Influence of Modified Medical Stone on Behavior of Sulfur during Pyrolysis of Longma Coal

Transcription

1 Scientific Research China Petroleum Processing and Petrochemical Technology 2017, Vol. 19, No. 1, pp March 31, 2017 Influence of Modified Medical Stone on Behavior of Sulfur during Pyrolysis of Longma Coal Li Jingkuan 1,3 ; Zhao Shuguang 2 ; Wang Baofeng 2,3 ; Jin Yan 1 ; Zhang Jinjun 2 ; Cheng Fangqin 3 (1. College of Electrical and Power Engineering, Taiyuan University of Technology, Taiyuan ; 2. School of Chemistry & Material Science, Shanxi Normal University, Linfen ; 3. Research Institute of Resources and Environment Engineering, Shanxi University, State Environmental Protection Key Laboratory of Efficient Utilization of Waste Coal Resources, Taiyuan ) Abstract: The influence of CoMoP/medical stone and SO 2-4 /medical stone on sulfur behavior during the Longma coal pyrolysis was investigated in a fixed bed reactor. Moreover, the kinetics was also studied. It is found that adding SO 2-4 /medical stone was favorable to removal of volatile matter, while adding CoMoP/medical stone could inhibit the emission of volatiles. Moreover, the results also showed that adding CoMoP/medical stone made the total sulfur retention higher, while adding SO 2-4 / medical stone made the total sulfur retention lower. Adding modified medical stone was beneficial to removal of sulfate sulfur and pyritic sulfur, while it was beneficial to retaining organic sulfur in the residue. Furthermore, adding CoMoP/medical stone and SO 2-4 /medical stone all could increase the emission of H 2 S when the temperature was higher than 450 o C. Judging from the kinetics study, it also can be known that addition of the natural minerals could result in a decrease of the pre-exponential factor and also change the apparent activation energy upon comparing the apparent activation energy and the pre-exponential factor of raw Longma coal at o C. Key words: coal; modified medical stone; sulfur behavior; pyrolysis; kinetics 1 Introduction Coal is one of the main energy sources in the world, especially in China. As we know, coal contains variable amount of sulfur which exists in inorganic and organic forms. The inorganic sulfur occurs as sulfides or sulfates while the organic sulfur is associated with organic structures existing in coal [1]. As one of the major pollution sources, sulfur in coal can inhibit the effective utilization of coal [2-3]. So, how to remove sulfur before utilization of coal is important. To grapple with this problem, one should know the mode of occurrence and the transformation of sulfur species in coal during its pyrolysis, gasification and combustion. Fixation of sulfur in the char during pyrolysis of coal is an efficient method to reduce the emission of sulfur. There are many studies regarding the transformation of sulfur during coal pyrolysis [4-11]. Our previous study showed that application of additives such as tourmaline, medical stone and sodium bentonite could influence the behavior of sulfur [12]. Moreover, literature reports [13-17] showed that some catalysts such as modified minerals could influence the product distribution and the behavior of sulfur during coal treatment. A previous study [15] also showed that the Co-Mo/Al 2 O 3 catalyst and SO 2 4 /ZrO 2 catalyst had an obvious catalytic effect on the treatment of coal; and the previous study [18] showed that CoMoP/Al 2 O 3 also had good catalytic activity. Furthermore, as it has been known, the medical stone is a porous material and has strong adsorption capacity [19], which is 2000 times the adsorption capability of activated carbon. So, in our study, we used medical stone as a support, and loaded CoMoP and SO 2 4 onto it. In this work, the effect of modified medical stone, viz.: the CoMoP/medical stone and the SO 2 4 /medical stone, on sulfur behavior during coal pyrolysis was studied. Moreover, the kinetics were also studied to further Received date: ; Accepted date: Corresponding Author: Wang Baofeng, Telephone: ; wangbaofeng1234@sina.com. Jin Yan, Telephone: ; jinyan@tyut.edu.cn. 81

