Effect of char on co-pyrolysis of biomass and coal in a free fall reactor
Graphical abstract
Introduction
The growing shortage of oil resources and increasing oil prices have been promoting an urgent search for alternative liquid fuels. However, in the foreseeable future, coal is believed to be a major energy source in China, and a large number of coal tar are produced each year through coal carbonization and liquefaction [1], which can be further processed to produce liquid fuels. But the tar yield of coal pyrolysis is low, and in which the content of heavy components is high owing to its low H/C molar ratio. Accordingly, to increase the tar yield and quality, it is necessary to supply H to coal pyrolysis from other sources [2], [3], [4]. Compared with coal, biomass is becoming important as a renewable alternative energy resource and more environmentally friendly when utilized for energy production due to its CO2 neutrality. Besides, its high thermochemical reactivity and high content of volatiles facilitate the thermal conversion and upgrading of the fuel, and the high molar ratio of H/C in biomass suggests that biomass could act as H-donors in co-pyrolysis of biomass and coal blends and some synergetic effects to produce more volatile products might be expected. Recently, interest in co-pyrolysis of coal and biomass has been growing significantly [5], [6], [7], [8], and synergies to produce more volatile products could be observed. The main reasons for synergies are the hydrogen transfer from biomass to coal and the catalytic effect of inorganic species, especially alkali and alkaline earth metal during the co-pyrolysis [9], [10], [11], [12], [13].
The pyrolysis process of solid fuels includes the primary degradation of fuel particles and the secondary reactions of volatiles, involving a series of physical and chemical processes. Char, one of the main intermediate products in the pyrolysis reaction system, not only has many cavities but also contains some active sites and inherent metallic minerals [14], [15]. It will undoubtedly play an important role in the secondary reactions of primary volatiles. Thus the volatiles–char interactions have significant effects on the product distributions during the co-pyrolysis process. Recently, many studies involving the catalytic effect of char on the tar reforming during the pyrolysis of biomass and coal have been conducted and most of these studies [15], [16], [17], [18], [19], [20], [21], [22], [23] focused on the off-situ char catalysis. But it is different from the nascent char, because the structure characteristic and reactivity will change during the processes that the nascent char is cooled down and again heated to high temperature from low temperature [24], [25]. Xu et al. [26] reported that in-situ char has a higher capability of cracking tar than off-situ char at the temperature as high as 1100 °C. But little attention [27] was paid to the interactions between in-situ char and volatiles, especially under moderate conditions.
In the present study, examinations have been made on the effects of in-situ char–volatiles interactions on the pyrolysis and co-pyrolysis of biomass and coal, employing a particular type of free fall reactor that enables investigation of the secondary reactions of primary volatiles in the presence of char bed.
Section snippets
Feedstocks
The biomass feedstock used in this study is pine sawdust (SD) from Dalian, China and the coal is sub-bituminous coal (SB) from Wyoming's Powder River Basin, USA. The feedstocks were sieved, classified and dried for 3 h at 105 °C before experiments. The particle sizes of biomass and coal were in the range of 0.45–0.90 mm and 0.30–0.45 mm, respectively. The proximate and ultimate analyses of the feedstocks are shown in Table 1.
Experimental apparatus and methods
The fast pyrolysis and co-pyrolysis of biomass and coal were conducted in
Pyrolysis of individual fuel
Fig. 2, Fig. 3 show the product distributions and gas compositions from fast pyrolysis of the individual SD and SB, respectively, with and without nascent char bed at the reactor temperature of 700 °C and the gas–solid separator temperature of 600 °C. As seen in Figs. 2(a) and 3(a), in the case of with char bed, the tar yield increases significantly while the char yield decreases compared to the result without char bed. For example, the tar yield from biomass increases from 5.2 wt.% (daf) in
Conclusion
Fast pyrolysis and co-pyrolysis of SD and SB in a free fall reactor were investigated in order to determine the influence of nascent char on the secondary reactions of primary volatiles. The nascent char has shown encouraging results for the production of tar either for individual pyrolysis and co-pyrolysis. During co-pyrolysis, the presence of char bed can effectively promote tar generation and suppress water formation, the water yield reduces to a minimum value (3.7%) at the BR of 0.50. The
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 51306029), the China Postdoctoral Science Foundation (No. 2013M530920), the Fundamental Research Funds for the Central Universities (No. DUT12RC(3)58) and the Program for Liaoning Excellent Talents in University (2009R10).
References (39)
- et al.
Resources, properties and utilization of tar
Resour. Conserv. Recycl.
(2010) - et al.
Kinetics of copyrolysis of coal with polyamide 6
J. Anal. Appl. Pyrolysis
(2004) - et al.
Influence of reaction parameters on brown coal–polyolefinic plastic co-pyrolysis behavior
J. Anal. Appl. Pyrolysis
(2007) - et al.
Pyrolysis of some whole plastics and plastics–coal mixtures
Energy Convers. Manag.
(2006) - et al.
Synergies in co-pyrolysis of Thai lignite and corncob
Fuel Process. Technol.
(2008) - et al.
Synergetic effect during co-pyrolysis/gasification of biomass and sub-bituminous coal
Fuel Process. Technol.
(2013) - et al.
Interaction between biomass and different rank coals during co-pyrolysis
Renew. Energy
(2010) - et al.
Thermogravimetric study of interactions in the pyrolysis of blends of coal with radiata pine sawdust
Fuel Process. Technol.
(2009) - et al.
Catalytic gasification of char from co-pyrolysis of coal and biomass
Fuel Process. Technol.
(2008) - et al.
Rapid co-pyrolysis of rice straw and a bituminous coal in a high-frequency furnace and gasification of the residual char
Bioresour. Technol.
(2012)
Co-pyrolysis characteristics of sawdust and coal blend in TGA and a fixed bed reactor
Bioresour. Technol.
Co-pyrolysis of low rank coals and biomass: product distributions
Fuel
Thermogravimetric study of the pyrolysis characteristics and kinetics of coal blends with corn and sugarcane residues
Fuel Process. Technol.
Rapid pyrolysis of brown coal in a drop-tube reactor with co-feeding of char as a promoter of in situ tar reforming
Fuel
Roles of inherent metallic species in secondary reactions of tar and char during rapid pyrolysis of brown coals in a drop-tube reactor
Fuel
Tar reforming using char as catalyst during pyrolysis and gasification of Shengli brown coal
J. Anal. Appl. Pyrolysis
Decomposition and gasification of pyrolysis volatiles from pine wood through a bed of hot char
Fuel
Catalytic reforming of tar during gasification. Part II. Char as a catalyst or as a catalyst support for tar reforming
Fuel
Tar reduction in pyrolysis vapours from biomass over a hot char bed
Bioresour. Technol.
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2020, Applied EnergyCitation Excerpt :Zhang et al. [13] also found that the blending of a high proportion of biomass was conducive to increasing the tar yield. Also, the synergistic effect from the quality of tar was reported from the co-pyrolysis of pine sawdust and sub-bituminous coal [14]. Both Chen et al. [15] and Quan et al. [16] found that the negative synergistic effect occurred in the formation of volatile products.