Nashrieh Shimi va Mohandesi Shimi Iran
Year:2008 | Volume:27 | Issue:3|Papers Count:10

One of important of mixer-settler design parameters is drop size distribution due to achieve optimum performance conditions. In this research work, several experiments were done in a single stage mixer-settler with helica-type impeller in different hold-ups and impeller speeds. In every experiment, drop size and hold-up were measured in different operational conditions. Generally, according to results we concluded that an increasing in impeller speed causes decreasing in drop sizes at constant hold-up, and also at constant impeller speed, an increase in hold-up causes an increase in drop sizes. More over, an experimental model proposed for drop sizes. This model is compared with four different models. The results were shown this model satisfy only with one model (because of impeller type). For this type of impeller, this model is proposed for first time.

In this present paper effect of phase inversion on mass transfer in a horizontal mixer-settler is investigated. Experiments showed that with respect to chemical systems (Toluene/ Water/ Acetone) and (n-Butyl acetate/Water/Acetone), if water has been considered as a continuous phase, the amount of mass transfer and overall mass transfer coefficient are higher than the case of (toluene) or (n-butyl acetate) was as a continuous phase. Since phase inversion of experimental systems occurs in high-value of dispersed phase hold-up after phase inversion occurs, the amount of secondary dispersed phase hold-up declines sharply. Low dispersed phase hold up cause’s double decline in amount of mass transfer. Also with comparison between overall mass transfer coefficients of presented systems, it is obvious that first system has larger drops in the same hold-up. Large drops of first system leads to eddy diffusion in mass transfer mechanism. While second system in most of the hold-up has molecular diffusion. Depiction of Sauter mean diameter profile versus hold-up showed that near the phase inversion point coalescence of drops speeds up. High speed of coalescence causes that the largest drops in dispersions occurs exactly before phase inversion point. Investigation on the effect of mass transfer phenomenon directing showed that when (c®d) mass transfer occurs, Marangoni effect causes production of larger drops, so that mass transfer and mass transfer coefficients in this case are higher than the case of opposite direction (d®c).

One of the most important problems of the oil industry with regards to extraction and storage of crude oil in surface vessels and the transport of crude oil and heavy hydrocarbon materials is the formation of heavy organics (Asphaltene and wax) followed by establishment of deposits in oil structures and pipelines. Due to the need of prediction of the asphaltene precipitation, taking into account the thermodynamic phenomena of precipitate is necessary. Accordingly the effort in this project is to develop and represent a model which is not only able to predict the phase behavior of reservoir fluids but also is able to predict the content and onset of asphaltene precipitation. SRK equation of state is used to predict the amount and onset of asphaltene precipitation. In developed model asphaltene phase is assumed as a solid phase and VLE two phase equilibria is used to determine the bubble point while LSE two phase equilibria as well as VLSE three phase equilibria are used to determine the onset of asphaltene precipitation in different temperature. Splitting the heavy plus fraction of oil into single carbon number groups is based on gamma distribution function and the properties of these components are calculated. The developed model is able to predict the condition of asphaltene precipitation in various situations such as temperature, pressure and different compositions and also gas injection. The results of this model with acceptable error are comparable to laboratory data.

Occurrence of errors is measured parameters of an industrial unit including steam cracking furnaces due to operator and/or equipment fault is inevitable. In this research a method for data reconciliation of measured parameters in a steam cracking process is presented. Scientific-statistical data reconciliation methods are used to detect errors in measured process variables as well as to eliminate or to reduce the errors. The errors in measured data of an industrial steam cracking furnace are estimated by solving three different data reconciliation problems, and the results compared together. The problem contains an objective function (error function) with equality equation constraints, mass, heat, and momentum balances, and inequality variable constraints. Least square, Cauchy and M-Estimator objective functions are used to in the three data reconciliation problems respectively. The used radical mechanism in the balance equations contains 400 radical reactions with 56 and 19 molecular and radical species respectively. The accuracy of the mass, energy, and momentum balance an equation was checked by comparing the model simulated results with the industrial reactor design. There is good conformity between the results. The search simplex method and the Rung-Kutta method with the LU decomposition were used to solve the data reconciliation problem, and the differential balance equations used as the constraints. The results show that the used data reconciliation problems are good methods for detecting, reducing, and elimination of the errors. The results obtained by the different methods show that the M-Estimator method as the best method will properly detect the errors.

