Effective Utilization of Water Hyacinth Resource by Co-Gasification with Coal: Rheological Properties and Ash Fusion Temperatures of Hyacinth-Coal Slurry

Effective Utilization of Water Hyacinth Resource by Co-Gasificationwith Coal: Rheological Properties and Ash Fusion Temperatures ofHyacinth-Coal SlurryHaifeng Liu,*,†,‡ Menghan Xu,†,‡ Qiang Zhang,†,‡ Hui Zhao,†,‡ and Weifeng Li†,‡

†Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Scienceand Technology, No. 130 Meilong Road, Shanghai 200237, People’s Republic of China‡Shanghai Engineering Research Center of Coal Gasification, No. 130 Meilong Road, Shanghai 200237, People’s Republic of China

ABSTRACT: Water hyacinth has attracted extensive attention due to its capability to capture carbon dioxide and remove excessnutrients and toxic metal ions; however, its exuberant growth also leads to environmental problems. In this study, water hyacinthwas introduced to prepare bioslurry fuels with coal in the entrained-flow gasification process. Water hyacinth was modified withthe addition of Fe2(SO4)3. Rheological properties and ash fusion temperatures of the modified-hyacinth-coal slurry (MHCS)were investigated. MHCS with solids loading of 60.0 wt % was prepared by adding 19.2 g of modified water hyacinth to 100 g ofcoal that showed more stability and shear-thinning behavior (thixotropy) than those of coal-water slurry. The ash fusiontemperatures of most water hyacinth-coal blends are lower than those of coal and water hyacinth. The modified water hyacinthcould further reduce the ash fusion temperature of coal because low-melting eutectic mixtures were formed.

1. INTRODUCTION

A huge amount of water hyacinth is harvested every year tocontrol its exuberant growth in India, South Africa, USA, andChina.1−3 Water hyacinth produces about 140 tons of dry massper hectare per year and is an ideal plant for carbon dioxidecapture and biomass production.4−6 Moreover, water hyacinthis capable of removing excess nutrients and toxic metal ionsfrom environment.7−10 Common methods for water hyacinthutilization include anaerobic digestion, composting, and itsusage as fodder, silage, or green manure; however, these are notenough to deal with their excessive harvest from the seasonalexuberant growth in large water bodies.1,5,11 Besides, waterhyacinth suffers from its low energy density and high moisturecontent, so it is not economically viable to dry water hyacinthfor various uses.12,13 A few proper treatment methods limitwater hyacinth to play a greater role in environmentalprotection. Therefore, it is urgent to develop a suitable waterhyacinth treatment technology to reduce environmentalproblems and treatment costs. Preparing bioslurry fuels withwater hyacinth and coal followed by processing it in anentrained-flow gasifier could be an effective strategy to utilizebiomass as direct fuel.14 The preparation of hyacinth-coal slurry(HCS) does not require predried water hyacinth because acertain quantity of water is needed during the slurry gasificationprocess. Therefore, both the water and calorific value in waterhyacinth can be adequately utilized. Since the main solidspresent in HCS are coal, it would help in effective gasification,thereby meeting the industrial criterion for its use.The primary factors responsible for the use of HCS depend

on the influence of water hyacinth on (i) the rheologicalproperties of slurry15 and (ii) the ash fusion temperatures ofcoal as it is an important factor in the entrained-flow gasifieroperation.16−18 High solids content and low viscosity of HCSare important criteria for its storage, transportation throughpipelines, subsequent atomization, and gasification. It is difficult

to convert water hyacinth into slurry because it contains manypolar oxygen-containing functional groups. During the slurryformation, water can easily interact with the hydrophilicfunctional groups, and, therefore, the content of free waterwould be reduced, resulting in an increase in the viscosity of theslurry.19−22 To improve the maximum solids loading of HCS,easy and affordable pretreatment of water hyacinth is required.The entrained-flow gasification technology requires that thecoal ash fluid temperature should be lower than 1400 οCbecause of the thermal properties of refractory materials ofgasifier. If it is off-limits, it would bring many operationalproblems like reducing the life of refractory materials. Becauseof the liquid-phase epitaxy slag, the reduction of ash fusiontemperature can favor the smooth operation of entrained-flowand reduce the oxygen consumption.Li and co-workers have applied algae and sewage sludge to