2 Li Jingkuan, et al. China Petroleum Processing and Petrochemical Technology, 2017, 19(1): understand the influence mechanism related with the natural minerals. 2 Material and Methods 2.1 Samples The Longma (LM) coal is excavated from Linfen City in Shanxi Province of China. The lump coal was first airdried and then crushed, ground and sieved to obtain the coal sample with a grain size ranging from 0.15 mm to 0.25 mm. Medical stone (M) used in the experiments was gathered from Linshou in Hebei Province of China. The medical stone was ground and sieved to a grain size of less than 75 μm before use. The proximate and ultimate analysis of LM coal and the forms of sulfur species in LM coal were referred to in our previous study[12]. Moreover, in order to know the mechanism related with the influence of the medical stone on sulfur behavior, we also chose several simple minerals, which were contained in the medical stone, and mixed them uniformly according to a specified ratio. Table 1 Main composition of blended minerals (w, %) Sample SiO2 Al2O3 Fe2O3 CaO KCl Na2CO3 Blend Table 1 shows the composition of the blends. The modified medical stone, viz.: CoMoP/ medical stone and SO42-/medical stone, were obtained by the solution dipping method, as mentioned in previous study[20]. Figure 1 shows the XRD patterns and FT-IR spectra of the medical stone and its minerals-containing modified forms. Figure 2 is the SEMEDX micrographs of the medical stone and its mineralscontaining modified forms. It can be seen from Figure 1 and Figure 2 that the medical stone has been modified veritably by the solution dipping method. Figure 1 XRD patterns and FT-IR spectra of the medical Figure 2 SEM-EDX micrographs of the medical stone stone and its modified minerals and its minerals modified forms 82

3 2.2 Pyrolysis experiment The pyrolysis experiments were performed in a fixed-bed reactor. The reactor and the experimental procedure were all the same as those referred to in our previous study [12]. 2.3 Analysis and characterization methods The amount of total sulfur in the solid residue was analyzed according to the Chinese Standard GB/T The content of pyritic sulfur and sulfate sulfur in coal and the solid residue obtained from pyrolysis were determined according to the Chinese standard GB/T , and the organic sulfur content was obtained by difference. 2.4 Calculation methods The yield of the solid residue and the retention of each type of sulfur in the solid residue (including total sulfur, organic sulfur and inorganic sulfur) were calculated by the equation mentioned in the previous literature [12]. 3 Results and Discussion 3.1 Influence of modified medical stone on total sulfur retention during coal pyrolysis Figure 3 shows the solid residue yield and the sulfur retention during LM coal pyrolysis at different temperatures upon adding the minerals-modified medical stone. It can be seen from Figure 3(a) that upon comparing the solid residue yield when the medical stone was added, the addition of CoMoP/medical stone made the solid residue yield higher except at 550 o C, while adding SO 2-4 /medical stone made the solid residue yield lower. This result means that adding SO 2-4 /medical stone is beneficial to the evaporation of volatiles, while adding CoMoP/medical stone can inhibit the emission of volatile matter. It can be seen from Figure 3(b) that upon comparing the total sulfur retention with the addition of medical stone, adding CoMoP/ medical stone made the total sulfur retention higher, while adding SO 2-4 / medical stone made the total sulfur retention lower. This fact just coincides with the result of solid residue yield. When more volatiles are discharged, more sulfur compounds are removed with the volatiles. Then it is true that the higher the solid residue yield, the higher the Figure 3 Solid residue yield (a) and sulfur retention (b) during LM coal pyrolysis at different temperatures with addition of the minerals modified medical stone LM; LM+M; LM+CoMoP/M; LM+SO 2-4 /M total sulfur retention. This result is also consistent with the result obtained in the previous study [11]. 3.2 Influence of minerals modified medical stone on the retention of different forms of sulfur during coal pyrolysis Figure 4 shows the sulfate sulfur, pyritic sulfur and organic sulfur retention during LM coal pyrolysis at different temperatures with addition of the minerals modified medical stone. It can be seen from Figure 4(a) that during LM coal pyrolysis, the sulfate sulfur retention decreased with an increasing temperature. Upon comparing the sulfate sulfur retention in the presence of medical stone, adding CoMoP/medical stone made the sulfate sulfur retention lower, while adding SO 2-4 /medical stone made the sulfate sulfur higher when the temperature was less than 550 o C. When the temperature increased from 550 o C to 750 o C, 83

