CO Ratio Syngas Production from Chemical Looping

Jan 6, 2016 - ABSTRACT: Chemical looping gasification (CLG) in a dual fluidized bed gasifier was proposed to increase the H2/CO ratio and to simplify ...
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High H2/CO Ratio Syngas Production from Chemical Looping Gasification of Sawdust in a Dual Fluidized Bed Gasifier Jimin Zeng, Rui Xiao,* Dewang Zeng, Yang Zhao, Huiyan Zhang, and Dekui Shen Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, People’s Republic of China ABSTRACT: Chemical looping gasification (CLG) in a dual fluidized bed gasifier was proposed to increase the H2/CO ratio and to simplify the process in gasification. The gasifier offered two separate fluidized bed reactors, fuel reactor (FR) and steam reactor (SR), for biomass gasification and H2 production. Iron ore was used as the oxygen carrier (OC), providing lattice oxygen for gasification in the FR, transferring to the SR for reacting with steam to produce H2, and then achieving the circulation and reoxidation through the loop seal. The product gas from the FR and the SR could be controlled to make high H2/CO ratio syngas by this process. The experiment for the CLG of sawdust was conducted in a dual fluidized bed gasifier, regarding the influence of different FR temperatures, SR temperatures, steam/biomass (S/B) ratios, and steam preheating temperatures. The optimum operating condition was obtained by the analysis showed as follows: the FR temperature of 820 °C, the SR temperature of 910 °C, the S/B ratio of 1.50 kg kg−1, and the steam preheating temperature of 500 °C. At this condition, the cold gas efficiency in the FR was 77.21% and the H2 yield in the SR was 0.279 Nm3 kg−1. Overall, the CLG process of sawdust carried out in the present work suggests that a high H2/CO ratio syngas production was simple and promising.

1. INTRODUCTION Biomass is a renewable energy source with the potential to be a substitute of fossil fuels. The main motivation to increase the use of this resource is the longer availability and the security of the energy supply.1,2 Currently, biomass can be converted to high valuable energy forms via numerous processes, including thermal, biological, mechanical, or physical processes.3,4 Biomass gasification is one of the technologies to convert biomass into convenient gaseous fuels or chemical feedstock.5,6 It generally contains three steps: (i) pyrolysis, which is a thermal decomposition process for partially removing carbon from the feed (reaction 1),

conversion efficiency. The process divides a given reaction (reaction 5) into multiple sub-reactions (reactions 6−8), with each being typically carried out in separate reactors2,10 A+B+C→D+E+F

which divides into

(1)

(ii) partial combustion of some gases, vapors, and char, and (iii) gasification of decomposition products. Steps ii and iii are mainly for the char conversion (reactions 2 and 3). Most H and O in biomass have become small molecules in step i, and just a small part of them remained.7,8 char (mainly C) + H 2O → H 2 + CO

(2)

char (mainly C) + CO2 → 2CO

(3)

Through the three steps, especially the char conversion in steps ii and iii, the syngas from the gasifier is deemed of low H2/CO ratio, usually less than 1 mol mol−1. Therefore, the gas conditioning (mainly using the water-gas shift reaction, reaction 4) is necessary to enhance the H2/CO ratio, and it makes the gasification process complicated and expensive.9,10 CO + H 2O → CO2 + H 2

(6)

B + MexOy − 2 → E + MexOy − 1

(7)

C + MexOy − 1 → F + MexOy

(8)

Special Issue: 5th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies

(4)

Received: September 24, 2015 Revised: January 5, 2016

The chemical looping (CL) process is a strong candidate for using the renewable resource to achieve higher energy © XXXX American Chemical Society

A + MexOy → D + MexOy − 2

The oxygen carrier (OC) particles are provided for the link between sub-reactions, and they are reduced and regenerated in a cyclic fashion through the progress of the sub-reactions. Recently, the CL process has been investigated by many universities and research institutes for the lower energy penalty and low-cost equipment.11−15 Our research group did much previous work on the chemical looping combustion (CLC) process.16−20 Besides, an advanced CL process for producing some fuels and chemicals has much potential industrial applications,10 and Xiao et al. in our group studied the chemical looping hydrogen (CLH) process for packing energy into chemical bonds. However, the process was conducted on a fixed bed reactor, and it could not achieve producing hydrogen continuously.21,22 For generation of high H2/CO ratio syngas conveniently and efficiently, a novel chemical looping gasification (CLG) process

pyrolysis

biomass ⎯⎯⎯⎯⎯⎯⎯→ char (mainly C) + CO + CO2 + H 2 + CH4 + H 2O + tar

(5)

