MINERAL MATTER TRANSFORMATIONS DURING SASOL- LURGI FIXED BED DRY BOTTOM GASIFICATION. GTT Workshop June Dr. Johan van Dyk

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1 MINERAL MATTER TRANSFORMATIONS DURING SASOL- LURGI FIXED BED DRY BOTTOM GASIFICATION GTT Workshop June 2007 Dr. Johan van Dyk Sasol Technology, R&D, P.O. Box 1, Sasolburg, 1947, South Africa, (Tel), (Fax)

2 Roadmap of presentation Background of Sasol Sasol-Lurgi Fixed Bed Dry Bottom Gasification Understanding mineral matter transformations - WHY? Applications of FactSage Utilizing HT-XRD and FACTSAGE modelling as characterization tool (IP Approval PP0017) Manipulation of gasification coal feed in order to increase the ash fusion temperature of the coal to operate the gasifiers at higher temperatures (IP Approval PP0090 and Patent PCT/IB2006/050277) copyright reserved 2003, department, company

3 Where is South Africa? USA China Africa Middle East India India Asia Pacific Tokyo Hong Kong South America Singapore Australia South Africa

4 Where are the Sasol operations based in South Africa? Zimbabwe Namibia Botswana Pretoria Mozambique Johannesburg Secunda Sasolburg Cape Town South Africa Mossel Bay Port Elizabeth Durban Richards Bay Refineries Synfuels and Chemical Plants

5 Sasol Facts Initial driver to commercialize CTL in RSA...fuel independence on crude imports Secondary objective to convert low grade coal to petroleum products and chemical feedstocks Today Sasol produces > barrels per day Manufactures >200 fuel and chemical products Syngas production increased ±15% over the last 10 years 60% due to increased gasifier throughput 20% due to the reduction of CO 2 produced in gasification 10% due to the recovery of coal lock off gas 10% due to increased gasifier availability / reliability

6 Sasol s current global FT activities USA Qatar Petroleum/Sasol Chevron evaluating further Projects in Qatar and Algeria European Union Qatar Petroleum/Sasol bbl/d Qatar Started-up Sasol Iran study on GTL On hold Sasol/Shenhua/Ningxia 2 x bbl/d China feasibility phase China CTL GTL evaluating Opportunities South America CNL & NNPC bbl/d Nigeria Under construction Africa South Africa India Sasol Synfuels bbl/d South African Operation Sasol bpd Mafutha Under evaluation Evaluating opportunities 1 x bbl/d Sasol Chevron Australia Study on GTL opportunity progressing Australia

7 Sasol s FT Processes Convert Locked-in resources to easily transportable liquid fuels H 2 hydrocarbon source oxygen Feed Gas Generation Fischersyngas Tropsch Conversion Product waxy Upgrading syncrude GTL/CTL FUEL O 2 CO H 2 O by-product

8 Sasol-Lurgi fixed bed dry bottom (FBDB) gasification

9 Sasol-Lurgi (FBDB) gasification (cont.) Coal Drying Devolatilisation Gas Gasifier top Coal Gas Gasification Combustion Ash Steam, oxygen or air Ash Steam, oxygen or air Ash Gasifier bottom Temperature ( C)

10 Sasol-Lurgi (FBDB) gasification (cont.) Heating and Drying Pyrolysis Gas-Solid Reactions Gas-phase Reactions H 2 O Heat Volatile gases: CO, CO 2, H 2, H 2 O, Light hydrocarbons, tar CO + H 2 O CO 2 + H 2 CO 2 2 CO CO ½ O2 CO + 3H 2 CH 4 + H 2 O char Thermal front penetrates particle Porosity increases CO H 2 O H2 Endothermic reactions 2H 2 CH 4 Exothermic reactions

11 Understanding mineral matter transformations WHY? Ash fusion temperature (AFT) is one property of coal that gives an indication of suitability for Sasol-Lurgi Fixed Bed Dry Bottom Gasification purposes Ash fusion temperature results in an average temperature where bulk mineral composition starts to become soft and melt is an indication to what extent agglomeration / clinkering is likely to occur within the gasifier is currently used to predict average slagging properties of coal sources and not at what temperature the first melt/sinter occurs Ash clinkering can cause channel burning, pressure drop problems, unstable gasifier operation, etc

