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Secondary cracking of volatile and its avoidance in infrared-heating pyrolysis reactor
Accepted Manuscript Secondary cracking of volatile and its avoidance in infrared-heating pyrolysis reactor Somprasong Siramard, Jin-Hui Zhan, Zhennan Han, Shipei Xu, Guangwen Xu PII: DOI: Reference:
S2588-9133(18)30051-6 https://doi.org/10.1016/j.crcon.2018.09.001 CRCON 29
To appear in:
Carbon Resources Conversion
Received Date: Revised Date: Accepted Date:
24 July 2018 28 August 2018 10 September 2018
Please cite this article as: S. Siramard, J-H. Zhan, Z. Han, S. Xu, G. Xu, Secondary cracking of volatile and its avoidance in infrared-heating pyrolysis reactor, Carbon Resources Conversion (2018), doi: https://doi.org/10.1016/ j.crcon.2018.09.001
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Secondary cracking of volatile and its avoidance in infraredheating pyrolysis reactor Somprasong Siramarda,c, Jin-Hui Zhana,* Zhennan Hanb, Shipei Xua,c and Guangwen Xua,b,* a
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
b
Institute of Industrial Chemistry and Energy Technology, Shenyang University of Chemical Technology, Shenyang 110142, China
c
University of Chinese Academy of Sciences, Beijing 100049, China
* Corresponding Author, Tel: +86 10 82544886, Fax: +86 10 82629912. E-mail: [email protected] (J.-H. Zhan), [email protected] (G.W. Xu).
Abstract: This study aims to compare the pyrolysis behavior of Huadian oil shale in two infrared heating fixed bed reactors with different directions of infrared beam. Our previous work has shown that fast pyrolysis of oil shale conducted in the shallow fixed bed infrared heating reactor (co-current) presented the massive secondary reactions, which lowered the shale oil production (Energy & Fuels, 31, 2017: 6996-7003). Conversely, the cross-current infrared achieved shale oil yields higher than the Fischer Assay oil yield (13.07 wt.% of dry basis), such as 117.7% of the Fischer Assay yield at our realized highest heating rate of 7 ˚C/s under a specified pyrolysis temperature of 550 ºC. The shale oil from the cross-current infrared heating reactor was obviously heavier than the oil obtained from the co-current heating reactor. Thus, the infrared cross heating evidently suppressed the secondary reactions toward volatile. Our realized shale oil yield could reach 13.67 wt.% or 122.5% of the Fischer Assay yield under reducing pyrolysis pressure of 0.6 atm, indicating that lower pressure is also beneficial to the release of volatile and reduction of the secondary cracking reactions. This work shows essentially that the infrared cross heating provides an effective merge of the advantages from quick heating and minimization of secondary cracking reactions to enable the shale oil yields being higher than the Fischer Assay oil yield. Keywords: Pyrolysis; Secondary cracking; Volatile; Infrared heating; Oil shale.
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1.
Introduction Pyrolysis of oil shale is the well-known technology for the utilization of oil shale to
produce shale oil as an alternative of petroleum fuels. Basically, the oil shale pyrolysis occurs in two steps of the decomposition of kerogen molecule in oil shale (primary reactions) and the subsequent reactions of the generated volatile (secondary reactions) [1]. The extent of these secondary reactions had the influence on the distribution and composition of the pyrolysis products especially liquid shale oil. To control the quality and quantity of pyrolysis products, it is generally subjected to many operating conditions, for example, pyrolysis temperature [24], heating rate [3-6], pyrolysis pressure [7-9], residence time of volatile [10], particle size [11-14], mineral matrix [15] and others. Pyrolysis can broadly divide into slow and fast pyrolysis according to its heating rate [16]. Many studies focused on exploring oil shale pyrolysis behavior under the slow heating rate. Increasing the heating rate to 10 ºC/min increased the shale oil production due to the higher self-generated gas sweep rates during retorting which allowed the high recovery of shale oil. However, the shale oil yield slightly decreased with further increasing heating rate to 30 ºC/min, which may be attributed to the fact that a large number of pyrolytic volatile produced cannot be rapidly diffused, resulting in the secondary cracking reactions [17-18]. Moreover, Wang et. al. [19] reported the increases of the light oil fraction and the noncondensable gas with increasing the heating rate from 5 to 20 ºC/min. Regarding to fast pyrolysis, it is a well-known approach to produce high volatile matter content [20]. There are many techniques used to investigate the decomposition of solid under rapid heating such as wire mesh reactor [21-22], micro pyrolyzer with a combination of GC/MS [23-24] and thermogravimetry analysis [25]. Besides, infrared radiation is used as the heating source for many applications such as food processing, surface heating and solid decomposition, which is an efficient technique for fast heating process since the energy from the radiation of infrared is directly transferred to the material. The fast pyrolysis of Huadian oil shale in the shallow fixed bed mounted with infrared heating presented a high extent of secondary cracking for the rapid pyrolysis of oil shale. The direction of the infrared radiation 2
is parallel to that of the volatile flow in this concurrent reactor, causing the volatile matter to occur secondary reactions at high temperature. In this respect, the modification of heating method to the cross flow of volatile could suppress the degree of secondary reactions. In order to realize the maximum yield of shale oil, this article is devoted to investigating the pyrolysis characteristics of Huadian oil shale in the cross-current infrared heating reactor and to comparing that obtained in the co-current infrared heating reactor under varied heating rates and pyrolysis pressures. It is expected to understand the effect of different approaches of infrared radiation on secondary reactions, and to verify whether the cross-current infrared heating is possible to alleviate the secondary reactions to generated volatile.
