Gasification of low-rank coal for hydrogen-rich gas production in a dual loop gasification system

Fuel Processing Technology 171 (2018) 110–116

Contents lists available at ScienceDirect

Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc

Research article

Gasification of low-rank coal for hydrogen-rich gas production in a dual loop gasification system

T

⁎

Yahui Xiaoa, Shaoping Xua, , Yangbo Songa, Chao Wanga, Shaobo Ouyangb a

State Key Laboratory of Fine Chemicals, Institute of Coal Chemical Engineering, School of Chemical Engineering, Dalian University of Technology, No. 2 Linggong Road, Dalian 116024, China b School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, 86 Hongqi Road, Ganzhou 341000, Jiangxi, China

A R T I C L E I N F O

A B S T R A C T

Keywords: Low-rank coal Decoupling gasification Dual loop Hydrogen-rich gas Tar removal Olivine

A dual loop gasification (DLG) system consisting of three separated reactors and two bed material circulation loops has been proposed for steam gasification of low-rank coal to obtain hydrogen-rich gas with low tar content. The system decouples the gasification process into fuel gasification, tar destruction and residual char combustion, which occur in three independent reactors correspondingly, i.e. a gasifier, a reformer and a combustor. Both the gasifier and the reformer are separately interconnected with the single combustor, forming two bed material circulation loops in parallel. In this way, both the gasifier and the reformer could be operated individually under optimized conditions. With Shenmu bituminous coal as feedstock and calcined olivine as both solid heat carrier and in-situ tar destruction catalyst, the performance of the system for the steam gasification of the coal has been investigated. It has been found that the tar was effectively removed under higher reformer temperature and in the presence of the olivine catalyst, and the coal gasification was promoted at higher gasifier temperature, S/C and ER.

1. Introduction Coal will continue to be an important energy source contributing to the world's energy system in the foreseeable future, but its utilization has faced serious environmental issues [1,2]. To alleviate such problems, great efforts have been made to develop new technologies for clean and efficient utilization of coal. Gasification therein has been recommended to be an attractive choice as it is capable of efficiently converting coal into either clean energy, i.e. heat and electricity, or high value-added chemicals [3]. In particular gasification of low-rank coal under mild condition (atmosphere pressure and temperature lower than 1000 °C) has received great attention recently in consideration of operation cost, energy recuperation and ash-related problem [4,5]. Gasification with steam as gasification agent is a well-known process for hydrogen-rich gas production [6]. The process is highly endothermic and generally has to introduce air or oxygen as a part of gasification agent to maintain the process autothermic. It intrinsically includes a series of reactions, e.g. fuel pyrolysis, char gasification, tar destruction and combustion of carbon residues and combustible gases. In traditional gasification technologies, all the above-mentioned reactions occur in a single reactor. Hence, the reactions are closely interrelated with each other and against to be individually regulated to

⁎

facilitate gasification performance, adapt fuel property and match downstream applications. Specifically, when air is used, the product gas will be seriously diluted by nitrogen introduced with the air. In contrast, decoupled gasification separates these reactions into at least two reactors or zones, and thus provides an effective solution to promote the desired reactions or suppress those unexpected to facilitate the gasification performance [7,8]. Typically, in order to break the interaction between combustion and gasification to improve quality of product gas, the so-called dual bed gasification has been intensively investigated [9–12]. The gasification system separates the gasification and combustion reactions into two isolated reactors, i.e. a gasifier where fuel gasification occurs with steam as gasification agent, and a combustor where char combustion takes place with air as combustion agent. Bed material as solid heat carrier is circulating through the two reactors to carry the heat from the combustor to the gasifier. In this case, the flue gas from the combustor and the product gas from the gasifier are separated, and so that the hydrogen-rich product gas without dilution by nitrogen and combustion-generated carbon dioxide can be available. Typical example of the system is the so-called fast internally circulating fluidized bed (FICFB) gasification at Vienna University of Technology, Austria [13]. The system combines a bubbling fluidized bed reactor as fuel gasifier and a fast fluidized bed

Corresponding author. E-mail address: [email protected] (S. Xu).

https://doi.org/10.1016/j.fuproc.2017.11.014 Received 30 September 2017; Received in revised form 14 November 2017; Accepted 18 November 2017 0378-3820/ © 2017 Elsevier B.V. All rights reserved.

