A comparative investigation of the properties of coal-water slurries prepared from Australia and She

Mining Science and Technology( China)21(2011)343-347Contents lists available at Science Direct盖dIecMining Science and Technology( China)SEVIERjournalhomepagewww.elsevier.com/locate/mstcA comparative investigation of the properties of coal-water slurries preparedfrom Australia and Shenhua coalsYun Zengjie * Wu Guoguang Meng Xianliang, Zhang Yuliang, Shi Frank, He Yaqun", Luo XiaoqiangSchool of Chemical Engineering and Technology. China University of Mining and Technology. Xuzhou 221008, ChinaJulius Kruttschnitt Mineral Research Centre, Brisbane 4068, AustralARTICLE INFOABSTRACTTwo coal samples of similar rank were chosen from Australia and China to investigate the differences inReceived 3 October 2010Coal-Water Slurry( CWS)made from them. the effect of ash content and particle size gradation on theseReceived in revised form 29 October 2010properties was also studied Different grinding times were used when grinding the two coals and particleAccepted 1 December 2010Available online 8 June 2011size analysis of these ground coals was used to select samples with adouble-peak"particle size distri-bution. All the"double-peak"samples were used to prepare a CwS. The concentration, viscosity fluidity.and stability of each CwS were measured. The results show that the properties of a CwS prepared from aoal-Water Slurrycoal sample with a"double-peak"size distribution are better than those CwS prepared from sampleswith a mono-modal particle distribution. The ash content of Australian coal is 21.72% higher than theSlurry abilityash content of Shenhua coal. the highest coal concentration in slurry from the Australia coal is 11.01%higher than in CWS from the Shenhua coal. The fluidity and stability of the CwS prepared from theAustralian coal are both better than the fluidity and stability of slurry prepared from Shenhua coal Highash content in the australian coal improves the pulping results of a Cws made from it.o 2011 Published by Elsevier B V. on behalf of China University of Mining Technology1 Introductionout for many years [5-10 A recently patented technology for pre-paring high concentration CWS from low rank coals has been pubCoal-Water Slurry( CwS)technology was developed during the lished showing how the concentration of coal in the CwS can beworld wide oil crisis of the 1970,s to produce a novel and clean increased by 3-5% (111fluid fuel as a substitute for petroleum the slurry is prepared asThe two coal samples used in the experiments described hereina mixture of 62-70% fine coal, 29-37% water, and about 1% addi- are from australia and China. they are both low rank coals withtives determined specifically for each different process [1]. cws similar coalification. One of the key points for preparing CwS istechnology was developed and applied systematically in China particle size gradation. Appropriate particle gradation can achieveluring the early 1980's. The technique is gradually being perfected a high packing efficiency and increase the coal concentration in thetoday and it is now entering commercial application [2].CWS. The influence of particle gradation on Cws properties isAlthough medium rank bituminous coals are suitable for Cws reported here. Differences of the CwS properties when usipreparation they are typically used for coke making because they Australia coal or Shenhua coal are discussed. Experimental studyare not particularly abundant in the world. The low rank coals, such of CWS preparation from the Australia coal is significant for theas lignite, long flame coal, and non-caking coal, are used for Cws preparation and application of aws in australia.preparation to supply feed material for coal gasification or combus-tion(3]. The properties of coal, such as inherent moisture, oxygencontaining functional groups, Hardgrove grindability index(HGi),2. Experimentalo/C ratio, and ash content have great influence on the pulping re-sults during CWS preparation[4 The high moisture content and 2.1. Coal samplespoor grindability