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

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<ul><li><p>Eective Utilization of Water Hyacinth Resource by Co-Gasicationwith Coal: Rheological Properties and Ash Fusion Temperatures ofHyacinth-Coal SlurryHaifeng Liu,*,, Menghan Xu,, Qiang Zhang,, Hui Zhao,, and Weifeng Li,</p><p>Key Laboratory of Coal Gasication and Energy Chemical Engineering of Ministry of Education, East China University of Scienceand Technology, No. 130 Meilong Road, Shanghai 200237, Peoples Republic of ChinaShanghai Engineering Research Center of Coal Gasication, No. 130 Meilong Road, Shanghai 200237, Peoples Republic of China</p><p>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-ow gasication process. Water hyacinth was modied withthe addition of Fe2(SO4)3. Rheological properties and ash fusion temperatures of the modied-hyacinth-coal slurry (MHCS)were investigated. MHCS with solids loading of 60.0 wt % was prepared by adding 19.2 g of modied 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 modied water hyacinthcould further reduce the ash fusion temperature of coal because low-melting eutectic mixtures were formed.</p><p>1. INTRODUCTION</p><p>A huge amount of water hyacinth is harvested every year tocontrol its exuberant growth in India, South Africa, USA, andChina.13 Water hyacinth produces about 140 tons of dry massper hectare per year and is an ideal plant for carbon dioxidecapture and biomass production.46 Moreover, water hyacinthis capable of removing excess nutrients and toxic metal ionsfrom environment.710 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 suers 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-ow gasier could be an eective 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 gasicationprocess. Therefore, both the water and caloric value in waterhyacinth can be adequately utilized. Since the main solidspresent in HCS are coal, it would help in eective gasication,thereby meeting the industrial criterion for its use.The primary factors responsible for the use of HCS depend</p><p>on the inuence 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-ow gasieroperation.1618 High solids content and low viscosity of HCSare important criteria for its storage, transportation throughpipelines, subsequent atomization, and gasication. It is dicult</p><p>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.1922 To improve the maximum solids loading of HCS,easy and aordable pretreatment of water hyacinth is required.The entrained-ow gasication technology requires that thecoal ash uid temperature should be lower than 1400 Cbecause of the thermal properties of refractory materials ofgasier. If it is o-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-owand reduce the oxygen consumption.Li and co-workers have applied algae and sewage sludge to</p><p>make bioslurry with coal for entrained-ow gasier.20,23</p><p>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 eect of dierent ratios of water hyacinth onthe slurryability of HCS was investigated. A method formodication of water hyacinth is introduced to improve thesolids loading and owability of HCS. The rheologicalproperties (such as viscosity, yield stress, and thixotropy),stability, and ash fusion temperature of the HCS were studiedand compared to CWS.</p><p>Received: July 8, 2013Revised: October 9, 2013Accepted: October 31, 2013Published: November 7, 2013</p><p>Article</p><p>pubs.acs.org/IECR</p><p> 2013 American Chemical Society 16436 dx.doi.org/10.1021/ie402163c | Ind. Eng. Chem. Res. 2013, 52, 1643616443</p></li><li><p>2. EXPERIMENTAL SECTION</p><p>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 signicantly higher thanthose of coal. Mixing water hyacinth with coal is hopeful toovercome these problems. Sodium naphthalene sulfonateformaldehyde condensate (A1) and modied sodium lingo-sulfonate (A2) were used as the dispersing agent.2.2. Experimental Procedure. Raw coal was comminuted</p><p>in a ball-milling machine and passed through 40200 and 200mesh screens to obtain particles of two particle sizedistributions. The mean volume diameters of coarse particlesand ne particles are 36 and 140 m, respectively. First, waterhyacinth was washed to remove sand and soil and then milledin a planetary ball mill for 20 min. Modied 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 ne coal particles were mixed</p><p>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 dened assolids content of slurry with viscosity (1,000 100) mPas at ashear rate of 100 s1.20 The moisture in water hyacinth isreckoned into the total water of slurry.For ash preparation, a series of water hyacinth-coal blends</p><p>were dried and converted to ashes according to the ChineseGB/T212-2001 standard. The dried sample was placed on acupel and heated in a