Performance Of Fluidized Bed Reactor Research Articles

Changes in microbial communities during high-rate microbial selenate reduction in an up-flow anaerobic fluidized bed reactor

Biological fluidized bed reactor (FBR) is a promising treatment option for removing selenium oxyanions from wastewater by converting them into elemental selenium. The process can achieve high rates and be efficiently operated at low hydraulic retention times (HRT). However, the effects of HRT on the changes in microbial community in the FBR process have not been previously explored. In this study, dynamic changes of microbial communities both on biofilm carrier and in suspension of a selenate-reducing FBR were explored at various HRTs (0.3–120 h). Based on partial 16S rRNA gene sequencing of the microbial communities, alpha diversity of microbial communities in suspension rather than in the biofilm were impacted by low HRTs (0.3 h–3 h). Members from genera Geobacter, Geoalkalibacter, and Geovibrio were the main selenate-reducing bacteria on carrier throughout the FBR process. Genus Geobacter was dominant in FBR carrier at HRT of 24 h–120 h, whereas Geoalkalibacter and Geovibrio dominated at low HRT of 0.3 h–6 h. Suspended microbial communities detected in the FBR effluent were more sensitive to HRT changes than that in biofilm. “Shock loading” at HRT of 0.3 h had a great impact on microbial community compositions both in the biofilm and effluent. Reactor operation in batch mode and long HRT of 24 h helped recover the community from “shock loading” and improved selenite reduction and ethanol oxidation. Redundancy analysis revealed that HRT, influent pH and selenate loading were key operational parameters impacting both the FBR performance and the composition of microbial communities associated with both the FBR carrier and effluent. Overall, the microbial communities in FBR biofilm flexibly responded to the changes of HRT and showed resilience to the temporary shock loading, enabling efficient selenate removal.

A computational fluid dynamics model coupled with ethylene polymerization kinetics for fluidized bed polyethylene reactor

This work aims at exploring the effect of macro operating conditions on the distribution of temperature field and chain microstructures of polymer in a gas phase ethylene polymerization fluidized bed reactor (FBR) by coupling polymerization kinetics with computational fluid dynamics (CFD). An ethylene polymerization kinetic model in terms of the method of moments was introduced to CFD model. In the modeling framework, the Flory's distribution and custom field functions were used to predict the molecular weight distribution (MWD). The results show that the average molecular weight decreases with the increasing of reaction temperature, and MWD becomes wider because of the increase of temperature gradient. With the increase of hydrogen concentration, the average molecular weight and MWD becomes smaller and narrower, respectively. Unlike the hydrogen concentration, an increase in the ethylene concentration leads to an increase in the average molecular weight, polydispersity distribution index (PDI), and temperature. An increase of gas velocity improves the heat transfer of FBR but results in a very wide MWD when gas velocity exceeds the optimum fluidizing velocity. This model is helpful to understand how the operating conditions affect the performance of FBR and can provide theoretical guidance for the operation and design of polyolefin FBR.

Quantitative Measurement of Solids Holdup for Group A and B Particles Using Images and Its Application in Fluidized Bed Reactors

Solids holdup as one of the main parameters in characterizing the performance of fluidized bed reactors is widely concerned. With its development and improvement, visualization technology has been applied in fluidization because of its little disturbance to the flow. In this study, four types of particles with different properties are tested in a narrow rectangular fluidized bed equipped with a high-speed video camera. Calibration curves of these different types of particles are achieved by correlating the grayscale of the digital images with the corresponding solids holdup. These calibration curves are further applied to obtain the average solids holdup across the sectional area and local solids holdup from the center towards the wall in both a gas-solids turbulent fluidized bed and a circulating fluidized bed to verify the results. The calibration method works well for solids holdup of different types of particles in both dense and dilute fluidization systems. This method is important to characterize the fluidization quality and reactor performance with a wide operating condition.

