Reactor Height Research Articles

Assessing the performance of an industrial SBCR for Fischer–Tropsch synthesis: Experimental and modeling

The main objective of this study is to predict the performance of an industrial‐scale (ID = 5.8 m) slurry bubble column reactor (SBCR) operating with iron‐based catalyst for Fischer–Tropsch (FT) synthesis, with emphasis on catalyst deactivation. To achieve this objective, a comprehensive reactor model, incorporating the hydrodynamic and mass‐transfer parameters (gas holdup, εG, Sauter‐mean diameter of gas bubbles, d32, and volumetric liquid‐side mass‐transfer coefficients, kLa), and FT as well as water gas shift reaction kinetics, was developed. The hydrodynamic and mass‐transfer parameters for He/N2 gaseous mixtures, as surrogates for H2/CO, were obtained in an actual molten FT reactor wax produced from the same reactor. The data were measured in a pilot‐scale (0.29 m) SBCR under different pressures (4–31 bar), temperatures (380–500 K), superficial gas velocities (0.1–0.3 m/s), and iron‐based catalyst concentrations (0–45 wt %). The data were modeled and predictive correlations were incorporated into the reactor model. The reactor model was then used to study the effects of catalyst concentration and reactor length‐to‐diameter ratio (L/D) on the water partial pressure, which is mainly responsible for iron catalyst deactivation, the H2 and CO conversions and the C5+ product yields. The modeling results of the industrial SBCR investigated in this study showed that (1) the water partial pressure should be maintained under 3 bars to minimize deactivation of the iron‐based catalyst used; (2) the catalyst concentration has much more impact on the gas holdup and reactor performance than the reactor height; and (3) the reactor should be operated in the kinetically controlled regime with an L/D of 4.48 and a catalyst concentration of 22 wt % to maximize C5+ products yield, while minimizing the iron catalyst deactivation. Under such conditions, the H2 and CO conversions were 49.4% and 69.3%, respectively, and the C5+ products yield was 435.6 ton/day. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3838–3857, 2015

Helminth Egg Removal Capacity of UASB Reactors under Subtropical Conditions

This research was conducted to study the anaerobic sludge filtration capacity regarding helminth egg removal in upflow anaerobic sludge blanket (UASB) reactors. Two 25 L lab-scale UASB reactors were operated at an ambient temperature which varied between 17.1 and 28.6 °C. Ascaris suum egg was selected as the model egg considering its similarity in terms of size and morphology to Ascaris lumbricoides, a human pathogen. Ascaris suum eggs were obtained from female parasites of infected pigs. The anaerobic sludge filtration capacity was performed applying upflow velocities between 0.09 and 0.68 m·h−1. Three sludge bed heights in the range of 0.30–0.40 m, 0.50–0.60 m and 0.60–0.70 m were applied. These sludge bed heights corresponded to 19%–25%, 31%–38% and 38%–44% of the total reactor height, respectively. Under the mentioned conditions, the average helminth egg removal efficiency was reciprocally correlated to the imposed upflow velocity. The studied lab-scale reactors reported an average helminth egg removal between 34%–100%, 30%–91% and 34%–56%, when the sludge bed in the UASB reactor was 19%–25%, 31%–38% and 38%–44% of the total reactor height, respectively. The decreased filtration capacity at increasing sludge bed heights might be likely related to biogas production and channeling formation. The average helminth egg removal efficiency in the control experiments performed without any sludge bed, by plain sedimentation, varied between 44% and 66%.