4 the weight loss rate of LM coal, so the sulfate sulfur retention became higher. Figure 4(b) shows the pyritic sulfur retention with addition of medical stone or modified medical stone at different temperatures. It can be seen from Figure 4(b) that the pyritic sulfur retention upon addition of CoMoP/medical stone or SO 2-4 /medical stone almost had no obvious difference with the case using the medical stone only except at 550 o C. At 550 o C, adding CoMoP/medical stone made the pyritic sulfur retention lower, indicating that adding the CoMoP modified medical stone was beneficial to removal of pyritic sulfur especially at 550 o C. Figure 4(c) shows the organic sulfur retention with addition of medical stone or modified medical stone at different temperatures. It can be learned from Figure 4(c) that adding medical stone and modified medical stone all could improve the organic sulfur retention, whereas in comparison to the organic sulfur retention obtained with addition of medical stone, adding CoMoP/medical stone made the organic sulfur retention higher, while adding SO 2-4 /medical stone made the organic sulfur retention lower. Judging from the above data, one could know that adding the modified medical stone was beneficial to removal of sulfate sulfur and pyritic sulfur, while it could inhibit removal of organic sulfur in the residue during LM coal pyrolysis. 3.3 Influence of modified medical stone on the emission of H 2 S and COS during coal pyrolysis Figure 4 Sulfur retention of: (a) sulfate sulfur, (b) pyritic sulfur, and (c) organic sulfur during LM coal pyrolysis at different temperatures with addition of the minerals modified medical stone LM; LM+M; LM+CoMoP/M; LM+SO 2-4 /M adding CoMoP/medical stone and SO 2-4 /medical stone changed the sulfate sulfur retention slightly. When the temperature was higher than 750 o C, adding CoMoP/ medical stone and SO 2-4 /medical stone all made the sulfate sulfur retention higher. This phenomenon might occur because at a temperature of higher than 750 o C the decomposition rate of sulfate sulfur was lower than Figure 5 illustrates the emission of H 2 S and COS during LM coal pyrolysis. It can be seen from Figure 5(a) that for the raw LM coal, the maximum emission of H 2 S was identified at 450 o C, while in the presence of medical stone or the minerals modified medical stone, the maximum emission of H 2 S was detected at 500 o C. Moreover, it can also be noticed that when the temperature was lower than 450 o C, adding the modified medical stone had no obvious effect on H 2 S emission, and when the temperature increased from 450 o C to 750 o C, adding CoMoP/medical stone and SO 2-4 /medical stone both could increase the emission of H 2 S. When the temperature was higher than 750 o C, adding the two kinds of modified medical stone samples could all inhibit the emission of H 2 S. According to the literature report, the peak of H 2 S emission is 84

5 Figure 5 H 2 S and COS emission curve during LM coal pyrolysis at different temperatures with addition of the minerals modified medical stone LM; LM+M; LM+CoMoP/M; LM+SO 2-4 /M attributed to the decomposition of pyrite, the shoulder at lower temperatures (<400 o C) corresponds to the decomposition of aliphatic sulfur (such as thiols, dialkyl and aryl-alkyl sulfides, etc.), and the right shoulder (>600 o C) is related to the decomposition of aromatic sulfides [21]. Then it is easy to infer that adding the modified medical stone samples can intensify the decomposition of pyrite. This result can just coincide with the results of Figure 4(b), showing that when the temperature was lower than 650 o C, the pyritic sulfur retention with addition of the modified medical stone was lower than that of raw LM coal. It also can be noticed from Figure 5(a) that when the temperature increased from 600 o C to 700 o C, addition of the modified medical stone also made the emission of H 2 S higher, so that one could infer that adding the modified medical stone also was beneficial to the decomposition of aromatic sulfides. It can be seen from Figure 5(b) that only a small amount of COS was emitted at o C during LM coal pyrolysis, and this result was similar to that reported in the previous study [19]. When the temperature was lower than 400 o C, adding