application of factsage equilibrium simulations to ... · outline of presentation background...

APPLICATION OF FACTSAGETM EQUILIBRIUM SIMULATIONS TO QUANTIFY THE EFFECT OF

MINERAL TYPES ON SLAG FORMATION DURING THERMAL CONVERSION OF COAL

JC van Dyk and MJ Keyser, Sasol TechnologyIP Approval PP001228 and PP001069

Copyright reserved 2012, Sasol Technology, R&D

International Freiberg ICG Conference, 21 May 2012, Germany

Outline of presentation

Backgroundg

Objective of study

Experimental and simulation informationExperimental and simulation informationSampling and preparation of discardFACTSAGETM equilibrium simulation

Discussion and resultsCharacteristics and composition of discard material (sink fraction at a relative density > 1.95)y )FACTSAGETM equilibrium calculations

Conclusions and comments


Interpretation of “mineral composition on AFT phenomena” - literaturephenomena - literature

Phase (thermo) equilibrium can be successfully applied tounderstand mineral transformations and liquid characterization of coal / mineral matterunderstand mineral transformations and liquid characterization of coal / mineral matterprediction of AFT and for blending strategies

Jak, E. and Hayes, P.C., Applications of the new F*A*C*T database to the prediction of melting behaviour of coal mineral matter,Coorperati e Research Centre for Black Coal Utilisation P rometall rg Research Gro p The Uni ersit of Q eenslandCoorperative Research Centre for Black Coal Utilisation, Pyrometallurgy Research Group, The University of Queensland,Australia, p.1-9, 2002.Jak, E., Prediction of coal ash fusion temperatures with the FACT thermodynamic computor package, Fuel, 81, 2002, p. 1655-1668

However, specific phenomena do not follow the AFT trends

Kaolinite, for example, is a common clay mineral with high concentrations offluxing agents like Si and Al that can react with other fluxing agents like sodium orcalcium to form products that melt at significantly higher or lower temperatures

Ross, D.P., Kosminski, A. and Agnew, J.B., Reactions between sodium and silicon minerals during gasification of low-rank coal, 12th International Conference on Coal Science, 2003, Australia, p. 1-9


Background

Coal chemical and physical properties directly impact on gasifier or boilerbehaviour, and more specifically on the ash flow temperature (FT in thestandard AFT analysis) and slag-liquid formation.The AFT analysis coal is widely used in marketing and utilization to accesscoal quality, ash fusibility and melting characteristics, as well as to predictthe melting behaviour of the coal in a coal conversion process [Jak, 2002].Detail characteristics are essential to predict operating performance whena specific coal source is to be gasified or combusted, either for movingbed, fluidized bed, entrained flow gasification or combustion purposes.One analysis that is used to measure the suitability of a coal source fory yconversion purposes is the standard AFT test [ISO 540].


Background (cont.)

Alpern (1984) has shown that this may not represent the actual flowtemperature of certain minerals and mineral phases.Other authors [Seggiani (1999) and Alpern et. al. 1984] have reported andexpressed the fusibility of the ash as a function of the content of theprincipal oxides frequently found in coal ash, i.e. SiO2, Al2O3, TiO2, Fe2O3,CaO, MgO, Na2O and K2O, with the acid/base ratio the most frequentlyused parameter for correlating ash fusibility with coal ash composition.Coal ash fusibility characteristics are difficult to determine precisely, partlybecause coal ash contains many components and does not have a sharpmelting point like a pure compound [Slegeir, 1988].Correlations between AFT data and ash composition indicate that, althoughthe regression approaches are more complicated, in many cases they areno more accurate than the approaches based on the acid-base formula.Correlations are thus not obtained with single elements, but as aninteraction between different ash elements. Fluxing components in the ash,specifically Ca, Mg and Fe, provide a fair indication of the expected ashf i b h i [S i i (1999) d Al l 1984]


fusion behaviour [Seggiani (1999) and Alpern et. al. 1984].

Background (cont.)