Fuel Processing Technology 171 (2018) 110–116

Y. Xiao et al.

2. Experimental

reactor as char combustor, which has been successfully demonstrated in Güssing [14] and Oberwart [15], Austria, respectively. Some similar designs can also be found in literatures [16–20]. Despite of great advantage for nitrogen-free and hydrogen-rich gas production, the system suffers from tar formation in product gas during coal gasification under mild condition, which will impose restriction on the end-use application of the gas as well as block downstream equipment [21]. In order to minimize the impact of such tar-related problems, various gas cleanup approaches have been attempted to decrease tar content in product gas [22]. Among these methods, in-bed catalytic destruction is a preferred option because of thermal integration and high tar conversion even at a low temperature [23]. Several kinds of inbed catalysts for tar removal in dual bed gasification, e.g. natural minerals, alkali and alkali earth metals and supported transition metals, have been investigated [24–28]. Despite of inferior activity in tar removal, olivine, a naturally occurring iron‑magnesium mineral with high attrition resistance and mechanical strength, is widely employed in dual fluidized bed gasifier [29]. In typical dual bed gasification system, the extent of tar destruction is limited even using in-situ tar destruction catalyst as bed material due to short residence time of volatiles in the gasifier and inadequate contact between the volatiles and the catalyst. That is essentially due to the fact that fuel gasification and tar destruction reactions are still interacted in the same space, making it impossible to enhance tar destruction for efficient tar removal. In this respect, decoupling tar destruction from the fuel gasification could provide a solution to optimize reaction condition of tar destruction. Accordingly, Xu et al. [30] proposed a twostage dual fluidized bed gasification system, in which the single-stage bubbling fluidized bed gasifier is substituted by two stage fluidized bed gasifier. The product gas from the first stage is upgraded further in the second stage, which is favorable for increase of gasification efficiency and decrease of tar content. Göransson et al. [20] installed an in-situ reformer above the dense zone of the fluidized bed gasifier but under the hot bed material return position to intensify the contact of volatiles and catalytic bed material for efficient tar reforming. Our group [31] has developed a decoupled triple bed gasification (DTBG) system to improve tar destruction. In the system, tar destruction, fuel gasification and char combustion reactions are decoupled into three separated reactors, i.e. a reformer, a fuel reactor and a combustor, which are connected in series with the help of circulating solid heat carrier. In this way, tar destruction can be strengthened under optimized reaction conditions. Nevertheless, the coal gasification performance of the DTBG is still inferior to that of other gasification systems [13,17] in regards of gas yield, carbon conversion and cold gas efficiency due to limited coal gasification under mild condition. The key issue is that the fuel reactor temperature is restricted by the reformer temperature in one single circulation loop and then against for coal gasification. In order to modify the DTBG, a dual loop gasification system (DLG) composed of three decoupled reactors and two bed material circulation loops has been proposed to improve both fuel gasification and tar destruction under mild condition. The two circulation loops, i.e. one char combustor-fuel gasifier loop for fuel gasification and the other char combustor-tar reformer loop for tar destruction, share the single combustor. In this way, the fuel gasifier and the tar reformer could be controlled individually, which provides a solution to strengthen both fuel gasification and tar destruction to benefit the performance of coal gasification. The system has already been employed to increase tar destruction in steam gasification of biomass [32]. This study aims to validate the feasibility of the DLG for steam gasification of low-rank coal under mild condition. With calcined olivine as both solid heat carrier and in-situ tar destruction catalyst, the effect of reaction condition on steam gasification performance of two low-rank coals has been investigated.

