PREDICTING THE SLAGGING PROPENSITY OF SASOL-LURGI GASIFIER COAL FEEDSTOCK

Transcription

1 PREDICTING THE SLAGGING PROPENSITY OF SASOL-LURGI GASIFIER COAL FEEDSTOCK Chris van Alphen and Henry Matjie Indaba Conference th October 2006

2 Objective present a new ash formation and slag prediction model for Sasol Lurgi-gasifier Content Coal feedstock mineralogy Coarse ash mineralogy Model

3 Coal Feed Stock Coal O 2 H 2 O Slagging/clinkers might block and damage rotating grate Coarse Ash

4 Samples analysed Sasol feedstock (August 2004) Separated into 1.5 g/cm 3, g/cm 3 and >1.8 g/cm 3 density fractions CCSEM analysis of each density fraction Chemical analysis Sasol feedstock (October 2004) One bulk sample CCSEM analysis Chemical analysis

5 A E A B A: fine grained kaolinite (Al 2 Si 2 O 5 (OH) 4 ) and quartz (SiO 2 ) inclusions in coal B: coarse/fine grained subarkosic sandstone rock (quartz, feldspar (KAlSi 3 O 8 ), mica (KAl 3 Si 3 O 10 (OH) 4 ), rutile (TiO 2 ), kaolinite D D A C B C dolomite (CaMg(CO 3 ) 2 inclusion in coal D large extraneous pyrite (FeS 2 ) and calcite (CaCO 3 ) (>700 um) Width of image 2.7mm E dolomite cleats

6 B A: Coarse grained sandstone A B C C A (quartz, muscovite, feldspar) B: Siltstone/mudstone rock fragments (kaolinite, muscovite, quartz, orthoclase, rutile, apatite) C: minute pyrite, kaolinite and quartz inclusions in coal B B D: large pyrite associated with fine grained sandstone Width of image 2.7mm

7 <1.5 g/cm 3 Ep > g/cm 3 >1.8 g/cm 3

8 Typical coal mineral proportions Mineral Formula Aug Oct CQA (xls) Kaolinite Al 4 [Si 4 O 10 ](OH) Quartz Pyrite Calcite Dolomite SiO 2 FeS 2 CaCO 3 CaMg(CO 3 ) Muscovite Illite Feldspar (orthoclase, microcline) K 2 Al 4 [Si 6 Al 2 ]O 20 (OH) 4 K Al 4 [Si,Al] 8 O 20 (OH) 4 (K,Na)AlSi 3 O Magnetite, hematite, limonite) Siderite Ankerite Apatite Fe 3 O 4 Fe 2 O 3 FeCO 3 Ca(Mg,Fe,Mn)(CO 3 ) 2 Ca 5 (PO 4 ) 3 (OH,F,Cl) Rutile TiO Coal C,H,N,O

9 Density variation of slagging minerals Legend <1.5 g/cm g/cm3 >1.8 g/cm Pyrite Calcite Dolomite

10 Density variations Legend <1.5 g/cm g/cm3 >1.8 g/cm Kaolinite Quartz Muscovite/illite Microcline

11 Particle classification Black coal Mudstone and siltstone Layered coal Patchy coal Arkosic sandstone Grey coal Kaolinite infilled cell cavities Mixed layered and patchy Extraenous calcite and pyrite cleat fragments

12 Mass-% particle types Particle types Aug. Oct. Black coal Layered coal Grey coal Patchy coal Mixed layered patchy Siltstone/Mudstone Sandstone Kaolinite in cell cavities Extraneous pyrite cleats Extraneous calcite/dolomite cleats Extraenous pyrite and cleat fragments Total

13 Particle type summary Mass-% Carbon rich (MM <60%) Stone Cell cavities Extraenous cleat August October

14 Gasifier ash and clinker Principally consist of rock matrix

15 Q Q Q Q Q: quartz Ka Ka OM: K-Al-silicate (muscovite, microcline) OM Ka Ka Q Q Q Ka Ka

16 Rock fragment Rock fragment Anorthite laths Mullite needles in glass

17 Mass-% Ash compositions Ca-Fe aluminosilicat e Glass Si-rich glass K-bearing glass Anorthite Mullite Quartz Alumino silicate Quartz Kaolinite Fe-oxide Ca CaMgOxide Aug Oct

18 Model assumptions Anorthite and mullite are crystalised from molten glass and not formed by solid state reactions. Model assumes that anorthite and mullite were originally molten glass. All carbon is gasified and not included in model (Estimated 97% of carbon) Gasifier is closed system, no ash lost

19 < Included Model methodolgy CCSEM Particle Data Set particle threshold (30,35,40,45,50,55,60 area-% MM) > Extraneous Glass Anorthite Mullite Slag prediction Model Compute Mass-% mineral Mass-% element distribution Quartz Aluminosilicate Fe-oxide Ca/CaMgOxide K-glass Compute absolute difference Model and measured Determine best threshold value

20 Mass-% glass August October Aug. Measured Oct. Measured Threshold value (area-% MM in particle)

21 Model phase proportions August October Absolute d Model threshold value - area-% mineral matter

22 Model element proportions August October Coal particles with less than 55 volume-% minerals are the major 58.3 Absolute d source of the glass phases Model threshold value - area-% mineral matter 39.0

23 Impact of coal feedstock mineralogy 90 Carbon rich (MM <60%) Stone Cell cavities Extraenous cleat Mass-% glass, anorthite, mullite August October Aug. Measured Oct. Measured Mass-% Threshold value (area-% MM in particle) August October

24 Impact of coal feedstock mineralogy Aug. Oct. Mass-% Glass Mass-% Included Minerals Mass-% glass, anorthite, mullite % % Threshold value (area-% MM in particle) 60% 40% 20% August October Aug. Measured Oct. Measured 0% Pyrite Aug. Pyrite Oct. Quartz Aug. Quartz Oct. Kaolinite Aug. Kaolinite Oct. Calcite Aug. Calcite Oct. Dolomite Aug. Dolomite Oct. MM Aug. MM Oct. Included Extraneous

25 Role of the stones composition effect glass Stone Fragments Stone appear to react with glass

26 Q Q Q Q Ka Ka dehydrate, no evidence of mullite Ka Ka OM Q Q: quartz unaltered, except cracks Q Q Ka Ka OM: K-Al-silicate (muscovite, orthoclase) molten glass

27 Glass composition - stone Quartz rich siltstone reach with glass, increase SiO 2 content, promote crystallisation of mullite Mullite Quartz rich stone

28 Phase diagram SiO G1 G2 Am G3 Wh An Mug Mu Mu Ge CaO Al2O3

29 Clinker formation concept? In terms of clinkering propose three Rock fragments high proportions of mineral transformations are in-situ. Quartz remains unaltered, kaolinite dehydrate and K-bearing form molten glass. localised glass composition impact of crystallization Coal particles with less than 55 mass-% included minerals are major source of glass phases. Large extraneous pyrite and calcite transform within the particle. Pyrite transform to pyrrhotite-fe-s-oxide and Magnetite/Hematite. Sulphur is released into the system. Extraneous calcite transform to Ca-oxide, releasing CO 2

30 Clinker formation concept? Mineralogy of source feedstock influences the proportion and composition of glass. Higher proportion of included minerals, promote glass formation. Increase in the proportion of sandstone rock fragment, increase liquidus temperatures, reducing sintering strength.

31 Funding from Sasol R&D to undertake investigation address: