Lab-scale Packed Bed Reactor Research Articles

Modelling and optimization of biodiesel production from waste fish oil using nano immobilized rPichiapastoris whole cell biocatalyst with response surface methodology and hybrid artificial neural network based approach

In this study, zinc oxide (ZnO) nano particle immobilized recombinant whole cell biocatalyst (rWCB) was used for bioconversion of waste fish oil in to biodiesel in a lab scale packed bed reactor (PBR). Central composite design and hybrid artificial neural network (ANN) models were explored to optimize the production of biodiesel. Developed rWCB exhibited maximum lipase activity at 15 % (v/v) of glutaraldehyde concentration and 6 % (w/v) of ZnO nanoparticles at pH of 7. Maximum biodiesel yield reached about 91.54 ± 1.86 % after 43 h in PBR using hybrid ANN model predicted process conditions of 13.2 % (w/v) of nano immobilized rWCB concentration and 4.7:1 of methanol to oil ratio at 33 °C. Importantly, developed nano immobilized rWCB was adequately stable for commercialization. Thus, production of biodiesel from waste fish oil using ZnO nano immobilized rWCB could become potential candidate for commercialization.

Numerical modeling of chemical looping oxidative dehydrogenation of ethane in parallel packed beds

Chemical looping oxidative dehydrogenation (CL-ODH) of ethane has the potential to be a highly efficient alternative to steam cracking for ethylene production. Accurate reactor modeling is of critical importance to efficiently scale up and optimize this new technology. This study reports a one-dimensional, heterogeneous packed bed model to simulate the CL-ODH of ethane to ethylene with a Na2MoO4-promoted CaTi0.1Mn0.9O3 redox catalyst. The overall reaction kinetics was well-described by coupling the gas-phase steam cracking of ethane with the reduction kinetics of the redox catalyst by H2 and C2H4. The impact of H2 on the formation rate of CO2 byproduct from C2H4 conversion was also thoroughly investigated to validate the applicability of the kinetic model under operational environments. The temperature variation within the different CL-ODH steps and the temperature distribution along the bed were also carefully considered. The accuracy of the model was validated by experiments conducted in a large lab-scale packed bed reactor (200 g catalyst loading), with an average deviation of 2.8% in terms of ethane conversion and ethylene yield. The model was subsequently used to optimize the operating parameters of the CL-ODH reactor, indicating that up to 63.7% single-pass C2 + olefin yield can be achieved with the current redox catalyst bed whereas further optimization of the redox catalyst to inhibit C2H4 activation can result in 69.4% single-pass C2 + yield while maintaining low CO2 selectivity.

Oxygen separation via chemical looping of the perovskite oxide Sr0.8Ca0.2FeO3 in packed bed reactors for the production of nitrogen from air

A redox chemical looping process is investigated as an add-on deoxygenation unit for the production of high-purity nitrogen from air using pressure swing adsorption systems. A material screening study indicated the non-stoichiometric perovskite oxide Sr0.8Ca0.2FeO3−δ as a promising candidate redox material with fast kinetics and a 75% greater gravimetric oxygen capacity compared to state-of-the-art SrFeO3 at the desired process conditions. Granules of Sr0.8Ca0.2FeO3 were manufactured and characterised according to their thermodynamic and kinetic redox properties. A lab scale packed-bed reactor was experimentally tested as proof-of-concept and used to validate a convection–diffusion model of mass transfer within the reactor. The model was further applied for scaling up to a production of 1000 Nm3h−1 of high-purity nitrogen. The results indicate good performance of the packed-bed configuration and a favourable energy demand compared with existing nitrogen production technologies. The proposed technology could greatly extend the useable oxygen impurity range of pressure swing adsorption systems for nitrogen production.