A

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Figure 1. Schematic diagram of a dual fluidized bed gasifier for the CLG process.

was proposed and investigated in a dual fluidized bed gasifier, as shown in Figure 1. The gasifier offered two separate fluidized bed reactors, fuel reactor (FR) and steam reactor (SR), for biomass gasification and hydrogen production. Iron ore was used as the OC for the circulation in the gasifier. In the FR, the OC particles reacted with sawdust particles for the gasification step. (x + y)Fe2O3 + yC → yCO + 2x Fe + 2y FeO

2. MATERIALS AND METHODS 2.1. Material Preparation. Pine sawdust being obtained from Baoying (Jiangsu, China) was used as feedstock in the tests. The sample was crushed and sieved into particles with a size range of 0.2− 0.6 mm and then dried in a 105 °C oven for 12 h before the experiment. Proximate and ultimate analyses were shown on Table 1.

Table 1. Proximate and Ultimate Analyses of Pine Sawdust (9) parameter

(3x + y)Fe2O3 + (x + y)CO → 2x Fe3O4 + 2y FeO + (x + y)CO2

(10)

The reduced OC particles were transferred to the SR, reacting with H2O for generating H2, and the rich H2 syngas (mainly H2, with a little CO and CH4 contained) was obtain from the exit of the SR.21,23 3Fe + 4H 2O → 4H 2 + Fe3O4

(11)

3FeO + H 2O → H 2 + Fe3O4

(12)

a

Then, the OC particles were transported to the loop seal (as an oxidizer), to achieve the circulation of the gasifier. Meanwhile, the air was introduced to the loop seal, and oxygen from the air reacted with Fe3O4 to make a total oxidation (reaction 13), in which the reactions could be controlled by the circulation rate. 4Fe3O4 + O2 → 6Fe2O3

value

proximate analysis (ad,a wt %) moisture volatile fixed carbon ash ultimate analysis (ad, wt %) Cad Had Oadb Nad low heating value (MJ/kg)

1.44 80.78 16.28 1.50 44.90 6.38 44.98 3.74 18.33

ad = air-dried basis. bCalculated by difference.

The OC particles used in this study were from Companhia Vale (Brazil). They were imported and provided by Nanjing Meishan Steel, Shanghai Baosteel Co., Ltd. These particles were one kind of hematite, and they showed good performance compared to several other iron ores during previous work in our group.18,19 The particle size range was within 0.125−0.300 mm. 2.2. Experimental Setup and Procedure. The experiment was conducted in a dual fluidized bed gasifier (Figure 1). It contained a FR, a SR, a loop seal, a hot gas cooler, a biomass feeding unit, a water/gas feeding unit, a steam generator, a temperature control unit, and a gas analysis system. The gas was analyzed online by gas analyzers (MRU Co., Ltd., Germany, which was imported by Beijing York Co., Ltd.). The FR was a fast fluidized bed with a diameter of 45 mm contracting to 30 mm in the height of 550 mm, and the total height was 1700 mm. The SR was a bubbling fluidized bed with a circular column of 89 mm in diameter and 900 mm in height. The outlets of the FR and SR were linked by a cyclone. A rectangular loop seal with a cross-section of 40 × 80 mm2 and a height of 160 mm connected the SR and FR. The biomass feeding unit was 100 mm in height, fixing at the right bottom of the FR, and sawdust was fed into the reactor by two continuous feeding screw feeders. The first screw feeder was

(13)

In this way, the reactions in the two reactors could be separated in good condition and the process features fewer solid handling issues and greater flexibility in operational aspects of the dual fluidized bed gasifier. Thus, the gases from the two reactors could be adjusted to produce high H2/CO ratio syngas in a simple and low-cost way. In this study, the effects of the FR temperature, SR temperature, steam/biomass (S/B) ratio, and steam preheating temperature were extensively investigated, in terms of gas distribution, cold gas efficiency in the FR, and H2 yield in the SR. The optimum condition was screened and obtained from these parameters, which confirmed the experimental facilities operating in a low-cost and efficient condition. B

