bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical Modeling of Coal Gasification in a Fluidized Bed Reactor Using a Eulerian Granular Description
Authors: Cornejo Pablo , Farías Oscar
Published: April 2012

A three-dimensional computational model was developed to describe the coal-gasification processes inside fluidized-bed reactors. The commercial multi-purpose CFD code FLUENT 6.3 was employed, taking into account drying, volatilization, combustion and gasification processes. Both gas phase and solid phase were described using a eulerian approach to model the exchanges of mass, energy and momentum between phases. The disperse phase was described using the kinetic theory of granular flows. The chemical model involved five heterogeneous and five homogeneous chemical reactions, tracking seven species in the gas phase (CO2, CO, H2O, CH4, H2, O2 and N2) and one specie in the solid phase (C(s)). Drying and volatilization rates were estimated by mass conservation. Heterogeneous reaction-rates were determined by combining an Arrhenius kinetic-rate and a diffusion rate using the kinetics/diffusion Surface Reaction Model; the model was implemented within FLUENT through UDFs (User Defined Functions). Homogeneous reaction-rates were described by a turbulent mixing rate using the Eddy Dissipation Model available in FLUENT. Calibration and validation were performed by using existing experimental data from a benchmark coal-gasification case available in the literature. Results are in good agreement with experimental data, capturing known phenomena like fluidization-bed height, temperature distribution and species concentrations. The main contribution of the present work was implementing the necessary sub-models within the FLUENT code in order to handle reactive fluidized-beds in complex geometries. This allowed combining the flexibility of a commercial CFD code with the accuracy of simplified models developed in academic frameworks.
Parameteric Optimization of Dye Removal by Electrocoagulation Using Taguchi Methodology
Authors: Srivastava Vimal Chandra , Patil Digvijay , Srivastava Kaushal Kumar
Published: April 2012

This paper utilizes a statistical approach, the Taguchi optimization methodology (L16 orthogonal array), to determine the optimum conditions for the orange-G (OG) dye removal from aqueous solution by electrocoagulation (EC) using iron plate electrodes. The experimental parameters investigated were initial dye concentration (C0): 50-200 mg/l; initial pH (pH0): 2-8; supporting electrolyte (NaCl) concentration (m): 0-1.5 g/l; electrode gap (g):1-2.5 cm; and applied voltage (Vap): 6-24 V. These parameters were varied at four levels to see their effects on the removal efficiency (RE). Vap was found to be the most significant factor with a 24.6 percent contribution, followed by parameter C0 with 20.2 percent contribution to the RE. The predicted optimum value of RE for C0 = 200 mg/l was found to be 84.9 percent. Confirmation experiments have been performed to prove the effectiveness of the Taguchi technique after the optimum levels of process parameters are determined.
Sol-gel Synthesis and Photocatalytic Properties of the Nano-ZnO Network
Authors: Liang Ying , Tian Zhigao , Liu Ying , Liu Huajun
Published: April 2012

The fluffy porous structure ZnO nanocrystals have been successfully synthesized using citric acid assisted sol-gel method. The ZnO nanocrystals were systematically characterized by XRD, SEM, UVS, and TGA/DSC. Finally, the ZnO nanocrystals were investigated in the photodegradation experiment. The results indicated that the highly photocatalytic activity was exhibited using ZnO nanocrystals as photocatalyst.
A Comparative Study of the Flow Dynamics in Two Observation Cells for Measuring the Kinetics of the Fast Redox Reaction between Cu2+ and S2O32-
Authors: Unguresan Mihaela-Ligia M.
Published: April 2012

For the study of Cu2+ - S2O32- reaction kinetics was used an experimental stopped flow apparatus with two types of observation cells. The first has a toroidal mixing chamber, and the other, with a separate mixing chamber has the entrance of the reactants on two perpendicular directions. The reaction rate and the residence time have been calculated during the flow in the mixing chambers and the observation cells. The calculated values have been compared with the real formation and decomposition time of the reaction intermediate. The deviations due to the residence-time in the toroidal chamber and in the observation cell respectively are smaller than those for the cell with separate mixing chamber due to its different geometry. The shape of the experimental curves I = f(t) with the toroidal cell lead to kinetic parameters which are different than the ones obtained with the other cell.
A Stochastic Model of Microbial Bioconversion Process in Batch Culture
Authors: Wang Lei , Xiu Zhilong , Feng Enmin
Published: April 2012

The stochastic counterpart to the deterministic description of batch fermentation with ordinary differential equation is investigated in the process of glycerol bio-dissimilation to 1,3-propanediol by Klebsiella pneumonia. We briefly discuss the batch fermentation process driven by five-dimensional Brownian motion and Lipschitz coefficient, which is suitable for the actual fermentation. Subsequently, we study the existence and uniqueness of solutions for the stochastic system as well as the boundedness of the Two-order Moment and the Markov property of the solution. Finally, computer simulation results reveal the peculiar role of randomness in the dynamical responses of the batch culture.
Modeling and Optimizing of Mechanically Agitated Vessels by Central Composite Rotatable Design Method
Authors: Zadghaffari Ramin , Moghaddas Jafarsadegh , Fakheri F. , Razmi H. , Heidari H.
Published: April 2012

