Laboratory-scale Fluidized Bed Reactor Research Articles

CFD modelling of particle shrinkage in a fluidized bed for biomass fast pyrolysis with quadrature method of moment

An Eulerian-Eulerian multi-phase CFD model was set up to simulate a lab-scale fluidized bed reactor for the fast pyrolysis of biomass. Biomass particles and the bed material (sand) were considered to be particulate phases and modelled using the kinetic theory of granular flow. A global, multi-stage chemical kinetic mechanism was integrated into the main framework of the CFD model and employed to account for the process of biomass devolatilization. A 3-parameter shrinkage model was used to describe the variation in particle size due to biomass decomposition. This particle shrinkage model was then used in combination with a quadrature method of moment (QMOM) to solve the particle population balance equation (PBE). The evolution of biomass particle size in the fluidized bed was obtained for several different patterns of particle shrinkage, which were represented by different values of shrinkage factors. In addition, pore formation inside the biomass particle was simulated for these shrinkage patterns, and thus, the density variation of biomass particles is taken into account.

Recarbonization of drinking water in fluidized-bed reactor

Investigation of drinking-water recarbonization process is the main aim of this work. Experiments aimed at increasing of Ca2+ and Mg2+ in water were carried out in laboratory scale fluidized-bed reactor. This technique offers potential for increasing of reaction surface area and overall reaction rate, and represents a new approach in drinking-water industry. Measurements of hydraulic characteristics of the fluidized bed were performed. The results of comparison of two different recarbonization agents, dolomite and half-calcined dolomite, show that half-calcined dolomite is more efficient for increasing concentration of Ca2+ and Mg2+ from value below the recommended limit to 3.4 mmol L−1. Effect of carbon dioxide on enrichment of water by calcium and magnesium was also investigated and positive effect was observed. Concentration of Ca2+ and Mg2+ with CO2 present was increased by factor 2.6 in comparison without addition of CO2 to the system at the same conditions. The use of fluidized-bed reactor resulted in significantly higher remineralization rate in comparison with static filtration column.

6-4.模擬ゴミ燃焼に伴うダイオキシン類生成挙動(Session 6 リサイクル)

6-4.模擬ゴミ燃焼に伴うダイオキシン類生成挙動(Session 6 リサイクル)

Measurement of reaction rates for pulverized fuel combustion in air and oxyfuel atmosphere using a novel fluidized bed reactor setup

The reaction rate of char from pulverized Columbian coal (Mina Norte) is investigated in synthetic air (N2/O2), oxyfuel atmosphere (CO2/O2) and CO2/N2 using a lab-scale fluidized bed reactor (FBR). Reactor temperatures range from 823 to 1273K for combustion and 1173 to 1373K for gasification (Boudouard). The oxygen volume concentration is varied between 15 and 30vol.%, while gasification is investigated in a mixture of 10–75vol.% CO2 in nitrogen. Using an nth order Arrhenius approach, activation energies as well as apparent order of reaction are calculated for the combustion and gasification reactions.It is found that the combustion reaction with this particular fuel evolves between +17% (873K) and +75% (1223K) faster in N2/O2 than in CO2/O2. The results of Arrhenius fit suggest that activation energy of combustion reaction does not differ significantly between synthetic air (regime I: 120.9kJ/mol, regime II: 62.9kJ/mol) and oxyfuel atmosphere (116.6kJ/mol, 64.3kJ/mol). Comparing results for oxyfuel and air, a difference of approximately 50K in the transition temperature from regime I to regime II is observed but this finding is not statistically firm, yet. The apparent order of reaction has been calculated to n=0.72 in air (combustion), n=0.66 in oxyfuel (combustion) and n=0.49 in CO2/N2 (gasification).A comparison with available literature data confirms that the results achieved with the fluidized bed are comparable to the two most common experimental setups used in combustion research: Entrained flow reactors and thermogravimetric analyzers. The experimental setup also represents a novelty in FBR systems, as it quantitatively captures reactions with an apparent 90% carbon conversion timet90 of 3s, which is a third of the time of comparable setups described in literature.