Lab-scale experimental demonstration of Ca[sbnd]Cu chemical looping for hydrogen production and in-situ CO2 capture from a steel-mill

In the present work, a lab-scale packed bed reactor has been used to decarbonize mixtures of inlet gases simulating the typical composition of blast furnace gases (BFG) and convert them to H2-rich streams by means of the CaCu chemical looping concept. The reactor was packed with 355 g of Cu-based oxygen carrier (OC) supported on Al2O3 and natural Ca-based sorbent. The three main reaction stages; namely (i) Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH), (ii) Cu oxidation and (iii) Regeneration of carbonated Ca-based sorbent were examined. In CASOH stage, BFG is converted into H2-rich stream (17% by vol.) under the experimental conditions of 600 °C, 5.0 bar and S/CO molar ratio of 2.0. A controlled oxidation causes a mere 3.5% of CaCO3 to decompose during the Cu-oxidation stage. This resulted in a nearly pure N2 stream at 600 °C and 5.0 bar operating conditions. During the regeneration stage, BFG and mixture of BFG and CH4 is used as a reducing fuel. To ensure the amount of heat needed for the decomposition of CaCO3 during the reduction of CuO, a 1.4 CuO/CaCO3 molar ratio has been used. It resulted in 46% CO2 in N2 at the end of the reduction/calcination stage.

New insights into Mn2O3 based metal oxide granulation technique with enhanced chemical and mechanical stability for thermochemical energy storage in packed bed reactors

High temperature thermochemical energy storage still requires a significant research effort. Most of the research has been carried out with materials at lab-scale, and proper material fabrication techniques need to be developed in order to make feasible the upscaling of the technology. Agglomeration, abrasion, or low volumetric energy density are some negative consequences observed when trying to pass from the powder state to the material shape and amount required for a thermochemical reactor. In this work, an established granulation technique is investigated, using a Si-doped manganese oxide as active material to determine the critical parameters that provide the best chemical and mechanical stability of the granules. The granulation process uses a polymeric binder to give consistency to the granules and later, it is removed to create a porous structure to facilitate the oxygen diffusion in and out of the granule. We identified the positive effect of decreasing the bath temperature to increase the volumetric energy density of the granules. Furthermore, it was observed that increasing the mechanical stability through a high temperature treatment did not decrease the chemical stability of the material. In order to provide the first insights into the scalability of the solution, the chemical and mechanical stability of the granules have been satisfactorily checked during 100 redox cycles, out of which 50 were carried out in a home-made lab-scale packed bed reactor with an inner diameter of 13 mm and another 50 redox cycles in a simultaneous thermal analyzer.

Abatement of oil residues from produced water using a thermocatalytic packed bed reactor

Produced water is a major waste and environmental concern in the oil and gas industry, since it contains dispersed oil and dissolved compounds, which may harm the aquatic environment. Thus, focus on the offshore treatment of the produced water is required. Current methods include hydrocyclones and water clarifiers that cannot achieve full abatement of the oily contaminants. Here we propose a novel thermocatalytic degradation of the dispersed oil using a thermocatalyst, namely Sr0.85Ce0.15FeO3 perovskite that benefits from the thermal energy contained in the produced water, which has temperatures of 40–50 °C when reaching the cleaning phase. It is found that the oil is removed faster with higher perovskite concentrations, and the initial removal is mainly adsorption to the perovskite surface followed by catalytic degradation. Based on batch testing, a lab-scale packed bed reactor (PBR) is modelled showing that oil can be continuously removed by sufficient residence time in the reactor.

