PREDICTING THE SLAGGING PROPENSITY OF SASOL-LURGI GASIFIER COAL FEEDSTOCK Chris van Alphen and Henry Matjie Indaba Conference 10-11 th October 2006
Objective present a new ash formation and slag prediction model for Sasol Lurgi-gasifier Content Coal feedstock mineralogy Coarse ash mineralogy Model
Coal Feed Stock Coal O 2 H 2 O Slagging/clinkers might block and damage rotating grate Coarse Ash
Samples analysed Sasol feedstock (August 2004) Separated into 1.5 g/cm 3, 1-5-1.8 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
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
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
<1.5 g/cm 3 Ep >1.5 1.8 g/cm 3 >1.8 g/cm 3
Typical coal mineral proportions Mineral Formula Aug. 2004 Oct. 2004 CQA (xls) Kaolinite Al 4 [Si 4 O 10 ](OH) 8 18.6 19.7 17.7 Quartz Pyrite Calcite Dolomite SiO 2 FeS 2 CaCO 3 CaMg(CO 3 ) 2 5.6 1.8 2.5 3.1 7.5 1.5 2.5 3.8 4.5 1.8 4.5 0.8 Muscovite Illite Feldspar (orthoclase, microcline) K 2 Al 4 [Si 6 Al 2 ]O 20 (OH) 4 K 1-1.5 Al 4 [Si,Al] 8 O 20 (OH) 4 (K,Na)AlSi 3 O 8 2.0 0.5 1.1 0.7 2.1 0.2 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) 0.1 0.1 0.2 0.0 0.0 0.2 0.0 0.0 0.7 Rutile TiO 2 0.2 0.1 0.3 Coal C,H,N,O 64.6 62.1 67.4
Density variation of slagging minerals 8 7 6 Legend <1.5 g/cm3 1.5-1.8 g/cm3 >1.8 g/cm3 5 4 3 2 1 0 7.8 5.4 4 3.1 1.8 1.4 1.5 0.6 0.9 Pyrite Calcite Dolomite
Density variations - 35 30 25 Legend <1.5 g/cm3 1.5-1.8 g/cm3 >1.8 g/cm3 20 15 33 10 22.3 19.2 5 0 5.1 3.6 4.3 1.3 2.2 2.3 0.4 0 0.2 Kaolinite Quartz Muscovite/illite Microcline
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
Mass-% particle types Particle types Aug. Oct. Black coal 6.0 12.0 Layered coal 16.4 13.6 Grey coal 11.9 7.8 Patchy coal 42.8 36.8 Mixed layered patchy 7.4 11.5 Siltstone/Mudstone 8.8 11.5 Sandstone 2.2 2.6 Kaolinite in cell cavities 0.6 1.3 Extraneous pyrite cleats 1.1 0.3 Extraneous calcite/dolomite cleats 1.5 2.0 Extraenous pyrite and cleat fragments 1.2 0.2 Total 100.0 100.0
Particle type summary Mass-% 90 80 70 60 50 40 30 20 Carbon rich (MM <60%) Stone 84.5 81.7 Cell cavities Extraenous cleat 10 0 11.0 14.1 August October
Gasifier ash and clinker Principally consist of rock matrix
Q Q Q Q Q: quartz Ka Ka OM: K-Al-silicate (muscovite, microcline) OM Ka Ka Q Q Q Ka Ka
Rock fragment Rock fragment Anorthite laths Mullite needles in glass
Mass-% Ash compositions 40 35 30 25 20 15 10 5 0 Ca-Fe aluminosilicat e Glass Si-rich glass K-bearing glass Anorthite Mullite Quartz Alumino silicate Quartz Kaolinite Fe-oxide Ca CaMgOxide Aug.04 36.4 4.8 4.3 10.3 1.5 9.3 22.2 6.6 2.2 2.1 Oct.04 32.6 2.6 2.3 6.0 1.8 10.7 29.3 8.5 3.5 2.4
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
< 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
65 60 55 50 45 40 Mass-% glass 35 30 25 August October Aug. Measured Oct. Measured 20 80 70 60 55 50 40 30 Threshold value (area-% MM in particle)
Model phase proportions 30 25 August October 20 15 29.2 10 17.3 19.3 Absolute d 5 0 10.0 5.1 6.1 6.8 3.6 5.0 11.5 60 55 50 40 30 Model threshold value - area-% mineral matter
Model element proportions 60 50 40 30 August October Coal particles with less than 55 volume-% minerals are the major 58.3 Absolute d 20 10 0 16.1 source of the glass 8.9 7.6 10.4 phases 12.0 13.4 33.7 23.9 60 55 50 40 30 Model threshold value - area-% mineral matter 39.0
Impact of coal feedstock mineralogy 90 Carbon rich (MM <60%) Stone Cell cavities Extraenous cleat 65 60 55 80 70 Mass-% glass, anorthite, mullite 50 45 40 35 30 25 August October Aug. Measured Oct. Measured Mass-% 60 50 40 30 20 80 70 60 55 50 40 30 Threshold value (area-% MM in particle) 20 10 0 84.5 81.7 11.0 14.1 August October
Impact of coal feedstock mineralogy 65 60 55 50 45 40 Aug. Oct. Mass-% Glass 53.0 43.0 Mass-% Included Minerals 59.7 44.2 Mass-% glass, anorthite, mullite 35 30 25 100% 20 80 80% 70 60 55 50 40 30 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 46.3 29.1 38.1 38.8 65.7 46 44.7 38.5 84.5 69.2 59.7 44.2 Extraneous 53.7 71.1 61.9 61.2 34.3 54 55.3 61.5 15.5 30.8 40.3 55.8
Role of the stones composition effect glass Stone Fragments Stone appear to react with glass
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
Glass composition - stone Quartz rich siltstone reach with glass, increase SiO 2 content, promote crystallisation of mullite Mullite Quartz rich stone
Phase diagram SiO2 10 90 20 80 30 70 60 50 40 G1 G2 Am G3 Wh An Mug 60 50 Mu 40 70 Mu 30 80 Ge 20 90 10 CaO 10 20 30 40 50 60 70 80 90 Al2O3
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
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.
Funding from Sasol R&D to undertake investigation email address: cncc@mweb.co.za