Laboratory-scale Fluidized Bed Reactor Research Articles

Kinetic models of an anaerobic bioreactor for restoring wastewater generated by industrial chickpea protein production

To assess the accuracy of kinetic models in predicting the behaviour of an anaerobic biodegradation process for cleaning up wastewater derived from the production of protein isolates from chickpea flour, the process was conducted in a laboratory-scale fluidised-bed reactor with saponite (magnesium silicate) as support for the mediating bacteria at 35 °C. The reactor operated satisfactorily at organic loading rates between 0.58 and 2.70 g total chemical oxygen demand (TCOD) L?1 d?1, hydraulic retention times between 14.9 and 3.5 d, and an average feed TCOD of 9.1 g L?1. The methane yield coefficient value, YG/S, of 0.33 L CH4 (at STP) g?1 TCODremoved, calculated on the basis of a substrate balance (TCOD) model, was virtually identical to that obtained from the experimental data. The cell maintenance coefficient, km, obtained by means of this balance was found to be 0.0057 g TCOD g?1 volatile suspended solids (VSS) d?1. The volumetric methane production rates correlated with the biodegradable TCOD concentration based on the Michaelis–Menten equation. In addition, the specific rate of substrate uptake, r (g soluble COD (SCOD) g?1 VSS d?1), also correlated with the concentration of biodegradable substrate, Sb (g SCOD L?1), according to the Michaelis–Menten equation. These proposed models predict the behaviour of the reactor accurately showing deviations <10% between experimental and theoretical values of methane production and substrate uptake rates, respectively.

Role of Chlorine in Combustion Field in Formation of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans during Waste Incineration

Combustion experiments performed in the presence of hydrogen chloride (HCl) in a laboratory-scale fluidized-bed reactor were carried out to elucidate the role of chlorine in the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs; together: PCDD/Fs) in various sections of a municipal waste incinerator. We first demonstrated that the homologue profile and the pattern of the congener proportions of PCDD/Fs for a model waste containing poly(vinyl chloride) (PVC) combusted in the absence of HCl were similar to those for a PVC-free waste combusted in the presence of HCl. This showed no difference between PVC in the waste and injected HCl in the role as a chlorine source in PCDD/F formation during incineration. Next, to investigate PCDD/F formation in each section of the incinerator, we carried out combustion experiments with the PVC-free waste, injecting HCl at different locations of the incinerator. The amounts of PCDDs and PCDFs formed were significantly reduced when HCI was not supplied to the main combustion section. The presence of HCI in the main combustion section was essential for the formation of PCDD/Fs, even in the downstream sections. This finding indicates that compounds that were able to form PCDD/Fs in the downstream sections were mainly formed in the main combustion section in the presence of HCl.

Reuse of Fly Ash from a Fluidized Bed Combustor for Sulfur Uptake: The Role of Ettringite in Hydration-Induced Reactivation

This study addresses the effectiveness of hydration-induced reactivation of fly ash from an industrial FBC to produce a sorbent suitable for further SO2 uptake during fluidized bed combustion. Ash reactivation was accomplished by water hydration at 70 °C for 48 h. Maximum extent and rate of SO2 sorption as well as attrition/fragmentation behavior of the reactivated ash were assessed. Testing of sulfur sorption capacity was carried out at 850 °C for 100 min in a laboratory-scale fluidized bed reactor under simulated combustion/desulfurization conditions. Characterization of the tested materials was based on X-ray diffraction and simultaneous differential thermal/thermogravimetric analyses. It was found that ettringite was extensively produced during water hydration and that effective enhancement of the sulfur uptake ability of the fly ash was achieved. The conversion degree of calcium to CaSO4 of the reactivated ash was as high as 92%. The very favorable performance of reactivated ash as a sulfur sorbent w...

