Reactivities of Shenfu Chars Toward Gasification with Carbon Dioxide

Jun. 2007Journal of China University of Mining & TechnologyVol.17 No.2Available online at www.sciencedirect.comSCIENCE (e doIREcT.J China Univ Mining & Technol 2007, 17(2): 0197 - 0200Reactivities of Shenfu Chars TowardGasification with Carbon DioxideZHANG Jia-wei', ZONG Zhi-min', W ANG Tao-xia', XIE Rui-lun', DING Ming-jie'2, CAI Ke-ying',HUANG Yao-guo', GAO Jin-sheng', WU You-qing , WEI Xian-yong'! School of Chemical Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221008, ChinaZLuohe Occupation Techrical College, Luohe, Henan 462000, China'College of Resource and Environmental Engineering, East China University of Science and Technology,Shanghai 200237, ChinaAbstract: Five Shenfu char samples were prepared from Shenfu raw coal at different temperatures (950, 1100, 1200,1300 and 1400 C) using a muffle furmace. Demineralization of the char samples was performed by treating them with10% nitric acid for 10 min in a CEM Discover microwave reactor. The gasification of the chars, and correspondingdemineralized chars, in a carbon dioxide (CO2) atmosphere was conducted in a Netzsch STA 409C131F tempera-ture-programmed thermogravimetry apparatus. The effects of charring temperature and demineralization on the gasi-fication reactivity of chars were systematically investigated. The results show that a char formed at a lower tempera-ture is more reactive except for demineralized char formed at 1100 C, which is less reactive than char formed at 1200C. Demineralization decreases the char reactivities toward gasification with CO2 to a small extent.Key words: demineralization; temperature-programmed thermogravimetry; reactivityCLC number: TQ 5461 Introductioneffects from increasing specific area and porosity ofthe char, and inhibiting effects from reduced mineralThe reactivity of coal chars toward gasificationmatter catalysis.with CO2 and steamt- , and toward combustion withIn this work, we examined the effects of CT andair or oxygen', has attracted extensive attentiondemineralization on the reactivities toward gasifica-from coal researchers because the nature of the chartion with CO2 of coal chars formed at different CTs.controls these processes'58. Xu et al investigated theeffects of charring conditions on coal char reactiv-2 Experimentality!. They concluded that higher charring tempera-ture (CT), slower heating rate and longer soaking2.1 Char samplestime cause lower reactivity of the resulting chars to-ward gasification. Tang et al suggested that high CTCoal chars were obtained by heating Shenfu coal incauses agglomeration and melting of mineral mattera muffle fumace to a temperature of 950, 1100, 1200 .in the char, which decreases the catalytic activity of1300 or 1400 C, at a rate of 6 C/min and then hold-the mineral matter toward gasification'o. Zhang et aling at temperature for 20 min. Char samples (FCs,investigated the effect of mineral matter on gasifica-fresh chars) were then prepared by pulverizing thetion reactivity of some typical Chinese anthracitecooled chars to pass through a 200 mesh screen. Thischars. Their conclusion is that demineralizationwas followed by drying in vacuum at 105 C for4 h.increases the reactivities of some anthracite chars, butTables 1 and 2 list the proximate and utimate analy-decreases the reactivity of others toward gasificationses of Shenfu coal and the FCs. The anomalous carbonwith CO2. There are diverse effects from deminerali-conte中国煤化τdintheCTrangeofzation on char gasification with CO2, i.e., enhancing1100:ntributions of CaC2TYHCNMHGReceived 09 December 2006; accepted 11 January 2007Projects 2004CB217704 supported by the Special Fund for Major State Basic Research Project, 104031 by the Key Project of Chinese Ministry of Education andJHB05-33 by the Program of the Universities in Jiangsu Province for Development of High-Tech IndustriesCorresponding author. Tel: +86-516-83885951; E-mail address: wei xianyong@ 163.com198Journal of China University of Mining & TechnologyVoL.17 No.2and SiC.rapid-rate (higher GT range) gasification. The reac-tivity of FC toward gasification decreases with in-Table 1 Proximate and ultimate analyses of Shenfu coalcreased CT, but there is no significant reactivity dif-Proximate analysisUlimate analysis (daf)S, (d)ference between FCs formed at 1200 C and 1300 CAsVMarCH_Nespecially at higher GTs of the third step. Wu, et al10.196.5037.6680.534.800.89 0.37_obtained similar results from isothermal thermogra-vimetric analysis. Raising the CT decreases porosityTable 2 Proximate and ultimate analyses ofFCs (%)and specific surface area of a FC and thereby de-Ultimate analysis (daf)creases FC reactivity toward gasification'CT(C)-As VMarC____ H Ns,(d)100 n950 10.3096.99 0.30.33 .0.42 .-0- 950C1.93100.310.170.4480- -。- 1100C1200 9.951.90 100.54 0 0.14 0.42--- 1200C300 10.08 1.13100.580.07、60 t-v- 1300C140 10.561.12100.100.03-+- 1400C2.2 Demineralized chars (DCs)40Demineralization was performed by treating FCs20with 10% nitric acid at ca. 50 C for 10 min in a CEMDiscover microwave reactor followed by repeatedwashing with deionized water, until no NO; could be60010001400detected in the wash water, and drying in vacuum atGT(C)105 C for 4 h. Mass recovery of DCs is higher thanFig. 