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Abstract Rotating packed bed (RPB) absorber using monoethanolamine (MEA) as the solvent to capture CO 2 is modelled at steady state condition in this study according to the first principles in gPROMS®. The effect of eight different kinetic reaction models and five enhancement factors is examined based on the newly developed model. Selection of kinetic model has a significant effect on the carbon capture level (CCL) but the effect of enhancement factor relation is not important. The steady state process model is validated against the experimental data and showed good agreement. The average absolute relative deviation for 12 case-runs is 3.5%. In addition, process analysis is performed to evaluate the effect of four factors namely rotor speed, MEA concentration in lean MEA solution, lean MEA solution temperature and lean MEA solution flow rate on CCL. Finally, the orthogonal array design (OAD) method is applied to analyse the simultaneous effect of the above-mentioned factors in the CCL and motor power of RPB absorber by considering 25 scenarios. The result of using OAD revealed that rotor speed has the most important effect on CCL, and after that lean MEA solution flow rate has the second importance. In addition, the OAD method is used to find the proper combination of four factors that resulted in about 90% CCL with low motor power. Highlights • Rate-based steady state model for RPB absorber using concentrated MEA solution is presented. • Correct thermodynamic, kinetic, transport, and hydraulic models are used. • Kinetic models and different enhancement factors are compared with each other. • Process analysis is performed by evaluating the effect of different parameters on CO 2 capture level. • OAD method is applied to examine the simultaneous effect of different parameters. [ABSTRACT FROM AUTHOR]

The conversion of CO2 into CO and O2 in a quartz cylindrical packed-bed dielectric reactor has been studied using CO2 and Ar gas mixtures at atmospheric pressure and near ambient temperature with quartz wool, γ-Al2O3, and TiO2 packing. The highest energy efficiencies and conversion rates were observed with TiO2 packing in 20% CO2 in Ar: 30% conversion with 2.9% energy efficiency, and 17.5% conversion with 5.0% energy efficiency. Both γ-Al2O3 and quartz wool also showed an enhancement in conversion over an unpacked reactor. The percentage of CO2 to Ar in the range of 20%–60% is shown to have only a minor effect on reactor performance. Conversion as a function of power input and flow rate is studied in detail for γ-Al2O3 and TiO2 packing with similar particle sizes. In both cases, simple chemical kinetic models show that the CO production rate is nearly equal for both materials, while reverse reaction rates to CO2 are doubled for γ-Al2O3 compared to TiO2. From detailed charge–voltage (Q-V) analysis of all four reactor configurations, it is revealed that the electric field at which discharging occurs is higher for both γ-Al2O3 and TiO2 as compared to the empty or quartz wool filled reactors. Comparing kinetic model results with the electrical Q-V analysis, it appears likely that the higher and similar magnitude electric fields occurring with γ-Al2O3 and TiO2 are directly responsible for the increased CO production rates via increased electron energies in the discharge. The higher reverse reaction rates for γ-Al2O3, and its subsequent poorer performance compared to TiO2, can be attributed to a significantly higher effective surface area, which increases undesirable surface reactions between CO and oxygen species. [ABSTRACT FROM AUTHOR]

A mixotrophic system consisting of heterotrophic and autotrophic denitrification (HAD) is a reliable system to enhance the denitrification performance of individual systems. In this study, a novel heterotrophic denitrification coupled with an electro-autotrophic denitrifying packed bed reactor (HEAD-PBR) was developed for the treatment of nitrate-contaminated groundwater. Because of the combination of electrochemical and biological denitrification processes in series, electrochemical inhibition of microorganisms was eliminated, and sufficient hydrogen was supplied safely. The efficiency of HEAD-PBR was evaluated using synthetic groundwater (containing 50 and 25 mg N/L of NO 3 − ) at different hydraulic retention times. A high nitrate removal efficiency (∼99%) was achieved, the electrolysis, heterotrophic denitrification, and autotrophic denitrification were responsible for 15.6%–23.4%, 44.6%–68.4% and 15.7%–31.7% of nitrate removal, respectively. This effective material conversion can be attributed to microbial ecological interactions such as sufficient utilization of sawdust and proper consumption of hydrogen, oxygen, and ammonia. The HEAD-PBR was found to be an efficient reactor system with high treatment capacity, but without accumulation of byproduct in effluent. Thus, HEAD-PBR is a promising reactor configuration for nitrate removal and implementation of HAD technology. [ABSTRACT FROM AUTHOR]