make bioslurry with coal for entrained-flow gasifier.20,23

However, few data are available where higher plants havebeen used to prepare bioslurry fuel with coal. In this study,HCS was prepared by mixing water hyacinth to coal as asubstitute for coal-water slurry (CWS) to use in hydrogenproduction. The effect of different ratios of water hyacinth onthe slurryability of HCS was investigated. A method formodification of water hyacinth is introduced to improve thesolids loading and flowability of HCS. The rheologicalproperties (such as viscosity, yield stress, and thixotropy),stability, and ash fusion temperature of the HCS were studiedand compared to CWS.

Received: July 8, 2013Revised: October 9, 2013Accepted: October 31, 2013Published: November 7, 2013

Article

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© 2013 American Chemical Society 16436 dx.doi.org/10.1021/ie402163c | Ind. Eng. Chem. Res. 2013, 52, 16436−16443

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2. EXPERIMENTAL SECTION

2.1. Materials. Shenfu coal from Inner Mongolia and waterhyacinth collected from Huangpu River, Shanghai, were chosenfor this study. As shown in Table 1, the moisture content offresh water hyacinth is more than 94%, and its ash, volatilematter, and nitrogen contents are significantly higher thanthose of coal. Mixing water hyacinth with coal is hopeful toovercome these problems. Sodium naphthalene sulfonateformaldehyde condensate (A1) and modified sodium lingo-sulfonate (A2) were used as the dispersing agent.2.2. Experimental Procedure. Raw coal was comminuted

in a ball-milling machine and passed through 40−200 and 200mesh screens to obtain particles of two particle sizedistributions. The mean volume diameters of coarse particlesand fine particles are 36 and 140 μm, respectively. First, waterhyacinth was washed to remove sand and soil and then milledin a planetary ball mill for 20 min. Modified water hyacinth wasprepared by adding 1.2 wt % of Fe2(SO4)3 (as-received waterhyacinth weight basis) during milling of water hyacinth.To prepare HCS, coarse and fine coal particles were mixed

by a mass ratio of 6:4. The resulting coal particles were mixedwith water hyacinth and 1.0 wt % dispersing agent (as-receivedbasis of the weight of dry solids) in a vessel containing a certainquantity of deionized water. Then, the mixture was stirred by amechanical agitator at 1,000 rpm for approximately 20 min toensure homogenization. The amount of water hyacinth addedto coal is expressed by the ratio of as-received basis of waterhyacinth to coal. The maximum solids loading is defined assolids content of slurry with viscosity (1,000 ± 100) mPa·s at ashear rate of 100 s−1.20 The moisture in water hyacinth isreckoned into the total water of slurry.For ash preparation, a series of water hyacinth-coal blends

were dried and converted to ashes according to the ChineseGB/T212-2001 standard. The dried sample was placed on acupel and heated in a muffle furnace up to 500 οC for 30 min.After keeping it at 500 οC for 30 min, the temperature wasraised to 815 οC at a rate of 25 οC min−1 and kept there for 1 h.At last, the temperature was reduced to room temperature, andthe sample ash was prepared.2.3. Analytical Procedure. The rheological property

measurements were performed using Malvern Bohlin CVOrheometer. The temperature was controlled at 25 ± 0.1 οC.The viscosity of slurry was measured as follows: shear rate wassmoothly increased from zero to 100 s−1 and then keptconstant at 100 s−1 for 30 s for further viscosity measurements.The yield stress of slurry was determined as follows: the criticalstress at which the suspension begins to flow was measured,such as the point at which slope of the strain (as a function ofshear stress) changes from a very low value to a high value, or arapid reduction in the measured viscosity occurs.24