of low rank coals make it difficult to form a highlyconcentrated CWs from them. Investigations into preparationIn these experiments two kinds of coals were chosen, one frommethods for Cws having high coal concentrations, low viscosities,the Shenhua mining Group, Ltd, and one from Australia Tarongand good fluidity starting from low rank coals have been carried Energy. These are low rank coals. The results of a quality analysison the two coals are shown in table 1The Shenhua coal is a weakly coking coal. The results in Table 1Corresponding author Tel +86 15949040834show that the volatile content of the two coals is similar and theE-mailaddress:yunzengji@126.com(ZYun).same is true for中国煤化工 the Australia coal1674-5264/s- see front matter e 2011 Published by Elsevier B.V. on behalf of China University of Mining什HCNMHGdoi:10.1016mstc201105014344Z Yun et aL/ Mining Science and Technology(China)21(2011)343-347Results from the coal quality analysis: SH Shenhua: Aus, australia.Proximate analysis (3)Ultimate analysis(‰)A785637980275.4213.22568730645999680.315122is 21.72% higher than for the shenhua coal. Because of this the grindability of the Australian coal is poorer than the Shenhua coal and0.16his benefits the CwS preparation.2.2. Infrared spectra of the coal samples0.10F Australia008Potassium bromide( 100 mg )and 1 mg of coal sample(dried at105-110C, particle size <300 mesh)were put into an agate mor-ar. The mixed powders were ground and then compressed into0. 1-1.0 mm thick transparent pellets using a press. The pelletShenhuawas fixed in a sample frame and then put into the infrared spectrometer chamber the spectra were recorded over the range from40003500300025002000150010005004000 to 400 cm-l with an instrument resolution of 0.5 cm-I and ascan number of 32Fig 1. Fourier transform infrared spectrogram of test coal.2.3. Surface potential analysis of the coal samplesCoal powder was slurried in deionized water solutions having(1)X-H stretching vibrations: This region contains O-H. N-H,different pH values by treatment for 5 min with an ultrasonicand C-H stretching vibrations. the range of frequencies isdispersion instrument. Then a micro-electrophoresis apparatusfrom 2500 to 4000 cm". if the environment of the hydroxyl(model JS94G made in Shanghai) was used to test the zeta poten-allows hydrogen bonding the absorption peak of o-h will betial. A PHS-2 pH meter was used to determine the phwide. The wide peak near 3400 cm is an 0-H stretchingvibration. The wave number of unsaturated hydrocarbonC-H stretching is above 3000 cm - The structure of the coal2. 4. Investigation of the coal grinding process and particle size analysisis mainly aromatic hydrocarbons. The C-H stretching vibration of saturated hydrocarbons falls below 3000 cm-i.Two coal samples prepared for experiment by grinding with anFig 1 shows that the o-H stretching vibrations ofthe ShenhuaXMB-70 type rod grinding mill. the grinding times were 20, 30,and the australia coals are near 3400.13 and 3423.37 cm-140, 60, 90, 120, and 150 min. The relationship between the grindingrespectively. these two coals are low rank coals with manytime and particle size distribution was examined using these sam-hydrogen bonds to carboxyl groups. Therefore the locationples. Samples of the same coal, one ground for a long time and theof hydroxyl absorption peaks shift to the violet, nearother for a short time, were mixed in equal proportion. the mixed3450 cm-1 from their normal location at 3300 cm-1.Thecoal samples were tested with a LS100Q Laser Particle Sizeak near 3030 cm"from the aromatic c-H stretching vibra-Analyzer to see which possesseddouble- peak"or"multiple-peaktion is weak for these two coals this shows that the aromatic.distributions. then each coal sample with either a"double-peak"ority of the two coals is low. The saturated hydrocarbon C-H"multiple-peak"distribution was used to prepare a CwS.stretching vibrations of these two coals are at 2919. 