2.1. Apparatus and procedure The principle and lab-scale facility of DLG have been described in detail in previous publication [32]. Briefly, the system consists of three separated reactors, i.e. a gas-solid countercurrent moving bed gasifier where fuel is gasified with steam and/or oxygen, a gas-solid radial cross flow moving bed reformer where tarry product gas from the gasifier radially pass through the bed and further cracked and reformed, and a fast fluidized bed combustor where residual chars from the fuel gasifier and deposited cokes on the surface of the circulating bed material particles from the reformer are combusted with air. Two circulation loops, i.e. the char combustor-fuel gasifier loop between the gasifier and the combustor and the char combustor-tar reformer loop between the reformer and the combustor, are in parallel and share the single combustor. A cyclone following the combustor is used to separate the circulating bed material from the flue gas of the combustor. Sealing legs are separately set at the top joint zones between the cyclone and the gasifier or the reformer and the bottom between the combustor and the gasifier or the reformer to prevent the undesired gas leakage, and so that the hydrogen-rich product gas and the flue gas are isolated. The distribution of bed material into the gasifier and the reformer was achieved by three mechanical valves separately set on the top sealing leg of the gasifier and the bottom sealing legs of the gasifier and the reformer. All the reactors are made of 310S stainless steel and externally heated by independent electrical furnaces to compensate heat loss. The temperature of each reactor is recorded by a K-type thermocouple placed at the middle part of the reactor. Manometers are placed at various points of the reactors to indicate the pressure profiles. Specifically in the reformer, a differential manometer is installed to monitor the gas pressure drop through the lateral particle layer and to insure the operation to be normal. The specific operating conditions of the experiments are shown in Table 1. 2.2. Feedstock and bed materials In this study, a Shenmu bituminous coal (SB) was adopted as feedstock, and an Inner Mongolia lignite (IL) was used for comparison (see Section 3.3). Before each experiment, the coal was crushed and sieved to an average particle size of 0.38–0.83 mm, and then dried at 105–110 °C for 3 h. Table 2 presents the results of the proximate analysis, ultimate analysis and lower heating value of the coals. Olivine from Yichang, China, was used as the bed material and catalyst. Before test, the olivine was crushed and sieved to an average Table 1 Operating conditions of the DLG

111

Total weight of bed material (kg)

7.2

Gasification circulation ratio (C/F) Reforming circulation ratio (C/F) Bed height in the gasifier (mm) Residence time of solid in the gasifier (min) Residence time of solid in the reformer (min) Steam to carbon mass ratio(S/C) (kg/kg) Coal feeding rate (kg/h) Gasifier temperature (°C) Reformer temperature (°C) Combustor temperature (°C) Gauge pressure in the gasifier (Pa) Gauge pressure in the reformer (Pa) Gauge pressure in the cyclone (Pa) Gauge pressure in the pre-fluidizer(Pa)

10 10 100 20 45 0.2–2.0 0.2 750–850 700–850 850 0 −100 to −50 0 0

Fuel Processing Technology 171 (2018) 110–116

Y. Xiao et al.

Tar content of product gas (g/Nm3) Mass of tar collected in the test (g) = Volume of the dry product gas (Nm3)

Table 2 Proximate analysis, ultimate analysis and lower heating value of the coals Sample Proximate analysisa (wt%, ad.) Moisture Ash Volatile Fixed carbon Ultimate analysisb (wt%, daf.) Carbon Hydrogen Oxygend Nitrogen Sulfur LHVc (MJ/kg, d.b.)

SB

IL

5.3 8.7 33.0 53.0

7.0 19.1 30.6 43.3

80.2 5.1 12.9 1.1 0.7 28.6

73.8 3.7 19.6 0.8 2.1 21.7

Cold gas efficiency (%) =

Lower heating value of the product gas (kJ/Nm3) × Gas yield (Nm3/kg) Lower heating value of coal fed into the system (kJ/kg)

− Mass of water collected in the test (g) Mass of water introduced into the system (g) × 100

Table 3 Chemical composition of olivine by XRF analysis (wt%) SiO2

Fe2O3

Al2O3

Cr2O3

CaO

NiO

51.80

36.50

9.14

0.88

0.60

0.37

0.36

(5)

Mass of water introduced into the system (g) Water conversion (%) =

particle size of 0.38–0.83 mm, then calcined in muffle at 900 °C for 3 h under air atmosphere. The result of chemical composition of the olivine particle analyzed by X-ray fluorescence (XRF) is shown in Table 3. Quartz sand with the same particle size as that of the olivine was used as inert bed material in blank test for comparison.

Each experiment was conducted for 2 h to ensure every parameter obtained at a stable reaction condition. After about 1 h when the system reached to the steady state, the product gas was sampled every 15 min in gas bag. The composition of the product gas was detected by a gas chromatograph GC7900 equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). The final gas composition presented in this paper is a dry gas composition excluding nitrogen, and averaged by at least three samplings with respect to time on stream. After each test, the outlet pipelines and condensers were washed with solvent tetrahydrofuran. The condensed products including tar, water and the solvent were filtered to remove dust, and then evaporated at 40 °C to remove the solvent under reduced pressure. The water was separated by extraction using ethyl acetate, and the tar was obtained by rotary evaporation at 45 °C under reduced pressure. Details about tar sampling and analysis method were described in our previous works [31,32].

