Optimization of Chemical Looping Pyrolysis System of Coal Tar by

Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX

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Optimization of Chemical Looping Pyrolysis System of Coal Tar by Combined Simulation and Experiments Mingxin Gong,† Jian Gong,† Xiude Hu,‡ Xiuli Zhang,§ Huawei Jiang,† Yongzhuo Liu,§ Yanhui Li,† and Cuiping Wang*,† †

College of Mechanical and Electrical Engineering, Qingdao University, Qingdao, Shandong 266071, China State Key Laboratory of High-Efficiency Coal Utilization and Green Chemical Engineering, Ningxia University, Yinchuan, Ningxia 750000, China § College of Chemistry and Chemical Engineering, Qingdao University of Science and Technology, Qingdao, Shandong 261500, China

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‡

ABSTRACT: A chemical looping pyrolysis (CLP) system using coal tar as the fuel and Fe2O3 as the oxygen carrier (OC) was established using Aspen Plus software. The variations in reaction rate and product yield in a fuel reactor (FR) and an air reactor (AR) under different operating conditions were measured and analyzed. Then, the simulation results were verified by performing experimental studies. The results show that during the CLP process in FR, the yield of carbon black (CB) and energy conversion efficiency first increased and then decreased with the increase in operating temperature and OC/coal tar ratio. The residence time of reactants in the FR had an insignificant effect on CB yield, whereas the yields of sulfur oxides and nitrogen oxides gradually increased with the increase in operating temperature and residence time. The yield of nitrogen oxides significantly increased with the increase in OC/coal tar ratio, whereas the yield of sulfur oxides remained unchanged. In the AR, with the increase in air/OC ratio, the oxidation rate of reduced iron-based OCs first increased and then maintained a steady value, whereas the temperature had a slight effect. The yield of nitrogen oxides increased with increasing temperature and air/ OC ratio. The operating parameters of the method were optimized as a temperature of 950 °C, an OC/coal tar ratio of 3, a residence time of 2 s in FR, and an air/OC ratio of 2.4 and a temperature of 1100 °C in AR. reforming (CLR), and so on. Zhou5 established process-level models of CLC in Aspen Plus, the entire CLC process, including the coal gasification from the reduction to oxidation of the oxygen carrier, is modeled, and the overall performance and efficiency of the systems are also evaluated. Gopaul and Dutta6 compared the simulation results of two CLG using the Aspen Plus. The sensitivity analyses were conducted for the main reactors to determine the optimal operating conditions. Khan7 developed a CLR system model in Aspen Plus and investigated the effect of various operating parameters such as mass flow rates of air, fuel, steam, and oxygen carrier and key reactor temperatures. In this paper, the CB production craft based on CLP is proposed in Aspen Plus and combined with the experimental to optimize the CLP method for CB production. The OC used in the CLP process is iron ore. The mainstream OCs are artificially prepared metal oxides from Ni, Fe, Cu, Co, etc.,8−11 exhibiting high reactivity, oxygen-carrying capacity, durable cycle capacity, and hightemperature resistance.12−16 However, the operation and manufacturing costs are so high that they are not suitable for large-scale industrialization. In contrast, iron ore has better application prospect because of its abundant reserves, low cost, strong oxygen-carrying capacity, and environmental friendliness.17−22 In this study, the OC of Fe2O3 was used in Aspen Plus, and the Fe/Al compounds were used in experimental,

1. INTRODUCTION Carbon black (CB) is a black powder produced by the incomplete combustion or pyrolysis of hydrocarbon fuels. As an important chemical raw material, CB plays a crucial role in the rubber industry and is the most important reinforcing agent and supplement for rubber. Among the current CB production methods, the oil furnace method with the highest level of automation is the mainstream production method, producing about 95% of the total CB, but the severe pollution caused by high energy consumption is the main problem that should be solved. Therefore, it is important to develop a cleaner production process. On the basis of chemical looping technology principle, the chemical looping pyrolysis (CLP) of coal tar could also be applied for the preparation of CB.1 Compared with the oil furnace method, the coal tar CLP method to produce CB significantly decreases the reaction temperature, which avoids the low life expectancy of materials, and avoids the high energy consumption and uselessness of wet flue gas caused by spraying cold water to high-temperature flue gas.2 At the same time, the lower temperature reaction inhibits the production of nitrogen oxides and reduces the thermal NOx emission. In addition, the reduced oxygen carriers (OCs) enters the air reactor (AR) for regenerative oxidation, which generates a large amount of heat carried by OC particles to be utilized in fuel reactor (FR), and the energy-saving effect should not be ignored.3 The study on the chemical looping technology using Aspen Plus software becomes popular,4 such as the chemical looping combustion (CLC), chemical looping gasification (CLG), chemical looping © XXXX American Chemical Society

Received: October 10, 2018 Revised: December 6, 2018

A

DOI: 10.1021/acs.energyfuels.8b03527 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

Figure 1. Schematic of the process model in Aspen plus.

