The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Chun-zhu Li - One of the best experts on this subject based on the ideXlab platform.
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Changes in Char Reactivity due to Char-oxygen and Char-steam reactions using victorian brown coal in a fixed-bed reactor
Chinese Journal of Chemical Engineering, 2020Co-Authors: Shu Zhang, Chun-zhu Li, Yonggang WangAbstract:Abstract This study was to examine the influence of reactions of Char–O2 and Char–steam on the Char Reactivity evolution. A newly-designed fixed-bed reactor was used to conduct gasification experiments using Victorian brown coal at 800 °C. The Chars prepared from the gasification experiments were then collected and subjected to Reactivity Characterisation (ex-situ Reactivity) using TGA (thermogravimetric analyser) in air. The results indicate that the Char Reactivity from TGA was generally high when the Char experienced intensive gasification reactions in 0.3% O2 in the fixed-bed reactor. The addition of steam into the gasification not only enhanced the Char conversion significantly but also reduced the Char Reactivity dramatically. The curve shapes of the Char Reactivity with involvement of steam were very different from that with O2 gasification, implying the importance of gasifying agents to Char properties.
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effects of biomass Char structure on its gasification Reactivity
Bioresource Technology, 2010Co-Authors: Mohammad Asadullah, Shu Zhang, Piyachat Yimsiri, Chun-zhu LiAbstract:Abstract The structural features and combustion Reactivity of Chars prepared from the fast pyrolysis of mallee wood were investigated using Raman spectroscopy and thermogravimetric analysis. The Raman spectra were curve-fitted by using 10 Gaussian bands, representing different structural features of Chars. The total Raman peak areas between 800 and 1800 cm −1 and combustion Reactivity of Chars were seen to decrease with increasing pyrolysis temperature. The curve-fitting Raman spectra represented that the formation of amorphous carbon structure with smaller polyaromatic rings are dominant in Chars from bigger particles of biomass and at lower temperature. The condensed and larger aromatic ring systems are preferentially formed in Chars from smaller particles and at higher temperature. The former structure is higher reactive than the latter one, which is reflected in the Char Reactivity. The retention of inherent catalytic species (AAEM) also plays an important role in Char Reactivity. However, our results suggested that the structure of Char played a more dominant role than the catalytic effects of AAEM species in the Char intrinsic combustion Reactivity.
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changes in Char Reactivity and structure during the gasification of a victorian brown coal comparison between gasification in o2 and co2
Fuel Processing Technology, 2010Co-Authors: Chun-zhu LiAbstract:Char Reactivity is an important factor influencing the efficiency of a gasification process. As a low-rank fuel, Victorian brown coal with high gasification Reactivity is especially suitable for use with gasification-based technologies. In this study, a Victorian brown coal was gasified at 800 °C in a fluidised-bed/fixed-bed reactor. Two different gasifying agents were used, which were 4000 ppm O 2 balanced with argon and pure CO 2 . The Chars produced at different gasification conversion levels were further analysed with a thermogravimetric analyser (TGA) at 400 °C in air for their reactivities. The structural features of these Chars were also Characterised with FT-Raman/IR spectroscopy. The contents of alkali and alkaline earth metallic species in these Chars were quantified. The reactivities of the Chars prepared from the gasification in pure CO 2 at 800 °C were of a much higher magnitude than those obtained for the Chars prepared from the gasification in 4000 ppm O 2 also at 800 °C. Even though both atmospheres (i.e. 4000 ppm O 2 and pure CO 2 ) are oxidising conditions, the results indicate that the reaction mechanisms for the gasification of brown coal Char at 800 °C in these two gasifying atmospheres are different. FT-Raman/IR results showed that the Char structure has been changed drastically during the gasification process.