Open-cell solid foams are tested for the first time as prospective structured packings in floating columns to evaluate their potential for offshore multiphase reactor applications. Using a hexapod ship motion simulator and low-intrusive wire-mesh sensors, the effect of floating vessel motions on the hydrodynamic behavior of SiSiC foam packed beds operated with concurrent descending gas-liquid flow was comprehensively investigated. The response of gas-liquid distribution, overall bed pressure drop, and liquid axial dispersion to column tilts as well as translational and rotational motions was acquired and compared to their corresponding stationary (onshore) analog configuration. Maldistribution sensitivity and susceptibility of solid-foam packed beds subject to ship tilts and accelerations were interpreted in terms of fluid uniformity factor. Moreover, a stimulus-response tracer pulse technique and a macro-mixing model were used to estimate the liquid mean residence time and Péclet number. Similar to random packings, fluid maldistribution was found to prevail in solid-foam beds with deviations from uniformity greater for rotational than for translational perturbations. Vessel tilts and oscillations adversely affect open-cell foam bed hydrodynamic performance yielding transient gas-liquid segregated flow regimes, oscillations of pressure drop and uniformity factor, as well as notable deviation from liquid plug flow. [ABSTRACT FROM AUTHOR]

Palladium-based membrane-assisted fluidized bed reactors have been proposed for the production of ultra-pure hydrogen at small scales. Due to the improved heat and mass transfer characteristics inside such reactors, it is commonly believed that they can outperform packed bed membrane reactor configurations. It has been widely shown that the performance of packed bed membrane reactors can suffer from serious mass transfer limitations from the bulk of the catalyst bed to the surface of the membranes (concentration polarization) when using modern highly permeable membranes. The extent of concentration polarization in fluidized bed membrane reactors has not yet been researched in detail. In this work, we have quantified the concentration polarization effect inside fluidized bed membrane reactors with immersed vertical membranes with high hydrogen fluxes. A Two-Fluid Model (TFM) was used to quantify the extent of concentration polarization and to visualize the concentration profiles near the membrane. The concentration profiles were simplified to a mass transfer boundary layer (typically 1 cm in thickness), which was implemented in a 1D fluidized bed membrane reactor model to account for the concentration polarization effects. Predictions by the TFM and the extended 1D model showed very good agreement with experimental hydrogen flux data. The experiments and models show that concentration polarization can reduce the hydrogen flux by a factor of 3 even at low H 2 concentrations in the feed (10%), which confirms that concentration polarization can also significantly affect the performance of fluidized bed membrane reactors when integrating highly permeable membranes, but to a somewhat lesser extent than packed bed membrane reactors. The extraction of hydrogen also affects the gas velocity and solids hold-up profiles in the fluidized bed. [ABSTRACT FROM AUTHOR]

Hydrogen production by steam-methane reforming in membrane-assisted reactors has attracted substantial interest over the years. A variety of models for membrane-assisted reactors have been developed and suggested in the literature. In particular, examining the membrane models applied to the fixed packed bed reactor concept, there is no consensus or guidelines in the literature regarding the formulation of the heat balances (in terms of temperature). Thus, in the present study, different mathematical models for a fixed packed bed reactor with an integrated membrane have been compared in order to elucidate the effects of different model assumptions formulating the heat balance. The model formulations were examined by application to the steam-methane reforming process with hydrogen removal. The main findings of the present theoretical study are: • With an increased temperature difference between the reaction and permeation zones, the enthalpy associated with the mass flux across the membrane has an increased effect on the temperature in the permeation zone. • The temperature profile in the reaction zone is not influenced by the enthalpy difference across the membrane. Hence, in cases where it is not required with an accurate model prediction of the sweep gas temperature, the membrane reactor model can be simplified assuming isothermal condition in the permeation zone. The present study presents a rigorous derivation and examination of cross-sectional averaged models for membrane-assisted fixed packed bed reactors. Considering the level of details in the model formulations analyzed in this study, there exists currently no appropriate experimental data for model validations. [ABSTRACT FROM AUTHOR]

A simplified transient model for fixed-bed reactors was extended to account for the heat sink effect of the phase change material diluent in the Fischer-Tropsch reactor energy balance. The resulting model was found to accurately approximate the more rigorous two-dimensional model with significantly less computational requirements even at the hotspot, where the reactor enthalpy balance is most sensitive. As anticipated, the presence of the encapsulated phase change material in the reactor induced thermal inertia, thereby restricting the temperature ramp rate in the reactor to acceptably safe operational limits for the catalyst. Although there was a reduction in both the CH4 and C5+ productivity, the reduction in CH4 production was up to four times that of the C5+ at the same coolant temperature. [ABSTRACT FROM AUTHOR]

A comparative study of Fischer-Tropsch synthesis for synthesizing liquid hydrocarbons from syngas was carried out in a conventional packed bed reactor and in a water perm-selective membrane reactor over iron and cobalt catalysts. The process was performed under different operating conditions, such as inlet syngas feed molar ratio, total pressure, gas velocity, temperature, reactor dimensions and sweep fluid ratio. The main simulation results show that the use of the concept of membrane reactor can improve the process performance compared to that obtained in the case of the conventional packed bed reactor. Furthermore, under certain operating conditions, the process could be intensified by a reduction of carbon monoxide conversion magnitude via the water-gas shift reaction. This is possible by using a hydrophilic membrane. Our findings indicate that the membrane reactor provides a quasi-complete conversion of carbon monoxide over iron- or cobalt-based catalysts. [ABSTRACT FROM AUTHOR]