Table 1. Proximate and Ultimate Analyses of Coal Tara proximate analysis (wt %)

ultimate analysis (wt %)

M

V

A

FC*

C

H

O

N

S

QLHV (MJ/kg)

1.55

81.3

0.58

16.57

86.78

5.27

4.35

0.85

0.62

39.84

* indicates that the data were obtained by subtraction.

a

Table 2. Reactions in FR and AR FR

AR

C14H10 + 6Fe2O3 = 12C + 9FeO + CO + CO2 + 2H2O + 3H2 + Fe3O4 C + H2O = CO + H2 H2 + Fe2O3 = 2FeO + H2O CO + Fe2O3 = 2FeO + CO2 C + Fe2O3 = 2FeO + CO C + 2Fe2O3 = 4FeO + CO2 O2 + 4Fe3O4 = 6Fe2O3 O2 + 4FeO = 2Fe2O3

R1 R2 R3 R4 R5 R6 R7 R8

Figure 2. Fluidized bed reactor.

reactors during the flow reactions, and then the CLP method was optimized.

and coal tar was used as the fuel. The CLP method was analyzed to confirm the key operating parameters for two B


Article

Energy & Fuels

2. SIMULATION AND EXPERIMENT 2.1. Establishment of Process Model. A CLP process of coal tar established in Aspen Plus is shown in Figure 1. Coal tar and OCs were introduced into a FR to react with each other. After the separation from the gaseous products in a cyclone, the reduced OCs, mainly FeO and Fe3O4, entered an AR to react with oxygen in the air and oxidized to regenerate Fe2O3, which was sent to the FR to complete the cycle. The RKS-BM physical property method was selected in Aspen Plus, the separation efficiency of the cyclone was set to 98%, and the total flow rate of the OCs was set by the calculator function. The reaction kinetic parameters involved were calculated or chosen according to the literatures and thermogravimetric experiments. Both the initial conditions and the OC particle size (ranged from 100 to 300 μm) were determined after the serious thermal experiments. Because of the extremely complex composition, coal tar was simplified as C14H10 in Aspen Plus according to the fuel ultimate analysis. The fuel characteristics are shown in Table 1. The chemical reactions involved in FR and AR are shown in Table 2. R1 is the main pyrolysis reaction of coal tar with OCs, and R2−R6 are the possible side reactions dperature. R7 and R8 are the oxidation reactions of reduced OCs in AR.1 At high temperature, Fe2O3 is reduced to produce FeO, Fe3O4, and Fe in theory, but according to the previous analyses by X-ray diffraction (XRD) and scanning electron microscopy-energydispersive X-ray, there was indeed very little Fe in the reduced OCs products, so the amount of Fe produced in different operating conditions of varied oxygen carrier/coal tar molar ratios was neglected, to simplify the calculation and simulation. 2.2. Preparation of Experimental Materials. The Fe/Al compound OCs used in the experiment were prepared by the impregnation method. The coal tar used in the experiment was obtained from the coking plant of Qingdao Iron and Steel Group. It was black in color with a large viscosity, poor fluidity at room temperature, and a pungent smell. 2.3. Experimental Setup. A fluidized bed reactor was built, as shown in Figure 2. Coal tar and OCs were continuously fed into the reactor via two screw feeders. To avoid the blocking problem, the coal tar was preheated to at least 60 °C, and a water bath heat exchanger was added along the outside of the screw feeder, the viscosity of coal tar was reduced so the coal tar flew into the furnace continuously. After the experiment finished, the screw in the screw feeder was taken out and burned in a muffle furnace to prevent any remainder coal tar depositing on the screw. When the hot bottom bed material (sand) was fluidized to heat the coal tar and OCs, the touching reaction occurred. The products (fine reduced OC particles, CB, and gases) were removed from the reactor using the fluidized gas. The fine reduced OC particles were separated using a cyclone separator, and the finer CB particles were collected using a tail bag filter. The temperature of the reactor was regulated using an electric heating plate. Nitrogen was used as the fluidized gas and individually controlled by three rotameters to enter three gas chambers. The amount of bed material in bed was monitored by the pressure difference signal obtained using a pressure sensor.