The stability of slurry was measured according to “glass rodpenetration test” described by Qiu et al.25 Prepared slurry waspoured into a glass cylinder (3 cm in diameter) to 15 cm in

height at room temperature. A glass rod (5 mm diameter, 20 g)was spontaneously dropped from the slurry surface to thebottom of cylinder at a certain time interval, and it stoppedwhen the tip got in contact with the hard sediment. The timetaken by slurry to hold without hard sediment is defined as thestorage time.DSC 2910 (Thermo Analysis company) differential scanning

calorimeter equipped with a cooling device was used tomeasure the heat absorption (Q) of freezable water phasetransition in water hyacinth. Sample temperature was raisedfrom −30 to 30 °C at a rate of 10 °C/min. According to Z. H.Ping et al.,26 the mass of freezable water in water hyacinth isobtained as

= ΔW Q H g/ ( )c (1)

where ΔH is the melting enthalpy of bulk water (333.5 J/g).Infrared spectrum of the sample was analyzed using a Magna-

IR 550 Fourier transform infrared (FT-IR) spectrometer ofAmerican Thermo Nicolet Corporation. The chemicalcomposition of ash was determined using a X-ray fluorescencespectrometer (XRF-1800) produced by Shimadzu Corporationin Japan. Ash fusion temperatures of the samples weredetermined using a HR-A5 AFT autoanalyzer (Kaiyuan,China) under a reducing atmosphere according to the ChineseStandard GB/T219-2008. The reducing atmosphere wascreated by the incomplete combustion of black lead andcharcoal in a corundum tube during the heating of ash cones.On the basis of the “Seger Cone” method, the measurementswere carried out by heating the ash cone at a rate of 15 οC/minfrom room temperature to 900 οC and then to the maximumtemperature (1,600 οC) at a rate of 5 οC/min. During thisprocess, the deformation of cone with respect to thetemperature was photographed. According to the specificshapes of the ash cones, the initial deformation temperature(DT), softening temperature (ST), hemispherical temperature(HT), and fusion temperature (FT) were recorded.X-ray diffraction (XRD, Rigaku D/max-2550VB/PC diffrac-

tometer produced by Japan neo-Confucianism Company) wasused to identify the mineral composition in the ashes atdifferent temperatures. Each of the ash samples was heated in areducing atmosphere from 800 οC to FT with an interval of 100οC and then dampened in water. The mineral composition andtype of mineral were identified using XRD. The diffractionintensities were recorded in the 0−80ο 2θ range.20

3. RESULTS AND DISCUSSION

3.1. Effect of Water Hyacinth on the Viscosity ofSlurry. Obviously, the viscosity of slurry is very sensitive to theamount of water hyacinth. Figure 1 shows the dependence ofslurry viscosity on the water hyacinth ratio, evaluated at a singleshear rate of 100 s−1 when A1 was used as the dispersing agentand the solids loading is 60.0 wt %. The viscosity of HCSincreases rapidly with an increasing ratio of water hyacinth.

Table 1. Proximate Analysis and Ultimate Analysis of Shenfu Coal and Water Hyacinth

proximate analysis (wt %) ultimate analysis (wt %)b

sample Mara Ad

a Vda FCd

a Cd Hd Nd St,d Qdc (MJ·kg−1)

coal 7.17 6.58 39.7 53.72 69.23 4.72 0.86 0.49 28.36water hyacinth 94.02 30.95 55.32 13.73 25.86 2.19 3.11 0.85 12.70

aMar, Ad, Vd, and FCd refer to moisture, ash, volatile, and fixed carbon on a dried basis. bUltimate analysis is also on a dried basis. cQd refers to thecalorific value on a dried basis.

