getting burdened with heavy residues that are subsequently obtained by processing heavy crudes. Heavy crudes (≤ 20 ºAPI) yield large amount of residual fractions such as atmospheric residue (AR, initial boiling point, IBP > 343ºC) and vacuum residue (VR, IBP > 500ºC) as shown in Figure 1 (Boduszynski, 2002). The processes that convert these heavy ends into lighter, more value-added products are termed as bottom-of-the-barrel conversion processes or residue upgrading processes.Among the various processes available, the delayed coking process is a long-time workhorse as regards the bottom-of-thebarrel upgrading (Schulman et al., 1993). World coking capacity has reached about 210 MMTPA (Swaty, 2005), comprising India's World petroleum residue processing capacity has reached about 725 million metric tons per annum (MMTPA). The high demand for transportation fuels and the ever-rising heavy nature of crude oil have resulted in a renewed interest in the bottom-of-the-barrel processing using various conversion processes. Delayed coking, known for processing virtually any refi nery stream (which not only poses a serious threat to environment, but also involves a disposal cost) has garnered tremendous importance in the current refi ning scenario. Needle coke obtained from delayed coking process is a highly sought-after product, which is used in electric arc furnaces (in the form of graphite electrodes) in steel making applications. In the present communication, the published literature has been extensively analyzed and a state-of-the-art review has been written that includes: (1) importance and place of delayed coking as a residue upgrading process in the current refi ning scenario; (2) coking mechanism and kinetics; (3) design aspects; (4) feedstocks suitable for the production of needle coke; (5) characteristics of needle coke; (6) factors affecting needle coke quality and quantity; and (7) future market for needle coke. An attempt has been made to get the above-mentioned aspects together in a coherent theme so that the information is available at a glance and could be of signifi cant use for researchers and practising refi ners.La capacité de traitement des résidus pétroliers mondiaux a atteint environ 725 millions de tonnes métriques par année (MMTPA). La forte demande de carburants pour le transport et la nature de plus en plus lourde de l'huile brute ont renouvelé l'intérêt pour le traitement des résidus (fond de baril) à l'aide de divers procédés de conversion. La cokéfaction retardée, connue pour traiter virtuellement tout courant de raffi nage, qui non seulement constitue une menace sérieuse pour l'environnement, mais également implique des coûts d'élimination, a pris une importance considérable dans le scénario de raffi nage actuel. Le coke en aiguilles obtenu à partir du procédé de cokéfaction retardée est un produit très recherché, qui est employé dans les fours à arc électriques (sous la forme d'électrodes de graphite) dans les applications de fabrication de l'acier. Dans le présent article, on a analysé de m...

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In the present work, the relationship between the flow pattern and blending has been investigated. The flow patterns generated by around 40 axial flow impellers have been examined. The impellers differed in blade angle, blade twist, blade width, impeller diameter, impeller location, and pumping direction. The mean-flow and turbulence characteristics generated by all of the impellers have been measured using laser doppler velocimetry (LDV). On the basis of available LDV data, the flow pattern throughout the vessel was established by employing computational fluid dynamics (CFD) and subsequently used for the simulation of the blending process. The predicted mixing times were found to be in excellent agreement with the experimental measurements. It has been shown that the dimensionless mixing time (θ̄) varies inversely with the secondary flow number of the impeller. Comparison of the impellers on the basis of equal power consumption per unit mass has shown that θmix ∝ N P 1/3 T 2/3/N QS. The present CFD model has shown the possibility of reducing the eddy diffusivity to about 20% of the actual value and still achieving the same mixing time. This reduction in eddy viscosity represents substantial savings in operating costs.

Thermal cracking of vacuum residues and asphalts obtained from operating Indian refineries were studied in a batch reactor. The temperature was varied in the range 400−430 °C, and the batch time was varied from 0 to 15 min. The pressure was kept at a constant value of 1.2 MPa through out the experiment. The variation in the composition of the cracked gas fraction for each feed was studied by gas chromatography. The resulting visbroken products were further characterized in terms of its different industrially important boiling cuts. A five lump kinetic model, comprising of gas (C1−C5), gasoline (IBP-150), LGO (150−350), VGO (350−500), and VR (500+) has been developed. The variation in the kinetic parameters with change in the feed properties has been discussed. Also, an attempt has been made to seek a relationship between the feed properties with the kinetic rate parameters and the activation energies.