Kinetics investigation on the reduction of NO using straw char based on physicochemical characterization

Wang, Xuebin; Si, Jipeng; Tan, Houzhang; Zhao, Qinxin; Xu, Tongmo

doi:10.1016/j.biortech.2011.05.038

Cited by 30 publications

(11 citation statements)

References 39 publications

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“…The NO–char reaction has been experimentally determined to be fractional or near first-order, as seen in Table . ,,− Also, previous work in our laboratory confirmed that the NO–char reaction order is unity and pore diffusion effects are negligible under the conditions of this study …”

Section: Methodssupporting

confidence: 63%

Kinetics of NO Reduction by Coal, Biomass, and Graphitic Chars: Effects of Burnout Level and Conditions

et al. 2014

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During the combustion of coal and other carbonaceous materials, the heterogeneous reaction of NO with the evolving char created in the combustion process is important for understanding the formation and reduction of NO. This investigation quantifies the effects of char burnout level and conditions on the kinetics of NO reduction by chars made from coals ranging in rank from lignite to low-volatile bituminous (Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh #8, and Pocahontas #3) as well as graphite and coconut char. Kinetic data were measured in a packed-bed reactor at temperatures between 723 and 1173 K. The rate constant for the NO−char reaction was found to depend upon the extent of burnout/conversion and conditions under which the char was burned out. The NO−char rate constant consistently decreases with increasing burnout when the char burnout levels are accomplished in a drop tube reactor at 1800 K and 3−5% O 2 . However, the NO−char rate constant increases as char burnout increases (up to 90%) when the char burnout levels result from reacting the char with 3050 ppm of NO in a packed bed at 723−1173 K. For the latter case, the relationship of the NO−char rate constant (on the basis of moisture ash-free char mass) and char burnout is approximately linear with roughly the same upward slope between 20 and 80% burnout for all coal chars studied. The activation energy of the NO−char reaction is apparently independent of both char burnout level and burnout conditions. The CO 2 /CO ratio in the exhaust stream appears to correlate with the NO−char rate constant for the chars burned out at low-temperature conditions.

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Section: Methodssupporting

confidence: 63%

Kinetics of NO Reduction by Coal, Biomass, and Graphitic Chars: Effects of Burnout Level and Conditions

et al. 2014

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“…The size of the original biomass particles ranged from 50 μm to 2000 μm, whereas that of the coal particles was lower than 198 μm. Char was prepared in a fixed bed tube furnace in Ar atmosphere at 800°C for 1 h . The microstructure of the char was detected by Scanning Electron Microscope (SEM) (JSM‐6390A, JEOL, Japan), and the surface area was determined by N 2 ‐Brunner‐Emmet‐Teller (BET) (SA3100, Beckman Coulter, USA).…”

Section: Experiments and Methodsmentioning

confidence: 99%

“…Consequently, the char characteristics of biomass are distinct. Biomass should possess a large surface area and a high reactivity; in addition, these materials should be significantly affected by the catalysis of alkali metals . While oxy‐coal combustion has been extensively studied, oxy‐biomass combustion has elicited minimal attention because biomass is CO 2 neutral; the CO 2 emissions of biomass combustion need not be reduced for a sufficiently long time .…”

Section: Introductionmentioning

confidence: 99%

Kinetics investigation on the combustion of biochar in O₂/CO₂ atmosphere

Wang

Deng

et al. 2014

Env Prog and Sustain Energy

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Oxy-biomass combustion produces negative CO 2 emissions. This study investigated the combustion kinetics of biochar in O 2 /CO 2 atmosphere using a thermo-gravimetric analyzer. The effects of atmosphere, O 2 concentration, and fuel type were considered in this investigation. Results show that the reaction order of biochar combustion ranges from 0.5 to 1. Furthermore, the kinetic compensation effect can be observed between the apparent activation energy E and the frequency factor A. This relation is given by lnA 5 0.181E 2 14.618. Compared with O 2 /N 2 atmosphere, O 2 /CO 2 atmosphere delays biochar ignition and reduces activation energy. The ignition temperature of straw char is significantly lower than that of wood and coal char. The apparent activation energy of char combustion follows the inequality wood char > straw char > coal char. This result indicates that biochar combustion is more sensitive to temperature than coal char combustion. The reactivity of char combustion improves with increasing O 2 concentration, but biochar has a lower degree of improvement than coal char. The change from air combustion to oxy-fuel combustion and the increase in O 2 concentration exert minimal effects on biochar combustion than on coal char combustion.

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“…However, in line with most previous studies, Wang et al employed long pyrolysis times for producing their char, resulting in chars with a reactivity that is significantly different compared to chars in real pulverized fuel combustion. It has been found that the reaction rate of NO reduction over chars which experienced short time of thermal deactivation (in second to minute scale) ,, was generally 10–100 times larger than for chars which were deactivated over longer times (in hour scale). − For this reason, it is important to conduct experiments at high heating rates and short pyrolysis times to approximate the conditions of real pulverized fuel combustion.…”

Section: Introductionmentioning

confidence: 99%

NO Formation during Oxy-Fuel Combustion of Coal and Biomass Chars

2014

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The yields of NO from combustion of bituminous coal, lignite, and biomass chars were investigated in O 2 /N 2 and O 2 /CO 2 atmospheres. The experiments were performed in a laboratory-scale fixed-bed reactor in the temperature range of 850− 1150 °C. To minimize thermal deactivation during char preparation, the chars were generated by in situ pyrolysis at the reaction temperature. The NO yield clearly decreased and the CO yield increased when the atmosphere was altered from O 2 /N 2 to O 2 /CO 2 at 850 °C, but only small differences in NO and CO yields were observed between the two atmospheres at 1050−1150 °C. To examine how CO influences the NO yield, the effect of CO on NO reduction over char as well as NO reduction by CO over ash was investigated in the fixed-bed reactor. Furthermore, the influence of CO on the homogeneous oxidation of HCN, possibly a product of the char-N oxidation, was evaluated using a detailed chemical kinetic model. The results indicate that CO influences the NO yield from char combustion through two paths at 850 °C: (1) CO accelerates NO reduction over char and (2) CO accelerates HCN oxidation, increasing the possibility of NO reduction over char. Both effects were more pronounced at 850 °C than at 1050−1150 °C. The present work indicates that the effect of CO 2 on NO formation in oxy-fuel combustion in fluidized beds can partly be attributed to heterogeneous reactions, whereas for high-temperature pulverized fuel combustion, CO 2 mainly affects the volatile chemistry.

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Kinetics investigation on the reduction of NO using straw char based on physicochemical characterization

Cited by 30 publications

References 39 publications

Kinetics of NO Reduction by Coal, Biomass, and Graphitic Chars: Effects of Burnout Level and Conditions

Kinetics of NO Reduction by Coal, Biomass, and Graphitic Chars: Effects of Burnout Level and Conditions

Kinetics investigation on the combustion of biochar in O₂/CO₂ atmosphere

NO Formation during Oxy-Fuel Combustion of Coal and Biomass Chars

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Kinetics investigation on the reduction of NO using straw char based on physicochemical characterization

Cited by 30 publications

References 39 publications

Kinetics of NO Reduction by Coal, Biomass, and Graphitic Chars: Effects of Burnout Level and Conditions

Kinetics of NO Reduction by Coal, Biomass, and Graphitic Chars: Effects of Burnout Level and Conditions

Kinetics investigation on the combustion of biochar in O2/CO2 atmosphere

NO Formation during Oxy-Fuel Combustion of Coal and Biomass Chars

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Kinetics investigation on the combustion of biochar in O₂/CO₂ atmosphere