2. Experimental Section 2.1 Facility and procedure Two kinds of infrared heating fixed bed reactors which had different pathway between the heating direction and the flow of the generated pyrolysis vapor, cross-current and cocurrent, were used to compare the pyrolysis behavior of oil shale pyrolysis. Figure 1 shows a schematic diagram of the cross-current infrared heating fixed bed reactor. The reactor tube was made of quartz which had an inner diameter of 10 mm and a length of 300 mm. The reactor was indirectly heated by the infrared heating tubes with a cross direction to the release pathway of the generated pyrolysis vapor. The infrared heating tubes had a power of 10 kW to ensure the quickest heating rate of 7 ˚C/s to oil shale particles inside the reactor tube. Approximately 3 g of oil shale was loaded into the reactor tube. High purity N 2 gas with the flow rate of 100 ml/min was used as the carrier gas to sweep the generated pyrolysis vapor from the top to the bottom of the reactor. The entire system was purged with N2 gas for 15 min before running the experiment to ensure the inert atmosphere. Figure 2 shows a process diagram of the co-current infrared heating fixed bed reactor, which it was explained elsewhere [26]. Briefly, the infrared heating tubes with a total power of 27 kW were horizontally parallel to the sample plate, which had an inner diameter of 350 mm and a height of 10 mm, with a distance of 50 mm. A thin layer of 20 g of oil shale 3
particles was evenly spread on the sample plate. The infrared beam was directly radiated to the oil shale sample with the highest heating rate of 25 ˚C/s. The reactor chamber was evacuated to remove air and then was filled with high purity N2 gas to form an inert atmosphere. The Nitrogen carrier gas of 20 L/min flowed downward to sweep the generated volatile into the cooling tube bundle. The oil shale particles were directly heated by the infrared heating tubes to the final pyrolysis temperature with different heating rates. Herein, heating rate refers to the actual temperature of oil shale particles measured by K-type thermocouple for both infrared heating fixed bed reactors. For both reactors, the generated volatile was rapidly cooled down in the condensing tube and the condensed liquid was collected in a bottle. The remaining shale oil was further collected in the maximum extent by absorbing in the acetone washing bottles. The volume of non-condensable gas was metered and the purified pyrolysis gas by a sodium bicarbonate and a silica gel column was finally collected in gas bags for further gas composition analysis. The pyrolysis pressure was controlled to vacuum condition by vacuum pump for minimizing the secondary reactions to the pyrolysis volatile. After each experiment, the entire system was cleaned by acetone. The excessive acetone was removed using a rotary vacuum evaporator at temperature of 25 ºC and a reduced pressure of 0.2 atm. The condensed liquid was further dehydrated using MgSO4 and filtrated to remove the impurities. Finally, the filtrate was evaporated in the rotary vacuum evaporator to recover pure shale oil. The weight of shale oil was recorded to determine the shale oil yield. The shale char was also collected and weighed after cooling down the system to define the char yield. 2.2 Material and analysis The Huadian oil shale from Jilin province of China was used as the test sample. For the primate preparation, the oil shale sample was crushed and sieved to 0.5-1.0 mm and further dried at 110˚C for 24 h in an air oven. Table 1 shows the proximate and ultimate analysis for the Huadian oil shale. The volatile content was 26.3 wt.% and the shale oil yield determined by the Fischer Assay was 11.16 wt.% on dry base.
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The purified shale oil was analyzed using simulated distillation GC (Agilent 7890A) according to the ASTM D2887-01a standard to determine its boiling point distribution. The shale oil was further analyzed using a GC-MS spectrometer (Shimadzu QP 2010 Ultra) to identify major chemical composition of shale oil. The GC was equipped with a 30-m RTX5MS fused silica capillary column, and helium was used as its carrier gas. The temperature of GC injector and detector was 280 ˚C. The column temperature was first kept at 50 ˚C and then heated to 280 ˚C with 6 ˚C/min and finally held at 280 ˚C for 10 min. The solvent delay time for GC-MS analysis was 1.7 min, and the scanning range of mass was from 20 to 900 m/z. The proportion of peak area of each component to the total area of all peaks was calculated to determine the concentration of the corresponding compounds. The non-condensable gas was analyzed in a micro GC (Agilent 3000A) to define the concentrations of major gas species including H2, CH4, CO, CO2, C2H4, C2H6, C3H6 and C3H8. Herein, C2H4, C2H6, C3H6 and C3H8 are defined as C2+C3. 3. Results and Discussion 3.1 Pyrolysis at different heating rates for two reactors The pyrolysis of oil shale in two tested infrared heating fixed bed reactors which had different heating direction towards the pyrolysis volatile flow was conducted under various heating rate conditions, from 0.1 ˚C/s to maximum heating rate of each reactor, to investigate the influence of secondary reactions on the yield and quality of pyrolysis products. The direction of infrared radiation was co-current and cross-current against the flow of generated volatile for the co-current and cross-current infrared heating reactor, respectively. The highest heating rate of oil shale particle for these two infrared heating reactors was different. The cross-current infrared heating reactor allowed the operation to get the quickest heating rate of 7 ºC/s which was lower than that of the co-current infrared heating reactor (25 ºC/s), because the quartz tube used in the cross-current system diminished the energy of infrared radiation to oil shale particles. However, the infrared beam directly heated up the oil shale particle in the co-current infrared heating reactor. The tests in both reactors were conducted at the pyrolysis temperature of 550 ˚C with the variation of heating rate under atmospheric pressure. 5
Figure 3 compares the product distribution for two different infrared heating fixed-bed reactors at various heating rates. The yield of shale char gradually decreased with increasing heating rate in both reactors. The shale oil yield reached the maximum of 10.19 wt.% with the heating rate of 0.5 ˚C/s and slightly dropped to 9.65 wt.% with increasing heating rate to 25 ˚C/s in the co-current infrared heating reactor. Nevertheless, the shale oil yield gradually increased from 10.72 wt.% to 13.07 wt.% with increasing heating rate from 0.1 to 7 ˚C/s for the pyrolysis in the cross-current infrared heating reactor. This shale oil recovery at the quickest heating rate of 7 C/s was 117.7% against Fischer Assay oil yield. Increasing the heating rate from 0.1 to 7 C/s lowered the gas production from 5.08 wt.% to 3.85 wt.% for the pyrolysis in the cross-current infrared heating reactor, whereas the gas yield in the cocurrent infrared reactor increased from 7.86 wt.% to 10.11 wt.% with increasing heating rate from 0.1 to 25 C/s. Almost two times higher gas yield under rapid pyrolysis in the co-current system can be attributed to the high extent of secondary reactions of pyrolysis volatile. It indicates that the secondary reactions were obviously suppressed due to the change of heating direction in the cross-current system. Figure 4a presents the effect of heating rate on shale oil fraction based on its boiling points for oil shale pyrolysis in two different infrared heating fixed bed reactors at a temperature of 550 C under atmospheric pressure. The content of light oil (b.p. < 350 C) decreased from 36.66 wt.% to 31.82 wt.%, but the fraction of heavy oil (b.p. ≥ 350 C) increased from 63.34 wt.% to 68.18 wt.% with raising the heating rate from 0.1 to 7 C/s in the cross-current infrared heating reactor. On the contrary, increasing the heating rate from 0.1 to 25 C/s for the pyrolysis in the concurrent infrared heating reactor gradually lowered the heavy oil content from 66.42 wt.% to 56.4 wt.%, and increased the light oil fraction from 33.58 wt.% to 43.6 wt.%. This indicates the cracking of heavy oil to lighter species under fast heating conditions in the shallow infrared heating fixed bed reactor, whereas it suggests the suppression of the cracking reactions of heavy oil fraction in the cross-current infrared heating reactor. 6