CFD simulation of mesoscale structures in mono and bidispersed fluidized bed pyrolysis reactors

Pyrolysis of biomass and organic matter in fluidized bed reactors have become popular in recent years due to the efficient conversion of biomass to bio-fuels. Among others, the presence of mesoscale structures produced by the transient nature of gas solid flow governs the performance of fluidized bed reactors. In the present study, monodispersed system with the particle size of 155 µm and bidispersed system with particle sizes of 128 and 1500 µm are simulated by the multi-fluid model with the kinetic theory of granular flow closure laws. The objective is to investigate the effect of size distribution and solid volume fraction on the hydrodynamics of gas-solid flows. The ANSYS Fluent® software is used for the simulations and the slip velocity, heterogeneity index as well as mixing index are investigated. A two dimensional fully periodic domain is used to investigate the slip velocity at five different solid concentrations in dilute range. The slip velocity, which represents the interaction between solid particles and gas, calculated by simulation is higher than that calculated through Richardson-Zaki’s correlation. The mixing index is found to be minimum for a solid volume concentration of 5%. The heterogeneity index is significantly less than 1 for both cases with bidisperesed system having lower value as compared to monodispersed system. The image analysis of solid fraction contours exhibits that mesoscale structures are dense and non-uniform for solid fractions of 0.05 and are small and uniform of solid fractions of 0.025 and 0.075.

Influence of frictional packing limit on hydrodynamics and performance of gas-solid fluidized beds

The influence of frictional packing limit (FPL) on prediction of hydrodynamics and performance of fluidized bed reactors was studied. Dense gas-solid flows in non-reactive (under isothermal cold and at elevated temperatures) and reactive atmospheres (fluidized bed gasifier) were simulated using Eulerian-Eulerian methodology considering a range of values for FPL. Simulations under cold flow conditions were conducted to establish a range of FPL values that provides physically realistic predictions. It is noticed that bed pressure drop increases with increasing value of FPL when superficial gas velocity (U) is less than or equal to the minimum fluidization velocity. For larger values of U, predicted pressure drop is unaffected by the choice of value of FPL. However, in these cases, the distribution of particles, their velocities and bubbling behavior are significantly affected by FPL. Effect of FPL at elevated temperatures is similar to the one observed at cold flow conditions. It is further noticed that FPL not only affects the predictions on bed hydrodynamics but also has profound influence on reactive flow characteristics such as bed temperature and product gas composition. Sensitivity analysis under cold flow conditions could reveal better predictions when the ratio of FPL to close packing limit is chosen between 0.9 and 0.97.

Optimization of nitrate and selenate reduction in an ethanol-fed fluidized bed reactor via redox potential feedback control

Electron donors are a major cost-factor in biological removal of oxyanions, such as nitrate and selenate from wastewater. In this study, an online ethanol dosing strategy based on feedback control of oxidation-reduction potential (ORP) was designed to optimize the performance of a lab-scale fluidized bed reactor (FBR) in treating selenate and nitrate (5 mM each) containing wastewater. The FBR performance was evaluated at various ORP setpoints ranging between −520 mV and −240 mV (vs. Ag/AgCl). Results suggested that both nitrate and selenate were completely removed at ORPs between −520 mV and −360 mV, with methylseleninic acid, selenocyanate, selenosulfate and ammonia being produced at low ORPs between −520 mV and −480 mV, likely due to overdosing of ethanol. At ORPs between −300 mV and −240 mV, limited ethanol dosing resulted in an apparent decline in selenate removal whereas nitrate removal remained stable. Resuming the ORP to −520 mV successfully restored complete selenate reduction. An optimal ORP of −400 mV was identified for the FBR, whereby selenate and nitrate were nearly completely removed with a minimal ethanol consumption. Overall, controlling ORP via feedback-dosing of the electron donor was an effective strategy to optimize FBR performance for reducing selenate and nitrate in wastewater.