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie402163c | Ind. Eng. Chem. Res. 2013, 52, 16436−1644316437

When 25 g of water hyacinth is added to 100 g of coal, theslurry viscosity increases from 578 to 1,598 mPa·s. Therefore,in order to prepare a HCS with a low viscosity, pretreatment ofwater hyacinth is required.Two types of pretreatment methods are proposed as follows:

(i) by prolonging the milling time and (ii) by adding variousadditives during milling. Water hyacinth was added to the slurryat a constant ratio of 19.2 g/100 g coal, and the solids loadingof slurry was 60.0 wt %. The results obtained are shown inTable 2. Prolonging milling time helps to improve the degree offragmentation of water hyacinth resulting in the release ofintracellular water. Therefore, the amount of free water isincreased resulting in a decrease in the viscosity of the HCS.Although the viscosity of HCS decreased with increasingmilling time, the effect was not significant. Sodium hydroxide(NaOH), calcium hydroxide [Ca(OH)2], and ferric sulfate[Fe2(SO4)3] were chosen for chemical modification of waterhyacinth (1.2 wt %, as-received basis of water hyacinth weight).As shown in Table 2, Fe2(SO4)3 is more effective thanCa(OH)2, while NaOH leads to a slight increase in viscosity.The pH of slurry has no effect on the slurry viscosity, which isdifferent from the corresponding experimental results in case ofalgae.20 However, the viscosity of HCS decreases significantlyby increasing the metal ion valency from Na+ and Ca2+ to Fe3+

ions. Thus, Fe3+ ion is most effective for reducing the viscosityof HCS. This may be because the high valence metal ions havea good ability to compress the electrical double layer andthereby neutralize the charge. Thus, the composite structure ofwater hyacinth and coal particles is destroyed and more freewater is released. Two types of ferric salts [Fe(NO3)3 andFeCl3] were added with the same concentration of Fe3+ ions.Similar effects observed by the use of different ferric salts provethat Fe3+ ions could reduce the viscosity of slurry. Consideringthe negative effects of nitrogen and chlorine on entrained-flowgasifier, Fe2(SO4)3 was finally chosen for further investigation.The viscosity of modified-hyacinth-coal slurry (MHCS)

versus the water hyacinth ratio is shown in Figure 1. Thedifference in viscosity between HCS and MHCS increases withthe ratio of water hyacinth. For MHCS with acceptableviscosity (<1,000 mPa·s), the maximum ratio of water hyacinth

is 19.2 g/100 g coal. MHCSs with four different ratios of waterhyacinth were prepared and compared to CWS. The results areshown in Figure 2. It can be seen that the MHCSs and CWS

exhibit similar characteristics. The apparent viscosity decreaseswith increasing shear rate, and all the slurries show a certaindegree of yield pseudoplasticity. Figure 3 shows that the

maximum solids loading of CWS are 62.5 and 63.0 wt % whenA1 and A2 are used as the dispersing agents, respectively. Themodification of water hyacinth could increase the maximumsolids loading from 59.0 to 60.0 wt %. Dispersing agent A1 hasa better effect on slurryability than A2.

3.2. Effect of Water Hyacinth on the Yield Stress andThixotropy of Slurry. To further investigate the rheologicalproperties of slurry, three types of slurries were selected. Theratio of water hyacinth was 19.2 g/100 g coal, and theviscosities of all the slurries were around 1,000 mPa·s. As shownin Figure 4, irrespective of the type of dispersing agent used, theviscosity of CWS increases slightly with increasing shear stressat first and then decreases at low shear stress. CWS does notexhibit significant yield phenomenon. Compared to CWS, the

Figure 1. The influence of the water hyacinth ratio on the viscosity ofslurry.

Table 2. Effect of Pretreatment Methods for Water Hyacinth on the Viscosity of HCS

method (1) method (2)

milling time (min) 20 60 20 20 20 20 20adding additives / / NaOH Ca(OH)2 Fe2(SO4)3 Fe(NO3)3 FeCl3

viscosity of HCS(mPa·s) 1155 1099 1174 1050 999 991 986

Figure 2. The influence of the water hyacinth ratio on the rheologicalcharacteristics of slurries.

