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Chinese J.Chem.Eng., 14(6) 784789 (2006)

Application of the FactSage to Predict the Ash Melting Behavior in

Reducing Conditions*

LI Hanxu()a,**, Yoshihiko Ninomiya()

b, DONG Zhongbing()

a and

ZHANG Mingxu()c

aDepartment of Chemical Engineering, Anhui University of Science and Technology, Huainan 232001, ChinabDepartment of Applied Chemistry, Chubu University, Kasugai, Aichi 487-8501, Japanc Department of Material Science and Engineering, Anhui University of Science and Technology, Huainan 232001,China

Abstract FactSage has been used to predict the ash behavior and ash fusion temperature (AFT) at high tempera-ture under reducing atmosphere conditions. For Huainan coal ash samples, it has demonstrated a good agreementbetween the liquid phase formation as the function of temperature and the tested AFT. The tested and predicted flowtemperature (FT) for two typical Huainan coal ashes with the addition of CaO flux are quite fit with the maximumtemperature difference less than 74 which is within acceptable range. It can be concluded that FactSage in com-bination with X-ray diffraction (XRD) can be used to predict the reactions occurring between minerals, as well asthe mineral transformation and slag formation. This is probably an improved way to interpret melting properties ofmineral matter in coal and assist in quantifying slag formation in gasifier operation.

Keywords ash fusion temperature, FactSage, ash transformation, Huainan coals

1 INTRODUCTION

The coal ash related problems are major concernto many coal companies and electrical power utili-ties

[13]. The formation of slagging and fouling de-

posits in combustion, agglomeration in fluidized beds,ash slag flow in integrated gasification combined cy-cleIGCCand other slagging reactors are directlyrelated to the formation of liquid slag and to the sta-bilities of solid crystalline phases

[4,5]. The traditional

methods used to characterize the high temperature ash

behavior of the coal are becoming increasingly out-dated and are unable to accurately predict the behaviorof ash and slag in coal and coal blends in combustionand gasification technologies

[613]. Progresses in

chemical thermodynamic and viscosity models of ox-ide systems, the development of computational meth-ods, computer software and hardware now make itpossible to accurately predict the phase equilibriumconditions in complex multi-component coal ash slagsystems

[14,15].

Recently, studies on the prediction of ash fusiontemperature (AFT) were undertaken with the aid ofcomputer thermodynamic model

[1619]. FactSage

[20]

was introduced in 2001 and was developed jointly byboth the FACT-Win/F*A*C*T and ChemSage/SOLGASMIX thermochemical packages that werefounded over 28 years ago. The FactSage packageconsists of a series of information, database, calcula-tion and manipulation modules that enable one to ac-cess and manipulate pure substances and solution da-tabases. FactSage is an extremely powerful tool with

which one can perform a wide range of thermochemi-cal calculations useful to chemical and physical met-allurgists, chemical engineers, inorganic chemists,geochemists, electrochemists, environmentalists, etc.It provides information on the phases formed, theirproportions and compositions, the activities of indi-vidual chemical components and the thermodynamicproperties for all compositions, pressures and tem-peratures.

Having a significant impact on coal selection in-

ternationally (e.g. CRIEPI, ECN-Energy ResearchCentre of the Netherlands, EERC-North Dakota En-ergy & Environmental Research Center, Hongik Uni-versity in South Korea, Chubu University Japan),FactSage is already being used in the design ofstep-change technologies in the evaluation and selec-tion of coal for entrained flow coal gasification andblast furnace iron making by research teams in theworld. The most important features of the FactSagesystem are the large evaluated multi-component solu-tion databases giving the thermodynamic properties asfunctions of temperature and composition. FactSagecontains databases for 15-component oxide/glass so-

lutions, ceramic solution such as spinels, solid andliquid salt solution, metallic alloy solutions and aque-ous solutions, etc. Each of these databases has beenprepared by critical evaluation and optimization of allavailable data using appropriate solution models.

