CO 2 and SO 2 co-capture in a circulating fluidized bed carbonator reactor of CaO"

Transcription

1 CO 2 and SO 2 co-capture in a circulating fluidized bed carbonator reactor of CaO" B. Arias, J.M. Cordero, M. Alonso, J.C. Abanades CO 2 Capture Group National Institute of Coal (INCAR-CSIC) Trondheim CO 2 Capture, Transport and Storage Conference June, Trondheim, Norway

2 OUTLINE Introduction Objectives Experimental Thermogravimetric analysis Small pilot plant of 3 kwt Results and discussion Sulfation rates SO 2 retention under carbonation conditions Conclusions

3 SO 2 on Ca-looping post-combustion systems Flue gas without CO 2 Concentrated CO 2 Flue Gas CaCO 3 POWER PLANT CO 2 SO 2 CARBONATOR CaO CALCINER O 2 ASU Air Coal (Sulfur) Air CaCO 3 (F ) CaO Purge Coal (Sulfur) N 2 Reaction of CaO with SO 2 : CaO is being used routinely as desulfurization agent in CFB combustors Main differences between SO 2 capture in CFBC and carbonator: Range of temperatures Range of conversion Texture of CaO Previous findings SO 2 reduces maximum CO 2 carrying capacity Sulfation behavior of CaO is enhanced during cycling Sulfation rates of cycled CaO at carbonation conditions and SO 2 capture efficiency?

4 Outline Introduction Objectives Determination of sulfation rates of cycled CaO particles under carbonation conditions Study the SO 2 capture efficiency in a CFB carbonator Experimental Results and discussion Conclusions

5 Experimental facilities Thermo-gravimetric analyzer 3 kwt Pilot Plant at INCAR-CSIC Experimental conditions during TGA tests Mixtures of air/co 2 /SO 2 Calcination: T=95 ºC, Air Carbonation: T=65 ºC, 1% CO 2 in air Sulfation: T=65 ºC, SO 2 =5-3 ppm Number of cycles up to 5 Three different limestones Al 2 O 3 CaO Fe 2 O 3 K 2 O MgO Na 2 O SiO 2 TiO 2 Compostilla < Imeco <.5 Enguera < Main characteristics: Two CFB reactors (Height~6.5 m, diameter=1 mm) Electrically heated Measurement port (temperature, pressure, gas composition) Solid circulation measurements Solid samples characterization (TG analysis, C/S analyzer)

6 Experimental results: Sulfation rates Effect of number of cycles on sulfation behavior Effect of SO 2 concentration on CaO sulfation Sulfation conditions: T=65 ºC, SO 2 =5 ppm v.4 Fresh calcined limestone XCaSO Compostilla Imeco Enguera Compostilla limestone (N=1) XCaSO ppm 1 ppm 2 ppm 3 ppm.5 N= Time (s) Compostilla Imeco Enguera 3.E-3 2.5E-3 Time (s) Determination of reaction order respect to SO 2 After 2 cycles XCaSO N= Time (s) No pore plugging is present during sulfation of cycled particles up to reaction times of 2 min. XCaSO4/ t (s -1 ) 2.E-3 1.5E-3 1.E-3 Compostilla N=1 5.E-4 Imeco N=1 Enguera N=1 Compostilla N=2.E C SO2 (mol/m3) Results show that sulfation of CaO is Trondheim a first reaction CCS Conference order

7 Experimental results: Sulfation rates Interpretation of experimental data: Application of the Random Pore Model Chemically controlled reaction (k s ) 2 τ 1 ψ N X = 1 exp ψ N k SC t [ 1 ψ ln( 1 X) 1] = 2( ε) 1 s ψ 1 General expression of RPM dx dt = k s SC β Z ψ 1 ψ ln 1 ( X) ( 1) ( 1 ε) 1+ 1 ψ ln( 1 X) 1 2 Chemically/Diffusion controlled reaction (k s, D) X 1 ψ 1 1 exp ψ N 2 β Z 1 + β Z τ 1 ψ N ψ N ( β Z ) = 2 [ ( ) ] S D MCaO 1 ψ ln 1 X 1 = ( 1 ε) 2ρ Z CaO C t Derivation of reaction rate parameters Main model parameters: k s : reaction rate of surface reaction D: effective product layer diffusion ψ: structural parameter CaO conversion k s D Time (s)

8 Experimental results: Sulfation rates RPM model results Reaction rate parameters for studied limestones Compostilla Imeco Enguera k s (m 4 /mols) 6.38E E E-6 E ak (kj/mol) D (m 2 /s) 1.71E E-5 3.2E-5 E ad (kj/mol) h (nm) Comparison of experimental and calculated values using the RPM model XCaSO N=5 N=2 Compostilla For practical application purposes in a Ca-looping, only the chemically controlled stage can be considered XCaSO Time (s) N=5 N=2 Enguera dx dt = k s ( 1 ε ) ( ) S C( 1 X ) 1 ψ ln 1 X Time (s)

9 Introduction Objectives Experimental Thermogravimetric analysis Experiments in small pilot plant Results and discussion Determination of sulfation rates SO 2 retention in a CFB carbonator in presence of CO 2 Conclusions

10 Experimental results: SO 2 retention in a circulating fluidized bed carbonator bed 3 kwt Pilot Plant at INCAR-CSIC Gas from calciner Gas from carbonator CARBONATOR COMBUSTOR CALCINER CALCINADOR CARBONATOR COMBUSTOR -CARBONATADOR CALCINER Air inlet Coal Air CO 2 SO 2 Air

11 Experimental results: SO 2 retention in a circulating fluidized bed carbonator bed Volume fraction (%) CO2 capture efficiency EXAMPLE OF SO 2 CAPTURE EFFICIENCY Experimental conditions* -Flow to carbonator: 19 m 3 N/h -u gas =2.5 m/s -CO 2 inlet concentration = 12% -SO 2 inlet concentration: 19 ppm (1) 38 ppm (2) CO2 O2 SO :4 16:55 17:9 17:24 17:38 17:52 18:7 CO2 -Solid circulation = 1.9 kg/m 2 s -X sulf =.8 -X max -X carb =.3 -T carbonator = 668 ºC *Average values during experimental period shown 16:4 16:55 17:9 17:24 17:38 17:52 18:7 SO SO2 concentration (ppm) SO2 capture efficiency SO 2 mass balance during the experimental testing period %CaSO4 calculated SO 2 capture efficiency Carbonator Calciner SO2 capture efficiency % CaSO 4 experimental Inventory of solids (kg/m 2 ) :4 16:55 17:9 17:24 17:38 17:52 18: WCaO*Xave/FSO2 W CaO X ave /F SO2 (h)

12 CONCLUSIONS Sulfation of CaO cycled particles proceeds through an initial chemically controlled step followed by a second period where chemical reaction and diffusion through the product layer are the controlling resistances. Sulfation of CaO has been found to be a first reaction order with respect to SO 2 under carbonation conditions. Cycled particles do not undergo pore plugging due to the growth of the CaSO 4 layer during sulfation (for reaction times up to 2 min). The random pore model has been used to study the sulfation behavior of three limestones. Good agreement between experimental and calculated values has been found confirming the suitability of this model to describe the sulfation reaction under both reaction regimes. Post-combustion Ca-looping carbonators can be effective reactors for capturing SO 2 from flue gases even for low inventories of solids.

13 CO 2 and SO 2 co-capture in a circulating fluidized bed carbonator reactor of CaO" Thank you for your attention borja@incar.csic.es This work has been carried out as part of the FP7 CaOling Project. Trondheim CO2 Capture, Transport and Storage Conference June, Trondheim, Norway