Bed material-alkali interactions during fuel conversion in fluidized bed

Transcription

1 Bed material-alkali interactions during fuel conversion in fluidized bed Pavleta Knutsson Through curiosity and knowledge towards a sustainable world 1/2/2018 Chalmers Department of Chemistry and Chemical Engineering 1

2 Chalmers Unit GoBiGas Unit Gasification units in Gothenburg Bed inventory Temperature in the bed, gasifier [ C] Fuel flow, [kg daff /h] Fluidization level [kg steam /h] Temperature in the boiler, [ C] Chalmers Olivine GoBiGas Calcinated Serpentine Bed materials: Sand, bauxite, feldspar, ilmenite, manganese ores, iron ores Fuel: Coal, biomass, waste,

3 Bed material role in fluidized bed Gasification Tar formation in the product gas Agglomeration Bed material role Tar removal catalytically active material Low agglomeration potential Olivine, FeMgSiO 4 Bed materials Sand, bauxite Biomass components K and Ca Combustion Hot and cold spots in the reactor Agglomeration Bed material role Oxygen transport within the reactor Low agglomeration potential Ilmenite, FeTiO 3

4 Bed material activty (Activation) Agglomeration Gas Bed material interactions Fuel sticky layer Volatiles M oisture Salts in vapour Biofuel melt Bed material Agglomerate active layer Fluidization gas Bed material interactions are crucial for both agglomeration and activation

5 Role of Ca and K for agglomeration Bed material + ash XRD FactSage K Agglomer ation potential K+ sand K + Ca 2+ K 2 CO 3 +silica sand KSiO 4 K 2 Si 2 O 5 (s) strong K 2 CO 3 +bauxite KAlO 2 KAlO 2 (s) medium K 2 CO 3 +silica sand+bauxite CaCO 3 + silica sand CaCO 3 +bauxite KAlSiO 4 CaCO 3, SiO2 CaCO 3, Al 2 O 3, AlO(OH) KAlSiO 4 (s), KAlO 2 (s) Equilibrium composition not obtained CaAl 2 O 4 medium none none K+bauxite 500 μm CaCO 3 +silica sand+bauxite CaCO 3, SiO 2, Al 2 O 3, AlO(OH) CaAl 2 Si 2 O 8 (s), Ca 2 Al 2 SiO 7 (s) none Ca 2+ CaCO 3 +K 2 CO 3 +silica sand K 2 Ca 6 Si 4 O 15, K 4.8 Ca 0.6 Si 6 O 15, K 4 CaSi 3 O 9, Ca 2 SiO 4 K 2 SiO 3, Ca 3 Si 2 O 7 KAlO 2 (s), strong 500 μm

6 Yield (mol/kg daf fuel) Yield (mol/kg daf fuel) Yield (mol/kg daf fuel) Role of Ca for material activation Sand ref. H2 15 CO 10 CO2 5 CH C2H4 uo/umf 25 Bauxite uo/umf 25 Olivine uo/umf Courtesy of Teresa Berdugo Ca Ca Ca Ca Ca Al Si Al Al Si Si Bauxite Silica sand Olivine Bauxite Silica sand Olivine Bauxite Silica sand Olivine Ca-layer has been observed at active state around multiple bed materials particles Knutsson, P., Schwebel, G., Steenari, B.M., Leion, H. Effect of bed materials mixing on the observed bed sintering (2014) CFB-11: Proceedings of the 11th International Conference on Fluidized Bed Technology, pp

7 Combustion ilmenite case, activation 24h 107h 296h Courtesy of Angelica Corcoran No agglomeration is observed Oxygen carrying ability increases with time of exposure K,Ca-enriched layer (ash layer) increase in thickness with time of exposure Corcoran, A., Marinkovic, J., Lind, F., Thunman, H., Knutsson, P., Seemann, M. Ash properties of ilmenite used as bed material for combustion of biomass in a circulating fluidized bed boiler (2014) Energy and Fuels, 28 (12), pp

8 K and Ca distribution in the coating Ca Ca K 100 µm 100 µm 100 µm 100 µm K Ca and K signal found at the same locations in the outer layer

9 Coating changes with time SiO 4 4- AlO 2 - O 2- or? Ca and K signal found at the same locations in the outer layer

10 Ca and K state in the formed layers spe: Olivin - As-received Company Name _104.spe: Olivin - As-received Company Name 2017 Jun 12 Al mono 24.6 W µ ev e+004 max s 2017 Jun 12 Al mono 24.6 W µ ev e+003 max s Su1s/1: Olivin, D = mm/1 Ca2p/1: Olivin, D = mm/ _108.spe: Olivin - 2kV 21 min sputtering 2017 Jun 12 Al mono 24.6 W µ ev e+004 max Ca2p/1: Olivin, D = mm/1 c/s 10 x spe C KLL -K LMM -Ca LMM -O KLL -Fe2s -Fe2p -O1s -Ca2s -K2s -Ca2p -K2p Atomic % O1s 59.1 C1s 13.7 K2p 12.0 Si2p 7.6 Ca2p 6.4 Fe2p3 1.2 c/s Area ratio of State 1 & 2: 2:3 -Ca2p1 (State 2, ev) _104.spe -Ca2p1 (State 1, ev) -Ca2p3 (State 2, ev) -Ca2p3 (State 1, ev) c/s Area ratio of States 1 & 2 = 3: _108.spe -Ca2p1 (State 2, ev) -Ca2p1 (State 1, ev) -Ca2p3 (State 2, ev) -Ca2p3 (State 1, ev) Binding Energy (ev) 400 -C1s 200 -Si2s -Si2p -Fe3s -Fe3p -K3s -K3p Binding Energy (ev) Binding Energy (ev) Coexistence of mixed Ca and K at the activated materials K and Ca are predominantly as oxides at the outermost layer Knutsson, P., Cantatore, V., Tam, E., Seemann, M., Panas, I. Role of potassium for enhancement of the catalytic effect of calcium oxide for tar reduction (2018), Applied Catalysis B: Environmental 1/2/2018 Chalmers Department of Chemistry and Chemical Engineering 10

11 Role of K in CaO Replacing two Ca 2+ ion in the lattice by two K + is able to activate O 2 by binding it to the vacancy Theoretical calculations predict the oxidizing capacity of a K-enriched CaO Knutsson, P., Cantatore, V., Tam, E., Seemann, M., Panas, I. Role of potassium for enhancement of the catalytic effect of calcium oxide for tar reduction (2018), Applied Catalysis B: Environmental

12 Mechanism challenges K + or Ca 2+ O 2- K + or Ca 2+ incorporation, one or two layer K 2 SiO 3 vs. - Active bed material Agglomerating bed material CaSiO 3 Formation of mixed oxide initiating ion structure? Is it CaO? Where is the border line between activation and agglomeration? 1/2/2018 Chalmers Department of Chemistry and Chemical Engineering 12

13 Thank you for your attention!

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