Investigation into co-pyrolysis characteristics of oil shale and coal

Intemational Joumal of Mining Science and Technology 22(2012)245-249Contents lists available at SciVerse Science Direct氵International Journal of Mining Science and TechnologyELSEVIERjournalhomepageswww.elsevier.com/locate/ijmstInvestigation into co-pyrolysis characteristics of oil shale and coalMiao Zhenyong a * Wu Guoguang a b, Li Ping, Meng Xianliang.b, Zheng Zhileia b0%y, Xuzhou 221116. Chinaoratory of Coal Processing and Efficient Utilization, Ministry f Education, Xuzhou 221116 ChinaCUMT Dazheng Surface Engineering Techmology Co Ltd. Xuzhou 221116, ChinaARTICLE INFOABSTRACTSamples of five types of coal and oil shale from the Daqing region have been subjected to co-pyrolysis innding ratios with thermo-gravimetry (TG). given a heatingin revised form 10 July 2011a final tenre of 900C Investigations on pyrolysis of mixing coal and oil slAvailable online 14 April 2012out, indicating that the main scope of weight loss corresponbon oil and gasrelease was between 350 and 550C. At higher temperatures, significant weight loss was attributedcoke decomposition Characteristic pyrolysis parameters of blends from oil shale and the high rankedXZ coal varied with the blending ratio, but oil shale dominated the process. At the same blending proporhly volatile medium and low ranked coal of low moisture and ash content reacted well duringBlending coal samplesyrolysis and could easily create synergies with oil shale. Medium and high ranked coal with high mois-Blending ratioture content played a negative role in co-pyrolysiso 2012 Published by Elsevier B.V. on behalf of China University of Mining Technology.showed a distinct systematic shift of regions of maximum rate ofweight loss to higher temperatures when the rate of heating waswith an expected future decline in petroleum production, his. increased for the analysis of oil shale using TG [16, 17]. Dogantoric market forces are poised to change, which demands an in- and Haddadin have investigated the effect of temperature duringcrease in unconventional liquid fuel supplies in the future [1 Oil pyrolysis and shown higher weight losses at increased pyrolysisshale is considered to be the substitute for oil as a natural source temperatures 18, 19 Many studies have been conducted into pro.of energy. However the extraction of oil from oil shale is relatively cesses of pyrolysis of coal and blends of coal and other substancesxpensive and uneconomical at present expanse. therefore a high In the present investigation, thermo-gravimetric analysis wasvel of importance is attached to research into processes of oil shale introduced to reveal the co-pyrolysis characteristics of coal andutilization as a source of energy [2-5] Oil shale deposits in China oil shale, providing a theoretical foundation for further develop-are widespread in many regions: proven reserves amount to about ment and utilization of oil shale [20-251.32 billion ton and extensive exploration and processing researchAs well, several scientists have advanced ideas for a comprehenhas been conducted over the past decades 16.7). Coal could provide sive utilization of oil shale In first instance, oil shale is used to pro-hydrogen during thermal co-processing with oil shale, leading to an duce shale oil and then the residue is sent to a power generationincrease of liquid production. Some data indicate that a mixture of station in a circulating fluidized bed furnace. Restricted by the costoil shale with coal can be successfully converted into liquids using of refining. the oil shale industry is still at the stage of large-scaleenhanced oil yields. In short. it seems that co-treatment of oil shale and utilization of oil shale such as pyrolysis oil shale and coal areocesses could have potential for environmentally friendly trans both fossil fuels and the various ranks of coal have different pyroor mation of oil shale and coal to valuable productsis and combustion characteristics, Hence co-pyrolysis of oil shaleThermo-gravimetry(TG)of oil shale samples or mixtures of oil and coal is possible and can produce synergies and enhance theshale with coal have been extensively used as a means of deter- efficient use of oil shalearacteristics of devolatilisation and as well to deter-nine kinetic parameters of thermal decomposition of fuels or fuel 2. Experimentalmixtures, which is crucial to the design and operation of conversion systems [11-15]. For instance. Drescher and Rajeshewar 2.1. Thermo-gravimetryding author. TeL: +86 15862151177.