Preliminary evaluation and bench-scale testing of natural and synthetic CaO-based sorbents for post combustion CO 2 capture via carbonate looping

Transcription

1 th High Temperature Solid Looping Cycles Network Meeting Politecnico di Milano, Milan, Italy st - nd September 5 Preliminary evaluation and bench-scale testing of natural and synthetic CaO-based sorbents for post combustion CO capture via carbonate looping Z. Skoufa, A. Antzara, E. Heracleous, A. Lemonidou Lab. of Petrochemical Technology, Chemical Engineering Department, AUTH Chemical Processes & Energy Resources Institute- CPERI/CERTH Αristotle University of Thessaloniki

2 CO the most important air pollutant in Greece Greece: 3 th in CO emissions per capita in Europe IEA report Electricity generation:.8 TWh (coal 5%, natural gas 7%, oil 3%, hydro %, wind %) CO emissions from electricity generation~ % Largest coal-fired plant Saint Demetrius :, million tnco p.a. =,9 million cars!

3 COfree.com project Exploring novel routes for CO -free fossil fuel combustion Assessment of two main routes (a) in-situ CO capture with chemical looping combustion and (b) ex-situ CO capture with carbonate looping, for potential application in the Greek industry, with main focus on power production. CAL: Development of efficient CO -sorbent materials, preliminary evaluation and lab scale testing under realistic conditions CLC: Development of efficient OTM, preliminary evaluation and semi-pilot scale testing Investigation of different reactor configurations with advanced simulation tools Techno-economic investigation and environmental assessment 3

4 Development of efficient and stable CaO-based sorbents Development of both natural sorbents (limestone, dolomite etc) and novel synthetic sorbents of high sorption capacity and stability based on tailor made physicochemical properties % CaO Natural sorbents Hydrated lime, Ca(OH) (CaO Hellas) Direct 9 o C, h Ca(OH) -C9 7 C, h o C, h Ca(OH) -W-C 9 o C, h Ca(OH) -W-C9 % CaO + thermally stable binders: Kaolin, Bauxite, MgO Ca(OH) -KAOL Ca(OH) -Baux Ca(OH) -MgO Mixing in 7 o C, h Ca(OH) -MgO-RW Ca(OH) -Baux-RW Co-grinding in min Ca(OH) -MgO-GM Synthetic sorbents Promoted CaO-based sorbents with: Alumina Lanthana Magnesia Zirconia Ca-Al Ca-La Ca-Mg Ca-Zr Heating and stirring 5- ο C Gel formation ~ ο C Auto-combustion of sol-gel 3 ο C Calcination 9 ο C,,5h under air flow free CaO: wt% Sol-gel auto-combustion with CA

5 Physicochemical Characterization Natural sorbents Synthetic sorbents Sorbent Surface area (m /g) Ca(OH) -C9 5.. Ca(OH) -W-C 7..8 Ca(OH) -W-C9.8.9 Ca(OH) -KAOL 3..3 Ca(OH) -Baux Ca(OH) -MgO Ca(OH) -Baux-RW Ca(OH) -MgO-RW Ca(OH) -MgO-GM Pore volume (cm 3 /g) Sorbent Surface area (m /g) Ca-Mg 8.. Ca-La Ca-Zr Ca-Al.9. Pore volume (cm 3 /g) Natural sorbents XRD no formation of mixed components. Hydration of the calcined sample leads to an increase in surface area and porosity MgO seems to greatly affect both surface area and porosity. Synthetic sorbents Main crystal phase: CaO Formation of mixed Ca 3 Al O and CaZrO 3 in Ca-Al and Ca-Zr 5 Antzara et al., Applied Energy 5 (5) 33 33