88 and2920.00 cm for the Shenhua and Australia, respectively2.5. Preparation of the Cws(2)Double bond stretching vibration region: The region from 1500to 2000 cm is where stretching vibrations of C=C, C=0Coal samples with either adouble-peak"or"multiple-peak"C=N, and-NO2, and skeletal vibrations of aromatic hydro-particle size distribution were used for CwS preparation. Thecarbons, fall. the spectra show aromatic skeletal vibrationsupper size limit was 300 um and more than 75% of the particlesin the two coals. The C=o stretching vibrations of the Auswere smaller than 74 Hm. Naphthalene sulfuric acid-formalde-tralia and shenhua coal are similarhyde condensate was used as a dispersant(the weight of the dis(3)Single bond vibration region: C-H bending vibrationspersant was 1% of the dry coal weight). For further details on theare mainly in the wave number region from 1300 topreparation and test methods see Ref. 12]1500 cm. From 1100 to 1300 cm stretching vibrationsfrom-C-O and c-0-c appear aicha rochdi and Patrick landais thought that the absorptions at a wave number of3. Results and discussion1261 cm-I are symmetric ether bond stretching of unsaturated and aromatic hydrocarbons [13 these two coals show3. 1. Infrared spectral analysis of the raw coalsC-H bending at a wave number of 1425.06 or 1438. 21 cmfor Australia and Shenhua coal, respectively Fig. 1 also showsThe infrared spectra of the two coals are shown in fig.1.thethat the absorbance peaks of the australia coal are muchspectra may be used to examine how coal structure influenceshigher0 cm and from 500he Cwsto 80中国煤化工ear500and80cm1The vibrations of the functional groups are divided into threeare reshCNMHGsilicate and carbonate1100 cm-1 are theZ Yun et aL/ Mining Science and Technology(China)21(2011)343-347stretching vibrations of sulfate and silicate [14. Because silicate, carbonate ion and sulfate arise mainly from the miner-als in coal it appears the ash content of the australia coal ishigher than that of the Shenhua coal, which agrees with the0+150minproximate analysis.153.2. Surface zeta potential and the iso-electric pointShenhuaThe zeta potential of the two coals was determined. The rela20+120monship between pH value and zeta potential is shown in Fig. 2.350Fig. 2 illustrates that the zeta potential drops as the ph valueParticle diameter (um)increases. the isoelectric point of the Shenhua coal is a little lowerthan that of the australia coal. The value of the isoelectric pointFig 3. Particle size distribution of mixed shenhua coal samples.increases with an increase in coal rank [ 15]. Therefore Fig. 2 suggests that the coal rank of the australia coal is a little higher thanthe rank of the Shenhua coal. There are more negatively chargedoxygen-containing functional groups such as hydroxy and carboxylon the surface of the shenhua coal. therefore a greater h" concen-Austral0+120mintration should be needed to neutralize the negative charges andmake the potential zero on the surface of the coals.The zeta potential can reflect the hydrophilicity of a modifiedcoal surface. Hydrophilicity directly affects the apparent viscosity.australiathe rheological properties, and the static stability of the cws.Given a fixed dispersant concentration, a high zeta potential isfavorable for decreasing the viscosity of a CwS and for improvingits rheological properties. A low zeta potential favors stability ofthe slurry [16].Fig. 4 Particle size distribution of mixed Australia coal samples3.3. Preparation of coal samples for the Cws and particle size analysisthe al grounds fo Far hat time the for le g tim for zo mix w is 3.4, Properties of Ws prepared from different coad samplesnixed with the one ground for 150 min, and the sample ground forThe relationship between viscosity and shear rate for different30 min was mixed with the 150 min sample, etc. A particle size concentrations of coal in the cws prepared from Shenhua coal isanalysis was performed on the mixed coal samples anddouble-ak"samples were selected for Cws preparation, the results ofgThe properties and pulping results of Cws prepared from thearticle size analysis of the mixed coal samples are shown in figsShenhua coal are shown in Table 23 and 4Most the CWS samples were prepared from coal samples having are shown in Fig.6Similar viscosity curves for cwS prepared from Australian coalsadouble-peak"or multi-peak"particle size distribution. AsFigs. 