Fluidized Bed Reactor Operation Research Articles

Investigation of flow characteristics in a rectangular spouted fluidized bed using electrical capacitance volume tomography

The characterization of gas-solid flow behavior in rectangular spouted fluidized bed (RSFB) poses significant challenges due to the presence of complex gas-phase vortex flow within the bed. The flow characteristics of gas-solid two-phase flow in RSFB were investigated by using a self-developed 32-electrode electrical capacitance volume tomography (ECVT) system with an imaging speed of 105 frames per second when the spouting gas velocity Uf increased from 0.97 m/s to 1.78 m/s. Experimental results demonstrate that with increasing Uf, the flow transitions from weak bubbling/bubble fluidization to turbulent fluidization in the RSFB. The amplitude peak difference of particles in different planes of the fluidized bed gradually decreases, and the rising velocity of bubbles initially decreases and then increases. The gas-particle backmixing effect strengthens, while the entrainment effect during bubble rupture weakens. The research findings can provide valuable insights for understanding the flow behavior in RSFB and offer guidance for optimizing the process operation of fluidized bed reactors.

Hydrodynamics of a reactor for thermocatalytic oxidation of sewage sludge

One of the promising methods for the disposal of municipal sewage sludge is its thermocatalytic oxidation in fluidized bed reactors. An important factor determining the stability of the operation of fluidized bed reactors is the uniform introduction of the air flow, which, on the one hand, fluidizes a bed of catalyst solid particles and solid sewage sludge, and, on the other hand, the oxygen of the air flow serves as an oxidizing agent in chemical reactions occurring in the reactor. A pilot plant for thermocatalytic oxidation, created according to the technology of the Boreskov Institute of Catalysis, is operated at JSC Omskvodokanal (Omsk, Russia). The plant's capacity is 50 thousand tons per year of mechanically dehydrated sludge with a water content of 70–80 wt%. The cross-sectional area of the sludge combustion zone is 3.8 m2. The heat flow from the incoming sludge (physical heat and heat of combustion) is 6527000 kcal/h. The air flow was introduced into the fluidized bed reactor with a sparger of 6 perforated pipes arranged horizontally and in parallel. The purpose of this work is to investigate the influence of inlet conditions on fluidized bed hydrodynamics. The results obtained showed that despite the uneven distribution of air flow through the holes of the sparger tubes, each pair of adjacent sparger tubes mutually compensate each other in terms of air flow per unit area of the cross section of the reactor. It is also shown that during the operation of the reactor, air cavities are formed under the sparger pipes, which are practically free of solid particles. The position of such air cavities and their approximate volume are stationary in time for a developed fluidized bed, and the volume of the cavities is approximately proportional to the dimensions of the respective sparger tubes. These air cavities periodically eject bubbles into the overlying portions of the fluidized bed. The dimensions of the bubbles are comparable to the transverse dimensions of the pipes.

High-rate and -yield continuous fluidized-bed bioconversion of glucose-to-gluconic acid for enhanced metal leaching

Continuous low-cost bulk biolixiviant production remains as one of the main challenges of heterotrophic bioleaching towards large scale application. This study aimed at developing non-aseptic Gluconobacter oxydans-amended fluidized-bed reactor (FBR) process for continuous production of gluconic acid for efficient leaching of rare earth elements (REEs) and base metals from spent nickel-metal-hydride (NiMH) batteries. In preliminary experiments, the FBR became contaminated and massively overgrown by air-borne fungus, Leptobacillium leptobactrum. In a series of batch bioassays, operational conditions were investigated to discourage the fungal activity i.e., an ecologically engineered niche for gluconic acid production. High gluconate concentration (≥100 g/l) and/or low pH (≤2.5) gave a selective preference for G. oxydans growth over L. leptobactrum and controlled the activity of possible contaminants during FBR continuous operation. The highest gluconic acid production rate of 390 g/l∙d with corresponding glucose-to-gluconic acid conversion yield of 94% was obtained at hydraulic retention time (HRT) of 6.3 h and 380 g/l∙d glucose loading rate. Using the FBR effluents as leaching agents, respectively, total base metals and REEs leaching yields of up to 82% and 55% were achieved within 7 days at 1% (w/v) spent battery pulp density. The obtained glucose-to-gluconic acid conversion rates and yields were one of the highest reported for any glucose biotransformation process. The REE leaching yields were higher than those reported for similar high metal-grade REE secondary sources. The high-rate glucose-to-gluconic acid bioconversion in the non-aseptic system utilizing microbial ecology based FBR operation strategy rather than aseptic chemostats indicates industrial feasibility of gluconic acid production and thus, the applicability of heterotrophic bioleaching.

