Chemical Looping Combustion of a Typical Lignite with a CaSO4

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Chemical looping combustion of a typical lignite with CaSO4-CuO mixed oxygen carrier Bao-wen Wang, Jun Li, Ning Ding, Daofeng Mei, Haibo Zhao, and Chuguang Zheng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02584 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on November 27, 2017

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Chemical looping combustion of a typical lignite with CaSO4CuO mixed oxygen carrier Baowen Wanga,d*, Jun Lia, Ning Dingb, Daofeng Meic, Haibo Zhaod, Chuguang Zhengd a

Technological Research Institute for Coal Clean and Efficient Utilization, College of Electric Power, North China University of Water Resources and Electric Power, Zhengzhou, 450045, China b Hebei Ji-Yan Energy Science and Technology Research Institute, Shijiazhuang, 050000,China c College of Engineering, Huazhong Agricultural University, Wuhan 430070, China d State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, 430074, China

Abstract: Calcium sulfate (CaSO4) has attracted a great attention as a potential oxygen carrier (OC) to be applied in the chemical looping combustion (CLC) due to its high oxygen transfer capacity, wide distribution and easy accessibility, but its low reactivity and sulfur emission from side reactions of CaSO4 should be well resolved. In this research, the CaSO4CuO mixed OC was prepared using the template method combined with the sol-gel combustion synthesis (SGCS). Its reaction characteristics with a selected lignite (designated as YN) was investigated and the greatly enhanced reactivity of this mixed OC was confirmed relative to the single CaSO4 and CuO. Meanwhile, the comprehensive heat effect showed the desired exothermic characteristics for this mixed OC reaction with YN when the mass ratio of CaSO4 to CuO was fixed as 6:4. Furthermore, morphological analysis indicated that the solid products from YN reaction with the CaSO4-CuO mixed OC were porous without discernible sintering, mainly because the CaSO4 included not only provided the lattice oxygen involved for oxidation of YN coal, but also acted as the temporary inert support to improve the resistance of the reduced Cu to sintering. Finally, gaseous and solid products formed were systematically investigated and clearly indicated that the gaseous sulfur species formed from the side reactions of CaSO4 were effectively fixed with solid Cu2S formation, as such the potential harms incurred could be eliminated. Overall, this preliminary research revealed the greatly enhanced reactivity of this mixed OC as well as its good fixation capacity for sulfur emitted from the side reaction of CaSO4, which are much desired in the real CLC system. Keywords: CO2 capture, chemical looping combustion, lignite, CaSO4-CuO mixed OC

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*Corresponding author. Tel/Fax: (86)371-69127630; E-mail: [email protected].

1. Introduction Chemical looping combustion (CLC) has gained increasing interest for its prominent advantages in efficient capture of CO2 without great penalty, realization of the energy cascade utilization and inhibition of the NOx formation [1], where oxygen carrier (OC) was circulated between the fuel reactor and the interconnected air reactor to sequentially transfer the oxygen from air to fuel and ensure the fuel combustion. After condensation of the steam involved, a high concentration of CO2 stream could be obtained for easy sequestration in the downstream, which is far different from the normal combustion of fuel by direct contact with air, thereby the undesired consequence of the CO2 stream diluted by N2 is avoided. Especially, direct use of coal as fuel in CLC is quite attractive, due to the rich reserve of coal, lower price relative to other gaseous fuels available and its wide utilization. OC is one of the pivotal points to be considered for economical operation of a CLC system. And different criteria for OC should be met in the CLC system [2], such as sufficient oxygen transfer capacity, satisfactory reactivity, high mechanical integrity, good resistance to sintering, low cost as well as environmental benignity. Although various transition metals based OC, especially Fe2O3, CuO based OC, have been extensively applied in CLC, enough attention should be paid to their relative higher cost and potential secondary pollution to the environment. As compared to these metal based OCs, CaSO4 has received great interest as OC in CLC for its superior oxygen transfer capacity (0.46), which is two times higher than all the metal-based OCs available [3]. In addition, CaSO4 is widely distributed as natural resource or produced in large amounts as industrial wastes from chemical, fertilizer, desulfurization process or wet phosphate production [4], but CaSO4 waste is difficult to deal with or store safely without deleterious effect to the environment. Therefore, it is desired to apply the CaSO4 waste as OC in CLC for its low cost, wide distribution and easy availability.


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Currently, although CaSO4 owns great advantages as a potential OC for CLC application, such two great challenges as low reactivity and gaseous sulfur emitted from different side reactions of CaSO4 such as R1, R2 and R3 listed below should be well resolved [5], CaSO4+CO(g)→CaO+CO2(g)+SO2(g)

(R1)

CaSO4+H2 (g) →CaO+H2O(g) +SO2 (g)

(R2)

CaS+ 3CaSO4→4CaO+4SO2 (g)

(R3)

These side reactions not only cause the decay of the oxygen capacity of CaSO4 OC and deteriorate its reactivity, but also emit a large amount of gaseous sulfur species, causing great deleterious harms to the environment. In order to promote the reactivity of CaSO4, decoration of CaSO4 with active transition metal oxides, especially Fe2O3, has been adopted and intensively investigated [5-8], where the reactivity of the CaSO4-Fe2O3 mixed OC with syngas and coal of different ranks was found to greatly enhance due to the synergistic effect of CaSO4 with the added Fe2O3. While for inhibiting the side reactions of CaSO4 and preventing the formed gaseous sulphur species, CaO-based absorbent was suggested to dope with the CaSO4 for desulfurization [9-11]. Nevertheless, relative to Fe2O3, higher reactivity of CuO and its exothermic characteristics during reaction with different fuels [12], especially coal, should be a great advantage when CaSO4 was decorated with CuO. Furthermore, among Fe2O3 and other transition metal oxides such as NiO, CuO and Mn3O4, the affinity capacity of CuO to sulphur was validated as the strongest and could effectively prevent the gaseous sulphur emission [13]. Therefore, decoration of CuO on the CaSO4 waste should be a good solution as OC in the CLC for simultaneous promotion of the reactivity of CaSO4 as well as inhibition of the gaseous sulphur emission. As to the fuel, lignite reserve in the World is most abundant and reaches four trillion tons, making up approximately 45% of the global coal reserve, while in China, the lignite coal reserve is estimated as 130.3 billion tons [14]. Even in Turkey and Greece, lignite provides


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more than 50% of the primary energy in the two countries [15]. In spite of the rich reserve of lignite, it is still regarded as a low-grade fuel with limited commercial utilization due to such disadvantages as high moisture content, low calorific value, strong spontaneous tendency and potential risk during transportation and storage [16]. Therefore, it would be meaningful to utilize lignite as fuel in the CLC process. In this research, CaSO4-CuO mixed OC was prepared and its reaction characteristics with a selected lignite (YN) as well as the evolved heat flow were systematically investigated using thermogravimetric (TGA) and differential thermal analysis (DTA). The gaseous species emitted from this mixed OC reaction with YN was in situ analyzed using Fourier transform infrared (FTIR), while the solid products formed were studied using field emission scanning electron microscopy (FSEM) coupled with the energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). In addition, thermodynamic simulation was conducted to fully learn the fate of different sulfur species during YN reaction with the CaSO4-CuO mixed OC. Overall, this preliminary investigation was beneficial to the full understanding on this CaSO4CuO mixed OC, which was meaningful for its use in CLC.

2. Experimental Procedures 2.1 Materials preparation Template synthesis method is widely applied to controllable preparation of various nanomaterials with the desired structural, morphological and dimensional characteristics [17, 18], while the sol-gel combustion synthesis (SGCS) method developed by our group [19] has been validated as facile and versatile to prepare different OCs of good reactivity and high resistance to sintering, including CuO-based [12], Fe2O3-based [19], combined CuFe2O4 [20], etc. In this research, based on the bottom-up synthesis strategy, the CaSO4-CuO mixed OC at the mass ratio of 6:4 was prepared using the template synthesis in combination with the


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SGCS, where CuO was prepared using the SGCS and mediated by CaSO4 acting as the substrate template during the preparation stage. The starting material CaSO4 was obtained from a Chinese natural anhydrite ore with its weight fraction determined over 95%, which was further pulverized with around 100 µm particles collected for use. The CuO precursor Cu(NO3)2.5H2O and urea of chemical reagent grade were purchased and used as received without extra purification. The basic procedures for synthesis of the CaSO4-CuO mixed OC were listed. Firstly, stoichiometric amount of the Cu(NO3)2.5H2O and urea were weighted with their molar ratio determined by the propellant chemistry theory [21]. And then, these two mixtures were fully dissolved in the deionized water with the molar ratio of copper nitrate to the deionized water kept as 7.5. As followed, a suitable amount of the sieved CaSO4 particles was introduced into the aqueous solution prepared above, uniformly stirred and aged under the air atmosphere at 75 oC until the viscous sol was formed. The wet sol was further sequentially dried at 80 oC and 135 oC. Subsequently, the dried gel formed was ignited in a preheated muffle at 600 oC for 15 min and further sintered at 950 oC under the air atmosphere for 2h. Finally, the asprepared CaSO4-CuO OC was ground and sieved with the particle sizes of the CaSO4-CuO within 63-106 µm collected for use. As to fuel, the lignite used in this research was obtained from Indonesia and designated as YN, which was dried around 105oC overnight and further processed. After grinding and sieving, the 63-106 µm of YN particles was collected for use. Its properties, including proximate, ultimate and ash analysis, were tested and provided in Table 1. As seen in the table, YN lignite contained high moisture and low heating value. Especially, both its ash and sulfur contents were quite low. And thus, in this research, the research focus could be mainly concentrated on the sulfur species emitted from the CaSO4 OC and not from the YN coal itself as we did before [22].