A central composite rotatable design (CCRD) methodology was used to analyze the effect of some operating variables on gas-liquid two phase mixing time in an agitated tank driven by dual 6-blade Rushton turbines. The variables chosen were the impellers rotational speed (x1), gas flow rate (x2), probe location (x3) and tracer injection point (x4). The mathematical relationship of mixing time on the four significant independent variables can be approximated by a nonlinear polynomial model. Predicted values were found to be in good agreement with the experimental values (R-sq of 95.9 percent and R-Sq (Adj) of 95.7 percent for response Y). This study has shown that central composite design could efficiently be applied for the modeling of mixing time, and it is an economical way of obtaining the maximum amount of information with the fewest number of experiments.
Numerical Study of Bubbling Gas-Solid Fluidized Beds Hydrodynamics: Influence of Immersed Horizontal Tubes and Data Analysis
Authors: Asegehegn Teklay W. , Schreiber Matthias , Krautz Hans J.
Published: April 2012

Numerical simulations of two dimensional gas-solid bubbling fluidized beds with and without immersed horizontal tubes were performed using Eulerian - Eulerian Two Fluid Model (TFM). The influences of immersed horizontal tubes and different data analyses techniques on the bed and bubble hydrodynamics were investigated. The results were compared with experimental data and correlations available in the literature.Different ways for extracting and defining hydrodynamic properties, such as bed expansion ratio and bubble properties, were found to influence the simulation results. Furthermore, the time-averaged values showed greater sensitivity to the length of averaging time in the first few seconds. With regard to tube influence, immersed tubes were found to be the main source of bubble breakup. Thus, the calculated mean bubble diameters and rise velocities were found to be lower with tubes than without for the same bed geometry and superficial velocity. The bubble shapes were observed to elongate in the vertical direction in the tube bank region compared to the bed region below and above the tube bank. In addition, the TFM was found to successfully predict the overall time-averaged solid motion and distribution. For beds with immersed tubes, defluidized regions were observed at the upper part of the tubes where solid particles rested without moving. On the other hand, the lower parts of the tubes were usually covered with gas pockets. These effects were seen to reduce with increasing superficial velocity.
Experimental Study of Reactive Absorption of Carbon Dioxide in a Lab Scale Spray Dryer
Authors: Kavoshi Leila , Hatamipour Mohammad S. , Rahimi Amir
Published: April 2012

Reactive absorption of CO2 with NaOH as absorbent was evaluated experimentally in a lab scale spray dryer. Taguchi method was used for design of experiments. Results showed that the most important factors are inlet CO2 concentration, nozzle size, absorbent concentration and temperature, respectively. The optimum conditions are 150°C for temperature, 10% (w/w) for NaOH concentration, 10% for CO2 concentration, and 0.5 mm for nozzle diameter. By conducting experiments under the optimum conditions, the removal efficiency was obtained as 69.4%.
The Investigation of Electrochemical Oxidation of Formic Acid on Pt, Pd and PtRu Modified Gas Diffusion Layer
Authors: Köleli Fatih , Beytaroglu Anya , Röpke Derya , Röpke Thorsten , Aydin Rezzan
Published: April 2012

Catalytic activities of platinum (Pt), palladium (Pd) and platinum-ruthenium (PtRu black) modified gas diffusion layers (GDL), so called gas diffusion electrodes (GDE),were studied for electrooxidation of formic acid in aqueous acidic solution. The effects of formic acid concentration and medium temperature on the oxidation were investigated. Additionally, cyclic voltammetric investigation (CV), electrochemical impedance spectroscopy (EIS) and amperometric measurements were carried out by using modified catalysts. Electrochemical measurements indicated that the modified PtRu/C black exhibits higher electrocatalytic activity than Pt/C and Pd/C catalysts.
Carbon Nanotube Structures as Support for Ethanol Electro-Oxidation Catalysis
Authors: Kivrak Hilal , Kuliyev Sadig , Tempel Hermann , Schneider Joerg , Uner Deniz
Published: April 2012

In the present study, the effect of support for ethanol electro-oxidation reaction was investigated on 20 percent Pt/C (E-Tek), 20 percent Pt/commercial CNT, and 20 percent Pt/home-made CNTs. Homemade CNTs were prepared by template synthesis method via chemical vapor deposition (CVD) method. Twenty percent Pt/commercial CNTs and 20 percent Pt/home-made CNTs were prepared by polyol method. The metal dispersions were determined from volumetric chemisorption measurements. These catalysts were tested as anode catalysts for the ethanol electro-oxidation reaction at room temperature by cyclic voltammetry. An optimization study was conducted to find out the optimum scan rate and optimum potential change for ethanol electro-oxidation reaction on 20 percent Pt/C (E-Tek) catalyst. Then, ethanol electro-oxidation measurements were performed on 20 percent Pt/C (E-Tek), 20 percent Pt/commercial CNTs, and 20 percent Pt/home-made CNTs catalysts in 0.5 M H2SO4 +0.5 M ethanol solution at 0.05 V/s scan rate and 1.2 V vs. NHE. Although the raw data indicated that the 20 percent Pt/commercial CNTs exhibited the worst performance, the performances of all of the catalysts were identical after normalizing the current values with respect to the exposed Pt site obtained from the volumetric hydrogen chemisorption measurements. These results indicate that only the metal dispersions improved ethanol electro-oxidation reaction and support did not have any effect on ethanol electro-oxidation reaction under the conditions used in this study.
Experimental Study of Hydrodynamic Characteristics and CO2 Absorption in Producer Gas Using CaO-sand Mixture in a Bubbling Fluidized Bed Reactor
Authors: Mahadzir M.M. , Zainal Z.A.
Published: April 2012