Determination of pyrolysis behavior of brown coal in a pressurized drop tube reactor

Pyrolysis of a pulverized German brown coal was investigated using a new high pressurized drop tube reactor. Influence of temperature (600, 700, 800 °C), pressure (25, 60 bar (g)) as well as residence time (variation of heated reactor length: 500, 1500, 2500 mm) on pyrolysis product yields as well as char and gas composition were evaluated. Particle heating and residence times of gas and particle in the heated reactor section were calculated based on the obtained data. To trace the pyrolysis progress during particle drop in the reactor tube gas sampling over reactor height was done. A good reactor performance and reliable results for the pyrolysis experiments could be obtained for the new reactor equipment. Only a slight pressure influence on product yields, char composition, and gas composition was found, which was contrary at the different temperatures. This indicates competing reactions taking place at the given conditions. Gas species evolution over the reactor height is mainly promoted by rising temperatures. The long gas residence times in the reactor and the obtained CH4, H2, and C2 and C3 hydrocarbon yields are a result of secondary cracking of tar and gaseous hydrocarbons at temperatures above 600 °C. Furthermore, it was found, that heterogeneous gasification reactions take place at higher temperatures as well. Comparison between thermogravimetric experiments in “drop-in” mode and the DTR results show significant differences attributed to heat transfer limitations in the particle bulk (TGA) and to the long gas residence times (78–368 s) in the drop tube reactor.

The Adsorption and Desorption Breakthrough Behavior of Hydrogen Chloride Gas Mixture on Zeolite 13X Pellet in a Fixed Bed Reactor

The adsorption and desorption breakthrough test of hydrogen chloride (HCl) was performed by loading zeolite 13X pellet (molecular sieve 13X, Aldrich Co., U.S.A.), a commercial adsorbent, onto a fixed bed reactor (height 15 cm, inside diameter 0.5 cm). The breakthrough test was carried out by changing various experimental conditions such as inlet flow rate (0.5, 1, 1.5, 2 L/min), HCl concentration (200, 350, 500, 650 ppm), reaction temperature (30, 50, 70, 90°C), and reaction pressure (1, 5, 10, 15, 20 bar) with considering the retention time and space velocity. After evaluating the adsorption and the desorption characteristics of HCl on the MS-13X, the consecutive cyclic test (5 times of adsorption step, 4 times of desorption step) was carried out with optimum condition. At the adsorption step, pressure was 20 bar, temperature was 30°C, HCl concentration was 200 ppm, total inlet flow rate was 0.5 L/min (HCl+N2). At the desorption step, pressure was 1 bar (atmospheric pressure), temperature was 280°C, total inlet flow rate was 0.5 L/min (N2 only), desorption time (regeneration time) was 7 h. The optical, physical, and chemical characteristics of MS-13X were analyzed using BET, XRD, SEM, EDX, and TGA before and after breakthrough tests.

CFD Modeling of a Carbonation Reactor with a K‐Based Dry Sorbent for CO2 Capture

AbstractA 2D CFD simulation of the carbonation reactor is carried out to evaluate the performance of potassium‐based dry sorbent during the CO2 capture process. A multiscale drag coefficient model is incorporated into the two‐fluid model to take the effects of clusters into account. The influence of several parameters on CO2 removal is investigated. The results indicate that increasing the reactor height and reducing the gas velocity can lengthen the residence time of particles and enhance the CO2 removal. The operating pressure has a significant influence on the performance of solid sorbents. A higher pressure will decrease the CO2 removal efficiency.

The Impact of Water Distribution System on the Internal Flow Field of EGSB by Using CFD Simulation

The internal flow field of EGSB (Expanded Granular Sludge Bed) reactor was investigated by using CFD simulation. A three-dimensional Eulerian–Eulerian two phase (sewage-granular sludge) fluid model was applied to investigate the impact of water distribution system on the internal flow field by considering the ratio α of hole area to reactor area. Results showed that the flow state of sludge granules changed periodically when the sludge bed reached a stabilization stage, and every cycle included two periods (U period and D period), where U stands for up-flow of the granular sludge and D represents down-flow. Keeping the upward-flow velocity of reactor at 3 m/h and reducing ratio α from 1.44% to 0.25%, the flow state of the two periods changed differently and was closely related to the height of reactor. Besides, the ratio α could affect the homogeneity of sludge granules, which could further influence the performance of the reactor. In addition, a validation experiment was conducted to verify the practical applicability of the fluid model, a good relationship between simulation and experiment was discovered, which further confirmed that the ratio α of water distribution system has significant impact on the internal flow field of EGSB.