(6)

Steam to carbon mass ratio (S/C) Mass of steam introduced into the system (kg) = Mass of carbon in coal fed into the system(kg)

(7)

Air equivalence ratio (ER) Oxygen to fuel weight ratio used in the test = Oxygen to fuel weight ratio for stoichiometric combustion

(8)

Gasification circulation ratio(C/F) Mass of bed material into the gasifier per hour (kg/h) = Mass of coal fed into the system per hour (kg/h)

(9)

Reforming circulation ratio(C/F) Mass of bed material into the reformer per hour (kg/h) = Mass of coal fed into the system per hour (kg/h)

2.3. Sampling and analysis

(10)

3. Results and discussion 3.1. Tar destruction in the reformer In the configuration of DLG, the reformer is decoupled from the gasifier, and so that the volatiles from the gasifier could be further cracked and reformed in the reformer under optimized reformer temperature and in the presence of catalytic bed material. In order to validate the advantage of the system for tar removal, experiments were conducted at varied reformer temperature and bed materials, maintaining the gasifier temperature at 800 °C, S/C 1.2 and C/F 10. As shown in Table 4, the gasification performance obtained under lower reformer temperature (run 1) was poor even with olivine as bed material in regards of H2 concentration, carbon conversion, water conversion and cold gas efficiency as well as tar content and tar yield. Specifically, the tar content and tar yield were as high as 165.3 g/ Nm3 and 5.0%, respectively. It suggests that the tar destruction was limited to a great extent in the gasifier due to short residence time of the volatiles and poor contact between the volatiles and the olivine catalyst in the upper free space of the gasifier. With the increase of reformer temperature (run 2 and run 3), the dry gas yield, carbon conversion, water conversion and cold gas efficiency increased slightly. H2 concentration increased evidently, and those of CO, CO2 and light hydrocarbons (C2–C3) decreased gradually. Notably, the tar content and tar yield significantly dropped by about 10 and 7 times respectively with increasing the reformer temperature from 700 °C to 850 °C. It indicates that the tar destruction was surely strengthened at higher reformer temperature. The comparison between run 3 and run 4 shows that the olivine had a better catalytic activity for tar destruction, which gave rise to higher H2 concentration and lower tar content and tar yield.

2.4. Date processing The reaction parameters are defined as follows:

Dry gas yield (Nm3/kgdaf) Volume of the dry product gas (Nm3) Mass of biomass of dry ash − free basis fed into the system (kg) (1)

Tar yield (%) =

Mass of carbon in the product gas (kg) Mass of carbon in coal fed into the system (kg) × 100

SB-Shenmu bituminous coal; IL-Inner Mongolia lignite; LHV-Lower heating value a Conducted by ASTM D 3172. b Performed by a vario EL III elemental analyzer. c Calculated by Dulong's formula. d Calculated by difference.

=

(4)

× 100

Carbon conversion (%) =

MgO

(3)

Mass of tar collected in the test (g) × 100 Mass of coal of dry ash − free basis fed into the system (g) (2) 112

Fuel Processing Technology 171 (2018) 110–116

Y. Xiao et al.

tendency. It suggests that the steam gasification was strengthened with the S/C. Nevertheless, tar destruction reaction was restricted because of the residence time of the volatiles in both the gasifier and the reformer was greatly shortened by unreacted steam and increased product gas. H2 concentration increased sharply while those of CO and CH4 decreased as a function of the S/C, which caused a dramatic increment of the H2/CO ratio. It could be explained by the promoted water gas shift reaction. Notably, the tar yield and tar content in product gas at lower S/C were still at a low level, indicating that tar could be self-reformed with H2O and CO2 generated from coal pyrolysis. The results are in accordance with that reported by Min et al. [33].