CB yield φ =

mtar

mc × 100% × 0.8678

(1)

energy conversion efficiency ηb =

mc × Q c + ∑ Vi × Q i mtar × Q net

(2)

OC/coal tar ratio in FR α =

air/OC ratio in AR ψ =

× 100%

OCs flow (mol/s) coal tar flow (mol/s)

air flow (mol/s) OCs flow (mol/s)

(3)

(4)

In eqs 1 and 2, mc and mtar are the masses of CB and coal tar (kg), respectively; Qi, Qc, and Qnet in eq 2 are the calorific values of gaseous products, CB, and coal tar (kJ/m3), respectively. Vi is the volume of each gas component (m3). Energy conversion efficiency, the ratio of the energy of products to the energy of reactants, is an important indicator to evaluate the system performance. The CB yield and energy conversion efficiency parameters reflect the system performance. The higher the value of these parameters, more energy of the raw material was converted into the products, indicating a smaller energy loss of the system. In the experiment, carbon black was collected at the bag filter linked with the outlet of the cyclone, less carbon black bled into the atmosphere. Some carbon black adhered to the wall of the tail pipe, which could be determined by the weight variation of the tail pipe. There was also a very small amount of carbon black adhering to the surface of the oxygen carrier particles, could be analyzed by the TG analyzer experiments, and then the error of carbon black collection was determined. Combining the carbonous gases, the system’s carbon balance value is over 99%. 3.1. Effect of Operating Temperature in FR. Figure 3 shows the effect of operating temperature on CB yield in FR

Figure 3. Variation in CB yield with temperature.

when α was 2 and the residence time was 2 s. The simulation and experimental results showed good agreement in the trend. As the temperature increased from 850 to 1050 °C, the CB yield first increased and then decreased, reaching a maximum at 950 °C. This is because the reactivity of OCs increased in the temperature range of 900−1000 °C, promoting the pyrolysis reactions. When the temperature was higher, the reactivity of OCs decreased because of a small amount of sintering. In addition, the competitive reactions R5 and R6 of

3. RESULTS AND DISCUSSION To evaluate the CLP process of coal tar, several parameters were defined, as shown in eqs 1−4. They were calculated from both the Aspen Plus simulation data and experimental data. C


Article

Energy & Fuels CB with OCs occurred at a higher temperature to generate CO and CO2, as shown in Figure 4. This is one of the reasons for

Figure 6. Variation in energy conversion efficiency with temperature.

Figure 4. Variation in gaseous products with temperature.

the decrease in CB yield. The experimental value was slightly lower than the simulation data, probably because of two aspects: one reason is more complex competitive reactions R2−R6, leading to more CB consumption in FR in practice. The other reason is that not all CB were collected during the experiment, actually some of it adhered to the surface of OCs (carbon deposition) and inner pipe. Figure 4 shows that H2 decrease was caused by the competitive reaction of active H2 with Fe2O3 as the temperature increased. The CO content first decreased and then increased after 950 °C. This is because a part of CB reacted with Fe2O3 above 950 °C, resulting in a sharp increase in CO content. Figure 5 shows that the contents

Figure 7. Changes in CB yield with different α.

approximately the same as the simulation results. Both of them first increased and then decreased with the increase in α. When α < 3, the CB yield rapidly increased. At this time, coal tar did not completely react, and the amount of OCs was the key factor limiting the yield of CB. With the increase in α, the growth in the yield of CB slowed down and reached the peak value at α = 3. When α > 3, the OCs were excess, and the CB reacted with excess OCs and was consumed. Figure 8 shows

Figure 5. Variation in pollutants with temperature.