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Finally, after the preparation of CaSO4-CuO mixed OC and YN coal, stoichiometric amount of the prepared CaSO4-CuO OC with YN coal were evenly mixed in a laboratory mortar at the fixed mass ratio determined accorded to the mass balance method developed in our previous research [23]. 2.2 Experimental methods Reaction characteristics of the CaSO4-CuO mixed OC with YN coal was studied using the non-isotherm method in a synchronous thermal analyzer (STA 409 C, Netzsch Corp., Germany), where reaction behavior and the evolved heat flow were simultaneously evaluated. About 12 mg of the mixture between the CaSO4-CuO and YN coal at the fixed mass ratio as determined above was heated from ambient to 900 oC at 25 oC/min and then kept at this final temperature for 10 min for the sufficient conversion of coal. As to the reaction atmosphere for YN with the CaSO4-CuO mixed OC, though in the realistic coal-fuelled CLC process, reaction of coal with OC was initiated under the high concentration of CO2 and steam, in order to simplify the experimental process and avoid the potential interference from the introduced CO2 and steam, as many researchers did before [24-26], N2 of high purity was used in this experiment and its flow rate was determined as 80 ml/min to overcome the deleterious effect from heat and mass transfer and ensure the results reproducible. In addition, several reference experiments, including pyrolysis of YN under the pure N2 atmosphere and combustion by air as well as further reaction of YN with the single CuO and CaSO4 were conducted following the same experimental protocol designed above. 2.3 Characterization of the products of YN reaction with the CaSO4-CuO mixed OC After TGA research on the reaction characteristics of YN coal with the mixed CaSO4CuO, the gaseous products formed in the TGA furnace were simultaneously transferred to a FTIR spectrometer (EQUINOX 55, Bruker Corp., Germany) for further analysis.


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And then, the as-prepared CaSO4-CuO mixed OC and its solid reaction products with YN coal were carefully collected and analyzed as followed. After relevant sputter-coating of the samples with Au, their morphology and elemental compositions were analyzed using FESEM (Siron 200, FEI Company, Netherlands) coupled with an EDX (Genesis, EDAX, Inc.). Meanwhile, using the specially tailored sample die, the crystalline phases involved were further identified by XRD (X'Pert PRO, PANalytical Corp., Netherslands). 2.4 Thermodynamic investigation of YN reaction with the CaSO4-CuO mixed OC Finally, in order to fully understand the complex reaction of YN lignite with the CaSO4CuO mixed OC, including coal conversion, oxygen transfer from the mixed OC, migration of the gaseous sulfur species from CaSO4, further interaction between the solid reduced products of the mixed OC and the main minerals involved in YN, thermodynamic simulation of YN reaction with the mixed CaSO4-CuO was conducted as a supplement, though this method has the inherent deficiency without consideration of the realistic kinetic process [27]. Based on our previous similar simulation practices [20, 22, 28], according to the properties listed in Table 1 for YN lignite, a more complex reaction system for YN reaction with the CaSO4-CuO mixed OC was designed and more than 490 potential species were involved, where besides the CaSO4-CuO mixed OC and its possible reduced counterparts, the main organic structure of YN lignite with the C, H, N, S, O elements, various minerals present in YN and their intermediates with the reduced CaSO4-CuO were considered for a more realistic simulation.

3. Results and Discussion 3.1 Sample characterization Coal generally contains complex chemical structural units, which have close connection with its thermochemical reaction performances, such as carbonaization, combustion and gasification. Therefore, in this research, carbon chemical strucure of the original YN lignite


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was firstly studied by XRD analysis. As shown in Figure 1(a), a prominent and asymmetrical diffraction pattern within 10-50o was observed with a high background diffraction intensity, which implied that the original carbon structure of YN was greatly disordered and a significant fraction of amorphous carbon was involved [29]. Meanwhile, some graphite-like crystalline carbon also existed as well. In order to ascertain the carbon structural characteristics better, based on the curve-fitting method widely proposed [29, 30], as shown in Figure 1(b), the XRD profile of the original YN within 10-50o was background-subtracted and resolved into three Gaussian peaks with their diffraction characteristic bands (002), γ and (10) residing around 20o, 26o and 42o, respectively. The strong (002) band was correlated to the stacking of aromatic layers [31], while broad γ band was ascribed to the saturated carbon structure such as the long aliphatic chains between the coal crystallites [32]. As to the (10) band around 42o, it was very weak and nearly not discernible, which corresponded to the extension of the aromatic molecules in the plane of the layer [33]. Furthermore, to quantitatively evaluate the chemical stability of YN during its transformation, aromaticity (fa) of YN was calculated using the equation as followed [34], fa=Car/(Car+Cal)=A002/(A002+Aγ), where the integrated area for carbon atoms present in the aromatic rings (Car) was divided by the sum of the integrated area in the aliphatic side chains (Cal) and that of Car. And A002, Aγ were referred to the integrated areas of the fitted (002) and γ band, respectively. According to the fitted (002) and γ bands shown in Figure 1(b), the aromaticity of YN lignite was determined as 0.533, though close to that of a Turkish lignite Yatagan-Tinaz (0.536) [30], the chemical structure of YN was quite distinct, which would be further studied below. As to minerals in YN, their contents were also quite low as inferred by the ash content of YN in Table 1. Only quartz (SiO2) at its characteristic band around 26.6o was clearly manifested and shown in Figure 1(a)-(b), but kaolinite was not found even at its most intense band around 12.4o, mainly due to its low content or good dispersion in YN in an amorphous state,


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though kaolinite was generally considered as the most abundant clay mineral and widely distributed in coal [35]. During reaction with coal in CLC, the crystalline, morphological and structural characteristics of the prepared CaSO4-CuO mixed OC were important for its oxygen transfer and further reaction with coal. And thus, the crystalline phases invovled in the as-prepared CaSO4-CuO OC were identified via XRD. As shown in Figure 2(a), the reference CuO prepared from the SGCS method was well developed with separate CuO grains formed, while from the diffraction pattern of the CaSO4 ore shown in Figure 2(b), besides the desired CaSO4, some impurities such as CaCO3 and SiO2 were found to exist due to their good association with the natural gypsum [36]. Relative to these two reference components, as shown in Figure 2(c), the prepared CaSO4-CuO mixed OC mainly consisted of CaSO4 and CuO. Meanwhile, due to the hygroscopicity of anhydrite (CaSO4) [37], traces of the hydrated CaSO4, such as CaSO4.2H2O and CaSO4.0.5H2O, were existent either in the CaSO4 ore or the prepared CaSO4-CuO mixed OC. Furthermore, based on the major XRD reflections of the CuO, CaSO4 and their mixed ones shown in Figure 2(a)-(c), their average crystallite sizes were calculated by the general Scherrer’s equation [38] and presented in Table 2. And the crystallite sizes of CaSO4 either in the CaSO4 ore or the mixed CaSO4-CuO OC were stabilized around 80 nm, while the crystallite size of CuO formed from the mixed CaSO4CuO was only 59.2 nm, nearly half that of the reference SGCS-made CuO (~107.3 nm), mainly due to the steric confinement effect from the underlying CaSO4 [39], which prevented the overgrowth of the CuO grains. Meanwhile, the morphological characteristics of the mixed CaSO4-CuO and its two reference components were studied. From Figure 3(a), the reference CuO prepared using SGCS was found to melt and form micron-scaled aggregates due to its inferior resistance to sintering, while the CaSO4 ore shown in Figure 3(b) was observed as impervious and smooth


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except for several big cavities around the micron scale. But for the CaSO4-CuO mixed OC, from Figure 3(c), the nanosized CuO grains were noticed to densely adhere on the outside surface of the underlying CaSO4 substrate and to form the core-shell structure with CaSO4 encapsulated by CuO grains. Because the CaSO4 substrate effectively inhibited the growth of the CuO grains and avoided their further coalescence, the structural parameters of the mixed CaSO4-CuO presented in Table 2 were far different from the two reference components with the largest specific surface area, total pore volume whilest the smallest pore size, which was advantageous to reaction of the mixed OC with coal, as further studied below. 3.2 Reaction characteristics of YN coal with CaSO4-CuO OC Reaction characteristics of YN lignite with CaSO4-CuO OC, including their reaction behavior and evolution of the heat flow, were important for evaluation of its reaction peculiarity and further application in a realistic CLC system. And thus, the reaction characteristics of the prepared CaSO4-CuO OC with YN were investigated as followed. 3.2.1 TGA investigation of the reaction behavior of YN with CaSO4-CuO mixed OC In order to learn the reaction behavior of YN lignite better, the two reference reactions for pyrolysis of YN under the pure N2 atmosphere and combustion in the air stream were firstly conducted in the TGA. And then, TGA investigation of YN coal reaction with the mixed CaSO4-CuO OC at the stoichiometric amount was further performed. Both the weight loss (TG) and the differential weight loss rate (DTG) for pyrolysis, combustion of YN coal and its further reaction with the CaSO4-CuO mixed OC and the two reference oxides are presented in Figure 4 and Figure 5, respectively. Firstly, as shown in Figure 4, without CaSO4-CuO OC added, the reference thermal reactions of YN lignite, including its pyrolysis under the N2 atmosphere and combustion by air, were conducted. As to the pyrolysis of YN lignite, after dehydration below 200oC, only one discernible reaction stage was observed with the peak temperature centering at 443.2 oC.


