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[Display omitted] • A fluidized bed type microwave plasma-assisted combustor was developed. • An experimental study using cellulosic fuel and silica sand was conducted. • The device requires good states of fluidization, mixing, and plasma formation. • The highest fuel conversion ratios were obtained at 4 L/min and 4 kPa. • Cellulosic fuel did not remain in the fluidized bed combustor after the experiment. A novel waste treatment method that can efficiently decompose waste, suppress by-product generation, and operate at a low cost is urgently required. Herein, a microwave plasma-assisted combustor was developed and its combustion characteristics were investigated for application in solid waste treatment. The experimental conditions for obtaining good states of fluidization, mixing, and plasma formation were examined prior to the combustion experiments. Subsequently, the optimal experimental conditions, such as the filling amount of bed particles, bed particle diameter, microwave irradiation position, and microwave output, required for good combustion were achieved. Combustion experiments based on these conditions revealed that a good fluidization state is required to obtain a good combustion state in this device, although the combustion condition does not necessarily depend on the system pressure at each O 2 flow rate. Comparison of the conditions with similar fluidization states at O 2 flow rates of 1–4 L/min revealed a maximum fuel conversion ratio at 4 L/min owing to the combustion promotion caused by increased O 2 partial pressure. The fuel did not remain in the fluidized bed combustor after the combustion experiments. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) is mainly composed of combustible substances emitted from various combustors, with combustion technology improvement resulting in decreased PM diameter. Since the effective collection of small PM particles by existing removal devices is challenging, we fabricated a PM removal device of the continuous regeneration type, utilizing low-temperature fluidized bed combustion and relying on adhesion forces for the effective collection of small PM particles. For the above device, PM collection and combustion efficiencies increased with decreasing PM diameter due to the increased role of adhesion forces observed on a small scale and the adherence of dispersed PM to the surface of bed-forming particles (enhancing contact with oxygen), respectively. Furthermore, the constructed device was operated in a continuous regeneration mode, featuring simultaneous PM collection and combustion. Although existing continuous regeneration devices require temperatures of 600–650 °C for PM combustion, the device reported herein could be operated at a bed temperature of 400 °C. [ABSTRACT FROM AUTHOR]

Fluidized bed has been used in a PM removal device to remove PM2.5 effectively through the use of adhesion force, experimentally demonstrating the capability for effective PM2.5 removal. In the present work, numerical simulations of this device have been performed using the Eulerian–Eulerian method for the further development of this device. The results obtained by the Gidaspow drag force model and using the EMMS method are compared to the reference data to verify the drag force model, and it is shown that the EMMS method is better than the Gidaspow drag force model. The filtration mechanism of Clift et al. was incorporated in the simulation code to calculate the behavior of PM adhesion in the fluidized bed type PM removal device. However, the predicted results differ substantially from the experimental results. Therefore, a PM adhesion model that considers PM deposition has been incorporated in the simulation code, and numerical simulations have been conducted to analyze the behavior of PM adhesion in the fluidized bed type PM removal device. It was found that these numerical simulations represent the characteristics of PM adhesion in the fluidized bed type PM removal device with a high degree of accuracy. The predicted results show that PM adheres mainly to the surface of the bed particle at the high volume fraction of the bed particle phase and is approximately uniformly collected over the entire bed particle phase. [ABSTRACT FROM AUTHOR]

Highly efficient PM 2.5 filtration has been obtained experimentally using a fluidized bed. In this work, a CFD-DEM simulation was conducted to investigate the effects of operating conditions such as the superficial velocity, fluidization state, and PM size. These effects were assessed in terms of the capture ratio and the forces acting on the PM. A high collection efficiency is reproduced at PM diameters of less than 20 μm and superficial velocities of 0.3–0.6 m/s. Most of the PM is captured by adhesion in the bottom two to six layers of bed particles, where the void fraction is low. The adhesion force is the dominant force, and the drag force is negligible even at a superficial velocity of 0.6 m/s. After the PM is captured, it moves with the bed particles in this system. The adhesion force is still dominant for a 30 μm PM at 0.4 m/s. The capture ratio is 87.5%. However, the PM–bed particle collision velocity increases with increasing superficial velocity, and the repulsive force becomes large. The capture ratio decreases dramatically with increasing superficial velocity. The repulsive force becomes dominant for PM diameters above 40 μm, and most of the PM cannot be filtered. Unlabelled Image • CFD-DEM numerical simulation of PM filtration using a fluidized bed was conducted. • Highly efficient fine PM filtration was reproduced based on the van der Waals force. • Most PM is captured in bottom bed layer, where bed particles are nearly close-packed. • PM (≤20 μm)–bed particle adhesion force is dominant and, drag force is negligible. • Captured PM is stirred by fluidization but is retained on bed particles. [ABSTRACT FROM AUTHOR]

