Advancement of Chemical Looping with Oxygen Uncoupling

Transcription

1 155 South 1452 East Room 380 Salt Lake City, Utah Advancement of Chemical Looping with Oxygen Uncoupling Kevin J. Whitty Department of Chemical Engineering Institute for Clean and Secure Energy The University of Utah Salt Lake City, Utah, USA 2014 Clean Coal Technology Fund Research Symposium Laramie, Wyoming August 20-21, 2014

2 Outline Introduction to chemical looping combustion and CLOU Oxygen carrier development and characterization Analysis of carrier conversion and rates Reactor development and scale up Process modeling Conclusions 2

3 Chemical Looping Combustion Process for energy production with inherent separation of CO 2 Uses metal-metal oxide complex to separate oxygen from air and transfer to fuel Overall balance same as for conventional combustion Determined to have lowest impact on cost of electricity of any low-carbon energy technology Cost of Electricity (cents/kwh) Influence of CO 2 Cost on COE for Various Technologies Oxy-fuel Marion et al. (2004) IGCC MEA Chilled Ammonia Oxygen trans. membrane Chemical looping Cost of CO 2 ($/ton) Without Capture 3

4 CLC with Natural Gas Air Reactor: N 2, O 2 Me x O y H 2 O, CO 2 ½ O2 + MexOy 1 MexOy Fuel Reactor: CH4 + 4 MexOy MexOy H2O + CO2 Air reactor Fuel reactor Air Me x O y-1 CH4 4

5 (Indirect) CLC with Solid Fuel N 2, O 2 H 2 O, CO 2 Air Reactor: Me x O y ½ O2 + MexOy 1 MexOy Gasifier: C + H2O H2 + CO C + ½ O2 CO Fuel Reactor: CO + MexOy MexOy 1 + CO2 H2 + MexOy MexOy 1 + H2O Air reactor Air Fuel Me x O y-1 Fuel reactor Gasifier H2, CO H2O, O2 5

6 (Direct) CLC with Solid Fuel Air Reactor: N 2, O 2 H 2 O, CO 2 ½ O2 + MexOy 1 MexOy Me x O y Fuel Reactor: C + H2O H2 + CO C + CO2 2 CO Air reactor Fuel reactor Fuel CO + MexOy MexOy 1 + CO2 H2 + MexOy MexOy 1 + H2O Me x O y-1 H2O, CO2 Air 6

7 Chemical Looping with Oxygen Uncoupling (CLOU) Oxygen (O2) is spontaneously liberated in the fuel reactor Allows for direct processing of solid fuels Selection of oxygen carrier combination is key 7

8 Equilibrium of the Reaction Cu2O + ½ O2 2 CuO O2 Partial Pressure (atm) CuO Cu2O Temperature ( C) 8

9 Why Does CLOU Work? Cu2O(s) + ½ O2(g) 2 CuO(s) Thermodynamics At higher temperatures, equilibrium of the metal oxidation reaction is pushed towards the left Equilibrium partial pressure of O2 is appreciable at combustion temperatures Reactor system configuration Air reactor has relatively high concentration of O2, which forces the reaction above to the right Fuel reactor has low concentration of O2 (since it is rapidly consumed by the fuel), pushing the above reaction to the left Only a few metal/metal oxide combinations that exhibit CLOU behavior in a reasonable temperature range have been identified 9

10 Copper-Based CLOU of Coal N2, O2 CO2, H2O Air Reactor 2 Cu2O + O2 4 CuO (EXOthermic) CuO Cu2O Fuel Reactor 4 CuO 2 Cu2O + O2 (ENDOthermic) C + O2 CO2 (EXOthermic) C + 4 CuO 2 Cu2O + CO2 (EXOthermic) Air BOTH reactors are exothermic! Coal (represented by C) 10

11 CLOU with Solid Fuel (Chemical Looping with Oxygen Uncoupling) Air Reactor: N 2, O 2 H 2 O, CO 2 ½ O2 + MexOy 1 MexOy Me x O y Fuel Reactor: MexOy MexOy 1 + ½ O2 C + O2 CO2 Air reactor Fuel reactor Fuel Air Me x O y-1 H2O, CO2 11

13 Oxygen Carriers: Off the shelf 50_TiO2_MM 50% CuO by weight TiO 2 support Mechanically mixed, then extruded, calcined, sieved Provided by ICPC, Poland 45_ZrO2/MgO_FG 45% CuO by weight MgO-stabilized ZrO 2 support Mechanically mixed, then freeze granulated, calcined Provided by Chalmers U, Sweden 13