6 Sorption Capacity, mol CO /gr sorbent Sorption Capacity, mol CO /gr sorbent Sorption capacity, mol CO /kg sorbent Preliminary evaluation in TGA Carbonation: 5 ο C, 5% CO /N Calcination: 85 ο C, % N Natural sorbents Synthetic sorbents Ca(OH)-C9 Ca(OH)-W-C Ca(OH)-W-C No. cycle 5 3 Ca(OH)-MgO Ca(OH)-MgO-RW Ca(OH)-MgO-GM Ca(OH)-Baux Ca(OH)-Baux-RW Ca(OH)-KAOL Ca(OH)-C No. cycle No. cycle Ca-Al Ca-La Ca-Mg Ca-Zr Optimum materials chosen for fixed bed reactor tests Initial capacity (mol CO /kg) Initial CaO conversion (%) Deactivation after cycles (%) Ca-Al Ca-Zr Ca(OH) -C Ca(OH) -MgO-GM

7 Fixed bed reactor testing Evaluation of materials sorption capacity and stability under industrially relevant conditions Carbonation Τ=5 ο C % CO / 3.% O / % H O/N Calcination Τ= 5 8 ο C 3% Η Ο/Ν Sorptioncapacity, mol CO /kg t M CO dt X(t),%= *% n CaO sorbent = t M CO w init dt

8 Sorption capacity, mol CO /kg sorbent Fixed bed reactor testing Ca-Al & Ca-Zr Carbonation: 5 o C, % CO /%H O/3.%O /Ν Calcination: 5 8 o C, 3%H O/ N 8 Ca-Zr Ca-Al 8 8 Number of cycle Deactivation (%) After cycles Initial sorption capacity (mol CO /kg sorbent) Ca-Al Lab unit (TGA) Ca-Zr Lab unit (TGA).5 (3.).9 (3) 9.9 (.) 9. (.) Sorption capacity: CO captured in the kinetically controlled regime Fixed bed vs TGA: ~ sorption capacity stability Both sorbents present high activity and satisfactory stability after consecutive carbonation/calcination cycles

9 CO concentration, % Sorption rate, mmol CO /kg/sec CO concentration, % Sorption rate, mmol CO /kg/sec Fixed bed reactor testing Ca-Al Carbonation: 5 o C, % CO /%H O/3.%O /Ν - Calcination: 5 8 o C, 3%H O/ N 3.5 gr, GHSV= 3 h - Pre-breakthrough period ~min.8. Pre-breakthrough period ~9min st cycle th cycle Kinetically controlled carbonation step: constant CO concentration < %vol., constantly high CO capture rate st cycle: pre-breakthrough period ~ min 9.9 mol CO /kg sorbent ~8% CaO conversion th cycle: kinetically controlled period (9 min).5% deactivation

10 CO concentration, % Sorption rate, mmol CO/kg/sec CO concentration, % Sorption rate, mmol CO/kg/sec Fixed bed reactor testing Ca-Zr Carbonation: 5 o C, % CO /%H O/3.%O /Ν - Calcination: 5 8 o C, 3%H O/ N.7 gr, GHSV= 38 h - Pre-breakthrough period ~7min.. Pre-breakthrough period ~min st cycle th cycle Kinetically controlled carbonation step: constant CO concentration < %vol., constantly high CO capture rate st cycle: pre-breakthrough period ~7 min 9. mol CO /kg sorbent ~77% CaO conversion th cycle: kinetically controlled period ( min) 3% deactivation

11 Fixed bed reactor testing Synthetic sorbents Deactivation mechanism Sorbent Kinetically controlled regime (mol CO /kg sorb.) Total sorption capacity (mol CO /kg sorb.) st cycle th cycle st cycle th cycle Ca-Zr Ca-Al Total sorption capacity remains constant after cycles Practically no loss of intrinsic activity Deactivation due to loss of easily accessible surface sites? Characterization of used samples

12 Fixed bed reactor testing- Characterization of used samples SEM, BET of Ca-Zr fresh ~μm used ~μm ~μm ~μm Fresh sample Small particles in the range of μm Grape-shaped structure Used sample Significant agglomeration Larger particles Porous structure is retained ~5μm ~5μm Ca-Zr Fresh Used-cycles Surface area (m /g).5. Pore volume (cm 3 /g).3.