Table 4 Effect of reformer temperature and bed materials on steam gasification performance of coal (gasifier temperature 800 °C, S/C 1.2 and C/F 10) Bed material

Gasifier temperature (°C) Reformer temperature (°C) Dry gas composition (vol%) H2 CO CH4 CO2 C2H4 C2H6 C3H6 C3H8 H2/CO ratio Dry gas yield (Nm3/kg daf) Tar yield (%) Tar content (g/Nm3) Carbon conversion (%) Water conversion (%) Cold gas efficiency (%)

Run 1

Run 2

Run 3

Run 4

Olivine

Olivine

Olivine

Quartz sand

800 700

800 800

800 850

800 850

43.5 9.1 11.4 32.9 1.3 0.9 0.7 0.2 4.8 0.34 5.0 165.3 13.6 − 0.6 14.1

49.6 7.6 10.8 30.0 1.2 0.6 0.3 < 0.1 6.5 0.46 1.1 25.7 16.0 0.1 18.0

50.9 7.5 11.9 27.8 1.4 0.4 0.1 < 0.1 6.8 0.46 0.7 16.8 16.1 3.1 19.5

48.1 10.0 11.5 27.7 2.1 0.4 0.2 < 0.1 4.8 0.45 3.3 80.4 15.7 3.9 19.8

3.2.3. Effect of ER In order to further promote the coal gasification and provide a secondary heat source for steam gasification of the coal, oxygen was introduced into the gasifier as a part of gasification agent. The experiments were performed by varying ER in a range of 0–0.3, fixing gasifier temperature at 800 °C, reformer temperature 850 °C, S/C 1.2 and C/F 10. As expected in Fig. 3, with the increase of ER, the dry gas yield, carbon conversion and cold gas efficiency remarkably increased as results of the intensified oxidation reaction of the coal. The tar content in product gas was sharply reduced but the tar yield remained at a relative constant value with the ER, suggesting that the tar destruction in the gasifier has not been evidently affected by the oxygen introduction. The reason is that the gasifier operated in a gas-solid countercurrent moving mode. The water conversion increased slowly with the ER, indicating that the steam gasification was promoted in the presence of oxygen. That phenomenon could be explained by the fact that the exothermic oxidation reactions provided additional heat to enhance the exothermic steam gasification. At higher ER, the concentrations of CO and CO2 ascended evidently whereas those of H2 and CH4 showed an opposite trend, which was attributed to the promoted oxidization reactions. The increase of CO concentration and decrease of H2/CO ratio displayed that the oxidization reaction of the coal played an important role in the investigated ER range.

3.2. Coal gasification in the gasifier As discussed above, separation of the reformer from the gasifier is of great help to extend residence time of the volatiles and improve contact between the volatiles and the catalyst, and thus allows for further tar destruction in the reformer under appropriate temperature and in the presence of the olivine catalyst. Nevertheless, the tar conversion has a little contribution to the gasification performance of the coal in terms of dry gas yield, carbon conversion and cold gas efficiency due to limited devolatilization of the coal. In order to increase the coal gasification performance, the pyrolysis and gasification of the coal should be strengthened. In the DLG, the reactions would be enhanced by increasing gasifier temperature and S/C, still introducing a part of oxygen as a gasification agent.

3.3. Gasification performance of two type coals and comparison with DTBG Comparison of gasification performance between SB and IL were conducted at gasifier temperature 800 °C, reformer temperature 850 °C, S/C 1.2 and C/F 10. As seen in Table 5, at the same reaction condition, the steam gasification performance of IL in terms of the dry gas yield, tar yield, carbon conversion, water conversion and cold gas efficiency was much better than that of SB. The H2 concentration in product gas was in the same level as that of SB. The CO and CO2 were a little higher, and the CH4 and tar content were slightly lower. That could be attributed to the higher volatiles content and gasification reactivity of IL. In order to validate the advantages of DLG, the coal gasification performance of DLG was also compared with that of DTBG [31]. It can be seen from Table 5 that the gasification performance of DLG in regards of H2 concentration, dry gas yield, carbon conversion, water conversion and cold gas efficiency was superior to that of DTBG. That was mainly attributed to the promoted steam gasification in the gasifier of the DLG, which was achieved by operating the gasifier at higher temperature It is noticed that the tar contents and tar yields of both DLG and DTBG were in low level. The tar content and tar yield of DTBG was lower, which could be attributed to the longer residence time of the volatiles (lower gas yield) and the more catalytic bed material olivine contacted with the tar (at higher C/F) for efficient tar destruction. As discussed above, in the DLG, the configuration that separation of the reformer from the gasifier and arrangement of them into two independent bed material circulation loops provides an effective way to individually optimize both coal gasification and tar destruction at appropriate reaction conditions. Nevertheless, the water conversion of steam gasification of coal in the DLG was at the low level, because it

