Coal Ash Slag Penetration Behavior on Cr2O3-Al2O3-ZrO2 Bricks

China's RefractoriesCHNPTang Lihua, born in Jan. 1965, obtained his bachelor's degree, master's degree, and doctorsdegree from East China University of Science and Technology(ECUST)in 1987, 1996, and 2004, respec-tively. He is now the lead teacher of core course of Chemical Technology and mainly engages in the researchof coal transformation technology and waste solid resourcing technology. He also holds a part-time job as thejudge expert of Ministry of Education Study-abroad-returm Scientific Research Start Fund and member ofChina Chemical Industry Society. He has authored and co-authored 48 papersCoal ash Slag penetration behavior onCr.. -Zro, bricksTANG Lihua, GAO Ling, WANG Qiong, CHEN Dongxia, ZHOU YamingWANG Wenmei, WU Yongqiang, ZHU Zibin1 Engineering Research Center of Large Scale Reactor Engineering and Technology, East ChinaUniversity of Science and Technology, Shanghai 200237, China2 Shanghai Coking Chemical Corporation, Shanghai 200241, ChinaAbstractpared with the other gasifiers, slagging coal gasiThe penetration behavior of different kinds of coal joys great advantages in technical operationash slags into chrome corundum bricks was studied by ment, and supporting refractories. At presentcup test. As a preliminary attempt, the oxides of Fe20, most popular slagging coal gasifier in China is Texcoand MgO were added into coal ash to reduce the erosion gasifier, which operates at 1 300-1 500C under 2.7of refractories. Different cup tests were carried out to6. 5 MPaJ. Under such harsh conditstudy coal slag erosion to the refractories. Factsage was slag forms when coal ash flows down the refractoriesused to simulate the phase diagram of the main chemical lined wall. The slag penetrates into porous refractoriescompositions in coal ash and in the refractories. Both re- matrix, and subsequently corrosive reactions occursults agreed with each other. The results show that the which may lead to refractories degradation and spalelements in coal slag can penetrate into bricks and the ling. Therefore, the high cost of refractories replace-penetration deepens wih the duration increasing: it is ment( approximately USD I million)and long downdifficult for Fe but easier for Ca and Si to penetrate into time(3-6 weeks) make the industry experts rank imbricks; different kinds of melting coal ashes penetrate in- proving refractory durability No. I in a list of 20 re-to refractories differently and the penetration depth of sil- search and development needs.Previous studiesicon and calcium can be significanly reduced by adding have shown that slag penetration and chemical corrosionKey words: Coal ash slag, Chrome oxide-alumina- gasifier" y causes for refractories degradation in ance the slag refractories interaction iszirconia brick, Penetrate, FactSageunderstood, it becomes possible to develop solutionsminal composition and4 ntrodcti。ving中国煤化工 educe thCN MHGof great importanceThe gasification process is one of the most impor- to promote theof the gasificaant means to increase Chinas energy supply andStudies and gasifier operation results have showneet the expanding needs of chemical products. Com- that chrome oxide or chrome oxide -alumina refracto-China's Refractories Vol 19. No, 4,2010 5CHNRCoal Ash Slag Penetration Behavior on Cr,O, - -Zro, Bricksries has good performances such as low slag solubility mm were drilled in these cubic bricks. Then theseand good corrosion resistance 4-6. A number of re- holes were filled with coal ash samples. The refractorysearchers have used different methods to investigate slabs were placed in the muffle fumace and were heatedcoal ash slag penetration and chemical corrosion on to 1 300 C with different durations. After furnacehigh-chrome oxide refractories. For example, J. Raw- treatment, each cup test slab was sliced into half.Oneers. Alton and Chend cup test to study section was metallographically polished and observedinterface reactions of oxides with the high-chrome re- using a scanning electron microscope(SEM)to deterfactoriesMichael investigatedof mine the depth of coal slag penetrationrefractories in CADCAFI.Sundaram3-4got a coal position of the used slag was measured using SEM-enash slag penetration model. However, althoughergy dispersive X-ray spectroscopy(EDS)approaches can give good results when applied to2. 