Potassium type zeolite L was synthesized at different ratios of reactant mixture, silica sources and mixing mode. By using impregnation and ion-exchange method, Pt/KL, Pt/Cs-KL and Pt-Re/KL catalysts were then prepared for aromatization of n-hexane. Effects of a number of parameters on n-hexane aromatization, such as zeolite KL crystal size and morphology, its alkalinity and also H2/HC ratio in the feed were studied. Zeolite crystallinity and morphology were measured using XRD and SEM and its elemental analysis were carried out by XRF, ICP and AAS. Product from the micro reactor was analyzed using gas chromatography.

Disposal of agricultural and agro-food industry by-products has become an increasing environmental problem. Drying is one of the possible conditioning processes that can be applied to these by-products before using them as cattle feed or soil conditioner. In this paper dynamic modeling of the Rotary dryer is presented. The dryer was divided in to 10 sections and mass and energy balances were established in each of them and several partial differential equations have been achieved that these differential equations were converted to ordinary differential equations. Solving of the equations has been accomplished by using proper boundary and initial condition with Matlab software. The results have been validated in a semi industrial dryer. The model predicts air and product moisture and temperature depending on working conditions of the Rotary dryer. Inlet air temperature followed by volumetric flow rate has been shown to be the variable that has the greatest effect on the drying process.

Nowadays new technologies innovate for production transportation and utilization of natural gas and especially new idea outbreak for transportation of natural gas in hydrate (solid form). For formation of natural gas we need high pressure and temperature close to freezing point of water. Because of high pressure working condition the process in expensive and researcher want to find the methods for decreasing it like using additives to form structure- H that needs more less pressure than other structure also high gas storage capacity. In this research effect of additives Methyl cyclo hexane, Methyl cyclo pentane and Ethyl cyclo pentane investigate to reduce required pressure to formation hydrate structure- H. The result show that Methyl cyclo hexane afford the most reduction pressure (45%). Simple economic calculation show that this reduction of pressure can reduce until 60% investment costs.

Effect of air superficial velocity and fluid properties on bubble diameter (d32) and gas hold-up (eg) were studied in a draft-tube airlift bioreactor (0.01 m3 volume) containing diesel and its water in oil microemulsions as the model solutions of petroleum biodesulfurization. The results show that an increase in gas velocity for pure petroleum fractions with low viscosity and the microemulsions resulted in increase in eg , the former being higher prominent. Also, for high viscosity-low surface tension microemulsions increase in viscosity and gas velocity up to 0.6cm/sec resulted in significant increase in bubble diameter. Empirical correlation was developed that related d32 to eg and n under bubbly flow regime inside the bioreactor.

The performance of an aerated submerged fixed film reactor (ASFFR) in upgrading process of Parkandabad wastewater treatment plant (WWTP) was studied in a pilot plant. The experiments were performed at hydraulic retention times (HRTs) of 6, 12, 18 and 24 h (based on empty reactor volume) and the performance of the ASFFR was evaluated based on the removal of organic matter (BOD5 and COD), SS, and NH4+-N. The average BOD5 and COD removal efficiencies were in the ranges of 83.0-92.2 % and 80.7-90.7 %, respectively, depending on HRT. The relationship between the organic loading rate and organic removal rate was linear and the maximum organic removal rate was obtained as 1.74 kg BOD5/m3.d which was at organic loading rate of 2.10 kg BOD5/m3.d. The average SS removal efficiencies at HRTs of 6, 12, 18 and 24 h were obtained to be 81.8, 83.4, 82.0 and 87.1 %, respectively. The ammonia nitrogen removal efficiency increased slightly as the HRT increased. Therefore, by increasing HRT from 6 to 24 h, the average NH4+-N removal efficiency increased from 53.7 to 63.3 %. Also the NH4+-N removal rate was as a linear function of the NH4+-N loading rate within the range of loading rates studied. The results indicated that the reactor was a feasible alternative for the upgrading of Parkandabad WWTP.

Kraft pulping delignification kinetics of three hardwood chips (hornbeam, poplar and ironwood) is investigated. Equations were developed for both bulk and residual delignification phase at three chip thicknesses of 2, 4 and 6mm. Then the intersection of bulk and residual delignification equations was calculated. Results showed that delignification of hornbeam wood is faster than either poplar or iron wood, and between the other two woods, delignification proceed faster for poplar than ironwood. Residual lignin at transition point for bulk to residual delignification phase was calculated at 2.8 percent for hornbeam chips at 6mm thickness. The same amount of residual lignin (2.9 percent) was calculated for poplar chips at 4mm thickness and ironwood chips at 2 millimeters thickness (3.8 percent) lignin. Reducing the chip thickness increased the delignification rate further. But as the chip thickness reduces, then delignification approaches a common rate. This indicates that the transport distance is the limiting factor for chemical movement into wood. So if the combined pulping of these three hardwoods is intended, then thicker hornbeam and poplar chips must be combined with thinner ironwood chips.