The chemical compositions of shale oil from the analysis by GC/MS were classified into four groups of alkanes, alkenes, aromatic species and heteroatom compounds. The relative concentration of these chemical compounds determined by integrating their corresponding peak areas is compared in Figure 4b. Increasing heating rate gradually lowered the area percentage of alkane compounds (46% to 38%) but increased the area percentage of alkenes (36% to 41%) and aromatic species (3% to 5%) for the pyrolysis of oil shale in the co-current infrared heating reactor. Conversely, increasing heating rate did not significantly vary the area percentages of alkanes (52% to 55%), alkenes (23% to 29%) and aromatic compounds (0.2% to 0.6%) for the pyrolysis in the cross-current system. The area percentages of heteroatom species were 14% to 16% and 16% to 21% for the co-current and cross-current reactors, respectively, which were insignificantly different with the variation of heating rate for both reactors. Furthermore, the relative concentrations of alkene and aromatic compounds in the co-current system were obviously higher than those in cross-current system, but the content of alkane hydrocarbons was lower than that in the cross-current system at all tested heating rates. These indicate the high conversion of alkane hydrocarbon to alkene and aromatic species through cracking and aromatization in the co-current reactor [27]. Therefore, it suggests the intensive secondary reactions for the oil shale pyrolysis in the co-current infrared heating reactor particularly under rapid pyrolysis. These results demonstrate that the different approaches of infrared radiation for these two reactors had the influence on the secondary reactions of volatile. The radiation direction of infrared heating is parallel to the volatile flow in co-current system, which directly radiated not only to the oil shale particle but also to the released volatile. Thus it prolonged the residence time of volatile and thus lowered the shale oil yield and increased the gas production in the co-current infrared heating reactor. While the heating direction is perpendicular to the volatile flow in the cross-current infrared heating system, which shortened the volatile residence time within the radiation region of infrared beam, minimizing the heating to volatile. This verified the actual reduction of secondary reactions, particularly
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for cracking reactions, leading to the obviously higher oil yield for the pyrolysis of oil shale in the cross-current infrared heating reactor. The shale oil compositions obtained by GC-MS for Infrared heating reactors were compared with the Fischer Assay results, as shown in Figure 5. The area percentages of alkane and alkene hydrocarbon for the cross-current infrared heating reactor and Fischer Assay were identical (54% and 29%, respectively). On the other hand, the shale oil from the co-current heating infrared reactor had significantly lesser alkane (37.87%) and more alkene compounds (41.66%). The area percentages of aromatics were insignificantly different for the co-current heating reactor and Fischer Assay (3-5%), but there was almost no content (just 0.15%) in the case of the cross-current heating infrared reactor. The area percentages of heteroatom species were similar for all tested reactors. These results show the cross-current infrared heating reactor has the advantages of reducing the cracking and aromatization of the volatile comparing with Fischer Assay and the co-current infrared heating system. Figure 6 presented the influence of heating rate for oil shale pyrolysis on the yield of major non-condensable gas in two different reactors at a temperature of 550 C under normal pressure. Increasing heating rate gradually increased all gas yields for the pyrolysis of oil shale in the co-current infrared heating reactor, whereas most of the major gas yields were maximum at the heating rate of 0.5C /s and gradually decreased with increasing heating rate for the cross-current system. Furthermore, the pyrolysis in the co-current apparently produced almost twice yields of H2, CO2 and C2 + C3 in comparison with the pyrolysis in the crosscurrent reactor, particularly under rapid pyrolysis. This large increasing of H2 and C2 + C3 can be attributed to the massive secondary cracking of shale oil, and the high production of CO2 was from the decarboxylation of the organic compounds [28]. Therefore, the modification of heating method to the cross-direction with the flow of pyrolysis products contributed the suppression of secondary reactions and the yield increase of shale oil.
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3.2 Pyrolysis with minimized secondary reactions Many literatures have reported that vacuum pyrolysis has a potential to increase shale oil yield due to the quick extraction of the volatile from the materials and the high temperature region of the reactor [29, 30]. Therefore, the pyrolysis of oil shale should be conducted under reduced pyrolysis pressure, e.g. 0.6 atm, to investigate the pyrolysis behavior under the conditions with minimized secondary reactions. According to the results of pyrolysis product distribution with the variation of heating rate, the pyrolysis at the heating rate of 0.5 and 7 C/s for the co-current and cross-current infrared heating fixed bed reactor, respectively, showed the conditions with the maximized suppression of secondary reactions. Thus, the oil shale pyrolysis would perform under the heating rates mentioned above with a pyrolysis temperature of 550 C. Figure 7 shows the product yield and hydrogen allocation distribution of oil shale pyrolysis by Fischer Assay and that with the highest shale oil yield for two infrared heating reactors. There was insignificantly difference in the char yield and hydrogen proportion for both infrared heating reactors, which were relatively lower than Fischer Assay did. The crosscurrent infrared heating reactor produced the maximum of shale oil yield with the highest proportion of hydrogen. This shale oil yield (13.67 wt.%) was over 120 wt.% against Fischer Assay. On the contrary, the co-current infrared heating reactor produced the lowest yield of shale oil with relatively low hydrogen proportion. Furthermore, this co-current reactor produced the highest gas yield in comparison with other reactors. This shows the relatively high degree of secondary reactions to volatile for the pyrolysis of oil shale in the co-current infrared heating reactor even at the minimized secondary conditions. Conversely, it indicates the great suppression of secondary reactions in the cross-current infrared heating reactor for the maximization of shale oil yield. This suppression of secondary reactions resulted from the pyrolysis conditions under fast heating and reducing pressure which shortened the volatile residence time by quick generating and removing the volatile from the shale particles and hot zone of the reactor. Moreover, direct infrared radiation to the volatile was avoided due to the
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cross-current heating to the flow of volatile, which contributed to the minimization of secondary reactions in the cross-current infrared heating reactor under rapid pyrolysis with reducing pyrolysis pressure condition. The distillated fractions of shale oil from Fischer Assay and two infrared heating reactors at the minimized secondary reactions conditions were shown in Figure 8a. The shale oil from Fischer Assay had the highest light oil fraction of 42.7 wt.% and the lowest VGO content of 53.62 wt.%. The light oil lowered to 33.62 wt.% and 30.85 wt.% but the fraction of VGO increased to 61.87 wt.% and 65.6 wt.% for the pyrolysis of oil shale in the co-current and cross-current infrared heating reactor, respectively. The heavy oil fractions of shale oil from all three reactors had no significantly difference. This suggests that the cracking and generation of heavy oil compounds in the cross-current infrared heating reactor reach to a balance relative to other reactors. The distillated yield of the corresponding shale oil fraction in Figure 8b supports the superior suppression of secondary reactions in the cross-current infrared heating reactor. The pyrolysis in the cross-current infrared heating reactor under the tested conditions produced the highest yield of VGO fraction (8.96 wt.%), 4.21 wt.% of light oil and 0.49 wt.% of heavy oil fraction. The light oil yield of 4.21 wt.% was higher than that in co-current reactor, but slightly lower than that in Fischer Assay. The fraction of heavy oil was similar in all three reactors. These results verify the minimization of secondary reactions in this cross-current reactor under this tested condition. Figure 9 presents the yields of major gas components for oil shale pyrolysis in two infrared heating reactors and Fischer assay. The yields of H2 and CO were similar for three reactors. Nevertheless, the yields of CH4 and C2+C3 were obviously higher in the case of the co-current infrared heating reactor. This shows the co-current heating infrared reactor contributes to the appearance of cracking reactions toward the generated volatile, whereas the modification of heating pathway to the cross-current with the volatile flow dominates the avoidance of secondary reactions.
