Micro Fluidized Bed Reaction Analyzer Research Articles

Multistep Reduction Kinetics of Fine Iron Ore with Carbon Monoxide in a Micro Fluidized Bed Reaction Analyzer

The reduction kinetics of Brazilian hematite by CO is investigated in a Micro Fluidized Bed Reaction Analyzer (MFBRA) using an analyzing method based on Johnson-Mehl-Avrami (JMA) model at temperatures of 973 K (700 °C), 1023 K (750 °C), 1073 K (800 °C), and 1123 K (850 °C). The solid products at different reduction stages are evaluated by SEM/EDS and XRD technologies. Results indicate that the reduction process is better to be discussed in terms of a parallel reaction model that consists of the reactions of hematite to wustite and wustite to iron, rather than a stepwise route. Meanwhile, the controlling mechanism of the reduction process is found to vary with temperature and the degree of conversion. The overall process is controlled by the gas–solid reaction occurring at the iron/wustite interface in the initial stages, and then is limited by the nucleation of wustite, and finally shifts to diffusion control. Moreover, the reactions of hematite to wustite and wustite to iron take place simultaneously but with different time dependences, and the apparent activation energies of hematite to wustite and wustite to iron are determined as 83.61 and 80.40 KJ/mol, respectively.

Non-isothermal coal char gasification with CO2 in a micro fluidized bed reaction analyzer and a thermogravimetric analyzer

The so-called micro fluidized bed reaction analyzer (MFBRA) and a thermogravimetric analyzer (TGA) were adopted to comparatively investigate the non-isothermal gasification of coal char with CO2. Experimental results demonstrated that heating rate obviously affected the coal char gasification reaction. Raising heating rate evidently increased the temperatures at the initiating reaction (Ti), the maximal reaction rate (Tm) and the finishing reaction (Tf). Nonetheless, it decreased the char conversion at a given reaction temperature and also the activation energy estimated by the single heating rate method. Comparing the data tested by TGA and MFBRA under the same heating rate clarified that the temperatures of Ti, Tm, and Tf were all relatively lower for MFBRA. The difference for such characteristic reaction temperatures between TGA and MFBRA increased with raising the heating rate. The measurement in MFBRA also led to the higher activation energy estimated according to both the single heating rate and the combination heating rate methods. Perhaps all these results are attributed to the lower limitation from heat and transfer including gas diffusion in MFBRA than in TGA.

Isothermal Gasification of in Situ/ex Situ Coal Char with CO2 in a Micro Fluidized Bed Reaction Analyzer

The so-called micro fluidized bed reaction analyzer (MFBRA) was adopted to implement the isothermal gasification of in situ coal char with CO2 under minimized external diffusion inhibition. It was done by keeping the reaction atmosphere and temperature in the MFBRA for both coal pyrolysis and char gasification. This was further compared to the gasification of two other kinds of ex situ chars. While the gasification of ex situ char 1 referred to the coal pyrolysis in Ar and then CO2 gasification of the resulting hot char without thermal annealing (cooling) in the same MFBRA, that of the ex situ char 2 was by first a separate coal pyrolysis in Ar and then gasification of the char in the MFBRA after thermal annealing (cooling). Reaction characterization and kinetic parameters based on the measured time-series product gas composition of CO clarified that the in situ coal char had the highest gasification reactivity and the lowest activation energy, whereas the ex situ coal char 2 showed the lowest gasification reactivity and the highest activation energy. Comparing the gasification behavior of chars made with Yima (YM) bituminous coal and Xilinhaote (XLHT) lignite further demonstrated that the char of XLHT lignite had the higher reactivity and smaller activation energy, complying with the higher gasification activity of lignite char than that of bituminite char.

Characterization of coal char gasification with steam in a micro-fluidized bed reaction analyzer

In this study, the so-called micro-fluidized bed reaction analyzer (MFBRA) was used to characterize the isothermal reaction of char gasification with steam at 0.1MPa. With minimal inhibition of heat and mass transfer, the article examined the effect of reaction temperature and partial pressure of steam on char gasification behavior and reaction kinetics. It was found that at the experimental temperatures varying in 750–1100°C, the char–steam gasification reaction can be divided into two regions according to temperatures of 750–950°C and 950–1100°C. The reaction was well described by the shrinking core model, and the activation energies of char–steam gasification in such two regions are 166.94kJ/mol and 79.4kJ/mol, respectively. The activation energy in the kinetically controlled low-temperature region is very similar to that reported in the literatures, validating the reliability of MFBRA for characterizing char gasification and estimating its kinetics. Furthermore, the reaction order for steam partial pressure was found to be about 0.5 under the tested conditions.