3 Equilibrium Phase Diagram Simulationash samples with the similar chemical composition, it isThe thermodFactSage is aless effective when applied to samples from different fusion of two well-known software packages in computa-sources.Hence,it is necessary to study penetration be- tional thermochemistry: Fact-Win and ChemSagehavior of some representative Chinese coal ash to Fact Sage consists of a series of information, databaseschrome oxide - corundum zirconia brick, whichcalculations, and manipulation modules that enable oneprovide theoretical basis to propose new ways toto access and manipulate pure substances and solutionprove refractories for Chinese representative coals.he phaseformed, their proportions, compositions, the activities2 Experimental Proceduresof individual chemical components and the thermodynamic properties for all compositions, pressure and2. 1 Starting Materialstemperature is. FactSage(version 5. 4)was used toThree representative Chinese coal samples were simulate equilibrium phase diagram of chemical compo-adopted in this study. The ash samples were preparedin a mume fumace at 800 C for 24 h according to Chi-sitions in coal ash and in the refractories. The equilibnese standard GB 212-91. The chemical compositions of rium phase diagram can give us a better understandingofthe three coal ash samples are listed in Table 1. Inthe slag-refractories interactionddition, an artificial slag was prepared by adding 12%Fe,O, and 3%MgO into SF coal ash. Refractories8 Results and Discussionare the chrome oxide- corundum -zirconiawhich are widely used in the commercial Texco3.1 Representative Coal Ash Slag PenetrationBehaviorsers. The refractories contains Cr, O,( approximately90 wt%), AL, O,, and a little binder. The elementFigure 1 shows the vertical view, cross-section andanalysis results of refractories are shown in Table 2partial crack view of cup slabs of SF coal ash with dif-ferent durations. All the cup bottom surfaces undergoTable 1 Chemical composition of coal ash sample/wr%I Coal ash sample Fe, 0, Mgo SiOz Al, 0, Cao noticeable morphological changes, from which we ca9,461.8234.5910.8621.02observe the trace of slag penetration. The depth of slapenetration increases as duration increases. There is noLN8.52 1.26 33 58 13.03 20.33 crack in cup slabs with duration less than 100 h. The4.330.4936.7511.9222.99cracks are observed both on the surface and inside ofTable 2 Element analysis of refractories /wt%cup test slabs with duration over 250 h.AlCr3. 2 Chemical Compositions of Corroded Cup5.190.59by sF Coal AshSix points were marked to get the analysis sample2. 2 Cup Test and characterizationin the schematic illustration is givenFi中国煤化工points is 0.5 mm,chrome refractories were accomplished by a modifiwhileCN MH Gnd the sixth poinmall cuboids with the size of 50 mm x 50 mm x 50 the second point is on the refractories, which means thatmm. Holes with diameter of 10 mm and height of 10 the slag-refractories interface is between the first point6 China's Refractories Vol 19, No, 4, 2010NG Lihua, GAO Ling, WANG Qiong, et alCHNRand the second point. As Fig. 2 shows, the white line range of white dotted line, the color of refractories isndicates the slag -refractories interface. Within the lighter than the rest which is the key in this study(a) 50 h vertical view(b) 50 h cross-section(c)50 h crack(d)100 h vertical view(e)100 h cross-section(0100 h crack(g) 250 h vertical- view(h)250 h cross-section()250 h crackG)400 h vertical view(k) 400 h cross-section(400 h crackTYH中国煤化工CNMHG(m) 600 h vertical view(n) 600 h cross-section(o) 600 h crackFig. 1 Penetration photos of SF into refractories with different durationsChina's Refractores Vol 19. No 4. 