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4. Conclusions The pyrolysis of oil shale was performed in two different infrared heating fixed bed reactors, co-current and cross-current reactors, to investigate the characteristics of pyrolysis products under fast infrared heating conditions with different directions of infrared radiation to the flow of volatile. The rapid pyrolysis of oil shale in the co-current infrared heating reactor (heating rate of 25 C/s) generated relatively lower shale oil yield but higher gas yield in comparison to that in the cross-current infrared heating reactor (heating rate of 7 C/s). The radiation of infrared beam in the co-current infrared heating reactor directly radiated to the generated volatile and caused the great extent of volatile cracking, which decreased the oil yield and favored the production of gas. Conversely, the infrared radiation in the cross-current reactor had little action on the generated volatile due to the rapid departure of the volatile from the radiation beam, thus allowing the higher shale oil yield and lower production of gas. The shale oil yield produced from the rapid pyrolysis in the cross-current infrared heating reactor reached 117.7 wt.% and 122.5 wt.% of the Fischer Assay yield under the atmospheric pressure and reduced pressure of 0.6 atm, respectively. The obtained shale oil from the pyrolysis in the cross-current infrared heating reactor had higher content of light oil and vacuum gas oil (VGO) than that in the co-current reactor. Moreover, it also had more hydrogen proportion than the co-current infrared heating reactor and Fischer Assay did. These verify the minimization of secondary reactions under the rapid pyrolysis in the cross-current infrared heating reactor. Therefore, the modification of the heating method that avoids the direct radiation of infrared beam to the generated volatile truly greatly reduced secondary reactions to volatile and allows the production of more shale oil.
5. Acknowledgement The study was financially supported by the National Basic Research Program of China (2014CB744303), National Natural Science Foundation of china (91534125) and CASTWAS President’s Fellowship for International PhD Students.
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Table 1. Characterization of tested Huadian oil shale. Proximate analysis (wt.%, db) A
V
FC
67.36
26.3
6.34
Fischer Assay (wt.%, db)
Ultimate analysis (wt.%, db) C
H
O*
N
S
21.72 2.71 0.60 0.59 0.68
*By difference.
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Char
Shale oil
Water
Gas
78.86
11.16
4.60
5.37
1. Nitrogen gas; 2. Mass flow controller; 3. Thermocouple; 4. Infrared heating Furnace; 5. Reactor tube; 6. Condenser; 7. Collection bottle; 8. Acetone washing bottle; 9. Wet gas meter; 10. NaHCO3 washing bottle; 11. Silica gel bottle; 12. Gas sampling Figure 1. A schematic diagram of the cross-current infrared heating pyrolysis reactor.
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1. Nitrogen gas; 2. Mass flow controller; 3. Pressure gauge; 4. Gas distributor; 5. Infrared heating tubes; 6. Thermocouple; 7. Sample plate; 8. Condenser; 9. Collection bottle; 10. Acetone washing bottle; 11. Vacuum pump; 12. Wet gas meter; 13. NaHCO3 washing bottle; 14. Silica gel bottle; 15. Gas sampling Figure 2. A schematic diagram of the co-current infrared heating pyrolysis reactor.
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Figure 3. Distribution of products for oil shale pyrolysis in cross-current infrared heating (IFR-Cross) and co-current infrared heating (IFR-Co) reactors at a pyrolysis temperature of 550 ˚C but varied heating rates under the atmospheric pressure.
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Figure 4. Variation of shale oil composition based on (a) simulated distillation analysis and (b) GC-MS analysis for oil shale pyrolysis in cross-current infrared heating (IFR-Cross) and co-current infrared heating (IFR-Co) reactors at a pyrolysis temperature of 550 ˚C but varied heating rates under the atmospheric pressure.
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Figure 5. Comparison of shale oil components based on GC-MS analysis for oil shale pyrolysis by Fischer Assay and two infrared heating reactors (IFR-Cross and IFR-Co) at a pyrolysis temperature of 550 oC.
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Figure 6. Comparison of pyrolysis gas composition for oil shale pyrolysis in (a) cross-current infrared heating and (b) co-current infrared heating reactors under varied heating rates but the atmospheric pressure and a pyrolysis temperature of 550 C.
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Figure 7. Comparison of product yield and hydrogen allocation distribution for pyrolysis by the Fischer Assay and that with the highest shale oil yield for both cross-current infrared heating and co-current infrared heating at a reaction temperature of 550 oC.
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Figure 8. Comparison of (a) shale oil fraction and (b) oil distillate yield for pyrolysis by the Fischer Assay and that with the highest shale oil yield for reactors of cross-current (IFR-Cross) and co-current (IFR-Co) infrared heating at a reaction temperature of 550 oC
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Figure 9. Comparison of pyrolysis gas composition for oil shale pyrolysis by the Fischer Assay and two infrared heating reactors at a pyrolysis temperature of 550 oC
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Graphical Abstract
26
Highlights • • • •
Infrared radiation can significantly enhance the heating rate to oil shale particles. The co-current infrared radiation heats not only particles but also volatile generated from pyrolysis. The adopted cross-current infrared heating reactor reached 122.5% of the Fischer Assay yield. The cross-infrared heating effectively merges quick heating and minimization of secondary reactions.