Figure 3. The influence of solids loading on the viscosities of threedifferent types of slurries.



viscosities of HCS and MHCS increase rapidly with theincrease in shear stress and then level off at a high viscosity. Itimplied that HCS and MHCS are very hard to flow at low shearstress. The yield stresses of HCS-A1, HCS-A2, MHCS-A1, andMHCS-A2 are 0.178 Pa, 0.526 Pa, 0.165 Pa, and 0.379 Pa,respectively. The chemical modification of water hyacinth has agood effect on yield stress reduction. The yield stresses ofslurries using A2 as the dispersing agent are always higher thanthe corresponding slurries using A1 as the dispersing agent.The viscosity test results at larger shear rates are shown in

Figure 5. All of the six slurries are shear-thinning fluid. HCSand MHCS have higher viscosities than CWS under low shearrate. The thixotropy loop areas of HCS and MHCS are muchlarger than those of CWS because the “bridges” formed bymacromolecular organic compounds present in water hyacinthare destroyed and become difficult to reconstruct undershearing. Since Fe(OH)3 formed by hydrolysis of Fe3+ ioncan also produce network structures between the coal particles,MHCS has the largest thixotropic loop. Thixotropy of slurrywas tested by shearing the slurry at a shear rate of 0.02 s−1 for180 s followed by damaging its structure at a shear rate of 100

s−1 for 60 s and then at a shear rate of 0.02 s−1 again to identifythe changes in the slurry structure, as shown in Figure 6a. Forall the slurries, viscosities decrease rapidly when the shear rate ischanged from 0.02 to 100 s−1. At a shear rate of 100 s−1, theviscosity of CWS reaches a steady value after 30 s. However, theviscosity of HCS and MHCS decreases continuously during theentire 60 s. More time and energy are needed to destroy thestructure of HCS and MHCS and reach a steady state. Theviscosity of CWS quickly reaches its original value within 20 swhen shear rate changes from 100 to 0.02 s−1. Though theshear rate decreases immediately, the viscosity of HCS andMHCS do not reach their original values even after high-speedstirring. Therefore, the structures generated by water hyacinthcannot be fully restored before stopping shearing.

3.3. Modification Mechanism of Water Hyacinth. FT-IR was taken to analyze the surface functional groups ofsamples. As shown in Figure 7, the water hyacinth modified byFe2(SO4)3 has a very similar infrared spectrum as theunmodified water hyacinth. The strong absorption bandsbetween 3600−3000 cm−1 are caused by O−H stretchingvibration. Peaks in the region of 1680−1610 cm−1 for bothwater hyacinth and modified water hyacinth are most possiblydue to CO and N−H type structures. The IR bands in theregion of 1060−1100 cm−1 are due to ester groups and primaryor secondary hydroxyl groups. All three samples haveadsorption peaks at 2920 and 2851 cm−1, which are due tomethyl or methylene C−H stretching vibrations. Doubleabsorption peaks at 1450 and 1375 cm−1 indicate that coalmainly has methyl groups, while water hyacinth and modifiedwater hyacinth mainly have methylene groups because theyhave a single peak at 1375 cm−1. For Shenfu coal, the peak at1610 cm−1 is most possibly due to the presence of aromaticrings, and the characteristic IR absorption bands in the regionof 1100−1300 cm−1 indicate the presence of many C−C bondsin coal.It is obvious that the surface of coal is dominated by

hydrophobic functional groups such as methyl, C−C, and

Figure 4. Effect of water hyacinth on the yield stress of three differenttypes of slurries.