2010CHNACoal Ash Slag Penetration Behavior on Cr,O-ALo2-Zro, Brickspenetrate deeply into refractories. The penetration be-haviors of Ca and Si are very similarAnalysis results show that there is nodifference of Fe penetration depth with different dura-tions, Most Fe concentrates on the surface of refracto-ries, Fe concentration near the interior wall of the cupis higher than that in the coal ash slag, and it decreases quickly with the increasing depth. Although thedepth of Fe penetration increases wiFig. 2 Schematic illustration of EDS analysis locationduration, it mainly concentrates within 2 mm awaySEM-EDS analysis results of the cup slabs cross- from the interior wall of the cup. It is because Fe203section with different durations are shown in Fig 3. might react with Cr,0, and Al,0, to formFigure 3 demonstrates the penetration depth of Fe, Ca, Fe( Cr, Al)204, which can form a dense layer andand Si of SF coal ash. On the whole, Fe mainly con- change the slag -refractories interface strucentrates near the interior wall of cup while Ca and Si50h100h250h250h250h600h95153555759595153555759515135PosttionmmPosition /mmPosition/mmFig. 3 Elements content in different positions( distance away from interior wall)Compared with Fe, Ca penetrates into refractories ashes penetration depth into refractories with the dura-much deeper. The depth increases with the increasing tion are shown in Fig. 4. There is no significant differ-duration. Ca concentration is less than 1% at the ence of Fe in different coal ashes penetration intodepth of about 2 mm with the duration of 50 h, while it factories, most Fe concentrates on the surface of theis less than 1% at the depth of approximately 1l mm refractories. Meanwhile, Ca penetrates into refractorieswith the duration of 600 h. The result of this study is much deeper than Fe. The depths of Ca in LN and SFconsistent with the results of the previous studies on re- coal ashes penetration into the refractories are veryactions of artificial blends of coal slag oxides with high close. Ca concentration is less than 1% at the depth ofhrome refractories. Ca0 reacts with the high chrome about 4 mm and 4.5 mm of Ln and SF coal ashes.Atrefractories to form a lower melting Ca([ Cr, Al]02)2 the depth of less than 3 mm, the Ca concentration isalmost the same as that of the two coal ashes. It isThe penetration of Si is quite similar with that of much easier for Ca in YL coal ash to penetrate into reCa. The penetration depth of Si increases with the in- factories. The depth of Ca penetration in YL coal ashcreasing duration. Si concentration is less than 1% at is the deepest. Ca concentration is less than 1% at thethe depth of nearly 2.5 mm with the duration of 50 h, depth of about 10 mm. The penetration behavior of Siwhile it is less than 1%at the depth of about 13 mm into中国煤化工 shes is similar withwith the duration of 600 hCNMHis more than that3. 3 Elements Penetration of Different Coal of Ca.aru utan ua in YL coal ash,Ashes into Cupsand at the depth of nearly 12 mm Si concentration isThe relations of Fe. Ca, and Si of different coal less than 1%8 Chinas Refractories Vol. 19. No 4,2010TANG Lihua, GAO Ling, WANG Qiong, et alCHNR100h一LN- SF- SFSF4051.53.5557.59511.50.51.5355.575951.5Position/mmFig. 4 Elements content in different positions( distance away from interior wallThe penetration depths of the elements in iN and cross-section of artificial slag with 100 h duration areSF coal ashes into the refractories are quite similar, given in Fig. 5. Fe concentration is higher than that inwhile the elements of YL coal ash penetrate into refrac- SF coal ash at the same penetration depth. Fe in artifi-tories much deeper. As shown in Table 1, concentra- cial ash penetrates 1 mm deeper than that in SF coal ashtions of the oxides in LN and SF coal ashes are very with the same duration. After 100 h penetration, for ar-close, which is quite different from YL coal ash. The tificial coal ash Ca concentration is less than 1% aboutpenetration depth difference of coal ashes into refracto- 2 mm from interior wall. However, for SF coal ash, Caries has much to do with the different chemical