Producer gas, from biomass gasification process can be used to generate power as an alternative to fossil fuel. Carbon dioxide (CO2) content in the producer gas is acts as a diluent gas resulted in low heating value. We used limestone (which is of rather wide occurrence in Malaysia) that consisted mainly of the mineral calcite (calcium oxide, CaO) as calcium based sorbent to absorb CO2 in the producer gas. Removing the CO2 from the producer gas will improved its heating value. In this paper, the first step was to study the behavior of CaO-sand mixtures in a cold model experiment. The effects of the CaO-sand mixtures, the CaO particle sizes, the volume flow rate and the pressure of air intake were investigated experimentally. Then, the hot model experimental was conducted to investigate CO2 absorption at the optimum condition obtained from the cold model experiment resulted. The CaO percentages of 50 and 40 in sand were found to have a good fluidization at all air pressures (200-600 kNm-2). In addition to that, the 1000 micron particle size of the CaO-sand mixture and the volume flow rate of air between 0.00025- 0.00092 m3s-1 were also found to give a good fluidization. In the hot model experiment, the best CO2 absorption occurred at 50 percent CaO mixture with simulated gas pressure of 300 kNm-2 and the volume flow rate of 0.00075 m3s-1 at 650-750°C in a bubbling fluidized bed reactor (BFBR).
Orthogonal Flow Impinging on a Wall with Suction or Blowing
Authors: Khan Najeeb Alam , Ara Asmat , Ali Syed Anwer , Jamil Muhammad
Published: April 2012

The goal of this work is the approximate solutions of a viscous incompressible fluid impinging orthogonally on a porous flat plate. The equation governing the flow of an incompressible fluid is investigated using the homotopy perturbation method (HPM) with the aid of Padé-approximants. The approximate solutions can be successfully applied to provide the value of the skin-friction. The reliability and efficiency of the approximate solutions were verified using numerical solutions in the literature.
Low-Temperature Pyrolysis and Gasification of Biomass: Numerical Evaluation of the Process Intensification Potential of Rotating- and Circulating Rotating Fluidized Beds in a Static Fluidization Chamber
Authors: Staudt Nicolas , De Broqueville Axel , Rosales Trujillo Waldo , De Wilde Juray
Published: April 2012

The process intensification potential of rotating- and circulating rotating fluidized beds in a static fluidization chamber when used for the low-temperature pyrolysis and gasification of biomass is numerically evaluated. The species continuity equations and energy balance equations are based on complete mixing for the particles within given zones of the particle bed and plug flow for the gas. The reaction mechanism accounts for pyrolysis of biomass and tar, gas-phase combustion, the water gas shift reaction, and combustion and gasification of char. A comparison with current circulating fluidized bed riser technology is made. The circulation of inert solid with a high heat capacity and the separation of the flue gas from the production gas are also studied.
Maximum Power Output of Multistage Continuous and Discrete Isothermal Endoreversible Chemical Engine System with Linear Mass Transfer Law
Authors: Chen Lingen , Xia Shaojun , Sun Fengrui
Published: April 2012

The maximum power output of a multistage isothermal endoreversible chemical engine system operating between a finite potential capacity high-chemical-potential reservoir and an infinite potential capacity low-chemical-potential environment with the linear mass transfer law is investigated in this paper. For the fixed initial time and fixed initial concentration of the key component in the high-chemical-potential reservoir, the continuous model is optimized by applying Hamilton-Jacobi-Bellman (HJB) theory and Euler-Lagrange equation, respectively, and the discrete model is optimized by applying dynamic programming method and discrete maximum principle, respectively. Numerical examples for the discrete model with three different boundary conditions are provided, and the results are also compared with those for the continuous model. The results show that both of the maximum power outputs of the limiting continuous and multistage discrete isothermal endoreversible chemical engine systems are equal to the difference between their classical reversible thermodynamic performance limits and a dissipation term. The relative concentration of the key component in the high-chemical-potential reservoir for the maximum power outputs of the continuous and discrete models decreases with the increase of time linearly. The relationships among the maximum power output of the system, the process period and the final concentration of the key component in the high-chemical-potential fluid reservoir are discussed in detail.
Hydrodynamic Studies on Three-Phase Combined (Internal & External) Loop Airlift Fluidized Bed Reactor Using Newtonian and non-Newtonian Liquids: Minimum Fluidization Velocity and Liquid Holdup
Authors: Venkatachalam Sivakumar , Palaniappan Akilamudhan , Kandasamy Kannan
Published: April 2012

