1D modelling of membrane-assisted chemical looping reforming

Modelling of fluidized bed reactors—VI(b): The nonisothermal bed with stochastic bubbles

Experimental study on reactor performance of gas–solids low-velocity fluidized beds

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

Modeling of autothermal reforming of methane in a fluidized bed reactor with perovskite membranes

Chemical Looping for Energy Technology: A Special Issue

A mathematical model for thermo-catalytic decomposition of methane over carbon black catalysts in a fluidized bed was proposed. The simplified isothermal, uniform flow model was considered and implemented into a computer code to predict the reactor performance. The experiment of methane decomposition into hydrogen and carbon was carried out in a fluidized bed of I.D of 0.055 m and height of 1.0 m. The range of reaction temperature was 850–900 °C, gas velocity was 1.0–3.0 Umf, and catalyst loading was 50–200 g. The reaction parameters for model equation were determined from the curve fittings and the comparison of experimental data with simulation results showed good agreement for fluidized bed reactor system. From the simulation results, the fluidized bed performance with different operating conditions were obtained, and this simple model can be used to predict the performance of a larger scale fluidized bed reactor and also in determining the optimum operating conditions.

In this work, the business Computational Fluid Dynamics (CFD) is used for the numerical simulations of an air-solid fluidized bed container in the solid phase involving a multi-fluid Eulerian multiphase model and the Kinetic Theory of Granular Flow (KTGF). The height of the fluidized bed setup is 1.5 m while its diameter is 0.2 m. With it, a series of experimentations were obtained using Helium tracer to determine the Residence Time Distribution (RTD) at various normalized velocities, that is, mixing of air-solids at different degrees. 2 and 3 dimensions of the fluidized bed container are simulated. The main purpose of this study is to understand the hydrodynamic behavior of air-solid fluidized bed container through a framework of Eulerian multiphase model and to analyze the hydrodynamic behavior of the air-solids mixing. As a first approach, the CFD model is validated using the experimental results of the residence time study. The numerical results of RTD corresponded well with the experimental findings. This shows that the CFD modeling might be used to indicate the performance of a fluidized bed reactor. Key words: Computational fluid dynamics, fluidized bed, residence time distribution (RTD), gas-solids mixing, turbulence.

Global modeling and simulation of a three-phase fluidized bed bioreactor

During the production of oil and gas, large amounts of water are brought to the surface and must be disposed of in an environmentally sensitive manner. This is an especially difficult problem in offshore production facilities where space is a major constraint. The chief regulatory criterion for produced water is oil and grease. Most facilities have little trouble meeting this criterion using conventional oil-water separation technologies. However, some operations have significant amounts of naphthenic acids in the water that behave as oil and grease but are not well removed by conventional technologies. Aerobic biological treatment of naphthenic acids in simulated-produced water has been demonstrated by others; however, the system was easily overloaded by the large amounts of low-molecular-weight organic acids often found in produced waters. The objective of this research was to determine the ability of an anaerobic biological system to treat these organic acids in a simulated produced water and to examine the potential for biodegradation of the naphthenic acids in the anaerobic environment. A small fixed-film anaerobic biological reactor was constructed and adapted to treat a simulated produced water. The bioreactor was tubular, with a low-density porous glass packing material. The inocula to the reactor was sediment from a produced-water holding pond from a municipal anaerobic digester and two salt-loving methanogenic bacteria. During start-up, the feed to the reactor contained glucose as well as typical produced-water components. When glucose was used, rapid gas production was observed. However, when glucose was eliminated and the major organic component was acetate, little gas was generated. Methane production from acetate may have been inhibited by the high salt concentrations, by sulfide, or because of the lack, despite seeding, of microbes capable of converting acetate to methane. Toluene, a minor component of the produced water (0.1 g/L) was removed in the reactor. Batch tests were conducted to examine naphthenic acid biodegradability under several conditions. The conditions used were seed from the anaerobic reactor, wetland sediments under aerobic and anaerobic conditions, and a sterile control. The naphthenic acid was from a commercial source isolated from Gulf Coast petroleum as was dosed at 2 mg/mL. The incubations were for 30 days at 30 C. The results showed that the naphthenic acids were not biodegraded under anaerobic conditions, but were degraded under aerobic conditions. Despite poor performance of the anaerobic reactor, it remains likely that anaerobic treatment of acetate, toluene, and, potentially, other produced-water components is feasible.