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Energy & Fuels applied to definite quantitative determination, and the secondary screw feeder was applied for feeding the feedstock in the reactor rapidly. The hopper was swept with N2 to maintain an inert environment of the feeding unit. The flow rate of the introduced gases (N2 or air) was controlled by rotameters and preheated by heating tape to 250 °C before they were introduced into the reactors. The steam generator was an intelligent control water pump for generating steam through a preheating furnace. The gasifier was operated in 0.12 kg/s to achieve the circulation of the OC particles, in which a series of cold condition tests were performed before the experiments. Table 2 gave an overview of the main operating parameters of the experiments presented within this work. The FR and SR temperatures

ηe =

3

γH = 2

unit

value 4 0.12 700−880 700−970 0.50−3.00 300−800

(14)

Carbon conversion efficiency (ηc, %) in the gasifier was defined as the proportion of the carbon converted into gaseous products from the total carbon in the sawdust fed into the FR

22.4MC

× 100%

(16)

where YFR (Nm3 kg−1), YSR (Nm3 kg−1), and MC (%) were the gas yield from the FR, the gas yield from the SR, and the carbon fraction in the biomass, respectively, YCj,FR (%) represented the gas volume fraction from the FR, and YCj,SR (%) represented the gas volume fraction from the SR (Cj = CO, CO2, CH4, and C2Hm). The lower heating value (LHVFR, kJ Nm−3) of the gas products from the FR is calculated as24

LHVFR = 126VCO + 108VH2 + 359VCH4 + 635VC2Hm

(19)

3. RESULTS AND DISCUSSION 3.1. Effect of the FR Temperature. The FR temperature significantly affected the CLG process because the chemical reactions were complicated in the dual fluidized bed gasifier. In the present work, the temperatures varied from 700 to 880 °C in 30 °C increments. The SR temperature, S/B ratio, and steam preheating temperature were kept constant at 910 °C, 1.50 kg kg−1, and 500 °C, respectively. The test results under different temperatures were presented in Figure 2 and Table 3. Figure 2a showed the overall cumulative product gas composition in the FR on a dry basis at different FR temperatures. With the increase of the temperature, the H2 fraction increased from 42.47 to 49.24%. The CO fraction slightly increased from 31.51 to 33.13%, while the CO2 fraction decreased from 13.70 to 6.08%. The CH4 fraction was in the range of 11.55−13.75%. Figure 2b showed different trends on the gas composition in the SR. The H2 fraction was above 80%, while the CO fraction decreased from 15.11 to 8.29%, when the FR temperature was higher than 790 °C in the SR. The CH4 fraction was obtained under 3.94%. Figure 2c demonstrated that the H2/CO ratio of syngas from the FR increased smoothly, while this ratio of syngas from the SR increased rapidly, with the increase of the FR temperature. Table 3 showed that the cold gas efficiency of product gas in the FR and hydrogen yield of the SR changed with different FR temperatures. The cold gas efficiency in the FR increased from 70.85 to 77.21% at 820 °C and then decreased to 74.44% at a higher temperature. The hydrogen yield in the SR was kept in the range of 0.256−0.286 Nm3 kg−1. Results obtained from the experiments indicated that the FR temperature favored the H2 and CO yields in the FR. Besides, there was some amount of char transferring to the SR because some CO fraction was obtained in the SR. It led to the increase of the hydrogen yield in the SR (from 0.256 to 0.286 Nm3 kg−1). At a higher temperature (>880 °C), the condition favored the Boudouard reaction (reaction 3) and made the H2 fraction increase much slower. The water-gas reaction (reaction 2) was still one of the main reactions that contributed to the process.6,25 3.2. Effect of the SR Temperature. The SR temperature is crucial for the rich H2 syngas production in the SR. Meanwhile, through the circulation of the dual fluidized bed gasifier, the syngas produced by the FR could also be affected. Therefore, the effect of the SR temperature was investigated in terms of gas composition produced by both the FR and SR (Figure 3). The SR temperature increased from 700 to 970 °C, and the FR temperature, the S/B ratio, and the steam

where ṅin was the total inlet gas molar flow rate, xi was the volume fraction of gas species i (i = H2, CO, CO2, CH4, and C2Hm) measured by the gas analyzer, and xN2,in and xN2,out were the volume fractions of nitrogen entering and exiting the reactor, respectively. The gas relative concentration (ci, %) of each run in the FR was calculated as x ci = i × 100% ∑ xi (15)