13 Fixed bed reactor testing- Characterization of used samples SEM, BET of Ca-Al fresh ~μm used ~μm ~μm ~5μm Fresh sample Larger particles than Ca-Zr Sponge-like structure Used sample Little agglomeration Similar particles as in fresh sample Porous structure is retained Ca-Al Ιδιότητες Fresh Used-cycles Surface area (m /g) Pore volume (cm 3 /g).7.97 ~μm ~μm

14 CO concentration, % Sorption rate, mmol CO/kg/sec CO concentration, % Sorption rate, mmol CO/kg/sec Fixed bed reactor testing Natural sorbents Carbonation: 5 o C, % CO /%H O/3.%O /Ν - Calcination: 5-8 o C, 3%H O/ N Ca(OH) -C9 ~8min >8min.. Ca(OH) -MgO-GM ~5min ~5min Significantly lower sorption capacity compared to synthetic sorbents Intense deactivation in the first 5 cycles CO captured in the diffusion controlled regime > kinetics-controlled regime Smaller pores (mesopores) for natural sorbents compared to synthetic samples that mainly present macroporosity Less easily accessible surface sites compared to synthetic sorbents

15 Sorption capacity, mol CO/ kg sorbent Fixed bed reactor testing Ca(OH) -C9 8 Carbonation: 5 o C Calcination: 5 8 o C, 3%H O/ N A: standard experimental conditions B: Hydration step after each cycle: after desorption, cool down to 8 o C under 3%H O/N C: No steam in feed during sorption (feed comp. %CO /3.%O /N ) A B A C 8 8 Number of cycle Hydration: containment of sorbent deactivation significant increase (~8%) in sorption capacity The presence of steam in the feed increases CO capture efficiency and promotes sorbent stability

16 CO flow, cm 3 /min CO flow, cm 3 /min CaO conversion, % CO flow, cm 3 /min CO flow, cm 3 /min Kinetic modelling for synthetic Ca-Al sorbent Kinetic experiments blank-5 sorbent blank- 5 sorbent- 5 blank-55 sorbent-55 8 blank-5 sorbent gr Ca-Al, 5 cm 3 /min, % CO / 3.% O / %H O/ N

17 CaO conversion, % CaO conversion, % CaO conversion, % CaO conversion, % lnk Kinetic modelling for synthetic Ca-Al sorbent Simple uniform model dx dt = k( X X u ) n Time,min sim_ exp_ n= T, ο C k, min - X u Time,min sim_55 exp_ y = -79.x +.77 R² = /T, K - k o = 5. min - E a =39.8kJ/mol.... sim_ exp_.. sim_5 exp_ Time,min Time,min 7

18 Conclusions Synthetic sorbents High sorption capacity and stability in TGA-preliminary evaluation Zr and Al-doped CaO based sorbents: high sorption capacity and satisfactory stability due to porous structure, presence of thermally stable Ca-Zr and Ca-Al mixed phases Simple uniform model best describes carbonation kinetics Natural sorbents Inferior results Regeneration via hydration seems possible The presence of steam in the flue gases seems to enhance sorption capacity and stability

19 Acknowledgements SYNERGASIA Exploring novel routes for CO -free fossil fuel combustion- COfree.com Dpt. Chemical Engineering/AUTH ΙΔΕΠ/ΕΚΕΤΑ Dr. L. Nalbantian, Prof. V. Zaspalis Dr. Ε. Iliopoulou 9

20 th High Temperature Solid Looping Cycles Network Meeting Politecnico di Milano, Milan, Italy st - nd September 5 Preliminary evaluation and bench-scale testing of natural and synthetic CaO-based sorbents for post combustion CO capture via carbonate looping Z. Skoufa, A. Antzara, E. Heracleous, A. Lemonidou Lab. of Petrochemical Technology, Chemical Engineering Department, AUTH Chemical Processes & Energy Resources Institute- CPERI/CERTH Thank you for your attention zskoufa@auth.gr