Crude unit columns

The desalting and distillation units are shown in Figs. 18.8-18.10 along with the crude fractions from the crude distillation column. The relationships between some finished products and downstream processing steps will be expanded upon later in the chapter. 

Shown in Figure 4.2 is a simple refinery flow-sheet. There are many refineries in the world configured in this manner. These are often referred to as simple refineries. In many of these refineries, the crude oil column has greater capacity to the downstream processing units and the refinery sells the excess intermediate streams such as naphtha on the oil market. 

The overhead product of the crude unit contains hydrogen, methane, carbon dioxide, hydrogen sulfide, and hydrocarbons up to butanes and some pentanes. It is usually sent to a set of distillation columns known as a saturate gas plant for recovery of propane and butane for sale. The lighter gases are then used as refinery fuel. 

Fig. 8 is a schematic representation of a vacuum column, sometimes called a flasher, intended to produce asphaltene-free cracking feed and heavy black fuel oil. The fired preheat furnace is similar to the crude unit heater, except that tolerable tube skin temperatures are somewhat lower because of the absence of light hydrocarbons. 

Occasionally, foaming in the preflash column can limit throughput to the crude unit. Organic surfactants or water carry-over from the desalters can be the cause of the problem. Silicones, usually of 60,000-cSt viscosity, are normally used in this process. However, sometimes the normal silicones are too soluble in the crude to be effective in controlling foam. In... 

A common troublespot in refinery crude units is the desalter relief valve, which often relieves into the crude column. Lifting of this relief valve has caused pressure surges. Guidelines 4 and 5 are important with regard to the location of this valve (296). It is best to have this relief valve discharge elsewhere. 

If a crude unit contains only a two-column atmospheric unit, then in the main column a moderate vacuum has to be kept ( 0,8 atm) with the help of vacuum-creating equipment joined with c reflux drum. 

Two years later, I was working for ARCO on a vacuum tower problem in Ferndale, Washington, when my colleague at AXECO called again. He related that the tower on No. 2 crude unit had been opened for inspection and that they wanted me to fly down to their plant to inspect the stripping trays. Figure 1-2 shows what 1 found when I entered the column. 

II) Turbine (12) Rectification column (pressure section) (13), (16), (19) combined condenser-evaporator unit (14) Rectification column (low-pressure section) (15) Crude argon column (17) Pure argon column (18) Reboiler (20) Ar- process pump (21) Internal compression pump (22) Throttle valve. 

The oxygen-enriched Hquid from the sump of the pressure column is also expanded and then, on the one hand, fed as liquid into the low-pressure column (i) and, on the other hand, evaporated in the two combined evaporator-condenser units (16), (19) on top of the crude argon column (15) and the pure argon column (17). This cools the two argon columns head condensers, thereby providing the necessary reflux for these columns. The evaporated oxygen - enriched liquid is fed into the low-pressure column. 

A fire occurred at the refinery crude unit, flames and a column of smoke were visible in the air, which affected nearby residents. Corrosion in a 40-year-old pipe caused a leak that initiated the fire. Reportedly 15,000 nearby residents sought treatment after breathing emissions from the fire. Company received 25 citations from Cal/ OSHA. 

This section documents some of the key steps required to model the representative crude unit described in the previous section. We use a 50%-50% mixture of the assays presented in Table 2.5 to Table 2.8 as the feed to the column. In the workshop examples accompanying this chapter, we will simulate this column on the basis of back-blending alone and compare the results. 

Concentration of Rare Gas Crudes. The distillation of air is classically carried out in the double-column and auxihary equipment of Figure 5. Dry, C02-free air, chilled to partial liquefaction by heat exchange, is introduced into the lower nitrogen or high pressure column. This unit is typically... 

Product Recovery. The aHyl chloride product is recovered through the use of several fractional distillation steps. Typically, the reactor effluent is cooled and conducted into an initial fractionator to separate the HCl and propylene from the chloropropenes, dichloropropanes, dichloropropenes, and heavier compounds. The unconverted propylene is recycled after removal of HCl, which can be accompHshed by adsorption in water or fractional distillation (33,37,38) depending on its intended use. The crude aHyl chloride mixture from the initial fractionator is then subjected to a lights and heavies distillation the lighter (than aHyl chloride) compounds such as 2-chloropropene, 1-chloropropene, and 2-chloropropane being the overhead product of the first column. AHyl chloride is then separated in the second purification column as an overhead product. Product purities can exceed 99.0% and commercial-grade aHyl chloride is typicaHy sold in the United States in purities about 99.5%. 