中国煤化工 r mixtures were subjectedress: zymiaoocumt edu cn(Z Miao).CNMHGan inert atmosphere of2095-2686/s- see front matter o 2012 Published by elsevier B V. on behalf of China Universitydoi:101016jmst20110900Z Miao et od / Intemational Jourmal of Mining Science and Technology 22 (2012)245-249nitrogen. A NETZSCH STA409C TGA analyzer was used to measureand record the mass changes in the samples as a function ofemperature over the course of the pyrolysis reaction. Thermo-gravimetric curves were obtained at a heating rate of 30.C/ mina final temperature of 900C Nitrogen gas was used as an inerturge gas to displace the air in the pyrolysis zone thus avoidingwanted oxidation of the samples. A flow rate of around00 mL min was fed into the system from a point below the sam-5∞80506ple with a purge time of 60 min(the air was eliminated from thesystem and the atmosphere remained inert).010020030040050060700809002. 2. SamplesSamples of oil shale from Daqing(DQ) were selected. We optedFi 1. TG graphs of oil shale and coal.for coal of five different ranks from Longkou( LK), Inner mongoliaEji (EJ) Xuzhou Jiahe (H), Anhui Linhuan(LH)and YongchengXinzhuang (XZ). All samples were ground to sizes between 0 and0.2 mm.3. Characteristics of pyrolysis of oil shale and coal3. 1. Basic data of oil shale and coalLENTable 1 shows the basic data of oil shale samples from DQ andthe five coal samples from LK, E]. JH, LH and Xz. These includemoisture(Mad) ash(Ad). volatile matter(Vaar) and fixed carbonFCaar), calculated as percentages of weight. The table shows thatoil shale has a characteristic low carbon content a high ash con-0100200300400500600700800900tent, low calorific value and is highly volatile, i. a fuel withTemperature℃)high-ash content and low calorific value. The order, from high toFix 2 DTG graphs of oil shale and coaL.low, of the mass of volatiles released, ranks from LK. E]. JH. Lh toEJ. JH, LH and Xz, respectively. Coal curves 1 and 2 show the3. 2. Characteristics of pyrolysis of coal andtrough, followed by the high ranked xZ coal and in theTG and differential thermo-gravimetry(DTG)curves of oil shale amounts of external and intrinsi ponding to the fact thahigh as 20%, The amount of water in both 1 and 2 declines withrepresent samples of oil shale from dQ and the five coal samples the improvement in coal quality. The amounts of extemal andfrom LK.LH and XZ, respectively These figures show that intemal water in coal from JH and lh appear to be the smallests than 1%) In the high ranked anthracite, given the increasehe oil shale has a maximum weight loss of 45.95% For all coal of pulverization of the coal particles caused by condensation ofamples, xZ has the least weight loss, ie, about 9. 81%, correspon the shrinkage stress, the amounts ofing to the results of coal analyses [24, 25 However, the loss ofexternal and internal waterweight of the coal changes in a nonlinear fashion as a function of ave increased. The amount of internal water can even reach 4%coal rank and time. the pyrolysis reaction and product composi-As shown in Fig. 2, the weight loss curves decrease rapidly netion of the low ranked coal (1 and 2)largely depend on the amount350C. Depolymerization and decomposition occur mainly at thisof oxygen in the functional coal groups. The reaction of high vola- stage with gas and tar precipitation and then turn coal into chartile bituminous coal (3, 4 and 5). rich in aliphatic side chains, is The integrated and differential curves increase gently during theainly determined by aromatic rings and aliphatic side chains next stage. Char condensates into coke with the precipitation of26,27methane and hydrogen gas during the step of poly-condensationFig 2 shows that the various curves have a small trough alreaction. Furthermore the differential curves show a typical shoul-100C. referred to as the precipitation phase of the adsorbate lar-der peak at