12[YFR ∑ jVCj ,FR + YSR ∑ jVCj ,SR ]

Q biomass

where xH2,SR (kmol h ) was the mole yield of H2 in the SR and Qbiomass (kg h−1) represented the added biomass.

were the temperatures measured in the vertical middle of each fluidized bed. Every data was the average of the experimental tests being repeated 3 times. 2.3. Data Evaluation. The outlet dry syngas consists mainly of H2, CO, CO2, CH4, C2Hm, and N2, because H2O was removed. With the gas volume fractions measured by the gas analyzer and the feeding N2 balance gas flow rate, the outlet molar flow rate could be calculated on the basis of the nitrogen mass balance

ηc =

22.4x H2,SR −1

kg kg h−1 °C °C kg kg−1 °C

⎛ x N ,in ⎞ ⎛ x N2,in ⎞ nout ⎟ ̇ = n in ̇ ⎜⎜ 2 ⎟⎟ = n in ̇ ⎜ x ⎝ 1 − ∑ xi ⎠ ⎝ N2,out ⎠

(18)

−1

where YFR (Nm kg ) was the gas yield of the production and LHVFR (kJ Nm−3) and qbiomass (kJ kg−1) were the lower heating value of the product gas from the FR and total heating value of biomass at room temperature, respectively. The hydrogen yield in the SR (γH2, Nm3 kg−1) was defined as the accumulated amount of hydrogen produced in the iron−steam process divided by the total amount of the dry sawdust added to the reactor

Table 2. Overview of the Operating Parameters of Experiments iron ore (bed material) feeding rate FR temperature SR temperature S/B ratio steam preheating temperature

LHVFR YFR × 100% qbiomass

(17)

where VCO, VH2, VCH4, and VC2Hm were the volume fractions of CO, H2, CH4, and C2Hm in the product gas from the FR, respectively. Cold gas efficiency in the FR (ηe, %) was defined as the ratio of the low heating value of the products from unit mass biomass gasification and the low heating value of unit biomass C

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Figure 2. Effect of the FR temperature on the (a) outlet gas composition at FR, (b) outlet gas composition at SR, and (c) H2/CO ratios.

Figure 3. Effect of the SR temperature on the (a) outlet gas composition at FR, (b) outlet gas composition at SR, and (c) H2/CO ratios.

Table 3. Effect of the FR Temperature of the CLG Process

preheating temperature were set to 820 °C, 1.50 kg kg−1, and 500 °C, respectively. As indicated in Figure 3a, in the FR, the H2 fraction increased smoothly from 39.47 to 48.38%, while the CO fraction decreased from 38.28 to 30.77%, when increasing the SR temperature. The CH4 fraction decreased from 16.32 to 13.11% in the FR. The H2/CO ratio of the gas from the FR increased from 1.03 to 1.55 mol mol−1 with the increase of the SR temperature, as shown in Figure 3c. In the SR, the H2 fraction increased from 70.18 to 84.34%, over a temperature range from 700 to 930 °C, and then it decreased a bit (Figure 3b).

temperature (°C) 700 730 760 790 820 850 880

cold gas efficiency in the FR (%) 70.85 71.40 74.54 75.32 77.21 75.13 74.44

± ± ± ± ± ± ±

0.47 0.43 0.42 0.43 0.50 0.46 0.47

hydrogen yield in the SR (Nm3 kg−1) 0.260 0.257 0.256 0.277 0.279 0.286 0.277

± ± ± ± ± ± ±

0.001 0.002 0.002 0.002 0.002 0.002 0.002 D

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Energy & Fuels Table 4 demonstrated the effect of the SR temperature on the cold gas efficiency of the gas from the FR and the hydrogen yield in the SR. In Table 4, the hydrogen yield increased with the SR temperature on the stream and reached the maximum of 0.279 Nm3 kg−1 at 910 °C, and then there was a small reduction in its yield at higher SR temperatures. The cold gas efficiency slightly decreased from 81.56 to 74.88%. Table 4. Effect of the SR Temperature of the CLG Process temperature (°C) 700 730 760 790 820 850 880 910 940 970

cold gas efficiency in the FR (%) 81.56 81.06 79.26 78.80 78.83 78.86 77.62 77.21 75.33 74.88

± ± ± ± ± ± ± ± ± ±

0.53 0.50 0.22 0.49 0.50 0.53 0.52 0.51 0.46 0.40

hydrogen yield in the SR (Nm3 kg−1) 0.154 0.157 0.180 0.216 0.219 0.251 0.267 0.279 0.275 0.274