Monitoring the fluidized bed reactor for polyethylene polymerization based on fibre optic acoustic emission sensor

AbstractThis paper presents applications of a new class of fibre optic acoustic emission (FOAE) sensor to monitor the operation of fluidized bed reactors used in polyethylene production. Specifically, the sensor was implemented to detect undesired, abnormal phenomena related to particle agglomeration, wall sheeting, fine overflow, and variations in the superficial gas velocity. The experiments were executed using a fluidized bed cold model setup for polyethylene powders with average particle sizes of 250, 1000, and 2000 μm. The results demonstrated that the presence of agglomerated particles in the fluidized bed reactor increases the kurtosis of the acoustic emission (AE) signal. Furthermore, the overflow of small particles can be detected by mounting the FOAE sensor below the gas distributor plate and monitoring an increase in the root mean square (RMS) of the AE signal. The AE signal RMS increased with the rising superficial gas velocity. Besides, forming a sheet layer on the reactor wall decreased the AE signal RMS. The proposed sensor's main benefits are its simple design, rapid response to abnormal conditions in the fluidized bed reactor, immunity against electromagnetic noise, high‐temperature resistance, and safety in hazardous areas.

Design and performance verification of a fast-reaction thermogravimetric analyzer

Ca(OH)2/CaO fluidized thermochemical heat storage can provide considerable heat storage power, and is a promising large-scale energy storage technology. Owing to the limitations of existing gas–solid reaction kinetics research equipment, there is a lack of Ca(OH)2/CaO reaction kinetics research under fluidization conditions, with a lack of reliable reference data for the design and operation of fluidized bed reactors. In response to the above-mentioned problem, and through our research, we developed a fast-reaction thermogravimetric analyzer to provide samples with excellent heat and mass transfer conditions close to fluidization. The fast-reaction thermogravimetric analyzer enables the reaction of Ca(OH)2 to mainly take place under isothermal conditions by rapidly moving the high-temperature reactor, as well as inputting purge gas at a high flow rate to provide excellent mass transfer conditions for the sample, while obtaining real-time and reliable mass data for thermal analysis kinetics studies. Through an in-depth performance verification, the apparent activation energy of char combustion in a TGA (144.82 kJ/mol), fast-reaction thermogravimetric analyzer (88.32 kJ/mol), and fluidized bed reactor (47.23 kJ/mol) were obtained by the model-free method (iso-conversional). The comparison of data proved that the fast-reaction thermogravimetric analyzer could obtain kinetic parameters similar to a fluidized bed reactor, which was also verified using other materials. Therefore, the fast-reaction thermogravimetric analyzer developed in this study can provide a new solution for studying the reaction kinetics of fluidized thermochemical heat storage for Ca(OH)2/CaO, in addition to acting as a reliable reference for the design and operation of fluidized bed reactors.