mue furnace up to 500 C for 30 min.After keeping it at 500 C for 30 min, the temperature wasraised to 815 C at a rate of 25 C min1 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</p><p>measurements were performed using Malvern Bohlin CVOrheometer. The temperature was controlled at 25 0.1 C.The viscosity of slurry was measured as follows: shear rate wassmoothly increased from zero to 100 s1 and then keptconstant at 100 s1 for 30 s for further viscosity measurements.The yield stress of slurry was determined as follows: the criticalstress at which the suspension begins to ow 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</p><p>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</p><p>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 dened as thestorage time.DSC 2910 (Thermo Analysis company) dierential scanning</p><p>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</p><p>= W Q H g/ ( )c (1)</p><p>where H is the melting enthalpy of bulk water (333.5 J/g).Infrared spectrum of the sample was analyzed using a Magna-</p><p>IR 550 Fourier transform infrared (FT-IR) spectrometer ofAmerican Thermo Nicolet Corporation. The chemicalcomposition of ash was determined using a X-ray uorescencespectrometer (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 C/minfrom room temperature to 900 C and then to the maximumtemperature (1,600 C) at a rate of 5 C/min. During thisprocess, the deformation of cone with respect to thetemperature was photographed. According to the specicshapes of the ash cones, the initial deformation temperature(DT), softening temperature (ST), hemispherical temperature(HT), and fusion temperature (FT) were recorded.X-ray diraction (XRD, Rigaku D/max-2550VB/PC dirac-</p><p>tometer produced by Japan neo-Confucianism Company) wasused to identify the mineral composition in the ashes atdierent temperatures. Each of the ash samples was heated in areducing atmosphere from 800 C to FT with an interval of 100C and then dampened in water. The mineral composition andtype of mineral were identied using XRD. The diractionintensities were recorded in the 080 2 range.20</p><p>3. RESULTS AND DISCUSSION</p><p>3.1. Eect 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 s1 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.</p><p>Table 1. Proximate Analysis and Ultimate Analysis of Shenfu Coal and Water Hyacinth</p><p>proximate analysis (wt %) ultimate analysis (wt %)b</p><p>sample Mara Ad</p><p>a Vda FCd</p><p>a Cd Hd Nd St,d Qdc (MJkg1)</p><p>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</p><p>aMar, Ad, Vd, and FCd refer to moisture, ash, volatile, and xed carbon on a dried basis.bUltimate analysis is also on a dried basis. cQd refers to the</p><p>caloric value on a dried basis.</p><p>Industrial &amp; Engineering Chemistry Research Article</p><p>dx.doi.org/10.1021/ie402163c | Ind. Eng. Chem. Res. 2013, 52, 164361644316437</p></li><li><p>When 25 g of water hyacinth is added to 100 g of coal, theslurry viscosity increases from 578 to 1,598 mPas. 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:</p><p>(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 eect was not signicant. Sodium hydroxide(NaOH), calcium hydroxide [Ca(OH)2], and ferric sulfate[Fe2(SO4)3] were chosen for chemical modication of waterhyacinth (1.2 wt %, as-received basis of water hyacinth weight).As shown in Table 2, Fe2(SO4)3 is more eective thanCa(OH)2, while NaOH leads to a slight increase in viscosity.The pH of slurry has no eect on the slurry viscosity, which isdierent from the corresponding experimental results in case ofalgae.20 However, the viscosity of HCS decreases signicantlyby increasing the metal ion valency from Na+ and Ca2+ to Fe3+</p><p>ions. Thus, Fe3+ ion is most eective 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 Fe</p><p>3+ ions.Similar eects observed by the use of dierent ferric salts provethat Fe3+ ions could reduce the viscosity of slurry. Consideringthe negative eects of nitrogen and chlorine on entrained-owgasier, Fe2(SO4)3 was nally chosen for further investigation.The viscosity of modied-hyacinth-coal slurry (MHCS)</p><p>versus the water hyacinth ratio is shown in Figure 1. Thedierence in viscosity between HCS and MHCS increases withthe ratio of water hyacinth. For MHCS with acceptableviscosity (</p></li><li><p>viscosities of HCS and MHCS increase rapidly with theincrease in shear stress and then level o at a high viscosity. Itimplied that HCS and MHCS are very hard to ow 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 modication of water hyacinth has agood eect 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</p><p>Figure 5. All of the six slurries are shear-thinning uid. 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 dicult to reconstruct undershearing. Since Fe(OH)3 formed...</p></li></ul>