A novel combined airlift loop fluidized bed reactor was proposed in this work. The internal and external loops were combined and the hydrodynamic parameters like minimum fluidization velocity and liquid holdup were studied for Newtonian and non-Newtonian fluids. Studies were conducted using Newtonian fluids of water, n-butanol, 60% and 80% glycerol and non - Newtonian fluids such as 0.25%, 0.6% and 1.0% Carboxy Methyl Cellulose (CMC) aqueous solutions were employed in the liquid phases. Spheres, Bearl saddle and Raschig ring with different sizes were used as solid phase. The experimental results indicated that the increase in particle size and sphericity increased minimum fluidization velocity whereas increase in superficial gas velocity decreased minimum fluidization velocity. In addition, the liquid holdup increased with increase in particle size and superficial liquid velocity. Furthermore, an increase in superficial gas velocity decreased the liquid holdup for Newtonian and non-Newtonian systems. Two separate correlations were developed to predict the minimum fluidization velocity and liquid holdup based on the experimental results for both Newtonian and non-Newtonian liquids for a wide range of operating conditions. The capability of the proposed correlation for minimum fluidization velocity and liquid holdup was examined and reasonable agreement between predicted and experimental results of Newtonian and non-Newtonian liquids suggested the applicability of the proposed correlations.
Production of L-asparaginase from Natural Substrates by Aspergillus terreus MTCC 1782: Optimization of Carbon Source and Operating Conditions
Authors: Gurunathan Baskar , Sahadevan Renganathan
Published: April 2012

In the present work, the effect of different carbon sources, namely glucose, sucrose, maltose, fructose and lactose, was studied for extracellular L-asparaginase production by Aspergillus terreus MTCC 1782 in submerged fermentation. The best carbon source and operating conditions such as initial pH, inoculum size, temperature and agitation rate were optimized. Glucose was found to be the best carbon source for L-asparaginase production using modified Czapek-Dox media containing L-proline as substrate. Sucrose was found to be the best carbon source for L-asparaginase production using modified Czapek-Dox media containing groundnut oil cake flour as substrate. Glucose was found to be the best carbon source for maximum L-asparaginase production using modified Czapek-Dox media containing soya bean meal flour as substrate. The soya bean meal flour was found to be the best natural substrate for maximum L-asparaginase activity of 35.3 IU/mL using 0.6% glucose as carbon source at the optimal culture conditions of initial pH 6, inoculum size 2%, temperature 35°C and agitation rate 160 rpm.
Some Exact Solutions for Helical Flows of Maxwell Fluid in an Annular Pipe due to Accelerated Shear Stresses
Authors: Jamil Muhammad , Fetecau Constantin , Khan Najeeb Alam , Mahmood Amir
Published: April 2012

Some exact solutions corresponding to helical flows of Maxwell fluid between two infinite coaxial circular cylinders are determined by means of finite Hankel transform, presented in series form, satisfied all imposed initial and boundary conditions. The motion is produced by the inner cylinder that applies the torsional and longitudinal time-dependent accelerated shear stresses to the fluid. The corresponding solutions for Newtonian fluid and large-time solutions are also obtained as limiting cases and effect of material parameters on the large-time solutions are discussed. Finally, the influence of pertinent parameters as well as a comparison between Maxwell and Newtonian fluids on the velocity components and shear stresses profiles is also examined by graphical illustrations.
A Novel Route for Conversion of Free Fatty Acids in Acidic Oils to Methyl Esters by In-Situ Hydrolysis of Methyl Acetate
Authors: Ch Vijaya Lakshmi , R.V.S Uday Bhaskar , Kotra Viswanath , Bankupalli Satyavathi
Published: April 2012

Biodiesel from clean oils is comparatively easier than production from crude and non-edible oils. To achieve maximum yield of biodiesel, a two stage process is adopted in which non-edible oils are used as feed-stock: an acid catalyzed esterification of free fatty acids followed by base catalyzed transesterification. Presence of water formed during esterification reaction is detrimental to a viable transesterification process. In the present work, an alternate method for removal of water by in situ hydrolysis reaction of methyl acetate is introduced. The dehydration using methyl acetate during esterification has yielded good results as the soap formed during transesterification was minimal. The results indicated high conversion of triglycerides to methyl ester for lower oil to methanol ratio and at a lower temperature. For 1:3 molar ratio of oil to methanol, the conversion obtained was less than 90 percent and is equivalent to conversions with higher alcohol ratios during esterification in the absence of methyl acetate. These results are indicative of the fact that use of methyl acetate reduces the alcohol to oil ratio without affecting the conversions. Moreover, higher conversions are possible at lower temperatures in the presence of methyl acetate. It is further observed that the oils that are subjected to free fatty acid conversions in the presence of methyl acetate record very little soap formation during the transesterification reactions, thereby resulting in higher grade of biodiesel.
The Homotopy Analysis Method for Fractional Cauchy Reaction-Diffusion Problems
Authors: Das Subir , Kumar Rajnesh , Gupta Praveen Kumar
Published: April 2012

In this article, homotopy analysis method is successfully applied to obtain the approximate analytical solutions of the characteristic Cauchy reaction-diffusion equation with fractional time derivative. The beauty of the article is the wonderful application of Caputo fractional order time derivative. The linear interactions of the merging populations are examined using perturbation theory and the method of matched asymptotic expansions. The solutions of the problem for different particular cases are presented graphically.
The Potential of Different Saline Solution on the Extraction of the Moringa oleifera Seed's Active Component for Water Treatment
Authors: Madrona Grasiele Scaramal , Bergamasco Rosangela , Seolin Vanessa Jurca , Fagundes Klen Marcia R.
Published: April 2012