Experimental evaluation of the convection heat transfer coefficient of large particles moving freely in a fluidized bed reactor

Heat transfer is a key aspect in the performance of fluidized bed reactors. In particular, the dense phase heat transfer coefficient, which determines the heat exchanged between the bed and fuel particles, is of special relevance. This work presents a study on the heat transfer that occur when introducing pelletized particles of dry ice in a fluidized bed. The convection heat transfer coefficient is experimentally evaluated by means of the sublimation of dry ice particles using a novel methodology, which consists in a measurement system based on a macro-TGA fluidized bed and the corresponding evaluation of the acquired data. The system is capable of measuring the real time mass of the fluidized bed, which is a direct measure of the mass loss of the dry ice particles. The evaluation of such measurements allows to determine the convection heat transfer coefficient between the dry ice particles and the bed. Fixed and fluidized bed regimes, varying the excess gas velocity from -0.03 m/s up to 0.35 m/s, were tested for two different bed materials, namely Ballotini glass beads and alumina. The results of the sublimation and heat transfer coefficients are in good agreement with values reported in the literature, confirming the reliability of the experimental and postprocessing methodologies. In general, higher gas velocities enhance the dry ice particles mixing in the bed up to a limit in which the sublimation and convection heat transfer coefficients do not further increase. Additionally, the influence of the buoyancy behaviour of the dry ice particles in the bed on the convection heat transfer coefficient is discussed. The convection heat transfer coefficient decreases substantially if the dry ice particles present a flotsam behaviour and the gas velocity is not sufficiently high to ensure a proper circulation of the particles in the whole bed.

Development and confirmation of a simple procedure to measure solids distribution in fluidized beds using tracer particles

The spatial distribution of solid particles is a key factor affecting the performance of fluidized bed reactors. Non-invasive techniques including radioactive particle tracking (RPT) and positron emission particle tracking (PEPT) are deployed to measure the solids distribution. Different methods to calibrate the particle tracking measurements have been developed to quantify mean solids concentration. In this paper, gas-solid flows in a traveling fluidized bed are simulated with CFD-DEM and the behavior of different particles, including bulk sand particles and tracer particles are investigated. The simulated hydrodynamics are compared with experimental measurements. Analyses are carried out to derive the mean solids concentration from the tracer particle data. Different calibration approaches are examined, and the simple calibration method is verified. It is shown that the mean solids concentration can be measured reliably using representative tracer particles. The experimental RPT data are then revisited with the new calibration method which yields more realistic results.

Effect of upflow velocity on the performance of a fluidized bed reactor to remove phosphate from simulated swine wastewater

This study investigated the effect of upflow velocity (200–500 cm/min) on the performance of a bench-scale fluidized bed reactor to remove phosphate from simulated swine wastewater. Experiments were conducted at an inflow pH of 9, a phosphate concentration of 89 mg P/L, a Mg:P ratio of 1:1 adjusted using MgCl2 and a recycle ratio of 20. Decreasing upflow velocity enhanced the phosphate removal efficiency. Thermodynamic simulations showed that the struvite crystallization did not reach equilibrium at high velocity. The phosphate reduction inside the reactor (SOPin) showed two crystallization periods, of which the quick period was well fitted with a linear model. High upflow velocity promoted the phosphate reduction rate, but it reduced the crystallization time inside the reactor. Hence, the crystallization did not reach equilibrium, decreasing the phosphate removal efficiency. Low upflow velocity did not affect the nutrient release behaviour of struvite pullets despite yielding low crushing strength and purity. The nutrient release was determined by the solubility of struvite rather than the product quality. Furthermore, kinetics of SOPin reduction provides a basis for the design of FBR aiming to optimize the removal of phosphate and yield struvite products with good quality.

The BubbleTree toolset: CFD-integrated algorithm for Lagrangian tracking and rigorous statistical analysis of bubble motion and gas fluxes for application to 3D fluidized bed simulations