Study on the Pyrolysis Kinetics of Blended Coal in the Fluidized-bed Reactor

The micro fluidized bed reaction analyzer (MFBRA) was employed to investigate the emission characteristics and the formation kinetics of methane which was released from different kinds of coal and the blended coal during the coal pyrolysis. The results show that under the same pyrolysis condition, the initial release temperature of methane and the pyrolysis activation energy (E) decreases with increasing volatile content of the coal, while the maximum releasing rate and the total volatilization amount of methane increased, indicating that the higher the volatile content of coal, the easier the pyrolysis reaction. Coal blending can change the quality parameters of the single coal. The water content, volatile content and ash content of the blended coal were equal to the weighted average of corresponding single coal, while the activation energy (E) of blended coal was not equal to the weighted average of corresponding single coal.

Characterization of Char Gasification in a Micro Fluidized Bed Reaction Analyzer

This study is devoted to characterizing the isothermal reaction kinetics of char gasification with CO2 in a micro fluidized bed reaction analyzer (MFBRA) in comparison to the measurement in a thermogravimetric analyzer (TGA). Under minimized inhibition of heat and mass transfer, the reaction rate was found to be much higher in the MFBRA than in the TGA. The maximal rate appeared at a conversion of about 0.15 in the MFBRA but at 0.45 in the TGA. The shrinking core model described well the char-CO2 gasification reaction in both the MFBRA and TGA. In the temperature range of 760-1000 degrees C, the char-CO2 gasification reaction can be divided into two stages. At lower temperatures, the activation energy from the MFBRA and TGA is very close, validating the reliability of the MFBRA for analyzing gas-solid reaction kinetics. At higher temperatures, the estimated activation energy was obviously higher for the MFBRA than for the TGA, showing the lower diffusion limitation prevailing in the MFBRA. The frequency factor for the Arrhenius equation was found to be much higher for the MFBRA than for the TGA, complying with the higher reaction rate observed in the MFBRA. The variation in the reaction atmosphere composition during gas switching in the TGA was also investigated.

Reduction of NO over biomass tar in micro-fluidized bed

The so-called micro-fluidized bed reaction analyzer (MFBRA) that enables the evaluation of rapid chemical reactions was used to investigate the NO reduction characteristics by biomass tar agent in terms of its activity and efficiency for reducing NO. Biomass char was used as a comparative reduction agent in this study. The employed biomass tar and char were made from pyrolyzing distilled spirit lees (DSL), a massive fermentation waste generated in China. The results showed that the NO reduction defined for the same mass (10mg) of reactant was more efficient for tar than for char. The identified peak NO reduction efficiency (inlet: 1800ppm) was high as 73.8% for 10mg tar but only 39.3% for the same amount of char. Testing the NO reductions by five typical model tar compounds including acetic acid, toluene, phenol, naphthalene and 1-hydroxy-naphthalene demonstrated that all these components contributed to the capability of tar for NO reduction. The article estimated as well the kinetic parameters of NO reduction by tar based on the MFBRA-measured data according to the isothermal differential approach, finding that the apparent activation energy of NO reduction reaction by tar was 122kJ/mol.

Kinetics and Mechanism of Direct Reaction between CO2 and Ca(OH)2 in Micro Fluidized Bed

Even at present it is still difficult to characterize the reaction between CO2 and Ca(OH)2 at high temperature and atmospheric pressure using traditional instruments such as thermogravimetric analyzer and differential scanning calorimeter. This study was devoted to characterizing such a reaction in a newly developed micro fluidized bed reaction analyzer (MFBRA) under isothermal conditions in the temperature range of 773-1023 K. The results indicated that the MFBRA has not only a good adaptability for characterizing the above-mentioned reaction but enables as well a new insight into the mechanism of the reaction. An obvious time delay was identified for the release of the formed steam (H2O) in comparison with the onset of its CO2 absorption, which might be attributed to the formation of an unstable intermediate product Ca(HCO3)2 in the reaction process between CO2 and Ca(OH)2. The activation energy for forming Ca(HCO3)2 was found to be about 40 kJ/mol, which is much lower than that of the reaction between CO2 and CaO.