Fluidized bed filters exhibit high PM 2.5 collection efficiency, as shown in our previous work. In this study, a CFD-IBM-DEM simulation was conducted to elucidate the filtration mechanisms for the further development of these filters. A preliminary numerical simulation of a small fixed-bed filter was performed to determine the appropriate CFD grid size for computational accuracy and cost, and the grid of bed particles/10 was applied for PM filtration simulation of the fluidized bed. Numerical collection efficiency is high value of 92.06%, with bed particles of 420 μm and a superficial velocity of 0.4 m/s. Fluidization becomes violent at 0.6 m/s, which decreases the collection efficiency to 84.12%. However, gentle fluidization is maintained even at 0.6 m/s using bed particles of 600 μm, and the fluidization is the same as that observed using bed particles of 420 μm and 0.4 m/s. These fluidization states exhibit similar collection efficiency. [Display omitted] • CFD-IBM-DEM simulation was conducted to elucidate fluidized bed filter mechanisms. • Bottom layer is maintained close-to-packed bed state and filtered most of the PM. • Adhesion acting on PM is dominant, and captured PM is stabilized on bed particles. • Captured PM is stirred by fluidization while being maintained on bed particles. • Same fluidization states exhibit similar collection efficiencies. [ABSTRACT FROM AUTHOR]

• Low-temperature regeneration with fluidized bed filter achieved using catalyst. • Catalytic PM combustion kinetics was investigated via new TGA and simulations. • PM combustion depends on relative velocity between gas-solid in a fluidized bed. • Rough surface bed particle increases both doped catalyst and combustion amounts. • Continuous regeneration can occur at 300 °C, which is close to that of exhaust heat. A fluidized bed filter can perform highly efficient PM collection and low-temperature continuous regeneration. However, to further reduce continuous regeneration temperature, a rough surface bed particle was selected herein. It is expected that the rough surface increases and stabilizes doped catalyst on bed particle even in fluidized bed. This bed particle can stably support 9.48 g-catalyst/kg-bed particle of doped catalyst versus 1.58 g-catalyst/kg-bed particle in previous research. This increase in catalyst amount increases the probability of good PM-catalyst contact, and collection efficiency can easily maintain its initial value due to catalytic PM combustion. PM combustion also depends on fluidization. Thus, combustion kinetics in a fluidized bed was investigated via a newly developed thermogravimetric analyzer that considered PM-gas relative velocity, and a constructed kinetic model was applied to numerical simulation. PM combustion obeyed an Arrhenius relationship, and the effect of PM-gas relative velocity was included in the kinetic model as a mass transfer term. A continuous regeneration experiment was conducted under optimal conditions, and the continuous regeneration temperature is 330 °C. As water vapor occurs in combustor exhaust, we added 10 vol% water vapor and found that the continuous regeneration is further reduced to 300 °C. [ABSTRACT FROM AUTHOR]

The relative velocity dependence of PM combustion rate. • Fluidized bed was used as continuous regeneration PM removal device. • PM combustion model in fluidized bed was constructed by our new thermogravimetry. • Our kinetic model represents PM combustion in fluidized bed type PM removal device. • PM combustion depends on relative velocity between gas and solid in fluidized bed. The size of particulate matter (PM) generated by combustion has decreased with the improvement of combustion technology. While small PM has a significant negative impact on the human body, it is difficult for a conventional PM removal device to collect small PM. We developed a fluidized bed type PM removal device with a focusing adhesion force. This device collects small PM effectively and can be operated as a continuous regeneration device at low temperature. To further develop this device, it is important to investigate the PM combustion characteristics in this device. The kinetic model constructed in conventional thermogravimetry could not accurately represent the combustion rates of the solid fuel in the fluidized bed. Therefore, a new thermogravimetric apparatus was constructed in this study that generates the direct collision of air with carbon to reproduce the fluidized bed combustion. The influence of the relative velocity between PM and gas on the combustion rate was investigated. The effect of relative velocity was represented as the mass transfer coefficient of kinetic model. It is observed that the combustion rate shows Arrhenius behavior, and kinetic parameters were determined by fitting. The kinetic model was applied to the numerical simulations of the PM removal device. The numerical collection efficiency was in good agreement with the experimental data. PM adhesion and combustion characteristics were investigated in numerical simulations. It is observed that the adhesion rate is high at a low void fraction and that the combustion rate is high at a high relative velocity. The PM combustion amount is high for the high adhesion and combustion rates. The total combustion amount is determined to be 55% of the total amount of PM deposition after 180 min at each set of conditions. [ABSTRACT FROM AUTHOR]