In order to understand the ash behavior ofHuainan coals, the FactSage Thermodynamics Model(FactSage 5.1) was used to evaluate the liquid phase

Received 2005-09-01, accepted 2006-01-08.* Supported by the Natural Science Foundation of the Education Ministry of Anhui Province (2004kj125) and the Key Project of

Huainan (2003001).

** To whom correspondence should be addressed. E-mail: hxli@aust.edu.cn

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amounts and ash transformation at high temperatureunder reducing conditions. The theoretical predictionswere also testified by experimental investigations ofash fusion temperature (AFT) test and X-ray diffrac-tion (XRD) for the quenched ash samples.

2 RESEARCH METHOD

FactSage Thermodynamic Model was used forpredicting multi-phase equilibria, proportions of theliquid and solid phases in specified atmosphere for themulti-component system.

Calculation conditions for FactSage Thermody-namic Model:(1) Chemical composition

The ash composition of Al2O3, CaO, Fe2O3,Na2O, K2O, MgO, SiO2, SO3, P2O5, TiO2was input inthe table of the software.(2) Solution species

FACT-SLAG solution included MgO, FeO, Na2O,

SiO2, TiO2, Ti2O3, CaO, Al2O3, K2O, MgS, CaS, FeS,Na2S, Na3PO4, Ca3(PO4)2, Mg3(PO4)2, Fe3(PO4)2.(3) Gas atmosphere

The reducing atmosphere of 60% CO and 40%CO2was employed in the FactSage calculation.(4) Pressure

The pressure for the FactSage calculation was0.1MPa.(5) Temperature

The initial temperature and final temperature forthe FactSage calculation were 800 and 1600,respectively with the interval of 20.

3 EXPERIMENTAL STUDY AND ANALYSIS

3.1 Coal samplesSix typical coal samples, selected from Huainan

coal basin, Anhui Province of China, were ground toless than 0.063mm (250 meshes). Coal samples areashed in air at 815 according to the Japan IndustrialStandard (JIS). All ash samples were analyzed usingRigaku RINT X-Ray Fluorescence (XRF).

The chemical compositions of the ash samplesanalyzed by Rigaku X-ray fluorescence and the melt-ing temperatures of coal ash samples are presented inTable 1.

As shown in Table 1, the ash composition ofHuainan coal samples is rich in SiO2 and Al2O3(75%). The contents of TiO2 is higher than 1% onaverage, the Na2O and MgO lower than 0.5% and 1%,respectively. The contents of CaO and FeO varygreatly from about 1% to 10% with coal samples.

The ground and dried coal was mounted in wax

and allowed to harden. The mount was cross-sectionedand polished, coated with carbon layer to eliminate theelectrostatic effects, and placed in the com-puter-controlled scanning electron microscope(CCSEM) for analysis. Six typical coal samples wereanalyzed by JEM-5600 with CDU-LEAP SEM-EDXand CCSEM. For CCSEM analyses, three magnifica-tions, namely 150 for the 22.0211.0m, 250 for the4.622.0m and 800 for the 0.54.6m were usedto obtain the backscattered image of samples. TheCCSEM was used to measure the size, composition,and abundance of mineral grains in the coal.

3.2 Ash fusion temperature test

The melting test was carried out under a reducingcondition of 60% CO and 40% CO2. The ash sampleswere shaped into triangular cones. The cones wereinserted into a furnace and heated at 5min

1ramp

rate. The limit temperature of the furnace is 1500.In order to compare the predicted AFT with the

tested AFT, the AFT of HN115 and HN106 coal ashwith different flux addition contents was tested andcalculated by FactSage respectively.

3.3 Experiment on ash by XRDA laboratory vertical gas-tight tube furnace ap-

paratus was set up to heat the samples to high tem-perature under controlled atmosphere. About 1g of ashsamples was heated in the apparatus which was modi-fied to allow rapid heating and quenching of ash sam-ples. The sample was dropped in the furnace and re-acted for 5min at desired temperature range from1050 to 1450, and then was quenched into water.Total quenching time was normally 5s. Quenchedsamples were examined by using Rigaku RINT X-raypowder diffractometry.

