Browsing by Author "Zhao, Changsui"

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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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    Migration and emission of mercury from circulating fluidized bed boilers co-firing petroleum coke and coal
    (Elsevier, 2017-12-01) Cui, Jian; Duan, Lunbo; Jiang, Ying; Zhao, Changsui; Anthony, Edward J.
    The migration and emission of mercury (Hg) were studied for three 410 t/h circulating fluidized bed (CFB) boilers co-firing petroleum coke and coal. Both the Ontario Hydro Method (OHM) and US Environmental Protection Agency (EPA) Method 30B were employed to sample gas phase emissions of mercury from the flue gas, and to compare the agreement for these different measurement methods in industrial application. Concurrent with flue gas sampling, solid and liquid samples including fuel, bottom ash, fly ash and gypsum, wastewater, etc., were also collected to determine the total mass balance and map the mercury migration from the power plant. The results showed that the mass balance rates ranged from 83.9% to 122.7%, which can be considered to be both acceptable and reliable. The vast majority of mercury emitted was distributed in the fly ash and stack gas, accounting for 61.36–67.71% and 22.22–33.35%, respectively. The total Hg concentration measured by OHM is comparable with that determined by EPA Method 30B; however, EPA Method 30B possesses advantages in terms of flexibility. The fabric filter (FF) has better Hg0 and Hg2+ removal efficiencies than the electrostatic precipitator (ESP). Because the Hg contained in the liquid waste streams greatly exceeded Chinese regulations, the main emphasis of future work should be focused on wastewater treatment. The mercury emission factors in this study are in the range of 0.69 g/TJ-0.80 g/TJ, which provides basic data for such CFB power plants in China. The CFB boilers equipped with ESP + WFGD or FF + WFGD appear to have the potential to significantly reduce Hg emission to the atmosphere.
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    Nitrogen and sulfur conversion during pressurized pyrolysis under CO2 atmosphere in fluidized bed
    (Elsevier, 2016-10-25) Duan, Yuanqiang; Duan, Lunbo; Anthony, Edward J.; Zhao, Changsui
    Pressurized oxy-fuel combustion (POFC) is a promising technology for CO2 capture from coal-fired power plants, offering both high efficiency and a low penalty. However, the high partial pressure of CO2 in a POFC furnace has important impacts on fuel-N and fuel-S conversion during the coal pyrolysis process, and understanding this will help to achieve further control of SOx/NOx. In this study, coal pyrolysis experiments were conducted in a pressurized fluidized bed with the pressure range of 0.1–0.7 MPa under N2 and CO2 atmosphere. The gaseous products were monitored by a Fourier transform infrared spectroscopy analyzer (FTIR) and the char residue was characterized by an X-ray photoelectron spectroscopy (XPS) analyzer in order to acquire the species information for S-containing and N-containing compounds. Results show that the enrichment of CO2 in the local atmosphere enhances the fuel-N conversion to HCN in the pyrolysis process, which serves as a favorable precursor to N2O. The generation of HCN and NH3 increase simultaneously with the increase of overall pressure. SO2 concentration in the gaseous product is relatively low, and as the pressure increases, the concentration decreases slightly due to CO reduction of SO2 to COS. Sulfur content in the char decreases as the pressure goes from 0.1 MPa to 0.7 MPa indicating higher CO2 pressure accelerates the decomposition of sulfur compounds in the coal, which is further confirmed by the XPS results.
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    Partitioning behavior of Arsenic in circulating fluidized bed boilers co-firing petroleum coke and coal
    (Elsevier, 2017-06-05) Duan, Lunbo; Cui, Jian; Jiang, Ying; Zhao, Changsui; Anthony, Edward J.
    The emission of Arsenic from coal-fired power plants has generated widespread environmental and human health concerns. This paper discusses Arsenic partitioning from three 440 t/h circulating fluidized bed (CFB) boilers co-firing petroleum coke and coal. All the boilers were equipped with electrostatic precipitator (ESP) or fabric filter (FF), and wet flue gas desulfurization (WFGD). Flue gas was sampled simultaneously both up- and down-stream of the ESP/FF and at the outlet of the WFGD based on EPA Method 29. Concurrent with flue gas sampling, feed fuel, bottom ash, ESP/FF ash, WFGD gypsum, WFGD wastewater, limestone slurry and flush water were also collected. The results show that, for three tested CFB boilers, the overall mass balance ratios of As ranged from 80.0%–114.2%, which can be considered to be acceptable and reliable. Most of the As was distributed in the bottom ash and ESP/FF ash with the values of 17.4%–37.5% and 55.6%–77.5%, respectively. Speciation analysis suggests that As5 + was the major water-soluble species in the feed fuel, bottom ash and fly ash, while As3 + was found to be the dominant species in WFGD wastewater. For three CFB boilers, the concentrations of total As in the stack emission were 0.97, 0.32 and 0.31 μg/m3, respectively. The CFB boiler equipped with ESP/FF + WFGD was shown to be able to provide good control of the emission of As emitted into the atmosphere.
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    Partitioning of trace elements, As, Ba, Cd, Cr, Cu, Mn and Pb, in a 2.5 MWth pilot-scale circulating fluidised bed combustor burning an anthracite and a bituminous coal
    (Elsevier, 2016-02-14) Duan, Lunbo; Sun, Haicheng; Jiang, Ying; Anthony, Edward J.; Zhao, Changsui
    Coal combustion introduces large amounts of pollutants into the atmosphere, including trace elements originally bonded in the coal matrix. The emission of these elements raises considerable environmental and human health concerns. To optimise process parameters and reduce gaseous trace element emissions, it is of significant importance to investigate the solid–gas partitioning behaviour of trace elements during combustion processes. To date, limited numbers of experimental studies have been carried out, especially using pilot circulating fluidised bed (CFB) combustion plants. This paper discusses the partitioning behaviour of seven elements (As, Ba, Cd, Cr, Cu, Mn and Pb) in different product streams during combustion tests on anthracite and bituminous coal. The combustion tests were carried out in a 2.5 MWth CFB unit equipped with multi-stage control of solids, which is well suited for trace element partitioning studies. The mass balance ratio of the elements studied ranged from 56%–137%, which is, considering their concentrations, both satisfactory and reasonable. Most of the elements were found in the bottom ash and fly ash during CFB combustion, while small amounts of As, Cd and Pb were emitted to the atmosphere along with fine particulates. The trace elements are more likely to be retained in the bottom ash from the bituminous coal but not in the case of anthracite. For the volatile elements, the enrichment in solid streams follows the trend of: bag filter ash > cyclone ash > IBHX (in-bed heat exchanger) solids > bottom ash, indicating that the volatile elements tend to be enriched in fine particles. Anthracite, when compared to bituminous coal, shows lower emission factors for all monitored elements, except for Pb. This study can serve as a good reference for trace element control strategies in coal-fired CFB boilers.