CFD study of the hydrodynamics and biofilm growth effect of an anaerobic inverse fluidized bed reactor operating in the laminar regime

The unsteady laminar flow of an inverse fluidized bed reactor was addressed in this study using computational fluid dynamics (CFD). Three-dimensional (3D) and two-dimensional (2D) simulations were carried out using the Eulerian-Eulerian approach with the Syamlal O'Brien and Gidaspow models for modeling the drag between the solid and liquid phases. Reported data of solids expansion and bed porosity were used to validate the simulations. Results show that 2D simulations can satisfactorily reproduce experimental data of fluidized bed reactors, which are essentially equal to those obtained on 3D simulations. The model of Syamlal O'Brien was found to be in better agreement with experiments than that of Gidaspow. It is shown that commonly used correlations for predicting bed porosity fail to provide a reasonable overall description of the evaluated operating conditions. The flow patterns for both phases in the bed section exhibit chaotic recirculation zones with high values of shear stress, and after this, the flow quickly becomes fully developed. The effect of biofilm thickness increase on bed porosity, under similar apparent densities of colonized particles reported for this system, is analyzed. Biofilm growth generates a decrease in the Archimedes number (i.e., decreases the buoyancy of particles) and an increase in the particle Reynolds numbers (Rep), affecting significantly the final porosity of the bed. However, this effect vanishes for Rep < 0.25. Results from this work can be used to develop scale‐up criteria and to establish safe operating conditions (e.g., maximum liquid velocity and biofilm thickness) to avoid loss of support particles.

Design and Optimization of Fluidized Bed Reactor Operating Conditions for Struvite Recovery Process from Swine Wastewater

Struvite crystallization using fluidized bed reactors (FBRs) is one of the most commonly used methods for nutrient recovery from different waste streams. However, struvite recovery from swine wastewater containing much higher solids using FBR has not been studied extensively. In this study, we therefore designed and optimized the key operating conditions parameters, i.e., pH (9.0, 9.5, and 10.0), circulation rate (CR) (1.5, 3.0, and 4.5 L/Lreactor·h), and hydraulic retention time (HRT) (1, 3, and 5 h) of FBR to ensure efficient nutrient removal and struvite crystallization from swine wastewater using response surface methodology (RSM) with central composite design (CCD) as experimental design. A magnesium/phosphorus (Mg/P) molar ratio of 1.3 was maintained with MgCl2 according to ortho-phosphate (O-P) concentration of influent and an air diffuser was set to supply air with 0.03 L air/Lreactor·min. The O-P recovery efficiency of over 91% was achieved through the entire runs. Among the operational parameters, pH did not show any significant effect on NH4-N recovery, particle size, and struvite production rate (SPR). The optimal CR over 2.94 L/Lreactor·h was found to be appropriate for efficient removal of nutrients and struvite crystallization. While optimizing the HRT, priority of the process operation such as the production of larger struvite particles or increased struvite productivity should be considered. Therefore, the optimal operational parameters of pH 9.0, CR &gt; 2.94 L/Lreactor·h, and HRT of 1 or 5 h were chosen to obtain better responses through RSM analyses. The findings of this study would be useful in designing and operating either pilot- or full-scale FBR for struvite crystallization from swine wastewater.

The effect of nanoparticle morphology in the filtration efficiency and saturation of a silicon beads fluidized bed

AbstractPolysilicon is a key commodity required for both electronics and solar photovoltaic modules. The traditional route to produce polysilicon involves the Siemens reactor, an energy intensive batch process. A more efficient, but more complex alternative process is the fluidized bed reactor (FBR). In an FBR silane is pyrolysed producing chemical vapor deposition (CVD) and aerosols. Efficient FBR operation requires yield optimization together with continuous and stable operation of the reactor. Such optimization is not straightforward because the aerosol formation mechanisms and incorporation into the FBR beads are not completely understood. In this work, two model aerosols with different morphology were tested and their filtration efficiency between 20 and 800 nm was determined. Bead saturation at different times was determined for each morphology and the scavenging factor over time for each case is reported. Such information can be of interest for establishing bed recirculation needs in a silicon FBR.

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.

