Developments in Lime Reactivation through Superheating of Ca(OH) 2

Transcription

1 Developments in Lime Reactivation through Superheating of Ca(OH) 2 2 nd IEA GHG - High Temperature Solid Looping Network Conference, Alkmar By Vlatko Materic ; Robert Holt

2 Lime-Limestone Thermochemical Cycle with Hydration Based Reactivation CaCO 3 Heat (>850C) Diluted CO 2 Concentrated CO 2 Ca(OH) 2 Every n cycles Heat ( C) CaO

3 Hydration restores CO 2 activity

4 Repeated Hydration Weakens the Particles After 17 Carbonation/Calcination Cycles 39 Cycles and 12 Hydrations (n = 3) IRL discovered is a method that counteracts this particle weakening The method is based on a novel phenomenon dubbed Superheating

5 Fluid Bed Test Reactor Filter RH MFM T CPU Computer Control MFC CO2 T P dp MFC N2 Water Pump T

6 Ca(OH) 2 Superheating - Bubbling Fluid Bed H 2 O off N 2 on H 2 O Off CO 2 On Time (min) Dehydration in N 2 occurs at 400 C Standard Dehydration Dehydration in CO 2 occurs at 620 C Superheated Dehydration CO 2 Off N 2 On H 2 O Off CO 2 On Dehydration in CO 2 also occurs when CO 2 is removed

7 Particle morphology in BFB experiments After 37 Carbonation/Calcination Cycles After 37 cycles, Standard Hydration every 3 cycles After 37 cycles, Superheating every 3 cycles Standard Hydration Superheating

8 IRL s Breakthrough- Ca(OH) 2 Superheating Superheating Ca(OH) 2 improves sorbent performance in BFB CO 2 Activity 60% of theoretical maximum Fragmentation comparable to No Reactivation Tested with 910 C atmospheric calcinations and 3 different Limestones 60% 50% Over 39 Carbonations and 12 Reactivations (n = 3) 12.00% 10.00% 40% 8.00% 30% 6.00% 20% 10% 0% No Reactivation, 16% Standard Hydration, 36% IRL's SD Reactivation, 56% 4.00% 2.00% 0.00% No Reactivation, 0.99% Standard Hydration, 11.13% IRL's SD Reactivation, 1.44% Average Activity - Lhoist Limestone % Fines < 90 um - Lhoist

9 Presentation Overview Part I Engineering and Development Progress Part II Research and Scientific Progress

10 CFB Attrition Tester Furnace Zone Furnace Zone CO 2 / N 2 Gas IN Solid Injection Area Main Attrition Sources : Impact (jet) Abrasion (cyclones) Chemical structure change

11 Current Engineering Development Work 3kg/day BFB Reactivator to produce materials for large CFB pilot tests 3kg/day Reactivator

12 Presentation Overview Part I - Engineering and Development Progress Part II - Research and Scientific Progress

13 Reactivation Cycle Optimal setup Spent CaO H 2 O / Gas Hydration 300 C Heat (to steam cycle) CO 2 Annealing 500 C CO 2 (recycle) Air + CO2 (Flue gas?) Dehydration + Carbonation 620 C Reactivated CaCO 3 H 2 O / Gas

14 Proposed Overall Process Active CaCO3 Spent CaO IRL s Reactivator 400C Amended from Abanades et al., Environ. Sci. Technol. (2005) 39,

15 Why does Ca(OH) 2 superheat? 100 C prior to dehydration, Ca(OH) 2 protons become mobile and free water is formed. The temperature of dehydration can be increased by the presence of proton donor species adsorbed on the surface e.g. Boric Acid (+ 90 C) CO 2 is acidic but not a proton donor we postulate that CO 2 interacts with free water to form H 2 CO 3 which can inject protons and delay dehydration. In-situ FTIR can confirm. Ca Ca Ca Ca O O O H H H H H H O O O Ca Ca Ca Ca Layered Brucite Structure

16 Surface properties control Superheating Steam Hydrated (30%) CO 2 Off N 2 On Mass. Temp, Steam Hydrated (60%) CO 2 Off N 2 On CO 2 On CO 2 On Time Time Comercial Hydroxide CO 2 On CO 2 Off N 2 On Time Hydroxide Superheating behaviour varies with hydration method and sorbent history. XRD and IR spectra are identical Difference in Surface Properties BET and pore size distribution.

17 Superheating Carbonation Mechanism CO2 On Carbonation mechanism during superheating is not simply : Ca(OH) 2 CaO + H 2 O CaO + CO 2 CaCO 3

18 Carbonation mechanism for Ca(OH) 2 Adsorbed water on Ca(OH) 2 surface controls the extent of reaction, reaction proceeds through formation H 2 CO 3 During Superheating water comes from within the crystal and then interacts with CO 2. In-situ FTIR experiments could confirm this. Carbonation of Ca(OH) K, 0.65 kpa CO 2 RH= 88% RH= 68% RH= 73% The interaction of free water and CO 2 leads to Proton Injection into the lattice further delaying Dehydration Formation of Carbonate in a time independant Mechanism RH= 40% Beruto et al. J. Eur. Cer. Soc

19 Conclusion Superheating is effective with different limestones in realistic calcination conditions in BFB. Batches of Reactivated material will be produced pretested for CFB tests to come. The superheating behaviour can be controlled by hydration technique most spent limes can be made to superheat.