Numerical study on jet effect in the vertical showerhead MOCVD reactor

Numerical simulations are conducted about jet effects in the vertical showerhead MOCVD reactor. By varying the reactor height, nozzle spacing, jet speed and susceptor rotating speed, the flow, temperature and concentration fields in the reactor are simulated, so as to gain insights into the jet effect in vertical MOCVD reactor. It is concluded that (1) in the reactor chamber below the showerhead, velocity, temperature and concentration are all in periodic fluctuation, and the fluctuations decay gradually from the susceptor center to the edge; (2) the vertical velocity at the susceptor center is larger than that in the edge, the precursor concentration in the center is higher than that in the edge, and the temperature in the center is lower than that in the edge; (3) increasing the reactor height and the susceptor rotating speed, decreasing the nozzle spacing and the jet outlet velocity, the radial fluctuations of both axial jet velocity and precursor concentration will be depressed.

The influence of reactor height adjustment on properties in GaN films grown on 6H-SiC by metal organic chemical vapor deposition

The influence of reactor height adjustment on properties in GaN films grown on 6H-SiC by metal organic chemical vapor deposition (MOCVD) was investigated. The property of GaN epilayer was investigated by atomic force microscopy, X-ray diffraction, low-temperature (10 K) photoluminescence and the Raman scattering. It is found that, as the spacing between showerhead and susceptor decreased, the growth rate increased and the tensile stress decreased. This result may be useful to control the stress in GaN thin films grown on silicon carbide substrate by MOCVD.

A three dimensional CFD simulation and optimization of direct DME synthesis in a fixed bed reactor

In this study, a comprehensive three-dimensional dynamic model was developed for simulating the flow behavior and catalytic coupling reactions for direct synthesis of dimethyl ether (DME) from syngas including CO2 in a fixed bed reactor at commercial scale under both adiabatic and isothermal conditions. For this purpose, a computational fluid dynamic (CFD) simulation was carried out through which the standard k-ɛ model with 10% turbulence tolerations was implemented. At first, an adiabatic fixed bed reactor was simulated and the obtained results were compared with those of an equivalent commercial slurry reactor. Then the concentration and temperature profiles along the reactor were predicted. Consequently, the optimum temperature, pressure, hydrogen to carbon monoxide ratio in the feedstock and the reactor height under different operation conditions were determined. Finally, the results obtained from this three-dimensional dynamic model under appropriate industrial boundary conditions were compared with those of others available in literature to verify the model. Next, through changing the boundary conditions, the simulation was performed for an isothermal fixed bed reactor. Furthermore, it was revealed that, under isothermal conditions, the performed equilibrium simulations were done for a single phase system. Considering the simultaneous effects of temperature and pressure, the optimum operation conditions for the isothermal and adiabatic fixed bed reactors were investigated. The results of the H2+CO conversions indicated that, under isothermal condition, higher conversion could be achieved, in compared with that under adiabatic conditions. Then, the effects of various operating parameters, including the pressure and temperature, of the reactor on the DME production were examined. Ultimately the CFD modeling results generated in the present work showed reasonable agreement with previously obtained data available in the literature.

Salient features of deactivation of an iron oxide catalyst for dehydrogenation of methylbutenes to isoprene in industrial adiabatic reactors

The problems of deactivation of iron oxide catalysts in the process of industrial dehydrogenation of methylbutenes to isoprene have been considered. The dependence of deactivation of the catalyst fixed bed on the time on-stream of different sections of the catalyst along the reactor height has been examined. The cause of poor performance of a part of the catalyst bed has been revealed and substantiated. Based of the results of the study, the authors propose an approach to predicting the catalyst performance during a long time on-stream.

