Journal of Chemical and Petroleum Engineering
Volume:43 Issue: 1, Oct 2009

In this paper, combustion of char in the riser of circulating fluidized bed was modeled using ASPEN PLUS. Since physical and chemical phenomena are involved in the process, the model integrates the two-phase hydrodynamic sub-model with the reaction sub-model derived from the literature. In the proposed model, the fluidized bed is divided into several sections and the behavior of each section was simulated by a combination of ideal reactor found in the simulator depending on the hydrodynamics of emulsion and bubble phase. The performance of the proposed model is tested against the experimental data reported in the literature. It is shown that this model provides acceptable results in predicting the performance of the fluidized bed reactors. The results of this study can easily be used by industrial simulators to enhance their abilities to simulate the fluidized bed reactor properly.

Kinetics of single cell protein production from natural gas by a microorganism (a Methylomonas sp.) was studied experimentally and by modeling at equal amount of air and natural gas. Kinetic models of Monod, Moser, Teissier, Aiba, Andrews, and Noack were used for illustrating cell growth. Methane and oxygen were considered as limited substrates with concentration in the range 2-10 mg/lit. Death coefficient is considered variable versus time for predicting stationary and death phase. The results showed that mathematical models could describe dynamic of biomass production from lag to death phase. Kinetic parameters were achieved by tuning with experimental data. Further, the results showed that, Monod and Moser models can correlate the experimental data very well.

In this paper, the effects of several factors such as surfactant concentration, solute concentration, impeller speed and holdup on the mean drop diameter () during emulsification have been studied in a single-stage mixer-settler extractor. A video technique has been developed in order to measure drop size distribution in the mixing chamber using a digital camera. The results show decreases with an increase in solute concentration. decreases significantly in low concentrations of surfactant, while in general, droplet diameter decrease with surfactant concentration. Though it maybe negligible. Three correlations are derived: without solute and surfactant, with solute, and with surfactant. These correlations showed a good agreement with experimental data and Hinze-Kolmogorov theory has been well proved by all of them. The experimental results in the first case were compared with Godfrey’s model and it has a minor deviation from Godfrey’s model. For the second and the last case, there weren’t any models or experimental data to compare with. In fact, the last two cases were investigated for the first time.

In this study the thermal conductivity and the volumetric heat capacity of non-Newtonian fluids are investigated. These fluids find many applications in chemical, medical and food industries. They mostly have viscoelastic behavior and generally differ from Newtonian fluids. Two non-Newtonian fluids, solutions of xanthan and carboxy methyl cellulose in water with various concentrations have been prepared and investigated. The apparatus developed has been based on two coaxial cylinder concept for measurement of thermal conductivity and volumetric heat capacity. The thermal conductivity measurement was done from steady state condition data while the volumetric heat capacity was determined from unsteady state experiments. Influence of temperature in the range of 25-80 degrees centigrade and concentration up to 20% has been studied and experimental curves are obtained for both solutions. Based on the data gathered, the empirical correlations obtained, expresses thermal conductivity and volumetric heat capacity as a function of temperature and concentration.

In spite of the fact that the principles of impinging stream reactors have been developed for more than half a century, the performance analysis of such devices, from the viewpoint of the mathematical modeling, has not been investigated extensively. In this study two mathematical models were proposed to describe particulate matter drying in tangential impinging stream dryers. The models were developed based on Markov-Chain analysis and the theory stirred tanks in series. The required parameters for each model were determined by using RTD data obtained in a tangential impinging stream dryer and then the governing equations were solved numerically. Comparing the models with available experimental data shows that the stirred tanks in series model successfully explains the drying behavior in impinging stream dryers. Nevertheless, the developed results of the model that is based on Markov-Chain analysis, are not in exact agreement with corresponding experimental data. Also, the effects of some operating parameters on performance of such dryers were investigated. The results indicate that the moisture removal efficiency of dryer increases when the solid to gas ratio and initial moisture content of particles decreases and the temperature of carrier gas increases.

In this paper, distributed parameter process systems behavior is studied in frequency domain. Based on the dominant gain concept that is developed for such studies, a method is presented to control distributed parameter process systems. By using dominant gain concept, the location of open loop zeros, resulted from the time delay parameter in the process model, were changed from the right half plane to the left half plane. This will result in improvement in the performance of the control loop since open loop behavior is changed from non-minimum phase to minimum phase characteristic. Actually, the dominant gain concept is introduced in the control loop as a dominant gain constraint by the use of a first order compensator in the control loop.

In this research, a cold model of internally circulating fluidized bed is investigated. The aim is to find the effects of some of the operating parameters on the performance of the reactor. Experiments were carried out in a glass column (30 mm i.d. and 25 cm height) with a centrally located draft tube (11 mm i.d. and 5 or 7 cm height). The bed was loaded with white silica particles (dp = 0.15 - 0.25 mm,? s = 9500 kg/m3, Umf = 1.6 cm/s,? mf =0.61). Specified amount of air was supplied separately into two zones. Increasing the gas velocity inside the draft tube led to an increase in pressure deference between two zones, and also led to pulling the solid particles into the draft tube. On the other hand, increasing the gas velocity inside the annular zone resulted in an increase in the movement of the particles which in turn increased the circulating rate of the solid particles

In this investigation a simplified arc discharge apparatus was used to synthesize mullti-wall carbon nanotubes. Because of not requiring vacuum equipment, heat exchange system, active or inert gases, this method is found to be cheaper and simpler than traditional arc discharge in gas environment. Using this method, CNTs are produced by performing an arc discharge between two graphite electrodes which are submerged in an aqueous solution. In this article the effect of different catalysts on quality of CNTs by using NaCl solution as reaction environment were investigated and also different concentration of Ni-Mo as bimettalic catalyst were used in the synthesis of these structures. Products were examined and compared by scanning electron microscopy (SEM), Raman spectroscopy and transmission electron microscopy (TEM).