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Nearly 35% of the volatile matter was emitted through various competitive and parallel reactions and the maximal weight loss rate reached 0.4941 wt%/min. Accompanied by the volatiles emitted, complex variation in the chemical structure of YN lignite occurred, which were deeply analyzed using the curve-fitting method applied by Shi, et al.[40] and Li, et al.[41]. The DTG profile of YN pyrolysis under the N2 atmosphere shown in Figure 4(b) was fitted into six reaction regions between 30 oC and the final 900 oC. According to the direct relationship between the peak temperature of the fitted sub-curves and the energies involved for cleavage of the bonds [40], evolution of the different functional groups involved in these six regions were illuminated. The region one at the peak temperature 95.7 oC was ascribed to removal of the absorbed water [42], and then the region two was mainly assigned to disintegration of the weak bonds such as Cal-O [43], but the peak temperature was shifted to 288.0 oC, a little lower than other reports [40] and our previous research [44], mainly due to the different coal rank and chemical structure of YN as analyzed above. And then, the four fitting regions left were sequentially assigned to cleavage of the relatively strong Cal-Cal/CalH bonds at 432.0 oC and strong Car-Cal/Car-O bonds at 594.1 oC, decomposition of carbonates at 686.3 oC and then slow condensation of the aromatic rings in YN coal at 787.2 oC [43, 45]. And among these six fitted regions for pyrolysis of YN, cleavage of Cal-Cal/Cal-H bonds at the region three was identified as the largest contributor. In addition, even when the pyrolysis temperature was increased to 900 oC and extended for another 10 min, the pyrolysis of YN was not completed with nearly 8% of the gaseous products emitted through reorganization of the main carbon matrix of YN coal. But for YN coal combustion in air, from Figure 4(b), similar to pyrolysis of YN coal, only one discernible reaction stage was identified but the maximal weight loss rate reached up to 2 wt%/min at the peak temperature 285.1 oC. After full combustion, the residual ash of YN left was 4.6 wt%, completely consistent with the ash content presented in Table 1.


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But far different from pyrolysis and combustion of YN alone, when the mixed CaSO4CuO and its two reference components were added, the reaction behavior of YN changed greatly. From Figure 5(a) for YN reaction with the reference CuO, two reaction stages were presented after dehydration and the peak temperatures resided at 436.1 oC and 808.2 oC, respectively, which was far different from pyrolysis of YN alone shown in Figure 4(b). Meanwhile, the maximal weight loss rate at the second reaction stage reached 0.1649 wt%/min, higher than that at the first reaction stage, indicating that more residual char reacted with CuO at the second stage, which was attributed to the beneficial effect from the higher temperature [46] and direct reaction of the CuO with the residual char by close contact [47]. Of course, serious sintering of CuO and its reduced counterpart should be well considered. As to the reaction of YN with the reference CaSO4, as shown in Figure 5(b), four reaction stages occurred with their respective peak temperatures discerned as 280.0, 450.7, 716.8 and 897.4 oC, respectively. Among the four reaction stages, the first stage at 280.0 oC presented a sharp mass loss rate and was mainly attributed to the loss of the adsorbed water of CaSO4 [48], as observed in Figure 2(a) above by XRD analysis. And the second peak at 450.7 oC was mainly ascribed to pyrolysis of YN coal alone, which clearly indicated the lower reactivity of CaSO4 than that of CuO. As followed, reductive decomposition of CaSO4 with YN started at the sequential peak temperatures around 716.8 and 897.4 oC, which were higher than the reported temperature values by Yani and Zhang for an Australian lignite with CaSO4 [49], but lower than the value reported by Zheng et al.[50] for reductive decomposition of the gypsum as obtained from the desulfurization process by anthracite, mainly due to the differences in the coal and CaSO4 samples, their mixing mode and the reaction conditions. Yet for reaction of YN with the mixed CaSO4-CuO OC, as shown in Figure 5(d), three more complex reaction stages were observed over 200oC. According to the analysis above for


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YN reaction with the reference CuO and CaSO4, the first reaction stage was ascribed to YN reaction with the CuO in the mixed OC, but the the peak temperature 415.0oC was lower than that of YN reaction with the reference CuO, mainly due to the higher reactivity of the CuO involved in the CaSO4-CuO mixed OC as analyzed above. Subsequently, the second reaction stage corresponded to reductive decomposition of CaSO4 by YN coal, which also implied that the CuO involved in the mixed OC was preferentially reduced by YN than that of CaSO4 due to its higher reactivity. But as compared to that of YN with the reference CaSO4 shown in Figure 4(c), the peak temperature of the mixed OC at the second stage was shifted to the lower temperature 710.0 oC, mainly due to the beneficial catalytic effect of the elemental Cu as obtained from the first reaction stage for YN with CuO [51]. Furthermore, at the third reaction stage for YN with the CaSO4-CuO mixed OC, the reaction peak temperature was moved to 875.0 oC, lower than that of YN reaction with the reference CaSO4 as 897.4 oC. But the weight loss rate was found to greatly increase to 0.5843 wt%/min, more than one times and a half higher than that of YN with the reference CaSO4 and nearly four times higher than that of YN with the reference CuO. To our best knowledge, such a high reaction rate for this case is first reported and the inherent reason was worthwhile to be followed up. At the third reaction stage around 875.0 oC for YN reaction with the CaSO4-CuO OC, the reduced Cu should be in a melting state due to its low Tamann temperature as 405 oC [52], while both the CaSO4 and the reduced CaS at their interface were kept in an eutectic state as well [53], which was advantageous for the melting Cu to migrate and fully contact with the eutectic CaSO4 at the reaction interface. And then, similar to oxidation of Fe by CaSO4 proposed by others [5, 51, 54], further oxidation of the accessed Cu by the eutectic CaSO4 was initiated, 4Cu+CaSO4→4CuO+CaS Moreover, the formed CuO would directly decompose to emit O2 as listed below,


(R4)

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4CuO→2Cu2O+O2(g)

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(R5)

And the generated O2 would accelerate combustion of the YN residual char left as shown in R6, similar to the reaction of coal char with CuO in the oxygen uncoupling process [55]. C+O2(g)→CO2(g)

(R6)

In addition, besides the oxygen uncoupling effect as illuminated above, the beneficial catalytic effect from the reduced Cu to the water-gas shift reaction (CO+H2O→CO2+H2) [56] and activation of the intractable C-C/C-H groups involved in the residual char of YN [57] should be considered as well. Overall, all these factors together contributed to so high a weight loss rate for YN reaction with the mixed CaSO4-CuO, and thus the enhanced reactivity of this mixed OC was realized. Of course, if the mixed CaSO4-CuO was applied to the CLC as OC, the melting state of Cu and the eutectic CaSO4-CaS coexistence at the reaction interface might cause such concerns as the partial agglomeration of the bed inventory and malfunction of the good fluidization. But the previous research experiences on the CaSO4 decorated by Fe2O3 [6, 7], K2CO3 [58] and even the ternary eutectic salts of Li2CO3, Na2CO3 and K2CO3 [59] in the labscaled fluidized bed reactor indicated both good fluidization and stable redox cycles, though serious surface sintering and agglomeration occurred. Therefore, the CaSO4-CuO developed in this research was reasonably inferred to own the good application potential to the realistic CLC system, though further evaluation in a more realistic CLC system was needed. Meanwhile, another two advantages of the CaSO4-CuO mixed OC were reached, including the high oxygen transfer capacity and prominent reactivity as desired, which would mean a fewer bed inventory and lower transfer rate in CLC. 3.2.2 Evaluation of the heat effect of the YN coal reaction with CaSO4-CuO mixed OC Heat balance between the two connected reactors in CLC is of great importance to determine the relevant OC transfer rate as well as to sustain the desired fuel reactor