12 Window of operation between sintering and slagging >1350 o C Temperature ( C C) Initial deformation temperature Flow temperature Sasol coal sources <1300 o C

13 Syngas and ash producer Coal Ash flow temperature of coal > 1250 o C Gas Gasifier top Coal Gas Steam, oxygen or air Ash Steam, oxygen or air Ash Gasifier bottom Temperature ( C) Window of operation Courtesy of RH Matjie

14 Coal Coal Drying Devolatilisation Drying Devolatilisation Gas Gasification Combustion Ash Gasification Combustion Ash Steam, oxygen or air Ash Steam, oxygen or air Ash

15 FACTSAGE modelling approach Coal Drying Gas Devolatilisation Gasification Combustion Ash Steam, oxygen or air Ash

16 FACTSAGE input w.r.t. coal properties Component Mass % Mass flow (kg/hr) Moisture Fixed carbon Volatile matter Ash TOTAL Mineral Formula Mass % Pyrite FeS Quartz SiO Microline KalSi 3 O Muscovite / Illite Kal 3 Si 3 O 10 (OH) Kaolinite (Al 2 O 3 )(SiO 2 ) 2 (H 2 O) Anatase TiO Calcite CaCO Dolomite CaMg(CO 3 ) Apatite Ca 3 (PO 4 ) 3 (FOH) Gypsum CaSO 4 (H 2 O) TOTAL Property Mass % Mass flow (kg/hr) H 2 O H CH CO CO Mass flow N (kg/hr) Tar and oils Property TOTAL Mass % Mass flow (kg/hr) Carbon (C) Hydrogen (H) Nitrogen (N) Sulphur (S) Oxygen (O) by difference TOTAL

17 Drying and devolitilization zone Coal 100 o C 700 o C Gas 1250 o C 600 o C 350 o C Steam, oxygen or air Ash

18 Gasification zone Coal 100 o C Gas 700 o C 1250 o C 600 o C 350 o C Steam, oxygen or air Ash

19 Gasification zone (cont.) Slag-liquid composition (mass kg/hr) Base case MgO 150 FeO 315 SiO TiO 2 37 Ti 2 O CaO 219 Al 2 O K 2 O 3 MgS CaS FeS K 2 S 0.001

20 Combustion zone Coal 100 o C Gas 700 o C 1250 o C 600 o C 350 o C Steam, oxygen or air Ash Flow of material in gasifier cooling process in combustion zone

21 Combustion zone (cont.) Coal 100 o C 700 o C 1250 o C Gas Mineral composition of ash (crystalline material) SiO 2 quartz CaAl 2 Si 2 O 8 anorthite CaAl 4 Si 2 O 10 (OH) 2 margarite 600 o C 350 o C Steam, oxygen or air Ash Mg 5 Al 2 Si 3 O 10 (OH) 8 Kal 3 Si 3 O 10 (OH) 2 muscovite Fe 3 Al 2 Si 3 O 12 almandine (FeO)(TiO 2 ) ilmenite

22 Summary of FACTSAGE results Coal 100 o C 700 o C 1250 o C 600 o C 350 o C Gas Kaolonite disappeared between 600 o C and 650 o C >650 o C meta-kaolonite forms from kaolonite Carbonates, calcite and dolomite decompose Mullite starts to form Intensities of mullite and quartz reflections decrease as a result of melt formation Anorthite crystallizes between 1000 o C o C Above 1200 o C only quartz and anorthite remain stable in the liquidus Steam, oxygen or air Ash

23 HT-XRD results platinum Theta - Scale temperature [⁰C] kaolinite quartz mullite anorthite gehlenite? calcite dolomite Recorded X-ray spectra with crystalline phase 50 o C and 100 o C intervals. Bars on right illustrate the temperature range during which the various crystalline phases are present.