about 700C due to the decomposition of minerals ingely consisting of hydrogen and gas. the curves 1-6 indicate theFor the high quality coal, i. e, that of xZ, the differential curvesamples of oil shale from DQ and the five coal samples from lk does not change much before 550C, and declines gently after atthis point. The low H, o content indicates an absence of methoxyTableand carboxyl in its structure, while the average length of the alkylCharacteristics of oil shale and coal ( 3)side chains is the shortest. Pyrolysis of high ranked coal is a decom-Sample Proximate analysisously and does not form a plastic mass nor ld cipitating continu-position process with small amounts of gas pre77333.034761523977646541.2910433.a370562957157442080034中国煤化工CN MH Mainly refer to the initialten1134110068the final temperature which can be obtained from the analysis andZ Miao er al/International Joumal of Mining Science and Technolog 22(2012)245-2491curs here. The trough value of jH gas coal is a maximum, while thatof XZ coal a minimum. the reason may be that gas coal is a mediumranked coal, while a high volatile steam coal, with its hydrogen con-tent and aliphatic side chain structures relatively rich, has a lowdegree of aromatic condensation. Hence it is amenable to thermo-gravimetric treatment at a low heating speed. The maximumweight loss rate of other types of coal decreases with coal rank,except for that of the EJ coa20400500600700800900rature (T4. Co-pyrolysis of oil shale and coalFly 3 Schematic diagram of characteristic pyrolysis temperatures4.1. Efect of blending ratios on pyrolysisThe highest volatile content in LK coal and the lowest in XZ coalprocessing with Netzsch software. Fig. 3 is a schematic diagram were blended with oil shale in different weight proportions to eval-illustrating the method to solve the characteristic pyrolysis tem- uate the effect of blending ratios on co-pyrolysis. The oil shale wasrature As shown in this figure the trough temperature of weight blended with LK and XZ coal in the proportion of 9: 1. 8: 2, 7: 3. 6: 4.loss rate(Tmax)is precisely the temperature corresponding to the 4: 6 and 2: 8. referred to as: DQLK1, DQLKZ, DQLK3. DQLK4, DQLK5trough of weight loss rate of the dtG curve. The initial pyrolysis DQLK6 DQXZ1, DQXZ2, DQXz3, DQX24, DQXz5 and DQXz6 Figs 4mperature(T, )refers to the point of intersection of the tangentand 5 are the TG-DTG curves of these samples and their thermalhown at the gentle section of weight loss of the tG curve between parameters are listed in Table200 and 400C; the other curve is made at the point of intersection The pyrolysis parameters derived from these blends of oil shalef the TG curve perpendicular to the trough point of the dtG curve. and low ranked LK coal change slightly with the blending ratio, dueThe method of deciding the final pyrolysis temperature(Tn is sim- to similar pyrolysis and temperature characteristics of the tweilar to that of T. D is the characteristic index of pyrolysis productscomponents. The pyrolysis of the blends made up from oil shalflecting the characteristic pyrolysis of oil shale and is calculated and the high ranked XZ coal changes as follows with the increaseas follows: D(dwidt)max/(Tmax. Ts. AT,2) when the characteris- of the temperature aroused by tG of Xz coal: as the starting precip-tics of pyrolysis improve, d will show an increase and the products itation temperature of the volatile increases, the maximum rate ofof pyrolysis will be released in a more concentrated form [28, 29). volatilization decreases gradually. The corresponding temperatureTable 2 indicates that the initial pyrolysis temperature of coal in- gradually increases, which results in a decrease of the precipitationcreases with coal rank. In general, the thermal stability of LK coal is index of the volatile. when the blending ratio of the XZ coal is lessinferior, its initial pyrolysis temperature lower, while these charac- than 60%, the pyrolysis is affected mainly by the oil shale and pyro-teristics of JH and LH coal are superior, with initial pyrolysis lysis parameters change within a small range. If the blending ratiotemperatures higher. With the increase in coal rank, the trough of XZ coal is more than 