High-rate thiosulfate-driven denitrification at pH lower than 5 in fluidized-bed reactor

This study investigated the potential of a fluidized-bed biofilm dominated by Thiobacillus denitrificans to sustain thiosulfate-driven denitrification under increasingly acidic conditions. A fluidized-bed reactor (FBR) performing denitrification via thiosulfate (S2O32−) oxidation of a nitrate-contaminated synthetic wastewater was first operated under decreasing feed pH values from 7.00 to 5.25. Denitrification efficiency >99% was observed even at feed and effluent pH of 5.75 and 5.30, respectively. At lower feed pH values, the denitrification efficiency decreased rapidly due to inorganic carbon deficiency. The addition of a carbonation unit continuously feeding anaerobic grade CO2 to the FBR biofilm allowed to investigate denitrification at pH values lower than 5.0. This new configuration, i.e. FBR with a carbonation unit, was able to sustain a complete and stable denitrification even at pH as low as 4.75. Denaturing gradient gel electrophoresis (DGGE) showed the evolution of the denitrifying biofilm during the FBR operation, resulting in a robust and high-performing mixotrophic consortium of chemolithotrophic and heterotrophic bacteria dominated by T. denitrificans. Batch activity tests performed at three different stages of the FBR operation (feed pH 7.0, 6.0 and 5.25) showed that low pH cultivation enhanced the denitrification activity (mgN/gVSd) of the FBR biofilm at acidic pH values.

Modeling the kinetics of biolubricant production from castor oil using Novozym 435 in a fluidized-bed reactor

Biolubricant production by Novozym 435-catalyzed methanolysis of castor oil was studied in a fluidized-bed reactor operating in the batch recirculation mode. With 1g of enzyme and a methanol-to-oil molar ratio of 6:1, the highest yield of methyl ester was obtained (99.6%) after 24h at 40°C and a 30mL/min flow rate. The ping-pong bi-bi mechanistic model was used to treat the experimental data. Using non-linear regression analysis, a model with substrate inhibition by both methanol and castor oil gave the best fit, with kinetics constants Vmax=7.97mmol/Lmin, Km,oil=90.07mM, Km,methanol=733.27mM, Ki,oil=923.23mM, and Ki,methanol=317.11mM. The Km,oil value was indicative of the higher affinity of the lipase toward the oily substrate, and the castor oil was less inhibitory than methanol (Ki,methanol<Ki,oil). The reusability of Novozym 435 was also evaluated using repeated batch experiments, and no significant decreases in the methanolysis yields were observed after ten cycles.

The transition velocities in a dual circulating fluidized bed reactor with variation of temperatures

The extra-heavy oil fraction upgrading process, which consisted of a pyrolyzer and a bubbling bed as a combustor/gasifier, was developed. Prior to operating a dual circulating fluidized bed reactor, the transition velocities of flow regime were determined at different temperatures using silica sand particles as the bed material. The transition velocities included minimum fluidization velocity (Umf), transition velocity to turbulent fluidization (Uc, Uk) and transport velocity (Utr). The minimum fluidization velocity determined by measuring bed pressured drop with increasing gas velocity was observed to decrease with increasing temperature. Both the transition velocities from bubbling to turbulent fluidized bed behavior determined by measuring bed pressure drop fluctuation and transport velocity from turbulent to fast fluidized bed behavior by emptying time method increased with increasing temperature. Based on the experimental data, correlations are proposed to predict the transition velocities at different temperatures. As the actual dual circulating fluidized bed reactor operation occurs at relatively high temperature, the correlations obtained in this study are directly applicable to the extra-heavy oil fraction upgrading process. Thus, the transition velocities and flow regimes in a dual circulating fluidized bed reactor are determined.