24 Summary of HT-XRD results counts) Intensity (HT-XRD Kaolinite decomposion Carbonates starting to decompose Mullite starting to form Anorthite starting to form kaolinite calcite dolomite mullite anorthite Temperature ( o C)

25 Conclusions Taken into account the results obtained from HT-XRD that <500 o C the starting material mainly composed of kaolonite (Al 2 SiO 5 (OH) 4 ), calcite (CaCO 3 ) and dolomite (CaMg(CO 3 ) 2 ), while quartz (SiO 2 ) remained unchanged between 500 o C and 700 o C kaolonite decomposes first, followed by calcite and dolomite around 1000 o C anorthite (CaAl 2 Si 2 O 8 ) becomes stable due to partial melting of the phase assemblage above 1350 o C the whole phase assemblage of the coal was molten

26 Conclusions (cont.) it can be concluded that HT-XRD does supply insight into specific mineral reactions and slag formation at temperatures below the average flow temperature obtained by AFT analyses Results are supported with phase diagrams on the SiO 2 - CaO-Al 2 O 3 -MgO system Although the amount of melt was fairly low at 1000 o C, a percentage of melt is definitely present, which is not reflected by AFT analyses

27 Manipulation of coal feed to gasification A method of increasing the AFT of a coal blend (decreasing the amount of slag propensity), in order to operate the gasifiers at higher temperatures Current operating philosophy to add excess steam to control the H 2 /CO ratio and control operating temperature below the AFT However, when oxygen load is decreased, gas production is also decreased, thus, the preferred way in controlling the gasifier and temperature, is by varying the steam consumption, thereby having a direct effect on carbon utilization H 2 O + CO CO 2 + H 2

28 Proposed solution to increase AFT Additives (e.g. Ca and Fe) added to decrease the AFT for slagging gasifiers In fixed bed gasifiers slagging of ash is undesirable and has to be operated at a temperature below the AFT of the coal Addition of AFT increasing agent such as kaolonite (Al 2 Si 2 O 5 (OH) 4 ), alumina (Al 2 O 3 ), silica (SiO 2 ) or titania (TiO 2 ) The observed effects to be explained by considering the reactive chemical species

29 Coal used in this study ELEMENT Result of coal sample used in this study (mass %) Coal characteristic as used during previous base case tests Average (mass %) Variation (minimum and maximum) (mass %) SiO Al 2 O Fe 2 O P 2 O TiO CaO MgO K 2 O Na 2 O SO

30 Effect of silica, alumina and titania as pure components on AFT Ash flow temp perature ( o C) Additive (mass %) Al2O3 TiO2 SiO2 Confirmed results as found on northern hemisphere coal sources Vassilev, et. al., 1995 by

31 Effect of silica, alumina and titania as pure components on AFT 3(Al 2 O 3.2SiO 2.2H 2 O) 3(Al 2 O 3.2SiO 2 ) + 6H 2 O Al 6 O 5 (SiO 4 ) 2 + 6H 2 O With the addition of free Al 2 O 3 to the coal, the free SiO 2 (quartz) in the coal can react with the Al 2 O 3 to directly form mullite (Al 6 O 5 (SiO 4 ) 2 ). Around 1000 o C anorthite (CaAl 2 Si 2 O 8 ) becomes stable. Less SiO 2 now available, which implies less anorthite.

32 Discussion of results by means of 3-component systems Current coal blend Plane where CaO = 10% normalized for the 3- component system Area of highest ash flow temperature Current coal blend Plane where Fe 2 O 3 = 30.0% normalized for three-component system Plane where Fe 2 O 3 = 8.0% normalized for 3-component system Current coal blend

33 FACTSAGE results % Decrease in slagliquid 10.8% 12.1% 13.7%

34 FACTSAGE results (cont.)

35 Conclusions Al 2 O 3 has the biggest / significant effect on AFT, with the effect of SiO 2 and TiO 2 very similar with regards to the effect on AFT Less Al 2 O 3 was needed to increase the AFT to a similar AFT level in comparison to the SiO 2 and TiO 2 Al 2 O 3 keeps the oxygen molecules stronger bound to the structure. When the element becomes free, with free electrons, a different mineral phase can form with a different flow property AFT is non-additive (not a linear weighted calculated average) as was expected for the other coal properties such as the ash content, and therefore difficult to predict

36 Conclusions (cont.) Decrease in slag (anorthite) formation can be obtained by physical (DILUTION)) or chemical (NEW PRODUCT) formation result of dilution is the worst case scenario Increase in crystalline material decreases slag formation Chemical reactions in the gasifier are taking place on micron scale irrespective of feed particle size distribution Reaction of sillimalite towards mullite formation takes place in advance of anorthite formation mullite formation thus limits anorthite formation

37 THANK YOU