Particle design and evaluation of dry [formula omitted] recovery sorbent with a liquid holding capability

For CO 2 capture at high-temperature/high CO 2 partial pressure conditions a new dry CO 2 removal sorbent was developed based on lithium silicate with additives to accelerate CO 2 sorption. To avoid adhesion and defluidization associated with the formation of the liquid carbonate phase in the temperature range of 500 – 600 ∘ C , the sorbent particles were designed whereby the granulated lithium silicate core was coated with a layer of coarse alumina particles. This prevents the liquid lithium carbonate from wetting the sorbent surface. Several different types of sorbents were manufactured by granulation and coating with different ceramic sol binders and different prescriptions in a tumbling fluidized bed. Minimum fluidization velocity, fluidizing behavior and adsorption/desorption properties of the sorbent particles were determined in a laboratory scale fluidized bed reactor (i.d., 0.03 m) in the temperature range up to 1073 K. During a repeated cyclic adsorption/desorption, a gradual decrease in both the overall conversion and maximum adsorption capacity took place. Nevertheless, the performance obtained for the sorbent manufactured with alumina sol was found to be the most successful one characterized by no defluidization and a high adsorption capacity of 50% in conversion (10 wt% including the coat layer) over 60 cycles.

Development of a Membrane-Assisted Fluidized Bed Reactor. 1. Gas Phase Back-Mixing and Bubble-to-Emulsion Phase Mass Transfer Using Tracer Injection and Ultrasound Experiments

A small laboratory-scale membrane-assisted fluidized bed reactor (MAFBR) was constructed in order to experimentally demonstrate the benefits of this reactor concept, especially the enhanced bubble-to-emulsion phase mass transfer and the reduced overall axial gas phase back-mixing, due to the presence of the membranes and permeation of gas through the membranes. With steady-state tracer gas injection experiments, it was demonstrated that the experimental reactor exhibited approximately plug flow behavior for all the operating conditions investigated in this work as a result of the elimination of macroscale circulation patterns due to the presence of the membranes and, even more importantly, the permeation of gas through the membranes. With an ultrasound technique, the gas residence time distribution (RTD) of the MAFBR was measured over a wide range of fluidization velocities for two different bed heights. Interpretation of the RTD measurements with a phenomenological two-phase reactor model extending the bubble assemblage model proposed by Kato and Wen (Kato, K.; Wen, C. Chem. Eng. Sci. 1969, 24, 1351) showed that the average bubble diameter is significantly decreased for higher ratios of gas permeated through the membranes relative to the total gas flow rate.

Development of a Membrane-Assisted Fluidized Bed Reactor. 2. Experimental Demonstration and Modeling for the Partial Oxidation of Methanol

A small laboratory-scale membrane-assisted fluidized bed reactor (MAFBR) was constructed in order to experimentally demonstrate the reactor concept for the partial oxidation of methanol to formaldehyde. Methanol conversion and product selectivities were measured at various overall fluidization velocities, reactor temperatures, methanol and oxygen overall feed concentrations, ratios of gas fed via membranes relative to gas fed via the bottom distributor, and aspect ratios of the fluidized bed. High methanol conversions and high selectivities to formaldehyde were achieved with safe reactor operation (isothermal reactor conditions) at very high methanol inlet concentrations, much higher than currently employed in industrial processes. It was experimentally demonstrated that with distributive feeding of oxygen in a MAFBR the overall formaldehyde yield and throughput could be increased without a pronounced and undesirable conversion of formaldehyde to carbon monoxide. Furthermore, a one-dimensional two-phase phenomenological reactor model has been developed with which the experimentally observed conversion and selectivity as a function of the operating conditions could be well described.