유동상 반응조를 이용한 하수의 혐기성 처리에 관한 연구

Anaerobic sewage treatment is drawing attentions due to high energy consumptions and sludge production associated with aerobic treatment. This study evaluates the treatment characteristics and energy balance of a fluidized bed reactor (FBR) for treating domestic sewage at <TEX>$20^{\circ}C{\sim}25^{\circ}C$</TEX> for 245 days. Sewage fed to the FBR was a primary clarifier effluent of a domestic sewage treatment plant with COD of 99-301 mg/L and <TEX>$BOD_{5}$</TEX> of 37-149 mg/L. Effluent <TEX>$SBOD_{5}$</TEX> and its removal efficiency at HRT of 1~3 h were 6~15 mg/L and 73.4~85.5%, respectively, achieving high removal efficiency for soluble organic substances even at short HRTs. COD removal efficiency and its effluent concentration were 53.8~75.9% and 51~83 mg/L, respectively. The energy production potential from gaseous methane was 0.009-0.028 kWh/<TEX>$m^{3}$</TEX>, which satisfies the energy required for the FBR operation.

Abatement of SO2 in a Multi-stage Counter-current Gas-solid Fluidized Bed Reactor.

A multistage counter-current gas-solid fluidized bed reactor operating in three stages has been designed, constructed and operated to investigate the hydrodynamics of the system. Staging of a fluidisation column with horizontal screens reduces the axial mixing of the phases and limits the formation and growth of the bubbles. The gas-solid flow mechanism, pressure drop and the solids holdup have been studied in continuous regime for two phase system over a wide range of stable operating conditions. The result of this study has great industrial importance for scale-up, design and steady operation of a multi-stage fluidized bed reactor for control of gaseous pollutants.

Continuous Production of Oxytetracycline in Fluidized Bed Bioreactor by Immobilized Cells of Streptomyces varsoviensis MTCC-1537: Effect of Dilution and Glucose Loading Rates

Oxytetracycline (OT) production using glutaraldehyde cross-linked calcium alginate immobilized cells of Streptomyces varsoviensis in continuous fluidized bed reactor (FBR) was investigated. Initially, batch experiments were carried in stirred tank reactor (STR) and FBR using calcium alginate immobilized cells. Higher OT production of 0.45 gm/L was achieved by FBR when compared with 0.33 g/L of OT in STR. All subsequent studies were carried out in continuous mode of operation in FBR. During 21 days of operation, effect of glucose concentration and different dilution rates were studied. A maximum of 0.75 g/L OT was achieved in the medium having 10 g/L of glucose concentration. The highest OT concentration of 0.92 g/L and the highest yield of OT with respect to biomass at 0.1713 g/g were obtained at the dilution rate of 0.25 day(-1).

Kinetics study of the fluorination of uranium tetrafluoride in a fluidized bed reactor

The kinetics of reaction of the uranium tetrafluoride conversion to the uranium hexafluoride with fluorine gas taking place in a fluidized bed reactor operating in industrial conditions have been studied. The external and internal diffusion effects are investigated by Mears and Weisz–Prater criterions. The kinetic equation for the fluorination of uranium tetrafluoride is developed in the absence of diffusional limitation using an integral method by assuming that the gas flow is of plug or perfectly mixed type. A good agreement is observed between the experimental data and a first-order model with respect to fluorine in the CSTR system. The activation energy of the reaction and the pre-exponential factor are obtained using analytical results from a better model.

Simple organic electron donors support diverse sulfate-reducing communities in fluidized-bed reactors treating acidic metal- and sulfate-containing wastewater

Bacterial diversity of lactate- and ethanol-utilizing sulfate-reducing fluidized-bed reactor (FBR) communities was investigated with culture-independent methods. The FBRs were fed for 500 days with synthetic mineral processing wastewater containing sulfate, zinc and iron with hydraulic retention time of 16–24 h. Sodium lactate or ethanol was used as electron donor for microbial sulfate reduction. For microbial characterization, 16S rRNA gene clone libraries and denaturing gradient gel electrophoresis (DGGE) fingerprinting were employed. The FBR communities were diverse and contained many previously undescribed bacteria. The clone library indicated significant differences between bacterial communities of the two reactors. Most notable was the large number of Proteobacterium sequences retrieved from the ethanol-fed reactor, whereas in the lactate-fed reactor, sequences clustering with Nitrospira phylum were most abundant. Ethanol-utilizing FBR culture was more diverse than the lactate-utilizing one. Some sequences from each reactor were closely related to known sulfate reducers, such as Desulfobacca acetoxidans, Desulforhabdus amnigenus, and species of Desulfovibrio. DGGE profiling showed some changes in the bacterial communities over 393 days of continuous FBR operation. This study showed that it is possible to maintain diverse sulfate-reducing consortia using simple electron donors, lactate or ethanol in an open engineered ecosystem.