A phase equilibrium approach, as an additional tool, can be successfullyapplied to the understanding of mineral transformations and liquidcharacterization of coal mineral matter [Jak, et. al., 1998].AFT’s can be correlated with FACTSAGE™ equilibrium calculations, whereFACTSAGE™ is a powerful predictive tool, which can be applied to a widerange of coal utilization technologies [Jak, 2002].Specific phenomena do not follow the normal AFT trends. Kaolinite, forexample, is a common clay mineral with high concentrations of Si and Althat can react with other elements, like sodium that can also be a fluxingagent, to form products that melt at significantly higher temperatures.


Do you know what mineral property is important / correct to measure for suitability?correct to measure for suitability?

Non-reversibleFlow temperature recordedISO 540

A B C D E

Flow temperature recorded(E), although all materialmay not be 100% slag

ISO 540

A B C D E

(A)Original cone before heating(B)Initial deformation temperature where first rounding of cone tip is taking place (IDT)(C)Softening or sphere temperature where the cone height = cone width (ST)(D)Hemispherical temperature where cone height = ½ cone width (HT)(E)Fluid or flow temperature where cone height = 1.6mm (FT)

C t f ti b t C d D f l i bl ThiCone transformation between C and D, for example, is non-reversable. This implies that any phase crystallization (or decrease in slag-liquid formation) will not be observed during a conventional AFT measurementFlow patterns are observed based on “critical mass” in liquid form and not


Flow patterns are observed based on critical mass in liquid form and not where 100% material is in liquid format

Understanding viscosity of coal

5.56

Strong deposits

44.5

5

10 p

oise

)

Weak deposits

Strong deposits

33.5

4

osity

(log

Weak deposits

Strong depositsWeak deposits

1.52

2.5

Visc

o

Molten liquidMolten liquid

11000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500

T t (oC)


Temperatuur (oC)

A complex answer!

4.5

5

5.5

6

pois

e)

Predictions of slagcompositionAverage

Weak deposits

1.5

2

2.5

3

3.5

4

4.5

Visc

osity

(log

10

p

Strong deposits

Molten liquid

11000 1050 1100 1150 1200 1250

Temperature (oC)

IDT=1300oC IDT=1311oC IDT=1321oC FT=1346oC

100100

Cooled slag or glas


0

Crystalline material

Experimental and simulation information- FACTSAGETM equilibrium simulation- FACTSAGE equilibrium simulation

FACTSAGE™ modelling provides the ability to calculate and manipulatephase diagrams but established mainly in the field of complex chemicalphase diagrams, but established mainly in the field of complex chemicalequilibrium and process simulations. The FACTSAGE™ development,already started in the late 70’s, is today the largest thermochemicalpackage and database available for inorganic solids and slag.package and database available for inorganic solids and slag.Supply insight into specific mineral interactions, slag formation and slag-liquid temperatures of mineral compositions.The specific value in this study will be that these thermochemistry modelsThe specific value in this study will be that these thermochemistry modelscan be used to analyze equilibrium conditions for reactions occurringbetween inorganic and/or organic materials, as well as providing insight intothe mineral transformation and slag formation processthe mineral transformation and slag formation process.The database will assist in understanding, as well as predicting, what mighthappen with specific coal and mineral sources during gasification orcombustion processescombustion processes.


Experimental and simulation information- FACTSAGETM equilibrium simulation (cont )- FACTSAGE equilibrium simulation (cont.)

In a study conducted by the University of Queensland [Biggs, 1986] thefocus was on the relationship between ash flow temperature andfocus was on the relationship between ash flow temperature andFACTSAGE™ liquidus calculations. FACTSAGE™ computer software anddatabase can be successfully applied for the prediction of AFT, as well as forthe development of blending strategies.the development of blending strategies.

The focus of this study will be on slag-liquid formation and mineral changesat varying temperatures and mineral type compositions (discard) within theat varying temperatures and mineral type compositions (discard) within thecoal and discard blend - considered relevant to any coal conversion process.