Kinetics of thermal decomposition of hydrated minerals associated with hematite ore in a fluidized bed reactor

The kinetics of removal of loss on ignition (LOI) by thermal decomposition of hydrated minerals present in natural iron ores (i.e., kaolinite, gibbsite, and goethite) was investigated in a laboratory-scale vertical fluidized bed reactor (FBR) using isothermal methods of kinetic analysis. Experiments in the FBR in batch processes were carried out at different temperatures (300 to 1200°C) and residence time (1 to 30 min) for four different iron ore samples with various LOIs (2.34wt% to 9.83wt%). The operating velocity was maintained in the range from 1.2 to 1.4 times the minimum fluidization velocity (U mf). We observed that, below a certain critical temperature, the FBR did not effectively reduce the LOI to a desired level even with increased residence time. The results of this study indicate that the LOI level could be reduced by 90% within 1 min of residence time at 1100°C. The kinetics for low-LOI samples (<6wt%) indicates two different reaction mechanisms in two temperature regimes. At lower temperatures (300 to 700°C), the kinetics is characterized by a lower activation energy (diffusion-controlled physical moisture removal), followed by a higher activation energy (chemically controlled removal of LOI). In the case of high-LOI samples, three different kinetics mechanisms prevail at different temperature regimes. At temperature up to 450°C, diffusion kinetics prevails (removal of physical moisture); at temperature from 450 to 650°C, chemical kinetics dominates during removal of matrix moisture. At temperatures greater than 650°C, nucleation and growth begins to influence the rate of removal of LOI.

High-rate autotrophic denitrification in a fluidized-bed reactor at psychrophilic temperatures

In this study, high-rate autotrophic denitrification driven by thiosulfate (S2O32−) was maintained under psychrophilic conditions in a lab-scale fluidized-bed reactor (FBR) with a Thiobacillus-dominated biofilm. The temperature effects on the denitrifying performance of the FBR were monitored by gradually decreasing the temperature from 20 to 3°C. The potential of the FBR biofilm to maintain thiosulfate-driven denitrification at 3°C was further investigated at different HRTs (5.4, 3 and 1h) and influent NO3− concentrations (200, 600 and 1078mg/L), resulting in a gradual increase of the nitrogen loading rate (NLR) from 0.20 to 3.3kg N-NO3−/m3d. Complete thiosulfate-driven denitrification could be maintained at all temperatures, HRTs and influent NO3− concentrations tested. PCR-DGGE analysis revealed the dominance of the sulfur-oxidizing chemolithotrophs T. denitrificans and T. thioparus at all temperatures investigated. The FBR operation at a temperature as low as 3°C promoted bed expansion and increased the dissolved organic carbon (DOC) concentration in the effluent, but had no significant effects on the denitrification efficiency. The findings of this study are highly significant for the treatment of cold nitrogen-contaminated waters poor in organics and confirm the FBR as a robust and powerful bioreactor system for autotrophic denitrification.

Effect of steam on the performance of Ca-based sorbents in calcium looping processes

This study addresses the role of water vapour in Calcium Looping (CaL) cycles, and is based on results of an experimental campaign performed in a lab-scale fluidized bed reactor under operating conditions that are representative of a realistic CaL process. Tests have been designed so as to characterize the effect of steam in either the calcination or the carbonation stages, or in both. A reference limestone has been used, and its CO2 capture capacity, propensity to fragmentation and morphological and microstructural changes have been investigated upon iterated looping cycles. Results are discussed to highlight the role of steam on the course of calcium looping.

On the oxy-combustion of lignite and corn stover in a lab-scale fluidized bed reactor

This paper addresses an experimental investigation concerning oxy-combustion of coal and biomass in a lab-scale fluidized bed reactor. While co-firing has been widely studied under conventional air conditions, few experiences are available to date for O2/CO2 atmospheres. The research is focused on SO2 and NOx emissions, along with the deposition rates and ashes mineralogy. The influences of the atmosphere (air vs. 30/70% O2/CO2), the coal-to-biomass energy input ratio (80/20%, 90/10%), the chlorine mass fraction in the biomass (0.35%, 1%, 2%) and the Ca:S mole ratio (2.5, 4) are reported and discussed in the paper, for two specific fuels: high sulfur lignite and high chlorine corn stover. Concerning SO2 emissions a correlation among the sulfur and the chlorine contents is clearly detected, being affected by the direct desulfurization mechanism occurring under oxy-firing conditions. The single effect of the chlorine content is found to be almost 1.5% of the desulfurization efficiency. NOx emissions are otherwise more dependent on oxygen excess and CO concentration in the reactor, rather than the fuel share or the chlorine supplied. Thick deposition is only detected when chlorine content in the corn is 2%. Potassium aluminosilication is found to be enhanced in comparison to potassium sulfation under oxy-firing, especially for the highest Ca:S mole ratio: observed aluminosilication is five times higher when Ca:S ratio is increased from 2.5 to 4. A significant enrichment in iron is also detected for the fly ash composition, with an increase of 30–50% in comparison to air combustion.