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volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of victorian brown coal part v combined effects of na concentration and Char structure on Char Reactivity
Fuel, 2004Co-Authors: Hongwei Wu, Junichiro Hayashi, Tadatoshi Chiba, Takayuki Takarada, Chun-zhu LiAbstract:Abstract A set of NaCl-loaded Loy Yang brown coal was pyrolysed in a thermogravimetric analyser between 600 and 900 °C. The Char sample after pyrolysis was cooled down directly for in situ Reactivity measurement with air. The results indicated that the volatilisation of Na during pyrolysis is an important reason for the existence of catalyst loading saturation level with Na as a catalyst in Char because the Char prepared at high temperature had a limited holding capacity for Na. Under the experimental conditions in this study, the Char Reactivity showed good linear correlation with the Na concentration in the reacting Char. Peak pyrolysis temperature, affecting the release of Cl and distribution of Na in Char, is an important factor governing the correlation between the Char Reactivity and Na concentration in Char. The catalytic activity of Na is a result of the interaction between Na and Char and thus is greatly dependent on the Char/carbon structure. At high Char conversion levels where the Char structure is more inert and highly condensed, the catalytic activity of Na is reduced compared with its activity at low Char conversion levels. The catalytic activity of Na depends on the structure of Char.
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volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of victorian brown coal part iv catalytic effects of nacl and ion exchangeable na in coal on Char Reactivity
Fuel, 2003Co-Authors: Dimple Mody Quyn, Hongwei Wu, Junichiro Hayashi, Chun-zhu LiAbstract:Abstract The purpose of this study is to investigate the catalytic effects of Na as NaCl or as sodium carboxylates (–COONa) in Victorian brown coal on the Char Reactivity. A Na-exchanged coal and a set of NaCl-loaded coal samples prepared from a Loy Yang brown coal were pyrolysed in a fluidised-bed/fixed-bed reactor and in a thermogravimetric analyser (TGA). The reactivities of the Chars were measured in air at 400 °C using the TGA. The experimental data indicate that the Na in coal as NaCl and as sodium carboxylates (–COONa) had very different catalytic effects on the Char Reactivity. It is the chemical form and dispersion of Na in Char, not in coal, that govern the catalytic effects of Na. For the Na-form (Na-exchanged) coal, the Char Reactivity increased with increasing pyrolysis temperature from 500 to 700 °C and then decreased with pyrolysis temperature from 700 to 900 °C. The increase in Reactivity with pyrolysis temperature (500–700 °C) is mainly due to the changes in the relative distribution of Na in the Char matrix and on the pore surface. For the NaCl-loaded coals, when Cl was released during pyrolysis or gasification, the Na originally present in coal as NaCl showed good catalytic effects for the Char gasification. Otherwise, Cl would combine with Na in the Char to form NaCl during gasification, preventing Na from becoming an active catalyst. Controlling the pyrolysis conditions to favour the release of Cl can be a promising way to transform NaCl in coal into an active catalyst for Char gasification.
Hongwei Wu - One of the best experts on this subject based on the ideXlab platform.
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Volatile–Char interactions: Roles of in situ volatiles with distinctly-different chemistry in determining Char structure and Reactivity
Proceedings of the Combustion Institute, 2020Co-Authors: Xujun Chen, Hongwei WuAbstract:Abstract This study reports the roles of volatiles with distinctly-different chemistry in determining Char Reactivity and Char structure during in situ volatile–Char interactions under non-catalytic conditions. Volatiles were generated in situ from polyethylene (PE), double-acid washed biosolid (DAWB), polyethylene glycol (PEG) or cellulose and interacted with Char prepared from DAWB that is free of catalytically-active inorganic species in a two-stage reactor at 1000 °C. The experimental results show that both H- and O-containing reactive species play different roles during in situ volatile–Char interactions. It has been found that Char Reactivity decreases substantially after in situ volatile–Char interactions. Results from Raman analysis of the Char after in situ interactions with the PE volatiles show H-containing reactive species substantially enhance the condensation of the aromatic ring systems within the Char, thus slightly decreasing the H content in Char and also making Char carbon structure considerably less reactive. It has also been found that the Reactivity of Char after in situ volatile–Char interactions increases with increasing O/H molar ratio of volatiles. The results indicate that O-containing reactive species in volatiles can react with Char to form C O complex oxides that mitigate the carbon structure from condensing into large aromatic ring systems, thus increasing O and H contents in Char and enhancing Char Reactivity.