Optimization of CO2 Adsorption and Physical Properties for Pelletization of Zeolite 5A

This research investigated the effects of compression force, compression time, and addition of bentonite binder on zeolite 5A pelletization. Carbon dioxide (CO2) adsorption of zeolite 5A pellets was tested in a laboratory-scale packed-bed reactor at 298 K, atmospheric pressure and 2 l/h flow rate. Zeolite 5A pellets were prepared using a pelletization technique at 200-400 MPa compressive force, 5-15 min compression time, and with 0-15% wt. of bentonite binder. The specific surface area and density of zeolite 5A pellets increased with increase of compression force. Compression force led to increase in specific surface area and resulted in an agglomeration of zeolite pellets, making CO2 molecules more difficult to become active sorbent. The addition of bentonite into zeolite 5A pellets with more compression time resulted in the reduction of specific surface area. The compression force and mass fraction of the binder were found to offer significant control over CO2 adsorption capacity. No addition of binder, 200 MPa compression force and 5 min compression time resulted in a maximum CO2 adsorption capacity of 3.64 mmol CO2/g. This research indicated that zeolite 5A pellets have a beneficial effect and high potential as an adsorbent, especially in terms of CO2 adsorption and environmental applications

Kinetic Characterization of Tar Reforming on Commercial Ni-Catalyst Pellets Used for In Situ Syngas Cleaning in Biomass Gasification: Experiments and Simulations under Process Conditions.

Filtering-catalytic candles, filled with an annular packed-bed of commercial Ni-catalyst pellets (∼600 g), were successfully tested for in situ syngas cleaning in a fluidized-bed biomass steam gasifier [Fuel Process. Technol.2019, 191, 44−53, DOI: 10.1016/j.fuproc.2019.03.018]. Those tests enabled the macroscopic evaluation of gasification and gas cleaning as a whole, requiring a more specific assessment of the catalyst performance inside the filter candle. To this end, steam reforming tests of tar key compounds (naphthalene and toluene; thiophene in traces to observe sulfur deactivation) were performed with a laboratory-scale packed-bed reactor containing the same catalyst pellets (<7 g). A lumped kinetics was derived, referred to a pseudocomponent representing tars. This was then validated by simulation of the annular catalytic packed bed inside the filter candle, obtaining numerical results in fair agreement with gasifier outputs. As a result, the lab-scale investigation with a small amount of catalyst provides reliable predictions of tar catalytic reforming in industrial-scale filtering-catalytic candles.

Modeling and optimization of tannase production with Triphala in packed bed reactor by response surface methodology, genetic algorithm, and artificial neural network.

In this research, optimization of the production medium to enhance tannase production by Bacillus gottheilii M2S2 in laboratory-scale packed bed reactor was studied. Amount of substrate Triphala, moisture content, aeration rate, and fermentation period was chosen for optimization study. During one variable at a time optimization, the highest tannase activity of 0.226U/gds was shown with Triphala as a substrate at the fermentation period of 32h. Furthermore, the optimum conditions predicted by response surface methodology (RSM) and genetic algorithm (GA) were found to be 11.532g of substrate Triphala, 47.071% of the moisture content, and 1.188L/min of an aeration rate with uppermost tannase activity of 0.262U/gds. In addition, the single hidden layer feedforward neural network (SLFNN) and the radial basis function neural network (RBFNN) of an artificial neural network (ANN) were adopted to compare the prediction performances of the RSM and GA. It revealed that the ANN models (SLFNN, R 2 = 0.9930; and RBFNN, R 2 = 0.9949) were better predictors than the RSM (R 2 = 0.9864). Finally, the validation experiment exhibited 0.265U/gds of tannase activity at the optimized conditions, which is an 11-fold increase compared to unoptimized media in shake flask.

Solid state fermentation of Bacillus gottheilii M2S2 in laboratory-scale packed bed reactor for tannase production