Where is naphthenic acid corrosion found Naphthenic acid corrosion occurs primarily in crude and vacuum distillation units, and less frequently in thermal and catalytic cracking operations. It usually occurs in furnace coils, transfer lines, vacuum columns and their overhead condensers, sidestream coolers, and pumps. 

Nevertheless, a number of gas chromatographic applications exist, epecially those for the determination of crude oil indicators. Such indicators are used as geochemical parameters for the thermal history of the crude as well as to indicate the possible relationship between crudes from different wells. These indicators comprise a number of isomeric aromatic species, such as the individual alkylnaphthalenes (44, 45), the individual Cio-mono-aromatics or the individual C9-mono-aromatics. The ratio between these isomers gives a definite indication of the crude oil. In general, these systems use a Deans switching unit to make a heart-cut, which then is focused, reinjected and separated on a second column with a different polarity. 

The atmospheric reduced crude is the feedstock for the vacuum distillation unit. To prevent thermal decomposition (cracking) of the higher boiling point hydrocarbons in the crude oil, the pressure in the vacuum distillation fractionation column is reduced to about one-twentieth of an atmosphere absolute (one atmosphere pressure is 14.7 psia or 760 mm Fig). This effectively reduces the boiling points of the hydrocarbons several hundred degrees Fahrenheit. The components boiling below about 1050°F (565°C) are vaporized and removed as vacuum gas... 

Atmospheric distillation separates the crude oil complex mixture into different fractions with relatively narrow boiling ranges. In general, separation of a mixture into fractions is based primarily on the difference in the boiling points of the components. In atmospheric distillation units, one or more fractionating columns are used. 

Fig. 4. Elution of the crude polyhexapeptide (Pro-Ala-Gly-Pro-A]a-Gly) from a Biogel P4 column. (34 X 1400 mm, 200-400 mesh, 0.05 M acetic acid, 50 ml/h, 20 °Q. The upper curve was obtained by the first chromatography, the curves below were obtained by the fifth rechromatrogra-phy. e = absorbance at 230 nm, Ve = elution volume, VD = 310 ml, n — number of hexapeptide units...

The separation of benzene from a mixture with toluene, for example, requires only a simple single unit as shown in Figure 11.1, and virtually pure products may be obtained. A more complex arrangement is shown in Figure 11.2 where the columns for the purification of crude styrene formed by the dehydrogenation of ethyl benzene are shown. It may be seen that, in this case, several columns are required and that it is necessary to recycle some of the streams to the reactor. 

The cell-bound amylopullulanase was solubilized with detergent and lipase. It was then purified to homogeneity by treatment with streptomycin sulfate and ammonium sulfate, and by DEAE-Sephacel, octyl-Sepharose and puUulan-Sepharose column chromatography (12). The final enzyme solution was purified 3511-fold over the crude enzyme extract with an overall recovery of 42% and had a specific activity of 481 units/mg protein. The average molecular weight of the enzyme was 136,500 determined by gel filtration on Sephacryl S-200 and SDS-PAGE, and it had an isoelectric point at pH 5.9. It was rich in acidic and hydrophobic amino acids. The purified enzyme was quite thermostable in the absence of substrate even up to 90°C with essentially no loss of activity in 30 min. However, the enzyme lost about 40% of its original activity at 95 C tested for 30 min. The optimum tenq)erature for the action of the purified enzyme on pullulan was 90°C. However, the enzyme activity rapidly decreased on incubation at 95°C to only 38% of the maximal 30 min. The enzyme was stable at pH 3.0-5.0 and was optimally active at pH 5.5. It produced only maltotriose and no panose or isopanose from pullulan. 

Both the failure of the isolation valves to hold and the difficulty in draining the system were due to solid build up in the circuit. In the previous two-year period, the refinery had changed its crude feedstock resulting in operating difficulties on the unit desalter. Carryover of salts led to accelerated corrosion in the crude column and associated piping circuits. 

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