Table 1 Chemical composition and melting temperature for the coal ash samples

Composition, % (by mass) T,Coal

SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 P2O5 TiO2 DT ST FT

HN106 39.8 41.8 9.19 1.13 0.36 0.24 2.29 0.71 0.20 3.35 >1500 >1500 >1500

HNC13 42.1 40.2 3.94 5.77 0.59 0.41 1.13 1.78 1.22 2.26 >1500 >1500 >1500

HN115 42.3 34.5 6.17 8.55 1.00 0.21 0.76 3.20 0.55 2.24 1335 1360 1400

HN119 42.0 36.9 3.21 9.93 0.44 0.37 0.17 3.82 0.2 2.08 1434 1451 1480

KL1 47.1 35.3 4.72 5.67 0.75 0.26 1.33 2.22 0.19 1.96 1450 1500 >1500

HNP01 50.1 32.9 8.42 1.37 0.62 0.45 2.17 1.00 0.34 1.51 1425 1495 >1500

Expressed as mass fraction (%) equivalent oxide, dry basis.

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4 RESULTS AND DISCUSSION

4.1 The mineral matter composition of Huainan

coal samples

The composition of mineral matter in Huainancoals can be seen from Table 2. The mineral chemicalcomposition of Huainan coal includes the followingmain groups: kaolinite, montmorillonite, quartz, pyrite,

calcite, dolomite, unknown groups and other minormineral matter. The most abundant mineral matter inHuainan coal is that of the aluminosilicate clay miner-als with quartz. They account for more than 60% ofthe total mineral matter in coal. Pure kaolinite meltsmore slowly than the other clay minerals because of

the more restricted chemistry and the absence ofcations such as K, Na and Ca. Therefore, the AFT of acoal is mainly impacted by the contents of kaolinite ina coal sample and the contents of cations such as K,Na, Fe and Ca in minerals of coal (K, Na, Fe and Cawhich are not in the structure of aluminosilicate).During the ash fusion process, quartz starts to dissolve

slowly in the aluminosilicate matrix of coal ash. Al-though smaller quartz grains fuse and are assimilatedin slag more readily, larger quartz grains may persistlonger in slag phase. Therefore, quartz as a main min-eral matter in Huainan coals contributes to high AFTof Huainan coals. Carbonates generally formed in coal