Figure 5. Rheological properties of (a) CWS, (b) HCS, and (c) MHCS with different dispersing agents.



aromatic rings. The structures of both water hyacinth andmodified water hyacinth have a large quantity of hydrophilicfunctional groups such as hydroxyl, amino, and aldehyde

groups. These hydrophilic functional groups can interact withfree water through hydrogen bonding resulting in the increasein slurry viscosity.27,28 Meanwhile, hydrophobic functionalgroups of water hyacinth and modified water hyacinth couldcombine with coal particles to form spacial structures. Thesestructures could, on one hand, prevent the relative motion ofthe particles and further increase the viscosity and, on the otherhand, prevent the sedimentation and coalescence of particles,thus increasing the stability of slurry.25,29 Modification of waterhyacinth by Fe3+ ions leads to a change in the O−H absorptionof water hyacinth from 3380 to 3410 cm−1 that provescomplexation reactions occurring between the hydroxyl groupsand Fe3+ ions.30 Since the quantity of hydrophilic functionalgroups decreases, the quantity of bound water decreases.DSC results of water hyacinth samples were obtained by

heating a sample from −30 to 30 °C at the scanning rate of 10°C/min. A peak near 0 °C is discovered in each sample, and theheat absorptions of water hyacinth and modified water hyacinthare 266.403 J/g and 298.199 J/g, respectively. The nonfreezable

Figure 6. Thixotropy of CWS, HCS, and MHCS with different dispersing agents.

Figure 7. FT-IR spectra of samples. A−modified water hyacinth, B−water hyacinth, C−Shenfu coal.



water (bound water) can be obtained by subtracting freezablewater (free water) from total water in water hyacinth. Theresults show that nonfreezable bound water in water hyacinthdecreases by 67.40% through modification, from 0.1414 g/g to0.0461 g/g. Thus, free water in modified water hyacinthincreases, and the viscosity of MHCS decreases.3.4. The Stability of HCS. The storage time tests indicate

that water hyacinth, especially modified water hyacinth, couldsignificantly improve the storage time of slurry. The CWS cansustain for ∼1 and 1.25 h without forming hard sediment whenA1 and A2 are used as the dispersing agents, respectively. Thestorage times of HCS are 60 and 62 h, while those of MHCSare 88 and 96 h with A1 and A2 as the dispersing agents,respectively.As mentioned above, hydrophilic functional groups of water

hyacinth such as hydroxyl, carboxyl, and aldehyde groups caninteract with the coal particles and thereby form spatialstructures. Water hyacinth works as a stabilizer. The yield stress,shear-thinning property, and thixotropy are all related withregard to the formation of spatial structures.31 MHCS has thebest storage performance because of the complexation withFe3+ ions that strengthens the structure. Different from A1, A2is a type of high molecular-weight dispersing agent with acertain quantity of hydroxyl groups and can form a weakstructure just as water hyacinth does. Therefore, by using A2 asthe dispersing agent, the slurry could have higher yield stressand higher viscosity. Obviously, A1 is a more suitable dispersingagent to prepare HCS and MHCS.3.5. The Influence of Water Hyacinth on the Ash

Fusion Temperature of Coal. The difference in chemicalcomposition of ash between the samples could cause thechange of ash mineral composition during the heating process.Thus, the ash fusion temperature would be affected. As shownin Table 3, it is clear that the main oxides in coal ash are SiO2,

Al2O3, Fe2O3, CaO, and SO3. The amounts of SiO2, K2O, andP2O5 in water hyacinth ash are much more than those presentin coal ash. Further, in modified water hyacinth, the content ofFe2O3 and SO3 are higher than those in unmodified waterhyacinth, because Fe2(SO4)3 is used in the water hyacinthpretreatment process. The ash fusion temperature of water

hyacinth is much higher than coal, while the pretreatment ofwater hyacinth significantly reduces the ash fusion temperatureof water hyacinth from 1,344 to 1,215 οC.The influences of water hyacinth and modified water

hyacinth on the ash fusion temperature of coal are presentedin Figure 8 and Figure 9, respectively. The amount of added