of nitrogen oxides (mainly NO and a small amount of NH3) and sulfur oxides (mainly H2S and SO2) increased as the temperature increased. With the increase in temperature, the reaction rate between nitrogen and sulfur elements in coal tar and the lattice oxygen released from OCs increased. The energy conversion efficiency curve is shown in Figure 6. The calculation results were compared with the experimental results: the two curves had the same variation trend, and both reached the maximum value at 950 °C. Therefore, the temperature in FR was finally determined to be 950 °C. 3.2. Effect of OC/Coal Tar Ratio in FR. At a temperature of 950 °C and residence time of 2 s, the changes in products and energy conversion efficiency in FR with α range 1−4 were studied. The results are shown in Figures 7−10. As shown in Figure 7, the trend of CB yield obtained in the experiment was

Figure 8. Changes in gaseous products with different α.

that as α increased, more coal tar underwent pyrolysis to produce more CO. In addition, the increase in the amount of OCs also promoted the reaction between OCs and CB, generating more CO and CO2. The increase in the flow rate of H2O was smaller than those of CO and CO2, therefore its content decreased. Figure 9 shows that α had a slight effect on sulfur oxides. This is because sulfur easily reacted with oxygen, D


Article

Energy & Fuels

Figure 9. Changes in sulfur and nitrogen pollutants with different α.

Figure 11. Variation in CB yield with residence time.

and they completely reacted under small α. However, the content of nitrogen oxides rapidly increased with the increase in α. This is because the nitrogen (which is harder to react than sulfur) in coal tar reacted completely with more lattice oxygen released from more OCs. The two curves in Figure 10

Figure 12. Variation in gaseous products with residence time.

Figure 10. Changes in energy conversion efficiency with different α.

show the changes in the energy conversion efficiency with α in the simulation and experiment. The trends of the two showed good agreement, and both increased with the increase in α and then decreased. The maximum value was obtained when α = 3. 3.3. Effect of Residence Time in FR. The temperature and α were set to 950 °C and 3, respectively, and the residence time (2−3.5 s) was changed to determine the changes in products and energy conversion efficiency in FR, as shown in Figures 11−14. Figure 11 shows that as the residence time increased from 2 to 3.5 s, the CB yield from the simulation and experimental results slightly decreased. Only a small amount of CB was consumed because of the involvement in the competitive reactions in FR, indicating that the yield of CB is less affected by the residence time in the range of 2−3.5 s. Figure 12 shows that the contents of H2 and H2O remained the same as the residence time increased. The content of CO continuously decreased, whereas the content of CO2 showed the opposite trend. This is because some CO were converted into CO2. Figure 13 shows that the contents of nitrogen oxides and sulfur oxides continued to increase because of sufficient residence time, so that the nitrogen and sulfur elements in coal tar reacted completely. Both the simulation and experimental results in Figure 14 indicate that the energy conversion efficiency slightly decreased with the increase in residence time. Considering the yield of CB and energy conversion

Figure 13. Variations in sulfur and nitrogen pollutants with residence time.

efficiency, it can be concluded that the pyrolysis reaction of coal tar in FR was completed in about 2 s. An increase in the residence time of coal tar in the reactor would lead to the occurrence of competitive reactions. During the experiment, the residence time was adjusted by changing the amount of fluidized gas, therefore for the convenience of control, the residence time was set as 2 s. 3.4. Effect of Air/OC Ratio in AR. The above simulation results were compared with the experimental results in FR to verify the correctness of chemical reaction model and its simulation. In the CLP of coal tar, the reduced OCs of solidphase products in FR were sent to the AR for regeneration. Therefore, the data of reduced OC mixture output from FR E


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Energy & Fuels

Figure 16. Variation in solid products with Ψ.

Figure 14. Variation in energy conversion efficiency with residence time.

were taken as the AR input to simulate and predict the oxidation reaction characteristics in the AR. The reaction model of AR was established as R7 and R8. A mixture of FeO and Fe3O4 was sent to the AR, and the oxidation reaction of reduced OCs with air was carried out to regenerate Fe2O3. The oxidation reactions in AR produced a large amount of heat, which was recycled to FR by Fe2O3. The AR was operated at 1 atm and 1100 °C. Ψ was adjusted from 1.7 to 2.7 to determine the changes in the gaseous and solid products. Nitrogen in the air reacted with oxygen in the air or lattice oxygen in the OCs to generate thermal NOx at a high temperature. Figure 15 shows that when Ψ < 2.3, the NO Figure 17. Variation in pollutants with temperature.