Of particular importance is not only the maximumOf particular importance is not only the maximum(peak) temperature which is reached duringcombustion or gasification which affects the amountof slag / liquid, but the operating zone of a coal

i d t i if th h ill ltconversion process determines if the ash will meltexcessively and also to what extent. The importantassumption to take note of is that thermodynamicequilibrium is reached, and that it is assumed that


equ b u s eac ed, a d t at t s assu ed t atthere are no reaction kinetic limitations.

Quick trend on specific elements


CaO versus slag-liquid formation [Jak et al 2002][Jak, et. al., 2002]


Slag-liquid formation in South-African Highveld coalHighveld coal

Simulated slag-liquid withPublished data

South-African Highveld coal

60.0

65.0

70.0

%)

45.0

50.0

55.0

-liqu

id (m

ass

30.0

35.0

40.0Slag

10 12 14 16 18 20

CaO content (mass%)


Objective of study

During previous studies, coal was prepared by beneficiation at a relativedensity of RD=1.95 [Van Dyk and Keyser, 2005] and a detail characterizationof each stone fraction (relative density >1.95) conducted. This presentationwill not deal with that part of the work.The primary objective of this study is to quantify the effect of discardmaterial on slag-liquid formation and ash flow temperature.The secondary objective is also to highlight the limitations in only utilizingthe standard AFT analyses.

It is important to understand the effect of discard material on slag-liquid formation, as a destoning / beneficiation process was appliedon the coal before conversion A thermo equilibrium simulationon the coal before conversion. A thermo-equilibrium simulationapproach based on FACTSAGE™ will be applied.


Experimental and simulation information- Sampling and preparation of discard- Sampling and preparation of discard

During the coal blend preparation, representative samples of the discard product (RD > 1 95) were taken from the discard stockpile Samples wereproduct (RD > 1.95) were taken from the discard stockpile. Samples were visually inspected by a Sasol geologist and divided into the following classification groups: “roof”, “floor”, “pyrite”, “C-shale”, “carbonates” and “siltstone”.siltstone .

The following analyses were conducted on each sample :each sample :

Proximate analysis (moisture, volatile matter and ash content – fixed carbon by difference)Ultimate analysis (C, H, N, S – O by difference)Ash composition (elemental composition)Ash melting temperatures (oxidizing to 1600oC).XRD-analysis (mineral composition)


Experimental and simulation information- Fluidized bed gasification [Holt 2006]- Fluidized bed gasification [Holt, 2006]


Experimental and simulation information- Moving bed gasification [Holt 2006]- Moving bed gasification [Holt, 2006]


Experimental and simulation information- Entrained flow gasification [Higman 2007]- Entrained flow gasification [Higman, 2007]


Characteristics and composition of discard material (sink fraction at a relative density > 1 95)material (sink fraction at a relative density > 1.95)

Mineral type Average(mass %)

“C b t ” 6 0“Carbonates” 6.0“C-Shale” 18.5 “Pyrite” 12.5 “Roof” 17.5 “Floor” 23.0“Siltstone” 22.5

Average “Carbonate”

Average “C-shale”

Average “Pyrite”

Average “Roof”

Average “Floor”

Average “Siltstone” y

% Volatile matter (mass %) 26.0 12.9 25.0 5.9 9.1 11.8

% C (AD mass %) 23.6 19.7 24.1 2.7 4.5 16.8 % H (AD mass %) 1.0 1.0 1.0 0.5 0.5 0.5 % N (AD mass %) 1 0 5 0 5 0 1 0 1 0 2% N (AD mass %) 1 0.5 0.5 0.1 0.1 0.2 % S (AD mass %) 17.0 1.5 15.4 1.7 1.1 1.6 % O (AD mass %) 2.0 6.0 4.0 4.0 5.0 6.0 SiO2 (mass %) 21.8 65.3 18.8 80.1 71.5 67.0 Al2O3 (mass %) 6.9 21.9 7.1 11.3 22.1 21.3 F O ( %) 41 1 3 8 43 7 3 6 1 9 3 6Fe2O3 (mass %) 41.1 3.8 43.7 3.6 1.9 3.6 CaO (mass %) 16.3 2.0 15.1 1.2 0.4 1.8 Ash melting temperature (FT)(oC) ±30oC