5 and 6 show that the viscosity of the Cws decreases withshown in Figs. 3 and 4 the Shenhua 20 and 120, and 20 and 150, increasing shear rate and that it is a pseudoplastic fluid. The viscos-minute coal samples are bimodal. The mixed Australia coal sam- ity of the cws increases as the concentration of coal increasesples from 20 and 120, and 20 and 150, minute mixed samples when measured at the same shear rateare also"double- peaked. "These are suitable for Cws preparation.Table 2 illustrates that the pulping results using Shenhua coalFor comparison a mixed Shenhua coal 30 and 150 min grind, and a are poor. The viscosity of the CwS changes slightly with an in-mixed Australia coal 30 and 150 min grind, which are without crease in concentration. Both the fluidity and stability of the Cwsdouble-peaked particle distributions were also used to prepare are poor. Although the fluidity is acceptable at a high concentrationcoal-water slurriesof coal the stability is poor over time. The stability is good at a lowconcentration but now the fluidity is completely immobile. Theslurry concentration of the three blended samples from Shenhuacoal is low in every case. The highest concentration is onlyAustralia58.27%. All three of these CWS samples appear"hard settling"ata high concentration The Cws appears to separate much waterat lower concentrations. Therefore, preparing a Cws from theShenhua coal is difficultTable 3 shows that the fluidity of the Cws from the blendedAustralia samples is good. They are all uninterrupted flowingShenhuThe slurry concentration of the CwS prepared from the sampleswith adouble- peak"particle distribution is higher than that fromthe sample without adouble-peak". The slurry concentration ofthe sample from the 20 plus 150 min grinds is 69. 28%, which isobviously higherharo concentrationsare6793‰and中国煤化工 s show that it isility ofFlg. 2. Zeta potentials iCNMHat differentalues of the two coals.the CwS preparedles is better thanZ Yun et aL/ Mining Science and Technology( China)21(2011)343-3476012320059.739582128058.71%5793%5643%E256.27956.05%205761%53.99%8000204060801020406080e(s")Shear rate(s")(s)(a)20 min mixed with 120 min grind(b)20 min mixed with 150 min grind(c)30 min mixed with 150 min grindFig. 5. Viscosity versus shear rate for various coal concentrations in the CwS; Shenhua coal.Table 2Iping results of weakly caking coal after different grinding timesCoal sampleConcentration(%) Viscosity(mPa s) FluidityStability Slurry concentration(%)Shenhua(20+ 120 min) 60.1202Interrupted flowin5790Shenhua(20+ 150 min) 60. 12Uninterrupted flowing D59.7356.43mShenhua(30+ 150 min) 57.10Immobile55.5056.051197853.994528Note: Stability of the CWS:"A"stands for no water separation, comparatively soft settling: "B", a little water separation, comparatively softsettling: ""C". much water separation, comparatively soft settling: "D", no water separation, comparatively hard settling: "E", a little waterseparation, comparatively hard settling:"F", much water separation, comparatively hard settling.a我400020006836%70.15%1800一67.0G3000实16006549%一6841600250067.18%120015001000801002040608010020406080Shear rate(s")hear rate(s)Shear rate(s)(a)20 min mixed with 120 min grind(b)20 min mixed with 150 min grind(c)30 min mixed with 150 min grindFig. 6. Viscosity versus shear rate for various coal concentrations in the CWS: Australia coal.Table 3Pulping results of the australian coal after different grinding timesConcentration(%) Viscosity(mPa s)Stability Slurry concentration(%)Australia(20+ 120 min) 69. 171553.0Uninterrupted flowing B682411660Australia(20+150 min) 70. 