Figure 15. Variation in pollutants with Ψ. Figure 18. Variation in solid products with temperature.

content was constant, but when Ψ > 2.3 the NO content sharply increased. This is mainly because when Ψ was relatively small, O2 in the air mainly participated in the oxidation of OCs. With the increase in Ψ and at a high temperature, the excess O2 reacted with N2 to generate thermal NOx, mainly NO. Figure 16 shows that Fe2O3 was derived from different reduced iron-based OCs. With the increase in Ψ, the reaction rate of reduced OCs with oxygen rapidly increased. When Ψ was increased to 2.4, the regeneration rate of OCs reached 99.7%. Combined with Figures 15 and 16, the optimal Ψ was selected as 2.4. 3.5. Effect of Temperature in AR. Under condition of 1 atm and Ψ = 2.4, the contents of NOx and OC products in AR as a function of temperature (800−1300 °C) are shown in Figures 17 and18. At a higher temperature, the yield of thermal NO sharply increased from 1200 °C, therefore the reaction temperature in AR should not be higher than 1200 °C. Figure

18 shows that when the temperature was increased from 800 to 1300 °C, the regeneration rate of Fe2O3 remained stable at more than 99%. Then, the oxidation reactions of reduced OCs could be carried out at a lower temperature. From the reaction rate and generation of pollutants, the temperature in AR was selected as 1100 °C. To verify the oxidation ratio of the OCs, the experiment was carried out under the conditions of 950 °C and higher air/OC ratio. The XRD analysis was performed on the OC particles from AR outlet. The resulting curve is shown in Figure 19. Figure 19 shows that the OC compounds after oxidation mainly are consist of Fe2O3 and Al2O3, and there are a very small amounts of Al3Fe5O12 and unoxidized Fe3O4 remained. The oxidation ratio Fe3O4 and FeO to Fe2O3 was 89.9%, slightly lower than the simulated value of 99%. For the gas− solid reaction in a small fluidized bed, some reduced OCs were F


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Energy & Fuels

CB yield and energy conversion efficiency, the system is still endothermic. But in the experimental, the CB deposited on the reduced OCs in FR would burn in AR, which would increase the heat release and send more heat back to FR to compensate the endothermic heat. This victim CB supplied the compensation of the heat gap, which cannot be reflected in Aspen Plus simulation.

4. CONCLUSIONS On the basis of the two indexes of CB yield and energy conversion efficiency, the coal tar CLP system was optimized by simulation and experimental analysis. The key operating parameters of FR, including the operating temperature, α, and residence time, were determined as 950 °C, 3, and 2 s, respectively. The product contents of sulfide and nitrogen oxides in FR increased with the increase in temperature and residence time. As α increased, the content of nitrogen oxides increased significantly, whereas the content of sulfur oxides remained unchanged. The performance of AR was optimized according to the NOx production and OC regeneration rate as the aim indexes. The optimal air/OC ratios in AR and operating temperature were 2.4 and 1100 °C, respectively. With the increase in air/ OC ratio and operating temperature, the content of NOx gradually increased. The regeneration rate of OCs reached 99% in theory and 89.9% in experimental. The Fe/Al OCs performed a steady performance without obvious sintering and decaying occurred under the optimization parameters during the CLP cycle experiments. The mass and energy balance of coal tar CLP system were analyzed under the optimal conditions. The heat load of the entire system was 47.487 kJ, indicating an endothermic system.

Figure 19. XRD analysis of regenerated OCs from AR.

not in sufficient contact with air, resulting in insufficient oxidation existence. 3.6. Mass and Energy Balance Analysis of System. On the basis of the coal tar treatment capacity of 103 g/h in the experiment, the mass and energy balance of coal tar CLP system under optimal conditions were analyzed. From the previous discussion, the optimal operating parameters of FR were T = 950 °C, α = 3, and t = 2 s. The optimal operating parameters of AR were Ψ = 2.4 and T = 1100 °C. As shown in Table 3, the solid products in the FR outlet are composed of CB and different reduced OCs, and the CB accounting for 68.73% of the total molar amount of solid products. A lot of CO2 was present in the gaseous products, and the syngas (CO, H2) accounted for 52.19% of the total. OCs were mainly reduced to FeO. The gaseous products in the AR mainly include the remaining N2 and a small amount of O2. The reduced OCs of FeO and Fe3O4 were oxidized to regenerate Fe2O3. In terms of energy balance, the heat loads of the FR and AR were 830.4016 and −782.9146 kJ, respectively. The net heat load of the entire system was 47.487 kJ, therefore this is an endothermic system. When calculating if the heat release of the AR can compensate for the heat absorption of the FR, the heat loss (including the heat diffusion of reactors, pipes, and the waste heat of emission gases) was not considered. On the basis of the

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AUTHOR INFORMATION

ORCID

Cuiping Wang: 0000-0002-4249-709X Notes

The authors declare no competing financial interest.