Performance of an anaerobic-aerobic reactor and kinetic study of organic matter removal of cattle slaughterhouse effluent

This paper sought to evaluate the behavior of an upflow Anaerobic-Aerobic Fixed Bed Reactor (AAFBR) in the treatment of cattle slaughterhouse effluent and determine apparent kinetic constants of the organic matter removal. The AAFBR was operated with no recirculation (Phase I) and with 50% of effluent recirculation (Phase II), with θ of 11h and 8h. In terms of pH, bicarbonate alkalinity and volatile acids, the results indicated the reactor ability to maintain favorable conditions for the biological processes involved in the organic matter removal in both operational phases. The average removal efficiencies of organic matter along the reactor height, expressed in terms of raw COD, were 49% and 68% in Phase I and 54% and 86% in Phase II for θ of 11h and 8h, respectively. The results of the filtered COD indicated removal efficiency of 52% and k = 0.0857h-1 to θ of 11h and 42% and k = 0.0880h-1 to θ of 8h in the Phase I. In Phase II, the removal efficiencies were 59% and 51% to θ of 11h and 8h, with k = 0.1238h-1 and k = 0.1075 h-1, respectively. The first order kinetic model showed good adjustment and described adequately the kinetics of organic matter removal for θ of 11h, with r² equal to 0.9734 and 0.9591 to the Phases I and II, respectively.

Controlling the freeboard temperature applying a novel design of fluidized bed

An experimental study on controlling the temperature of gases in the freeboard applying a novel fluidized bed configuration has been carried out. A bubbling fluidized bed reactor of 300mm ID is equipped with a jet pipe of 38.1mm ID to adopt the novel configuration. A part of air is fed through the jet pipe to be issued vertically near the bed surface creating a large fountain of particles in the freeboard. The remaining part of air is fed through the distributor plate to fluidize bed solids. A third stream of hot air at 300°C is introduced in the freeboard beyond the main bed to simulate a heat generation source. The hot air is evenly distributed over the reactor cross section using a special pipe. Due to contacting the hot air with the entrained particles, its temperature is dampened while the bed solids heat-up. After a certain period of time the bed temperature profile evens out. The obtained results demonstrate that the fountain particles are very effective in transporting heat from the freeboard gases to the bed that minimizes the temperature difference between them, i.e., better control of the freeboard temperature. The bed stabilizes at a higher temperature while the freeboard temperature is better controlled with increasing the jet velocity and with decreasing bed particles sizes. Moreover, by applying the novel configuration the freeboard temperature can be effectively controlled to a higher extent along the reactor height compared with the splashing zone of conventional operation.

Investigation of Air and Air-Steam Gasification of High Carbon Wood Ash in a Fluidized Bed Reactor

The pulp and paper industry in an effort to offset fossil fuel demand uses woody biomass combustion as a renewable energy source to meet their ever-growing energy demands. Boiler combustion systems are often used to provide this energy. However, large amounts of high carbon ash are produced from some boilers resulting in technological, economic and environmental challenge. This high carbon ash is considered to be of very little economic and environmental value and is typically sent to landfills. Reuse of this ash in some boilers requires upgrading and is not economically feasible. Therefore, this study investigates the feasibility of gasifying high carbon wood ash of particle sizes smaller than 3 mm, while comparing its behaviour to that of unburned wood. Gasification was conducted in a stainless steel bubbling fluidized bed reactor 3-inch diameter and height of approximately 800 mm using air and air-steam as gasifying agents. Parameters of interest included equivalence ratio (ER), gas calorific value, carbon conversion efficiency and produced gas yield. High carbon ash was successfully gasified at low temperatures and atmospheric pressure and showed similar trends as woody biomass. The higher heating value (HHV) and carbon conversion efficiency increased with increasing temperature. The H2/CO molar ratio was higher for the air-steam process. Future areas of research could include investigating the viability of producing a gas of even higher heating value.