60%, the changes in the pyrolysis parametemperatures of the maximum rate of weight loss improves gradu- ters are more pronounced. Finally, given the condition that the pro-ally: the greater the differences in coal rank, the greater the values portion of the XZ coal is high, the devolatilization time will bebetween trough temperatures of the maximum rate of weight loslonger, less concentrated, but the comprehensive analysis of theThe maximum trough of the corresponding differential curve oc- characteristics of devolatilization is better than that of anthracite.Characteristic parameters during pyrolysis of oil shale and coalTeu ('o)ATg(°)D(10°xmne42715.40E532811646647551581651.152112345672. DQLKI中国煤化工10200300400500Tamperature()CNMHGFh 4 TG DTG curves of blends of LK coal and od shaleZ Miao et al/International Joumal of Mining Science and Technology 22(2012)245-249100200304005006007008009000100200300400parure℃Temperature(℃)5. TG DTG curves of blends of XZ coal and oil shale.Table 3Characteristic parameters during co-pyrolysis of DQ oil shale with coal.Tr('c△T1a(")446437317317DQLK5515.1426.55172532333363613536534691815113044. 2. Efects of blending coal on the characteristics of co-pyrolysismoisture content, the ash content and pyrolysis characteristics, oilshale and LK coal easily combine to generate a synergistic effect.Oil shale was subjected to pyrolysis with LK. E]. JH, LH and xz The medium ranked JH coal, with its low moisture and ash contentcoal in a blending ratio of 7: 3 with blends identified as DQLK, is highly volatile, has good pyrolysis characteristics and can alsoDQEJ3, DQJH3, DQLH3 and DOXZ3produce synergistic effects during Co-pyrolysis with oil shale. TheFig 6 shows TG and DtG curves of oil shale and coal of different high moisture content in E coal is not a favorable factor duringrank during Co-pyrolysis and Table 3 presents the pyrolysis param- pyrolysis and results in poor pyrolysis characteristics, Botheters derived from these TG/DTG curves, As Fig. 6 shows, the blend and XZ coal are high ranked types of coal with a high ash contentC Ej coal and oil shale experienced the largest weight loss, while and poor pyrolysis characteristics and it is difficult to generate syn-some evidence of the positive effect of oil shale on the pyrolysisof E coal. The blend of XZ coal and oil shale has the lowest weight 5 Conclusionsloss but the pyrolysis parameters also increased, suggesting that oilshale performs similarly an co-pyrolysis(1)Pyrolysis parameters change slightly with the blendA comparison of Tables 2 and 3 shows that, among the fiveof oil shale and low ranked LK coal, but vary withing ratio when oil shale and high ranked XZ coal arof oil shale. LK is a highly volatile brown coal. Due to their similarFor this specific blend, the pyrolysis is domineth the blend-中国煤化工005006007008009000800900CNMHGFlg 6. TG/DTG curves of oilith coal of different rank (oil shale: coal-7: 3).Z Miao et al/Intemational Jourmal of Mining Science and Technology 22(2012)245-249shale and the pyrolysis parameters are more dosely linked 113) williams PT. Nasir A tnvestigation of oil-shale pyrolysis processing conditionsto oil shale(2)In the blending ratio of 7: 3, among the five coal samples,114l Bockhorn H. Hormung A Hormunonly LK and JH coal reacted positively during pyrolysis of1151 Aguado R, Olaza M, Gaisan B, Prieto R Bilbao j Kinetic stpyrolysis in a conical spouted bed reactor. IndAcknowledge116! Drescher EA Bassil CA Rolinski EJ. The kinetics of the thermal decompositionand the Special Found of Central Universities for Basic Scientific Re-8145:253-63.search Projects(No. 2011QNB061181 Dogan aM, Uysel BZ. Non-isothermal pyrolysis kinetics of three Turkish oil-References[20] Wang M. Yang H, He x. Chang L Effect of Fe-based minerals on pyrolysis[2] EI harn K,A. Ben Chanda M. Efect of water vapor on the pyrolysis of [211 Yan]. Cui H, Yang l, Liu Z Researchsis behavior of Yanzhou coal usingG/MS J China Univ Min Tectno[3I El harn K,C. Mokhlisse A, Ben Chanda M, Lemee L Joffre ]. et al [22] Li w. Tian F. u B. Analysis of preSupercritical nuid extraction of Moroccan(Timahdit) ail shale with water. Jcoal with plastics. J China Univ Min Technolby isothermal pyrolysis of the Moro