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volatile Char interactions roles of in situ volatiles with distinctly different chemistry in determining Char structure and Reactivity
Proceedings of the Combustion Institute, 2019Co-Authors: Xujun Chen, Hongwei WuAbstract:Abstract This study reports the roles of volatiles with distinctly-different chemistry in determining Char Reactivity and Char structure during in situ volatile–Char interactions under non-catalytic conditions. Volatiles were generated in situ from polyethylene (PE), double-acid washed biosolid (DAWB), polyethylene glycol (PEG) or cellulose and interacted with Char prepared from DAWB that is free of catalytically-active inorganic species in a two-stage reactor at 1000 °C. The experimental results show that both H- and O-containing reactive species play different roles during in situ volatile–Char interactions. It has been found that Char Reactivity decreases substantially after in situ volatile–Char interactions. Results from Raman analysis of the Char after in situ interactions with the PE volatiles show H-containing reactive species substantially enhance the condensation of the aromatic ring systems within the Char, thus slightly decreasing the H content in Char and also making Char carbon structure considerably less reactive. It has also been found that the Reactivity of Char after in situ volatile–Char interactions increases with increasing O/H molar ratio of volatiles. The results indicate that O-containing reactive species in volatiles can react with Char to form C O complex oxides that mitigate the carbon structure from condensing into large aromatic ring systems, thus increasing O and H contents in Char and enhancing Char Reactivity.
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volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of victorian brown coal part v combined effects of na concentration and Char structure on Char Reactivity
Fuel, 2004Co-Authors: Hongwei Wu, Junichiro Hayashi, Tadatoshi Chiba, Takayuki Takarada, Chun-zhu LiAbstract:Abstract A set of NaCl-loaded Loy Yang brown coal was pyrolysed in a thermogravimetric analyser between 600 and 900 °C. The Char sample after pyrolysis was cooled down directly for in situ Reactivity measurement with air. The results indicated that the volatilisation of Na during pyrolysis is an important reason for the existence of catalyst loading saturation level with Na as a catalyst in Char because the Char prepared at high temperature had a limited holding capacity for Na. Under the experimental conditions in this study, the Char Reactivity showed good linear correlation with the Na concentration in the reacting Char. Peak pyrolysis temperature, affecting the release of Cl and distribution of Na in Char, is an important factor governing the correlation between the Char Reactivity and Na concentration in Char. The catalytic activity of Na is a result of the interaction between Na and Char and thus is greatly dependent on the Char/carbon structure. At high Char conversion levels where the Char structure is more inert and highly condensed, the catalytic activity of Na is reduced compared with its activity at low Char conversion levels. The catalytic activity of Na depends on the structure of Char.
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volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of victorian brown coal part iv catalytic effects of nacl and ion exchangeable na in coal on Char Reactivity
Fuel, 2003Co-Authors: Dimple Mody Quyn, Hongwei Wu, Junichiro Hayashi, Chun-zhu LiAbstract:Abstract The purpose of this study is to investigate the catalytic effects of Na as NaCl or as sodium carboxylates (–COONa) in Victorian brown coal on the Char Reactivity. A Na-exchanged coal and a set of NaCl-loaded coal samples prepared from a Loy Yang brown coal were pyrolysed in a fluidised-bed/fixed-bed reactor and in a thermogravimetric analyser (TGA). The reactivities of the Chars were measured in air at 400 °C using the TGA. The experimental data indicate that the Na in coal as NaCl and as sodium carboxylates (–COONa) had very different catalytic effects on the Char Reactivity. It is the chemical form and dispersion of Na in Char, not in coal, that govern the catalytic effects of Na. For the Na-form (Na-exchanged) coal, the Char Reactivity increased with increasing pyrolysis temperature from 500 to 700 °C and then decreased with pyrolysis temperature from 700 to 900 °C. The increase in Reactivity with pyrolysis temperature (500–700 °C) is mainly due to the changes in the relative distribution of Na in the Char matrix and on the pore surface. For the NaCl-loaded coals, when Cl was released during pyrolysis or gasification, the Na originally present in coal as NaCl showed good catalytic effects for the Char gasification. Otherwise, Cl would combine with Na in the Char to form NaCl during gasification, preventing Na from becoming an active catalyst. Controlling the pyrolysis conditions to favour the release of Cl can be a promising way to transform NaCl in coal into an active catalyst for Char gasification.