Bubbling dynamics and distribution of gas flow critically influence the performance of fluidized bed reactors and must be quantified accurately for their design and performance optimization. In this study, a new toolset called the BubbleTree toolset (BT) was developed using Python and the Visualization Tool Kit (VTK) for analyzing computational fluid dynamics simulation data and performing statistical analysis of bubbling dynamics such as their volume, location, and velocity. In addition, the BT toolset provides the capability to (a) track bubbles through coalescence and splitting events and (b) compute throughflow by integrating gas fluxes through the bubble surface. The toolkit was verified using the method of manufactured solutions as well as by comparing bubbling dynamics predictions in large-scale simulations with relevant open-source software. The BT toolset also incorporates tools for rigorous statistical analysis in selected regions of interest as well as the reactor in its entirety. The BT will be integrated with MFiX CFD simulations which will enable the fundamental investigation of gas-solids flow interaction in complex reacting particulate flows, in situ estimation of bubbling (and cluster) dynamics dependent sub-grid models and performance optimization of fluidized bed reactors using CFD-simulations.

Generation and evaluation of an artificial optical signal based on X-ray measurements for bubble characterization in fluidized beds with vertical internals

The performance of fluidized bed reactors strongly depends on the bubble behavior, for which reason knowledge concerning the bubble properties is important for modeling and reactor optimization. X-ray measurements can be used to characterize bubbles within the cross-section of a fluidized bed on a laboratory scale, but cannot easily be extended to hot, pressurized large scale plants. For future measurements at hot conditions in a fluidized bed methanation reactor, we have developed an optical probing system that can be employed under these conditions. However, optical sensors are only able to investigate the local fluidization patterns at a defined position in the bed. The objective of this study is to characterize differences in bubble properties between local optical measurements and an X-ray tomography method that is able to detect bubbles over the entire cross-section. Therefore, an artificial optical signal is created out of existing hydrodynamic X-ray measurement data obtained at a cold flow model of a pilot scale methanation reactor. The determined bubble properties of both methods (i.e. evaluation of the derived artificial optical probe signal and image reconstruction based on the evaluation of original X-ray tomographic data) are compared with regard to the bubble rise velocity and the bubble size (for the X-ray method) or pierced chord length (for the optical evaluation method), respectively. The comparison shows that for the evaluation of the optical probe data, statistical effects have to be considered carefully. The detected mean chord length of the optical method does not immediately correspond to the mean bubble size determined by the X-ray method. Moreover, also differences regarding the bubble rise velocity were detected for some fluidization states. The reason for the discrepancies between both methods could be identified and corrected, amongst others by means of a Monte Carlo simulation in which rising bubbles in a fluidized bed were simulated and characterized by a local virtual optical sensor.

Improvement of the simulation of fuel particles motion in a fluidized bed by considering wall friction

The mixing of fuel particles is a key issue on the performance of fluidized bed reactors. In this work, the motion of a non-reactive fuel particle in a pseudo-2D bubbling fluidized bed operated at ambient conditions is simulated employing a hybrid-model and introducing a new friction term that accounts for the effect of the bed vessel front and rear walls. The hybrid-model, implemented in the code MFIX, simulates the dense and gas phases using a Two-Fluid Model (TFM) whereas the fuel particles are modeled using a Discrete Element Method (DEM). The importance of the present hybrid-model is that the interaction of the continuum phases with the fuel particles behavior is fully coupled.To improve the accuracy of the simulated fuel particle motion in a bubbling fluidized bed, a model accounting for the effect of the bed front and rear walls on the continuum solid phase is combined with the hybrid-model. The rising and sinking velocity of the fuel particles, the circulation time and statistical parameters associated to the location of the fuel particle in the bed were obtained from the simulations and compared with experimental measurements. According to the results, the prediction of these parameters is clearly improved when the friction term is included in the simulation.

3-D face-masking detection and tracking algorithm for bubble dynamics: Method and validation for gas–solid fluidized beds

The transient behavior of rising bubbles plays a critical role on the performance of fluidized bed reactors, but predicting bubble dynamics is difficult. CFD has been shown to be capable of reproducing bubbling phenomena, but data interpretation and visualization is challenging. In this study, a 3-D detection and tracking algorithm, called face-masking, is developed and validated by numerical simulations of lab-scale and pilot-scale gas–solid fluidized beds. This algorithm identifies discrete bubbles using the instantaneous whole-field void fraction data. Individual bubbles are characterized in detail, including size, shape and location. The algorithm tracks bubbles across successive time frames and computes axial and lateral bubble velocities. Bubble dynamics predicted by the face-masking algorithm are validated against four different published experimental measurements. The face-masking algorithm provides a new tool for post-processing large-scale three-dimensional fluidizedbed simulation data. The bubble surfaces found by this algorithm will enable computation of normal fluxes through the surface. This algorithm can also be applicable in other areas of multiphase flows where characterization of bubbles, droplets, and clusters is necessary.

