Sharif Digital Repository

Gas detection systems are now recognized as an essential component of safety in process units.but their successful performance depends strongly on the number and location of the detectors.As for the limited resources available (detectors), the placement of gas detectors can be considered as an optimization problem with different objective functions. In this research, an attempt was made to provide models and methods that quantitatively and from a practical point of view to optimum locate the detectors. Initially, a risk-based method was presented that defines the necessary steps for the arrangement of fire gas detectors with the aim of covering the maximum risk of leakage scenarios (risk:... 

Among probable hazards in chemical industries: vapor cloud explosion (VCE) is one of the worst and most destructive ones. More than half of the major process inci¬dents, according to the statistics, are VCEs. VCE causes the most serious consequences; therefore, it attracts many attentions to itself. Accordingly, plenty of researches have been done for the purpose of protection against VCE effects. All efforts in this field can be categorized in two different main activities; firstly, prescribing safety distances between groups of hazardous equipment and vulnerable areas, secondly, using facilities which reinforce vulnerable areas against explosion blasts. Regardless to which category is... 

Inherent safety means that the process is naturally safe and the conditions of occurrence of unsafe cases and situations are eliminated from the system so that unsafe conditions can be controlled and prevented from occurrence by means of layers of protection. In general, evaluation of inherent safety may be studied in two different conditions; the first one is associated with the units that are not completely designed and built yet. In the initial steps of developing a process, there is much freedom in the determination of materials, equipment, and designing variables. As soon as the process enters its life cycle, making changes in the process will be very difficult and expensive. Therefore,... 

Time series of asset returns display specific regularities such as bell-shaped distribution, leptokurticity and volatility clustering. Economists have made continuous efforts to develop models that explain these patterns and can be used to predict the return and the risk of holding an asset. These efforts can be classified into 3 eras: Bachelier Era (1900-1960) in which the random walk model was developed for speculative prices. Mandelbrot Era (1960-1980) in which the normality assumption was replaced with the Pareto-Levy family of distributions which are flexible enough to justify leptokurticity and infinite variance. And finally, the Dynamic Volatility era in which the focus was on... 

In order to better understand the performance of the Iranian health insurance industry, household decisions to purchase private health insurance are analyzed using a two-stage (Heckman) model on Survey of Family Income and Expenditure data. Probit and OLS regressions are used to examine the factors influencing the probability and amount of private health insurance purchased. Generally, factors affecting the probability of having insurance also influence the amount of insurance coverage purchased. The results show the importance of some demographics on the insurance decision, particularly age, gender and marital status. Socio-economic factors such as education, income, employment sector,... 

Sustainable and renewable energy sources are of fundamental importance in the development of strategic and sustainable economies. Therefore, in recent decades, water electrolysis has been widely used to produce pure hydrogen and oxygen without emitting carbon materials and is considered as a method for producing electrical energy alongside other renewable sources (such as wind and solar energy). Here, we report the synthesis of CoFe double-layered hydroxides (CoFe-LDHs) and their application as electrocatalysts for water splitting in alkaline environments. CoFe-LDHs were prepared via a new hydrothermal route from the metal-organic framework MIL-88A (MOF). The Co to Fe ratio in LDHs was... 

The environmental pollutions besides wasting the valuable materials as two main challenges in pyrometallurgical processes have brought up the tendency towards the hydrometallurgical processes. In the present study, the recovery of germanium from leaching residues of zinc plant has been investigated. Firstly, the required tests for concentrating the residues through washing of the zinc were designed by taguchi method, and optimum condition for maximum leaching of zinc accompanied by minimum desolution of germanium were obtained. The sulfuric acid concentration, time, termperature of reaction, solid to liquid ratio and rate of stirring are the parameters studied in this research. The obtained... 

There are different well-established strategies for making a process plant inherently safer. The benefits of applying these strategies on reducing the overall risk inside a plant are obvious. However, some of these changes are rejected many times because they appear to be too costly. But if the effects of applying inherently safer design strategies are investigated not only on the processing costs of a plant but also on the potential accident costs, the decision would in fact be different. In this paper an optimization procedure is proposed which integrates both processing and accident costs for different design schemes. In this procedure, some of the design variables are chosen with regard... 

Hydrogen gas was introduced as a fuel with high energy density and environmentally friendly, and the electrolysis of water is one of the widely used methods to produce this gas. In order to reduce the energy required for this process, the introduction of electrocatalysts with high activity and stable is on the agenda. In this research, the electrocatalytic performance of a composite of MgCo2O4 and Ni3S2 on a nickel foam substrate was investigated in order to produce oxygen in an alkaline environment. To prepare MgCo2O4 compound, hydrothermal method and Ni3S2 compound, electrochemical deposition method with the help of cyclic voltammetry technique was used. According to the results of XRD... 

Asphaltenedeposition is a major problem during natural depletion and EOR processes due to formation damage issues. It is necessary to reveal asphaltene deposition mechanisms and its effective parameters to prepare an acceptable prevention strategy. Therefore, different natural depletion and EOR experiments must performed on core samples. In this research, Effect of CO2 injection on asphaltene deposition phenomena has been surveyed. Two carbonate core samples and one sandstone core sample was used in experiments. The oil used in these experiments was recombinedoilfrom one of Iranian offshore oilfield.In order to estimate permeability reduction during experiment, injection of oil and CO2 was... 

Domino accidents are one types of incidents that lead to irreparable damage to industrial units. Since the consequences of such incidents are far more than the first level incident, consideration of this issue and the provision of appropriate strategies for identifying and evaluating this type of incident is very important. Major efforts have been made in the area of process safety is in risk assessment and identify possible scenarios and their probability of occurrence, and have not addressed the financial consequences of an incident. In this research, an algorithm has been developed to estimate the financial losses incurred with an industrial unit due to a domino incident and various...