Changshuai Du - One of the best experts on this subject based on the ideXlab platform.
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Importance of volatile AAEM species to Char Reactivity during volatile–Char interactions
RSC Advances, 2020Co-Authors: Changshuai DuAbstract:The volatile alkali and alkaline earth metallic (AAEM) species are an important component of the involved reactants during volatile–Char interactions and are beneficial to Char Reactivity. A fluidized-bed/fixed-bed combination reactor was employed to investigate the effects of volatile AAEM species on the Char Reactivity at 800 °C. ICP-OES and X-ray Photoelectron Spectroscopy (XPS) were utilized to reveal the evolution of AAEM species and Char structures during volatile–Char interactions. The results indicate that a large proportion of volatile AAEM species would migrate onto the Char substrate, amounting to over 50% of the volatilization amount of AAEM species derived from Char during volatile–Char interactions. Concentrations of AAEM species accord well with the oxygen atomic concentrations on the Char surface. The volatile AAEM species migrated onto the Char would bond with the oxygen preferentially, likely to stabilize the oxygen-containing structures. The Reactivity of the Char reacted with the volatile loading of AAEM species is about two times higher than that reacted with the volatile free-of-AAEM species. It is believed that the volatile AAEM species show a better catalytic activity than the residual AAEM species in original Char, possibly due to the more stable bonds between volatile AAEM species and the Char matrix, or the better dispersion of volatile AAEM species in Char. The conclusions clearly demonstrate that the volatile AAEM species play a significant role in the Char Reactivity.
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Variation of Char Reactivity during catalytic gasification with steam: comparison among catalytic gasification by ion-exchangeable Na, Ca and Na/Ca mixture
Energy & Fuels, 2017Co-Authors: Changshuai DuAbstract:The Reactivity profile of Char during catalytic gasification is crucial for designing and optimizing the gasification process, and it is greatly affected by the types and changes in activity of the catalyst during gasification. The catalytic gasification of Na-Char, Ca-Char, and Na/Ca-Char mixtures with different concentrations of steam was conducted within the temperature range of 700–900 °C using a microfluidized bed reaction analyzer. The results indicate that the Reactivity of Na-Char is always higher than that of Ca-Char during the initial gasification stage (0–Xi) and then lower than that of Ca-Char in the later stage. The observations are mainly attributed to the different deactivation paths for the Na and Ca catalysts. The drastic loss of Na during gasification corresponds well to the sharp decrease of Na-Char Reactivity within the initial carbon conversion, and the gradual change of the Ca dispersion contributes to the deactivation of the Ca catalyst. It is also demonstrated that the catalysis of...
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importance of volatile aaem species to Char Reactivity during volatile Char interactions
RSC Advances, 2017Co-Authors: Changshuai DuAbstract:The volatile alkali and alkaline earth metallic (AAEM) species are an important component of the involved reactants during volatile–Char interactions and are beneficial to Char Reactivity. A fluidized-bed/fixed-bed combination reactor was employed to investigate the effects of volatile AAEM species on the Char Reactivity at 800 °C. ICP-OES and X-ray Photoelectron Spectroscopy (XPS) were utilized to reveal the evolution of AAEM species and Char structures during volatile–Char interactions. The results indicate that a large proportion of volatile AAEM species would migrate onto the Char substrate, amounting to over 50% of the volatilization amount of AAEM species derived from Char during volatile–Char interactions. Concentrations of AAEM species accord well with the oxygen atomic concentrations on the Char surface. The volatile AAEM species migrated onto the Char would bond with the oxygen preferentially, likely to stabilize the oxygen-containing structures. The Reactivity of the Char reacted with the volatile loading of AAEM species is about two times higher than that reacted with the volatile free-of-AAEM species. It is believed that the volatile AAEM species show a better catalytic activity than the residual AAEM species in original Char, possibly due to the more stable bonds between volatile AAEM species and the Char matrix, or the better dispersion of volatile AAEM species in Char. The conclusions clearly demonstrate that the volatile AAEM species play a significant role in the Char Reactivity.