A fluidized bed type particulate matter (PM) removal device has been developed by focusing on the adhesion force under condition of non-water vapor. This device efficiently collects fine PM and can be operated as a low-temperature continuous regeneration device. The exhaust gas of a combustor includes water vapor at concentrations of 5–15 vol%. To further develop this device, the effect of water vapor on the continuous regeneration was investigated. The collection efficiency increases due to the water vapor. The reaction rate constant increases with increasing water vapor and with decreasing PM diameter. It is shown that water vapor promotes PM combustion at 250–400 °C. A smaller PM suits PM collection and combustion because smaller PM results in relatively larger adhesion force and well contacts the oxidant by dispersing it on the bed particles. The continuous regeneration temperature decreases to 380 °C due to the water vapor under optimal conditions. Unlabelled Image • A fluidized bed is used as a continuous regeneration PM removal device. • The effect of water vapor on continuous regeneration was investigated. • Optimum conditions were found for the reaction rate. • The continuous regeneration temperature is 380 °C due to water vapor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Processing gas flow rate in a fluidized bed filter increases by large bed particles. • Similar fluidization state leads to similar collection efficiency. • Large bed particles have slightly larger BET surface areas than small bed particles. • The amount of catalyst on a large particle is comparable to that on a small particle. • Continuous regeneration can be achieved at 320 °C with a collection efficiency 100%. To increase the processing gas flow rate in a fluidized bed filter, the effects of superficial velocity and fluidization state on PM filtration and combustion were examined by experiments using large bed particles (710 μm). The fluidization state at 710 μm was measured by image analysis and recurrence plot, and the superficial velocities as experimental conditions were determined to obtain almost the same fluidization state and filtration efficiency as those for small bed particles (420 μm) in previous studies. The BET-surface area of 710 μm is slightly larger than that of 420 μm, and the amount of potassium catalyst doped on large bed particles is comparable to that at 420 μm. The gas phase velocity is increased by increasing the processing gas flow rate, and the contact probability between PM and oxidizer increases. The PM combustion reaction is significantly promoted owing to the effects of the potassium catalyst and the increase in the gas phase velocity, and the minimum continuous regeneration temperature is 30 °C lower than that at 420 μm. As a result, fluidized bed filters using large bed particles can be operated in continuous regeneration mode at a bed temperature of 320 °C while maintaining a filtration efficiency of 100%. [ABSTRACT FROM AUTHOR]

• A fluidized bed was used as a continuous regeneration PM removal device. • The effects of catalyst on continuous regeneration were investigated. • Reaction mechanisms of PM combustion in fluidized bed were proposed. • The continuous regeneration temperature is 350 °C with catalyst. • Water vapor reduces the continuous regeneration temperature to 330 °C. A fluidized bed type PM removal device was developed by focusing on adhesion force as a highly efficient device for PM collection and low-temperature continuous regeneration. To further reduce the continuous regeneration temperature of this device, catalytic PM combustion was investigated. Alkaline and alkaline earth metals (potassium and calcium, respectively) are effective for PM combustion and are among the least expensive catalysts. The positive effects of these catalysts on PM combustion were compared. As their catalytic performances are almost identical, potassium was used for the continuous regeneration of this device. Potassium was doped on the bed particle via the impregnation method. Moreover, the amounts of doped potassium were compared based on the effects of PM combustion on collection efficiency, and the optimum value was determined to be 1.58 g-catalyst/kg-bed particle. Catalyst characterization was conducted via XRD and FTIR analysis of the cleaned gas. K 2 CO 3 is detected on bed particle surface from the XRD patterns. The FTIR results show that potassium promotes PM combustion and selectively enhanced CO 2 generation. CO 2 is generated from the oxidation of K 2 CO 3 and transformation of K 2 O 2 to K 2 O with the consumption of PM. K 2 O is converted to K 2 CO 3 with the re-absorption of CO 2. The lowest continuous regeneration temperature decreases to 350 °C with maintaining the collection efficiency 100% owing to the catalytic PM combustion. Furthermore, the effect of water vapor, which is present in exhaust gas, was investigated. It promotes PM combustion and further reduces the continuous regeneration temperature to 330 °C. [ABSTRACT FROM AUTHOR]