Combined Coal Gasification and Methane Reforming for Production of Syngas in a Fluidized-Bed Reactor

The concept of combining coal gasification and methane reforming for syngas production in a fluidized-bed reactor, as a means for utilization of both coal and coal-bed methane, was proposed and evaluated experimentally. Preliminary experiments were performed in a laboratory-scale fluidized-bed reactor operating at ∼1000 °C, using two Chinese coals: a bituminous coal (Coal A) and an anthracite (Coal B). To demonstrate combined coal gasification and methane reforming, the reactor was fed with 1.5−2.5 kg/h coal, 0.4−0.5 Nm3/h methane, 1.45−2.0 Nm3/h oxygen, 0.4 Nm3/h air, and 2.0−2.4 kg/h steam. Up to 90% methane conversion and 70% carbon conversion were achieved, and the resulting syngas had a composition of 35%−39% H2, 31%−34% CO, and 20%−22% CO2, balanced by N2. For comparison, the results of the gasification of Coal A and Coal B without added methane were also reported. These results proved the feasibility of such an integrated coal gasification and methane reforming process. Further kinetic studies and process development opportunities were also identified.

Combustion of isolated bubbles in an elevated-temperature fluidized bed

Combustion of isolated bubbles was investigated with a laboratory-scale fluidized-bed reactor. Two different combinations of oxygen and argon were employed as the fluidizing gas. Single bubbles of methane were injected into an incipiently fluidized bed maintained at elevated temperatures. Gas composition inside the bubbles was measured using a suction probe connected to an on-line mass spectrometer, and the temperature of the bubbles was monitored using a fast-response thermocouple. The effects of bed particle type, particle size, bubble size, bed temperature, and oxygen concentration in the emulsion phase were examined for bed temperatures between 923 and 1203 K. A theoretical model of homogeneous combustion within the bubble phase was developed for comparison to the experimental results. The model accounted for the heat and mass transfer between bubble and emulsion phases, but only considered combustion within the bubble. The results indicated that small bubble size and high oxygen concentrations in the emulsion phase enhanced bubble-phase combustion. The bed temperature also proved to be an important parameter, with higher temperatures promoting bubble combustion, but unlike some other investigations, no critical ignition temperatures were observed in either experiments or model results. The fluidized bed's particle size and particle composition influence the heat and mass-transfer coefficients, and therefore the bubble-phase combustion, but these have a smaller influence than bed temperature and bubble size. Model results for bubble-phase gas composition and temperature compared favorably with the experimental measurements.

307 模擬ゴミ燃焼に伴うダイオキシン類排出挙動(大気環境改善技術(2),大気・水保全技術)

Formation/decomposition mechanisms of PCDDs and PCDFs were investigated in combustion experiments of model wastes using a laboratory-scale fluidized-bed reactor with a high-temperature hold section at 600℃. The temperature-hold section was equipped after a furnace for the reduction of the PCDD/F emission. The amounts of PCDDs and PCDFs formed were reduced and their homologue profiles were shifted toward lower chlorinated species at downstream sampling points in the temperature-hold section. The ratios of the concentrations of PCDD congeners at the downstream sampling points to those at the inlet point in the temperature-hold section were more dispersed than those of PCDF congeners. This may indicate that PCDDs are decomposed through dechlorination reactions more than PCDFs in these experiments. In addition, the condensation reaction of precursors such as chlorophenol was observed in the PCDD congener distributions. The condensation reaction is not negligible in the various pathways of PCDD formation/decomposition in this temperature range. The PCDF congener formed through the dechlorination reaction after the formation from carbon/PAHs was observed in their congener proportions. These results show that the PCDD/F formation reactions occur in parallel with their decomposition reactions and the reactions have a different dependence on experimental conditions.

Iron Ore Reduction in a Laboratory-scale Fluidized Bed Reactor-Effect of Pre-reduction on Final Reduction Degree

Fluidized bed processes for iron ore reduction (e.g. FIOR®, FINMET®, FINEX®) operate in a continuous multi-staged countercurrent mode. To optimize iron ore reduction, different operating conditions occur in each stage.Significant influence of the first reduction stage on the final reduction degree was observed in industrial plant. The iron ore particles seem to “memorize” the precursor autoclave conditions.To optimize iron ore reduction, as well as to develop new reduction processes, it is necessary to understand this phenomenon. Industrial plants operate on pressures up to 12 bar and temperatures up to 900°C. So a laboratory-scale pressurized fluidized bed reactor was built to perform experiments similar to industrial conditions.Two-stage experiments with Mt. Newman hematite ore from Western Australia at variable operating conditions show significant influences of temperature and residence time of the pre-reduction stage on the final reduction degree. Microscopical analysis showed the influence of mineralogy and texture on the reduction behavior of original respectively partly reduced iron ore. Formed magnetite in the pre-reduction stage causes a degradation of final reduction degree. Additionally the amount of newly formed magnetite depends on pre-reduction temperature, composition of the reducing gas and residence time.