1 Conversions of different FCs at different GTs95%. The ash contents of the DCs with CTs of 950,1100, 1200, 1300 and 1400 C are 4.78%, 2.49%,3.2 Effect of CT on DC reactivities3.98%, 4.98% and 4.06%, respectively.Unlike the FC situation, DC gasification can be di-2.3 Char gasificationvided into two steps, slow-rate (GT range: room tem-The gasification runs were performed in a Netzschperature to 900 C for DC formed at 950 c and to ca.STA 409C131F thermogravimetric analyzer. Each1000 C for DC formed at higher CTS) and rapid-ratechar (ca.15 mg) was heated from room temperature to(higher GT range) gasification, as shown in Fig. 2.1400 C at rate of 20 C/min under a 90 mL/min CO2The reactivity of DC toward gasification generallyflow. The reactivity of each char toward gasificationdecreases with increased CT, but there is almost nowas evaluated by the char conversion X, the weightdifference in the reactivity between the DCs formedloss percentage based upon the weight (daf) of theat 1100 and 1200 C. The much lower ash content offeed charthe DC formed at 1100 C may cause a significantX=m-mdecrease in reactivity that reduces the difference be-tween this and the 1200C sample. If true, this im-nplies that demineralization decreases the char reactiv-where m; is the initial mass of organic matter and mity toward gasification with CO2.the mass of organic matter at time t. The weightchange of the sample was corrected to account for ashcontent. This was done by considering the sample100weight at the end of the experiment when, after thecompletion of organic matter gasification, only ash80 -o- 100-*- 1200C .residue remains'”60 t-*- 1400C3 Results and Discussion40 ;3.1 Effect of CT on FC reactivityAs shown in Fig. 1, FC gasification largely pro-ceeds in three steps which occur at different gasifica-ion temperature (GT) ranges: slow-rate (GT range:中国煤化工00 1400room temperature to 600 C), medium-rate (GT range:600- -905 C for FC formed at 950"C, to 979 °C for FC.MHCNM H G.at different GIGTsig.。、UUvCISIUD u ulicilll usformed at 1100 C and to 1005 -1028 C for FCsformed in the CT range of 1200- 1400 C) andZHANG Jia-wei et alReactivities of Shenfu Chars Toward Gasifcation with Carbon Dioxide1993.3 Effect of demineralization on char reactivitiesmore complete removal of mineral matter from theThe FC and DC formed at 950 C show almost theFC formed at 1100 C than from the other FCs. Thissame conversion vs. GT curves (Fig. 3a) The reactivi-suggests that some mineral species promote chaities of DCs formed at 1100-1400 C are appreciablygasification to a greater extent than the increase inlarger than the reactivity of FCs in the lower GT rangesurface area and porosity caused by demineralization.Liu et al investigated the effect of inorganic matter(Figs. 3b- e). At higher GT ranges, the FC and the DCon reactivity and kinetics of pyrolysis of two Chineseformed at 1200 C also exhibit similar conversion Vscoals. They concluded that some inorganic species,GT curves (Fig. 3c). On the other hand, a significantsuch as CaO, K2CO3 and Al2O3, added to a deminer-difference in reactivity between the FC and the DCalized coal accelerated coal pyrolysis. Our furtherformed at 1100 C, and an appreciable difference in thework will focus on the difference in mineral compo-reactivity between FCs and DCs formed at 1300 C orsition between FC and DC formed at CT 1100 C to1400 C (in the higher GT range), can be seen in Figs.understand what kinds of mineral species catalyzed3b, d and e.The significant difference in reactivity between thethe char gasification.FC and the DC formed at 1100 C is consistent with100100 r100，0f80-30}50一二DC六FC50一FC< 40of02(0 2000 1000 14000 200 6001000 140020060010000 1400GT(C)GT ('C(a) Formed at950 C(b) Formed at 1100C(C)Formed at 1200C0t一DC20 t200600100000 14000 20060000 140(d)Formed a 1300C(e) Formed at 1400CFig. 3 Comparison of conversions of FCs and DCs4 ConclusionsAcknowledgements1) FC gasification largely proceeds in three steps:This work was subsidized by the Special Fund forslow-rate, medium-rate and rapid-rate gasification,Major State Basic Research Project (Projectwhereas DC gasification can be largely divided into2004CB217704), the Key Project of Chinese Ministrytwo steps: slow-rate and rapid-rate gasification.of Education (Project 104031) and the Program of the2) Reactivities of both FCs and DCs toward gasifi-Universities in Jiangsu Province for Development ofcation with CO2 decrease with raising CT, especiallyHigh-Tech Industries (Project JHB05-33).in the higher GT range.3) Deep demineralization of FC significantly re-duces the char reactivity toward gasification with中国煤化工CO2 in the higher GT range.MHCNMHG200Journal of China University of Mining & TechnologyVol.17 No.2_References[1] Everson R C, Neomagus E W J P, Kasaini H, et al. 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