1275 1546 1394 >1600 1593 1553


Pyrite (mass % as mineral in discard type)

56.8 4.2 65.6 2.7 1.4 4.2

Characteristics and composition of discard material (sink fraction at a relative density > 1 95) (cont )(sink fraction at a relative density > 1.95) (cont.)

The high pyrite content in the “carbonates” is confirmed by the high Fe2O3and S-content The ash flow temperatures are in the order of 1250oC-and S content. The ash flow temperatures are in the order of 1250 C1300oC. This relatively low ash flow temperatures of carbonates comparedto the other mineral types are caused by the high CaO and Fe2O3 content.“C-shale” showed a high concentration of SiO and Al O XRD-analysesC-shale showed a high concentration of SiO2 and Al2O3. XRD-analysesindicated that the quartz and kaolonite content of “C-shale” are highconfirming the higher SiO2 and Al2O3, which also resulted in a higher ashflow temperature of >1500oCflow temperature of >1500 C.The group “pyrite” showed a high pyrite content of >60% based on XRD.“Roof” showed a high SiO2-content of >80%. XRD-analyses showed highquartz (>50%) and kaolonite (20%) contents confirming the high SiOquartz (>50%) and kaolonite (20%) contents confirming the high SiO2-content. Ash flow temperature >1600oC.“Floor” showed similar characteristics as “roof”, with a high SiO2-content(70%) d Al O t t (20%) XRD l l i di t d hi h t(70%) and Al2O3-content (20%). XRD-analyses also indicated high quartz,illite and microline contents. Ash flow temperature is also ±1600oC.“Siltstone” also has a high SiO2-content (70%) and Al2O3-content (20%).XRD l h d hi h t d k l it t t Th h fl


XRD-analyses showed high quartz and kaolonite contents. The ash flowtemperatures are in the order of 1500-1550oC.


PROXIMATE (mass %) Coal# Carbonate C-shale Pyrite Roof Floor Siltstone (mass %)

Moisture 4.1 2.4 2.6 2.5 0.8 1.2 2.3 Fixed carbon 52.6 17.4 16.7 19.6 1.9 3.1 14.2 Volatile matter 23.5 26.0 12.9 25.0 5.9 9.1 11.8 A h t t 19 8 54 2 67 8 53 0 91 4 86 6 71 7Ash content 19.8 54.2 67.8 53.0 91.4 86.6 71.7Ash composition (mass %)SiO2 44.6 21.8 65.3 18.8 80.1 71.5 67 Al2O3 26.9 6.9 21.9 7.1 11.3 22.1 21.3 Fe O 2 5 41 1 3 8 43 7 3 6 1 9 3 6Fe2O3 2.5 41.1 3.8 43.7 3.6 1.9 3.6P2O5 1.0 1.4 0.3 1.5 0.1 0.1 0.3 TiO2 1.4 0.6 2.3 0.5 0.5 0.7 2.1 CaO 10.1 16.3 2 15.1 1.2 0.4 1.8 MgO 3.5 1.5 0.8 1.5 0.3 0.3 0.6gK2O 0.6 0.6 1.3 0.5 1.4 1.4 1.3 Na2O 0.8 0.2 0.4 0.2 0.2 0.3 0.3 SO3 7.3 9.4 1.6 10.1 0.7 0.1 0.9 LOI 1.4 0.2 0.3 1 0.6 1.2 0.8

TAKE NOTE THAT WHEN COAL IS REFERED TO OR MENTIONED IN ALL FURTHER DISCUSSIONS IT REFERS TO THE BASE CASE COAL PROPERTY WHICH CONTAINS NO DISCARD MATERIAL AT RD=1 95 (DESTONED COAL)