The main objective of the present work is to study the efficiency in terms of removing color and turbidity of raw water in order to obtain drinking water. For this purpose, different coagulant solutions were obtained utilizing different salts, NaCl, KCl and MgCl2, in concentration 1M, distilled water combined with the Moringa oleifera Lam seed. Each coagulant solution obtained was studied with concentrations ranging from 25 to 300 mg/L of Moringa in salt solution. The tests were performed in the Jar Test, and the efficiency of the process was assessed in terms of color and turbidity. The results show no difference in the coagulation for extracts using the salts KCl, NaCl and MgCl2 1 Molar. The best results were found employing the coagulant solutions extracted with salt, in various concentration ranges (125 to 300 mg/L); as the concentration of protein in solution becomes higher, the greater is its power as a coagulant. The lowest content of protein was found in the solution extracted with water, which consequently had the lowest values of color and turbidity removal. Finally, the results obtained by the present work show that the seed of Moringa oleifera Lam is a great alternative for use as a coagulant in drinking water treatment systems.
Esterification Catalysis through Functionalized Membranes
Authors: El-Zanati Elham Abouel Fetouh , Ritchie Stephen M. , Abdallah Heba Mohamed , Ettouny Rim , El-Rifai Mahmoud A.
Published: April 2012

Breaking the thermodynamic equilibrium in reversible esterification reactions is achieved through water adsorption on a functionalized membrane. The used functionalized catalytic membrane contains sulfonated polystyrene grafts which act as an alternative to conventional esterification process catalysts. A set of parameters influencing the esterification reaction have been studied. These include feed reactants molar ratio, temperature, different styrene percentages in the membrane, and membrane area. The results show that the increase of molar ratio, temperature, styrene percentage, and membrane surface area increases the reaction conversion and product yield. The high reaction rate obtained on the onset of the reaction, which is attributable to water removal by adsorption, is offset as the reaction proceeds owing to the deactivation of the catalytic active sites by the water adsorbed within the membrane. Therefore, the conversion rate increases up to a maximum and then decreases owing to catalyst deactivation as the membrane becomes progressively saturated with the adsorbed water. The maximum conversion reached was 93.78 percent after a processing time of 10 sec when using 10:1 molar ratio ethanol to acetic acid, 5 percent styrene in the grafted membrane having a diameter of 14.2 cm (1.52 meq of catalyst/g) at 30ºC, and a membrane internal adsorption surface area of 252,450 cm2.
Experimental Flow Measurements of a Spouted Bed Using Pressure Transducer and X-Ray CT Scanner
Authors: Wu Bangyou , Orta Ana , Kantzas Apostolos
Published: April 2012

Flow behaviour of an air-glass bead spouted bed (20 cm diameter, 1.31 m high) was investigated using wall pressure fluctuation measurements and X-ray Computed Tomography (CT) scanning. Spout shape, spout dimension, fountain shape and fountain height were visualized from CT images. Statistical and spectral analyses were applied to pressure fluctuation series measured along the column wall. Local and global gas-solids flow dynamics were compared. Gas velocity greatly affects hydrodynamics of the spout bed. A stable spouting regime was identified. This study enhances the understanding of gas-solid flow patterns and provides detail hydrodynamics for further modelling work.
Augmentation of the Performance of Batch Electrocoagulation Unit by Using Gas Sparging
Authors: Elshazly Ahmed Hassan
Published: April 2012

The present work investigates the effect of gas sparging in improving the performance of a batch electrocoagulation unit used to treat wastewater generated from the dyeing industry. Monopolar cylindrical aluminum electrodes were used. Many variables were investigated such as superficial gas velocity, current density, initial dye concentration, area ratio (cathode/anode), time of operation and the effect of adding chemical coagulant as FeSO4. The results show that the percentage of dye removal has been increased by a factor ranging from 2.52 to 5.14 by increasing the gas flow rate from 0.4 to 0.8 liter/min respectively and that about 93.5 percent of the dye can be removed within 60 minutes. Also it was found that using gas sparging is more efficient than adding chemical coagulant as ferrous sulfate for the removal of dye from wastewater. The power consumption for the unit was measured for different gas flow rates and different current densities; the results show that lower gas flow rate can improve the economy of the process.
Multi-Objective Optimization of an Ethylene Oxide Reactor
Authors: Vandervoort Allan , Thibault Jules , Gupta Yash P.
Published: April 2012

In this study, multi-objective optimization is performed for a reactor producing ethylene oxide from ethylene. The optimization considered three objectives: the maximization of the ethylene oxide production and selectivity, and the maximization of a safety factor related to the presence of oxygen in the reactor. The Pareto domain for this optimization problem was first approximated using the Objective-Based Gradient Algorithm, and the Pareto-optimal solutions were ranked using the Net-Flow procedure to determine the best operating conditions. From the optimization results, it is recommended that the ethylene oxide reactor be operated at high inlet pressure and gas temperature, and low inlet volumetric gas flowrate and chemical reaction moderator concentration. These operating conditions led to the highest ranked compromise solution, balancing the trade-off between each of the three objectives. Finally, it was found that a decrease in the inlet pressure or variation in the volumetric gas flowrate could readily lead to operating conditions outside of the Pareto domain, and these input variables should therefore be carefully controlled throughout operation of the reactor.
Numerical Investigation of Flow Friction and Heat Transfer in a Channel with Various Shaped Ribs Mounted on Two Opposite Ribbed Walls
Authors: Wongcharee Khwanchit , Changcharoen Wayo , Eiamsa-ard Smith
Published: April 2012

