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Multilevel Inverters (MLI) created a milestone due to increasing demand in high power medium voltage applications. To decrease the harmonics content and stress across power semiconductor devices, multilevel inverters are used. In this paper, a nine-level inverter is presented with a auxiliary circuit that requires a minimum number of power devices compared to the traditional MLI topologies. The suggested nine-level inverter's control circuitry is controlled by an ATmega8 microcontroller in this study. Opto-isolators with galvanic isolation supply the triggering pulses to operate switches. A nine-level inverter to power 100 W load is implemented using two proposed auxiliary circuits for renewable energy applications. The presented nine-level inverter's control switches are driven using a DC level shifting method. The suggested inverter's functionality and feasibility are confirmed by the experimental and simulation findings. [ABSTRACT FROM AUTHOR]

At equilibrium, ternary two-phase alloys have a single degree of freedom at a given temperature according to Gibbs Phase Rule. This feature manifests itself during precipitate growth in an interesting way. A difference in diffusivities of solute elements can lead to a difference in their fluxes and hence a different local equilibrium at the interface compared to the situation of both the solutes having equal diffusivities. We have studied the effect of diffusivity ratio (:) on the precipitate growth kinetics in the scaling regime and choice of local equilibrium at the interface during growth in scaling regime using our phase field model. [ABSTRACT FROM AUTHOR]

Incipient detection and diagnosis of stator winding shorted-turn faults in induction machines is essential for reliable and economical operations in industries. The problem of detecting shorted-turn faults in stator windings has been difficult. Although, from the supply currents, major winding faults can easily be detected, minor faults with less than five per cent of winding turns are not easily detectable. If not detected early, such faults can lead to major winding faults which may further lead to the disruption of the machine and causes production shutdowns. This paper describes the discrete wavelet transform (DWT) based diagnosis technique that analyses stator currents under faulty (stator shorted-turn) and healthy conditions. The developed technique depends on the band pass filtering carried out by the DWT, facilitating the extraction of the harmonic components produced by the shorted-turn faults. The discrepancies energy spectrum for three frequencies from the residual of de-noising analysis enables us to classify the fault index. From 38 seconds, the shorted turn begins to show significant difference in the energy spectrum, and if this is not detected in time, it may lead to a more serious fault. [ABSTRACT FROM AUTHOR]

In petroleum refineries, estimation of rate of catalyst deactivation is important in order to evaluate and compare the performances of different hydrotreating catalysts. However, in hydrotreating operation, catalyst deactivation is slow due to coke formation at normal operating conditions and usually catalyst activity drops significantly after 12 to 18 months period. In the present work, a testing method is developed and employed to a commercial hydrotreating catalyst for a period of 300 hrs in a pilot plant with diesel as a feedstock and by using accelerated deactivation technique. Kinetic parameters of hydrodesulfurization reaction are estimated by measuring the product sulfur before deactivation level and at the end of 100 hrs, 200 hrs and 300 hrs of deactivation. It is found that the value of kinetic parameters decreases with increase in time on stream. The quality of products hydrotreated at different levels of deactivation is also studied in the present work. The value of saturates are found to decrease with time on stream, whereas the value of carbon residue and polyaromatic hydrocarbons found to increase with time on stream. [ABSTRACT FROM AUTHOR]

The performance of different hydrotreating catalysts was evaluated in a pilot plant trickle bed reactor using a feedstock collected from an industrial diesel hydrodesulfurization unit. The feed is a typical blend of straight run diesel fractions from crude distillation units, FCC cycle oils, heavy naphtha, etc. It contains 1.11 wt% of sulfur, 0.12 wt% of nitrogen, and 34.6 wt% of total aromatics. The catalyst samples evaluated in the present work are commercially available high activity new generation catalysts being used in many refineries for diesel hydrodesulfurization application. The experiments were carried out at a constant pressure of 40 kg/cm 2 and a constant H 2 /oil ratio of 200 l/l. Experiments were performed to study the influence of reactor temperature and liquid hourly space velocity on product quality. The reactor temperature was varied from 320–360°C at different liquid hourly space velocities. The liquid hourly space velocity was varied from 1.0 to 2.5 h -1 at different reactor temperatures. The feed and product samples hydrotreated in the pilot plant reactor were analyzed to determine their physical properties and measure sulfur, nitrogen, olefinic, poly-, di-, monoaromatic, and naphthenic hydrocarbons. Catalyst C was found to have the highest hydrodesulfurization activity among the catalysts studied. The hydrodesulfurization activity of catalyst A and catalyst B are similar. Catalyst D was found to have lower hydrodesulfurization and higher hydrodenitrogenation activity compared to catalyst C. [ABSTRACT FROM AUTHOR]

Hydrocracking is a very important secondary refining process used to convert low value vacuum gas oils into high value fuels. The chemistry of the hydrocracking process is very complex due to the involvement of high molecular weight complex hydrocarbons in the reactions. Process modeling and simulation of the hydrocracking unit is very challenging due to the complexities of chemistry and the process. In the present work, a mathematical model is described to analyze the performance of the hydrocracking process in terms of product yields. A four lump discrete lumping approach is employed with a hydrocracking reaction scheme involving six reactions. The kinetic constants for the reactions were estimated by minimizing the error between the experimental and predicted yields of kinetic lumps. Experimental data reported by Ali et al. (2002) were used to validate the proposed model. The model predictions were found to agree well with the experimental data. The proposed model can be used to simulate the performance of commercial hydrocrackers using kinetic parameters estimated from pilot plant experiments. [ABSTRACT FROM AUTHOR]