water hyacinth is expressed by the ratio of as-received waterhyacinth to coal. As seen in Figure 8, the ash fusiontemperature decreases at first and then increases with increasingthe proportion of water hyacinth to coal, and the FT of eachsample is <1,200 οC. The ash fusion temperature decreases tothe minimum value when 66.7 wt % of water hyacinth to coal isused, and the FT is 1,132 οC. The influence of modified waterhyacinth on the ash fusion temperature of coal shows the samebehavior as water hyacinth, as shown in Figure 9. Waterhyacinth modified by Fe2(SO4)3 can further reduce the ashfusion temperature of coal than unmodified water hyacinth.When the ash fusion temperature of coal reaches the minimumvalue, the proportion of modified water hyacinth to coal is 66.7wt %, and the FT is 1,089 οC. At the same time, slurry viscosityshould be taken into consideration. When water hyacinth isadded in the highest ratio of 19.2 g/100 g coal, the ash fusiontemperature of coal is 1,140 οC. For modified water hyacinth,the ash fusion temperature of coal can reduce from 1,153 to1,115 οC.

3.6. Minerals Composition Identified by XRD. Differentsamples display different absorbed or reflected X-rays pattern.XRD patterns are related not only to the mineral type but alsoto the mineral content. For a certain type of mineral, thediffraction intensity can be approximately varied in response to

Table 3. Ash Chemical Composition and Ash FusionTemperature of Coal, Water Hyacinth, and Modified WaterHyacinth

ash samples coalwater hyacinth

modified waterhyacinth

ash chemicalcomposition (wt %)

SiO2 33.71 44.18 40.16Al2O3 12.54 13.37 12.15Fe2O3 10.31 8.60 11.45MgO 1.31 1.83 1.66CaO 24.15 7.16 6.51Na2O 1.58 1.33 1.21K2O 1.26 12.38 11.25TiO2 0.70 0.75 0.68P2O5 0.09 4.60 4.18MnO 0.27 1.75 1.59SO3 13.36 2.44 7.67

ash fusion temperature(οC)

DT 1101 1296 1179ST 1147 1338 1205HT 1150 1342 1213FT 1153 1344 1215

Figure 8. The influence of water hyacinth on the ash fusiontemperature of coal.

Figure 9. The influence of modified water hyacinth on the ash fusiontemperature of coal.



its content.17 In order to investigate how water hyacinthinfluences the ash fusion temperature of coal, the mineralcomposition of coal ash, water hyacinth ash, and modified waterhyacinth ash produced at 815 οC were analyzed by XRD, asshown in Figure 10.The results show that the main mineral matters in coal ash

are quartz, anhydrite, hematite, and calcite. In water hyacinthash, main mineral matters are quartz, anhydrite, hematite,leucite, anorthite, and potassium calcium phosphate. The mainmineral matters in modified water hyacinth ash are quartz,anhydrite, hematite, leucite, chladniite, and aphthitalite.Compared to water hyacinth ash, sulfur compounds and alarge number of iron-containing minerals are present inmodified water hyacinth ash because of Fe2(SO4)3.Water hyacinth-coal mixtures were gasified at 900 οC, 1,000

οC, 1,100 οC, and FT respectively, and the XRD diffractogramsof ashes are shown in Figure 11. The proportion of fresh waterhyacinth to coal is 66.7 wt %. We can see that the mainminerals in mixture are quartz, anhydrite, hematite, nepheline,and gehlenite at 900 οC. As the temperature increases, theheight of diffraction peaks for quartz and anhydrite decreases,