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S2588-9133(18)30051-6 https://doi.org/10.1016/j.crcon.2018.09.001 CRCON 29
To appear in:
Carbon Resources Conversion
Received Date: Revised Date: Accepted Date:
24 July 2018 28 August 2018 10 September 2018
Please cite this article as: S. Siramard, J-H. Zhan, Z. Han, S. Xu, G. Xu, Secondary cracking of volatile and its avoidance in infrared-heating pyrolysis reactor, Carbon Resources Conversion (2018), doi: https://doi.org/10.1016/ j.crcon.2018.09.001
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Secondary cracking of volatile and its avoidance in infraredheating pyrolysis reactor Somprasong Siramarda,c, Jin-Hui Zhana,* Zhennan Hanb, Shipei Xua,c and Guangwen Xua,b,* a
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
b
Institute of Industrial Chemistry and Energy Technology, Shenyang University of Chemical Technology, Shenyang 110142, China
c
University of Chinese Academy of Sciences, Beijing 100049, China
* Corresponding Author, Tel: +86 10 82544886, Fax: +86 10 82629912. E-mail: [email protected] (J.-H. Zhan), [email protected] (G.W. Xu).
Abstract: This study aims to compare the pyrolysis behavior of Huadian oil shale in two infrared heating fixed bed reactors with different directions of infrared beam. Our previous work has shown that fast pyrolysis of oil shale conducted in the shallow fixed bed infrared heating reactor (co-current) presented the massive secondary reactions, which lowered the shale oil production (Energy & Fuels, 31, 2017: 6996-7003). Conversely, the cross-current infrared achieved shale oil yields higher than the Fischer Assay oil yield (13.07 wt.% of dry basis), such as 117.7% of the Fischer Assay yield at our realized highest heating rate of 7 ˚C/s under a specified pyrolysis temperature of 550 ºC. The shale oil from the cross-current infrared heating reactor was obviously heavier than the oil obtained from the co-current heating reactor. Thus, the infrared cross heating evidently suppressed the secondary reactions toward volatile. Our realized shale oil yield could reach 13.67 wt.% or 122.5% of the Fischer Assay yield under reducing pyrolysis pressure of 0.6 atm, indicating that lower pressure is also beneficial to the release of volatile and reduction of the secondary cracking reactions. This work shows essentially that the infrared cross heating provides an effective merge of the advantages from quick heating and minimization of secondary cracking reactions to enable the shale oil yields being higher than the Fischer Assay oil yield. Keywords: Pyrolysis; Secondary cracking; Volatile; Infrared heating; Oil shale.
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1.
Introduction Pyrolysis of oil shale is the well-known technology for the utilization of oil shale to
produce shale oil as an alternative of petroleum fuels. Basically, the oil shale pyrolysis occurs in two steps of the decomposition of kerogen molecule in oil shale (primary reactions) and the subsequent reactions of the generated volatile (secondary reactions) [1]. The extent of these secondary reactions had the influence on the distribution and composition of the pyrolysis products especially liquid shale oil. To control the quality and quantity of pyrolysis products, it is generally subjected to many operating conditions, for example, pyrolysis temperature [24], heating rate [3-6], pyrolysis pressure [7-9], residence time of volatile [10], particle size [11-14], mineral matrix [15] and others. Pyrolysis can broadly divide into slow and fast pyrolysis according to its heating rate [16]. Many studies focused on exploring oil shale pyrolysis behavior under the slow heating rate. Increasing the heating rate to 10 ºC/min increased the shale oil production due to the higher self-generated gas sweep rates during retorting which allowed the high recovery of shale oil. However, the shale oil yield slightly decreased with further increasing heating rate to 30 ºC/min, which may be attributed to the fact that a large number of pyrolytic volatile produced cannot be rapidly diffused, resulting in the secondary cracking reactions [17-18]. Moreover, Wang et. al. [19] reported the increases of the light oil fraction and the noncondensable gas with increasing the heating rate from 5 to 20 ºC/min. Regarding to fast pyrolysis, it is a well-known approach to produce high volatile matter content [20]. There are many techniques used to investigate the decomposition of solid under rapid heating such as wire mesh reactor [21-22], micro pyrolyzer with a combination of GC/MS [23-24] and thermogravimetry analysis [25]. Besides, infrared radiation is used as the heating source for many applications such as food processing, surface heating and solid decomposition, which is an efficient technique for fast heating process since the energy from the radiation of infrared is directly transferred to the material. The fast pyrolysis of Huadian oil shale in the shallow fixed bed mounted with infrared heating presented a high extent of secondary cracking for the rapid pyrolysis of oil shale. The direction of the infrared radiation 2
is parallel to that of the volatile flow in this concurrent reactor, causing the volatile matter to occur secondary reactions at high temperature. In this respect, the modification of heating method to the cross flow of volatile could suppress the degree of secondary reactions. In order to realize the maximum yield of shale oil, this article is devoted to investigating the pyrolysis characteristics of Huadian oil shale in the cross-current infrared heating reactor and to comparing that obtained in the co-current infrared heating reactor under varied heating rates and pyrolysis pressures. It is expected to understand the effect of different approaches of infrared radiation on secondary reactions, and to verify whether the cross-current infrared heating is possible to alleviate the secondary reactions to generated volatile.