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temperature for sufficient conversion of coal. Therefore, evolution of the heat flow during YN reaction with the CaSO4-CuO mixed OC was further investigated using DTA analysis and shown in Figure 6. Meanwhile, heat effect from both pyrolysis of YN alone and its reactions with the two reference CuO and CaSO4 were also included for comparison. From Figure 6(a) for pyrolysis of YN under the N2 atmosphere, it could be observed that there were two broad endothermic peaks with their two peak temperatures centering at 119.0 o

C and 592.6 oC, similar to the observation of Ceylan, et al. [60], which were related to

dehydration and further primary pyrolysis of YN through dissociation of various bonds with volatiles emitted. As followed, a broad but shallow exothermic peak occurred, which resulted from the cleavage and reorganization of the residual carbon matrix of YN at its final pyrolysis stage [61]. But for YN reaction with CuO, as shown in Figure 6(b), after the endothermic area for removal of the adsorbed water below 200 oC, there existed one much broad exothermic peak, mainly attributed to reaction of CuO with the volatiles of YN pyrolysis at the primary stage and further reaction with the residual char left, which clearly manifested the exothermic characteristics of CuO with coal [24]. As to YN reaction with the reference CaSO4, from Figure 6(c), after the first sharp endothermic peak from the removal of the adsorbed water at the characteristic temperature 208.2 oC, on the basis of the pyrolysis behavior of YN with CaSO4 shown in Figure 5(c) above, the narrow and small endothermic peak centering at 432.4 oC was ascertained to the pyrolysis of YN alone. And then, another prominent and broad endothermic peak for YN with CaSO4 was observed, indicating the overall net endothermic effect for YN with CaSO4 with various competing reactions involved, including CaSO4 reaction with some volatiles of YN, further with the YN residual carbon as well as various side reactions of CaSO4 (e.g. R1-R3) [8]. Finally, in order to regulate the overall endothermic characteristics of YN with CaSO4 and keep the heat balance of CaSO4 OC reaction with coal in the fuel reactor, some CuO was


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introduced to the CaSO4 to form the CaSO4-CuO mixed OC and the heat behavior of this mixed OC reaction with YN was further studied. As presented in Figure 6(d), after the first endothermic peak below 200 oC, a small but discernible exothermic peak at the characteristic temperature 427.1 oC was formed from the CuO reaction with YN. Hereafter, accompanied by the combined reaction of YN with the formed CuO via R4-R6 and CaSO4, another broad and shallow exothermic peak was developed, which meant that the heat released from YN reaction with the formed CuO was enough to offset the heat needed for YN reaction with CaSO4. As such, the overall exothermic effect for the mixed CaSO4-CuO with YN was reached, which was advantageous to keep the heat balance in a realistic CLC system and sustain the fuel reactor temperature for good conversion of coal. 3.3 FTIR analysis of the gaseous products for YN reaction with CaSO4-CuO OC After TGA investigation of the reaction behavior of YN with the CaSO4-CuO mixed OC, the gaseous products evolved from both pyrolysis of YN alone and its reaction with the mixed OC were further studied by FTIR, as presented in Figure 7(a) and (b), respectively. Firstly, as a reference, gaseous products evolved from pyrolysis of YN under the N2 were analyzed. From Figure 7(a), besides the formed H2O, the main gaseous products for YN pyrolysis were identified as CO2, CO, SO2 and some hydrocarbon gases. Among the identified gases, CO2 occurred between 200-800oC with double peaks of the IR spectra. The former CO2 peak at the relatively low temperature around 210 oC mainly resulted from the carboxylic groups in the YN coal, while the latter peak at the high temperature around 549 oC was derived from carboxylic acid salt, esters or lactones at the different energetic sites [44]. Especially for the CO2 at the higher temperature, the CO2 yield increased with the pyrolysis temperature until the related oxygen-bearing heterocyclic groups with great thermal stability were fully consumed [28]. As followed with CO2, a little SO2 was emitted around the characteristic temperature 345 oC, which mainly resulted from decomposition of the iron


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sulfate [62] or organic sulfones present in the YN coal [63]. And then, some light hydrocarbons at the absorbance region of 2850-3200 cm-1 were observed with CH4 dominated around 480 oC, which was mainly formed from the scission of the methyl groups in YN coal [64]. After 435 oC, CO began to form due to the secondary cracking of the tars formed during pyrolysis of YN [65]. But above 700 oC, the CO formed was mainly from disintegration of the phenolic oxygen groups or cracking of various ether groups [66]. In addition, though H2 was reported to produce by cleavage and reorganization of the main carbon matrix at high temperature during coal pyrolysis, it was not found in this gaseous FTIR analysis due to the IR limitation [67]. But after reaction of YN with the CaSO4-CuO mixed OC, the main gaseous product identified was CO2 and steam, which resulted from the sufficient reaction of YN coal with CaSO4-CuO. As observed from Figure 7(b), the double-peak CO2 profile was formed from YN sequential reaction with CuO and CaSO4 at the different stages as discussed above. It should be noted that the SO2 formed from the side reactions of CaSO4 as listed above in R1R3 was not found, which was ascribed to complete fixation of the formed SO2 by CuO as analyzed in more detail below. 3.4 FESEM-EDX and XRD analysis of the solid products of YN with CaSO4-CuO OC After TGA-FTIR investigation of YN reaction with the mixed CaSO4-CuO OC, in order to gain a more comprehensive knowledge of the prepared CaSO4-CuO mixed OC and further discern the migration and transformation of the sulfur species evolved from CaSO4 during its reaction with YN, the morphological variations of the solid residues for pyrolysis of YN under the N2 atmosphere and its further reaction with the mixed CaSO4-CuO were characterized using FESEM and shown in Figure 8(a)-(d). Meanwhile, the elemental compositions distributed in the related solid residues were further analyzed using EDX


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coupled with the FESEM and listed in Table 3. Furthermore, crystalline phases involved were identified using XRD and presented in Figure 9. Firstly, as reference, from Figure 8(a) for the pyrolysis of YN under the pure N2 atmosphere, it could be observed that the solid residue left after YN pyrolysis was quite porous due to emission of voluminous gaseous products. Therefore, only one point was optionally selected on the surface of the solid residue from YN pyrolysis for elemental analysis. As shown in Table 3, after pyrolysis of YN, the atomic fraction of the C was dominated as 67.39%. Meanwhile, the main elemental compositions left were related to various Si, Al and Fe based minerals, which were identified in Figure 9(a) as quartz (SiO2), iron sulfide (FeS) and other aluminum silicates such as silimanite (Al2SiO5), gehlenite (Ca2Al2SiO7), etc. But after reaction of YN with the reference oxides CuO and CaSO4, their morphologies changed greatly. As shown in Figure 8(b) for YN reaction with CuO, due to the inferior resistance to sintering for the reduced elemental Cu, serious melting and agglomeration of the reduced Cu crystallines occurred with a little macropores larger than 1µm formed. According to the EDX analysis of the solid products for YN reaction with CuO in Table 3, the Cu atomic fractions on the point 1 and point 2 of the solid residue of YN with CuO were a little diverged as 77.22% and 82.73%, mainly due to the preferential mobility of the reduced Cu to the outside [20]. Although the oxygen involved in CuO were nearly completely consumed, the C present in YN was not completely converted with its residual contents left reaching 13.43% and 21.02% on the point 1 and point 2, due to the serious deterioration of the reactivity for single CuO without inert supports. While for YN with the reference CaSO4, after their reaction, it was observed that the YN coal and CaSO4 could not be fully contacted except for the outside interfaces. Relative to the appearance of the original CaSO4 ore presented in Figure 3(b) above, the reduced CaSO4


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shown in Figure 8(b) was plate-like and still impervious with some channels left on its surface. According to the EDX analysis presented in Table 3, the residual C left on the different selected points changed greatly from 22.46, 44.65 to even 70.45%, which indicated that full conversion of YN was not reached mainly due to the lower reactivity of CaSO4 as well as the insufficient contact of the YN with CaSO4. Meanwhile, the Ca atomic concentrations on the three selected points diverged greatly from 11.99, 23.08 to 30.00%, but the S concentrations were kept as 10.85, 20.39 and 27.37%, lower than those Ca concentrations on the related points, which was ascribed to the significant effect from the side reactions of CaSO4 with gaseous SO2 emitted via R1-R3 mentioned above. Furthermore, based on the research above for pyrolysis of YN and its reaction with the two reference oxides CuO and CaSO4, YN reaction with the mixed CaSO4-CuO was studied. As shown in Figure 8(d), the solid surface morphology of YN with the CaSO4-CuO was quite different. Because the firstly reduced Cu grains with low melting point (~1085oC) were distributed among the CaSO4 grains with higher melting point(~1460oC), where CaSO4 not only acted as the temporary inert support of the reduced Cu grains to prevent their further agglomeration, but also was applied as OC to further react with YN coal. As such, less sintering occurred for the mixed OC. And the formed pores changed greatly with most pore sizes lower than 1µm. The reduced product grains were evenly distributed with their sizes lower than 10 µm. Meanwhile, direct combustion of the YN residual char was initiated by the O2 emitted from the formed CuO via R4-R6 as discussed above. Therefore, from Table 3, after reaction of YN with the mixed CaSO4-CuO, the contents of the residual C left were much lower than those from YN reaction with either CuO or CaSO4, which further verified the higher reactivity of this mixed OC. As to the reduced CaSO4-CuO, after its reaction with YN, from Table 3, it could be observed that especially for Cu, it was evenly distributed at the different points with their atomic fractions around 28%, but the S distribution was far