Biofilm and biomass characteristics in high-performance fluidized-bed biofilm reactors

Two laboratory-scale fluidized-bed biofilm reactors (FBBRs) were used to investigate the biomass concentration and the biofilm characteristics in a high-performance FBBR used for the denitrification of exceptionally high-nitrate wastewater (1000 mg N/L). Reported correlations by other workers for predicting the biomass concentration in FBBR were examined for their validity in comparison with the experimental results of this study and the best set of applicable correlations was recommended. The effects of the two main operational parameters, the superficial velocity and nitrogen loading rate on the biomass concentration in the FBBR were also studied. Correlations for the drag coefficient and the expansion index from the literature, together with the biofilm dry density correlation produced from this study were found to produce the best prediction of the FBBR biomass concentration compared to other reported correlations. The average biomass concentration in the FBBR decreased with the increase of the superficial velocity in the range of 45-65 m/h at all applied nitrogen loadings (i.e. 6, 8, 12 and 16 kg N/m3bedd).

Role of copper chloride in the formation of polychlorinated dibenzo- p-dioxins and dibenzofurans during incineration

Combustion experiments in a laboratory-scale fluidized-bed reactor were performed to elucidate the role of copper chloride in formation of polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) during model waste incineration. The amounts of PCDDs and PCDFs formed, the homologue profiles, and the isomer distributions were measured in the flue gas from incineration of model wastes containing various levels of copper. A correlation was found between the Cu content of the waste and the proportion of each congener. An increase in copper enhanced the formation of certain congeners, showing that copper acts as a catalyst for formation of PCDDs and PCDFs. An increase in the copper content of the waste decreased the CO concentration in the flue gas and reduced the formation of PCDDs and PCDFs during incineration. This indicates that copper also works as an oxidation catalyst to promote combustion, leading to lower concentrations of products of incomplete combustion. It is indispensable to consider both roles of the catalyst, i.e., enhancement and suppression, in the formation of PCDDs and PCDFs during waste incineration, which are estimated separately from the isomer distributions and the amounts of PCDDs and PCDFs formed.

Optimization of Reaction Conditions in a Fluidized‐Bed for Silane Pyrolysis

AbstractThe fluidized‐bed chemical vapor deposition (CVD) process for polycrystalline silicon production is considered to be the most attractive alternative to the conventional bell‐jar process. In order to obtain stable operation, high space‐time‐yields and high purity of the product several obstacles have to be eliminated. Reaction conditions must be optimized to avoid the homogeneous decomposition of silane and minimize silicon dust formation. The effect of temperature, silane partial pressure, gas velocity and the size of bed particles has to be identified. These dependencies and the interaction between hydrodynamics and kinetics of homogeneous and heterogeneous CVD‐reactions were studied in a laboratory‐scale fluidized‐bed reactor.

Degradation products of the process of thermal recovery of copper from lamina scraps in lab-scale fluidized bed reactor

This paper presents experimental results dealing with a process for recovering copper in the scrap composite materials issued from electronic laminas industry. This environment-friendly process consists in the thermal treatment of scrap in a fluidized bed whose particles fix the harmful gases emitted by the organic glue gasification. A series of experiments was carried out in a thermobalance coupled to FTIR spectrometer and GC/MS with small lamina samples. These experiments demonstrated the thermal behavior of scrap composite materials, and identified the major degradation reaction gases. A series of experiments was performed with bigger scrap samples hung in a laboratory-scale fluidized bed coupled to FTIR and MS, at 350 °C; the results confirmed those obtained in thermobalance. Experiments showed that a residence time lasting less than 5 min is sufficient to recover the metallic copper, and exhaust gases are not harmful.