CoMoP/ medical stone made the COS emission a little higher, while at a temperature exceeding 400 o C, adding CoMoP/ medical stone made the COS emission lower. As regards the SO 2-4 /medical stone, when the temperature was lower than 500 o C or higher than 650 o C, adding SO 2-4 /medical stone made the COS emission a little higher, and when the temperature increased from 500 o C to 650 o C, adding SO 2-4 /medical stone made the COS emission lower. According to what we have known, carbonyl sulfide (COS) is mainly derived from pyrite and organic sulfur through secondary reactions [21]. Just as mentioned above, adding the modified medical stone is not beneficial to the removal of organic sulfur compounds from coal, so addition of CoMoP/medical stone can make the COS emission lower. Previous study [22] showed that CO 2 and CO contained in volatiles can react with the sulfur species to produce COS in line with the following reactions: H 2 S + CO 2 = COS + H 2 O; and H 2 S + CO = COS + H 2. Upon comparing Figure 5(a) and Figure 5(b), it can be noticed that the emission of H 2 S from pyrolysis of raw LM coal with or without addition of medical stone was all less than that the case with addition of the modified medical stone, while the emission of COS was all higher than the latter with addition of the modified medical stone. This phenomenon might be caused by the fact that H 2 S in the volatiles can react with CO 2 and CO, so that the higher the emission of COS is, the lower the emission of H 2 S would be. 3.4 Influence of blends of simple minerals on sulfur retention during coal pyrolysis Influence of blends on total sulfur retention and solid residue yield Figure 6 shows the solid residue yield and the total sulfur retention upon adding medical stone and the blends consisting of several simple minerals similar to the composition of the medical stone. Moreover, in order to know the influence of the inherent minerals on the retention of sulfur [23] in Longma coal, the sulfur retention of the demineralized LM coal (LMdem) during its pyrolysis was also studied. It can be seen from Figure 6(a) that adding medical stone or the blends all led to an increased solid residue yield, and 85

6 result obtained by Hu Haoquan [13]. The reason might be caused by the inherent minerals in the LM coal that are different from those in the Yanzhou coal as studied by Haoquan Hu. Moreover, it can also be learned from Figure 6(b) that adding the blends also led to increased total sulfur retention, which just could coincide with the results mentioned above. It can be seen from the results that the influence of the blends on total sulfur retention is not exactly the same as that achieved by the medical stone Influence of the blends on retention of forms of sulfur Figure 6 Solid residue yield (a) and the total sulfur retention (b) during LM coal pyrolysis with addition of blended minerals LM; LM+M; LM+Blends; LM-dem upon comparing the solid residue yield obtained by adding medical stone only, addition of the blends of minerals increased the solid residue yield. The reason might be that although the composition of the blends was the same as that of the medical stone, however, the interaction between the constituents of medical stone was stronger, so the catalytic activity of medical stone was stronger too. Then the solid residue yield obtained upon adding medical stone was lower than the case with addition of the blends. Furthermore, it can be seen from Figure 6(a) that the solid residue yield of LM-dem was the lowest. It also can be seen from Figure 6(b) that the total sulfur retention of LM-dem was higher as compared to that of raw Longma coal, from which one could infer that removing the inherent minerals in Longma coal is beneficial to keeping sulfur in the residue, denoting that the existence of the inherent minerals is favorable to total sulfur removal. Unfortunately, this result does not agree well with the Figure 7 shows the sulfur retention at different temperatures. It can be seen from Figure 7(a) that when the temperature was lower than 550 o C, the sulfate sulfur retention upon adding the blends was lower than the case with addition of the medical stone, and when the temperature was higher than 550 o C, the sulfate sulfur retention with addition of the blends almost had no obvious difference with the addition of medical stone. It can be seen from Figure 7(b) that at the