14 Oxygen Carriers: UofU SiO 2 -based SiO 2 support Formed by starting with SiC, then calcining Two forms of SiC used - SiC powder (abrasive grit) - SICAT SiC spheres (catalyst support) CuO added by wet impregnation Rotary evaporator technique Bake-then-coat vs coat-then-bake 15, 20, 40 and 60% CuO loadings Number of CuO impregnation cycles was varied from 1 to 10 Peterson, S.B.; Konya, G.; Clayton, C.K.; Lewis, R.J.; Wilde, B.R.; Eyring, E.M.; Whitty, K.J. Characteristics and CLOU Performance of a Novel SiO2-Supported Oxygen Carrier Prepared from CuO and β-sic, Energy & Fuels 27(10): (2013). 14

15 Oxygen Carriers: UofU Copper-on-Ilmenite Ilmenite (FeTiO 3 ) used as support Conventional CLC carrier (Ti/Fe) Well characterized Inexpensive (< $100/ton) Wet impregnation Rotary evaporator technique Tested activated and non-activated ilmenite 20 and 30% CuO loadings CuO added in 6 to 9 cycles Under review: Clayton, S.K., Peterson, S.B.; Konya, G.; Eyring, E.M.; Whitty, K.J. A Novel Material for Chemical-Looping with Oxygen Uncoupling: The Performance of an Ilmenite Copper Bimetallic Carrier 15

16 Oxygen Carrying Capacity Oxygen carrying capacity evaluated by TGA CuO content thus determined Pure Cu 2 O gains 10% mass when converted to Cu 20% CuO on SiO 2, 900 C Stability of carrying capacity evaluated over multiple cycles 16

18 Rate Determination: Overall Objectives Develop better understanding of oxidation and reduction mechanisms for Cu-based carriers Work recently performed at e.g. Chalmers, CSIC, Columbia U. Evaluate dependence of rates on carrier properties e.g., in the absence of mass transfer limitations, will all carriers with 30% CuO behave the same? Ultimately, develop universal rate expressions suitable for incorporation into system models, perhaps of the form For oxidation: For reduction: 18

19 Range of Interest for Reaction Rates X = fraction of Cu as CuO, with remainder as Cu 2 O PDU design assumption: Carrier cycling between X = 0.75 exiting air reactor and X = 0.30 exiting fuel reactor Fraction Cu as CuO (X) Normalized Time Oxidation: 2 Cu 2 O + O 2 4 CuO Reduction: 4 CuO 2 Cu 2 O + O 2 19

20 Oxidation of Cu 2 O to CuO Oxidation experiments present interesting challenge Driving force for oxidation decreases with temperature Fundamental chemical rate increases with temperature (E a ) Possible grain boundary sintering may also contribute to reduced rate at high temperature Resulting oxidation rate peak observed by many groups Deciphering true kinetics is challenging 20

21 Oxidation: Influence of O 2 Driving Force Constant temperature Constant p O2,eq Vary O 2 concentration in oxidizing gas 21

22 Oxidation: Influence of Temperature Various temperatures CuO Various O 2 partial pressures Maintain constant driving force (p O2 p O2,eq ) Cu 2 O 22

23 Measured Oxidation Rates Range of experimental conditions Temperature Reacting gas composition Four types of carrier materials Various production techniques Various CuO loadings 23

24 Modeling of Oxidation Rates Mechanism determined to be more challenging than simple reversible reaction kinetics Two regimes of reaction behavior identified Low temperature, non-clou region - Best described by pore blocking kinetic mechanism High temperature CLOU region - Activation energy must be separated into thermodynamic and kinetic barriers - Best described by nucleation and growth mechanism Clayton, C.K., Sohn, H.Y., Whitty, K.J. Oxidation Kinetics of Cu2O in Oxygen Carriers for Chemical Looping with Oxygen Uncoupling I&ECR 53: (2013). 24

25 Measurement of CuO Reduction Rates Similar to oxidation studies Range of conditions Temperature Gas composition Challenge to have absolutely zero O 2 in gas phase Reaction order in CuO = 0 Apparent E a = 274 kj/mol Conversion Time (minutes) Time (minutes) Ea = 264 kj/mole [CuO] - 0 th Order ln[cuo] - 1 st Order [CuO] - 0 th Order [CuO] - 0 th Order ln(rate) Ea = 284 kj/mole 1/[CuO] - 2 nd Order Time (minutes) 1/[CuO] - 2 nd Order Time (minutes) /T (K -1 ) 25