Table 2 The mineralogical composition in six Huainan coal

Composition, % (by mass)Category

XM HN115 HN119 KL1 HN106 HN113

quartz 4.29 6 4.1 3.6 0.79 1.22

iron oxide 1.58 0.65 0 0 0.48 0.36

periclase 0 0 0.02 0 0.06 0.03

rutile 0 0.44 0.03 0.42 0.41 0.15

alumina 0.38 1.47 0.71 0.75 0.62 2.96

calcite 1.79 5.93 11.57 3.01 0.16 8.63

dolomite 1.37 4.93 0.6 1.4 0 0.12

ankerite 0.55 1.39 0 0.49 0 0.1

kaolinite 32.67 50.15 67.63 64.99 55.31 70.92

montmorillonite 7.1 1.01 0.51 1.12 0.42 0.21

K Al-silicate 8.79 2.86 0 8.63 11.8 0.47

Fe Al-silicate 0.47 0.34 0 3.59 0.54 1.04

Ca Al-silicate 0.05 0.67 0.19 0.3 0.01 1.85

Na Al-silicate 0 0.03 0 0.79 0.18 1.67

aluminosilicate 0.28 0.14 0.05 0.07 0.04 0.14

mixed aluminosilicate 0.05 0.05 0 0 0.33 0

Fe silicate 0.05 0 0 0 0 0

Ca silicate 0.06 0.13 0 0.15 0 0.16

Ca aluminate 0.07 0 0 0 0 0.04

pyrite 10.53 12.25 6.03 2.94 10.06 0.73

pyrrhotite 1.07 0 0 0 0.1 0

oxidized pyrrhotite 0.22 0.01 0 0.27 0.45 0.24

gypsum 5.55 0.2 0 0.05 0.36 0.26

apatite 0 0.13 0 0.09 0 0.47

Ca-Al-P 0 0 0 0 0 0.09

NaCl 0.07 0 0 0.08 0.08 0.35

KCl 0 0.13 0 0 0.12 0

gypsum/Al-silicate 0.41 0.03 0 0 0.01 0.29

Si-rich 0.48 0.15 0.22 0 0.06 0

Ca-rich 0.07 0.11 1.55 0.1 0.11 0.06

Ca-Si rich 0 0 0 0.05 0 0

unknown 22.05 10.78 6.78 7.13 17.49 7.45

totals 100 100 100 100 100 100

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following the coalification process are typically foundin veins. Calcium, from calcite, may interact withtransforming clay minerals to produce calcium-richaluminosilicate ash particles and lower the AFT. Thevariation of pyrite content in Huainan coals indicatesthe different geological conditions during the coalifi-cation process. Pyrite in coals can have a significant

influence on ash fusion process. It decomposes andfuses at a relatively low temperature.

4.2 FactSage calculation and analysis

The FactSage calculations were performed from800 to 1600. Fig.1 shows clearly the mass per-cent of liquid phase as the function of temperature forsix typical Huainan coal ash samples. Although theamount of liquid phase is fairly low at 1000, a per-centage of which is definitely present, this temperatureis not reflected by AFT analysis. The mass percentageof liquid phase formed during the heating process

varied with coal ash samples over the temperatureranges. For HN115 and HN119, the initial liquid for-mation temperature is at about 1000. With an in-crease in temperature, the mass percentage of liquidphase increases quickly by 75% of the overall materialfor HN115 at 1400 and HN119 at 1450 respec-tively, which is quite fit for the tested AFT. ForHN106, the initial liquid formation temperature ishigher than that of HN115 and HN119 at about 1070. From 1070to 1110, the liquid phase increasesvery sharply from very low percentage to 35%. Over1110, the formed liquid increases smoothly by 63%at 1600, which means about 40% solid present inthe slag and demonstrates why the HN106 AFT is sohigh.

Figure 1 Mass percentage of liquid phase for representa-tive Huainan coal ash samples

--

HN115; ----HN119; HNC13;- - -

KLI;

HNP01;-

HN106

Figure 2 shows the main calculation results forash transformation of HN115 coal with the tempera-ture increase. The data shows that melilite(Ca,Na)2(Al,Mg,Fe

2+)(Si,Al)2O7, feldspar [XAl(1-2)-

Si(3-2)O8, X in the formula can be sodium, and/or po-tassium, and/or calcium], quartz (SiO2), mullite(Al6Si2O13), cordierite (Mg2Al4Si5O18), AlPO4, leucite(KAlSi2O6), rutile (TiO2), ilmenite (FeO)(TiO2) wasformed at 800. As the temperature increases toabout 1000, liquid starts to form. About all meliliteand 50% mullite phase react to form feldspar phase

which has significant effect on the ash fusion charac-

teristics. From 800 to 1000, the proportion offeldspar phase increases smoothly. At about 1000,the proportion of feldspar phase increases sharply andreaches maximum at temperature 1020. At tem-perature over 1020, the proportion of feldspar phaseand quartz decreases smoothly which results in a rapidincrease in the proportion of liquid phase. Quartz dis-

appeared at 1200. Feldspar phase disappeared at1400 which has excellent agreement with the testedAFT (see Table 1). For temperature increase from over1400 to 1600 the mass percentage of mullitedecreases from 23% to 3.4% and leucite begin to de-cline from 3% to 1.5%.

Figure 2 The ash transformation of HN115 coal as thefunction of temperature under reducing condition

melilite; feldspar; SiO2quartz; A16Si2O13mullite;

KAlSi2O6leucite; TiO2rutile; (FeO) (TiO2) ilmenite;

SiO2tridymite; +slag liquid;mullite

4.3 AFT measurements and the FactSage predic-

tions

Two typical Huainan coals, HN115 with FT1400and HN106 with FT higher than 1500, wereselected for the comparison of tested FT and predictedFT with the addition of CaO flux. An equivalent CaOlevel of 8%, 15%, 20%, 25%, 30%, 35%, 42% of ashmass were selected to estimate the results. The pre-dicted FT was defined as the temperature at which theformed liquid phase reaches 75% of the total material.The comparison results are shown in Table 3. The re-sults show clearly that the measured FT and the pre-dicted FT are quite close with the maximum tempera-ture difference less than 74which is within accept-able range.

