2005
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2
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Reactor Modeling of a NonCatalytic OCM Process
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2
genewline"> One method for conversion of methane to more valuable products is by noncatalytic gasphase oxidative coupling of methane (OCM), through which methane is converted into ethylene. The product of this process is ethylene, accompanied by acetylene, ethane, a small quantity of three carbon compounds as coupling products, and carbon oxides due to complete oxidation of hydrocarbons. The kinetic model proposed for the OCM process consists of 75 elementary reactions and 23 chemical species. In previous studies, the reactorkinetic modeling of this process, was implemented in a laboratory microreactor at constant temperature and pressure. Considering that this process proceeds with severe variation in the enthalpy, in the present study, in addition to isothermal, the operation of the system has also been modeled for the adiabatic state. The modeling has been carried out in a tubular reactor system. Comparison of the qualitative and quantitative results of the model with experimental data at constant temperature shows that the proposed kinetic model predicts the experimental results properly. Furthermore, in the present study, the effect of various parameters on the operation of the system has also been examined. These studies have been performed in the following ranges of pressure, temperature and CH4/O2 ratio respectively: 1≤ P ≤ 10 (bar), 950≤ T≤ 1100 (K), 4 ≤ CH4/O2 ≤ 10. It has been shown that, by increasing the temperature, the reaction rate increases. Raising the total pressure of the system causes an increase in methane conversion and selectivities of desired products as well as the reaction rate. On the other hand, increasing the residence time in the reactor will result in conversion of desired products to undesirable ones. Finally, it is shown that by decreasing the ratio of methane to inlet oxygen, conversion of methane increases, selectivities of the desired products decrease and the heat released during the reaction rises.
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SemiContinuous Cultivation of Photosynthetic Cells in a Flat Plate Photobioreactor
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From an engineering point of view, the effect of light intensity distribution on the stability of growth rate should be taken into account in designing effective photobioreactors and sustaining stable growth rates. In the experiments described here, in order to keep operational parameters at an almost constant level, a semicontinuous culture method was developed for cultivation of photosynthetic cells under defined light intensity distributions. In the semicontinuous culture, a portion of culture broth containing grown cells was repeatedly replaced with the fresh medium at a predetermined time interval to maintain the cell concentration and the volume of the broth constant at their initial values. Under illumination from one and both sides, photosynthetic cells were cultivated in a flat plate photobioreactor with various light path lengths. The results obtained showed that stability of the growth rate strongly depended on the distribution of light intensity and the ratio of light intensity in the illuminated to that in the dark zone inside a photobioreactor. These parameters should be taken into consideration for stable cultivation of photosynthetic cells.
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photobioreactor
Stability of growth rate
Light intensity distribution
Semicontinuous cultivation
Numerical Simulation of the Hydrodynamics of a TwoDimensional Gas—Solid Fluidized Bed by New Finite Volume Based Finite Element Method
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2
n this work, computational fluid dynamics of the flow behavior in a cold flow of fluidized bed is studied. An improved finite volume based finite element method has been introduced to solve the twophase gas/solid flow hydrodynamic equations. This method uses a collocated grid, where all variables are located at the nodal points. The fluid dynamic model for gas/solid twophase flow is based on the two fluid model where both phases are continues and fully interpenetrating. For the gas and solid phases the NavierStokes equation based on the concept of local average is obtained. Results are verified against experimental data reported in the literature.
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fluidized bed
Control volume
Finite element
gas solid
Twophase flow
The effect of wall strengtheners on the performance of doublestage electrostatic precipitators
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The presence of wall strengtheners in doublestage electrostatic precipitators affects gas velocity, electrical field and particle movement over the ESP. In this work we have used our previous mathematical model for doublestage ESP {Talaie et. al (2001) [10]] to study the effect of wall strengtheners on the performance of doublestage ESP. One of the important findings was that, due to the fact that wall strengtheners increase the degree of turbulence, the effect of gas turbulence on particle movement can not be ignored. The results of the calculations show that the simple Lagrangian model in which this effect is neglected is not suitable, whereas using an Eulerian approach provides much better results. The results of this model also revealed that the collection efficiency for small particles increases while that for large particles decreases when a baffle is used as wall strengthener.
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Mathematical model
Electrostatic precipitators
Wall strengtheners
Electrical field
Decolorization of Distillery Wastewater by UV irradiated spores of Aspergillus fumigatus
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An efficient microbial technique for decolorizing distillery wastewater was achieved using irradiated spores of Aspergillus fumigatus. The fungus was isolated from soil samples taken from the local distillery processing unit. By using the irradiated spores, wastewater decolorization increased by 14.3% as compared to that of the control treatment (68.8% vs. 54.5%). In the presence of sodium nitrate and maltose, as optimum sources of nitrogen and carbon, in the microbe's growth medium, the decolorization rose to 70%.
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49
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Aspergillus fumigatus
Decolorization
distillery wastewater
UV Irradiation
Some investigations on PHA production using activated sludge as inoculum
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This paper indicates that activated sludge under certain conditions can achieve levels of polyhydroxyalkanoates (PHA) accumulation which would enable the economic recovery of this precursor of biodegradable plastics. The effects of C/N ratio and temperature on polyhydroxyalkanoates production were evaluated. Acetate uptake, ammonium consumption, oxygen uptake and PHA production were studied under aerobic, growth rate limiting conditions. Sludge fed with acetate showed the capability to accumulate PHA to about 6% and 20.5% of cell dry weight at 30 °C and C/N =21.74 after 42 and 72 h, respectively. The accumulation of PHA strongly depends on temperature, with less PHA formation at higher temperature. The average values of maximum growth rate (q„•Cx), affinity constant (K02) and kLa were determined 0.266 mglY , 0.556 mgt' and 0.1422 s1, respectively.
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56
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Mixed culture
polyhydroxyalkanoates (PHA)
Activated sludge
CFD Simulations of Pressure Drop in KATAPAKS Structured Packing
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KATAPAKS is a type of structured catalytic packing, which is used in reactive distillation processes. The dry pressure drop characteristic (the pressure drop in the absence of liquid flow) is of significant importance for the investigation of process hydrodynamics. In this paper, the dry pressure drop within the catalyst packed channels of KATAPAKS has been investigated using Computational Fluid Dynamics (CFD). Results of the CFD simulations were validated using experimental pressure drop data and empirical correlations. The CFD results showed an excellent agreement with theoretical and experimental data. Keywords: KATAPAKS structures, Pressure drop, Structured packing, CFD
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