Nitrification of high-strength ammonium wastewater by a fluidized-bed reactor

A laboratory-scale fluidized-bed reactor with an external aeration loop was used for nitrification of high-strength ammonium wastewater (up to 500 mg NH4-N/L). The results demonstrated that the system is capable of handling ammonium removal rates of up to 2.5 kg NH4-N/m3 x d, while removal efficiencies were as high as 98% and independent of the applied ammonium loading rates. Ammonium loading rates higher than 2.5 kg NH4-N/m3 x d resulted in decreased ammonium removal efficiency. The data show that near complete ammonium removal occurred at DO concentrations as low as 0.3-0.5 mg/L. However, the nitrite-nitrogen fraction in the effluent increased from 3.5% to 23.2% when the DO dropped from 1.0 mg/L to approximately 0.4 mg/L, respectively. The high specific removal rates in this system are one order of magnitude higher than that of suspended-growth systems. This can reduce the supplementary reactor volumes required for nitrification to less than 10% of that needed in conventional activated sludge systems. These results clearly indicate the potential economic gains that could be achieved through implementation of this technology.

The impact of thermal pre-treatment on oil shale attrition and fragmentation in fluidized bed combustion

An experimental method allowing the study of thermal pre-treatment effect on fragmentation of oil shale solid particles from Tarfaya deposit (Morocco), processed in fluidized bed combustor (FBC), is described. The data are presented for a batch experiment in a laboratory-scale fluidized bed reactor to which a balance system was coupled. The reactor operated at different conditions of initial particle size, fluidization velocity, and reactor temperature. After reacting in the furnace of the balance system at a desired temperature, T t, and for some duration of time, the solid particles drop directly in the fluidized bed reactor. The influence of different factors such as chemical decomposition, characterized by fractional mass loss ( α=( m 0− m)/( m 0− m ∞)), bed temperature T b, original particle size, have been studied. Results show mainly that, during the first stage of thermal reaction ( α<0.1), fragmentation propensity is much important compared to that corresponding to the case where thermal pre-treatment is absent. The fine solid particles are formed during the first stage of the process. Size distribution changes strongly if fractional loss is of order 0.4: more than 60% of initial particles are destroyed in the first 5 min of shale processing at a temperature of 600 °C. Once shale is preheated fragmentation rates are experimentally estimated to be as high as three to five times those found in the case where no thermal pre-treatment is applied.

Reduction Behavior of Hematite to Magnetite under Fluidized Bed Conditions

Reduction kinetic tests of Mt. Newman hematite ore from Western Australia were carried out in a laboratory-scale fluidized bed reactor at temperatures from 623 to 873 K and an absolute pressure of 10 bar. The reducing gas mixture was thermodynamically in equilibrium with magnetite and consisted of a mixture of H2, H2O, CO, CO2 and CH4. The effect of temperature and residence time was studied. The original ore and its mineralogical and petrographical changes with increasing reduction time were analyzed. A reflected-light microscope technique with CCD-camera was used to determine the progress and the mechanism of reduction. According to the mineralogy and texture the ore could be classified in four types (coarse hematite, microplaty hematite, limonite and martite) with different reduction characteristics. Limonite and martite showed better reducibility than coarse and fine hematite.At all ore types the growth of dense magnetite rims was observed. The thickness of these layers was found to be linear proportional to reduction time. After analyzing the single steps of the reduction process the phase interface reaction turned out to be rate controlling between 673 and 773 K. Its activation energy is 91 kJ/mol.