Modeling of the CO2Absorption in a Wetted Wall Column by Piperazine Solutions

Theoretical and experimental investigations on the reactive absorption of CO2 in aqueous solutions of PZ using a wetted wall column are presented. A rigorous two dimensional absorption model, accounting for kinetics, hydrodynamics and thermodynamics, has been developed for a wetted wall column. Major innovative features of the model, compared to previous work, are the account on the variation of the gas-side CO2 concentration over the reactor height as well as the computation of the gas-liquid equilibrium by a thermodynamically consistent approach.A laboratory-scale wetted wall column was conceived and constructed and the gas-side mass-transfer coefficient was estimated. CO2 absorption experiments were carried out on unloaded and loaded aqueous solutions of PZ over the range of 298-331 K, and for total PZ concentrations varying from 0.2 to 1 M. The reactor model permitted to predict the absorption fluxes in loaded as well as in unloaded solutions with an excellent accuracy, i.e. 3.2% AAD. In loaded solutions, the gas-side CO2 concentration gradient, as well as the dicarbamate formation reaction has to be taken into account.

Effect of ultrasonic waves on pasteurization of sour cherry juice

The objective of this study was to explore the effects of ultrasound probe diameter, reactor diameter, and juice level in the reactor upon effectiveness of ultrasound waves on decontamination of sour cherry juice. Results showed that the effects of probe diameter, reactor diameter and reactor height were significant (P<0.01). In addition, by increasing the probe diameter from 30 to 40 mm no significant effect was seen in reactors with 65 and 75 mm diameter; however, for 85 mm diameter reactor, the effect of ultrasound waves diminished and, as a result, the total microbial count increased. Increasing the probe diameter from 20 to 30 and then 40 mm, on the average decreased the total microbial count by 15% and 5%, respectively. This effect was obvious at 85 mm diameter, and any increase in height steepened the slope of total microbial count. Finally, using the response surface method (RSM), optimum values were obtained for reactor diameter, reactor height, and probe diameter.

Experimental Investigation on Flow Behaviors in a Novel In Situ Gasification Chemical Looping Combustion Apparatus

A novel cold reactor apparatus for in situ gasification chemical looping combustion (iG-CLC) is proposed and investigated. It is mainly comprised of a circulating fluidized bed (CFB) riser as the fuel reactor and a cross-flow moving bed as the air reactor. The direct hydraulic link between the two reactors brings inherent simplicity and stabilization of the whole system. The CFB fuel reactor provides favorable gas–solids contacts over the whole reactor height. The realization of high solids flux operation conditions greatly enhances the solids holdups, and the gas–solids contacts and reactions in the riser. The moving bed air reactor has advantages in terms of having a low pressure drop, continuous solids flow, and large gas–solids contact area except for the risk of plugging and particle leakage caused by excessive high cross-flow gas velocity. Independent pressure adjustments between the two reactors could control the gas flow direction and restrain the gas bypassing to ensure high CO2 concentration wit...

Design of an ion transport membrane reactor for gas turbine combustion application

The use of ion transport membrane reactors to substitute the conventional gas turbine combustors is a promising technology for the applications of ZEPP. An ITM monolith structure reactor design is introduced in this study for substituting a conventional gas turbine combustor. Due to reactor symmetry, only 3D four quarters of four adjacent channels sharing one common edge are considered in all simulations using LSCF1991 membranes. Effect of feed and sweep flow rates have been considered and it was calculated in order to meet the power required for the reactor and keeping the reactor size as compact as possible. Effects of flow configurations, channel width and percentage of CH4 in the permeate side flow are introduced under constant inlet gas temperature of 1173K and fixed operating pressure of 1000000 Pa. The reactor geometry has been calculated based on the calculations of the minimum possible channel width. Counter-current flow configuration design resulted in improved oxygen permeation flux and improved heat transfer characteristics. However, this flow configuration resulted in unacceptable increase in the membrane temperature. It was found that any reduction in the channel width below 15mm results in large increase in the viscous pressure drop. Also, increasing the amount of CH4 in the permeate side over 5% was found to be non-applicable because of oxygen permeation flux limitation. The reactor length was fixed to 0.9m to be similar to that of real gas turbine combustors with 25,000 channels for each stream. The present reactor design resulted in a reactor height of 3.35m and overall volume and membrane surface area of 10m3 and 2700m2, respectively. The reactor is capable of delivering power ranging from 5 to 8MWe based on cycle first law efficiency.