2. Experimental Section 2.1 Facility and procedure Two kinds of infrared heating fixed bed reactors which had different pathway between the heating direction and the flow of the generated pyrolysis vapor, cross-current and cocurrent, were used to compare the pyrolysis behavior of oil shale pyrolysis. Figure 1 shows a schematic diagram of the cross-current infrared heating fixed bed reactor. The reactor tube was made of quartz which had an inner diameter of 10 mm and a length of 300 mm. The reactor was indirectly heated by the infrared heating tubes with a cross direction to the release pathway of the generated pyrolysis vapor. The infrared heating tubes had a power of 10 kW to ensure the quickest heating rate of 7 ˚C/s to oil shale particles inside the reactor tube. Approximately 3 g of oil shale was loaded into the reactor tube. High purity N 2 gas with the flow rate of 100 ml/min was used as the carrier gas to sweep the generated pyrolysis vapor from the top to the bottom of the reactor. The entire system was purged with N2 gas for 15 min before running the experiment to ensure the inert atmosphere. Figure 2 shows a process diagram of the co-current infrared heating fixed bed reactor, which it was explained elsewhere [26]. Briefly, the infrared heating tubes with a total power of 27 kW were horizontally parallel to the sample plate, which had an inner diameter of 350 mm and a height of 10 mm, with a distance of 50 mm. A thin layer of 20 g of oil shale 3
particles was evenly spread on the sample plate. The infrared beam was directly radiated to the oil shale sample with the highest heating rate of 25 ˚C/s. The reactor chamber was evacuated to remove air and then was filled with high purity N2 gas to form an inert atmosphere. The Nitrogen carrier gas of 20 L/min flowed downward to sweep the generated volatile into the cooling tube bundle. The oil shale particles were directly heated by the infrared heating tubes to the final pyrolysis temperature with different heating rates. Herein, heating rate refers to the actual temperature of oil shale particles measured by K-type thermocouple for both infrared heating fixed bed reactors. For both reactors, the generated volatile was rapidly cooled down in the condensing tube and the condensed liquid was collected in a bottle. The remaining shale oil was further collected in the maximum extent by absorbing in the acetone washing bottles. The volume of non-condensable gas was metered and the purified pyrolysis gas by a sodium bicarbonate and a silica gel column was finally collected in gas bags for further gas composition analysis. The pyrolysis pressure was controlled to vacuum condition by vacuum pump for minimizing the secondary reactions to the pyrolysis volatile. After each experiment, the entire system was cleaned by acetone. The excessive acetone was removed using a rotary vacuum evaporator at temperature of 25 ºC and a reduced pressure of 0.2 atm. The condensed liquid was further dehydrated using MgSO4 and filtrated to remove the impurities. Finally, the filtrate was evaporated in the rotary vacuum evaporator to recover pure shale oil. The weight of shale oil was recorded to determine the shale oil yield. The shale char was also collected and weighed after cooling down the system to define the char yield. 2.2 Material and analysis The Huadian oil shale from Jilin province of China was used as the test sample. For the primate preparation, the oil shale sample was crushed and sieved to 0.5-1.0 mm and further dried at 110˚C for 24 h in an air oven. Table 1 shows the proximate and ultimate analysis for the Huadian oil shale. The volatile content was 26.3 wt.% and the shale oil yield determined by the Fischer Assay was 11.16 wt.% on dry base.
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The purified shale oil was analyzed using simulated distillation GC (Agilent 7890A) according to the ASTM D2887-01a standard to determine its boiling point distribution. The shale oil was further analyzed using a GC-MS spectrometer (Shimadzu QP 2010 Ultra) to identify major chemical composition of shale oil. The GC was equipped with a 30-m RTX5MS fused silica capillary column, and helium was used as its carrier gas. The temperature of GC injector and detector was 280 ˚C. The column temperature was first kept at 50 ˚C and then heated to 280 ˚C with 6 ˚C/min and finally held at 280 ˚C for 10 min. The solvent delay time for GC-MS analysis was 1.7 min, and the scanning range of mass was from 20 to 900 m/z. The proportion of peak area of each component to the total area of all peaks was calculated to determine the concentration of the corresponding compounds. The non-condensable gas was analyzed in a micro GC (Agilent 3000A) to define the concentrations of major gas species including H2, CH4, CO, CO2, C2H4, C2H6, C3H6 and C3H8. Herein, C2H4, C2H6, C3H6 and C3H8 are defined as C2+C3. 3. Results and Discussion 3.1 Pyrolysis at different heating rates for two reactors The pyrolysis of oil shale in two tested infrared heating fixed bed reactors which had different heating direction towards the pyrolysis volatile flow was conducted under various heating rate conditions, from 0.1 ˚C/s to maximum heating rate of each reactor, to investigate the influence of secondary reactions on the yield and quality of pyrolysis products. The direction of infrared radiation was co-current and cross-current against the flow of generated volatile for the co-current and cross-current infrared heating reactor, respectively. The highest heating rate of oil shale particle for these two infrared heating reactors was different. The cross-current infrared heating reactor allowed the operation to get the quickest heating rate of 7 ºC/s which was lower than that of the co-current infrared heating reactor (25 ºC/s), because the quartz tube used in the cross-current system diminished the energy of infrared radiation to oil shale particles. However, the infrared beam directly heated up the oil shale particle in the co-current infrared heating reactor. The tests in both reactors were conducted at the pyrolysis temperature of 550 ˚C with the variation of heating rate under atmospheric pressure. 5
Figure 3 compares the product distribution for two different infrared heating fixed-bed reactors at various heating rates. The yield of shale char gradually decreased with increasing heating rate in both reactors. The shale oil yield reached the maximum of 10.19 wt.% with the heating rate of 0.5 ˚C/s and slightly dropped to 9.65 wt.% with increasing heating rate to 25 ˚C/s in the co-current infrared heating reactor. Nevertheless, the shale oil yield gradually increased from 10.72 wt.% to 13.07 wt.% with increasing heating rate from 0.1 to 7 ˚C/s for the pyrolysis in the cross-current infrared heating reactor. This shale oil recovery at the quickest heating rate of 7 C/s was 117.7% against Fischer Assay oil yield. Increasing the heating rate from 0.1 to 7 C/s lowered the gas production from 5.08 wt.% to 3.85 wt.% for the pyrolysis in the cross-current infrared heating reactor, whereas the gas yield in the cocurrent infrared reactor increased from 7.86 wt.% to 10.11 wt.% with increasing heating rate from 0.1 to 25 C/s. Almost two times higher gas yield under rapid pyrolysis in the co-current system can be attributed to the high extent of secondary reactions of pyrolysis volatile. It indicates that the secondary reactions were obviously suppressed due to the change of heating direction in the cross-current system. Figure 4a presents the effect of heating rate on shale oil fraction based on its boiling points for oil shale pyrolysis in two different infrared heating fixed bed reactors at a temperature of 550 C under atmospheric pressure. The content of light oil (b.p. < 350 C) decreased from 36.66 wt.% to 31.82 wt.%, but the fraction of heavy oil (b.p. ≥ 350 C) increased from 63.34 wt.% to 68.18 wt.% with raising the heating rate from 0.1 to 7 C/s in the cross-current infrared heating reactor. On the contrary, increasing the heating rate from 0.1 to 25 C/s for the pyrolysis in the concurrent infrared heating reactor gradually lowered the heavy oil content from 66.42 wt.% to 56.4 wt.%, and increased the light oil fraction from 33.58 wt.% to 43.6 wt.%. This indicates the cracking of heavy oil to lighter species under fast heating conditions in the shallow infrared heating fixed bed reactor, whereas it suggests the suppression of the cracking reactions of heavy oil fraction in the cross-current infrared heating reactor. 6