The role of limestone during fluidized bed oxy-combustion of coal and biomass

The interest in bio-CCS technologies is growing due to their potential to reduce CO2 emission in power generation. Oxy-co-firing in fluidized-bed units is one of the available techniques to develop bio-CCS, offering wide fuel flexibility and low SO2 and NOx emissions. This paper discusses the results of an experimental campaign carried out in a lab-scale fluidized bed reactor. The work focuses on the influence of limestone when oxy-firing blends of lignite and corn stover. Two different types of limestone with two Ca:S molar ratios were tested, and operational conditions were selected to compare the mechanisms governing desulphurization. Emissions of SO2, NO and HCl, together with deposition rates and ash mineralogy are studied in the paper. SO2 capture increases with the Ca:S ratio and bed temperature, but to a different extent depending on the limestone fragmentation. The amount of NO emitted rises with the Ca:S ratio and the presence of calcined limestone (indirect desulphurization). The HCl concentration in the gas phase is dominated by alkali sulfation. Finally, the conditions for the highest desulphurization efficiency diminished the deposition rates, but increased the risk for chlorine-induced corrosion.

Optimization of spray dried attrition-resistant iron based oxygen carriers for chemical looping reforming

In chemical looping reforming oxygen carriers suffer from attrition, which must be reduced to increase their lifetime. Therefore, the production of Fe-based carriers by spray drying was optimized in order to obtain mechanically strong particles with a homogeneous microstructure and dimensions fit for industrial fluidized CL-processes. The influence of the concentration of the binder and dispersing agent, the amount of solids and the milling procedure used in spray-drying suspensions on the morphology and microstructure of the resulting particles is studied by Hg-porosimetry, tapped density and optical and electronic microscopy. Increasing the amount of solids and reducing the amount of organic binder decreased the size of the internal cavity in the spray dried particles which led to a higher tapped density and better mechanical properties. The heat treatment during post-processing of these oxygen carriers also has a major influence on the remaining porosity of the oxygen carriers and is used to further optimize their mechanical properties as measured by the crushing strength and the attrition resistance. In this way spray-dried Fe-based oxygen carriers on an alumina carrier material with a crushing strength of 3.2N and an air jet index of 2.1% are obtained at a sintering temperature of 1225°C. The sample with the best mechanical properties was tested in a small lab-scale fluidized bed reactor during four cycles and compared with a more porous sample. The improvement of the morphology and the reduction of the porosity of the particles did not show a significant influence on the chemical performance of the oxygen carrier. The crushing strength of the oxygen carrier decreased to 2N during activation and during reaction a slight hercynite accumulation was observed.

Chemical looping with oxygen uncoupling of high-sulfur coal using copper ore as oxygen carrier

Chemical looping with oxygen uncoupling (CLOU) has been viewed as a promising candidate for solid fuel combustion with inherent CO2 separation at considerably low energy penalty. This work aimed to investigate the sulfur evolution behavior and performance of copper ore oxygen carrier (OC) within the CLOU process using a typical high-sulfur content coal in Sichuan (SC), China as fuel. Experiments at different temperatures and oxygen to fuel ratios were conducted in a laboratory-scale fluidized bed reactor and comparisons have been made between SC coal and Gaoping (GP) anthracite with low sulfur content. It was found that both the increase of temperature and decrease of oxygen to fuel ratio can enhance the generation of sulfurous gases. There were two SO2 peaks during the CLOU process of both SC and GP coals, due to the two relatively independent stages of coal combustion process: volatiles combustion and coal char combustion. The second peak was generally more sensitive to temperature, and a higher temperature would contribute to much more SO2 generation. Cyclic redox experimental results of SC coal in fluidized bed reactor showed stable sulfur evolution trend and moderate reactivity of copper ore OC. Moreover, calcium oxide (CaO) was introduced as desulfurizing agent to remove the sulfurous gases generated in the CLOU process of SC coal and the desulfurization efficiency was achieved as high as 98%. XRD and XPS analyses showed that no metallic sulfide was detected on the surface of the reduced OC samples and ESEM images indicated that no serious sintering problem occurred to the used particles.