Production of tannase was performed in packed bed reactor filled with an inert support polyurethane foam (PUF) using Bacillus gottheilii M2S2. The influence of process parameters such as fermentation time (24–72 h), tannic acid concentration (0.5–2.5% w/v), inoculum size (7–12% v/v), and aeration rate (0–0.2 L/min) on tannase production with PUF were analyzed using one variable at a time (OVAT) approach. The outcome of OVAT was optimized by central composite design. Based on the statistical investigation, the proposed mathematical model recommends 1% (w/v) of tannic acid, 10% (v/v) of inoculum size and 0.13 L/min of aeration rate for maximum production (76.57 ± 1.25 U/L). The crude enzyme was purified using ammonium sulfate salt precipitation method followed by dialysis. The biochemical properties of partially purified tannase were analyzed and found the optimum pH (4.0), temperature (40 °C) for activity, and Km (1.077 mM) and Vmax (1.11 µM/min) with methyl gallate as a substrate. Based on the SDS-PAGE analysis, tannase exhibited two bands with molecular weights of 57.5 and 42.3 kDa. Briefly, the partially purified tannase showed 4.2 fold increase (63 ± 1.60 U/L) in comparison to the submerged fermentation and the production of tannase was validated by using NMR spectrometer.

New salt hydrate composite for low-grade thermal energy storage

This study aims to develop a new salt-based thermochemical composite for long-term storage of low-grade thermal energy which enables overcoming mismatch between energy demand and supply. The energy density and dehydration behaviour of five different salts; Al2(SO4)3·18H2O and MgSO4·7H2O, CaCl2·6H2O, MgCl2·6H2O, and SrCl2·6H2O are examined. Subsequently, the performance of two low cost host porous structures; expanded clay and pumice, impregnated with the most suitable salt for storing low-grade thermal energy is studied over a few number of cycles using a lab-scale packed bed reactor. The results showed that SrCl2·6H2O has the highest energy density and lowest dehydration temperature so that >80% of its energy density can be stored at <90 °C. Thermal cycling the composite materials revealed that up to 29 kWh/m3 and 7.3 kWh/m3 energy can be stored using expanded clay-SrCl2 (40 wt%) and pumice-SrCl2 (14 wt%), respectively. However, the performance of expanded clay dropped sharply over four cycles while the generated power using pumice composite was sustained almost constant over ten cycles. Although pumice-SrCl2 is a promising composite in terms of cyclability, further research is required to improve its energy storage capacity to make it attractive for large scale applications.

Liquid hydrocarbon production via ethylene oligomerization over Ni-Hβ

We carried out oligomerization of ethylene using nickel supported on an acidic zeolite β (Ni-Hβ) catalyst in a laboratory-scale packed bed reactor for the synthesis of liquid hydrocarbons in milliliter quantities. We evaluated the effect of several process variables (temperature, pressure, weight hourly space velocity (WHSV), and nickel loading) on the ethylene conversion, liquid hydrocarbon/coke yield, and oligomeric product selectivity. Increases in pressure resulted in higher ethylene conversion, leading to a liquid yield of 13.0 wt%, with 10.0 wt% coke at 65 bar. As the pressure increased to 65 bar, the selectivity towards octenes reached 10%, along with a decrease in C4 to 34%, which suggested that higher pressures promoted butene dimerization. Under the conditions studied, a minimum temperature of 120 °C was required to produce liquid hydrocarbons. The liquid yield increased with temperature, with a maximum of 17.0 wt% at 190 °C. Higher temperatures led to the formation of odd-numbered oligomers primarily due to acid-catalyzed cracking reactions. In the range of WHSV tested, a moderate 2.0 h−1 resulted in a local maximum of 10.6 wt% of liquid hydrocarbon yield. A moderate nickel loading of 3.4 wt% also resulted in the highest liquid yield (10.6 wt%) out of the three loadings tested. The results strongly suggest that the ionic form of nickel is much more active catalytically than the NiO form. The variation in nickel loading revealed the importance of having a synergistic balance of nickel and acid sites on the catalyst to maximize ethylene conversion and maintain high liquid hydrocarbon yield. The results from this work formed the basis for pilot scale runs carried out at the Southwest Research Institute (SWRI) for the Advanced Hardwood Biofuels (AHB) project. The pilot runs highlighted the need for efficient removal of ethanol from the ethylene feed after the dehydration process.