same temperature in comparison with the pyritic sulfur retention of raw Longma coal, the pyritic sulfur retention of LM-dem was lower, denoting that the existence of inherent minerals was beneficial to retaining the pyritic sulfur in the residue. This result is similar to the result of the previous study made by Professor Hu [13], which has denoted that the inherent minerals in coal have little effect on the decomposition of pyrite. Moreover, it can be learned from Figure 7(b) that in comparison with the pyritic sulfur retention with addition of medical stone, adding the blends could increase the pyritic sulfur retention when the temperature was increased from 450 o C to 650 o C, and when the temperature was higher than 650 o C, the pyritic sulfur retention identified with addition of the blends was just the same as the case of adding the medical stone. The reason might be ascribed to the temperature in excess of 650 o C, at which most of the pyrite would be decomposed. It can be seen from Figure 7(c) that at the same temperature the organic sulfur retention of LM-dem was higher than that of LM coal, denoting that the inherent minerals were conducive to the organic sulfur removal. Interestingly, these results could coincide with the 86

7 the medical stone Influence of the blends on emission of H 2 S and COS Figure 8 shows the emission of H 2 S and COS achieved with adding the medical stone and the blends, respectively. It can be seen from Figure 8(a) that the emission of H 2 S from LM-dem was higher than that from the raw Longma coal. As we have known, most of sulfur species in pyrite can be transformed into volatile H 2 S. Since the LM-dem sample showed lower pyritic sulfur retention, it would have higher removal rate of pyritic sulfur, and the emission of H 2 S from pyrolysis of LMdem sample was higher than that obtained from pyrolysis of raw Longma coal. It can be seen from Figure 8(a) that when the temperature was lower than 500 o C, addition of the blends could prevent the emission of H 2 S, and when the temperature was higher than 500 o C (except for 700 o C), adding the blends resulted in the higher emission of H 2 S than that obtained by addition of the medical stone. It can Figure 7 Sulfur retention at different temperatures in terms of: (a) sulfate sulfur, (b) pyritic sulfur, and (c) organic sulfur LM; LM+M; LM+Blends; LM-dem result of the previous study made by Professor Hu [13]. It can be learned from Figure 7(c) that the organic sulfur retention with the addition of the blends was higher than that achieved by addition of the medical stone. It can be known from all mentioned above that although the composition of the blends was similar to that of the medical stone, however, because of the difference in the combination mode, the retention of sulfate sulfur, pyritic sulfur and organic sulfur obtained with addition of the blends was totally different from that achieved by adding Figure 8 H 2 S and COS emission curve during LM coal pyrolysis upon adding blended minerals LM; LM+M; LM+Blends; LM-dem 87

8 be learned from Figure 8(b) that the emission of COS from LM-dem sample was also higher than the case of raw Longma coal with the exception of the temperatures in the range from 500 o C-550 o C, denoting that removing inherent minerals also was beneficial to COS emission. This result also has been proved by Haokan Chen in previous study [24]. It can also be seen from Figure 8(b) that the addition of medical stone was beneficial to COS emission, while adding the blends could prevent the emission of COS. It has been known that during coal pyrolysis the COS is mainly produced from pyrite, organic sulfur or secondary reactions of organic sulfur among sulfur-containing compounds [23]. Just as it has been mentioned above, adding the blends can retain more organic sulfur in the residue, and on the other hand, about 78.3% of sulfur species in the LM coal are composed of organic sulfur species, so adding the blends can inhibit the emission of COS. 3.5 Kinetic study of pyrolysis of LM coal upon adding natural minerals TG/DTG curves of LM coal upon adding natural minerals In order to delve in the mechanism of influence of the natural minerals on sulfur behavior, the kinetics of pyrolysis of LM coal upon adding natural minerals was studied. Figure 9 shows the TG/DTG curves of LM coal and biomass upon adding natural minerals. The weight loss of raw LM coal