A single particle model of lime sulphation with a fractal formulation of product layer diffusion

A fractal-like formulation of the random pore model (RPM) is proposed for the reaction of a gas with a solid, with the rate controlled by both diffusion in the layer of solid product and the kinetics of reaction. This approach gives a time-dependent diffusivity in the product. The model’s predictions are compared with measurements of the removal of SO2 with limestone, carried out in a lab-scale fluidized bed reactor. The fractal-like RPM described the production of CaSO4 better than the standard RPM, which overestimated the uptake of SO2 in the first 40min. The decrease of diffusivity in the product layer with time was ascribed to the degree of crystallization of the product, CaSO4, increasing with time and resulting in a lower ionic mobility in its lattice. The equation proposed is a simple and general one for a gas reacting with a solid (alternative example: the carbonation of lime), whose microstructural properties change significantly with the extent of reaction.

Computational study of the bubbling-to-slugging transition in a laboratory-scale fluidized bed

We report results from a computational study of the transition from bubbling to slugging in a laboratory-scale fluidized-bed reactor with Geldart Group B glass particles. For simulating the three-dimensional fluidized-bed hydrodynamics, we employ MFiX, a widely studied multi-phase flow simulation tool, that uses a two-fluid Eulerian-Eulerian approximation of the particle and gas dynamics over a range of gas flows. We also utilize a previously published algorithm to generate bubble statistics that can be correlated with pressure fluctuations to reveal previously unreported details about the stages through which the hydrodynamics progress during the bubbling-to-slugging transition. We expect this new information will lead to improved approaches for on-line reactor diagnostics, as well as new approaches for validating the results of computational fluidized-bed simulations with experimental measurements.

Removal of nickel by homogeneous granulation in a fluidized-bed reactor

Heavy metal removal is a significant task that protects our water resources. Fluidized-bed homogeneous granulation process (FBHGP) was used to treat nickel containing wastewaters by recovering nickel in the form of nickel carbonate hydroxide granules with low moisture content rather than soft sludge. This study investigated nickel removal and recovery through HFBGP by determining the effects of varying influent nickel concentrations, [CO32−: Ni2+] molar ratios, and pH of the precipitant. This was conducted in a continuous process using a laboratory scale fluidized-bed reactor that determined the effects driven by supersaturation. The best operating conditions that resulted in a 98.8% nickel removal and 97.8% granulation efficiency were 200 mg L−1 influent nickel concentration, 2.0 M R of [CO3−2:Ni+2], and 10.7 pH of precipitant. Based on SEM analysis, the granules formed have sizes between 0.50 mm and 0.15 mm. EDS results showed that the atomic percentages of nickel carbon, and hydrogen were ∼50%, ∼9–12%, and ∼35% respectively, representing the nickel carbonate compound. The XRD results showed the low symmetry of the granules formed that confirmed the characteristics of nullaginite mineral of Ni2(CO3)(OH)2.

Understanding the Impacts of Water Vapor on CaO Sulfurization in a Laboratory-Scale Fluidized Bed

Limestone has been widely used to remove SO2 from circulating fluidized bed (CFB) boilers. As the main component of limestone, CaCO3 first undergoes calcination to CaO, which is then sulfated by SO2 to form CaSO4 in the furnace. Water vapor accounts for a high concentration in coal-fired CFB furnaces, which could influence CaO sulfurization. This work aims to understand this issue. Sulfurization experiments were conducted with the CaO calcined from a natural limestone in a laboratory-scale fluidized bed reactor. Scanning electron microscopy, a mercury injection apparatus along with a N2 adsorption instrument, and X-ray diffraction were employed to test the micromorphology, pore structure, and crystal structure of the sulfurization products, respectively. The results show that CaO sulfurization was improved by water vapor. In addition, an optimum amount of water vapor exists to achieve maximum sulfurization. The results of micromorphology results indicate that sintering, fusion, and growth of grains of sul...

Experimental verification of scalable model for the hydrochlorination reaction in a pilot-scale fluidized bed reactor

Silicon tetrachloride (STC) is a byproduct gas produced in the manufacture of semiconductor-grade silicon. STC can be converted back to the feed gas for the chemical vapor deposition reactors that produce polysilicon by means of a hydrochlorination reaction. A mathematical model, based on the Kunii-Levenspiel fluidization model, was previously developed, that accurately predicted the conversion of STC to trichlorosilane (TCS) in a laboratory-scale fluidized bed reactor. This paper introduces modifications to the laboratory-scale model to make it suitable for use with a pilot-scale reactor. The model's ability to predict yield was compared to experimental studies completed in a pilot-scale reactor. It was shown that the modified mathematical model predictions were excellent, with an average percent difference of less than 4% between yield predicted and experimentally observed.