This study explored the feasibility of fluoride removal from simulated semiconductor industry wastewater and its recovery as calcium fluoride using fluidized bed crystallization. The continuous reactor showed the best performance (>90% fluoride removal and >95% crystallization efficiency) at a calcium-to-fluoride ratio of 0.6 within the first 40 days of continuous operation. The resulting particle size increased by more than double during this time, along with a 36% increase in the seed bed height, indicating the deposition of CaF2 onto the silica seed. The SEM-EDX analysis showed the size and shape of the crystals formed, along with the presence of a high amount of Ca-F ions. The purity of the CaF2 crystals was determined to be 91.1% though ICP-OES analysis. Following the continuous experiment, different process improvement strategies were explored. The addition of an excess amount of calcium resulted in the removal of an additional 6% of the fluoride; however, compared to this single-stage process, a two-stage approach was found to be a better strategy to achieve a low effluent concentration of fluoride. The fluoride removal reached 94% with this two-stage approach under the optimum conditions of 4 + 1 h HRT combinations and a [Ca2+]/[F-] ratio of 0.55 and 0.7 for the two reactors, respectively. CFD simulation showed the impact of the inlet diameter, bottom-angle shape, and width-to-height ratio of the reactor on the mixing inside the reactor and the possibility of further improvement in the reactor performance by optimizing the FBR configuration.

Numerical investigation of hydrodynamics and cluster characteristics in a chemical looping combustion system

Postcombustion CO2 capture using CaO as a regenerable solid sorbent in a circulating fluidized bed (CFB) carbonator is emerging as a promising CO2 capture technology. Experimental validation of this concept is provided through a comparative analysis of the results obtained in two laboratory-scale dual fluidized bed (DFB) installations located at INCAR-CSIC (Spain) and IFK (Germany). The analysis is focused on the performance of the CFB carbonator reactors operated with continuous solid circulation of CaO. A reasonable closure of the carbon balances (i) between the CO2 that has disappeared from the gas phase, (ii) the CaCO3 circulating between the reactors, and (iii) the CaCO3 that is formed within the carbonator bed has been established. A necessary condition for the capture of a given molar flow of CO2 is experimentally demonstrated and requires that a slightly overstoichiometric molar flow of active CaO is supplied to the carbonator. The deactivation behavior of the sorbents during continuous looping conditions has been measured. The key parameter to interpret the carbonator reactor results has been the active space time, that is indicative of the CaO inventory per molar flow of CO2 participating in the carbonation reaction and of the reaction rate of the solid inventory in the reactor. Two different approaches have been utilized in order to find a suitable expression for this parameter, thus achieving its correlation with the CO2 capture efficiency. A simple model assuming instant mixing of solids and plug-flow of the gas has been tested. Based mainly on carbonator active space time variation, the CO2 capture efficiency are shown to lie between 30% and above 90%. These results confirm the technical viability of the calcium looping postcombustion CO2 capture process. They have been used for designing the current pilot-plant facilities which are scaled up 20–50 times in regard to the lab-scale units. Moreover, the lab-scale results obtained allow for simulation work to be initiated in regard to the full scale Ca looping application.

This work reports the integration of thin (∼3–4 μm thick) Pd-based membranes for H2 separation in a fluidized bed catalytic reactor for ethanol auto-thermal reforming. The performance of a fluidized bed membrane reactor has been investigated from an experimental and numerical point of view. The demonstration of the technology has been carried out over 50 h under reactive conditions using 5 thin Pd-based alumina-supported membranes and a 3 wt%Pt-10 wt%Ni catalyst deposited on a mixed CeO2/SiO2 support. The results have confirmed the feasibility of the concept, in particular the capacity to reach a hydrogen recovery factor up to 70%, while the operation at different fluidization regimes, oxygen-to-ethanol and steam-to-ethanol ratios, feed pressures and reactor temperatures have been studied. The most critical part of the system is the sealing of the membranes, where most of the gas leakage was detected. A fluidized bed membrane reactor model for ethanol reforming has been developed and validated with the obtained experimental results. The model has been subsequently used to design a small reactor unit for domestic use, showing that 0.45 m2 membrane area is needed to produce the amount of H2 required for a 5 kWe PEM fuel-cell based micro-CHP system.

Distillery wastewater is among the most polluting industrial effluent because it contains high organic load and significant amount of inorganic pollutants such as phosphates, sulphates, nitrates, chloride, calcium and potassium. Normally biological treatment is applied as the initial treatment step for the degradation of the biodegradable organic compounds. This is complemented by integrating with other treatment methods downstream such as chemical oxidation and physico-chemical processes for further removal of inorganic pollutants and biorecalcitrant organic compounds. Zeolite has favourable adsorption capacity and can be beneficial in improving the performance of integrated biological, chemical and physico-chemical process used in treating distillery wastewater. This work gives an elaborate review on the application of zeolite as a biomass support material in anaerobic digestion and as a catalyst support in photocatalytic treatment of distillery wastewater in fluidized bed reactors. An increase in biomass retention time of 8.5-folds and a low biomass detachment rate of 0.038 d−1 has been reported with organic load reduction of above 90% when zeolite is used in anaerobic digesters. Zeolite in anaerobic digester favours the growth of methanogens in the order Methanococcaceae, Methanosarcina and Methanosaeta, respectively. Further to this, factors such as catalyst-to-zeolite ratio and terminal velocity of zeolite particles are significant in the performance of a photocatalytic reactor. This work provides significant information on the use of zeolite to enhance biological and advanced chemical oxidation processes as an integrated approach for the treatment of distillery wastewater.KeywordsZeoliteDistillery wastewaterAdsorptionAnaerobic digestionAdvanced oxidation processes

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.