while that of gehlenite increases. At 1,000 οC, anorthite isobserved, and the intensity of diffraction peak of nephelineremains unchanged. At 1,100 οC, quartz and anhydritecontinuously decreases, accompanied by the increase inanorthite and the formation of aedelforsite. The intensity ofdiffraction peak of gehlenite reaches the maximum value at1,100 οC. The diffraction peaks of quartz and anhydritedisappear at 1,132 οC (FT), while the diffraction peaks ofanorthite and aedelforsite become stronger. Further, the mainmineral matters in ash form anorthite. Gehlenite also exists inash, but its diffraction peak becomes weaker. At FT, coexistingwith anorthite, aedelforsite, and gehlenite produces a low-melting eutectic mixture. This is the main reason why waterhyacinth lowers the ash fusion temperature of coal. Besides,water hyacinth contains a large quantity of alkali metal oxidessuch as K2O and Na2O, which could react with Al2O3, SiO2,and CaO to form low-melting eutectic mixtures at temperatureshigher than 900 οC.Hematite in water hyacinth-coal mixture ash can reduce the

ash fusion temperature of coal. In the weak reductionatmosphere, Fe2O3 is reduced to FeO. Further, FeO couldcombine with SiO2, Al2O3, mullite (3Al2O3·2SiO2), andanorthite to form fayalite (2FeO·SiO2), hercynite (FeO·Al2O3), almandine (3Fe2O3·Al2O3·3SiO2), and ferrosilite(FeO·SiO2), respectively. These mineral matters will producesome low-melting eutectic mixtures. Therefore, compared towater hyacinth, the modified water hyacinth containing a largequantity of Fe2O3 can function as a fluxing agent and furtherdecrease the ash fusion temperature of coal.

4. CONCLUSIONWater hyacinth was introduced to prepare bioslurry fuels withcoal for syngas production. To decrease the viscosity of HCS,water hyacinth was modified with the addition of NaOH,Ca(OH)2, and Fe2(SO4)3, respectively. The results show thatferric ions are most effective for the release of immobilizedwater resulting in the reduction of slurry viscosity. Slurry withsolids loading of 60.0 wt % was prepared by adding modifiedwater hyacinth in a ratio of 19.2 g/100 g coal. Slurry storage

Figure 10. XRD diffractograms of (a) coal ash, (b) water hyacinth ash, and (c) modified water hyacinth ash produced at 815 οC. S−quartz, C−anhydrite, H−calcite, F−hematite, K−leucite, N−aphthitalite, P−chladniite, R−potassium calcium phosphate, A−anorthite.

Figure 11. XRD diffractograms of water hyacinth-coal mixture ashesproduced at 900 οC, 1,000 οC, 1,100 οC, and FT (1,132 οC),respectively. S−quartz, C−anhydrite, F−hematite, K−leucite, A−anorthite, G−gehlenite, D−aedelforsite.



time can be prolonged from less than 2 h to >88 h by addingmodified water hyacinth.Besides, it was also concluded that water hyacinth can reduce

the ash fusion temperature of coal by 21 οC when theproportion of water hyacinth to coal is 66.7 wt %. The waterhyacinth modified by Fe2(SO4)3 can further reduce the ashfusion temperature of coal from 1,153 to 1,089 οC because ofthe formation of low-melting eutectic mixtures. Considering theoptimum proportion of modified water hyacinth for slurryviscosity, the ash fusion temperature of coal was found to be1,115 οC when modified water hyacinth was added in a ratio of19.2 g/100 g coal. In the future, we plan to further improve theproportion of water hyacinth and reduce the viscosity of HCSto achieve a minimum value for the ash fusion temperature ofcoal.

■ AUTHOR INFORMATION

Corresponding Author*Phone: +86-21-64251418. Fax: +86-21-64251312. E-mail:[email protected]. Corresponding author address: P.O. Box272, No. 130 Meilong Road, Shanghai 200237, People’sRepublic of China.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

This work was supported by National Natural ScienceFoundation of China (Grant No. 21176079) and NationalKey Program of Basic Research in China (2010CB227005).

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Effective Utilization of Water Hyacinth Resource by Co-Gasification with Coal: Rheological Properties and Ash Fusion Temperatures of Hyacinth-Coal Slurry