Effect of Vibrating Sparger on Mass Transfer, Gas Holdup, and Bubble Size in a Bubble Column Reactor

Abstract Bubble size has a key role in gas holdup and mass transfer in bubble column reactors. In order to have small and uniform bubbles, a new structure was designed; the reactor operates in two modes, with vibrating sparger and conventional bubble column in which sparger is fixed. In vibrating mode, the sparger vibrates gently during gas entering. The vibrating sparger performs like a paddle, resulting in a forced recirculation of gas–liquid inside the reactor; moreover, the bubble detachment is accelerated. The superficial gas velocity was between 0.003 and 0.013 ms− 1, and the vibration frequency was changed between 0 and 10.3 Hz. The bubble size was measured at three various positions of the reactor height by photographic method and using MATLAB 7.0.1 software. The mass transfer coefficient was determined by means of the dynamic gassing-out method. The results show that the bubbles were bigger in vibrating mode than those working without vibration. The bubble size decreases with increase in height from sparger. Gas holdup increased with increase in superficial gas velocity and vibration frequency. The effect of vibration increased the gas holdup with an average of 70% for all superficial gas velocities. Volumetric mass transfer coefficient was almost stable as vibration frequency increased.

Influence of sonochemical reactor diameter and liquid height on methyl orange degradation under 200 kHz indirect sonication

The relatively high sonochemical activity in the frequency range 200–600kHz, makes these high frequencies attractive for contaminant remediation. However, high frequency ultrasound also suffers from higher acoustic energy attenuation and inherent low intensity which limits the volume coverage and hence practical application. In this study, in order to clearly understand the relationship between the sonochemical activity and acoustic energy attenuation, calorimetric and degradation studies using methyl orange (MO) as a contaminant surrogate were investigated with indirect sonication at 200kHz (transducer diameter: 65mm) with various cylindrical glass reactors of different diameter (20, 48, 65, 95 and 117mm) and liquid height (21, 58, 81 and 118mm). It was clear that both reactor diameter and liquid height significantly influenced degradation efficiency. In addition to the inherent acoustic pressure distribution within the reactor due to the transducer acoustic pressure profile, the diameter of the reactor affected mainly attenuation of ultrasound in the radial direction, while attenuation in the axial direction was principally influenced by reactor height. A 95mm diameter reactor with a ratio (reactor diameter/transducer diameter) of 1.45, exhibited the highest sonochemical efficiency and acoustic energy transfer efficiency across a range of liquid heights.

Modeling and simulation of nitrogen oxides adsorption in fluidized bed reactors

NOx adsorption in a fluidized bed reactor was investigated by both experiment and simulation. In the experiment, NOx adsorption was tested at different temperatures, inlet NO concentrations and gas velocities. The experimental breakthrough curves were then used to tune the model, which consists of three mass balance equations for solid phase, gas in the dense phase and gas in the bubble phase, respectively. Adsorption isotherms were obtained separately from the fixed bed adsorption experiment with the same catalyst. Bed expansion was obtained experimentally in a fluidized bed with the same catalyst particles. The model showed good agreement with the experimental breakthrough curves and was used to simulate NOx concentration profiles in each phase along the reactor height. Simulation results showed that the NOx adsorption performance in fluidized beds could be improved by reducing particle size and the superficial gas velocity. The model was also applied to investigate the NOx adsorption performance in the adsorption zone of an internal circulating fluidized bed deNOx reactor.