Heat transfer and fluid flow characteristics through a channel with two - dimensional transverse ribs are numerically investigated. The effects of different shaped ribs (rectangular rib, triangular rib, cylindrical rib, concave-concave rib, convex-concave rib, long convex-short concave rib and long concave-short concave rib) are examined. The investigation is performed for the ribs mounted on top and bottom walls with rib pitch to height ratio (P/e) of 6.67, in Reynolds number between 3000 and 7000, under constant wall temperature condition. For the present case, the data predicted by SST k-omega turbulence model show better agreement with the experimental data, than those predicted by RNG k-epsilon turbulence model. The mean heat transfer, flow friction, temperature fields and the local heat transfer coefficients as well as the flow structure behaviors are reported. For the ribs considered, the channel with triangular-ribs yields the highest Nusselt number, the one with concave-concave rib provides the highest friction and the one with cylindrical rib show the best thermal enhancement. At the similar condition, the triangular rib gives higher Nusselt number than that provided by the cylindrical one by around 29.3 percent, while the cylindrical rib offers the highest thermal enhancement factor of 1.4 which is higher than that of the cylindrical one by around 1.33 percent while the cylindrical rib offers the highest thermal enhancement factor of 1.33 which is higher than that of the triangular one by around 9.6 percent. In addition, in spite of their high heat transfer, the concave-concave rib and long concave-concave rib yield low thermal performance factors, due to the prominent effect of high friction factor.
Experimental Characteristics of Pneumatic Pulse Jet Pumping Systems with a Venturi-Like Reverse Flow Diverter
Authors: Xu Cong , Huang Yi
Published: April 2012

The effects of area ratio of the diffuser entrance to the nozzle exit, displacement vessel volume, and suction gap configuration on the performance of pumping systems with a Venturi-like reverse flow diverter are investigated experimentally. The performance of a pumping system with area ratio of 1.5 is greater than one with area ratio of 1.0, but when the jet outlet velocity ranges from 1225 m/s, the performance of a suction gap in the shape of an axially-symmetric cylinder is the same as one with an arch-like configuration. The effective lifting factor should be more than 1.0, which means that the effective volume of the displacement vessel must be at least 1/(q-1) times the riser tube volume.
Facile Preparation of P-25 Films Dip-Coated Nickel Foam and High Photocatalytic Activity for the Degradation of Quinoline and Industrial Wastewater
Authors: Zhu Suiyi , Yang Xia , Wang Gu-Ning , Zhang Lei-Lei , Zhu He-Feng , Huo Ming-Xin
Published: April 2012

A kind of P-25 TiO2 films coated nickel foam was synthesized by a facile dip-coating/calcination route, and used to fabricate a continuous-flow three-phase photocatalytic reactor. The morphology, crystal phase structure, surface composition and specific surface area of P-25 films coated nickel foam were investigated by field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption measurements, respectively. The results indicated that the coated/ calcined P-25 films had the porous surface structure fabricated by nano-sized titanium dioxide consisted of two crystal phases and incorporated with a NiO interlayer. The increase of P-25 contents enhanced the specific surface area; however, 20 percent of initial P-25 sol would result in visible large cracks because of too high P-25 content and consequently cause the peeling of films. The photocatalytic activities of nickel foam with different coating amounts of P-25 for the degradation of quinoline aqueous solutions were investigated with a continuous-flow three-phase photocatalytic reactor based on the P-25 films coated nickel foam. The results suggested that nickel foam coated with 10 percent of P-25 sol had an optimal photocatalytic activity for the degradation of quinoline aqueous solutions. The continuous-flow three-phase photocatalytic reactor fabricated with P-25 films coated nickel foam with an optimal P-25 coating amount shows high photocatalytic activity and stability for the degradation of quinoline aqueous solutions and industrial wastewater. The treated industrial wastewater meets the international discharge standard.
Development of UV Distribution Model for the Non-Contact Type UV Disinfection System
Authors: Kim Sung Hong , Choi Young Gyun , Kim Dooil
Published: April 2012

Fouling on the quartz sleeve reduces the transmittance of UV light through the sleeve into the water in submerged UV disinfection system. The concept of a non-contact type of UV disinfection system was introduced in this study. UV lamps and their quartz sleeves hang over the water surface and there is no interface between the sleeve and water. Indeed, there is no fouling. Based on optical laws and UV distribution model, a detailed mathematical model for a non-contact type UV disinfection system was developed and simulated in this study. UV light passes through 4 media of air-quartz-air and water in case of non-contact type irradiation system. By the simulation of the mathematical model of the system, it is known that the non-contact type of UV system requires 2.5 times more powerful UV lamp or a lamp with longer exposure time than that of the submerged type of UV system. In a non-contact type of UV system, high-reflective ceiling material can increase the UV intensity of the water layer as much as 28 percent more than the case of non-reflective ceiling material. The non-contact type UV irradiation system requires more powerful lamp or one that have longer exposure time. Nevertheless, considering the fouling attenuation and maintenance problem associated with the fouling, non-contact type of UV disinfection system deserves to be practically considered, especially in a small to middle scale water or wastewater treatment plant.
Self-Diffusion Coefficient and Viscosity in Fluids
Authors: Novak Lawrence
Published: April 2012