Monitoring of particle motions in gas-solid fluidized beds by electrostatic sensors

Gas-solid fluidized beds are widely applied in numerous industrial processes. Particle motions significantly affect the performance of fluidized bed reactors and the characterization of particle movements is therefore important for fluidization quality monitoring and scale-up of reactors. Electrostatic charge signals in the fluidized bed contain much dynamic information on particle motions, which are poorly understood and explored. In this work, correlation velocities of Geldart B and D particles were measured, analyzed and compared by induced electrostatic sensors combined with cross-correlation method in the fluidized bed. The results indicated that the average correlation velocity of particle clouds increased and the normalized probability density distributions of correlation velocities broadened when the superficial gas velocity increased in the dense-phase region. Both upward and downward correlation velocities could be acquired in the dynamic bed level region. Under the same excess gas velocity, the average correlation velocity of Geldart D particles was significantly smaller than that of Geldart B particles, which was caused by the smaller bubble sizes caused by the dominant bubble split over coalescence and less volume of gas forming bubbles for Geldart D particles. The experimental results verified the reliability and repeatability of particle correlation velocity measurement by induced electrostatic sensors in the gas-solid fluidized bed, which provides definite potential in monitoring of particle motions.

Comparative study of propane oxidative dehydrogenation in fluidized and fixed bed reactor

ABSTRACTSupported vanadia catalyst was successfully synthesized using wet impregnation of γ-alumina to study propane oxidative dehydrogenation (POD). The prepared catalysts were characterized with X-ray diffraction and BET tests. To investigate performance of fluidized bed reactor in comparison to fixed bed micro-reactor, propane conversion and propylene selectivity were measured in temperatures of 480 to 550°C and GHSV of 48000, 60000, and 78000 cc/gr.hr at equimolar feed ratio of propane to oxygen. The results indicated that at constant temperature propane conversion obtained in the fixed bed reactor was higher. But fluidized bed is superior to fixed bed reactor in terms of propylene selectivity leading to considerably higher propylene yields over the fixed bed. It is suggested that pre-filtering effect induced by hydrodynamics of fluidized bed reactor has major effect in the enhancement of propylene selectivity beyond that of fixed bed micro-reactor.

Hydrodynamics and particle mixing/segregation measurements in an industrial gas phase olefin polymerization reactor using image processing technique and CFD-PBM model

Particle size distribution (PSD) has a significant impact on the performance of fluidized bed reactors due to uneven distribution in the segregation and mixing phenomena. This paper develops a new method of digital image processing that investigates the hydrodynamics of an industrial gas phase olefin polymerization reactor and studies the fluidization structure of a wide range of particle size distribution in an industrial gas phase polymerization reactor by means of a CFD-PBM coupled model, where the direct quadrature method of moments (DQMOM) was implemented to solve the population balance model. It was shown that the applied parameter assumptions and closure laws were appropriately chosen to satisfactorily predict the available operational data in terms of pressure drop and bed height. The transient CFD-PBM/DQMOM coupled model and image analysis technique are then implemented extensively to analyze bubble fluidization structure and segregation phenomena at different velocities. The particle segregation indicates that the small bubbles present in the bed are unable to induce vigorous mixing at low superficial gas velocity while particle mixing improves at a velocity above the minimum fluidization velocity. Further, the predicted results show higher axial segregation phenomena when compared to the radial direction.

