Solidification in gasifier slags

Transcription

1 1 Solidification in gasifier slags Daniel Schwitalla, Stefan Guhl, Bernd Meyer Institute of Energy Process Engineering and Chemical Engineering (IEC) TU Bergakademie Freiberg Berlin, Germany 3-8 June 18

2 Viscosity Motivation η Shear rate 50 1/s Shear rate 74 1/s Temperature Solids inside the slag cause steep increases in viscosity and nonnewtonian behavior identify sources of solids and the processes causing them to appear in the slag

3 3 Outline 1. Analytical algorithm 2. Measuring equipment 3. Examples of findings 4. Summary

4 Analytical algorithm XRF* Bulk composition Process samples XRD* Crystal species, amount Classification of phases Contributors to flow behavior Phase segregation SEM/EDX Phase composition, size, form *XRF: S8 Tiger (4kW Rhenium radiation ; XRD: Rietveld Method on Bruker D8 Discover using the ICDDs PDF-4 database 4

5 Measuring equipment Scanning electron microscope Select representative process sample Categorize findings Imbed 3 different samples into epoxy Compare samples to bulk composition and XRD Analyze 5

6 BGL process samples Input is sewage sludge, coal, and various waste High temperature of C should homogenize slag Composition of slag nearly impossible to backtrack Large input spectrum is likely to cause many slag impurities water quench should freeze phase composition *source: Sandner, Gasification Technologies, San Francisco 03 6

7 BGL 40 XRF vs slag EDS Na Mg Al Si P S Cl K Ca Ti Fe Cu XRF EDX area 1 EDX area 2 Slag composition differs across location 3 Questions: Where is Fe, S, Cu Why the abundance of Na, Mg, Al Why the differences in Ca-and P content 7

8 BGL 40 XRF vs EDS crystal Na Mg Al Si P S Cl K Ca Ti Fe Cu XRF EDX Spot 3 EDX area 3 Crystals change slag composition explains difference in Ca, Al, Si and the overall shift in composition anorthite is growing inside the slag (confirmed via XRD) 8

9 BGL 70 XRF vs EDX crystal Na Mg Al Si P S Cl K Ca Ti Fe Cu Y XRF EDX spot 1 EDX spot 2 Small crystals small changes in surrounding composition Phosphorous is usurped by crystallization XRD suggests Calcium carbonate phosphate; EDX suggests apatite 9

10 BGL XRF vs metal enclosures Na Mg Al Si P S Cl K Ca Ti Fe Cu Ni XRF EDX spot 5 EDX spot Pure metals agglomerate in iron-rich alloys some phosphorous is trapped in iron XRD suggests iron also in crystalline form in various oxidation states SiO2 was found in pure form 10

11 General Electrics (Texaco) Input is coal blend of subbit. & bit. Coal and petcoke Temperature is ca C* low T could cause incomplete melting refractory liner could be in slag slag is directly water quenched, thus freezing the phase composition * source: Gasification (2nd ed.) Higman & v.d. Burgt 08 **picture source: 11

12 General Electrics (Texaco) 60 XRF vs EDX Na Mg Al Si P S K Ca Ti V Fe Ni XRF EDX area 2 EDX area 3 Na, Mg, Al, Ca are enriched Si, Fe are found in a lesser amount S, V, Ni are missing from the main slag phase 12

13 General Electrics (Texaco) XRF vs Crystal 1 Na Mg Al Si P S K Ca Ti V Fe Ni XRF EDX area 1 EDX spot 2 EDX pot 3 Multiple Silicon dioxide (confirmed as christobalite via XRD) grains found soft edges suggest incomplete dilution opposed to new forming SiO2 grains affect slag flow by changing viscosity (usually raising it) 13

14 General Electrics (Texaco) 60 EDX vs metal enclosures Na Mg Al Si P S K Ca Ti V Fe Ni XRF EDX spot 1 EDX spot 4 Metal enclosures consist mostly of Ni, Fe, and S all S is in metal enclosures metal alloys are likely molten and swim in slag viscosity measurement of untreated slag only in Al2O3 possible round shape suggests they have been molten accumulation of metal deposits close to bubble borders (gas atmosphere could interact) 14

15 General Electrics (Texaco) XRF vs Vanadium deposits Na Mg Al Si P S K Ca Ti V Fe Ni XRF EDX spot 1 EDX spot 2 EDX spot 3 Very small vandium-rich deposits in the slag indicates that petcoke was fired shape does not suggest them to have been molten (sharp composition change also suggests this) due to small size and very low amount are not likely to affect viscosity much 15

16 Pilot scale Siemens gasifier Fuel was a mixture of hard coals Slag is cooled via the cooling screen slag Temperature profile is steep slag is water quenched (phase composition likely frozen) castable should not be inside slag * Halama et. al, J. Energy Resour. Technol 16 16

17 Siemens (coal 1) 1 XRF vs EDX Na Mg Al Si P S K Ca Ti V Fe Ni Cu XRF EDX spot 2 (light) EDX spot 3 (usual) EDX spot 4 (SiO2) EDX spot 1 Most of the slag is composed just like the bulk composition many dissolving SiO2 grains are found that are affecting the viscosity a very small portion of the slag is composed of FeS (Hypothesis: all S is in these enclosures) all pure metals (Ni, Cu) are inside the metal enclosures metal enclosures cause streams of largely different composition; otherwise homogenous and no crystals many pores could indicate coal particles that produced gas inside the slag 17

18 Siemens (coal 2) Close to reaction zone Cooling screen* Level of crystallinity increases with the vicinity to the cooling screen Homogeinity increases with temperature viscosity changes with location due to crystals, undissolved grains, and composition changes *interpretation of orientation of particle was determined via interview and thermochemical equilibrium calculations 18

19 Siemens (coal 2) XRF vs slag EDX Na Mg Al Si S K Ca Ti Fe XRF EDX area 1 EDX area 4 Slag is amorphous close to the reaction zone (hottest) Fe is depleted (indicator for metal segregation) Al, Ca, Mg, Na enriched 19

20 Siemens (coal 2) 1 XRF vs EDX slag Na Mg Al Si S K Ca Ti Fe F XRF EDX spot 3 EDX spot 6 EDX spot 1 EDX spot 2 Slag gets more crystalline closer to cooling screen (no flow possible) many metal enclosures often close to phase boundary layer (only spots where S in detected) SiO2 grains here as well

21 21 summary Liquid phase with differing composition test model liquid in lab for resulting viscosity Crystals with different sizes present confirms lab findings Anorthite seems to appear often and grow fast compare with FactSage SiO2 grain form suggests incomplete dissolution and no forming research impact Fe-rich Metal enclosures appear often and close to boundary layer research gas composition to cause this sulfur only detected in metal enclosures only trapped by metal melt Slag from pilot scale reactor is comparable to full scale samples

22 22 summary Quantification of solids through MLA or mapping could yield more results more evaluation of Carbon and Oxygen levels in findings effect of metal enclosures on viscosity should be measured crystallization kinetics could prove helpful in viscosity prediction simplified solidification in current CFD models could be reevaluated

23 Acknowledgement This research has been funded by the Federal Ministry for Economic Affairs and Energy of Germany in the framework of HotVeGas III (Project Number ). We also thank the DBI-Virtuhcon GmbH for graciously sharing their process samples TU Bergakademie Freiberg Institute of Energy Process Engineering and Chemical Engineering Freiberg - Germany Tel.: Fax: Daniel.Schwitalla@iec.tu-freiberg.de Web 23