Rate-based models suitable for equipment or transport-reaction modeling require a capability for predicting transport coefficients over a sufficient range of temperature and pressure. This paper demonstrates a relatively simple novel approach to correlate and estimate transport coefficients for pure components over the entire fluid region.The use of Chapman-Enskog transport coefficients for reducing self-diffusion coefficient and viscosity to dimensionless form results in relatively simple mathematical relationships between component dimensionless transport coefficients and residual entropy over the entire fluid region. Dimensionless self-diffusion coefficients and viscosities were calculated from extensive molecular dynamics simulation data and experimental data on argon, methane, ethylene, ethane, propane, and n-decane. These dimensionless transport coefficients were plotted against dimensionless residual entropy calculated from highly accurate reference equations of state.Based on experimental data, the new scaling model introduced here shows promise as: (1) an equation of state-based transport coefficient correlation over the entire fluid region (liquid, gas, and critical fluid), (2) a component transport coefficient correlation for testing transport data consistency, and (3) a component transport coefficient correlation for interpolation and extrapolation of self-diffusion coefficient and viscosity.
Synthesis and Physicochemical Characterization of Nanostructured Pt/CeO2 Catalyst Used for Total Oxidation of Toluene
Authors: Abbasi Zahra , Haghighi Mohammad , Fatehifar Esmaeil , Saedy Saeed
Published: April 2012

Nanostructured Pt/CeO2 with different loadings of platinum was successfully synthesized via redox reaction along with wet impregnation method. The catalytic performance of the synthesized nanocatalysts was evaluated for abatement of toluene from waste gas stream. The synthesized nanocatalysts were characterized using XRD, FESEM, TEM, N2 adsorption, FTIR and TPR-H2 techniques. Crystallographic analysis confirmed the formation of CeO2 as crystalline phase with average crystallite size of 10.5 nm. Morphological analysis showed that majority of the synthesized CeO2 particles were less than 100 nm with average particle size of 50.62 nm. TEM analysis illustrated that platinum particles were fairly well dispersed with an average size of 5-15 nm. Specific surface analysis revealed that the synthesized nanocatalysts had large enough surface area for catalytic oxidation of toluene. Temperature programmed reduction profiles indicated that Pt/CeO2 had more reducibility compared to pure ceria. The results of catalytic experiments showed that the synthesized catalysts had the ability to remove 99% of toluene via total oxidation. According to these results, the best loading of Pt on ceria was 0.5 wt% with higher activity compared to pure ceria.
Experimental and Theoretical Study on Fluidization of Stalk-Shaped Biomass Particle in a Fluidized Bed
Authors: Zhang Yong , Zhong Wenqi , Jin Baosheng
Published: April 2012

Detailed knowledge of the fluidization mechanics of biomass itself, or of mixtures of biomass and inert particles is critical to successful design and operation of fluidized bed involving biomass. In this study, the fluidization behaviors of biomass alone and sand-biomass mixture were experimentally and theoretically studied. A segmented fluidized bed equipped with multiple pressure transducers was used as the experimental apparatus. The cotton stalk with a shape of stalk was employed as biomass material, and three different sizes of sand were utilized as inert particle. By mixing cotton stalk and sand, three binary systems were obtained, in which only the weight percentage of biomass particle in each mixture is different. The fluidized beds experienced the following states, depending on gas superficial velocity and initial mixture fraction: fixed, bubbling fluidization and turbulent fluidization. It is found that the additive of sand has positive influence on the fluidization of biomass and the initial arrangement of bed has influence on the development of pressure drop with the gas velocity. The developed equation for predicting the minimum fluidization velocity (Umf) of binary mixture quite satisfactorily predicts the Umf values of mixture with low biomass concentration. In addition, the correlation expressed in terms of Reynolds and Archimedes numbers to predict transition velocity (Uc) is proposed. Calculated Uc is in excellent agreement with the experimental data.
CFD Simulation of Mass Transfer around Spherical Particles in Fluidized Bed
Authors: Vatani Zoha , Taghizadeh Majid , Orouj Reza
Published: April 2012

In this study, the mass transfer of three-dimensional nonreactive gas-solid fluidized bed was investigated computationally. The influence of the inlet gas velocity and temperature on mass transfer of air to wet particles was analyzed. The simulation results indicated that the mass transfer coefficients of air to spherical sand particles was decreased from 2.12 to 1.66 m/s with increment of temperature from 300 to 360 K. Sherwood numbers of gas to cluster increased with the increase of inlet air velocity. CFD model of the gas-particle heat transfer have been implemented, the result showed that the heat flux of gas to particles increased with the increase of Reynolds number. Distributions of water vapor concentration and velocity in this bed were numerically predicted and the computed Sherwood and Nusselt numbers were compared with the estimated values from empirical equations.
Effect of Operating Conditions for Higher Alcohols Synthesis from Synthesis Gas over Alkali-Modified Co-Rh-Mo Trimetallic Catalyst Supported on Multi-Walled Carbon Nanotubes
Authors: Surisetty Venkateswara Rao , Kozinski Janusz , Dalai Ajay K.
Published: April 2012