without natural minerals is expressed as follows: W m m o t = 100 % (1) mo where W is the weight loss of raw Longma coal without adding natural minerals,%; m o is the mass of the coal at the initial stage,%; m t is the mass of the coal at the time t. The weight loss of raw LM coal upon adding natural minerals is calculated as: mo mt mmo mmt c Wp = [( ) ( ) ] ( 1+ c) 100 % (2) mo mmo 1 + c where W p is the weight loss of raw LM coal with natural minerals,%; c is the mass fraction of the natural minerals; m o is the mass of the coal at the initial stage,%; m t is the mass of the coal at the time t; m mo is the mass of the natural minerals at the initial stage,%; and m mt is the mass Figure 9 The TG/DTG curves of LM coal LM; LM+T1; LM+N; LM+T2; LM+M of the natural minerals at the time t. In order to explain the difference of the influence by the four natural minerals, we define a parameter ΔC, ΔC=W p W (3) in which ΔC is the increment of the weight loss upon adding natural minerals. When ΔC<0, it means that addition of natural minerals is beneficial to the weight loss of coal; and when ΔC >0, it means that adding natural minerals can hold back the weight loss of coal. Figure 10 shows the variation in ΔC with temperature of LM coal or LM coal and biomass with natural minerals. It can be seen from Figure 10 that upon adding the Hebei tourmaline or sodium bentonite, ΔC < 0, which means that adding the Hebei tourmaline and sodium bentonite are all beneficial to weight loss of Longma coal. It can be seen from Figure 10 that when the temperature was higher than 350 o C, the positive effect was obvious, especially at 520 o C. When the temperature was lower than 500 o C,ΔC was close to zero upon adding the Inner Mongolia tourmaline or medical stone, and when the temperature was higher than 500 o C, ΔC > 0, denoting that when the temperature was higher than 500 o C, adding the Inner Mongolia tourmaline or medical stone could inhibit the weight loss, which agreed well with the results mentioned in the previous study Dynamic model [25-29] The weight loss rate is calculated as follows [24] : dx A E = x dt β ( 1 )exp( RT ) (4) 88

9 Figure 10 Variation of ΔC for coal with temperature upon addition of natural minerals 1 LM-T1; 2 LM-N; 3 LM-T2; 4 LM-M w0 wt x = w w 0 β = d T (6) dt where x is the weight loss fraction or pyrolysis conversion f (5) which can be calculated by the equation, in which A is the pre-exponential factor, E is the activation energy, T is the temperature, t is the time duration, and w o is the original mass of the test sample; w t is the mass at time t and w f is the final mass at the end of pyrolysis. By using the method of Coats-Redfern [25], we can obtain: 2 T E exp( ) = ( )exp( ) RT T RT RT E d 1 2 (7) o E E RT 1n( 1 X ) AR = ( 1 2 RT E )exp( ) 2 T β E E RT (8) In equation (8) since RT/E< <1, then we could assume (1-2RT/E) 1, so the equation can be written as: ln( 1 X ) ln = AR ln E 2 T β E RT (9) Table 2 is the kinetic parameter calculated according to equations (7 9) of LM coal. It can be seen from Table 2 that the apparent activation energy of raw Longma coal is about kj/mol at o C, and it is about kj/mol in the temperature range of o C, and about kj/mol in the temperature range of o C. Here one could see that the apparent activation energy at o C is higher than that at o C. As we have known, at o C the main reaction is the active thermal decomposition of the long-chain compounds that need more energy, while in the temperature range of o C, the main reaction is the cleavage of sidechains with poor stability and the active functional groups which need less energy. Then it is easy to understand why the apparent activation energy at o C is higher than that at o C. It can also be seen from Table 2 that adding the natural minerals can mainly influence the apparent activation energy at o C. Upon comparing the apparent activation energy and the pre-exponential factor of raw Longma coal at this stage, it can be noticed that addition of the natural minerals would result in a decrease of the pre-exponential factor, which just can coincide with the results obtained in previous study [13]. Moreover, it also can be seen that adding the Heibei tourmaline and sodium bentonite could reduce the apparent activation energy Table 2 Kinetic parameters of coal pyrolysis Sample Temperature, o C Conversion range, % E, kj/mol A, min -1 R LM LM+T LM+N LM+T LM+M