compo- concentration is less than 1% nearly 4.5 mm from inte-sitions. Compared with YL coal ash, LN and SF coal rior wall. Meanwhile, compared with SF coal ash withashes have much higher Fe,O, and Mg0 concentra- 50 h duration, Ca penetration depth of artificial coal ashtions. Fe,O, and MgO may react with Cr2O, and AL O, with 100 h duration is much lighter. The penetration be-to form a protective layer of new crystalline phase, havior of Si is similar with Ca, the penetration depth ofwhich prevents other elements in the coal ash slag from artificial coal slag is approximately 2 mm lighter thanng inthe refractories)coal ash with the same duration. It dem-Penetration of artificial ash into the refractories was onstrates that adding oxides can significantly prevent Siinvestigated. The SEM-EDS analysis results of cup and Ca from penetrating into refractoriesFe-100 hCa-100 hSi-100hArtifical ash-100 hArtifical ash- h备 Artifical ash-.OohSF-100hSF.100 h一SF100hSF-50 hSF- hr SF-50 h0.5051.525050.515253.545050515253.545Position /mmPosition/mmPosition /mmFig. 5 Elements content in different positions distance away from interior wall3. 4 Phase Diagram Simulation and Analysis by Cr,0-ALO,, Fe, 0, -Cr, 0.-Al,O,, Si0,-Cr, 0,FactSage中国煤化工MPa. The calcuThe main chemical compositions of gasifier coaoal latiorCNMHGon Gibbs'energyash slag are CaO, SiO2, and Fe203, while compations of refractories are Cr,O, and AlO,. FactSage wasPhase diagrams simulated by FactSage are shownused to simulate multi-phase equilibrium CaOin Fig. 6. From Fig. 6(a), it is found that when CaChina's Refractories Vol 19, No 4, 2010 9CHNACoal Ash Slag Penetration Behavior on Cr, o-AlO-Zro2 Bricksconcentration is about 34 wt at 1 320C, the system(3 CrO,(s)+Cr20,(s)+ FeCr2O,(s)+slag-liquidof Ca0-Cr2O3-AlO, forms low melting CaCr2O9 C02(s)+Cr,0,(s)+FeCr20(s)+ slag-liquidCa0 reacts with Cr,O, as follow5 CNO2(s)+ALO,(s4)+slag-liquid+Cr,0,(s)6 CrO2(s)+AlO3(w4)+slag-liquid+ Cr,0,(s)CaO+Cr2O3→CaCr2O4⑦A2Fe206()+C2O3()+A2O3(s3)The area containing liquids gets larger as tempera-(8 AL,FeO,+Cr,0,(s)+AL20,(44)ture and Ca concentration increase. Thus, it is much9 AlFe20(s)+Cr,0,(s)+Fe2O,(s)easier for Ca to penetrate into refractories. Th0cCr2O3()+A2O3(83)+Fe2O3(s)tration depth increases with the increasing durationQ Cr02(s)+AL,0,(s)+FeCr20(s)+Cr20,(s)mass Cr,O,( Cao+Al O, +Cr O 0.5④Al2Fe204(8)+C2O3(s)+CO2(a)+FeC04(8)15 Al Os(s)+gas-ideal+ FeCr, 04+Cr,0, (s)Fe20,0 AL, Fe20,(s)+gas-ideal+ FeCr2 0(s)Q8 Al, Fe,O,(s )+gas-ideal+ Cr20,(s140⑧⑦mass Cr,O,/(SIO, +AL, O,+Cr, O, H0.51mass Cao/(Cao+Al,o +Cr,o,)Slag-liquid +Cr0,()+CaCr2O,(s2)② Slag-liquid+CaO(·)+CnO2(s)③ Slag-liquid CrO24 Cr,0,(s)+slag-liquid+Cr0,(a)5 Cr,0,(s)+Cr02(s)+slag-liquid +CaCr,.(s2)mass SoY (SiO, +AlO, +Cr,O)6 Cr,0,(s)+Al20,(a4)+slag-liquid+CrO(D Cr,0,(s)+CaAl0,(8)+ CaCr2O(s)(8 Cr2O,(s)+CaAl0,(s)+CaAl2O1g(s)O Cr20,(s)+slag-liquid+CHO,(s)9 Cr20,(s)+CaAl, O1g(s)+Al,0,(s4)@2 Cr20,(s)+CH0,()+AL Si, O,3 (s)+slag-liquQ0 Cr2O,(s)+CaAl2 O,(s)+slag-liquid+CrO2(s)3 Cr2O,(s)+AL Si,O1(s)+Si02(6)AD Cr20,(s)+CaALO,(s)+slag-liquid +Cr02(8)4 Cr,0,(s )+Sio2 (s4)+Al.,(s)Q2 CaAL O, (s)+CaAl2 O(s)+CaCr,O,(s)6 Cr20,(6)+AlO,(M4)+AlSi,0,(s)Q3 Ca, Al,0s(g)+CaA,0.(s)+CaCr, 0.(s)6 Cr,O,(s)Cr0,(s)+Si0, (86)Q Ca, A, 0s(g)+CaCr,04(s)+CaoO Cr,0,(s)+AL0,(s4)+slag-liquid+C02(g)Q5 Slag-liquid +CaO(s)+Cro,(s)+CaCr0,(s)ag Slag-liquid+ Cr0,(s)+CaCr204(s)Fig. 6 FactSage equilibrium phase diagram for system asha Slag-liquid+ CaAl,O(s)+C02(s)+CaCr,O(s)slag -ALO, -Cr,,:(a)Cao,(b)Fe,O,,(c)QB Slag-liquid+ Ca, A2 0(s)+C02(s)+CaCr2O(oFe0-Al0-Cr, 0, ackAs shown in Fig. 6(b)concentramass Cr O (Fe 0+ALO,+Cr O, F0.Stion is about 37 wt at 1 380 C, liquids appear inO,-CrO3-AL,O3. Fe203Cr2O, and Al, 0, as foll1600Fe0+Cr2O3→FeCr2OA2O3+Fe2O3→→Al2Fe2ONevertheless, as chemical compositions of coalashes shown in Table 1. Fe, 0, is much less than CaO1000e,030.lcentra中国煤化工t1380℃.ItisCN MH Gct with Cr, 0, andAL, 0, forming low melting materials. This is the reason①Cn02(s)+ slag liquidwhy most Fe concentrates on the slag -refractories inQ CrO2(s)+slag-liquid+ Cr,0,(s)10TANG Lihua, GAO