4.4 The experiments investigation of ash trans-

formation by XRD

Figure 3 shows the main mineral componentschange of HN115 coal ash at different temperatureunder a simulated gasification environment (60%CO,40%CO2).

As temperature increases, thermal decomposition,transformation and interaction and phase change occuramong the components. Around 1150, anorthite(CaAl2Si2O8) becomes stable probably due to partialmelting of the phase assemblage. Quartz and anhydrite

decrease while mullite increases. From 1150 to

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1350, quartz phase decreases sharply and anorthitecontents show the tendency of first increasing greatlythen decreasing. The formed mullite phase shows theslow declining tendency with temperature over 1250.Above 1350 the major minerals identified are mul-lite and non-crystalline phase. The transformation re-sults for quartz, anorthite, mullite and non-crystalline

phase obtained from XRD are fairly consistent withthe FactSage results. The XRD findings were furthersupported with FactSage calculations and indicatedthat feldspar formation (including anorthite) correlatedwith slag formation at temperatures around 1000.It can be concluded from these comparisons thatFactSage, in combination with XRD can be used topredict the reactions occurring between minerals, aswell as the ash transformation and slag formation.This could probably be an improved way to interpretflow properties of mineral matter in coal and assist inquantifying slag formation in gasifier operation at

temperatures not reflected by AFT analyses.

5 CONCLUSIONS

(1) FactSage has been an important tool to pre-dict the ash behavior and AFT at high temperatureunder reducing atmosphere conditions.

(2) Huainan coal ash samples have demonstrateda good agreement between the liquid formation as thefunction of temperature and the tested AFT as well as

the ash transformation tendency with the changes intemperature. Two typical Huainan coals have beenselected for the comparison of tested FT and predictedFT with the addition of CaO flux. The results showclearly that the measured FT and the predicted FT arequite fit with the maximum temperature differenceless than 74which is within acceptable range.

(3) The ash transformation results by FactSagecalculation are consistent with the results by XRD. Itcan be concluded that FactSage in combination withXRD can be used to predict the reactions occurringbetween minerals, as well as the mineral transforma-

tion and slag formation. This is probably an improved

Table 3 Comparison of the tested FT and the predicted FT by FactSage

Ash samples Measured FT, Predicted FT, Temperature difference,

HN115 1400 1389 11

HN115(CaO,8%) 1445 1451 6

HN115(CaO, 15%) 1340 1396 56

HN115(CaO,20%) 1280 1302 22

HN115(CaO,25%) 1280 1294 14

HN115(CaO, 30%) 1310 1384 74

HN115(CaO,42%) >1500 1481

HN106 >1500 >1600

HN106(CaO,8%) 1470 1470 0

HN106(CaO,15%) 1450 1418 32

HN106(CaO,20%) 1360 1326 34

HN106(CaO, 25%) 1310 1288 22

HN106(CaO, 30%) 1310 1364 54

HN106(CaO,42%) 1500 1512 12

Figure 3 The XRD patterns of HN115 coal ash at different temperature under reducing atmosphere (Q-Quartz, M-Mullite,AN-Anorthite, G-Gehlenite)

T,: 11150; 21250; 31350; 41450

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way to interpret flow properties of mineral matter incoal and assist in quantifying slag formation in gasi-fier operation at temperatures not reflected by AFTanalysis.

ACKNOWLEDGEMENTS

This work was supported by the key project of

Huainan Municipal Government, Anhui Province(Project No.2003001) and the project of Japanese

Government Loan. The authors acknowledge the con-

tributions made by the members of Ninomiyas Lab,

Chubu University and the Ash Chemistry Lab of Anhui

University of Science and Technology.

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