3.2.1. Effect of gasifier temperature The steam gasification of coal was conducted at varied gasifier temperature from 750 °C to 850 °C with 50 °C interval, holding reformer temperature at 850 °C, S/C 1.2 and C/F 10. As seen in Fig. 1, the gasifier temperature had a significant influence on gasification performance but little on dry gas composition in product gas. With the increase of gasifier temperature, the dry gas yield dramatically increased from 0.43 Nm3/kg daf to 0.62 Nm3/kg daf. At the same time, the carbon conversion, water conversion and cold gas efficiency also increased evidently. Nevertheless, no significant change was observed in the tar yield. In product gas, the concentrations of H2 and CO2 had little changes. The CO concentration increased slightly and that of CH4 decreased slowly. It indicates that coal pyrolysis, steam gasification and Boudouard reaction were strongly promoted with the gasifier temperature but the tar destruction was inhibited to some extent by gradually shortened residence time of the volatiles from pyrolysis and steam gasification of the coal. The H2/CO ratio descended evidently as a function of the gasifier temperature, revealing that the reverse water gas shift reaction played an important role in the investigated gasifier temperature range. 3.2.2. Effect of S/C The S/C was varied from 0.2 to 2.2 by changing steam flow rate, keeping constant of gasifier temperature at 800 °C, reformer temperature 850 °C and C/F 10. As shown in Fig. 2, with the increase of the S/C, the dry gas yield, carbon conversion, water conversion and cold gas efficiency increased but the tar yield exhibited a little increase 113

Fuel Processing Technology 171 (2018) 110–116

Y. Xiao et al.

Fig. 1. Effect of gasifier temperature on gasification performance of coal (reformer temperature 850 °C, S/C 1.2 and C/F 10)

Fig. 2. Effect of S/C on gasification performance of coal (gasifier temperature 800 °C, reformer temperature 850 °C and C/F 10)

4. Conclusions

was operated under mild condition as were in other steam gasification systems [34,35]. Specifically, negative values of water conversion were obtained at the lower reformer temperature and S/C (as shown in Fig. 2). That could be partially because the water generation from the coal pyrolysis is more than water consumption from steam gasification and tar reforming under these conditions. Moreover, the reduction of Fe2O3 on the surface of the regenerated olivine particles [36,37] in both the gasifier and the reformer could consume part of hydrogen in product gas and further produce the water.

The feasibility of the DLG for steam gasification of Shenmu bituminous coal under mild condition has been validated with calcined olivine as both solid heat carrier and in-situ tar destruction catalyst. Tar destruction was significantly enhanced by increasing reformer temperature and using calcined olivine catalyst as bed material, which resulted in the decrease of tar yield. In comparison, the increase of gasifier temperature, S/C and ER promoted coal gasification, and thus 114

Fuel Processing Technology 171 (2018) 110–116

Y. Xiao et al.

Fig. 3. Effect of ER on gasification performance of coal (gasifier temperature 800 °C, reformer temperature 850 °C, S/C 1.2 and C/F 10)

References

Table 5 Gasification performance of two type coals and comparison with DTBG. Gasification system

DLG

Coal type Bed material Gasifier temperature (°C) Reformer temperature (°C) C/F S/C ER Dry gas composition (vol%) H2 CO CH4 CO2 C2H4 C2H6 C3H6 C3H8 H2/CO ratio Dry gas yield (Nm3/kg daf) Tar yield (%) Tar content (g/Nm3) Carbon conversion (%) Water conversion (%) Cold gas efficiency (%)

