Nashrieh Shimi va Mohandesi Shimi Iran
Year:2007 | Volume:26 | Issue:1|Papers Count:16

Both in pinch technology and mathematical programming, it is assumed that a single stream passes through either tubes or shells throughout its temperature span. Therefore a unique heat transfer coefficient can be used. This approach in many cases can cause a significant deviation between targeting and design stages. In this article an algorithm based on MINLP model used for HEN grassroot design with pressure drop consideration is suggested that has the following advantages: the pressure drop in each side of the exchanger (shell or tubes) can be assessed, heat transfer coefficient will be calculated based on maximum pressure drop to reduce the area of heat exchanger, heat transfer coefficient for individual heat exchanger can be determined and possibility of passing a stream through shell in one segment and in tubes in another segment in overall temperature span can be considered. The proposed model was compared with the results of two different case studies solved by Panjeh Shahi’s method. The comparison shows reduction of more than 36% in area of the exchangers, confirming the fact that more accurate evaluation of heat transfer coefficient for each individual stream can lead to a better network design.

Specification of the influence of design factors of cyclic steam injection can be used as an effective tool for optimization of performance and operational cost of this process in heavy oil reservoirs as main candidates for enhanced oil recovery by this method. For this purpose, a comprehensive simulation study for ranking operational parameters has been conducted. In simulation study of a typical Iranian heavy oil reservoir, an analytical model with capability of modeling of heat transfer and heat loss in surface, wellbore and reservoir for determination of temperature profile in heated zone, and estimation of production rate in drainage area of well model has been developed and tuned against available data. Selected parameters for this study are steam injection rate or steam slug size, soaking time, steam temperature, and steam quality. Response Surface Methodology has been used for processing and ranking of dimensionless parameters regards to cumulative oil production in the different injection and production scenarios. It is concluded that the design parameters in order of influence on performance of process are steam slug size, steam quality, soaking time, and steam temperature.

In this research, the effects of two kinds of additives in Barium Titanate ceramics were studied, in order to related the microstructure to electrical properties of the system. In the first series, the effects of Cerium (as a dopant) and in the second series the effects of Cerium along with lead on the electrical properties (with emphasis on the PTCR behavior) were evaluated. The amount of Ce was changed from 0.1% to 0.5% mole and the amount of Pb was 30% which was considered to be substituted to Ba sites. The first series were sintered from 1100 °C to 1350 °C and the second ones from 1100 °C to 1300 °C. After polishing and coating, the electrical properties were measured and analyzed. The results showed that Ce doping lowers the resistance of the systems (in both cases, without and with Pb) up to 0.3% mole and increased after that. The addition of Pb had increased the Tc of the system. The optimal sintering temperatures were about 1350 °C and 1200 °C in the first and second series respectively. In the first series, the Tc was about 125 °C and in the second series 180-200 °C. X-ray diffractometry showed that in the first series, the dominant phase was pure Barium Titanate and in the second series Barium Lead Titanate.

The purpose of this study was the recovery of lead from leaching residue of zinc oxidized ores. The samples were collected from the tailing generated in zinc leaching process in Dandy manufactory located in Zanjan which belongs to Calsimine Company. After primary characterization studies of samples and determining the lead sulphate in residue as major phase, the experimental work were carried out to recover lead from the residue, for this purpose brine leaching process was used in the presence of hydrochloric acid. The effects of several factors on leaching process were investigated and optimum conditions obtained as follows: pH: 1, pulp density: 50 g/l, temperature: 20 °C, rate of mixing: 1000 rpm. Time of leaching: 30 min. Under these conditions about 95% of lead was dissolved.

Phase inversion in liquid-liquid dispersions is a common phenomenon that occurs in many industrial processes. However, the mechanisms responsible for phase inversion and the effect of the physical and geometrical parameters on this phenomenon are not well understood. In this paper, the effect of agitation speed, type of chemical system and mineral salts on phase inversion behavior in batch-agitated vessels has been investigated. In order to study the phase inversion, a variable speed agitator and conductometer has been used. The results showed that with increasing agitation speed, the O/W dispersion invert at decreasing values of critical dispersed phase holdup, whereas W/O dispersions follow the reverse trend. Also, it is shown that decreasing interfacial tension of dispersion, shifts ambivalence limits downward and widening it. Also, addition of salt to water phase influenced phase inversion behaviour and facilitated the phase inversion of O/W dispersions and since the salt has higher ionic strength, its effect was higher.

A two phase model is proposed for describing the behavior of fluidized bed reactor of polyethylene production. In the proposed model, the bed is divided into several serial sections. The flow of the gas is considered as plug flow through the bubbles and perfectly mixed through the emulsion phase in each section. Polymerization reactions occur not only in the emulsion phase. but also in the bubble phase. The concentrations of particles in the emulsion and bubble phase are estimated from the dynamic two phase hydrodynamic model. The kinetic model are employed in this study is based on the moment equations. The results of the simulation are compared with experimental data in terms of melting index and polymer production rate of the product. A good agreement was observed between the simulation results and the actual data. It has been showed that about 20% of the polymer is produced inside the bubble phase and as such can not be neglected in modeling such reactors.

