Deasphalting unit

In work prior to this program, Kerr-McGee demonstrated that extremely rapid solids separation (deashing) on the order of 30 to 60 times faster than a conventional deasphalting unit and high deashing efficiencies producing less than 0.1 wt% ash on SRC product could be achieved. In addition, it has been demonstrated that the SRC could be fractionated into multiple residual fractions. 

One obvious method of cleaning the feed is to remove asphaltic material (asphaltenes plus resins) using a solvent such as propane in a deasphalting unit. The resulting deasphalted oil has less metals than the original feedstock but coke formation and catalyst deactivation are not completely eliminated. The byproduct stream is usually only acceptable as a raw material for asphalt manufacture. Even then, the asphaltic by-product may be unsuitable for a specification grade asphalt and require disposal by other means. 

FIGURE 1.1 Schematic of a refinery crude fractionation train and deasphalting unit. 

Bright stock is the most expensive conventional lube to manufacture and requires the addition of a deasphalting unit. 

The presence of asphaltenes in the feed to the propane dewaxer or in the propane will significantly reduce the filtration rate and must be avoided. Asphaltenes may be present in the heavy neutral due to entrainment from the VPS section below the heavy sidestream drawoff Contamination may occur if the lube deasphalting unit (LDU) and propane dewaxer share propane. 

Deasphalted Oil The extract or residual oil from which asphalt and resins have been removed by an extractive precipitation process called deasphalting. DeAsphalting Unit A process for removing asphalt from reduced crude or vacuum residua (residual oil) which utilizes the different solubilities of asphaltic and nonasphaltic constituents in light hydrocarbon liquids, e.g., liquid propane. 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

The cat products become feed to other units, such as alkylation and polymerization plants. High boiling liquid products are used to make lubes, and the gas goes into the refinery fuel systems. Cat cracking feed stocks come from atmospherie and vacuum stills, phenol extraction plants, hydrotreaters, deasphalters and cokers. 

The teed to the cat cracker in a typical refinery is a blend of gas oils from such operating units as the crude, vacuum, solvent deasphalting, and coker. Some refiners purchase outside FCC feedstocks to keep the FCC feed rate maximized. Other refiners process atmospheric or vacuum residue in their cat crackers. In recent years, the trend has been toward heavier gas oils and residue. Residue is most commonly defined as the fraction of feed that boils above 1,050°F (565 C). Each FCC feed stream has different distillation characteristics. 

To date, twenty-six commercial units have been installed to deasphalt residual oils for the production of lubricating oils and three units to deasphalt (decarbonize) heavy reduced crudes for preparation of catalytic cracking feed stocks. 

The liquid hydrocarbon causes separation of the asphaltenes and/or the resins from the feedstock leaving a deasphalted oil that contains substantially less sulfur and metals than the feedstock. On a commercial scale, propane is the most common solvent (Figure 7-21) and the units are designed to operate at 40 to 80°C (105 to 175°F) and at pressures of 400 to 550 psi with the solvent/ feedstock ratio usually falling in the range 5 1 to 13 1. 

The solvent contained in the asphalt and deasphalted oil is condensed in the fractionator overhead condensers, where it can be recovered and used as lean oil for a propane/butane recovery in the absorber, eliminating the need for lean oil recirculation from the naphtha stabilizer. The solvent introduced in the coker heater and coke drums results in a significant reduction in the partial pressure of asphalt feed, compared with a regular delayed coking unit. The low asphalt partial pressure results in low coke and high liquid yields in the coking reaction. 

The Demex process is an extension of the propane deasphalting process and employs a less selective solvent to recover not only the high quality oils but also higher molecular weight aromatics and other processable constituents present in the feedstock. Furthermore, the Demex process requires a much less solvent circulation in achieving its objectives, thus, reducing the utility costs and unit size significantly. 

The Chevron deasphalted oil hydrotreating process is designed to desulfurize heavy feedstocks that have had the asphaltene fraction removed by prior application of a deasphalting process (Chapter 7). The principal product is a low-sulfur fuel oil that can be used as a blending stock or as a feedstock for a fluid catalytic unit (Table 9-7). 

In the second step, the preprocessor builds and prints out tables showing the extracted crude assay data. The preprocessor also prints out in tabular form all information which the user has specified by card input for the following process units o Crude distillation unit o Propane deasphalter o FCC... 

In the fourth step, the preprocessor generates plant performance data for the FCC, gas oil hydrocracker, motor reformer and BTX reformer. For each of these process units, the preprocessor calls the appropriate process simulator which computes the usage of equipment and utilities, product yields, and product properties for all base and alternate operations specified by the user. For all of the FCC operations, the feed properties are those of the atmospheric plus vacuum gas oil from the base crude mix blended with a specified fraction of deasphalter overhead. 

Activities in the propane deasphalting (PDA) unit submatrix represent the operations on vacuum tower bottoms from the base crude mix and from the incremental crudes. The de-asphalter overhead streams from all activities enter one stream balance row with common properties. Each deasphalter bottoms enter a separate row for No. 6 fuel oil blending. 

Miscellaneous units-fluid catalytic cracking, monoethanolamine (MEA) extraction. HF alkylation, boiler, propylene polymerization, propane deasphalting. 

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