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heterogeneous with its fractions on the point 1 and point 2 around 18.83% and 30.77%. And the reduced counterparts of the CaSO4 in the CaSO4-CuO mixed OC was identified in Figure 9(b) mainly as CaS along with CaO formed from the side solid product of the CaSO4 and other derivatives such as Ca(OH)2, while the reduced counterparts of the CuO in the mixed OC were converted to CuS, Cu2S and a little of its deeply reduced product Cu1.8S, instead of Cu2O or the elemental Cu as shown in our previous research [12]. The reaction pathways of these copper sulfides formed were quite complex and illuminated as followed. One pathway for CuS presented in Figure 9(b) is formed through trapping the SO2 by CuO to form CuSO4 as shown in R7 and further reduced by H2 via R8 below. As iterated above, the side reactions of CaSO4 were prone to emit a large amount of SO2, which could be easily captured by the formed CuO (as shown in R4 above through oxidation of Cu by CaSO4) to form CuSO4, especially in the presence of the O2 generated via R5, similar to the flue gas desulfurization using the CuO adsorbent [68]. CuO+SO2(g)+1/2O2(g)→CuSO4

(R7)

And the formed CuSO4 would be further reduced by H2 to CuS [69]. CuSO4+4H2(g)→CuS+4H2O(g)

(R8)

Another pathway was proposed for the formed Cu2S and Cu1.8S. The SO2 formed from the side reactions of CaSO4 in R1-R3 was firstly reacted with H2 to form H2S via R9 below [70]. SO2(g)+3H2(g)→H2S(g)+2H2O(g)

(R9)

And then, the generated H2S in R9 would be favorably fixed by the Cu2O left through R5 to form Cu2S, as listed in R10 below. And part of the formed Cu2S could be further reduced to Cu1.8S in the reducing atmosphere. Cu2O+H2S(g)→ Cu2S+H2O(g)

(R10)

Of course, good regeneration of the reduced OC is also a basic criterion for OC in CLC. Therefore, the reduced CaSO4-CuO mixed OC by YN was further oxidized. As shown in


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Figure 9(c) by XRD analysis, the reduced CaSO4-CuO was found to be nearly completely regenerated to its original state except for the formed Ca2CuO3, which was also found by Kierzkowsak and Müller [71] in the calcium looping process using CaO-CuO mixed sorbent, where the formed Ca2CuO3 was verified feasible for CO2 sorption in the carbonation process, though its reactivity to coal should be subjected to further research in the future. In addition, distribution and transformation of the minerals present in YN should be noted. The CaO formed from the side reactions of CaSO4 was found to influence the mineral compounds greatly. As shown in Figure 9(b), during the reduction stage for the mixed CaSO4-CuO with YN, the CaO formed was found to interact with aluminum silicates present in YN to mainly form tricalcium silicate (Ca3SiO5) and anorthite (CaAl2Si2O8). But during the oxidation stage, as shown in Figure 9(c), if the mineralogical intermediates formed at the reduction stage were not effectively separated, they would further interact with CaO to form grossular (Ca3Al2(SiO4)3) [72]. And the potential effects from these mineralogical intermediates on the operation of the CLC system should be also considered in the future. Overall, through analysis of the gas and solid sulfur species of the mixed CaSO4-CuO with YN by gaseous FTIR, EDX and XRD, it fully indicated that the gaseous sulfur emitted from side reaction of CaSO4 could be effectively trapped by CuO to form different solid sulfides. And thus, the potential harms from the emitted SO2 could be avoided. 3.5 Thermodynamic investigation of the CaSO4-CuO mixed OC reaction with YN Finally, in order to gain a comprehensive understanding on the conversion of YN lignite, oxygen transfer of the mixed CaSO4-CuO OC, transformation of the possible sulfur species and distribution of the main minerals, thermodynamic simulation of the CaSO4-CuO reaction with YN was conducted. According the calculated results, various equilibrium species of interest are presented in Figure 10.


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From Figure 10(a) for conversion of the YN coal, with the reaction temperature increase, the main carbon structure of YN was oxidized by the mixed CaSO4-CuO OC and gradually disintegrated. As a consequence, the main gaseous product CO2 was generated as desired, with its yield rapidly increased from 16% at 100 oC to the maximal value 91.6% at 500 oC. And then, due to the side reaction of CaSO4 to form CaO as shown in R1-R3 above, a gradual decrease of CO2 occurred. Correspondingly, full conversion of YN was not realized with the unburned CO appearing, as also observed from the gaseous FTIR spectra in Figure 7(b) above. And the fraction of CO slowly increased from 11.9% at 600 oC to 20.5% at 1100oC. Meanwhile, accompanied by the reaction of YN with the mixed CaSO4-CuO, as shown in Figure 10(b), H2O was found to form with its fraction over 74% throughout the whole reaction stage. Besides the dominated H2O, H2 was also formed with its fraction increased to 26.4% at 600 oC. But then, the fraction of H2 was found to decrease mainly due to partial consumption of the formed H2 in the transformation and fixation of the SO2 formed from the side reaction of CaSO4, as shown in R8 and R9 above. And then, from Figure 10(c)-(e) for the CaSO4-CuO mixed OC, reduction of the mixed OC was initiated by YN coal with the increase in the reaction temperature. As shown in Figure 10(c), the CuO included in the CaSO4-CuO mixed OC was completely converted. At the low temperature below 700 oC, CuO was reduced to Cu and partially oxidized by CaSO4 to form CuO in R4, which was further converted to CuS and Cu2S via reduction of the formed CuSO4 by H2 in R8 and reaction of the formed Cu2O with H2S in R10. Whilst over 700 oC, CuO was wholly converted to Cu2S. As to Cu1.8S, though shown in Figure 9(b) by XRD analysis, it was not included in this simulation due to the limited material library of the commercial software used. But for the CaSO4 involved in the mixed OC, as shown in Figure 10(d), it could be observed that the CaSO4 was gradually reduced by the gaseous products of YN to form CaS as desired. In addition, a large amount of CaO was formed through various


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side reactions of CaSO4 as shown in R1-R3, which brought about great harmful effects. Besides the deterioration of the reactivity of the CaSO4, it also interacted with the silicates. As shown in Figure 10(e), the Ca-based silicate minerals varied greatly and the dominated Ca-based silicates were identified as Ca3SiO5, Ca2Al2SiO7 and Ca3Al2Si3O12, far different from the mineralogical silicates formed from pyrolysis of YN in Figure 9(a) by XRD analysis. And the potential effect from these Ca-based silicates on the operation of the CLC system was needed to evaluate in the future. Finally, SO2 emitted from the side reaction of CaSO4 was a great concern in CLC. Therefore, evolution and distribution of various sulfur species during the CaSO4-CuO mixed OC reaction with YN was studied. From Figure 10(f), at the main reaction temperature of interest in CLC around 800-1000oC, it could be found that the main solid sulfur compounds were only CaS and Cu2S with their total yield over 99.8%, which clearly indicated the gaseous SO2 formed from side reactions of CaSO4 was effectively captured and fixed as expected. Correspondingly, the possible harms of the gaseous SO2 evolved from the side reactions of CaSO4, such as the detrimental effect on the purity of the separated CO2 as well as the potential corrosions to the pipeline for CO2 transformation [73], could be avoided. As to the formed solid sulfur compounds of Cu2S and CaS, they could be easily separated and regenerated downstream through such measure as the post oxygen polishing, as introduced in more detail in our granted patent [74]. And the SO2 of high concentration formed through oxygen polishing could be conveniently recovered for other industrial process, such as sulfuric acid production [75].

