CO 2 Recycling via Reaction with Hydrogen

Transcription

1 CO 2 Recycling via Reaction with Hydrogen S. Kent Hoekman, Amber Broch, Curt Robbins, Rick Purcell Desert Research Institute, Division of Atmospheric Sciences John Ralston Recycle CO 2 Inc. EUEC Energy and Environment Conference Phoenix, Arizona February 4, 2009

2 Outline A. Introduction B. Experimental Set-up C. Experimental Conditions D. Results and Discussion Effect of reactant stoichiometry Effect of catalyst temperature Effect of space velocity (gas flow rates) E. Conclusions F. Next Steps 2

3 Introduction Power generation sector is a major contributor to total U.S. greenhouse gas emissions Carbon capture and sequestration (or storage), CCS, is being widely explored Carbon capture and recycle (CCR) is another approach for GHG mitigation Million Metric Tons CO 2 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 U.S. CO 2 Emissions by Sector Other Year Transportation Power Generation CO 2 Emissions data taken from DOE-EIA (2008) 3

4 Methanation Process: Sabatier Reaction CO H 2 Δ, Catalyst CH H 2 O Reduces CO 2 to methane at modest temperatures ( o C) Reverse reaction increases at temperatures >400 o C Highly exothermic reaction (ΔH = -167 kj/mol) Catalysts commonly include Ni or Ru Requires supply of Hydrogen H 2 must come from renewable sources (or nuclear) for GHG benefits 4

5 Experimental Schematic Synthetic Exhaust 2%CO 2 in N 2 Catalytic Reactor (Ni/AL 2 O 3 ) CH 4 + H 2 O H 2 O H 2 Wind Turbines Solar Photovoltaic Electrolyzer H 2 Storage O 2 Reactant gases: 2% CO 2 in N 2 ; 100% H 2 Methanation catalyst: Haldor Topsoe PK-7R 5

6 Design of Methanation Reactor Stainless steel tube: in. length x 3.14 in. diameter Catalyst packed bed: in. depth of catalyst - volume of 33.3 in 3 (0.55 Liter) Two thermocouple ports: - upper: 1/3 of bed depth - lower: 2/3 of bed depth Gas flow from top to bottom 6

7 Methanation Experimental Set-up 7

8 Methanation Experimental Set-up Photo of experimental apparatus inside trailer. Opening for inlet and exhaust lines H 2 Inlet Line H 2 Storage Tanks Synthetic Exhaust Inlet Line Reactor (with Heat Guard) Preheater Synthetic Exhaust Flow Controller Gas analyzers and synthetic exhaust cylinders located outside of trailer. 8

9 System Control and Monitoring Employed National Instruments Compact Field Point (cfp) unit: Control and record temps and gas flow rates Control safety shut-off Two continuous gas analyzers Before reactor: CO, CO 2, O 2, HC, NO x After reactor: CO 2, O 2, CH 4, NO x 9

10 Experimental Conditions Stoichiometric Conditions (H 2 /CO 2 = 4/1) 81.5 L/min of 2% CO 2 in N L/min of 100% H 2 Total flow of 88 L/min gives space velocity of 9000 hr -1 Variations in reactant gas ratios 7-step experiment Hold CO 2 /N 2 flow rate constant Increase H 2 flow rate in discrete steps from none to excess H 2 /CO 2 = 0, 2, 4, 6, 4, 2, 0 Four catalyst temperatures 200, 250, 300, and 350 o C 10

11 7-Step Reactant Variation Experiment H 2 Flow (SLPM) SLPM 6.52 SLPM 6.52 SLPM 3.26 SLPM 3.26 SLPM 81.5 SLPM Synthetic Exhaust Flow (SLPM) -60 Start data log H 2 solenoid OFF Preheat ON Reactor Heat ON Start flow profile when Cat. 1 reaches test temperature Time (min) Preheat OFF Reactor Heat OFF 0 All gas flow OFF END Test 11

12 Raw Data Output Reaction at 300 o C Lower Catalyst Temperature Gas Flow Rates Upper Catalyst Temperature % CH 4 out H 2 in (slpm) Temperature ( o C) % CO 2 out :00 05:00 10:00 15:00 Time (min:sec) 20:00 25:00 30:00 12

13 Data Analysis and Correction Only data from stable periods of operation were used (designated by shaded areas on previous plot) Corrected gas flows: reactor outlet flow rate does not equal inlet flow rate: 5 moles of reactant produce 3 moles of product Liquid water is produced during methanation Some inlet flow removed for analysis Corrections for analyzer drift and improper zeroing 13

14 Results: Total CO 2 Conversion 90% 80% H 2 :CO 2 = 6:1 CO 2 moles in- CO 2 moles out CO 2 moles in 70% 60% 50% 40% 30% 20% (Stoichiometric ratio) H 2 :CO 2 = 4:1 H 2 :CO 2 = 2:1 10% 0% Upper Catalyst Temperature 14

15 Results: CO 2 Conversion - Efficiency of Hydrogen Utilization* 18% CO 2 moles in- CO 2 moles out H 2 moles in 16% 14% 12% 10% 8% 6% 4% H 2 :CO 2 = 2:1 H 2 :CO 2 = 4:1 Stoichiometric ratio H 2 :CO 2 = 6:1 Maximum theoretical efficiency is 25% 2% 0% Upper Catalyst Temperature 15

16 Results: Effect of Space Velocity on CO 2 Conversion 80% Stoichiometric ratio: H 2 /CO 2 = 4/1 Catalyst temperature = 300 o C 75% 70% CO 2 in - CO 2 out CO 2 in 65% 60% 55% 50% 45% 40% Corrected Space Velocity (hr -1 ) 16

17 Summary and Conclusions 1. Sabatier reaction can be used to recycle CO 2 using renewably-produced hydrogen 2. Optimum conversion of CO 2 to CH 4 occurs at o C 3. Efficiency of H 2 utilization increases at lower H 2 /CO 2 ratios Preferred H 2 /CO 2 ratio is < stoichiometric ratio of 4/1 4. CO 2 conversion efficiency is reduced as flow rate increases Observed 15% reduction in conversion over 4-fold increase in space velocity 17

18 Next Steps 1. Scale-up reactor system Utilize two parallel reactors Implement active cooling of reactors 2. Utilize authentic exhaust from natural gas engine 3. Develop on-line H 2 measurement capability 4. Recycle produced CH 4 back to engine as a supplemental fuel 18

19 Acknowledgements Financial support: Recycle CO 2, Inc. Technical support: Larry Sheetz - DRI 19