Generation and growth of crystals and enrichment of elements during isothermal process in molten slag Presenter : Zhongjie Shen

Transcription

1 Generation and growth of crystals and enrichment of elements during isothermal process in molten slag Presenter : Zhongjie Shen East China University of Science and Technology (ECUST), China

2 Content Background Experiments Results and discussion Conclusions 2

3 1.Background Entrained-flow gasification high carbon conversion coal flexibility Methane, ammonia, hydrogen, liquid fuels and electricity Liquid slag Solid slag Refractory wall Char, ash, slag Gas High temperature Slagging condition Particle deposition Slag flow Char, ash, slag Temperature, velocity, thickness, Rheology, viscosity, Crystallization Slag layer 3

4 1.Background Particle deposition and reaction Gasification Combustion Bubbles In-situ experimental study of CO2 gasification of char particles on molten slag surface. Fuel 2015; 160: In situ experimental study on the combustion characteristics of captured chars on the molten slag surface. Combustion and Flame 2016; 166: In situ study on the formation mechanism of bubbles during the reaction of captured chars on molten slag surface. International Journal of Heat and Mass Transfer 2016;95:

5 Temperature ( C) 1.Background Method This study Chemical composition Isothermal temperature Crystallization behavior Kinetics Cooling rate Heating Melting Previous study Crystallization Time (min) Crystallization at 150 /min Effect of Continuous Cooling on the Crystallization Process and Crystal Compositions of Iron-Rich Coal Slag. Energy & Fuels 2015;29(3): Effect of Cooling Process on the Generation and Growth of Crystals in Coal Slag. Energy & Fuels (accepted) 5

6 2.Experiment method 2.1 Experimental materials Raw coal sample: bituminous coal, widely used in the industrial gasifier. Table 1 Proximate and ultimate analysis of the raw coal used in this study. Proximate analysis (wt.%) Ultimate analysis (wt.%) M V FC A C H S N raw coal Coal ash: The coal ash sample was prepared from a bituminous coal in a muffle furnace at 815. Chemical composition: x-ray fluorescence. Table 2 Chemical compositions (wt.%) of the coal ash sample. Component SiO 2 Al 2 O 3 Fe 2 O 3 CaO K 2 O TiO 2 MgO Na 2 O Coal ash Ash fusion temperature: Deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT) and flow temperature (FT). Table 3 The ash fusion temperatures (AFT) of the coal ash sample. Temperature ( C) DT ST HT FT Coal ash

7 2.Experiment method 2.2 Crystallization experiment 2.3 Element detection High temperature stage microscope (HTSM) Coal ash Molten slag Crystallization Time-of-flight secondary ion mass spectrometer (ToF-SIMS). Morphology Element composition Element distribution SEM-EDS ToF-SIMS HTSM 7

8 3. Results and discussion Crystal 0min 4min 15min (a) First isothermal molten process at 1300 (b) Cooling process from 1300 to min 6min 15min Crystal 8 (c) Heating process from 1100 to 1300 (d) Second isothermal molten process at 1300

9 3. Results and discussion Crystallization behavior Crystal t=0s t=210s t=480s t=1200s Crystal t=0s t=240s t=480s t=1200s Crystal t=0s t=180s t=480s t=1200s Fig. 3 Crystal growth 9

10 Crystal Size (μm) Crystal Size (μm) Crystal Size (μm) 3.Results and discussion 3.2 Crystal size s s Time (s) (a) Acicular crystal at s Time (s) (c) Hexahedral crystal at Time (s) (b) Hexahedral crystal at1300 Generation of crystal: a time scale of minute level, which varied with molten temperature. Crystal size: increased and then remained stable, differing from crystal types. Crystal at lower molten temperature: shorter growth time period and larger growth rate. 10

11 3.Results and discussion 3.3 Micro morphology and element composition Table 3 Element compositions (Atomic (%)) on crystal and amorphous phase (a)1275 C (b) 1300 C (c)1350 C Element O Na Mg Al Si K Ca Fe

12 3.Results and discussion 3.4 Surface element distribution Hexahedral crystal: Fig. 6. ToF-SIMS imaging for element distribution on the hexahedral crystal. Signal intensity Al Si Ca Na Mg K Fe Crystal surface ** * ** *** *** * * Amorphous phase ** *** ** * * ** ** Note:*- weak; **-moderate; ***-strong 12

13 3.Results and discussion 3.4 Surface element distribution Acicular crystal: Fig. 7. ToF-SIMS imaging for element distribution on the acicular crystal. Signal intensity Al Si Ca Na Mg K Fe Crystal surface ** * ** * *** * ** Amorphous phase ** *** ** *** * ** * Note:*- weak; **-moderate; ***-strong 13

14 Intensity (cps) 3.Results and discussion Intensity(cps) 3.5 Internal element distribution Na K 100 Mg Ca Al Fe Si Sputter time (s) 1000 Na K 100 Mg Ca Al Fe Si Sputter time (s) Fig. 8. ToF-SIMS depth profiling of ions in the hexahedral crystal and acicular crystal. Al, Si, Fe, Ca and Mg: first increase and then remain stable, homogeneously distributed inside the crystal. Mg and Fe: migrate and dope into the interior of crystal structure. Na and K: first increase and then decrease, migrate from interior of crystal to the surface. 14

15 3.Results and discussion 3.6 3D ToF-SIMS images for element distribution Hexahedral crystal Acicular crystal Fig. 9. 3D images for the distributions of Na, K and total elements during sputter time for hexahedral crystal and acicular crystal (xy plane express the sample surface: µm 2 for hexahedral crystal and µm 2 for acicular crystal, z axial denote the sputter depth for several nanometers). 15

16 4.Conclusions Internal chemical reaction promoted the crystallization behavior of coal slag during isothermal molten process. Crystals precipitated on molten slag surface and varied with slag molten temperatures. Crystal growth increased with decreasing the isothermal molten temperatures and performed as a minute level process, which would affect the slag flow and rheology. K mainly enriched on the amorphous phase and two crystal surfaces (hexahedral crystal and acicular crystal). Na tended to migrate onto the crystal surface while Mg migrated and doped into the interior of crystal. Fe performed different migration behaviors varied with the type of crystal. 16

17 Thank you! 17