Kinetic Study on Coal Char Combustion in a Microfluidized Bed

Abstract

The intrinsic kinetics of char combustion were commonly investigated using thermogravimetric analysis (TGA) in previous works at low temperatures to prevent oxygen limitations and temperature deviation. However, the low temperatures caused excess test time because the reaction rate was too slow. In this study, the microfluidized bed (MFB), which has effective heat and mass transfer, was used to investigate the intrinsic kinetics of char combustion at a higher temperature within less time. TGA was used to check the reliability of the MFB. The results suggested that, for fine particles (74–100 μm), the particle temperature deviation and gas distortion could be disregarded in the MFB. For four coal samples, the activation energy measured by the MFB was similar to the result measured by TGA, but the test time using the MFB was greatly shortened as a result of the higher temperatures. The kinetic parameters measured by the MFB were used to predict the char oxidation rate. The predicted rate fit the TGA experiment well at lower temperatures. These results demonstrated the reliability of the MFB and TGA measurements. However, at higher temperatures, the combustion rate in TGA was limited by oxygen diffusion, suggesting that the TGA measurement should be carried out at relatively low temperatures to prevent oxygen diffusion limitation. Instead, the MFB measurement was still valid at higher temperatures as a result of the effective mass and heat transfer.

Kinetic Study on Continuous Sampling of Coal Char from a Micro Fluidized Bed

“…Raw coal was ground and sieved to a diameter of 75–100 μm. We have investigated the effect of char diameter on char conversion in such MFBs in our previous study 24 and found that the carbon conversion rate did not increase with decreasing the particle size below 100 μm, indicating that the internal diffusion limitation could be disregarded when the particle size was less than 100 μm.…”

Reactivity characterization of municipal solid waste and biomass

“…where X is the conversion in time t. In this work, a similar analysis to Fang et al [27] is used, where the conversion is determined from the measured output gas composition instead of sample mass, as the gas composition is measured online unlike of the sample mass. All the carbon containing species n are added together for each time step i and compared to the total released carbon, presented in Equation 4.…”

“…Kijo-Kleczkowska et al [26] studied reactivity of pelletized samples suspended in an updraft reactor. Fang et al [27] utilized a small fluidized bed to study reactivity of coal char. Adamczyk et al [28] presented a method where the fuel particles are dropped into a horizontal "windtunnel" and changes in particle trajectories are analyzed to determine the reaction rate of the particles.…”

Acquiring real kinetics of reactions in the inhibitory atmosphere containing product gases using micro fluidized bed

“…In comparison to TGA, the MFBRA features: (1) high rates of heat and mass transfer, (2) capability of online instantaneously pulse feeding and super‐fast heating of powder reactant to bed temperature, (3) negligible external diffusion inhibition, and (4) fast on‐line measurement 19,20 . Until now, it has been successfully applied to study the mechanisms and kinetics of a variety of gas–solid reactions, including pyrolysis, 22–24 gasification, 14,25,26 combustion 27,28 of coal, biomass, oil shale and chars, calcination, 11,20 and reduction 29–32 of various materials as well as catalytic gas–solid reactions, 33,34 etc. These applications have demonstrated that MFBRA is effective, reliable, and adaptable to various gas–solids reactions.…”