Nashrieh Shimi va Mohandesi Shimi Iran
Year:2008 | Volume:26 | Issue:4|Papers Count:15

Adsorption/absorption combination is one of the successful methods for removal of H2S from natural gas. Silica gel particles soaked in N-Methyl-2-Pyrrolidin (NMP) produce an adsorbent with high adsorption capacity. In this article, NMP distribution and mass transfer mechanism in pores containing the two fluid phases (gas-NMP) have been determined using the experimental results of H2S adsorption on such adsorbents. It is shown that H2S is adsorbed via NMP (as the non wetting fluid) with pore diffusion mass transfer controlling mechanism. The adsorption behavior of H2S on the NMP-coated silica gel adsorbents at various concentrations of NMP were successfully demonstrated using a one-parameter transient mass-transfer model.

Temperature profile is the most important information enabling the analysis of the behavior of an exchanger. Many models have been developed to provide temperature profile most of which either due to extensive complexity and excessive use of correlations are less used or lack adequate accuracy. In this work initially a model is reproduced on the presumption of no baffles and therefore a plug flow regime on the shell side. A second model is then developed assuming a complete cross flow situation and therefore neglecting flow leakage. The two solutions obtained from these two models provide the limits of the exchanger operational conditions. Pressure drop and shell side flow calculations are carried out using Wills & Johnston method. Based on the flow analysis a combinatorial model is developed mixing the two basic models providing a more realistic view of the heat transfer and therefore temperature profiles. To study the accuracy of the model, it is used to reproduce the experimental results on E type exchanger reported in the Delaware Final Report.The exit temperature showed a ± 10% deviation from experimental results.

Risk assessment of probable hazards, is one of the major stages for upgrading safety level of existent process or a process in design phase. Risk assessment is a method for deciding is safety upgrading of a unit economical or not. In developed countries, risk assessment is essential for process unit. In this paper in order to introduce risk assessment, its implementation steps such as hazard identification, consequence modeling and risk calculation method such as risk matrix and F-N curve have been discussed. Consequence modeling of hazards such as fire, explosion and toxic releases, which may occur due to human error or failure of equipment, is an important stage of risk assessment that nowadays carried out by computer softwares. At last, a case study of risk assessment has been studied for ammonia storage tanks of a petrochemical complex by using software PHAST for consequence modeling.

Anchor mixer is frequently used for mixing of viscous liquids. In the present work, a novel mixer for mixing of viscous liquid has been introduced and its efficiency was compared with anchor mixer using computation fluid dynamics (CFD) method. In this comparison, velocity vectors and counters, velocity profile and shear stress have been compared for two agitators. In addition the mixing time in the tank has been investigated by injecting a tracer and considering the time variation of tracer concentration in three arbitrary points. The results show that in both cases homogenization in the lower region of the tank obtains faster than the upper region. The novel mixer produces more proper velocity profile in vertical and radial directions. This agitator, also, gives higher shear stress which results better turbulence and homogeneity so that the mixing time is about 50% less than for anchor mixer.

The paper addresses the behavior of a neural network PID-controller and its comparison with other conventional methods for tuning of adaptive controllers. The implemented methods are investigated in for the location of process model poles, the non-minimum phase process and change in the process model. The results show that the neural network PID-controller is tuned with less trial and error and in the case of model change of the process, it has a robust behavior. Moreover, the controller shows proper response to the periodic changes in the set-point.

Generally, gel injection is an appropriate method to decrease the rate of production of the water in oil reservoirs. In this paper the purpose is to determine the states of oil reservoirs during gel polymer injection process. The simulation is derived according to experimental results within some modification on corrent models. The fluid flow expressions are presented by using two phase flow assumption i.e. (oil-water). The physical properties of gel and polymer such as viscosity, adsorption and permeability reduction are extracted both theoretically and experimentally. Chemical transport equations are used to simulate the rate of components concentration including porosity, aqueous density and gel formation rate properties. The final equations are partial differential equations that would be solved numerically within suitable boundary conditions. Ultimately, the results obtained are compared with experimental data for one of the Iranian reservoir, which shows a desirable accuracy of the presented mathematical model.

Oxidative coupling of methane was investigated on the Mn/Na2WO4/SiO2 catalyst in both fixed and fluidized bed reactors. A wide range of operation condition was selected in order to observe the effect of reaction temperature, methane to air ratio, and resident time of reactants in the reactors. The best C2+ yield (the product of methane conversion and C2+ Selectivity) obtained was about %21.9. The ratio of ethylene to ethane selectivity for the whole range of operating conditions was greater than 1 which indicated a high dehydrogenation activity of the catalyst as compared to the other come on catalyst of OCM such as Li/MgO.

