepwise DC potential sweeps At zero current (no electrolysis) CO 2, H 2 consumed CO produced Reverse shift reaction Yield of syngas increased linearly with current Good agreement with INL-developed coelectrolysis model

11 Extensions of Coelectrolysis 100 Electrolysis cell Tubular reactor Ni catalyst Methanation of coelectrolysis products Water splitting 4H 2 O 4H 2 + 2O 2 RSR CO 2 + H 2 CO + H 2 O Methanation CO + 3H 2 CH 4 + H 2 O Net Reaction CO 2 + 2H 2 O CH 4 + 2O 2 Tests performed by Ceramatec for INL INL studying hybrid energy systems Linked electrolysis to natural gas, methanol, and DME production Test 1, Stack Inlet Test 1, Stack Outlet Test 1, Methanation Outlet Test 2, Stack Inlet Test 2, Stack Outlet Test 2, Methanation Outlet Test 3, Stack Inlet Test 3, Stack Outlet Test 3, Methanation Outlet Test 4, Stack Inlet Test 4, Stack Outlet Test 4, Methanation Outlet Test 5, Stack Inlet Test 5, Stack Outlet Test 5, Methanation Outlet CH 4 CO CO 2 N 2 H 2 + = Synthetic Methane, Liquid Methanol, DME

12 Navy Synfuel Program at Ceramatec Inc. Salt Lake City, Utah Syngas from coelectrolysis is Compressed Stored for batch processing Converted to liquid hydrocarbons via Fischer-Tropsch Oil fraction Water fraction

13 General Comments About Coelectrolysis current density, A/cm reaction ohmic net 0.2 heat flux, W/cm 2 fuel cell electrolysis thermal neutral voltage 0 open-cell potential operating voltage, V Open cell potentials for H 2 O and CO 2 electrolysis are about same (~0.9 V) Thermal neutral voltage Voltage at which endothermic heats of reaction balance ohmic heating Isothermal and adiabatic operating point Operation at V tn minimizes thermal stresses V tn,co2 > V tn,h2o, therefore V tn,coelectrolysis > V tn,h2o Coelectrolysis at V tn,coelectrolysis will have greater current throughput than same cell at steam electrolysis V tn,h2o

14 Electrolysis vs. Coelectrolysis? Assume your desired goal is to convert H 2 O/CO 2 to FT liquid using electrolysis electricity Steam Electrolysis H 2 O H 2 O Electrolysis H 2, H 2 O FT Reactor / Shift Reactor FT Liquid CO 2 electricity Coelectrolysis H 2 O CO 2 H 2 O/CO 2 Coelectrolysis with RSR Syngas FT Reactor FT Liquid Steam Electrolysis: 1. RSR occurs in FT reactor, RSR endothermic heat requirement can take advantage of heat rejected by FT reactor. Coelectrolysis: 1. Higher V tn for coelectrolysis means coelectrolysis at V tn,coelectrolysis will produce more H 2 than steam electrolysis at V tn,h2o 2. Reaction kinetics for RSR are better at elevated temperature of electrolysis cell electrode. Ignoring other considerations, steam electrolysis could be more logical choice for medium temperature Fe catalysts while coelectrolysis more logical for low temperature Co catalysts

15 Why Electrolytic Synfuels? Electrolysis efficiency Energy storage density (~10x greater energy storage density) Fits in existing distribution infrastructure Potentially no added CO 2 emissions Reduced work of compression Recycling CO 2 : conversion of Low value carbon (CO 2 - $55/ton Norway C tax) High Value Carbon Natural Gas $444/ton carbon Crude Oil $888/ton carbon (@$100/bbl) Refined Fuel (pre-tax) ~$1000/ton carbon Synergy with intermittent energy sources

16 Near-Term Coelectrolysis Deployment Strategy High temperature coelectrolysis has fast startup / shutdown times (ramping) makes it an attractive match for intermittent energy sources (wind, solar, etc.) Load leveling One could consider existing off-peak excess generating capacity as an intermittent source as well Electrolyzer can also supply electricity to help meet peak demand Large economic incentives to meet variable energy demands and Operate existing plants at maximum output Capture and utilize carbon rather than store (CO 2 recycling) Develop energy storage / conversion technologies

17 One Technology Multiple Modes of Operation NG Biogas Diesel JP-8 Coal Fuel Solid Oxide Stack Module Syngas Electricity CO 2 & Steam + Electricity Steam + Electricity Hydrogen (High Purity) & Oxygen

18 Sounds Wonderful What s the Problem? Economic projection assuming $50/MW-hr electric power costs assuming SOFC system capital costs of $400/kW (DOE SECA targets) coelectrolysis is not competitive with current $70/bbl oil but may be if oil prices once again climb above $130/bbl implementation of some sort of carbon emissions cost would further close the gap by $10-$20/bbl. Cell performance degradation Not commercially ready technology SOFC s have achieved performance degradation values < 1% / 1000 hours SOEC degradation rates much higher Improving SOEC durability is focus of INL research

19 Wrap-up of Coelectrolysis Technology High efficiency while using power from a diverse mix Nuclear Renewables (Wind, Solar, etc.) Biomass Conventional fossil-fuel-based power generation Synergies enabling greater penetration of renewable energy in generation mix Enables CO 2 recycling Converts a low-value carbon form (CO 2 ) to a high-value carbon form (syngas/synfuel)

20 Thank you!

21 Supplemental Why High Temperature