Table 3. Mass and Energy Balance of System mass balance FR

out (mol/h)

in (kJ/h)

out (kJ/h)

net (kJ/h)

coal tar: 0.5786

C: 5.454 CO: 0.5314 CO2: 0.8268 H2: 0.6725 H2O: 0.2683 NO, NH3: 0.004545 SO2, H2S: 0.002973 FeO: 2.047 Fe3O4: 0.4753 380.75 g/h N2: 3.334 O2: 0.05149 NO, NO2, N2O: 0.000159 Fe2O3: 1.7364 377.65 g/h 758.40 g/h

−2927.2914

−2096.8898

830.4016

−2124.5005

−2907.4151

−782.9146

−5051.7919

−5004.3049

47.487

Fe2O3: 1.736

AR

energy balance

in (mol/h)

380.75 g/h air: 4.1664 FeO: 2.047 Fe3O4: 0.4753 377.65 g/h 758.40 g/h

G


Article

Energy & Fuels

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(14) Adánez, J.; García-Labiano, F.; Diego, L. F. D.; Gayán, P.; Celaya, J.; Abad, A. Nickel-Copper Oxygen Carriers To Reach Zero CO and H2 Emissions in Chemical-Looping Combustion. Ind. Eng. Chem. Res. 2006, 45, 2617−2625. (15) Abad, A.; Mattisson, T.; Lyngfelt, A.; Rydén, M. Chemicallooping combustion in a 300 W continuously operating reactor system using a manganese-based oxygen carrier. Fuel 2006, 85, 1174− 1185. (16) de Diego, L. F.; GarcíA-Labiano, F.; Adánez, J.; Gayán, P.; Abad, A.; Corbella, B. M.; Palacios, J. M. Development of Cu-based oxygen carriers for chemical-looping combustion. Fuel 2004, 83, 1749−1757. (17) Wolf, J.; Anheden, M.; Yan, J. Comparison of nickel- and ironbased oxygen carriers in chemical looping combustion for CO2 capture in power generation. Fuel 2005, 84, 993−1006. (18) Wang, K.; Yu, Q.; Qin, Q.; Hou, L.; Duan, W. Thermodynamic analysis of syngas generation from biomass using chemical looping gasification method. Int. J. Hydrogen Energy 2016, 41, 10346−10353. (19) Gu, H.; Shen, L.; Xiao, J.; Zhang, S.; Song, T. Chemical looping combustion of biomass/coal with natural iron ore as oxygen carrier in a continuous reactor. Energy Fuels 2011, 25, 446−455. (20) Guo, Q.; Cheng, Y.; Liu, Y.; Jia, W.; Ryu, H. J. Coal chemical looping gasification for syngas generation using an iron-based oxygen carrier. Ind. Eng. Chem. Res. 2014, 53, 78−86. (21) Ma, J.; Zhao, H.; Tian, X.; Wei, Y.; Rajendran, S.; Zhang, Y.; Bhattacharya, S.; Zheng, C. Chemical looping combustion of coal in a 5 kW th interconnected fluidized bed reactor using hematite as oxygen carrier. Appl. Energy 2015, 157, 304−313. (22) Leion, H.; Mattisson, T.; Lyngfelt, A. Use of ores and industrial products as oxygen carriers in chemical-looping combustion. Energy Fuels 2009, 23, 2307−2315.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (51676102) and National Natural Science Foundation of China (51506105). The authors acknowledge the support from the Foundation of State Key Laboratory of Coal Clean Utilization and Ecological Chemical Engineering (Grant No. 2016-07) and Taishan Scholar Program of Shandong Province (201511029).

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ABBREVIATIONS CLP = chemical looping pyrolysis OC = oxygen carrier FR = fuel reactor AR = air reactor CB = carbon black CLC = chemical looping combustion CLG = chemical looping gasification CLR = chemical looping reforming OCs = oxygen carriers XRD = X-ray diffraction

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Optimization of Chemical Looping Pyrolysis System of Coal Tar by

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