A kinetic model for the methane steam reforming has been investigated. The performances are compared between the packed bed reactor and catalytic membrane reactor with metal foam catalyst support. The effects of various variables such as pressure, temperature of the reaction, ratio of methane to steam in feed, thickness of membrane and sweep gas on the total methane conversion and hydrogen production were investigated qualitatively. The comparison between these two types of reactors was carried out in the temperature range of 350 °C–750 °C and pressure range of 2–30 bar. Isothermal modeling has been performed and showed a higher performance of the membrane reactor rather than the packed bed reactor. Methane conversion can be reached 100% for lower temperatures than used with industrial PBR, and better performances are reached with an increase of the operating pressure. The maximum conversion of methane for the CMR is quickly reached while the conversion evolution observed for the PBR is smoother. [ABSTRACT FROM AUTHOR]

Abstract: A novel kind of biodegradable polymer, i.e., starch/polycaprolactone (SPCL) was prepared and used as carbon source and biofilm support for biological denitrification in a packed-bed bioreactor. The denitrification performances and microbial diversity of biofilm under different operating conditions were investigated. The results showed that the average denitrification rate was 0.64±0.06kgN/(m3 d), and NH3–N formation (below 1mg/L) was observed during denitrification. The nitrate removal efficiency at 15°C was only 55.06% of that at 25°C. An initial excess release of DOC could be caused by rapid biodegradation of starch in the surfaces of SPCL granules, then it decreased to 10.08mg/L. The vast majority of species on SPCL biofilm sample (99.71%) belonged to six major phyla: Proteobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Spirochaetes and Actinobacteria. Proteobacteria were the most abundant phylum (85.50%) and mainly consisted of β-proteobacteria (82.39%). Diaphorobacter and Acidovorax constituted 52.75% of the identified genera which were denitrifying bacteria. [Copyright &y& Elsevier]

Abstract: Packed beds are the commonly used storage units for air-based solar system. Stratification improves the efficiency of collector with the bed and a decrease of void fraction lead to an increase in stratification. Therefore an experimental study in a low range of void fraction is carried out in this paper so as to increase the stratification. Five different shapes of large sized storage elements of concrete were used and arranged differently to obtain four values of void fraction including the lowest possible void fractions that could be obtained for spherical elements. Correlations were developed for Nusselt number and friction factor by taking into account the effect of system parameters on them. The Nusselt number was maximum for spherical elements (ψ =1.0) and at the minimum value of void fraction (0.275) whereas the friction factor is found to be minimum for cubical elements (ψ =0.80) and at the maximum value of void fraction (0.48). The stratification coefficient has been found to be maximum for the minimum value of void fraction (0.275) and for the bed of spheres (ψ =1.0). With spherical elements and for lowest void fraction the thermo-hydraulic performance is having the maximum value. [Copyright &y& Elsevier]

Abstract: A heterogeneous model has been derived for a fixed-packed bed reactor producing methanol. The intra-particle mass diffusion fluxes are described according to the Maxwell–Stefan and dusty gas closure laws and a bi-dispersed random pore model is adopted to elucidate the effects of the pellet pore size distribution on the impact of the reactor performance. The simulation results reveal that the overall reactor performance is sensitive to the the bimodal description of the pore size within the catalyst pellet due to the Knudsen diffusion mechanism. Although the dusty gas model has been frequently adopted in chemical reactor modeling, the model has certain shortcomings that have been subjected to criticism in the literature. [Copyright &y& Elsevier]

The aim of this study was to investigate the performance of bench-scale packed-bed reactors for hydrogenotrophic denitrification with hydrogen produced from electrolysis of water and electric energy provided by a solar cell. Two configurations were used, a single filter and a triple-column reactor, with gravel of different sizes as support media. The effect of hydrogen and carbon dioxide supply on the performance of the two systems of bioreactors under continuous operation was examined. The multi-filter system achieved high performances as it could safely treat polluted water with a low hydrogen and carbon dioxide consumption. A denitrification rate of 2 kg/m3d was achieved for nitrate nitrogen and hydraulic loading of 1.44 g NO-3-N/d and 11.5 m3/m2d, respectively. Also, a mathematical model was developed by using growth kinetics expressions for four-nutrient limitation (nitrate, nitrite, hydrogen and carbon dioxide) with inhibition by nitrate. The proposed model is capable of describing accurately enough, hydrogenotrophic denitrification under continuous operation. [ABSTRACT FROM AUTHOR]

The article presents an experimental study of two types of packed-bed bioreactors for the production of animal cell culturing. It was reported that bioreactors were operated in the perfusion mode which does not provide hydrodynamic forces to the cell, which facilitate maximum growth of the cell and protein expression. It was found that alkaline phosphatase-secreting recombinant CHO cell line was used for the evaluation of the impact of bioreactor on the protein production. Cell production and cell proliferation were assayed on the basis of alkaline phosphatase (ALKP) production and glucose utilization