10 by 5 kj/mol and 8 kj/mol, respectively, while adding the Inner Mongolia tourmaline and medical stone could increase the apparent activation energy by 4.9 kj/mol and 2.5 kj/mol, respectively. Judging from all the abovementioned data, one could know that the addition of the natural minerals has a significant effect on the pyrolysis mechanism [27]. Moreover, it also can be learned that the sulfur removal has a relationship with the apparent activation energy and the weight loss. In comparison with the apparent activation energy and the weight loss of raw Longma coal during pyrolysis, the apparent activation energy upon adding sodium bentonite during Longma coal pyrolysis was lower, while the weight loss was higher, and the total sulfur retention became less. Upon adding the Inner Mongolia tourmaline, the apparent activation energy became higher, and the weight loss became lower, while the total sulfur retention became higher. All in all, the higher the apparent activation energy is, the lower the weight loss, and the higher the total sulfur retention would be. 4 Conclusions The influence of CoMoP/medical stone and SO 2-4 /medical stone on sulfur behavior during LM coal pyrolysis was investigated. Moreover, the kinetics was also studied. It is found that adding SO 2-4 /medical stone was beneficial to evolution of volatiles, while adding CoMoP/medical stone could inhibit the emission of volatiles. Moreover, the results also showed that adding CoMoP/medical stone made the total sulfur retention higher, while adding SO 2-4 /medical stone made the total sulfur retention lower. Adding modified medical stone was beneficial to the removal of sulfate sulfur and pyritic sulfur, while it was beneficial to retaining organic sulfur in the residue during LM coal pyrolysis. Furthermore, when the temperature increased from 450 o C to 750 o C, adding CoMoP/medical stone and SO 2-4 /medical stone all could increase the emission of H 2 S. Judging from the kinetics study, it can also be learned that adding the natural minerals mainly could influence the apparent activation energy at o C. In comparison with the apparent activation energy and the pre-exponential factor of raw Longma coal at this stage, addition of the natural minerals could result in a decrease of the pre-exponential factor, and at the same time, addition of the natural minerals could also change the apparent activation energy. Intrestingly, it is found that the higher the apparent activation energy is, the lower the weight loss, and the higher the total sulfur retention would be. Acknowledgements: Upon undertaking the Key Research and Development Program (International Cooperation) of Shanxi (Project Number: D421041), the financial supports of this work by the Provincial Key Scientific Research Projects on Coal-based Low Carbon Energy of Shanxi Province (Project Number: MD ), the National Natural Science Foundation of China-Shanxi Coal-based Low Carbon Joint Fund (U ) and the NSFC-National Natural Science Foundation of China (No ) are gratefully acknowledged. References [1] Singh P K, Singh AL, Kumar A, Singh MP. Control of different pyrite forms on desulfurization of coal with bacteria [J]. Fuel, 2013, 106: [2] Huang J Q, Bai Z Q, Guo Z X, et al. Effects of chromium ion on sulfur removal during pyrolysis and hydropyrolysis of coal [J]. J Anal Appl Pyrol, 2012, 97: [3] Calkins W H. The chemical forms of sulfur in coal: a review [J]. Fuel, 1994, 73(4): [4] Liu L J, Fei J X, Cui M Q, et al. XANES spectroscopic study of sulfur transformations during co-pyrolysis of a calciumrich lignite and a high-sulfur bituminous coal [J]. Fuel Process Technol, 2014, 121: [5] Mesroghli S,Yperman J, Jorjani E, et al. Evaluation of microwave treatment on coal structure and sulfur species by reductive pyrolysis-mass spectrometry method [J]. Fuel Process Technol, 2015, 131: [6] Gryglewicz G. Sulfur transformations during pyrolysis of a high sulfur Polish coking coal [J]. Fuel, 1995, 74(3): [7] Qi Y Q, Li W, Chen H K, et al. Desulfurization of coal through pyrolysis in a fluidized-bed reactor under nitrogen and 0.6% O 2 -N 2 atmosphere [J]. Fuel, 2004, 83(6): [8] Soneda Y, Mitsunori M, Hajime Y, et al. The effect of acid treatment of coal on H 2 S evolution during pyrolysis in hydrogen [J]. Fuel, 1998, 77(9/10): [9] Telfer M, Zhang D K. The influence of water-soluble and 90

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