26 Modeling of Carrier Reduction Rates Any oxygen in gas phase reduces driving force for reduction Used similar methodology to deciphering specific influences for oxidation Vary (p O2,eq p O2 ) at constant temperature Hold (p O2,eq p O2 ) constant at various temperatures Rate (go 2 /gcu/s) _TiO2_MM Series3 16_SiO2_IW 64_SiO2_IW Corrected Ea Apparent Ea Temp ( C) Could decipher constants in rate expression Universal rate expression: Clayton, C.K., Whitty, K.J., Measurement and Modeling of Decomposition Kinetics for Copper-Oxide Based Chemical Looping with Oxygen Uncoupling, Applied Energy 116: (2013). 26

27 Coal Conversion in Lab-Scale Fluidized Bed Three fuels tested Wyoming Black Thunder PRB Illinois #6 Green petcoke Two carriers tested 45% CuO on ZrO 2 50% CuO on TiO 2 Fuel introduced batch-wise Dropped onto top of bed shortly after turning off air Conversion performance determined based on concentrations of gases in reactor effluent 27

28 Coal Conversion Performance Ranking of fuel conversion PRB > Illinois #6 > petcoke Particle size matters Smaller is faster Largest particles not converted in the time needed to release all oxygen from CLOU particles - Consequence of batch design Carbon Conversion Air Flow Rate (SLPM) Time (Seconds) 28

30 Process Development Unit Design Goal to develop semi-pilot system for process studies Air and fuel reactors with circulating solids Continuous operation with continuous coal feed Design basis 100 kw th Wyoming PRB coal (sized for up to 250 kw th ) Oxygen carrier with 25% CuO loading 30% of Cu as CuO exiting fuel reactor, 75% as CuO exiting air reactor Design decision: Bubbling or circulating for each reactor Choice: Circulating for both (more scalable) Sizing based on measured reaction rates, fluidized bed relations, modeling Design decision: Metal or refractory-lined reactors Choice: Refractory lined (less complex, more industrial design) Other design decisions fuel reactor fluidization medium reactor integration and circulation separation of oxygen carrier and ash system heating 30

31 Balances and Detailed Design 31

32 PDU Construction 32

33 Chemical Looping PDU Air Reactor Fuel Reactor 33

35 Aspen Plus System Model Aspen Plus used to develop CLOU system model Fuel reactor module based on lab-scale results Conventional CLC system model also developed for comparison Basis: 100 kg/hr coal feed Easily scaled to larger system sizes RECYCLE REC-COMP Q SPLITTER Q GAS-SOL3 Q-RECYC FAST-REC REC-HEAT HOT-COMB HOT-REC COMB-GAS GAS-COOL COLD-GAS ASH COMBPURG Q Q-EXHAUS AIR-COOL DEC OMP BURN COLD-AIR IN-CUO COAL Q Q-CUO FUEL-REA HOT-CUO CUO-HEAT INBURN Q-DECOMP Q-FUEL GAS-SOL1 O2 Q-BURN CU-SOL Q LOSS CU-SOL2 AIR-REAC GAS-SOL2 ARX-PROD AIR-OUT CUO-REC Q Q-AIR Q Q HOT-AIR Q-AIRHOT AIR AIR-COMP AIR-HEAT FAST-AIR 35

36 System Model Design Assumptions Coal feed rate 100 kg/h Air flow rate 986 kg/h Average temperature of fuel reactor 950 C Average temperature of air reactor 935 C Mass flow rate of CuO at the inlet of the fuel reactor 3392 kg/h Mass flow rate of Cu 2 O at the inlet of the fuel reactor 1648 kg/h Mass flow rate of CuO at the exit of the fuel reactor 1560 kg/h Mass flow rate of Cu 2 O at the exit of the fuel reactor 3295 kg/h Amount of ZrO 2 circulating in the system 7836 kg/h Fraction of flue gas stream used for fluidization of fuel reactor 0.69 Particle density 2140 kg/m 3 Superficial velocity for fuel reactor 2.1 m/s Superficial velocity for air reactor 2.4 m/s 36

37 Model Results Energy System kw 37

38 Results: Costs of CLC vs. CLOU Relative capital costs (100 MW system) Relative operating costs 38

40 Conclusions Chemical looping combustion offers a comparatively inexpensive solution for capturing CO 2 from combustion of coal and other fuels CLOU and the associated release of gaseous O 2 results in much faster processing of solid fuels Robust, reactive Cu-based oxygen carriers can be manufactured using relatively low-cost raw materials Equilibrium of Cu 2 O-CuO results in a maximum rate of oxidation at approx 825 C. Oxygen release rate in fuel reactor is rapid, resulting in efficient processing of coal Size of reactors for CLOU are similar to those for CFB combustion Capital and operating costs for CLOU are lower than conventional CLC for equal size system 40