4. Conclusions CaSO4-CuO mixed OC was prepared using the combined method by the template synthesis and SGCS. Reaction characteristics of the prepared CaSO4-CuO mixed OC and heat flow evolution during its reaction with a typical lignite were evaluated. Meanwhile, both


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the gaseous products evolved and the solid products formed were systematically investigated. And the relevant conclusions were reached as followed. (1) TGA investigation of YN reaction with the CaSO4-CuO mixed OC verified the enhanced reactivity of this mixed OC relative to its two reference compoents due to the beneficial synergistic effect of CaSO4 decorated by CuO. (2) DTA analysis of the heat flow evolved from YN reaction with the CaSO4-CuO mixed OC indicated that the overall exothermic effect of this mixed OC, which was beneficial to sustain the reactor temperature and further operation of the CLC system. (3) SEM analysis of the morphological variation for the solid products of YN reaction with the mixed CaSO4-CuO showed that the CaSO4 grains included not only provided the lattice oxygen for coal oxidation, but also acted as the temporary inert support to improve the resistance of Cu to sintering. (4) Finally, both gaseous FTIR analysis and the solid products characterization revealed that the gaseous sulfur species emitted from the side reaction of CaSO4 were effectively fixed and thus the possible sulfur harms could be inhibited. Acknowledgements This work is supported by the National Natural Science Foundation of China (Nos. 51776073, 51276210), Key R&D program of Henan Province (Nos.162102210233, 142100210459), Innovative Research Team in S&T in University of Henan Province (No.16IRTSTHN017), North China University of Water Resources and Electric Power (No.70481). References: (1)

(2) (3)

Adanez, J.; Abad,A.; Garcia-Labiano,F.; Gayan,P.; de Diego,L.F. Progress in chemical-looping combustion and reforming technologies Prog. Energy Combust. Sci. 2012, 38 (2), 215-282. Tang, M.C.; Xu,L.; Fan,M.H. Progress in oxygen carrier development of methanebased chemical-looping reforming: A review. Appl. Energy 2015, 151, 143-156. Wang, B.W.; Yan,R.; Zheng,Y.; Zhao,H.B.; Zheng,C.G. Simulated investigation of chemcial looping combustion with coal-derived syngas and CaSO4 oxygen carrier. J.Fuel Chem.Technol., 2011, 39 (4), 1-7.


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Page 25 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13) (14) (15) (16)

(17) (18) (19)

(20)

(21)

Jeong, E.H.; Nam,C.W.; Park,K.H.; Park,J.H. Sulfurization of Fe-Ni-Cu-Co alloy to matte phase by carbothermic reduction of calcium sulphate. Metall. Mater. Trans. B 2016, 47 (12), 1103-1112. Zhang, S.; Xiao,R.; Liu,J.; Bhattacharya,S. Performance of Fe2O3/CaSO4 composite oxygen carrier on inhibition of sulfur release in calcium-based chemical looping combustion. Int. J. Greenhouse Gas Control 2013, 17, 1-12. Ding, N.; Zhang,C.W.; Luo,C.; Zheng,Y.; Liu,Z.G. Effect of hematite addition to CaSO4 oxygen carrier in chemical looping combustion of coal char. RSC Adv. 2015, 5 (69), 56362-56376. Song, T.;Zheng,M.; Shen,L.H.; Zhang,T.;Niu,X.; Xiao,J. Mechanism investigation of enhancing reaction performance with CaSO4/Fe2O3 oxygen carrier in chemicallooping combustion of coal. Ind. Eng. Chem. Res.2013, 52 (11), 4059-4071. Zheng, M., Shen,L.H., Feng,X.Q. In situ gasification chemical looping combustion of a coal using the binary oxygen carrier natural anhydrite ore and natural iron ore. Energy Convers. Manage.2014, 83, 270-283. Zhang, S.; Xiao,R.; Yang,Y.C.; Chen,L.Y. CO2 capture and desulfurization in chemical looping combustion of coal with a CaSO4 oxygen carrier. Chem. Eng. Technol. 2013, 36 (9), 1469-1478. Guo, Q.J.; Hu,X.D.;Liu,Y.Z.; Jia,W.H.; Yang,M.M.;Wu,M.; Tian,H.J.; Ryu,H.-J. Coal chemical-looping gasification of Ca-based oxygen carriers decorated by CaO Powder Technol. 2015, 275, 60-68. Abad, A.; Obras-Loscertales,M.de las; García-Labiano,F.; de Diego,L.F.; Gayán,P.; Adánez,J. In situ gasification Chemical-Looping Combustion of coal using limestone as oxygen carrier precursor and sulphur sorbent. Chem. Eng. J. 2017, 310 (part 1), 226-239. Wang, B.W.; Zhao,H.B.; Zheng,Y.;Liu,Z.H.; Yan,R.; Zheng,C.G. Chemical looping combustion of a Chinese anthracite with Fe2O3-based and CuO-based oxygen carriers. Fuel Process. Technol. 2012, 96, 104-115. Solune, R.D.; Veser,G. Integrating desulfurization with CO2 capture in chemicallooping combustion. Fuel 2011, 90 (2), 608-617. Wang, Q.S.; Liu,W.; Yuan,X.Li.; Zheng,X.N.; Zuo,J. Future of lignite resources: a life cycle analysis. Environ. Sci. Pollut. Res., 2016, 23 (24), 24796-24807. Mengaki, A.N.; Gurluk,S. Greece&Turkey: assessment and comparison of their renewable energy performance. Int. J. Energy Econ. Policy 2013, 3 (4), 367-383. Liu, P.; Zhang,D.X.; Wang,L.L.; Zhou,Y.; Pan,T.Y.; Lu,X.L. The structure and pyrolysis product distribution of lignite from different sedimentary environment. Appl. Energy 2016, 163, 254-262. Huczko, A. Template-based synthesis of nanomaterials. Appl. Phys. A-Mater. Sci.Process. 2000, 70 (4), 365-376. Hulteen, J.C.; Martin,C.R. A general template-based method for the preparation of nanomaterials. J. Mater. Chem. 1997, 7 (7), 1075-1087. Wang, B.W.; Yan,R.; Lee,D.H.;Zheng,Y.; Zhao,H.B.; Zheng,C.G. Characterization and evaluation of Fe2O3/Al2O3 oxygen carrier prepared by sol-gel combustion synthesis. J. Anal. Appl. Pyrolysis 2011, 91 (1), 105-113. Wang, B.W.; Zhao,H.B.; Zheng,Y.; Liu,Z.H.; Zheng,C.G. Chemical looping combustion of petroleum coke with CuFe2O4 combined oxygen carrier. Chem. Eng. Technol. 2013, 36 (9), 1488-1495. Jain, S.R.; Adiga,K.C.; Pai Verneker,V.R. A new approach to thermochemical calculations of condensed fuel-oxidizer mixtures. Combust. Flame 1981, 40, 71-79.


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(22)

(23)

(24)

(25)

(26)

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(28)

(29)

(30)

(31)

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(35) (36) (37)

(38)

Wang, B.W.; Cao,Y.M.;Li,J.; Wang,W.S.; Zhao,H.B.; Zheng,C.G. Migration and redistribution of sulfur species during chemical looping combustion of coal with CuFe2O4 combined oxygen carrier.Energy Fuels 2016, 30 (10), 8499-8510. Wang, B.W.; Yan,R.;Zhao,H.B.;Zheng,Y.;Zheng,C.G. Investigation of chemical looping combustion of coal with CuFe2O4 oxygen carrier.Energy Fuels 2011, 25 (7), 3344-3354. Cao, Y.; Casenas,B.; Pan,W.-P. Investigation of chemical looping combustion by solid fuels. 2. Redox reaction kinetics and product characterization with coal, biomass, and solid waste as solid fuels and CuO as an oxygen carreir.Energy Fuels 2006, 20 (5), 1845-1854. Chen, L.Y.; Bao,J.H.; Kong,L.; Combs,M.; Nikolic,H.S.; Fan,Z.; Liu,K.L. The direct solid-solid reaction between coal char and iron-based oxygen carriers and its contribution to solid-fueled chemical looping combustion. Appl. Energy 2016, 184, 918. Siriwardane, R.; Tian,H.J.;Richards,G.;Simonyi,T.;Poston,J. Chemical looping combustion of coal with metal oxide oxygen carrier and coal as fuel.Energy Fuels 2009, 23 (8), 3885-3892. Wang, B.W.; Yan,R.; Lee,D.H.;Liang,D.T.; Zheng,Y.; Zhao,H.B.; Zheng,C.G. Thermodynamic investigation of carbon deposition and sulfur evovlution in chemical looping combustion with syngas.Energy Fuels 2008, 22 (2), 1012-1020. Wang, B.W.; Gao,C.C.; Wang,W.S.; Kong,F.H.; Zheng,C.G. TGA-FTIR investigation of chemical looping combustion by coal with CoFe2O4 combined oxygen carrier. J. Anal. Appl. Pyrolysis 2014, 105, 369-378. Li, K.J.; Khanna,R.; Zhang,J.L.; Barati,M.; Liu,Z.J.; Xu,T.;Yang,T.J.; Sahajwalla,V. Comprehensive investigation of various structural features of bituminous coals using advanced analytical techniques.Energy Fuels 2015, 29 (11), 7178-7189. Baysal, M.; Yürüm,A.; Yildiz,B.; Yürüm,Y. Structure of some western Anatolia coals investigated by FTIR, Raman, 13C solid state NMR spectroscopy and X-ray diffraction. Int. J. Coal Geol. 2016, 163, 166-176. Li, M.F.; Zeng,F.G.; Chang,H.Z.; Xu,B.S.; Wang,W. Aggregate structure evolution of low-rank coals during pyrolysis by in-situ X-ray diffraction. Int. J. Coal Geol. 2013, 116-117, 262-269. Lievens, C.; Ci,D.H.; Bai,Y.; Ma,L.G.;Zhang,R.; Chen,J.Y.; Gai,Q.Q.;Guo,X.F. A study of slow pyrolysis of one low rank coal via pyrolysis-GC/MS. Fuel Process. Technol. 2013, 116, 85-93. Lu, L.; Sahajwalla,V.; Kong,C.; Harris,D. Quantitative X-ray diffraction analysis and its application to various coals.Carbon 2001, 39 (12), 1821-1833. Okolo, G.N.; Neomagus,H.W.J.P.; Everson,R.C.; Roberts,M.J.; Bunt,J.R.; Sakurovs, R.; Mathews,J.P. Chemical-structural properties of South African bituminous coals: Insights from wide angle XRD-carbon fraction analysis, ATR-FTIR, solid state 13C NMR, and HRTEM technqiues.Fuel 2015, 158, 779-792. Grigore, M.; Sakurovs,R.; French,D.; Sahajwalla,V. Mineral matter in coals and their reactions during coking. Int. J. Coal Geol. 2008, 76, 301-308. Chang, L.L.Y.; Howie, R.A.; Zussman, J. Non-silicates:Sulphates, Carbonates, Phosphates and Halides. Geological Society of London: 1996, Vol. 5B. Prasad, P.S.R.; Chaitanya,V.K.; Prasad,K.S.; Rao,D.N. Direct formation of the γCaSO4 phase in dehydration process of gypsum: In situ FTIR study. Am. Mineral. 2005, 90 (4), 672-678. Cullity, B.D.; Stock,S.R. Elements of X-ray Diffraction (3rd ed.) Pearson Education Limited: Edinburgh,2014.