Kinetic study of reaction of porous solids

This work focused on the research of reaction test and kinetic calculation method for the combustion of a high-surface-area carbon. Experiments have been performed by Micro Fluidized Bed Reaction Analyzer (MFBRA), which was developed by IPE, CAS, and commercial thermogravimeter under isothermal and programmed heating conditions, respectively. With these methods, for the 0~5 μm particles in a MFBRA in the air flow rate of 1.3 L/min, the activation energies were calculated using thermal kinetics analysis on solid conversion and applied chemical kinetics on gas diffusion and reaction in micro pores. Using thermal kinetics analysis method (FWO equation) to calculate the programmed heating test data by TG, the activation energy is about 137 kJ/mol inclusion the reaction and gas diffusion control. Using thermal analytic isoconversional method to calculate the experimental data in MFBRA, the activation energy is about 95 kJ/mol. Meanwhile, the activation energy, which was obtained using a random pore model to calculate the isothermal experimental data, is about 178 kJ/mol with a structure parameter about 0.17 m-3. This value is about twice of that from thermal analytic isoconversional method, and higher than the non-isothermal TGA results, and be closer to the intrinsic value.

Isothermal differential characteristics of gas–solid reaction in micro-fluidized bed reactor

The isothermal differential characteristics of the gas–solid reaction occurring in a micro-fluidized bed reactor were studied using the indigenously developed Micro-Fluidized Bed Reaction Analyzer (MFBRA). The combustion of graphite powder in micrometers was taken as the model reaction because of its negligible internal diffusion and chemical-reaction simplicity. With minimized inhibitions from both the internal and external diffusions, the reaction in MFBRA at a preset temperature was analyzed by using the isothermal kinetic approach, resulting in an activation energy of 165kJ/mol and a pre-exponential factor of 1061/s. The reaction was further found to be subject to the nucleation and growth model expressed by G(α)=−ln(1−α). Measuring this reaction in TG via the programmed heating method resulted in the similar activation energy and the same reaction function model (by extrapolating to zero conversion). Comparing with the non-isothermal approach for TG that involves complicated mathematical calculations, the isothermal differential approach for MFBRA allowed the separation of the temperature effect (i.e., the reaction rate constant) and kinetic function model, thus providing a simple and reliable determination of the gas–solid reaction kinetics.

Reaction kinetics and mechanism of biomass pylolysis in a micro-fluidized bed reactor

A Micro Fluidized Bed Reaction Analyzer (MFBRA) was used to study the pyrolysis of biomass in argon. Through on-line pulse feeding of reactant and continuously monitoring the composition changes of gas product, the MFBRA enables the measurement of reaction rates at arbitrary temperatures, the deduction of kinetic parameters and the analysis of reaction mechanism. By applying to biomass pyrolysis this article found that the pyrolysis reaction can finish in about 10 s, which is much shorter than the other literature values obtained in larger fluidized bed reactors but very close to the theoretically anticipated values. The detected evolving sequences of different gas species and the deduced kinetic parameters demonstrate further that the reactions between/among the formed different gas species in pyrolysis prevail to certain degree and there are different pathways for forming the different gas species. The activation energy and pre-exponential factor derived by treating the pyrolysis gas as a single product are 11.77 kJ/mol and 1.45 s −1, which are obviously lower than the literature values measured in thermogravimetric analyzers.

Kinetics and mechanism of solid reactions in a micro fluidized bed reactor

AbstractA novel gas–solid Micro Fluidized Bed Reaction Analyzer (MFBRA) was developed to deduce reaction rates and kinetic parameters through measuring time‐dependent composition changes of evolved gases from the reactions. Application of the MFBRA to the decomposition of CaCO3 powder resulted in an apparent activation energy of 142.73 kJ/mol and a pre‐exponential factor of 399,777 s−1. This apparent activation energy was much lower than the thermogravimetry‐measured value of 184.31 kJ/mol, demonstrating a quicker reaction in the MFBRA. This was further verified by CuO reduction in CO, as accelerated by the fast diffusion and high heating rate in the MFBRA. Measurement of pyrolysis of coal and biomass in MFBRA found that the reaction process was completed in about 10 s, a time much shorter than the literature‐reported values in larger fluidized bed reactors. By monitoring the release of gas species from reactions at different temperatures, the MFBRA also allowed deeper insight into the mechanism of pyrolysis reactions. © 2010 American Institute of Chemical Engineers AIChE J, 2010