WHICH CONTAINS NO DISCARD MATERIAL AT RD 1.95 (DESTONED COAL)


The measured flow t t f th l dtemperatures of the coal and the individual mineral types have an excellent correlation with the FACTSAGE™ flow temperature simulations. Differences are even smaller than the generally accepted e perimental error range of anexperimental error range of an AFT analysis of ±30oC.Differences observed with “roof” are due to the limitationroof are due to the limitation of AFT equipment that can only measure temperatures up to 1550-1600oC. The given ash f f “ fflow temperature of “roof” is thus only the point at which the experiment had to be terminated and not the actual

*This graph only reflects the inorganic components which transform into slag/liquid and not the crystalline phases or gas phases


terminated, and not the actual flow temperature.

into slag/liquid and not the crystalline phases or gas phases.


FACTSAGE™ simulation of the coal and discard stream indicated that the slag formation behaviour of both coal and di d i il b d t ddiscard are very similar, based on trend and flow temperature.

Some coal conversion technologies e.g. fluidized bed or moving bed gasification technologies, and combustion technologies - operate below the flow temperature of the specific coal. In order to illustrate the utility of the FACTSAGE™ simulation approach in such a scenario the slag-liquid


illustrate the utility of the FACTSAGE simulation approach in such a scenario, the slag-liquid formation of coal and 5%, 10% and 15% discard addition were simulated.


Measured flow temperature = 1420

Softening temperature

Hemisperical temperature

o

Initial deformation temperature



What is AFT telling us (OR NOT)


Measured flow temperature = 1420

Initial deformation temperature




Long vs short ash flow temperature

)

Coal source A

(mas

s %

)

Coal source B10oC10oC

form

atio

n

180oC

ag-li

quid

f

20oC

900 1000 1100 13001200 1400 1500 1600

Sl


900 1000 1100 13001200 1400 1500 1600Temperature (oC)

Conclusions and commentsConclusions and comments

The slag-liquid flow temperature simulations for coal and the individualmineral types compared favourably with the actual measured ash flowmineral types compared favourably with the actual measured ash flowtemperature and are within the experimental error of an AFT analysis of±30oC.The slag formation of the coal showed a more gradual increase in theThe slag formation of the coal showed a more gradual increase in theamount of slag formed compared to specific individual mineral types. Thiscan be explained by the ash composition of coal which has a more evendistribution of minerals compared to “roof” and “floor” or “carbonates” fordistribution of minerals compared to roof and floor or carbonates , forexample, which have a relatively high SiO2 content or CaO respectively.The slag formation tendency of the total discard moved significantly towardsthe slag formation behaviour of “carbonates” This again highlights thethe slag formation behaviour of carbonates . This again highlights thesignificant contribution of fluxing elements, such as CaO, in total slagformation and mineral behaviour.


Conclusions and commentsConclusions and comments

The flow temperature of the total discard is simulated as between 1400oCand 1425oC This is also confirmed from previous studies where CaO hasand 1425 C. This is also confirmed from previous studies where CaO hasthe most significant impact as fluxing component (lower flow temperatures)and on anorthite formation in a fixed bed gasifier. The coal sourcesproducing the highest concentration of Ca-Al-Si species (CaAl2Si2O8producing the highest concentration of Ca Al Si species (CaAl2Si2O8anorthite and CaAl4Si2O10(OH)2 margarite), are the coal sources with thebiggest concentration CaO. From this result it is also confirmed that flowtemperature properties are non-additive and cannot be calculated from ap p pweighted average principle.It can also be confirmed by FACTSAGE™ modelling that the addition ofdiscard blend for this specific coal source to the coal will have no significantp geffect, if any affect at all, on the flow properties of the blend. It has to behighlighted that this observation is only based on the average discard effectand not the effect of specific individual components such as carbonates withp pa high CaO content or floor with a high SiO2 content and also only valid forthis specific coal tested.


THANK YOU

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