SB Olivine 800 850 10.0 1.2 0

IL Olivine 800 850 10.0 1.2 0

IL Olivine 700 850 22.5 1.1 0

50.9 7.5 11.9 27.8 1.4 0.4 0.1 < 0.1 6.8 0.46 0.7 16.8 16.1 3.1 19.5

50.4 10.8 6.4 31.9 0.3 0.1 < 0.1 < 0.1 4.6 0.75 0.3 4.8 25.7 9.4 29.0

41.3 7.5 7.8 43.2 0.2 < 0.1 < 0.1 < 0.1 5.5 0.35 0.1 2.7 17.5 − 5.5 14.0

[1] F.X. Li, L.S. Fan, Clean coal conversion processes-progress and challenges, Energy Environ. Sci. 1 (2008) 248–267. [2] P. Chiesa, S. Consonni, T. Kreutz, R. Williams, Co-production of hydrogen, electricity and CO2 from coal with commercially ready technology. Part a: performance and emissions, Int. J. Hydrog. Energy 30 (7) (2005) 747–767. [3] K. Miura, Mild conversion of coal for producing valuable chemicals, Fuel Processing Technology 62 (2) (2000) 119–135. [4] C.Z. Li, Some recent advances in the understanding of the pyrolysis and gasification behaviour of Victorian brown coal, Fuel 86 (2007) 1664–1683. [5] J.I. Hayashi, S. Hosokai, N. Snonyama, Gasification of low-rank solid fuels with thermochemical energy recuperation for hydrogen production and power generation, ChemInform 38 (30) (2007) 409–419. [6] S.S. Seyitoglu, I. Dincer, A. Kilicarslan, Energy and exergy analyses of hydrogen production by coal gasification, Int. J. Hydrog. Energy 42 (4) (2017) 2592–2600. [7] J.W. Zhang, Y. Wang, L. Dong, S.Q. Gao, G.W. Xu, Decoupling gasification: approach principle and technology justification, Energy Fuel 24 (2010) 6223–6232. [8] C.Z. Li, G.W. Xu, Decoupled thermochemical conversion-preface, Fuel 112 (2013) 607–608. [9] T. Murakami, G.W. Xu, T. Suda, Y. Matsuzawa, H. Tani, T. Fujimori, Some process fundamentals of biomass gasification in dual fluidized bed, Fuel 86 (2007) 244–255. [10] H. An, T. Song, L.H. Shen, C.L. Qin, J.J. Yin, B. Feng, Coal gasification with in situ CO2 capture by the synthetic CaO sorbent in a 1 kW dual fluidized-bed reactor, Int. J. Hydrog. Energy 37 (19) (2012) 14195–14204. [11] J. Corella, J.M. Toledo, G. Molina, A review on dual fluidized-bed biomass gasifiers, Ind. Eng. Chem. Res. 46 (2007) 6831–6839. [12] K. Göransson, U. Söderlind, J. He, W. Zhang, Review of syngas production via biomass DFBGs, Renew. Sust. Energ. Rev. 15 (1) (2011) 482–492. [13] I. Aigner, C. Pfeifer, H. Hofbauer, Co-gasification of coal and wood in a dual fluidized bed gasifier, Fuel 90 (7) (2011) 2404–2412. [14] S. Koppatz, C. Pfeifer, R. Rauch, H. Hofbauer, T. Marquard-Moellenstedt, M. Specht, H2 rich product gas by steam gasification of biomass with in situ CO2 absorption in a dual fluidized bed system of 8 MW fuel input, Fuel Process. Technol. 90 (2009) 914–921. [15] M. Kraussler, M. Binder, H. Hofbauer, 2250-h long term operation of a water gas shift pilot plant processing tar-rich product gas from an industrial scale dual fluidized bed biomass steam gasification plant, Int. J. Hydrog. Energy 41 (15) (2016) 6247–6258. [16] G.W. Xu, T. Murakami, T. Suda, Y. Matsuzawa, H. Tani, Gasification of coffee grounds in dual fluidized bed: performance evaluation and parametric investigation, Energy Fuel 20 (2006) 2695–2704. [17] W.L. Saw, S.S. Pang, Co-gasification of blended lignite and wood pellets in a 100 kW dual fluidized bed steam gasifier: the influence of lignite ratio on producer gas composition and tar content, Fuel 112 (2013) 117–124. [18] L.G. Wei, S.P. Xu, J.G. Liu, C.L. Lu, S.Q. Liu, C.H. Liu, A novel process of biomass

DTBG [31]

facilitated gasification performance of the coal in terms of dry gas yield, carbon conversion and cold gas efficiency. H2 concentration in product gas also increased with the S/C but decreased at higher ER.

Acknowledgments The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (No. 50776013) and the National High Technology Research and Development Program (“863”Program) of China (No. 2008AA05Z407). 115

Fuel Processing Technology 171 (2018) 110–116

Y. Xiao et al.

[19] [20] [21]

[22] [23]

[24] [25]

[26]

[27]