Page 26 of 40

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(39)

(40) (41) (42) (43)

(44)

(45)

(46)

(47)

(48) (49) (50)

(51) (52)

(53)

(54)

(55) (56)

(57)

Fan, Q.T.; Dai,J.Y.;Wang,T.; Kuttner,J.;Hilt,G.;Gottfried,J.M.;Zhu,J.F. Confined synthesis of organometallic chains and macrocycles by Cu-O surface templating.ACS Nano 2016, 10 (3), 3747-2754. Shi, L.; Liu,Q.Y.; Guo,X.J.; Wu,W.Z.; Liu,Z.Y. Pyrolysis behavior and bonding inforamtion of coal - A TGA study. Fuel Process. Technol. 2013, 108, 125-132. Li, Z.-K.; Wei,X.-Y.; Yan,H.-L.;Zong,Z.-M. Insight into the structural features of Zhaotong lignite using multiple techniques. Fuel 2015, 153, 176-182. He, Q.Q.; Wan,K.; Hoadley,A.; Yeasmin,H.; Miao,Z.Y. TG-GC-MS study of volatile products from Shenli ligntie pyrolysis. Fuel 2015, 156, 121-128. Wang, Y.-G.; Wei,X.-Y.; Wang,S.-K.; LI,Z.-K.; Li,P.;Liu,F.-J.; Zong,Z.-M. Structural evaluation of Xiaolongtan lignite by direct characterization and pyrolytic analysis. Fuel Process. Technol.2016, 144, 248-254. Wang, B.W.; Wang,W.S.; Ma,Q.; Lu,J.; Zhao,H.B.; Zheng,C.G. In-depth investigation of chemical looping combustion of a Chinese bituminous coal with CuFe2O4 combined oxygen carrier Energy Fuels 2016, 30 (3), 2285-2294. Wang, J.-P.; Li,G.-Y.; Guo,R.; Li,A.-Q.; Liang,Y.-H. Theoretical and experimental insight into coal structures: Establishing a chemical model for Yuzhou lignite. Energy Fuels 2017, 31 (1), 124-132. Wang, B.W.; Ma,Q.; Wang,W.S.; Zhang,C.; Mei,D.F.; Zhao,H.B.; Zheng,C.G. Effect of reaction temperature on the chemical looping combustion of coal with CuFe2O4 combined oxygen carrier.Energy Fuels 2017, 31 (5), 5233-5245. Siriwardane, R.; Tian,H.J.; Miller,D.; Richards,G.; Simonyi,T.; Poston,J. Evaluation of reaction mechanism of coal-metal oxide interactions in chemical-looping combustion. Combust. Flame 2010, 157 (11), 2198-2208. Sebbahi, S.; Chameikh,M.L.O.; Sahban,F.;Aride,J.; Benarafa,L.;Belkbir,L. Thermal bhaviour of Moroccan phosphogypsum. Thermochim Acta, 1997, 302 (1-2), 60-75. Yani, S.; Zhang,D.K. An experimental study of sulphate transformation during pyrolysis of an Australian lignite. Fuel Process. Technol.2010, 91 (3), 313-321. Zheng, D.; Lu,H.L.; Sun,X.Y.; Liu,X.D.; Han,W.Q.; Wang,L.J. Reaction mechanism of reductive decomposition of FGD gypsum with anthracite. Thermochim. Acta 2013, 559, 23-31. Li, H.J.; Zhuang,Y.H. Catalytic reduction of calcium sulfate to calcium sulfide by carbon monoxide. Ind. Eng. Chem. Res. 1999, 38 (9), 3333-3337. Moreno-Castilla, C.; López-Peinado,A.; Rivera-Utrilla,J.; Fernández-Morales,I.; López-Garzón,F.J. The striking behavior of copper catalysing the gasification reaction of coal chars in dry air. Fuel; 1987, 66 (1), 113-118. Davies, N.H.; Hayhurst,A.N. On the formation of liquid melts of CaS and CaSO4 and their importance in the absorption of SO2 by CaO. Combust. Flame 1996, 106 (3), 359-362. Zadick, T.W.; Zavaleta,R.; McCandless,F.P. Catalytic decomposition of calcium sulfate to calcium sulfide with carbon monoxide. Ind. Eng. Chem. Process Des. Dev. 1972, 11 (2), 283-287. Mattisson, T.; Lyngfelt,A.; Leion,H. Chemical-looping with oxygen uncoupling for combustion of solid fuels. Int. J. Greenhouse Gas Controll 2009, 3 (1), 11-19. Rodriguez, J.A.; Hanson,J.A.; Wen,W.; Wang,X.Q.; Brito,J.L.; Martínez-Arias,A.; Fernández-García,M. In-situ characterization of water-gas shift catalysts using timeresolved X-ray diffraction. Catal. Today 2009, 145 (3-4), 188-194. Madix, R.J.; Telfor,S.G. Kinetic isotope effect for C-H bond activation on Cu(110):The effects of tunnelling. Surf. Sci. 1992, 277 (3), 246-252.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(58)

(59)

(60) (61)

(62) (63) (64) (65) (66) (67)

(68) (69)

(70) (71)

(72)

(73) (74)

(75)

Guo, Q.J.; Liu,Y.Z.; Jia,W.H.; Yang,M.M.; Hu,X.D.; Ryu,H.-J. Performance of Cabased oxygen carriers decorated by K2CO3 or Fe2O3 for coal chemical looping combustion. Energy Fuels 2014, 28 (11), 7053-7060. Zhang, P.F.; Ding,N.; Li,H.J.; Lv,M.M.; Guan,N.; Liu,Z.G. Effect of ternary eutectic salt on the calcium sulfate oxygen carrier for chemical looping combustion of coal char. Energy Technol. 2016, 5 (3), 469-480. Ceylan, K.; Baraca,H.; Önal,Y. Thermogravimetric analysis of pretreated Turkish lignites. Fuel 1999 78 (9), 1109-1116. Tromp, P.J.J.;, Kapteijn,F.; Moulijn,J.A. Characterization of coal pyrolysis by means of differential scanning calorimetry. 1. Quantitative heat effects in an inert atmosphere. Fuel Process. Technol. 1987, 15, 45-57. Ibarra, J.V.; Bonet,A.J.; Moliner,R. Release of volatile sulfur compounds during low temperature pyrolysis of coal. Fuel 1994, 73 (6), 933-939. Calkins, W.H. Investigation of organic sulfur-containing structures in coal by flash pyrolysis experiments.Energy Fuels 1987, 1 (1), 59-64. Liu, J.X.; Jiang,X.; Shen,J.; Zhang,H. Pyrolysis of superfine pulverized coal. Part 1. Mechanisms of methane formation. Energy Convers. Manage. 2014, 87, 1027-1038. Niksa, S. Flashchain theory for rapid coal devolatilization kinetics. 7. Predicting the release of oxygen species from various coals.Energy Fuels 1996, 10 (1), 173-187. Van Heek, K.H.; Hodek,W. Structure and pyrolysis behavior of different coals and relevant model substances.Fuel 1994, 73 (6), 886-896. Wang, S.Q.; Tang,Y.G.; Schobert,H.H.; Guo,Y.N.; Gao,W.C.; Lu,X.K. FTIR and simultaneous TG/MS/FTIR study of the Late Permian coals from Southern coal. J. Anal. Appl. Pyrolysis 2014, 100, 75-80. McCrea, D.H.; Forney,A.J.; Myers,J.G. Recovery of sulfur from flue gases using a copper oxide absorbent. J.Air Pollut.Control Assoc. 1970, 20 (12), 819-824. Macken, C; Hodnett,B.K. Reductive regeneration of sulfated CuO/Al2O3 catalystsorbents in hydrogen, methane, and steam. Ind. Eng. Chem. Res.1998, 37 (7), 26112617. Fenton, D.M., Gowdy,H.W. The chemistry of the beavon sulfur removal process. Environ. Int. 1979, 2 (3), 183-186. Kierzkowska, A.M.; Müller,C.R. Development of calcium-based,copperfunctionalised CO2 sorbents to integrate chemical looping combustion into calcium looping. Energy Environ. Sci. 2012, 5 (3), 6061-6065. Marinov, V.; Marinov,S.P.; Lazarov,L.; Stefanova,M. Ash agglomeration during fludized bed gasification of high sulphur content lignites. Fuel Process. Technol.1992, 31 (3), 181-191. Aspelund, A.; Jordal,K. Gas conditioning- the interface between CO2 capture and trsanport. Int. J. Greenhouse Gas Control 2007 1(3), 343-354. Wang, B.W.; Zhao,H.B.; Zheng,Y.; Liu,Z.H.; Zheng,C.G. Method and equipment for simulatenous in-situ decarbonization and desulfurizaiton of coal combustion. IPO,China: 2015. García-Labiano, F.; de Diego,L.F.; Cabello,A.; Gayán,P.; Abad,A.; Adánez,J.; Sprachmann,G. Sulphuric acid production via chemical looping combustion of elemental sulphur. Appl. Energy 2016, 178, 736-745.