Thermal Exploitation of Wastes with Lignite for Energy Production

The thermal exploitation of wastewood with Greek lignite was investigated by performing tests in a laboratory-scale fluidized bed reactor, a 1-MWth semi-industrial circulating fluidized bed combustor, and an industrial boiler. Blends of natural wood, demolition wood, railroad sleepers, medium-density fiberboard residues, and power poles with lignite were used, and the co-combustion efficiency and the effect of wastewood addition on the emitted pollutants were investigated. Carbon monoxide, sulfur dioxide, and oxides of nitrogen emissions were continuously monitored, and, during the industrial-scale tests, the toxic emissions (polychlorinated dibenzodioxins and dibenzofurans and heavy metals) were determined. Ash samples were analyzed for heavy metals in an inductively coupled plasma-atomic emission spectroscopy spectrophotometer. Problems were observed during the preparation of wastewood, because species embedded with different compounds, such as railway sleepers and demolition wood, were not easily treated. All wastewood blends were proven good fuels; co-combustion proceeded smoothly and homogeneous temperature and pressure profiles were obtained. Although some fluctuations were observed, low emissions of gaseous pollutants were obtained for all fuel blends. The metal element emissions (in the flue gases and the solid residues) were lower than the legislative limits. Therefore, wastewood co-combustion with lignite can be realized, provided that the fuel handling and preparation can be practically performed in large-scale installations.

Pyrolysis as a technique for separating heavy metals from hyperaccumulators. Part II: Lab-scale pyrolysis of synthetic hyperaccumulator biomass

Abstract Synthetic hyperaccumulator biomass (SHB) impregnated with Ni, Zn, Cu, Co or Cr was used to conduct 11 experiments in a lab-scale fluidized bed reactor. Two runs with blank corn stover, with no metal added, were also conducted. The reactor was operated in an entrained mode in a oxygen-free (N2) environment at 873 K and 1 atm . The apparent gas residence time through the lab-scale reactor was 0.6 s at 873 K . The material balance for the lab-scale experiments on N2-free basis varied between 81% and 98%. The presence of a heavy metal in the SHB decreased the char yield and increased the tar yield, compared to the blank. The char and gas yields appeared to depend on the form of the metal salt used to prepare the SHB. However, the metal distribution in the product streams did not seem to be influenced by the chemical form of the metal salt used to prepare the SHB. Greater than 98.5% of the metal in the product stream was concentrated in the char formed by pyrolyzing and gasifying the SHB in the reactor. The metal concentration in the char varied between 0.7 and 15.3% depending on the type of metal in the SHB. However, the metal concentration was increased 4 to 6 times in the char compared to the feed.

A comparison of Rh/CeO2/SiO2 catalysts with steam reforming catalysts, dolomite and inert materials as bed materials in low throughput fluidized bed gasification systems

Abstract The gasification of cedar wood in the presence of Rh/CeO2/SiO2 has been conducted in the laboratory scale fluidized bed reactor using air as a gasifying agent at low temperatures (823– 973 K ) in order to produce high-quality fuel gas for gas turbine for power generation. The performance of the Rh/CeO2/SiO2 catalyst has been compared with conventional catalysts such as commercial steam reforming catalyst G-91, dolomite and noncatalyst systems by measurements of the cold gas efficiency, tar concentration, carbon conversion to gas and gas composition. The tar concentration was completely negligible in the Rh/CeO2/SiO2-catalyzed product gas whereas it was about 30, 113, and 139 g / m 3 in G-91, dolomite and noncatalyzed product gas, respectively. Since the carbon conversion to useful gas such as CO, H2, and CH4 are much higher on Rh/CeO2/SiO2 catalyst than others at 873 K , the cold gas efficiency is much higher (71%) in this case than others. The hydrogen content in the product gas is much higher (>24 vol %) than the specified level (>10 vol %) for efficient combustion in the gas turbine engine. The char and coke formation is also very low on Rh/CeO2/SiO2 catalyst than on the conventional catalysts. Although the catalyst surface area was slightly decreased after using the same catalyst in at least 20 experiments, the deactivation problem was not severe.