Toshinori Kojima - One of the best experts on this subject based on the ideXlab platform.
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Gasification Reactivity of Char with CO2 at elevated temperatures: the effect of heating rate during pyrolysis
Asia-Pacific Journal of Chemical Engineering, 2010Co-Authors: Yongjun Huang, Shigeru Kato, Toshinori KojimaAbstract:Integrated coal gasification combined cycle (IGCC) technology is being promoted to make better use of energy resources, and an entrained-flow gasifier is a key item of equipment in the process due to its high gasification efficiency, smooth disCharge of molten ash, etc. The temperature and heating rate under entrained-flow gasification conditions are very high, and these two parameters can influence the gasification Reactivity of a Char with CO2. Therefore, the clarification of Characteristics and mechanisms of Char gasification under conditions close to entrained-flow gasification is very important. To obtain a valid kinetics of Char gasification, it is necessary to clarify the effect of heating rate during pyrolysis on Char Reactivity. The effect of heating rate during pyrolysis on the gasification Reactivity of three types of Chars in CO2 was investigated experimentally at elevated temperatures in a novel fluidized bed. It was shown that even at elevated temperatures, the heating rate has significant influence on the Char Reactivity during gasification. A higher heating rate during pyrolysis leads to higher Char Reactivity of gasification, however it has only limited effect on the activation energy of Char gasification with CO2. The Char Reactivity is closely related to its specific surface area and pore volume. The high Reactivity of a Char derived from pyrolysis at a high heating rate is most likely due to its enhanced porous structure as a result of the rapid release of volatile matter at a high heating rate. The effect of heating rate during pyrolysis on Char Reactivity is pronounced at low temperatures, and is very different for various coal types, i.e. very pronounced for a low-rank coal. The gasification Reactivity of a Char is related to both the Char pore structure and temperature, which suggests that even at elevated temperatures the gasification of a Char with CO2 is controlled by both chemical reaction and diffusion inside the particles. Our results demonstrate that it is necessary to derive the gasification kinetics of a Char at a high heating rate to obtain valid kinetic equations for an entrained-flow gasifier. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
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effect of pyrolysis time on the gasification Reactivity of Char with co2 at elevated temperatures
Fuel, 2004Co-Authors: Masahiro Kaneko, Shigeru Kato, Toshinori KojimaAbstract:Abstract Gasification of a Char has so far been mainly studied at low temperatures and low heating rates with a TGA (thermogravimetric analyzer). Studies on gasification of a Char in CO 2 at elevated temperatures and high heating rates are necessary to develop IGCC technology. With a unique fluidized bed, the effect of pyrolysis time on Char Reactivity was investigated. It was found that a longer pyrolysis time led to lower Reactivity of a Char, while this effect leveled off as pyrolysis time increased. The pyrolysis time also had an influence on the temperature dependence of gasification Reactivity. Initial Char gasification rate decreased as pyrolysis time increased. The pyrolysis time had effect on the entire process of Char gasification. The effect of pyrolysis time was more remarkable for a coal with high volatile matter content among the three coals tested. The gasification rate of a Char was very different from that of a raw coal (gasification without pyrolysis in advance), which suggested an influence of pyrolysis time and atmosphere on Char Reactivity. Accordingly, those results obtained from a TGA are necessary to be corrected when applied to a practical entrained flow gasifier.
