Copper Looping with Copper Oxide as Carrier and Coal as Fuel

Transcription

1 Copper Looping with Copper Oxide as Carrier and Coal as Fuel Richard Baraki, Edward M. Eyring, Gabor Konya, JoAnn Lighty, Asad Sahir, Adel F. Sarofim, Kevin Whitty Institute for Clean and Secure Energy University of Utah Salt Lake City The International Advanced Coal Technologies Conference Laramie, Wyoming June 23, 2010

2 Chemical Looping Combustion with Oxygen Uncoupling (CLOU). The oxygen carrier dissociates at high temperature and the fuel (represented here by C) reacts with the O 2. CLOU proposed by Mattison, T., Lyngelt, A., and Lieon, L., J. Greenhouse Gas Control, 3, (2009) Air Reactor 2M + O 2 = 2 MO (Exo) N 2, O 2 2M + O 2 2MO Air Reactor is exothermic 2MO 2M CO 2 2MO + C CO 2 + 2M Fuel reactor is exothermic Fuel Reactor oxidation occurs via dissociation of MO to yield O 2 2MO = 2M + O 2 (Endo) C + O 2 = CO 2 (Exo) 2 MO + C = CO 2 + 2M (Exo) Overall Reaction 2M + O 2 = 2 MO (Exo) 2MO + C = CO 2 + 2M (Exo) C + O 2 = CO 2 (Exo) Air Coal (represent by C)

3 Outline History of Chemical Looping Combustion with Oxygen Uncoupling (CLOU) Why CLOU? Augmentation of Carbon Gasification with CLOU Reduced loading of oxygen carrier Oxygen carrier circulation rate is independent of thermal balance Sulfur is released as SO 2. CuSO 4 decomposes above 650 C Energy penalty is less than half experienced by other CO 2 capture technologies (IGCC, Post combustion scrubbing, oxyfuel) Kinetics of CuO decomposition and Cu 2 O oxidation Order of Magnitude Design Considerations Concluding Comments

4 Earlier study of CLOU for non-combustion application (Lewis, Gilliland, and Sweeney, Chem. Eng. Prog., 57(5), ,1951) as well as U.S. Patent No. 2,665,972 for the Production of Carbon Dioxide. The experiment consisted of a batch, electricallyheated isothermal reactor; an initial batch of oxygen carrier was fluidized with an external CO 2 stream; after equilibration a batch of carbon was added; then the external CO 2 supply used for fluidization was replaced by the CO 2 generated in the reactor and recycled after cleaning and drying. Progress of the reaction was followed by analysis of 1. the product gas for CO 2 and CO + O 2 and 2. samples of the bed solids for carbon content and O/Cu ratio.

5 Reactor Utilized by Lewis, Gilliland, & Sweeney Fines Filter Gas Analysis for O 2 +CO and CO 2 Initial Mass Coke ~ 12.5 g CuO ~ g Cyclone Fluidized Bed Reactor Run CC-6 T = C Time of run = min Average Reactor Pressure =1.095 atm. Superficial Velocity = m/s Coke: Metallurgical Koppers Type Size of coke particles : μm C % in coke = 88.25% Size of CuO on Silica Gel : μm CuO wt.% on silica gel = 10-15% Dryer and Filter CO 2 supply to start experiment Recycle Pump

6 Run CC-6 from Lewis, Gilliland, & Sweeney Temp. = 955±5 C P = atm. Vel. = m/s Excess O 2 in effluent when O 2 release rate by CuO exceeds consumption rate by C Peak gasification rate > 60 times that for Fe carrier at about same T. CuO Cu 2 O CO released when consumption rate by Cu 2 O slower than formation rate from CO 2 /C reaction. CO inhibits gasification rate. Gasification rate due to 100% CO 2

7 Relative rates of gasification by O 2 and CO 2 (relation to local O 2 concentration)

8 CuO/Cu 2 O Kinetics

9 Cycling atmosphere to TGA between air (30 min) and nitrogen (40 min) at 850 C to determine stability of CuO as an oxygen carrier.(similar results for supported CuO supported on TiO 2, appended slides) Relative weight (%) Air Time (minute) N 2 Results suggest that 1. CuO decomposes to Cu 2 O based on weight loss (~10%), 2. Sintering at higher temperatures will necessitate the use of supported oxides.

