MINERAL PHASES IN VARIOUS FUEL ASHES USING DIFFERENT ASHING METHODS AND RELATED TEMPERATURES

Transcription

1 Institute of Energy Process Engineering and Chemical Engineering Chair EVT MINERAL PHASES IN VARIOUS FUEL ASHES USING DIFFERENT ASHING METHODS AND RELATED TEMPERATURES M. Reinmöller, M. Schreiner, S. Guhl, M. Neuroth, B. Meyer 11th European Conference on Coal Research and its Application (ECCRIA), Sheffield, England, United Kingdom 5th-7th September 2016

2 OUTLINE Motivation Materials and methods Fuel samples Different ashing methods X-ray fluorescence (XRF) analysis and scanning electron microscopy (SEM/EDX) Ash fusion temperatures (AFT) X-ray diffraction (XRD) Results and discussion Ash composition Ash fusion behaviour Mineral phases using different ashing methods Summary and outlook 2

3 MOTIVATION Ash strongly affects the possible processes of energy conversion for solid fuels Investigation of Different fuels Ashing methods and their related temperatures Mineral phases in the fuel and temperature-induced transformation Goals Reliable operation of power plants Estimation of the potential of fuels for co-utilisation 3

4 Materials and methods Fuel samples Refuse-derived fuel (RDF) Columbian hard coal (CHC) Oat husks (OAT) German brown coal (GBC) 4

5 Materials and methods Different ashing methods Low-temperature ash (LTA) Diener electronics Nano plasma surface apparatus Ashing time: h Temperature: around 200 C Medium-temperature ash (MTA) Temperature directly controlled inside the sample Ashing time: 26 h Temperatur: 450 C High-temperature ash (HTA) Similar procedure as MTA, but only control of oven temperature Temperature: 815 C (ashing temperature for coals DIN 51719) 5

6 Materials and methods X-ray fluorescence (XRF) analysis Bruker S8 Tiger Rhodium radiation source All elements are given as oxides Scanning electron microscopy (SEM/EDX) FEI Quanta FEG Acceleration voltage: 20 kv (BSE) Resolution: 50-fold Analysis of the element distribution by SEM/EDX 6

7 Materials and methods Ash fusion temperatures (AFT) Ash fusion tests according to standard DIN Leitz heating microscope Cylinder from <63 µm ash: height 3 mm and diameter 3 mm Atmosphere: air (oxidising) or CO/CO 2 (reducing) Maximum deviation for repetition of 40 K under oxidising atmosphere according to DIN

8 Materials and methods X-ray diffraction (XRD) Bruker D8 Discover Different detectors and beam focus setups Rhodium radiation 8

9 Results and discussion Ash composition (MTA) Oxides CHC GBC RDF OAT Mass fraction (XRF) / wt.% CO Na 2 O MgO Al 2 O SiO P 2O 5 <0.1 < SO Cl K 2 O CaO TiO <0.1 Fe 2 O Base-to-acid ratio (oxidising) / - B/A (mass)

10 Results and discussion Ash fusion temperatures (ashes after DIN / DIN EN 14775) AFT CHC GBC RDF OAT Temperature (oxidising) / C DT ST HT FT Ash fusion range (oxidising) / K (FT-DT) Base-to-acid ratio (oxidising) / - B/A (mass) M. Reinmöller et al., Fuel, 151 (2015)

11 Results and discussion Mineral phases using different ashing methods - CHC Mineral phase Stoichiometry LTA MTA HTA Mineral phases (normalised) / wt.% Gypsum CaSO 4 2H 2 O Anhydrite CaSO Corundum Al 2 O * - - Quartz SiO Maghemite Fe 2 O Hematite Fe 2 O Magnetite Fe 3 O Kaolinite Al 2 Si 2 O 5 (OH) Muscovite KAl 2 (AlSi 3 O 10 )(OH) Titanium oxide TiO x <0.1 Amorphous *Enriched due to grinding with Al 2 O 3 -based grinding beads. Main initial phases are simple oxides and silicates Formation of muscovite from Al 2 O 3, SiO 2, and transformation of kaolinite in MTA/HTA Formation of gypsum in HTA maybe enabled from water in the air 11

12 Results and discussion Mineral phases using different ashing methods - GBC Mineral phase Stoichiometry LTA MTA HTA Mineral phases (normalised) / wt.% Gypsum CaSO 4 2H 2 O Anhydrite CaSO Thenardite Na 2 SO Langbeinite K 2 Mg 2 (SO 4 ) Calcite CaCO Dolomite CaMg(CO 3) Periclase MgO Corundum Al 2 O * - - Quartz SiO Maghemite Fe 2 O Magnetite Fe 3 O Forsterite Mg 2 SiO Srebrodolskite Ca 2 Fe 2 O Brownmillerite Ca 2 (Al,Fe) 2 O Amorphous <5 *Enriched due to grinding with Al 2 O 3 -based grinding beads. Main initial phases are sulphate-based Simple oxides and carbonates in MTA, silicates and aluminates/ferrites in HTA 12

13 Results and discussion Mineral phases using different ashing methods - RDF Mineral phase Stoichiometry LTA MTA HTA Mineral phases (normalised) / wt.% Gypsum CaSO 4 2H 2 O Anhydrite CaSO <0.1 Calcite CaCO <0.1 Vaterite CaCO Dolomite CaMg(CO 3 ) Corundum Al 2 O Quartz SiO Rutile TiO Maghemite Fe 2 O Hematite Fe 2 O Magnetite Fe 3 O Na 5 Al(OH) Wollastonite CaSiO Diopside CaMgSi 2 O Hedenbergite CaFeSi 2 O Jasmundite Ca 11 (SiO 4 ) 4 O 2 S Sodalite Na 4 Al 3 Si 3 ClO Amorphous

14 Results and discussion Mineral phases using different ashing methods - RDF Main initial phases are sulphates, carbonates, and simple oxides Formation of silicates in HTA from the simple oxides and decomposition of carbonates existent in MTA/LTA However, sulphates not found in HTA, while carbonates present in all ashes It has to be considered, strong deviations due to low homogeneity mineral species in the fuel RDF 14

15 Results and discussion Mineral phases using different ashing methods - OAT Mineral phase Stoichiometry LTA MTA HTA Mineral phases (normalised) / wt.% Arcanite K 2 SO Calcite CaCO Magnesite MgCO Huntite CaMg 3 (CO 3 ) Corundum Al 2 O * Quartz SiO Cristobalite SiO Enstatite Mg 2 Si 2 O Microcline K(AlSi 3 O 8 ) Struvite KMg(PO 4 ) 6H )6H 2 O Berlinite AlPO Amorphous *Enriched due to grinding with Al 2 O 3 -based grinding beads. Main initial phases are sulphates, carbonates, and simple oxides Formation of phosphates and silicates in MTA Formation of simple oxides and a system SiO 2 -Al 2 O 3 -K 2 O in HTA, while potassium sulphates are stable 15

16 Summary and outlook Summary Ashing method and heterogeneity of the elements strongly gy influences the mineral phases found in the XRD study Temperature-dependent phase (trans-)formations are monitored and related to the ash fusion behaviour Initial minerals: sulphates, carbonates, simple oxides, and rarely silicates Temperature-induced d formation of minerals: Silicates from simple oxides and decomposed carbonates and sulphates Ferrites/aluminates from decomposed carbonates and sulphates Outlook Interaction of different mineral phases during co-utilisation of the fuels Influence of particle sizes and phase distributions on mineral phase mixing 16

17 Acknowledgement The support of this study by RWE Power AG is gratefully acknowledged. Thank you very much for your kind attention! ib 17