The chemical compositions of shale oil from the analysis by GC/MS were classified into four groups of alkanes, alkenes, aromatic species and heteroatom compounds. The relative concentration of these chemical compounds determined by integrating their corresponding peak areas is compared in Figure 4b. Increasing heating rate gradually lowered the area percentage of alkane compounds (46% to 38%) but increased the area percentage of alkenes (36% to 41%) and aromatic species (3% to 5%) for the pyrolysis of oil shale in the co-current infrared heating reactor. Conversely, increasing heating rate did not significantly vary the area percentages of alkanes (52% to 55%), alkenes (23% to 29%) and aromatic compounds (0.2% to 0.6%) for the pyrolysis in the cross-current system. The area percentages of heteroatom species were 14% to 16% and 16% to 21% for the co-current and cross-current reactors, respectively, which were insignificantly different with the variation of heating rate for both reactors. Furthermore, the relative concentrations of alkene and aromatic compounds in the co-current system were obviously higher than those in cross-current system, but the content of alkane hydrocarbons was lower than that in the cross-current system at all tested heating rates. These indicate the high conversion of alkane hydrocarbon to alkene and aromatic species through cracking and aromatization in the co-current reactor [27]. Therefore, it suggests the intensive secondary reactions for the oil shale pyrolysis in the co-current infrared heating reactor particularly under rapid pyrolysis. These results demonstrate that the different approaches of infrared radiation for these two reactors had the influence on the secondary reactions of volatile. The radiation direction of infrared heating is parallel to the volatile flow in co-current system, which directly radiated not only to the oil shale particle but also to the released volatile. Thus it prolonged the residence time of volatile and thus lowered the shale oil yield and increased the gas production in the co-current infrared heating reactor. While the heating direction is perpendicular to the volatile flow in the cross-current infrared heating system, which shortened the volatile residence time within the radiation region of infrared beam, minimizing the heating to volatile. This verified the actual reduction of secondary reactions, particularly
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for cracking reactions, leading to the obviously higher oil yield for the pyrolysis of oil shale in the cross-current infrared heating reactor. The shale oil compositions obtained by GC-MS for Infrared heating reactors were compared with the Fischer Assay results, as shown in Figure 5. The area percentages of alkane and alkene hydrocarbon for the cross-current infrared heating reactor and Fischer Assay were identical (54% and 29%, respectively). On the other hand, the shale oil from the co-current heating infrared reactor had significantly lesser alkane (37.87%) and more alkene compounds (41.66%). The area percentages of aromatics were insignificantly different for the co-current heating reactor and Fischer Assay (3-5%), but there was almost no content (just 0.15%) in the case of the cross-current heating infrared reactor. The area percentages of heteroatom species were similar for all tested reactors. These results show the cross-current infrared heating reactor has the advantages of reducing the cracking and aromatization of the volatile comparing with Fischer Assay and the co-current infrared heating system. Figure 6 presented the influence of heating rate for oil shale pyrolysis on the yield of major non-condensable gas in two different reactors at a temperature of 550 C under normal pressure. Increasing heating rate gradually increased all gas yields for the pyrolysis of oil shale in the co-current infrared heating reactor, whereas most of the major gas yields were maximum at the heating rate of 0.5C /s and gradually decreased with increasing heating rate for the cross-current system. Furthermore, the pyrolysis in the co-current apparently produced almost twice yields of H2, CO2 and C2 + C3 in comparison with the pyrolysis in the crosscurrent reactor, particularly under rapid pyrolysis. This large increasing of H2 and C2 + C3 can be attributed to the massive secondary cracking of shale oil, and the high production of CO2 was from the decarboxylation of the organic compounds [28]. Therefore, the modification of heating method to the cross-direction with the flow of pyrolysis products contributed the suppression of secondary reactions and the yield increase of shale oil.
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3.2 Pyrolysis with minimized secondary reactions Many literatures have reported that vacuum pyrolysis has a potential to increase shale oil yield due to the quick extraction of the volatile from the materials and the high temperature region of the reactor [29, 30]. Therefore, the pyrolysis of oil shale should be conducted under reduced pyrolysis pressure, e.g. 0.6 atm, to investigate the pyrolysis behavior under the conditions with minimized secondary reactions. According to the results of pyrolysis product distribution with the variation of heating rate, the pyrolysis at the heating rate of 0.5 and 7 C/s for the co-current and cross-current infrared heating fixed bed reactor, respectively, showed the conditions with the maximized suppression of secondary reactions. Thus, the oil shale pyrolysis would perform under the heating rates mentioned above with a pyrolysis temperature of 550 C. Figure 7 shows the product yield and hydrogen allocation distribution of oil shale pyrolysis by Fischer Assay and that with the highest shale oil yield for two infrared heating reactors. There was insignificantly difference in the char yield and hydrogen proportion for both infrared heating reactors, which were relatively lower than Fischer Assay did. The crosscurrent infrared heating reactor produced the maximum of shale oil yield with the highest proportion of hydrogen. This shale oil yield (13.67 wt.%) was over 120 wt.% against Fischer Assay. On the contrary, the co-current infrared heating reactor produced the lowest yield of shale oil with relatively low hydrogen proportion. Furthermore, this co-current reactor produced the highest gas yield in comparison with other reactors. This shows the relatively high degree of secondary reactions to volatile for the pyrolysis of oil shale in the co-current infrared heating reactor even at the minimized secondary conditions. Conversely, it indicates the great suppression of secondary reactions in the cross-current infrared heating reactor for the maximization of shale oil yield. This suppression of secondary reactions resulted from the pyrolysis conditions under fast heating and reducing pressure which shortened the volatile residence time by quick generating and removing the volatile from the shale particles and hot zone of the reactor. Moreover, direct infrared radiation to the volatile was avoided due to the
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cross-current heating to the flow of volatile, which contributed to the minimization of secondary reactions in the cross-current infrared heating reactor under rapid pyrolysis with reducing pyrolysis pressure condition. The distillated fractions of shale oil from Fischer Assay and two infrared heating reactors at the minimized secondary reactions conditions were shown in Figure 8a. The shale oil from Fischer Assay had the highest light oil fraction of 42.7 wt.% and the lowest VGO content of 53.62 wt.%. The light oil lowered to 33.62 wt.% and 30.85 wt.% but the fraction of VGO increased to 61.87 wt.% and 65.6 wt.% for the pyrolysis of oil shale in the co-current and cross-current infrared heating reactor, respectively. The heavy oil fractions of shale oil from all three reactors had no significantly difference. This suggests that the cracking and generation of heavy oil compounds in the cross-current infrared heating reactor reach to a balance relative to other reactors. The distillated yield of the corresponding shale oil fraction in Figure 8b supports the superior suppression of secondary reactions in the cross-current infrared heating reactor. The pyrolysis in the cross-current infrared heating reactor under the tested conditions produced the highest yield of VGO fraction (8.96 wt.%), 4.21 wt.% of light oil and 0.49 wt.% of heavy oil fraction. The light oil yield of 4.21 wt.% was higher than that in co-current reactor, but slightly lower than that in Fischer Assay. The fraction of heavy oil was similar in all three reactors. These results verify the minimization of secondary reactions in this cross-current reactor under this tested condition. Figure 9 presents the yields of major gas components for oil shale pyrolysis in two infrared heating reactors and Fischer assay. The yields of H2 and CO were similar for three reactors. Nevertheless, the yields of CH4 and C2+C3 were obviously higher in the case of the co-current infrared heating reactor. This shows the co-current heating infrared reactor contributes to the appearance of cracking reactions toward the generated volatile, whereas the modification of heating pathway to the cross-current with the volatile flow dominates the avoidance of secondary reactions.