Comparative Characterization of a Torrefied Wood Pellet under Steam and Nitrogen Atmospheres

Torrefaction is a pretreatment technology for biomass to enhance its fuel quality for thermal conversion. Torrefied biomass has many advantages for handling and storage including high energy density and hydrophobicity. It also improves the grindability, which is beneficial for cofiring with pulverized coal in a power plant. This study aims to investigate the optimum operating conditions for a biomass torrefaction process using steam as a purge gas. Wood pellets were torrefied using steam heated to between 230 and 300 °C in a lab-scale packed-bed reactor. The characteristics of the torrefied wood pellets (TWPs) were compared to those produced under nitrogen. The results showed that when the temperature increased from 230 to 300 °C, the TWP yield using steam decreased from 82 to 46 wt %, but the carbon content and heating value increased from 54 to 75 wt % and 21.14 to 28.85 MJ/kg, respectively. On the other hand, the TWPs using nitrogen had a slightly larger mass yield but with a lower carbon content and h...

Importance of spinel reaction kinetics in packed-bed chemical looping combustion using a CuO/Al2O3 oxygen carrier

Chemical looping combustion is especially competitive for electrical power generation with integrated CO2 capture when it is operated at high temperatures (1000–1200 °C) and high pressures (15 bar or higher). For these demanding conditions, dynamically operated packed bed reactors have been proposed, providing a good alternative to fluidized bed technology. This work addresses the importance of including the formation and reduction kinetics of spinel compounds to proper predict the packed bed reactor performance by validating a pseudo-homogeneous packed-bed reactor model to describe the redox kinetics of a CuO/Al2O3 oxygen carrier with experiments in a lab-scale packed bed reactor setup. A grain model describing the reaction kinetics of all solid species, including both spinel compounds (CuAl2O4 and CuAlO2), was included in a particle model and used to develop correlations for the effectiveness factor as a function of the particle conversion in order to account for internal solids concentration profiles and mass transfer limitations. The particle effectiveness factors were subsequently included in the source terms of the component mass balances of the reactor model accounting for all the reactions of the spinel compounds. Cyclic experiments (oxidation with air and reduction with a H2-N2 mixture) have been carried out in a lab-scale packed bed reactor with a 12.5 wt% CuO/Al2O3 oxygen carrier at different temperatures ranging from 600 to 1000 °C. The experimental results are well described by the packed bed reactor model, only when including the developed particle effectiveness factors to fully account for the kinetics of the formation and reduction of the spinel compounds. The results confirm that it is neccesary to include a detailed description of the redox kinetics at the particle level to be able to accurately estimate the breakthrough time, cycle time, final amount of Cu present in the bed and the temperature rise in the reactor after reduction/oxidation reactions for packed-bed chemical looping combustion with a CuO/Al2O3 oxygen carrier.

Compound changes in re-refined used lubricating oils using fabricated Packed-bed reactor

This study aimed at developing a laboratory scale packed bed reactor (PBR) and evaluating its performance in the re-refining of used lubricating oils, which will be of benefits from socio-economic and environmental points of view. Used and unused motor oil samples of two brands (Mobil Super SAE 20W-50 and Total Quartz 5000 SAE 20W-50) were used in this study. The sorbent materials were a blend of bentonite, limestone, diatomite, quartz and wood charcoal in the same mass ratio. The compound types of the oils eluted from the PBR and those of used and virgin oil samples were studied for comparison. Fourier-transformed Infrared Spectroscopy was employed to observe the variations in the types and nature of functional groups present in the various oils as well as to estimate the oxidation products of the oils using peak area increase (PAI). The constituent organic compounds were also identified and quantified using Gas Chromatography/Mass Spectrometer. The results revealed that some of the compounds exist in different isomers in the oil samples. The similarity in the classes of compounds is affirmed by their very similar Fourier transformed infrared (FT-IR) spectra. Gas Chromatography/Mass Spectrometry results indicated that the used oils contained the highest number of compounds, followed by the treated oils and also indicated similar treatment effects on the brands of lubricating oil. The study concluded that the developed reactor is a viable and sustainable technique for re-refining of used lubricating oils.