10 Isothermal 850 C ( one cycle: nitrogen for 40 minutes and air for 30 minutes) CuO decomposition Rel. weight (%) Time [min] Cu 2 O oxidation

11 Isothermal 950 C (one cycle between nitrogen 40 minutes and air 30 minutes) Rel. Weight (%) CuO decomposition Time [min] Cu 2 O oxidation

12 Rate constants for CuO decomposition and Cu 2 O oxidation in air 30 Prisedsky & Vinograd: Cu 2 O grains surrounded by fractured CuO k [1/msec] reduction oxidation Temperature [ C] Zhu, Minura, and Isshiki: The activation energy becomes..negative due to sintering of CuO grains & decrease in grain boundary diffusion

13 Kinetics used in Sytems Study 1. Determination of Oxygen Carrier Circulation Rate 2. Determination of Total Hold Up of Oxygen Carrier in Air and Fuel Reactors

14 Calculation of Mass Circulation Rate N C N Fuel Reactor N X CuO,AR X CuO,FR Let N be the mole flow rate of Cu circulating N C be the moles of carbon feed N CuO X CuO = N + 2N = mole fraction of Cu N C 2 {( N N )} ( from 4CuO 2Cu O + O ) N N C C N N C = N O 2 CuO Dividing = N = N = = {( X CuO, AR X CuO, FR )} ( X X )/ CuO, AR ( X X ) CuO, AR Cu CuO, AR by 4 O 2 N CuO, FR CuO, FR CuO, FR 2 / 4 4 / 4 in form of CuO

15 Mass of Copper circulated per MW th second (kg Cu/MW th second) Plot of Mass of Copper circulated per MW th second vs. Difference of Mole Ratio of CuO N.B. Oxygen carrier (OC) circulation =Mass of Cu/(Cu fraction in OC) X(CuO FR)=0.1 X(CuO,FR)=0.2 X(CuO,FR)=0.3 X(CuO,FR)=0.4 X(CuO,FR)=0.6 X(CuO,FR)= Difference of Mole Ratio of CuO; ΔX S = (X AR -X FR )

16 Mass of Copper loading per MW th (kg Cu/MW th ) Mole Loading of Copper in Air and Fuel Reactors = N ( τ + τ ) Plot of Mass of Copper loading per MW th vs. Mole Ratio of CuO at the exit of fuel reactor for different ΔX S (X AR -X FR ) X FR 0.35 ΔX S 0.45, X AR 0.8 AR FR N.B. OC loading =Mass of Cu/(Cu fraction in OC) ΔXS = 0.05 ΔXS = 0.1 ΔXS = 0.15 ΔXS = 0.25 ΔXS = 0.35 ΔXS = 0.45 ΔXS = 0.55 ΔXS = 0.65 ΔXS = X FR : Mole Ratio of CuO at the exit of Fuel Reactor

17 H 2 O = t/d O 2 = t/d CO 2 = t/d (at 950 C) CuO = t/d Cu 2 O= 192 t/d N 2 = t/d O 2 = t/d CO 2 = t/d (at 850 C) Coal =1000 t/d (at 950 C) Q = 57 MW Fuel Reactor (T = 950 C) 4CuO 2Cu 2 O+O 2 (X CuO =0.4) C + O 2 CO 2 ; (X C = 0.9) H 2 + ½ O 2 H 2 O;(X H2 =1) Air Reactor (T = 850 C) 2Cu 2 O+O 2 4CuO (X Cu2 O =0.9) C + O 2 CO 2 ; (X C = 0.1) Q = 238 MW Ash = 125 t/d Order of Magnitude Energy Balance Aspen Model) CuO= t/d Cu 2 O=19427 t/d C =73.4 t/d Air = t/d (at 850 C)

18 10000 Plot of Times for conversions of Char and Copper oxide particles with Temperature Time(seconds) on a logarithmic scale Pittsburgh#8-Char Burnout time by shrinking sphere-hurt and Mitchell(1992) CSTR Residence Time for 40% Conversion of Cupric Oxide CSTR Residence Time for 90% Pseudo-first order oxidation of Cuprous Oxide (kcu2o[cu2o]po2^0.5) CSTR Residence time for 90% Pseudo-first order oxidation of Cuprous Oxide (kcu2o[cu2o]po2^0.1) Temperature ( C)

19 Steps to Complete Order of Magnitude Calculations Calculate 1. carbon loading from the carbon burnout fraction for residence time in fuel reactor, 2. oxygen partial pressure in fuel reactor from competition between oxygen release by oxygen carrier and consumption by carbon, 3. use multiple reactors to approach plug flow behavior (e.g. Chalmers 10 kw CLC unit) 4. Aspen simulation

20 Concluding Comments CLOU offers a potential for greatly reducing times for carbon gasification, as has been previously shown by Lewis and Gilliland and Mattison, Leion and Lyngfelt. CuO decomposition kinetics and Cu 2 O are being generated to enable quantitative assessment of the potential of CLOU. Order of magnitude calculations show benefits of CLOU of 1. low oxygen carrier (OC) circulation rate, 2. low OC inventory, 3. flexibility in selecting temperatures of both fuel and air reactor because of exothermicity in both. Issues of OC support, contamination, attrition, sintering, optimum reactor configuration and operation need yet to be adequately resolved. System studies of CLOU are being complemented with studies of conventional CLC studies using hematite and ilmenite to provide basis for comparison of relative merits. CFD validation and application to evaluate system design.

21 Acknowledgments The authors wishes to acknowledge:. Lewis and Gilliland for introducing one of the authors (AFS) to the principles of chemical engineering. Andres Lynfelt, Tobias Mattison and Henrik Leion for introducing the same author to CLC and CLOU. This material is based upon work supported by the Department of Energy under Award Number FC26-08NT