Browsing by Author "Tong, Shuai"

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    Combustion characteristics of lignite char in a fluidized bed under O2/N2, O2/CO2 and O2/H2O atmospheres
    (Elsevier, 2018-12-21) Li, Lin; Duan, Lunbo; Tong, Shuai; Anthony, Edward J.
    As a possible new focus of oxy-fuel work, O2/H2O combustion has many advantages over O2/CO2 combustion, and has gradually gained increasing attention. The unique physicochemical properties (thermal capacity, diffusivity, reactivity) of H2O significantly influence the char combustion characteristics. In the present work, the combustion and kinetics characteristics of lignite char particle were studied in a fluidized bed (FB) reactor under N2, CO2 and H2O atmospheres with different O2 concentrations (15%–27%) and bed temperatures (Tb, 837–937 °C). Results indicated that the average reaction rate (raverage) and the peak reaction rate (rpeak) of lignite char in H2O atmospheres were slower than those in CO2 atmospheres at low O2 concentrations. However, as the O2 concentration increases, the rpeak and raverage of lignite char in H2O atmospheres significantly improved and exceeded those under CO2 atmospheres. The calculation result for the activation energy based on the shrinking-core model showed that the order of activation energy under different atmospheres is: O2/CO2 (28.96 kJ/mol) > O2/H2O (26.11 kJ/mol) > O2/N2 (23.31 kJ/mol). Furthermore, gasification reactions play an important role in both O2/CO2 and O2/H2O combustion, and should not be ignored. As the Tb increased, the active sites occupied by gasification agent were significantly increased, while the active sites occupied by oxygen decreased correspondingly.
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    Experimental study of a single char particle combustion characteristics in a fluidized bed under O2/H2O condition
    (Elsevier, 2019-09-23) Li, Lin; Duan, Lunbo; Yang, Zhihao; Tong, Shuai; Anthony, Edward J.; Zhao, Changsui
    Oxy-steam combustion is a potential new route for oxy-fuel combustion with carbon capture from coal-fired power plants. In the present work, the combustion behavior of single char particles were investigated in a transparent fluidized bed combustor under different operating conditions (i.e., gas atmosphere, oxygen concentration, coal rank, location, fluidization number, particle size, and bed temperature). Both pre-calibrated two-color pryrometry and a flexible thermocouple were used to measure the char particle temperature in the combustion tests. Results indicated that the pore structure of the char generated in H2O atmosphere was better than that generated in CO2 and N2 atmospheres. As expected, with increase of oxygen concentration, the burnout time (tb) decreased, and the particle temperature (Tp) increased. The sequence of burnout times for different rank coal char particles was: anthracite > bituminous coal > lignite. Interestingly, comparing O2/CO2 and O2/N2 combustion, a shorter tb and a lower Tp of char could be achieved simultaneously in O2/H2O combustion, regardless of location and oxygen concentration. Furthermore, the increase of fluidization number strengthened the mass and heat transfer between the char and the environment, thereby reducing the tb and Tp of char. With increasing of particle size, the Tp slightly decreased, the tb increased markedly, and the gasification reactions became more and more significant. As the bed temperature increased, the gasification rate increased exponentially, and the mass transfer coefficient increased gradually.
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    A kinetic study on lignite char gasification with CO2 and H2O in a fluidized bed reactor
    (Elsevier, 2018-10-25) Tong, Shuai; Li, Lin; Duan, Lunbo; Zhao, Changsui; Anthony, Edward J.
    Lignite char gasification experiments in CO2, H2O and their mixture were performed in a fluidized bed reactor over the temperatures range of 1060–1210 K. The active sites occupied by different gasifying agents in CO2/H2O mixture were separated and the kinetics was analyzed. Results show that the reactivity of gasification increases rapidly as the temperature rises. The average reaction rate in 50%CO2/50%H2O mixture is slower than the reaction rate in 50%N2/50%H2O atmosphere, which indicates that CO2 and H2O compete for the same active reaction sites on the char surface. Furthermore, with an increase of temperature, the competition capacity of CO2 gasification over H2O gradually increases, as a result, CO2 gasification occupies more active sites than H2O when the temperature is higher than 1160 K. Calculations of the activation energy in the kinetically controlled region based on the shrinking core model reveal that the activation energies follow the trend: N2/CO2 > N2/H2O > CO2/H2O.
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    Modelling the simultaneous calcination/sulfation behavior of limestone under circulating fluidized bed combustion conditions
    (Elsevier, 2019-08-28) Chen, Liang; Wang, Chunbo; Tong, Shuai; Anthony, Edward J.;
    The simultaneous calcination/sulfation (SCS) reaction is the realistic reaction process for limestone use in CFB boilers. A SCS reaction model based on the randomly-overlapped pore concept, which takes into consideration the calcination of CaCO3, the sulfation of CaO and the sintering effect simultaneously, was developed. The results of this model fit well with the results from the thermogravimetric analyzer (TGA) tests and, thus this model was used to study the characteristics of the SCS reaction. The SCS reaction consists of a mass-loss stage and a mass-growth stage, and the two stages are seperated by a minimum mass point. The mass-loss stage is dominated by the calcination of CaCO3, while the mass-growth stage is dominated by the sulfation of CaO. The minimum mass point is a balance point of the mass change caused by the two reactions. The calcination reaction occurred in a layer of the particle. As the calcination reaction progresses, the reaction front moves inward and a CaO layer is formed. The SO2 in the calcination atmosphere can react with the CaO layer and produce CaSO4. The CaSO4 can fill the pores of the CaO layer and narrow the pore width, increase the CO2 diffusion resistance and consequently slow the calcination reaction. The sulfation reaction becomes slower as the reaction progresses. There was an upper limit to the sulfation conversion, which is much higher in the outer layer of the particle. For a typical particle with a radius of 200 μm, the sulfation reaction ceases in the inner part (0-150 μm) of the particle due to the exhaustion of SO2, while in the outer part of the particle (150-200 μm), the decrease of the sulfation rate is caused by the simultaneous decline of the reaction surface area, surface Ca2+ ion concentration and SO2 concentration.