Investigations on thermochemical energy storage based on technical grade manganese-iron oxide in a lab-scale packed bed reactor

Thermochemical energy storage (TCS) based on gas–solid reactions constitutes a promising concept to develop efficient storage solutions with higher energy densities compared to widely investigated sensible and latent thermal energy storage systems. Specifically for high temperature applications multivalent metal oxides represent an interesting storage material, undergoing a reversible redox reaction with oxygen. Due to the inherently high working temperatures such a TCS system could potentially be implemented in future generation concentrated solar power (CSP) plants with central receiver technology, in order to increase the total plant efficiency and ensure the dispatchability of power generation.In this work an experimental test rig with a lab-scale tube reactor has been developed to analyze a packed bed of granular manganese-iron oxide storage material regarding heat and mass transport effects coupled with the chemical reaction. For this purpose manganese-iron oxide with a Fe/Mn molar ratio of 1:3 has been selected as a suitable reference material, which can be prepared from abundant, economical and nonhazardous raw materials. Consequently, in the context of this work the TCS technology is systematically approached based on the reference metal oxide in the temperature range between 800°C and 1040°C in order to derive the main influencing aspects of this storage concept.Experimental results showed the development of characteristic temperature profiles along the bed height, which proved to be dependent on the thermodynamic properties as well as kinetic behavior of the redox reaction. It was demonstrated that bed temperatures could be stabilized due to the proceeding redox reaction in dynamic charging and discharging operation modes. Parametric studies have been carried out to examine the influence of different operating parameters on thermal charging and discharging and to analyze the main limitations affecting the reaction progress. Finally, cycling experiments of the material in the lab-scale reactor exhibited no reactivity degradation over 17 cycles, verifying the comparability of the experimental results obtained from the conducted parametric studies. Analysis and comparison of the raw and cycled material, however, indicated signs of material alterations due to sintering processes.

Physical modeling of the laboratory-scale packed bed reactor for partial gas-phase oxidation of alcohol using gold nanoparticles as the heterogeneous catalyst

Packed bed reactors are often used for catalyst screening studies due to their simple construction and ease of operation. The use of gold nanoparticles for partial oxidation reactions of alcohols has arisen interest of the scientific community. A model was generated to explain the experimentally observed reactor behavior (conversion of alcohol, yields of products) in the alcohol oxidation over gold nanoparticles. The model for this gas-phase heterogeneously catalyzed multi-reaction system consisted of the dynamic mass and energy balances and Langmuir–Hinshelwood–Hougen–Watson, Mars van Krevelen or Power law expressions for the reaction kinetics. Fluid flow was described with convection and dispersion terms. A semi-empirical pressure drop correlation was used. This resulted in a rapidly running model by reducing the problem size significantly. Powerful gPROMS Modelbuilder software was used as the model development, simulation and parameter estimation platform. The primary task was to punctually define and solve the complete set of equations (Partial Differential Equations (PDEs) together with algebraic equations). The modeling effort focused on the selection of the complete set of equations to adjust the degrees of freedom 0 and on the simultaneous solution of the whole set. Numerical method of lines was applied to convert the partial differential equations to ordinary ones. All reactions were assumed to take place on evenly distributed active sites of the porous catalyst particles. The dynamic mass balances consisting of internal diffusion and surface reaction within the porous particles were solved simultaneously with the mass and energy balances of the whole reactor. The axial and radial concentration and temperature profiles inside the reactor and the concentration profiles within the particles were then obtained results. Starting from experiments performed at T=125–250°C, p=1atm and superficial gas velocity of 0.03m/s, a parameter estimation analysis was conducted. After the parameter estimation, the calculated alcohol conversion and yields of the main products (acetaldehyde and acetic acid) followed relatively closely the experimentally observed ones. The estimated parameters were the rate constants and the activation energies and the adsorption parameters (with LHHW kinetics, Mars van Krevelen kinetics) and reaction orders of oxygen (Power law kinetics). Simulation studies were done to show how feed temperature and catalyst loading influenced the results and how the Peclet number reflected on obtained results.