In view of increasingly stringent environmental regulations with respect to SOx and particulate emissions, the allowable sulphur and nitrogen levels in diesel and gasoline are reducing all over the world. Fluid catalytic cracking (FCC) unit is a major source of fuels produced from a refinery. Any attempt to reduce sulphur and nitrogen content of distillates produced from FCC unit will greatly improve the quality of fuels. In the present work, pilot plant studies were conducted to evaluate the options of hydrotreating and mild hydrocracking (MHC) of FCC feedstock. Experiments were conducted on commercially available catalyst samples using high nitrogenous vacuum gas oil (VGO) as feedstock. MAT experiments were also conducted to compare the conversions and yields of untreated, hydrotreated, and MHC VGO at constant operating conditions. Pilot plant data showed that MHC of VGO would produce additional fuels to the extent of 15% under moderate operating conditions besides improving the quality of FCC feedstock. The mild hydrocracked VGO as feed was found to increase FCC conversion by 2 wt%, increase fuels by 2.5 wt%, reduce residue by 2.8 wt% compared to untreated vacuum gas oil. [ABSTRACT FROM AUTHOR]

The demand for high quality middle distillates is increasing world wide while the demand for residue and fuel oil is decreasing. Hydrocracking is the major conversion process that meets the twin objectives of producing more middle distillates of very high quality. Since hydrocracking is a capital-intensive process, many refiners consider the option of converting their existing vacuum gas oil hydrotreating units into mild hydrocracking units. The use of mild hydrocracker bottom as FCC feedstock can improve the quality of FCC products. In view of the advantages of mild hydrocracking process, it is essential to understand the process, catalysts used, reactions, kinetics, and advantages. This article reviews recent literature on MHC process, various catalysts used, reactions involved and advantages of mild hydrocracking process in terms of improved product qualities and increased distillates. The kinetics of the mild hydrocracking process and kinetic challenges with respect to aromatic saturation have been summarized. The limitations of the process and future scope of work in this area are also discussed briefly. [ABSTRACT FROM AUTHOR]

A simple and convenient procedure for the rapid oxidation of a variety of selenides, selenoxides, tellurides, and telluroxides with aqueous sodium hypochlorite to selenones and tellurones, respectively, has been reported in dimethylformamide at ambient temperature. [ABSTRACT FROM AUTHOR]

A pilot plant study was conducted on mild hydrocracking of heavy vacuum gas oils derived from two different crude sources over a commercially available catalyst to determine the possibility of utilizing mild hydrocracker bottoms as fluidized catalytic cracking feedstock along with improved middle distillate yields. The mild hydrocracking experiments were conducted at 390°C, 60 kg/cm2, 1.0/h liquid hourly space velocity and H2/oil ratio of 390 l/l in a pilot plant trickle bed reactor using two catalyst beds for pretreatment and mild hydrocracking reactions. The experimental results showed that mild hydrocracking would result in valuable middle distillates with low sulphur and nitrogen content. With research octane number of 78, the naphtha obtained from mild hydrocracking was found to be a good blending stock for gasoline pool. The middle distillate fraction (140–370°C) obtained from mild hydrocracking product was found to have cetane number in the range of 48–54. The bottom product from mild hydrocracking of heavy vacuum gas oils was found to be a good feedstock for fluidized catalytic cracking unit because of its low sulphur, nitrogen and aromatic contents. The data obtained from pilot plant studies showed that the processing of mild cracker bottom in FCC unit would result in better quality fuels. [ABSTRACT FROM AUTHOR]

Worldwide public concern about environment and increased demand for better quality fuels by automobile industries has necessiated developed countries like USA, UK and Japan to stipulate stringent specifications for petroleum fuel products. Fluid catalytic cracking (FCC) is a major secondary process for fuel products and quality of products coming from FCC unit depends largely on the feedstock used. FCC naphtha makes up for 30–40% gasoline in a typical refinery pool. This FCC naphtha contributes to around 90% of the gasoline pool sulphur. Hence, sulfur and nitrogen reduction have become essential for meeting the quality requirements of fuel products resulting in the growing importance for pretreatment of FCC feedstock. In the present work, studies were carried out in pilot plant on hydrotreatment of feedstock for FCC unit. The results indicate better quality products for treated feedstock vis-a-vis untreated heavy vacuum gas oils from Persian Gulf (PG) crudes. Hydroprocessing of FCC feed has helped refiners in meeting the fuel products quality especially with feedstocks, which are characterized as heavy and refractory in nature. [ABSTRACT FROM AUTHOR]

A three phase heterogeneous model was used to analyse the performance of a pilot plant trickle bed reactor employed for hydrodesulphurisation of atmospheric gas oil fraction. have presented a three phase heterogeneous model for hydrodesulphurisation of vacuum gas oil in a trickle bed reactor and showed that it can be used to include the inhibiting effect of hydrogen sulphide on sulphur conversion. This model was based on two film theory and incorporated mass transfer phenomena at the gas–liquid and liquid–solid interface. The chemical reaction rates were described using Langmuir-Hinshelwood mechanism. Though heterogeneous models are assumed to be more rigorous than the pseudo homogeneous models, the validation data using different reactors and reaction systems is scarce. The present study aims to validate the model with particular attention to show the influence of hydrodynamic parameters and intrinsic rates of reaction on reactor performance. The model predictions were compared with experimental observation under wide range of operating conditions. The data generated on hydrodesulphurisation of an atmospheric gas oil fraction over commercially available CoO–MoO3/A12O3 catalyst was used to test the model. The simulation showed good agreement with the experiments carried out in a wide range of operating conditions. [ABSTRACT FROM AUTHOR]