The effects of operating conditions on the higher alcohols synthesis reaction from synthesis gas were studied in a single-pass tubular downflow fixed-bed reactor, using sulfided K-promoted trimetallic Co-Rh-Mo catalyst supported on multi-walled carbon nanotubes (MWCNTs). The p CO conversion increased monotonically with increasing reaction temperature (from 275 to 350°C) and pressure (from 800 to 1400 psi), while decreasing monotonically with increasing GHSV (from 2.4 to 4.2 m3 (STP)/(kg of cat./h)). To maximize the ethanol STY and selectivity, the optimum operating conditions were determined as 330°C, 1320 psi, and 3.8 m3 (STP)/kg of cat./h). Maximum ethanol STY and selectivity were obtained using gas with H2 to CO molar ratio around 1.25.
Mitigating NH3 Vaporization from an Aqueous Ammonia Process for CO2 Capture
Authors: Budzianowski Wojciech M.
Published: April 2012

An aqueous ammonia process (AAP) offers several advantageous technological features over other existing reactive absorption-based CO2 capture processes such as increased CO2 absorption loading capacity, no oxidative solvent degradation, no corrosion problems, high CO2 absorption fluxes and low energy input needed for solvent regeneration. It has also the potential of capturing multiple flue gas components (SO2, NOX, and CO2) and producing value added chemicals, such as ammonium sulfate, ammonium nitrate and ammonium bicarbonate, which are commonly used as fertilizers. Unfortunately, a major drawback of the AAP is NH3 volatility resulting in NH3vaporization to the flue gas. Therefore, the current article presents the results of experimental and numerical investigations directed at in-depth understanding of the AAP and at developing of new methods for mitigating the unwanted NH3 vaporization. For this purpose three types of reactor configurations are studied: (i) packed bed, (ii) falling film and (iii) membrane. The bench-scale experiments realized in the counter-current packed bed reactor reveal, that NH3 vaporization can be minimized under the conditions of low temperature, pH, and flow rate of flue gas and under the conditions of high pressure and flow rate of aqueous ammonia. Further, from the detailed 2D modeling of the AAP realized in the falling film reactor it is found, that NH3 vaporization can be mitigated by making use of the mechanisms of negative enhancement of mass transfer and of migrative mass transport. Finally, the potential benefits of using membrane facilitated AAP reactors are discussed.
Composite Distribution Solution for Minimizing Heat Loss in a Pyrolysis Reactor
Authors: Filtvedt Werner O. , Melaaen Morten , Holt Arve , Javidi Massoud , Olaisen Birger Retterstøl
Published: April 2012

The article presents a novel design for a distribution plate. The solution is suitable for a reactor vessel where a reactant gas needs to be maintained at a different temperature from the reaction chamber in order to avoid unwanted occurrences, such as clogging of the distribution plate. A normal procedure involves cooling of the distribution plate which is reported to either increase heat loss substantially or yield insufficient temperature in parts of the reaction chamber. The problem is especially important for reactors where the difference in reactant inlet temperature and desired reaction temperature is large. The investigated design utilized materials of very different thermal conductivity to only cool specific parts of the distribution arrangement and thereby minimize heat loss. Our system is a distribution plate for use in a fluidized bed reactor for silane pyrolysis. However, the solution is general and may be utilized in many types of vessels and chemical reactors.
Supercritical Activity Restoration for Fischer Tropsch Synthesis
Authors: Durham Ed , Roberts Christopher B.
Published: April 2012

Previous research has demonstrated that supercritical phase Fischer Tropsch Synthesis (SC-FTS) using hexanes as the solvent medium offers superior activity maintenance to traditional fixed-bed (gas phase) Fischer Tropsch Synthesis (GP-FTS) (Elbashir et al., 2005). This has prompted an investigation into whether supercritical media can reactivate a catalyst used in GP-FTS. To that end, a study was conducted in which a series of GP-FTS experiments of approximately 2 days each were performed, separated by in situ periods of catalyst reactivation using supercritical hexanes as well as SC-FTS.It was found that the supercritical hexanes media and SC-FTS reactivation periods were effective in partially restoring lost catalyst activity and selectivity. GP-FTS was demonstrated to have detrimental effects on subsequent SC-FTS operation while SC-FTS operation showed beneficial effects on subsequent GP-FTS operation. Specifically, SC-FTS reactivations reduced the methane selectivity in subsequent GP-FTS periods. The CO2 selectivity in SC-FTS is consistently lower than that in GP-FTS, while the olefin selectivity into the diesel range is higher in SC-FTS. While the propagation probability was initially higher in SC-FTS than GP-FTS, the propagation probability values converged as the experiment progressed.
How to Fix the Inefficiency of Global Cap and Trade
Authors: Cramton Peter , Stoft Steven
Published: April 2012

Global cap and trade equalizes the price of emissions and leads to efficient abatement across countries, but sets the abatement level inefficiently low. It is set too low, because the global cap is the sum of individual country targets set on the basis of self-interest. The efficiency of a single price does not overcome the inefficiency of the public-goods problem inherent in global cap and trade. Fortunately, other policies lead to more cooperative and, hence, more efficient outcomes. Replacing the national quantity targets of global cap and trade with a global price target improves outcomes. To improve outcomes further, the price target is combined with a Green Fund. As we demonstrate by example, the Green Fund can induce cooperation between rich countries that want a high global price and poor countries that are more concerned with Green-Fund payments.