± ± ± ± ± ± ± ± ± ±

0.001 0.002 0.001 0.002 0.001 0.002 0.003 0.002 0.002 0.003

Considering the reactions in the SR (reactions 11 and 12), when the SR temperature increased, the reactions became faster, which led to the increase of the hydrogen yield. The cold gas efficiency slightly decreased for the reactions of the hydrogen generation. It made some amount of char to be transported to the SR. Meanwhile, the H2/CO ratio of the gas from the FR changed because of the carried steam by the circulation of the OC particles through the gasifier (the steam introduced into the SR is much more than that reacted21,22). 3.3. Effect of the S/B Ratio. The S/B ratio was defined as the steam introduced into the SR in mass divided by the biomass fed into the FR in mass. The S/B ratio had a great impact on the H2 production in the SR on account of the chemical reactions that occurred in the gasifier. Simultaneously, some amount of the steam in the SR would be transferred to the FR through the circulation of the OC particles. The S/B ratio was exhaustively studied from 0.50 to 3.00 kg kg−1 in 0.25 kg kg−1 increments, and the FR temperature, the SR temperature, and the steam preheating temperature were fixed at 820, 910, and 500 °C, respectively. Figure 4 and Table 5 demonstrated the effect of the S/B ratio in gas composition, the cold gas efficiency of syngas in the FR, and the hydrogen yield in the SR. As shown in Figure 4a, the H2 fraction increased from 37.15 to 53.45%, while the CO fraction decreased from 37.50 to 33.03% with the increase of the S/B ratio. The CH4 fraction stayed approximately constant in the range from 0.50 to 1.50 kg kg−1 and then decreased at higher S/B ratios. The H2 fraction of gas from the SR and the H2/CO ratios of the gases from the FR and SR increased when increasing the S/B ratio, as indicated in panels b and c of Figure 4. In Table 5, the cold gas efficiency in the FR remained constant first and decreased at higher S/B ratios (>1.50 kg kg−1). The hydrogen yield increased rapidly from 0.50 to 1.25 kg kg−1, then increased slowly up to 2.00 kg kg−1, and remained almost constant at higher S/B ratios. It should be noted that the S/B ratio has a strong effect on the hydrogen production process that occurred in the SR. The results demonstrated that the initial increase of the S/B ratio let the reactions in the SR become faster, while it would improve the amount of steam being transported to the FR through the

Figure 4. Effect of the S/B ratio on the (a) outlet gas composition at FR, (b) outlet gas composition at SR, and (c) H2/CO ratios.

circulation of the OC particles. It resulted in the water-gas reaction (reaction 2) and the water-gas shift reaction (reaction 4).25,26 When the S/B ratio was higher than 2.00 kg kg−1, the steam in the SR was much more than that reacted and the gas compositions differed a little.22 3.4. Effect of the Steam Preheating Temperature. The steam preheating temperature was the temperature before the steam was introduced into the SR, and this temperature mainly influenced the chemical reactions in the SR because of the steam absorbing heat in the SR. Different temperatures might resulted in different H2 fractions in the SR. Figure 5 and Table 6 illustrated the effect of the steam preheating temperature on E

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Energy & Fuels Table 5. Effect of the S/B Ratio of the CLG Process temperature (°C) 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00

cold gas efficiency in the FR (%) 76.94 77.10 76.65 77.18 77.21 72.03 71.51 71.05 70.22 69.75 68.96

± ± ± ± ± ± ± ± ± ± ±

0.58 0.45 0.28 0.25 0.43 0.46 0.35 0.40 0.46 0.40 0.22

hydrogen yield in the SR (Nm3 kg−1) 0.094 0.120 0.180 0.261 0.279 0.301 0.307 0.308 0.308 0.308 0.308