The effect of gas permeation through vertical membranes on chemical switching reforming (CSR) reactor performance

A novel membrane assisted fluidized bed reactor concept has been proposed for ultra-pure hydrogen production with integrated CO2 capture from steam methane reforming. The so-called Chemical Switching Reactor (CSR) concept combines the use of an oxygen carrier for supplying heat and catalysing the steam methane reforming reaction and hydrogen perm-selective membrane (thin Pd-membrane) for hydrogen recovery. However, extraction of gas through the membranes influences the hydrodynamics of the fluidized bed by altering the bubble behaviour and the extent of gas back mixing. Bubble properties (size, number and velocity) strongly influence the performance of fluidized bed reactors as they play a major role in heat and mass transfer phenomena. This work experimentally investigates the effects of gas extraction via vertical membranes on the bubble properties using Digital Image Analysis (DIA) technique and numerically using the Two Fluid Model approach (TFM) closed by the kinetic theory of granular flow. The simulation studies were extended to investigate real reactive conditions. A pseudo 2D experimental setup with a multi-chamber porous plate mounted at the bottom of the back plate was used to simulate vertical membranes. This setup allowed for gas extraction in specific locations from the back of the column, thus facilitating studies on the effect of gas extraction rates and locations on the bubble properties. Results show that variation of gas extraction flow rates slightly influences the bubble behaviour, whereas variation of gas extraction locations (varying the area) significantly influences bubble properties. Cold flow simulations showed a reasonable comparison to experimental measurements and reactive simulations revealed very similar hydrodynamic responses to changes in gas extraction rate (membrane permeability) and location. Shifting gas extraction towards the centre of the bed proved to be beneficial in reducing gas back-mixing. Specifically, reducing the number of vertical membranes from 7 to 5 by removing the outer two membranes showed a slight increase in hydrogen extraction performance.

전산유체역학(CFD)을 이용한 유동층반응기 내부의 목질계 바이오매스 급속 열분해 모델 비교 및 검증

유동층반응기에서 바이오매스 급속 열분해의 모델화를 통해 열분해로부터 발생되는 바이오오일(Bio-oil) 및 비응축 가스(Non-condensable gas) 성분의 예측과, 이를 통한 수율 향상을 목표로 한다. 본 연구의 목적은 유동층반응기 내부에 투입된 바이오매스가 급속 열분해되는 동안 발생되는 생성물의 수율 예측과 실험 및 시뮬레이션 값을 비교 및 분석하는 것이다. 급속 열분해의 시뮬레이션을 위해 전산유체역학(Computational Fluid Dynamics, CFD) 프로그램이 사용되었으며, 바이오매스의 급속 열분해의 시뮬레이션을 위해 바이오매스 하위 구성 성분의 상세한 열분해 반응 경로가 적용되었다. 이 열분해 반응은 세부적으로 셀룰로오스(Cellulose), 헤미셀룰로오스(Hemicellulose) 및 리그닌(Lignin)의 반응을 포함하고 있으며, 열분해로부터 발생되는 주요 가스 성분은 이산화탄소(<TEX>$CO_2$</TEX>), 일산화탄소(CO), 메탄(<TEX>$CH_4$</TEX>), 수소(<TEX>$H_2$</TEX>), 에틸렌(<TEX>$C_2H_4$</TEX>)이다. 본 모델의 예측치와 기존 문헌(Mellin et al., 2014)의 실험 및 시뮬레이션 결과를 비교하였으며, 그 결과, <TEX>$CH_4$</TEX>, <TEX>$H_2$</TEX> 및 <TEX>$C_2H_4$</TEX>의 경우, 각각 3.7%p, 4.6%p 및 3.9%p로 비교적 일치하게 예측되었지만, <TEX>$CO_2$</TEX> 및 CO의 경우, 각각 9.6%p 및 6.7%p로 높게 예측되었다. 이러한 차이가 발생하는 이유는 이차 열분해 반응에서의 세부 반응조건에 해당되는 각각의 인자의 부재에 기인한 것으로 판단된다. 연구 결과, 시뮬레이션을 통한 모델화 접근이 가능한 것으로 판단되며, 추후에 연구된 모델화를 통해 바이오오일 및 기타 성분들의 예측도 가능할 것으로 판단된다. The modeling for fast pyrolysis of biomass in fluidized bed reactor has been developed for accurate prediction of bio-oil and gas products and for yield improvement. The purpose of this study is to analyze and to compare the CFD(Computational Fluid Dynamics) simulation results with the experimental data from the CFD simulation results with the experimental data from the reference(Mellin et al., 2014) for gas products generated during fast pyrolysis of biomass in fluidized bed reactor. CFD(ANSYS FLUENT v.15.0) was used for the simulation. Complex pyrolysis reaction scheme of biomass subcomponents was applied for the simulation of pyrolysis reaction. This pyrolysis reaction scheme was included reaction of cellulose, hemicellulose, lignin in detail, gas products obtained from pyrolysis were mainly <TEX>$CO_2$</TEX>, CO, <TEX>$CH_4$</TEX>, <TEX>$H_2$</TEX>, <TEX>$C_2H_4$</TEX>. The deviation between the simulation results from this study and experimental data from the reference was calculated about 3.7%p, 4.6%p, 3.9%p for <TEX>$CH_4$</TEX>, <TEX>$H_2$</TEX>, <TEX>$C_2H_4$</TEX> respectively, whereas 9.6%p and 6.7%p for <TEX>$CO_2$</TEX> and CO which are relatively high. Through this study, it is possible to predict gas products accurately by using CFD simulation approach. Moreover, this modeling approach should be developed to predict fluidized bed reactor performance and other gas product yields.