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4. Conclusions The pyrolysis of oil shale was performed in two different infrared heating fixed bed reactors, co-current and cross-current reactors, to investigate the characteristics of pyrolysis products under fast infrared heating conditions with different directions of infrared radiation to the flow of volatile. The rapid pyrolysis of oil shale in the co-current infrared heating reactor (heating rate of 25 C/s) generated relatively lower shale oil yield but higher gas yield in comparison to that in the cross-current infrared heating reactor (heating rate of 7 C/s). The radiation of infrared beam in the co-current infrared heating reactor directly radiated to the generated volatile and caused the great extent of volatile cracking, which decreased the oil yield and favored the production of gas. Conversely, the infrared radiation in the cross-current reactor had little action on the generated volatile due to the rapid departure of the volatile from the radiation beam, thus allowing the higher shale oil yield and lower production of gas. The shale oil yield produced from the rapid pyrolysis in the cross-current infrared heating reactor reached 117.7 wt.% and 122.5 wt.% of the Fischer Assay yield under the atmospheric pressure and reduced pressure of 0.6 atm, respectively. The obtained shale oil from the pyrolysis in the cross-current infrared heating reactor had higher content of light oil and vacuum gas oil (VGO) than that in the co-current reactor. Moreover, it also had more hydrogen proportion than the co-current infrared heating reactor and Fischer Assay did. These verify the minimization of secondary reactions under the rapid pyrolysis in the cross-current infrared heating reactor. Therefore, the modification of the heating method that avoids the direct radiation of infrared beam to the generated volatile truly greatly reduced secondary reactions to volatile and allows the production of more shale oil.
5. Acknowledgement The study was financially supported by the National Basic Research Program of China (2014CB744303), National Natural Science Foundation of china (91534125) and CASTWAS President’s Fellowship for International PhD Students.
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Table 1. Characterization of tested Huadian oil shale. Proximate analysis (wt.%, db) A
V
FC
67.36
26.3
6.34
Fischer Assay (wt.%, db)
Ultimate analysis (wt.%, db) C
H
O*
N
S
21.72 2.71 0.60 0.59 0.68
*By difference.
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Char
Shale oil
Water
Gas
78.86
11.16
4.60
5.37
1. Nitrogen gas; 2. Mass flow controller; 3. Thermocouple; 4. Infrared heating Furnace; 5. Reactor tube; 6. Condenser; 7. Collection bottle; 8. Acetone washing bottle; 9. Wet gas meter; 10. NaHCO3 washing bottle; 11. Silica gel bottle; 12. Gas sampling Figure 1. A schematic diagram of the cross-current infrared heating pyrolysis reactor.
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1. Nitrogen gas; 2. Mass flow controller; 3. Pressure gauge; 4. Gas distributor; 5. Infrared heating tubes; 6. Thermocouple; 7. Sample plate; 8. Condenser; 9. Collection bottle; 10. Acetone washing bottle; 11. Vacuum pump; 12. Wet gas meter; 13. NaHCO3 washing bottle; 14. Silica gel bottle; 15. Gas sampling Figure 2. A schematic diagram of the co-current infrared heating pyrolysis reactor.
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Figure 3. Distribution of products for oil shale pyrolysis in cross-current infrared heating (IFR-Cross) and co-current infrared heating (IFR-Co) reactors at a pyrolysis temperature of 550 ˚C but varied heating rates under the atmospheric pressure.
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Figure 4. Variation of shale oil composition based on (a) simulated distillation analysis and (b) GC-MS analysis for oil shale pyrolysis in cross-current infrared heating (IFR-Cross) and co-current infrared heating (IFR-Co) reactors at a pyrolysis temperature of 550 ˚C but varied heating rates under the atmospheric pressure.
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Figure 5. Comparison of shale oil components based on GC-MS analysis for oil shale pyrolysis by Fischer Assay and two infrared heating reactors (IFR-Cross and IFR-Co) at a pyrolysis temperature of 550 oC.
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Figure 6. Comparison of pyrolysis gas composition for oil shale pyrolysis in (a) cross-current infrared heating and (b) co-current infrared heating reactors under varied heating rates but the atmospheric pressure and a pyrolysis temperature of 550 C.
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Figure 7. Comparison of product yield and hydrogen allocation distribution for pyrolysis by the Fischer Assay and that with the highest shale oil yield for both cross-current infrared heating and co-current infrared heating at a reaction temperature of 550 oC.
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Figure 8. Comparison of (a) shale oil fraction and (b) oil distillate yield for pyrolysis by the Fischer Assay and that with the highest shale oil yield for reactors of cross-current (IFR-Cross) and co-current (IFR-Co) infrared heating at a reaction temperature of 550 oC
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Figure 9. Comparison of pyrolysis gas composition for oil shale pyrolysis by the Fischer Assay and two infrared heating reactors at a pyrolysis temperature of 550 oC
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Graphical Abstract
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Highlights • • • •
Infrared radiation can significantly enhance the heating rate to oil shale particles. The co-current infrared radiation heats not only particles but also volatile generated from pyrolysis. The adopted cross-current infrared heating reactor reached 122.5% of the Fischer Assay yield. The cross-infrared heating effectively merges quick heating and minimization of secondary reactions.
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