Browsing by Author "Li, Lin"

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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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    Flow characteristics in pressurized oxy-fuel fluidized bed under hot condition
    (Elsevier, 2018-06-28) Li, Lin; Duan, Yuanqiang; Duan, Lunbo; Xu, Chuanlong; Anthony, Edward J.
    Pressurized oxy-fuel fluidized bed (POFB) combustion is regarded as a promising technology for carbon capture from coal-fired power plants. High pressure and temperature conditions have important impacts on the flow characteristic of fluidized bed, and understanding them will help to optimize the design and operation of the POFB boiler. In this work, experiments were carried out in two pressurized fluidized bed (PFB) devices (a hot PFB and a “visual PFB”) both operated under high temperature (20-800 °C) and high pressure conditions (0.1-1.0 MPa). Four parameters including the minimum fluidization velocity (umf), the minimum bubbling velocity (umb), bubble diameter (Db) and bubble frequency (f) were examined in this study. Results showed that the umf decreases with rising pressure and temperature. Based on our results a formula was fitted for calculating the minimum fluidization velocity in PFB, with a relative error less than 15%. With the increase of fluidization number (w), the bubble size and tail vortex increased gradually, the bubbles tended to merge, and the shape of bubbles became more irregular. The Db decreases with the increase of temperature and pressure at the same w. The f increases with increased w, while it decreased with the increase of temperature and pressure.
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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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    Nash double Q-based multi-agent deep reinforcement learning for interactive merging strategy in mixed traffic
    (Elsevier, 2023-09-19) Li, Lin; Zhao, Wanzhong; Wang, Chunyan; Fotouhi, Abbas; Liu, Xuze
    The interaction between ramp and mainline vehicles plays a crucial role in merging areas, especially in the mixed-traffic environment. The driving behaviours of human drivers are uncertain and diverse, and the uncertainty makes it more complex for connected automated vehicles (CAV) to plan trajectories and merge into the mainline. To overcome this problem, a interactive merging strategy based on multi-agent deep reinforcement learning (MADRL) is designed, enabling the ramp vehicle (CAV) to consider the dynamic reaction of mainline vehicles. There are two agents in our interactive strategy, one of which is to predict and analyse the behaviour of mainline vehicles (human-driven vehicles, HDV, or non-connected vehicles). The other is created for exploring optimal merging actions of ramp vehicles. Firstly, game theory is used to model the competitive behaviours between ramp and mainline vehicles, and the Nash equilibrium of joint actions guides the ramp vehicle to learn best response to the mainline vehicle. Secondly, the Nash double Q algorithm is developed to ensure the outputs of Q networks are trained to efficiently converge to the Nash equilibrium point. The trained Q networks are then used for online control. Finally, our strategy is compared with single RL and existing MADRL algorithms in real on-ramp scenarios. Simulations show our strategy to be successful in coordinating both vehicles via analysis of human drivers, resulting in improved driving performance in terms of global safety, efficiency, and comfort.