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w e re m o d e r n i z e d at Neftekhimiya Co. As a result of replacing the internal contacts in the towers by valve and centrifugal trays, the output of the towers increased, the quality of separation with production of propylene of 95-98% purity improved, the residual content of propylene in the propane fraction decreased to 7-10%, and the pressure drop in the towers decreased.Neftekhimiya Co., part of Renova Orgsintez Holding Co., has modernized the existing propane-propylene fraction (PPF) separation plant to expand production of propylene.Problems of modernization: • to increase the unit's output to the maximum possible in replacing tower internals;• to improve the quality of separation with production of 95-and 97%-pure propylene and reduce the residual propylene content in the propane fraction to 10%.A comprehensive approach was used to solve these problems, consisting of optimization of the process scheme, selection of optimum process parameters (pressure, temperature, load on boilers), use of highly efficient equipment and modern control systems.A special feature of modernization consisted of replacing only the internals of existing towers with maximum utilization of existing equipment (boilers, condensers, etc.). As a result of a detailed comparative analysis of the internals of different modern domestic and foreign suppliers, high-yield tray equipment developed by Kedr-89 was selected. Two PPF separation process streams were modernized: in the first stream, the K-110.115 slotted tower, in the second, the K-14 tower. The characteristics of these towers and the process parameters of their operation are reported in Table 1.A feature of the modernization was the maximum utilization of existing connections and supporting elements of the "old" internals. Process and hydraulic calculations were first performed and engineering designs for replacing the tower internals were developed at Kedr-89 to ensure the required tower operating indexes. As a result, it was proposed that 90 valve trans be installed in tower K-110, 115, and 106 high-efficiency centrifugal
The basic trends in improving vacuum distillation of atmospheric resid are examined. The effect of the fundamental process parameters on the exhaustiveness of refining the feedstock is demonstrated.The urgency of exhaustive refining of atmospheric resid to increase takeoff of vacuum gasoil as feedstock for catalytic and hydrocracking units is increasing with the shrinkage of the boiler fuel market and the increase in the price of crude oil. At the same time, coking, deasphalting, and thermal cracking processes are imposing increasingly severe requirements on vacuum resid with respect to improving its quality indexes: viscosity, softening point (R&B), boiling point, etc., which will reduce the residual content of gasoil cuts in it.Increasing the degree of refining of atmospheric resid is determined by the possibilities of the vacuum block equipment in the AVT unit -furnaces, transfer lines, vacuum tower internals, the vacuum-creation system [1].Let us examine the effect of the fundamental process and design parameters on vacuum distillation of atmospheric resid and methods of improving it. The fundamental process parameters include the temperature of heating the atmospheric resid in the furnace, the residual pressure in the tower feed zone, and feeding of steam to the tower's distillation section.Temperature of heating atmospheric resid in the furnace. Increasing this temperature to increase takeoff of vacuum distillates is limited by thermal decomposition. The limiting heating temperature is a function of the nature of the feedstock and is determined by the design of the vacuum tower furnace coil and transfer pipeline. In practice, this temperature is increased by the following methods:• reducing the residence time of the atmospheric resid in the furnace coil by dividing the overall atmospheric resid stream into several streams;• feeding steam into the coil; • optimizing the configuration of the vacuum tower transfer line;• decreasing the residence time of the resid in the tower's distillation section and reducing the temperature in this section by using vacuum resid quenching.The transfer line and coils in the radiant and convective sections of the furnace are an indivisible block, which requires a comprehensive approach to designing it.
At Ufa Oil Refinery Co., the "furnace-type" visbreaking unit was fitted out with a vacuum block for additional takeoff of residue of the following products made in it: vacuum solar oil as a component of diesel fuel, vacuum gasoil as feedstock for the G-43-107 cat cracker, and vacuum resid as a component of boiler fuel.The basic plan for the vacuum block and manufacture and installation of the vacuum tower equipped with structured packing were executed by Kedr-89 Co., the vacuum block was connected to the unit, and the heat-exchange system was designed by Bashgiproneftekhim SUE. The vacuum system was developed by Tekhnovakuum LLC and the construction and assembly work was done by VNZM trust (Ufa). Less than oneyear elapsed between development of the basic plan to start-up of the unit.The vacuum tower (see Fig. 1) is equipped with four sections of structured packing designed by Kedr-89 -VAKUPAK and KEDR -with the corresponding steam and liquid distributors, a blade device for feedstock input, and an Ultraset safety trap under the tower steam outlet connecting pipe.The residue at the bottom of the visbreaking unit tower enters the feedstock input into the vacuum tower through a transfer line without heating in the furnace. Light cuts are stripped as a result of the pressure drop.The upper circulating reflux stream (CR) together with the vacuum solar oil is taken off from the collecting tray under the first (from the top) packing section. The upper CR is returned to the tower after cooling through an injector distributor above the first packing section, and the vacuum solar oil is removed from the unit. The second packing section is the fractional distillation section and separates the vacuum solar oil and vacuum gasoil.The lower CR is taken off from the collecting tray under the third section together with the vacuum gasoil and hot reflux from the washing section. The hot reflux stream from this section is returned to the tower to the low-pressure grooved liquid distributor over the fourth packing section. The lower CR stream is returned to the tower after cooling through the injection distributor over the third packing section, and the vacuum gasoil is removed from the unit.Vacuum resid is taken off from the tower still. Feed of cooled bottoms into the still as quenching oil is provided to maintain the temperature in the still no higher than 350°C to prevent coking.
The problem of obtaining motor fuels with improved environmental characteristics corresponding to standards is examined. The experience of Kedr-89 Scientific-Production Company in revamping of naphtha cut isomerization units is presented. The operating parameters of deisohexanizers developed by Kedr-89 Co. are reported. The possibility of including depentanization and deisopentanization towers in the network of isomerization units is considered.According to the requirements of the Euro-4 and Euro-5 standards, the content of not only benzene (less than 1 vol. %) but also of total aromatics (less than 35 vol. %) are restricted in gasolines. To satisfy these requirements, reformate in gasoline production is usually diluted with isomerizate in the ratio of 1:1. Due to this, isomerization in the gasoline refinery becomes the largest tonnage process after reforming.Isomerization "in one operation" is the simplest scheme for isomerization of straight-run pentane-hexane fraction, but in this case the research octane number (RON) of the isomerate is no higher than 82-83 [1]. The greatest increase in the RON takes place during isomerization in conversion of n-hexane (RON = 25) into 2,2-dimethylbutane (RON = 92) and 2,3-dimethylbutane (RON = 102).Replacing the catalyst with a more modern catalyst decreases the temperature in the isomerization reactor and increases the feedstock throughput and conversion into valuable high-octane components, even in one passage through the reactor.
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