± ± ± ± ± ± ± ± ± ± ±

0.001 0.001 0.001 0.001 0.002 0.001 0.001 0.002 0.002 0.002 0.001

the outlet gas composition, H2/CO ratio, cold gas efficiency of syngas from FR, and hydrogen yield in the SR. The FR temperature, the SR temperature, and the S/B ratio were constant at 820 °C, 910 °C, and 1.50 kg kg−1, respectively. As shown in panels a and b of Figure 5, the H2 fraction in either the FR or the SR had slightly changed under the different conditions. The CO fraction in the FR increased slightly for the temperature above 400 °C, while there was a small reduction in CH4 yields. For the SR, the CO yield increased up to the temperature of 500 °C and stayed constant at higher temperatures. However, the H2/CO ratio of the gas from the SR decreased when the temperature was up to 500 °C. In Table 6, the cold gas efficiency in the FR remained at approximately 77% under 500 °C and then slightly decreased to 74.03% at higher temperatures but the hydrogen yield in the SR increased from 0.163 to 0.283 Nm3 kg−1 with the increase of the steam preheating temperature. Because the SR temperature was higher than that of the steam, the steam would absorb less heat from the reactor when increasing the steam preheating temperature, which resulted in the reactions occurring in the SR, but it could slightly affect the gasification process in the FR because of the circulation through the gasifier (in the loop seal, the reoxidation was the exothermic reaction).12,21,27 3.5. Optimal Condition in the Dual Fluidized Bed Gasifier. From the above investigations, the optimal conditions for the CLG process of sawdust in the dual fluidized bed gasifier were screened on the basis of the higher cold gas efficiency in the FR and the higher hydrogen yield in the SR. From the different FR temperature conditions, when the FR temperature was at 820 °C, the cold gas efficiency came to the largest value and, at the same time, the hydrogen yield in the SR is not the largest; however, the FR was directly influenced by the FR temperature. Therefore, 820 °C was the most suitable temperature for the FR operation. For the different SR temperature conditions, the cold gas efficiency in the FR was decreased, while the hydrogen yield in the SR was increased rapidly. Therefore, the best SR temperature was 910 °C, obtained from the comparison. As for the S/B ratios from 0.05 to 3.00 kg kg−1, when it was at the condition between 1.50 and 1.75 kg kg−1, the cold gas efficiency in the FR decreased from 77.31 to 72.03% but the hydrogen yield in the SR increased from 0.279 to 0.301 Nm3 kg−1; in the meantime, more steam could not help the facility to operate in an efficient way.4,28 Therefore, the S/B ratio of 1.50 kg kg−1 was the optimal condition. Because the steam preheating temperature had no significant influence on the

Figure 5. Effect of the steam preheating temperature on the (a) outlet gas composition at FR, (b) outlet gas composition at SR, and (c) H2/ CO ratios.

Table 6. Effect of the Steam Preheating Temperature of the CLG Process temperature (°C) 300 400 500 600 700 800

F

cold gas efficiency in the FR (%) 77.69 77.42 77.21 76.58 75.34 74.03

± ± ± ± ± ±

0.16 0.11 0.16 0.17 0.11 0.27

hydrogen yield in the SR (Nm3 kg−1) 0.163 0.236 0.279 0.277 0.283 0.283

± ± ± ± ± ±

0.001 0.002 0.002 0.003 0.002 0.001

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gas composition of the FR and SR, when the temperature was more than 500 °C, the cold gas efficiency in the FR decreased but the hydrogen yield increased slightly. Therefore, 500 °C was the optimal steam preheating temperature.

4. CONCLUSION CLG tests using sawdust as fuel and iron ore as the OC were conducted in a dual fluidized bed gasifier. This process achieved producing high H2/CO ratio syngas in a low-cost and convenient way. The following conclusions could be drawn from this study: The H2/CO ratio in the syngas was significantly influenced by the FR temperature, the SR temperature, and the S/B ratio, while the hydrogen yield in the SR was mainly affected by the SR temperature, the S/B ratio, and the steam preheating temperature. The two separate reactors were linked by the OC particle circulation, which made the operating parameters in one reactor influence the other. The optimum operation in the gasifier was investigated and found as the FR temperature of 820 °C, the SR temperature of 910 °C, the S/B ratio of 1.50 kg kg−1, and the steam preheating temperature of 500 °C. At this condition, 77.21% of the cold gas efficiency in the FR and 0.279 Nm3 kg−1 of the hydrogen yield in the SR were obtained for the process. On the basis of this work, the CLG process will allow for determination of the most promising options for the novel gasification process.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support by the National Key Basic Research Program of China (973 Program, Grant 2012CB215306) and the National Natural Science Foundation of China (NSFC, Grants 51476035 and 51525601).

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REFERENCES

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DOI: 10.1021/acs.energyfuels.5b02204 Energy Fuels XXXX, XXX, XXX−XXX