A simple experimental apparatus was used to measure the number of moles of the consumed gas during hydrate formation and experimental data on the kinetics of propane hydrate formation were measured. The experiments were carried out in a semi-batch reactor at three temperatures between 274 and 276 K and at pressure ranging from 3.0 to 4.7 bar. The Varaminian-Danesh kinetic model was adopted to predict the growth of hydrates at different driving forces (DT) and efficiency of this model was check for structure II hydrate. This study is the first for the kinetic data of propane hydrate formation at constant temperature and pressure.  

Increasingly strict environmental and product-quality regulations, the shrinking market for high-sulfur fuels, and the price benefit of processing heavier and sour crude oils have pushed oil refiners worldwide to increase their hydrocracking and hydrotreating capacities. Refineries in Iran are faced with low gasoline production, requirements for clean fuels and processing heavier crude oils. Solving these problems needs increased hydrocracking and hydrotreating capacities and hydrogen management in refineries. Nearly all refineries receive a large amount of hydrogen as a by-product of catalytic reforming on their site. However, current trend to reduce aromatics in gasoline are constraining the use of catalytic reforming and thus revamping a source of hydrogen is necessary. The combined effect of all these trends is that many refineries are facing a deficit of hydrogen. In this paper, relevant issues of identifying hydrogen consumers (sinks), producers (sources), optimizing hydrogen purification and recovery processes, hydrogen management in refineries and identifying bottlenecks of hydrogen by hydrogen pinch technology are discussed. To facilitate decision-making, a new software is developed in Visual Basic environment that first receives process data of existing H2 sinks and sources (flowrate, purity and pressure), and in the second step, takes required conditions. Then, it selects and recommends the best process alternatives for linking the said consumers and producers via a recovery network. The software calculates H2 pinch point, identifies purity profiles and the so-called hydrogen surplus diagram, and calculates economic issues such as simple payback time, operating cost and capital cost of the recommended network. The final process can be selected by user from among alternatives recommended by the software. Several literature problems have been solved by the software to verify its capabilities.

Milk ultrafiltration is a membrane process where it is subjected to a hydrodynamic pressure difference across a porous membrane that causes the process to be highly complex innature. In this paper, fuzzy inference systems have been used to model and simulate the crossflow ultrafiltration of milk in a dynamic manner. The primary aim of this work was to predict permeate flux, fouling and the milk components rejection (i.e., protein, fat, lactose, and total solids), using Mamdani and Takagi-Sugeno models. The results shows that the permeate flux and the fouling resistance vary with time for each variables. Furthermore, the protein rejection is almost constant for each parameter with time; however, the rejection of other components has been raised significantly with time. The findings of this work also revealed that by applying fuzzy inference systems we can predict the permeate flux and the total hydraulic resistance and compute the system errors. Furthermore, the comparison of the two models also demonstrates that the Mamdani model exhibits a better result than that of the Takagi-Sugeno model.

By using the model proposed for excess Gibss free energy of binary hard sphere mixtures with large size ratio a new equation in the form of Znew=f(η1, η2) for compressibility factor is proposed, where η1 and η2 are respectively the packing fractions of hard spheres 1 and 2. The results of calculations for the binary hard sphere mixtures with large size ratio, by using Znew and fourteen other compressibility factors Z obtained from other theories, and comparing them with the Monte-Carlo compressibility factor indicated that the results for Znew has small error compared with the Monte-Carlo compressibility factor.

The application of ion current signals is one of the most recent approaches in engine management systems. Nowadays, this signal is used for control of some parameters such as; air to fuel ratio, spark advance, knock and misfire in internal combustion engines. Weak signal makes some problems for detection and weak detection can not be used for optimal implementation. Therefore investigation of parameters that affects on this signal is important. In this paper the effects of different parameters on ion current signal in SI engines, such as; temperature, equivalence ratio, fuel type, engine load, humidity, EGR and carbon deposits are investigated.

In this research work, the overall dispersed phase mass transfer coefficient for Water/Toluene/Acetone system is measured in a screw-type ten stage mixer-settler. The Sauter mean drop diameter is measured with direct-photography method. Also, the effects of operational parameters such as impeller speed, dispersed phase volumetric flow rate and continuous phase volumetric flow rate on overall mass transfer coefficient are studied. The model is established based on effective diffusivity correlation (or effective diffusion coefficient). In this method, we used Grober model for prediction of mass transfer coefficient in drops with effective diffusion coefficient instead of molecular diffusion coefficient. In conclusion, with this correction of Grober model by effective diffusion coefficient, we can determine the mass transfer coefficient in these types of mixer settler. 

Calcium Hpochlorite with perchlorine trade name is a strong oxidizing agent that is a good substitution for chlorine gas for disinfection of drinking and pool water. This product is produced in perchlorine plant in Shiraz, Tabriz and Esfahan Petrochemical Complexes. Required reagents for production of white granular calcium hypochlorite are chlorine gas, sodium hydroxide and lime. The aim of this research is the study of calcium carbonate effects in lime on purity and productivity of calcium hypochlorite. The said effects on drying process of perchlorine production are also investigated. These results show that increasing calcium carbonate in lime causes a relevant increase in the amount of calcium carbonate in cake and final product. Also water content in final product is increased and purity of final product is decreased.