[28]

hydrogen production, Int. J. Hydrog. Energy 38 (2013) 5226–5234. [29] F. Kirnbauer, H. Hofbauer, Investigations on bed material changes in a dual fluidized bed steam gasification plant in Güssing, Austria, Energy Fuel 25 (2011) 3793–3798. [30] G.W. Xu, T. Murakami, T. Suda, Y. Matsuzaw, H. Taniet, Two-stage dual fluidized bed gasification: its conception and application to biomass, Fuel Process. Technol. 90 (2009) 137–144. [31] Y.H. Xiao, S.P. Xu, Y. Tursun, C. Wang, G.Y. Wang, Catalytic steam gasification of lignite for hydrogen-rich gas production in decoupled triple bed reaction system, Fuel 189 (2017) 57–65. [32] Y.H. Xiao, S.P. Xu, Y.B. Song, Y.Y. Shan, C. Wang, G.Y. Wang, Biomass steam gasification for hydrogen-rich gas production in a decoupled dual loop gasification system, Fuel Process. Technol. 165 (2017) 54–61. [33] Z. Min, M. Asadullah, P. Yimsiri, S. Zhang, H. Wu, C.Z. Li, Catalytic reforming of tar during gasification. Part I. Steam reforming of biomass tar using ilmenite as a catalyst, Fuel 90 (2011) 1847–1854. [34] C. Pfeifer, R. Rauch, H. Hofbauer, In-bed catalytic tar reduction in a dual fluidized bed biomass steam gasifier, Ind. Eng. Chem. Res. 43 (2004) 1634–1640. [35] J. Corella, J.M. Toledo, G. Molina, Biomass gasification with pure steam in fluidized bed: 12 variables that affect the effectiveness of the biomass gasifier, Int. J. Oil Gas and Coal Technol. 1 (2008) 194–207. [36] G. Aranda, A. van der Drift, B.J. Vreugdenhil, H.J.M. Visser, C.F. Vilela, C.M. van der Meijden, Comparing direct and indirect fluidized bed gasification: effect of redox cycle on olivine activity, Environ. Prog. Sustain. Energy 33 (2014) 711–720. [37] R.J. Lancee, A.I. Dugulan, P.C. Thüne, H.J. Veringa, J.W. Niemantsverdriet, H.O.A. Fredriksson, Chemical looping capabilities of olivine, used as a catalyst in indirect biomass gasification, Appl. Catal. B Environ. 145 (2014) 216–222.

gasification for hydrogen-rich gas with solid heat carrier: preliminary experimental results, Energy Fuel 20 (2006) 2266–2273. W.J. Zou, C.C. Song, S.P. Xu, C. Lu, Y. Tursun, Biomass gasification in an external circulating countercurrent moving bed gasifier, Fuel 112 (2013) 635–640. K. Göransson, U. Söderlind, W. Zhang, Experimental test on a novel dual fluidized bed biomass gasifier for synthetic fuel production, Fuel 90 (2011) 1340–1349. J. Ashok, S. Kawi, Steam reforming of toluene as a biomass tar model compound over CeO2 promoted Ni/CaO–Al2O3 catalytic systems, Int. J. Hydrog. Energy 38 (32) (2013) 13938–13949. S. Anis, Z.A. Zainal, Tar reduction in biomass product gas via mechanical, catalytic and thermal methods: a review, Renew. Sustain. Energy Rev. 5 (2011) 2355–2377. I.F. Elbaba, C.F. Wu, P.T. Williams, Hydrogen production from the pyrolysis–gasification of waste tyres with a nickel/cerium catalyst, Int. J. Hydrog. Energy 36 (11) (2011) 6628–6637. S. Rapagnà, N. Jand, P.U. Foscolo, Catalytic gasification of biomass to produce hydrogen rich gas, Int. J. Hydrog. Energy 23 (7) (1998) 551–557. J. Corella, J.M. Toledo, R. Padilla, Olivine or dolomite as in-bed additive in biomass Gasification with air in a fluidized bed: which is better? Energy Fuel 18 (2004) 713–720. M. Naqvi, J.Y. Yan, M. Danish, U. Farooq, S.G. Lu, An experimental study on hydrogen enriched gas with reduced tar formation using pre-treated olivine in dual bed steam gasification of mixed biomass compost, Int. J. Hydrog. Energy 41 (25) (2016) 10608–10618. L.D. Felice, C. Courson, P.U. Foscolo, A. Kiennemann, Iron and nickel doped alkaline-earth catalysts for biomass gasification with simultaneous tar reformation and CO2 capture, Int. J. Hydrog. Energy 36 (9) (2011) 5296–5310. T.Y. Mun, J.W. Kim, J.S. Kim, Air gasification of dried sewage sludge in a two-stage gasifier: Part 1. The effects and reusability of additives on the removal of tar and

116