Ling, WANG Qiong, et alCHNEFrom Fig. 6(c), liquids appear in the system ofApplications and News. 2003, 8(4): 18-23Si02-Cr2O3-ALO, when SiO, concentration[6]Guo Zongqi, Han Boqi, Dong Hai. Effect of coal slag on46 wt% at 1 600C. This means that there is no newthe wear rate and microstructure of the ZrO2-bearing chro-mia refractories. Ceramics Intemational, 1997, 23(6)489-496condition. SiOz does not react with Crn 0, and AlyO, [71Rawers I, kwong KS. Bennett ). Characterizing coalto form a new melt. SiO, might penetrate into refractofier slag-refractory Interactions. Material at High Teries through the cracks formed by reactions betweenature,1999,16(4):219-22.CaO and Cr2O3. It is consistent with the previous [8] Rawers J, Collins K, Peck M. Oxides reactions with highchrome sesquioxide refractory. Joumal of Materials Sci-ence,2001,36(20):4837-4843Conclusione-o[9]Rawers J, Iverxon L, Collins K. Initial stage of coal slagteraction with high chromia sesquioxide refractories. Jour-1)Fe, Ca, and Si in coal ash cannal of Materials Science, 2002, 37(3),531refractories. The penetration depth increases with dura[ 10] Hunk A H, Chinn R E. A ceramographic evaluation ofchromia refractories corroded by slag. Structure 37tion increasing2002:6-102)It is quite easy for Ca and Si to penetrate into [11]Michael D Mannrefractories, while most Fe concentrates on the slagGasifier Refractory. December, Grand Forks: Departmentrefractories interfaceof Chemical Engineering of The University of North Dakor-D )Ca and Si in Yl coal ash penetrate much deeper than those in SF and LN coal ashes because SF and [12] Kim H B, OhM S. Changes in a microstructure of a highn coal ashes have more Fe,O, and Mgo than YL coalchromia refractory due to interaction with infiltrating coalslag in a slagging gasifier environment. Ceramics Interna-ash. Fe, O3 and Mg0 can form a protective layer to pretional,2008,34(8):2107-2116vent other oxides from penetrating into refractories. [13] Sundaram S K, Johnson K I, willifordRE, et al. An in-Fe2O, and Mgo as additives can significantly reducetegrated approach to coal gasifier testing, modeling andthe coal ash slag penetrationprocess optimization. Energy Fuel, 2009, 23(10): 4 7484)Fact Sage is an important tool to predict ash behavior at high temperatures. The analysis results of [14] WillifordR E, Johnson K l, Sundaram S K. Modeling ofaseam simulatedhigh-chromia refractory spalling in slagging coal gasifiers.agreement with the results of cup testCeramics Intermational, 2008, 34(8): 2 085-2 089[15 Chen Dongxia, Tang Lihua, Zhou Yaming, et al. CoalReferencesits penetration behavior. NaiLuo Cailiao( RefractoriesChinese version), 2007, 41(2): 85-88[1] Wang Wenxi, Geng Keming, Pan Jun, et al. Influences of [16] Liu Chuanjun, Jin Yan, Bi Xuegong. Thermodynamicsoperating conditions on service life of gasifier lining materianalysis on oxidizing slag containing AL,O,. Liugang Sci-al. Large Scale Nitrogenous Fertilizer Industry, 2008, 31ence and Technology, 2008,(3): 16-18(6):367-368[17] Cao Zhanmin, Song Xiaoyan, Qiao Zhiyu. Thermodynam-[2]Tang Jianping, Qi Xiaoqing, Wang Yufan, High chromeic modeling software FactSage and its application. Chineserefractories for water coal slurry gasifiers. Naihuo CailiaoJournal of Rare Metals, 2008, 32(2): 216-218factories, Chinese version ), 2002, 36(3): 156-[18] Li Hanxu, Yoshihiko Ninomiya, Dong Zhongbing, et alApplication of the FactSage to predict the ash melting be[3] Bennett, James P. Refractory liner materials used in slaghavior in reducing conditions. The Chinese Joumal ofging gasifier. Refractories Applications and News, 2004Chemical Engineering, 2006, 14(6): 784-7899(5):20[19] Guo Zongqi, Zhu Yusheng. Corrosion of molten slag of[4] Theodore M Bestmann. Thermochemicalof refrac.coal gasifier exposed to chromia-containing refractoriestory corrosion in slagging coal gasifiersAdvance in Material Science, 1990, 4(1): 64-70of Phase Diagrams and Thermochemistry中国煤化工[5] Taber, Wade A. Refractories for gasification. RefractoriesCNMHGeived in Aug-, 2010hina's Refractories Vol 19. No, 4. 2010 11