In this study, some experiments have been performed for determining parameters that affecting heavy oil recovery. In these experiments some hydrocarbon solvents such as Heptane, Octane and Decane have been used. In these experiments some parameters that are efficient in heavy oil recovery, like solvent type effect, hydrocarbon solvent injection rate, gravity segregation effect, injection orientation in uniform and oriented patterns, have been contemplated. A series of experiments performed whereby hydrocarbon solvents (Heptan, Octane and Decane) displaced heavy oil in micromodel pattern of different pore structure orientations. Successive images of invasion of solvents in heavy oil were taken at desired interval time during injection process. Image analysis technique is used to measure the oil recovery factor as a function of injected pore volume of solvents. The oil recovery factor versus pore volume of different injected solvents was plotted for different micromodel flow patterns, at different flow rates in both horizontal and vertical geometry. It has been found that the pore structure orientation have significant effect on oil recovery during solvent injection process this could be due to the enhancement or detraction of the longitudinal and transverse dispersion in the porous media. The results also indicated that gravity enhances the oil recovery in the case of vertical injection compared to the horizontal one. In addition solvents of lower molecular weight resulted in higher oil recovery.

In this paper the soluble impurity distribution in a PGV-1000 steam generator has been analyzed. A PGV-1000 steam generator is a horizontal one with 750 MW thermal powers that produces 1467 t/h steam. In this paper a two-dimensional model is proposed to simulate the soluble impurity distribution in the SG. It is shown that the model can estimate the impurity distribution with an error within 13%, in longitudinal direction, and within 35%, in traverse direction, of maximum impurity. With this model, various feed-water and blow-down systems are investigated. The calculated results show that the soluble impurity in a PGV-1000 steam generator can be considerably reduced. The computation results show that, in a standard feed-water and blow-down system, the average impurity can be reduced from about 100 times the impurity of the feed water to about 25 times, and that the maximum impurity can be reduced from 270 to 180. And in the improved feed-water and blow-down system for PGV-1000 with a modification to the feed water system the impurity can be reduced 40% approximately.

Iran with producing 18 percent of global date production is the major date producing country. In this research, fructose syrup production with various fructose content from date syrup were determined .High fructose syrup is one of the main sweetener in the world. Fructose and glucose separation from synthetic solution of these carbohydrates with different concentration were first determined and optimum concentration was 80 g/l. Date syrup properties were determined and ion exchange chromatography column with Amberlite CR1320Ca has been used for carbohydrate separation from date syrup. Glucose, Fructose and sucrose separation were determined after 35 minutes with HPLC method, fructose recovery was 42.9 percent and glucose recovery was 82.7 percent.

In copper electrorefining process, acceptable quality of cathodes will not achieved without using glue as an additional agent. Therefore measuring glue content in the electrolyte solution is very significant. In this research the glue content measured by use of modified Haring cell and the variables related to glue performance are investigated. The results show that by increasing glue content, the polarization rises to an optimum value. Although increasing temperature lower the optimum glue content in solution, but there is no considerable effect of current density on the required glue content.

In this work, two methods were developed to estimate the solubility of Photochromic dye in supercritical CO2. First method used Soave-Redlish-Kowang (SRK) and Peng-Robinson (PR) equations of state with Huran-Vidal mixing rules while second method used semi-empirical models (recommended by Mendez and Chrastil). Since there were not any data for critical properties of Photochromic dye, a new method for evaluating of C2 (mixing rule parameter), as a function of temperature and pressure, was recommended. This function for C2 has never been reported in the literature. This method in comparison with others such as group contribution methods, predicts good result. The amounts of Average Absolute Relative Deviation (%AARD) were obtained 13.7% for SRK-EOS and 18.15% for PR-EOS. Also, a semi-empirical modified equation is used with variable coefficients which results %AARD 6.9% employing Chrastil modified model and 6.2% employing Mendez modified model.

ABSTRACT: Investigation of mass transfer parameters and the effect of various operational variables such as flow rate of dispersed and continuous phases, sauter diameter and dispersed phase hold up in solvent extraction equipments on the mass transfer process were the key parameters for designing and selection of optimum conditions. The packed liquid-liquid extraction columns are mature apparatus for their flexibility and are widely used in different processes. In this paper, hydrodynamic and mass transfer parameters of continuous phase for two different chemical systems Toluene/ Water/Acetic acid and Butanol-1/Water/Acetic acid were studied in a packed column with raschig ring packings. According to finding data it was obvious that the influences of phase flow rate, phase dispersion and system properties on mass transfer were have found to be significant. Generally, in this work experimental values of Shc were obtained and a correlation of Shc was proposed for continuous phase mass transfer coefficient. The correlation yilelded an average absolute error (AARE) less than 8% for both experimental systems and this shows acceptable correspondence between correlation and experiments.

ABSTRACT: In this research, the effect of operating conditions, such as GHSV, temperature and CH4/O2 ratio was investigated on the catalytic performance of OCM in a Fixed-Bed reactor. 50 g of catalyst was loaded in a stainless steel reactor. Heat control in OCM is very important. With attention to this fact series of experiment were designed to investigate the influence of above-mentioned parameters on C2+ selectivity, CH4 conversion and the yield of C2+. The C2+ selectivity of 73 % was obtained at a CH4 conversion of 12.58% at 840oC, 1320 hr-1 GHSV and CH4/O2 ratio 4 to 1. The OCM reaction is strongly dependent on the operating condition particularly GHSV and the CH4/O2 ratio. The comparison of these results and micro reactor in literature, show that the scale up of fixed bed reactor in OCM reaction without too much change in yield and selectivity of C2+, CH4 conversion and COx selectivity, with an appropriate GHSV, CH4/O2 ratio is technically feasible and economic.