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development of fbr measurement of Char Reactivity to carbon dioxide at elevated temperatures
Fuel, 2001Co-Authors: T Watanabe, M Nakamura, Shigeyuki Uemiya, Toshinori KojimaAbstract:Abstract Gasification kinetics of Char is thought as a key factor in designing and operating gasifiers. The widely used present technique, TGA method, is limited in temperature and heating rate ranges. A fluidized bed reactor (FBR) method is described which is suitable for measuring Char Reactivity at elevated temperatures up to 1873 K by using CO 2 as the gasifying agent. It is capable of carbonizing coal samples under various conditions including rapid heating as well as slow heating, and in-situ measuring Char gasification rate directly after carbonization. Char Reactivity is evaluated from the time variation of CO concentration in the exit gas. The heterogeneous global model, incorporated with the two-phase model, is used to describe the reaction of Chars. On the basis of the model, the film mass transfer resistance and the bubble-emulsion mass transfer resistance are calculated and their influence on the measured results is assessed. Proper selection of operating parameters for assuring reasonable measurement is discussed. Data processing methods have been developed to give fundamental, quantitative measurements of Char Reactivity, allowing direct comparison of Reactivity between Chars.
N Paterson - One of the best experts on this subject based on the ideXlab platform.
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the zero emission carbon concept zeca extents of reaction with different coals in steam hydrogen tar formation and residual Char Reactivity
Energy & Fuels, 2008Co-Authors: N Paterson, Paul S Fennell, D R Dugwell, R KandiyotiAbstract:A high pressure wire mesh reactor has been modified to investigate the reactions underlying the zero emission carbon concept (ZECA) process. This is a novel power generation concept that involves producing hydrogen from coal. An earlier paper has described the concept, the wire mesh reactor used for laboratory scale tests, and results of tests with H2 and He. In this paper, results of tests with a range of coals are described, together with tar emission and Char Reactivity measurements. The tests with a range of coals (from lignite through to bituminous have shown that the performances of the different fuels do vary widely, but not as a direct function of their rank. With lignites, high conversions were achieved in a H2/steam mixture. Lower conversions were apparent with the other coals. However, reaction conditions were not optimized to achieve the highest conversion level. Pittsburgh No. 8 coal (high volatile bituminous) was also found to be reactive, whereas Wyodak (sub-bituminous) and Daw Mill (bitumi...
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The Zero Emission Carbon Concept (ZECA): Extents of Reaction with Different Coals in Steam/Hydrogen, Tar Formation and Residual Char Reactivity
Energy & Fuels, 2008Co-Authors: N Paterson, Paul S Fennell, D R Dugwell, R KandiyotiAbstract:A high pressure wire mesh reactor has been modified to investigate the reactions underlying the zero emission carbon concept (ZECA) process. This is a novel power generation concept that involves producing hydrogen from coal. An earlier paper has described the concept, the wire mesh reactor used for laboratory scale tests, and results of tests with H2 and He. In this paper, results of tests with a range of coals are described, together with tar emission and Char Reactivity measurements. The tests with a range of coals (from lignite through to bituminous have shown that the performances of the different fuels do vary widely, but not as a direct function of their rank. With lignites, high conversions were achieved in a H2/steam mixture. Lower conversions were apparent with the other coals. However, reaction conditions were not optimized to achieve the highest conversion level. Pittsburgh No. 8 coal (high volatile bituminous) was also found to be reactive, whereas Wyodak (sub-bituminous) and Daw Mill (bitumi...
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an investigation of the Reactivity of Chars formed in fluidized bed gasifiers the effect of reaction conditions and particle size on coal Char Reactivity
Energy & Fuels, 2006Co-Authors: A Cousins, N Paterson, D R Dugwell, R KandiyotiAbstract:Coal-derived Chars formed during air-blown gasification processes may rapidly lose Reactivity, and this can limit the extent of their conversion. To study this effect, a laboratory-scale fluidized bed reactor has been modified to enable Char samples to be prepared under strictly controlled conditions of temperature, pressure, particle size, gaseous environment, and residence time. This has been used to gain an insight into the deactivation of the Chars as they form and during their subsequent residence time in the bed of the gasifier. The work shows that the Char Reactivity declines rapidly during its formation as part of the pyrolysis of the coal. This is thought to result from the rapid deposition of secondary, unreactive Char within the pores of the material. In this work, it has been shown to occur within the initial 10 s in the reactor, but in reality, this effect probably occurred within 1 s. Temperature, pressure, and particle size have an impact on this process. Subsequently, and over a longer tim...