The investigation of the coal ignition temperature and ignition characteristics in an oxygen-enriched FBR

Oxygen-enriched circulating fluidized bed (CFB) technology is considered as one of the low carbon emission power generation technologies. By recycling the flue gas into the furnace, the CO2 concentration in the exhaust gas can reach over 90%. The coal ignition temperature and ignition characteristics are important factors for boiler design and for choosing the feeding temperature during the transition from air-firing to oxy-firing. The ignition and combustion processes of five types of coal under four different atmospheres (air, O2 27%, O2 40%, O2 53%) were measured in a laboratory scale fluidized bed reactor (FBR) with an under-bed preheat system. Using thermocouples and a gas analyzer, the changes in bed temperature and the concentrations of different components, such as O2, CO2 and CO, in flue gas were directly measured to determine the coal ignition temperature, TiF. It was found that TiF decreases with increasing O2 concentration. At lower bed temperatures, two-stage ignition processes were observed in certain ranges of initial bed temperature and oxygen concentration. The influence of initial bed temperature on volatile release and the SO2 emission in the ignition processes were also discussed.

Empirical Kinetic Model of a Stone Dust Looping Carbonator for Ventilation Air Methane Abatement

A novel stone dust looping (SDL) process for mitigation of ventilation air methane (VAM) was investigated. The SDL process uses limestone as a sorbent to capture CO2 emissions, similar to a conventional calcium looping (CCL) process. However, unlike CCL where lime (CaO) is introduced directly to a flue gas from a thermal power plant with CO2 concentrations as high as 12–15% in an oxygen-deficient environment, the SDL process uses CaO to catalytically oxidize VAM, with concentrations of CH4 up to 0.1–1 vol % in air, and simultaneously capture CO2 produced. In the present study, kinetic parameters were derived from experiments in a single lab-scale fluidized bed reactor. A random pore model (RPM) was used to determine the rate-controlling steps for the SDL process, and kinetic parameters, such as activation energy (EaK) and pre-exponential factor (ks0), were obtained for a SDL process carbonator. Kinetic parameters were then used to derive an empirical model for a continuous SDL process and consisted of res...

Modeling the hydrochlorination reaction in a laboratory-scale fluidized bed reactor

In the manufacturing process of high purity, electronics-grade silicon, the hydrochlorination reaction step for converting silicon tetrachloride (STC) to trichlorosilane (TCS) is usually carried out in a fluidized bed reactor. However, the design and operation of industrial-scale fluidized bed reactors for the conversion of STC to TCS is currently based on ad hoc rules of thumb and operator experience rather than on reaction engineering principles. In this paper, a fluidized bed model was developed by using the Kunii–Levenspiel fluidization framework. The predictive capabilities of this model were tested on laboratory-scale experimental data from the literature. It is shown that the modified Kunii–Levenspiel model accurately predicts the no catalyst addition and copper catalyst addition experiments of the hydrochlorination fluidized bed with an average percent difference of less than 6%. By making a suitable adjustment to catalytically active iron content, the model prediction is in excellent agreement with experimental data with hydrochloric acid in the feed stream. The modified Kunii–Levenspiel model is well suited for use in scale-up calculations for an industrial reactor as all the parameters are physically reasonable and can be predicted for larger reactors.

Sulfur behavior in chemical-looping combustion using a copper ore oxygen carrier

Chemical-looping combustion (CLC) is a promising technology that provides a novel route for CO2 capture with low cost and energy penalty. Interaction between the oxygen carrier and sulfur contaminants in fuel is a significant concern in chemical looping systems, which will degrade the captured CO2 purity and even affect the reactivity of oxygen carrier. Experiments of a sulfur-containing synthesis gas (4000ppm H2S, 25vol.% H2, 35vol.% CO, and 39.6vol.% CO2) as fuel and copper ore as oxygen carrier were performed by thermogravimetric analysis and Fourier transform infrared spectroscopy (TGA–FTIR). The effects of reducing atmosphere, temperature and redox cycle number were studied. A weight gain was observed in all TGA experiments with 4000ppm H2S synthesis gas as fuel, due to the sulfidation of the copper ore oxygen carrier. For the reaction of copper ore with H2S-containing synthesis gas, the main metal sulfide products were Cu2S and FeS, while the gaseous sulfur species were mainy SO2, COS, and CS2. H2S was easier to react with copper oxides than iron oxides. Moreover, the sulfidation of copper ore was further investigated in a laboratory scale fluidized bed reactor at 900°C, using copper ore as oxygen carrier and synthesis gases with/without H2S as fuel. The results showed that the sulfidation of copper ore degraded its oxygen transport capicity and reactivity to some extent.