مجله فرآیند نو
پیاپی 68 (زمستان 1398)

The boilers and other equipment utilized for steam generation suffer from a wide range of failure mechanisms particularly metallurgical failures, e.g. creep, graphitization, spheroidization and also different types of corrosion. In the current work, the causes of corrosion and premature failure of a carbon steel boiler bank tube used in an oil refinery was investigated by different microscopical and analytical techniques. The results showed that the main failure cause of the tube was localized corrosion which was happened due to formation of silicate deposits formed on the internal surface of the tube and consequently its caustic corrosion. At the end, some suggestions are given to mitigate such corrosion and failures.

Increasing of global warming mainly refer to increase in greenhouse gases and many other pollutant gas (like benzene) emission from companies’ outlet gases. This is the main reason of doing this research in which plasma technology is used for converting such pollutant gases. In recent study a gliding arc reactor is used to investigate the performance of it on Methane, CO2 and Benzene decomposition. The effect of main parameters like discharge power, gas flow rate, and different kind of carrier gas is investigated. Ar is used as carrier gas for Benzene conversion, however in case of Methane and CO2 splitting Ar and N2 are used as carrier gas. The results show the highest conversion rate for Benzene is around 70% which is comparable with other similar works. In Methane and CO2 dissociation, the main product is syngas (H2+CO) and small amount of O2.

In this work, influence of the twisted tape insertion on heat transfer rate and pressure drop characteristics in a double pipe has been numerically investigated. For this purpose, a 3-D double pipe heat exchanger with several types of twisted tape designed with two twist ratio (3, 5). The results obtained from the heat exchanges with twisted tape insert are compared with those without twisted tape that is plain heat exchanger. The numerical results revealed that the increase in heat transfer rate of twisted tape inserts with twist ratio 3 and 5 at Re=20000 is found to be 28% and 14% more than plain tube, respectively. It was found that with decrease twisted ratio, the amount of heat transfer rate and pressure drop increase rapidly. And by the point of pressure drop, at Re=20000, the amount of pressure drop of twisted tape inserts with twist ratio 3 and 5 are 58%  and 34% higher than plain tube, respectively.

In this study, a multicomponent industrial column for separating i-butane/n-butane is simulated based on multicomponent efficiencies. Simulations are performed at steady state with the calculation of Murphree point and plate efficiencies of individual components. The multicomponent point efficiencies are computed using the multicomponent mass transfer and the two-film theory. The plate efficiencies are calculated from point efficiencies when the degree of mixing in the plates have been determined. Finally, the plate efficiencies incorporate into the equilibrium relations. As the description of liquid mixing on the plates plays an important role in the prediction of efficiencies, in the present work various liquid mixing models are investigated and results for the composition of products and temperature profile are compared with reported measured data. Comparisons confirm that the partial liquid mixing and plug flow models are able to predict column condition with good accuracy, so that the discrepancy between the experimental data and simulation results is about 0. 5% and 21% for the plate temperatures and composition of products, respectively.