151429669281701.26606Australia(30+ 150 min) 68.3614746Uninterrupted flowing B67.627520the stability of the CWS prepared from a mono-disperse sample. of the slurries prepared from the Australia coal are better. The highThe pulping results using the sample comprised of 20 plus ash contentl. nl imnrntee the pulping results dur150 min grinds is very remarkableIng prepara中国煤化工 ash content is the greatCompared to Shenhua coal the highest slurry concentration of er the massd the higher the slurrythe Australia coal is 11.01% higher and the fluidity and stability concentratiCNMHtant packing efficiencyZ Yun et aL/Mining Science and Technology (China)21(2011)343-347The layered structures of the minerals existing in the Australia coal Acknowledgmentsgive a Cws with good thixotropy, which shows good stability andfluidityThis project received funding from the australian Goveas part of the Asia-Pacific Partnership on Clean Development and4. ConclusionsClimate.(1)The Shenhua weakly caking coal is hard to convert into a ReferencesCWS, while Australia coal is easily converted. The highestslurry concentration of the shenhua coal is 58. 27%. Whether [1] Hao LS, Peng jx. Preparation and application technology of CwS. Beijing: Coalconcentration is high or low the fluidity of the CWS ispoor and unrecoverable hard precipitate forms easily. The[2] Sun SM, Chen C Cao Pw. Brief discussion on coal water mixture and itsyeing Finish 2009: 11: 31-4 [ in Chineselslurry concentration of the Australia coal is as high as[3] Li HXJi M. uiJ. The effects of coal blending on the features of CWS. Coal Prep69.28%. The fluidity and stability of the CwS samples pre-echnol 2001: 3: 54-7 lin Chinese.quite good.4] L QH. Study on the preparation of coal water slurry for difficult -slurry coalsm(2)Based on these experimental results, coal samples with acoal blending. Xuzhou: China University of Mining and Technology 2007" double-peak"particle distribution provide a better ws [5] Sun CG, Wu js, u BQ. Surface properties of thermally upgraded low-rank coalsthan those that are mono-disperse. These differences areand their effect on the rheological behavior of coal water slurry. J Fuel Chemechnol 1996: 24(2): 174-80 (in Chineselbigger for the Shenhua coal where the difference in slurryferences in CWS properties for those samples prepared from wG tion. J China Univ Min Technol 2001: 30(6): 543-6 lin Chineselconcentration is as high as 2.77%. there are still obvious dif-double-peak"samples. The quality of the CwS preparedadditive for CWS and its effect. J China Univ Min Technol 2005: 34(6): 703-6[infrom the mixed coal from 20 and 150 min grinds is the best [8] Wu GG, Wang XC, Li QH. Study of the matching performance between additivefor both kinds of coals. this particle size ratio gives theof coal water slurry and coal molecular structure. J Univ Min Technolmaximum slurry concentration2006:35(4):454-7| in Chinese[9] Fu XH, Wang ZN. Chai BM. Li HF. Research on preparation and applica(3)The coal proximate analysis and infrared spectral analysisultra-clean micronized coal water slurry. J China Coal Soc 2004: 29(2): 2suggest the characteristics of the Australia coal are close tohose of gas coal in China and that the coal rank is a little 110) Zhou HC, Xiong F. waM market prospects in China and policy-sidecommendations. China Coal 2003: 29(8): 8-12 in Chinesel.higher than the rank of the Shenhua coal. However, the [11l Duan QB. He GF. Wang GF. Zhang S). The new technology of high concentrationasifying CWM from low rank coal. Coal Qual Technol 2009(5): 41-3.those with the Shenhua coal. The ash content of Australia 2 7ggg Rn c hneZ Technique of preparing water coal slurry. Beijing: Science Press:coal is 21.72% higher than that of the Shenhua coal. For a [13] Chryss AG, Bhattacharya SN. Maximum packing concentration of coal watersolidThe it volume and higher slurry concentrations (14) Wen L The Pntp 1491:21:85-92.constant packing efficiency, higher ash contents give motin the CWS. The layered structures of the minerals in the [15] Wang B] Li M. xie KC Relationslsurface potential and functionalAustralia coal give a Cws with good thixotropy that shows1330-4 in Chinese l.good stability and fluidity. So, the high ash content of the 6l e and dynamic Stote tia ela ioas p hete se iscosio s o echterAustralia coal improves the pulping effect of the Cws.04: 32(3): 12-4 in Chinese中国煤化工CNMHG