Effects of Electron Donors on Degradation of Pentachlorophenol in a Methanogenic Fluidized Bed Reactor

Anaerobic reductive dechlorination of pentachlorophenol (PCP) and other chlorophenols was studied in a laboratory-scale fluidized-bed reactor (FBR). Complete dechlorination of PCP and subsequent phenol removal were achieved at 35 °C with a mixed culture from anaerobic sewage sludge, soil and compost, but only after reinoculation with enrichments fed monochlorophenols. The FBR was fed a mixture of glucose, butyric acid and methanol to provide carbon and electrons for the anaerobic culture. FBR tests conducted after 8 months of operation demonstrated that glucose and butyric acid supported chlorophenol dechlorination significantly better than methanol. With 200 mg l−1 chemical oxygen demand (COD) from glucose or butyric acid, more than 96% dechlorination and 68% mineralization of 7 µmol l−1 PCP were observed during continuous FBR operation. Twenty mg l−1 COD from glucose resulted in 84% dechlorination and 55% mineralization of the PCP. After 10 months the FBR performance further improved; during this late period PCP was also extensively mineralized when methanol was supplied as electron donor. When PCP was spike fed and electron donor was continuously supplied, a PCP removal rate of 86 µmole l−1 d−1 was measured (0.94 µmole gVSS−1 h−1). Mineralization was slower by about a factor of 10. Most of the FBR tests demonstrated initial removal of meta- chlorines from PCP. The major PCP dechlorination pathway was as follows: 2,3,4,6-tetrachlorophenol, 2,4,6-trichlorophenol, 2,4-dichlorophenol, 2-monochlorophenol or 4-monochlorophenol, and phenol, which also was removed.

Comparative study of tuyere designs for fluidized beds

The work presented here analyses the different aspects of the design of tuyere plate distributors commonly used in fluidized bed reactors. The design of these tuyeres depends essentially on the pressure drop of the grid. However, various methods proposed in the literature give unreliable results for the determination of gas pressure drop across the tuyeres under industrial operation of fluidized bed reactors. This study is based on the comparison of experimental and theoretical pressure drops obtained on a pilot unit using tuyeres of different types. The aim of this comparison is to identify the main source of resistance to the gas flow. Experimental results are discussed and compared with values obtained from various models. The results obtained show that the main resistance is caused by the contraction of the gas at the exit nozzles of the tuyere. A numerical modelling approach is proposed and applied to the example of the tuyeres with four horizontal holes. This new approach shows that there is some limitation in the use of CFD programs for velocities higher than 60 m s −1 at the gas exit level.

Fluidized bed reactor operation for groundwater denitrification

Groundwater denitrification was carried out in a laboratory scale fluidized bed reactor using sand particles as the biomass carrier. This paper is concentrated on the fluidized bed reactor operation at very high nitrate loading rates (between 30 to 100 kg.NO3/m3 reactor/day) with corresponding short retention times (5 to 1.5 minutes). The effects of nitrate loading rate on nitrate and nitrite removal, as well as on reactor biomass profiles and biofilm characteristics, are presented in this article. The results of the present study indicate that this type of reactor can operate efficiently at retention times shorter than 3 minutes and at nitrate loading rates higher than 70 kg.NO3/m3/day. However, this system requires careful control of the biofilm thickness to achieve a reliable reactor operation.