Anaerobic up flow fluidized bed reactor performance as a primary treatment unit in domestic wastewater treatment

The fluidized bed UASB performance was studied in this experiment as a primary unit the anaerobic unit the advantage of better generated sludge characteristics and smaller tank volume.The reactor performance was investigated for the treatment of domestic wastewater with unexpected industrial water flows at different operational temperatures (14–25°C) and loading rates. For each temperature range the reactor performance was studied under different hydraulic loadings HRT (6, 4, 2.5h).The best methane yield rate and COD total removal rate are 0.285l/g COD total and 70.82% respectively at warm working temperature 19°C with OLR 7.76kg COD/m3/day and HRT 6h.On the low temperature operation, the average COD removal of the reactor was 55.28% and 50.33% for HRT of 4h and 2.5h respectively. The methane production dropped to 0.1623 & 0.0988L CH4/g COD with average organic loading rate of 5.34 & 10kg COD/m3/day for HRT of 4h and 2.5h respectively.The efficiencies of Total nitrogen removal ranged between 2.23 and 10.83% with an apparent decrease during the low temperature high rate stages. Nitrite removal was in the range of (23.08–77)% with up to the 2mg/L in the effluent water when obtaining high organic loading and warm temperature. These results demonstrated that the domestic wastewater could be anaerobically treated in a fluidized bed UASB reactor with very low HRT reaching 2.5h.

A CFD–PBM coupled model of hydrodynamics and mixing/segregation in an industrial gas-phase polymerization reactor

The particle size distribution (PSD) has a significant influence on the performance of fluidized bed reactors, as uneven distribution usually results from segregation and mixing tendencies. The objective of this paper is to study the segregation of wide range of particle size distribution in an industrial gas phase polymerization reactor by means of a CFD–PBM coupled model, where the direct quadrature method of moments (DQMOM) was implemented to solve the population balance model. It was shown that the model is able to satisfactorily predict the available operational data in terms of pressure drop and bed height. Model sensitivities of discretization scheme, maximum solid packing and fluidization/de-fluidization were also studied. The transient CFD–PBM/DQMOM coupled model is then utilized extensively to analyze minimum fluidization velocity, fluidization behavior and segregation phenomena at different velocities. The results suggested that third-order MUSCL discretization scheme, maximum solid packing value which is 0.01 higher than specific solid volume fraction and also fluidization process were mathematically and physically consistent with real observation. In addition, the segregation is strongly affected at minimum fluidization velocity range of particles. The PSD becomes well-mixed at high gas velocity while the quasi-layer inversion was predicted in low gas velocity.