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List of Tables and Figures: Table 1. Properties of Indonesia lignite sample; Table 2. Structural characteristics of the as-made CaSO4-CuO mixed OC; Table 3. Elemental analysis of the reaction of YN with the CaSO4-CuO OC by EDX (At%);

Figure 1. Structural characteristics of YN lignite; Figure 2. XRD analysis of the as-made CaSO4-CuO mixed OC; Figure 3. Morphological characteristics of the as-prepared CaSO4-CuO mixed OC; Figure 4. Reaction characteristics of YN under the N2 and air atmosphere; Figure 5. Reaction characteristics of YN with the CaSO4-CuO mixed OC; Figure 6. Evolution of heat flow during YN reaction with the CaSO4-CuO mixed OC ; Figure 7. FTIR spectra for the gaseous products evolved from YN reaction with CaSO4CuO mixed OC; Figure 8. FESEM-EDX analysis of the solid reaction products during YN reaction with the CaSO4-CuO OC; Figure 9. XRD analysis of the solid products of YN coal reaction with the (CaSO4-CuO) mixed OC; Figure 10. Distribution of the equilibrium species for YN reaction with the CaSO4-CuO mixed OC.


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Tables: Table 1. Properties of Indonesia lignite (YN) sample. Proximate analysis (wt.%) Ultimate analysis (wt.% , adb) a a a a Mad Vad Aad FCad C H N S Oc 6.06 49.69 4.63 39.62 71.13 4.64 0.94 0.13 12.47 Ash analysis (wt.%)

LHVd (MJ/kg) 18.36

SiO2

Al2O3

Fe2O3

SO3

CaO

TiO2

K2O

MgO

Na2O

Total

48.80

19.59

12.62

1.25

6.04

1.06

1.70

4.55

0.40

96.01

a

M: moisture content; V: volatile matters; A: ash content; FC: fixed carbon; ad: air-dried basis; b: dry basis; c: the O content was determined by difference; d: lower heating value.

Table 2. Structural characteristics of the as-made CaSO4-CuO mixed OC. Sample BET surface Single point absorptionAverage Main species and its Crystalline 2 Area (m /g) total pore volume pore size crystalline structure size (nm) (cm³/g) (nm) Monoclinic CuOa 0.5920a 0.000468a 15.9448a 107.32a Monoclinic CaSO4CuO: 59.20 12.2513 0.019127 6.24489 CuO CaSO4: Orthorhombic 81.48 CaSO4 0.2573 0.001475 45.1998 Orthorhombic 78.80 a :As referenced in our previous research [12].

Table 3. Elemental analysis of the reaction of YN with CuO-CaSO4 by EDX (At%). Sample C O Si Fe Al S Ca YN-N2

YN-CuO (Red) YN-CaSO4 （Red） YN-(CaSO4+CuO) （Red）

Spot 1 Spot 1 Spot 2 Spot 1 Spot 2 Spot 3 Spot 1 Spot 2

67.39 21.02 13.43 70.45 22.46 44.65 16.66 8.46

14.53 0.82 1.03 5.82 18.89 9.88 15.36 7.62

4.05 0.09 0.36 0.11 0.17 0.22 0.09 0.30

3.75 0.72 0.36 0.15 0.28 0.41 0.00 0.00


3.73 0.08 0.45 0.07 00.00 0.17 0.12 0.27

1.04 0.00 0.19 10.85 27.37 20.39 18.83 30.77

2.19 0.00 0.33 11.99 30.00 23.08 20.60 23.99

Cu 0.00 77.22 82.73 0.00 0.00 0.00 28.34 28.58

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Figures :

Figure 1. Strutural characteristics of YN lignite: (a) XRD pattern of the YN lignite; (b) Curvefitting of the YN XRD profile.


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Figure 2. XRD analysis of the as-made CaSO4-CuO mixed OC: (a) CaSO4 ore ; (b) SGCSmade CuO ; (c) As-made CaSO4-CuO.


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a: CuO

b: CaSO4 ore

c: CaSO4-CuO mixed OC

Figure 3. Morphological characteristics of the as-prepared CaSO4-CuO mixed OC:(a) SGCSmade CuO; (b) CaSO4 ore; (c) As-prepared CaSO4-CuO.


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Figure 4. Reaction characteristics of YN in the N2 and air atmosphere: (a) Weight loss (TG); (b) Weight loss rate (DTG).


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Figure 5. Reaction characteristics of YN with the CaSO4-CuO mixed OC: (a)Weight loss; (b) Weight loss rate of YN reaction with CuO; (c)Weight loss rate of YN reaction with CaSO4; (d)Weight loss rate of YN reaction with the CaSO4-CuO mixed OC.


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Figure 6. Evolution of heat flow during YN reaction with the mixed CaSO4-CuO mixed OC: (a)Pyrolysis of YN; (b) YN reaction with CuO; (c)YN reaction with CaSO4 ; (d) YN reaction with the mixed CaSO4-CuO mixed OC.


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Figure 7. FTIR spectra for the gaseous products evolved from YN reaction with the CaSO4-CuO mixed OC: (a) YN pyrolysis under N2; (b) YN reaction with the CaSO4CuO mixed OC.


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a: YN-N2

b: YN-CuO(Red)

1

2

1

1

1

1

c: YN-CaSO4(Red)

2

1

d: YN- (CaSO4+CuO) (Red)

1

3

1

1

1

2

1

1

Figure 8. FESEM-EDX analysis of the solid products fromYN reaction with the CaSO4-CuO mixed OC:(a) Pyrolysis of YN; (b) Reaction of YN with CuO; (c) Reaction of YN with CaSO4; (d) Reaction of YN with the CaSO4-CuO mixed OC.


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Figure 9. XRD analysis of the solid products of YN reaction with the CaSO4-CuO mixed OC: (a) Pyrolysis of YN; (b) Reduction of the CaSO4-CuO with YN; (c) Oxidation of the reduced CaSO4-CuO mixed OC by air. In this figure, 1.quartz [SiO2]; 2. silimanite (Al2SiO5); 3. gehlenite (Ca2Al2SiO7);4. kaliophilite (KAlSiO4); 5. cordierite (Mg2Al4Si5O18); 6. iron sulfide (FeS); 7. Calcium Sulfide (CaS); 8. covellite (CuS); 9. chalcocite (Cu2S); 10.digenite (Cu1.8S); 11. Calcium sulfate (CaSO4); 12. lime (CaO); 13. portlandite (Ca(OH)2); 14. Calcite(CaCO3); 15. anorthite (CaAl2Si2O8); 16. tricalcium silicate (Ca3SiO5); 17. grossular (Ca3Al2 (SiO4)3);18.copper oxide (CuO); 19. calcium copper oxide (Ca2CuO3).


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Figure 10. Distribution of the reaction equilibrium species for YN reaction with the CaSO4CuO mixed OC: (a) Carbon species; (b) Hydrogen species ; (c) Copper species; (d) Calcium species; (e) Calcium-based silicates; (f) Various sulfur species.


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Chemical Looping Combustion of a Typical Lignite with a CaSO4

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