Kinetic studies of CO2 methanation over a Ni/γ-Al2O3 catalyst.

The production of methane by reacting CO2 with H2 (CO2 methanation) has the potential for producing synthetic natural gas, which could be exported using the existing infrastructure for the distribution of natural gas. The methanation of CO2 was investigated over a wide range of partial pressures of products and reactants using (i) a gradientless, spinning-basket reactor operated in batch mode and (ii) a laboratory-scale packed bed reactor operated continuously. The rate and selectivity of CO2 methanation, using a 12 wt% Ni/γ-Al2O3 catalyst, were explored at temperatures 445-497 K and pressures up to 20 bar. Research with the batch reactor showed that the rate increased with increasing partial pressures of H2 and CO2 when the partial pressures of these reactants were low; however, the rate of reaction was found to be insensitive to changes in the partial pressures of H2 and CO2 when their partial pressures were high. A convenient method of determining the effect of H2O on the rate of reaction was also developed using the batch reactor and the inhibitory effect of H2O on CO2 methanation was quantified. The kinetic measurements were compared with a mathematical model of the reactor, in which different kinetic expressions were explored. The kinetics of the reaction were found to be consistent with a mechanism in which adsorbed CO2 dissociated to adsorbed CO and O on the surface of the catalyst with the rate-limiting step being the subsequent dissociation of adsorbed CO. The ability of the kinetic expressions to predict the results from the continuous, packed-bed reactor was explored, with some discrepancies discussed.

Investigation of a Fixed-Bed Reactor for the Calcination of CaCO3 by the Simultaneous Reduction of CuO with a Fuel Gas

The exothermic reduction of CuO to Cu using a fuel gas as a source of heat to carry out the simultaneous calcination of CaCO3 in a fixed bed has been evaluated. A dynamic pseudohomogeneous model has been developed to describe in detail the transient behavior of this operation. The experimental tests have been performed in a lab scale packed-bed reactor (i.d. × L = 38 mm × 920 mm) containing a mixture of CaO- and CuO-based particles (with 12 and 60 wt % of active phase, respectively). Preliminary heat-transfer studies have been carried out using inert gases at different temperatures to estimate the overall heat transfer coefficient of the system. An overall heat transfer coefficient of around 5 W/m2 K has been obtained, which is a sufficiently low value to claim an operation close to adiabatic conditions. Hydrogen has been chosen as reducing gas. A Cu/Ca molar ratio of 1.8 in the bed allows both the reduction and calcination fronts to advance together, with moderate maximum temperatures of around 870 °C, l...

Sulfate bioreduction and elemental sulfur formation in a packed bed reactor

A laboratory scale packed bed reactor (PBR) was fabricated and operated to study its feasibility on SO42∧ reduction. The reactor was packed with polyurethane foam cubes and operated under different feeding and operating conditions of HRT, COD/SO42∧ ratio and SO42∧ concentration. Microbial community characterization showed the presence of sulfate reducing bacteria (SRB) Desulfovibrio species in the bioreactor. The reactor performance was found to be highly efficient than those previously reported at COD/SO42∧ ratio below 0.7 and HRT of 24 h. A maximum SO42∧ reduction of 97% was achieved in the PBR when operated at an HRT of 24 h with SO42∧ concentration of 1500 mg/L and COD/SO42∧ ratio of 0.67. Formation of elemental sulfur was noticed even in absence of any dissolved oxygen which might probably be due to oxidation of sulfides by the intermediate sulfite.