Atmospheric crude still

Atmospheric Crude Stills Coefficient r for Heat Transfer Equation 6-26... 

Water Cooling Theory, Cooling Tower Design, Cooling Tower Fill, Gas Quench Towers, Quench Tower Design, Total Condenser Theory, Total Condenser Design, Partial Condenser Theory, Chlorine Gas Cooling, Vacuum Crude Stills, Atmospheric Crude Stills, Olefin Primary Fractionator, Olefin Water Quench Tower, Example Problem, Notation, References... 

In addition to the distillation of crude oil coming into the refinery, stills of various designs are used in other types of service throughout the refinery. Cracked products are separated in distillation equipment which is very similar to an atmospheric crude pipe still. The principal difference is that these products are hot from the cracking operation, so that a fired heater is not required. 

Normally, all of the heat is removed from the fractionator by three or more circulating reflux streams. The proportion of gas and naphtha in the cracked products is much higher than in crude oil, so it is seldom possible to reduce the diameter of the tower top as in atmospheric pipe still design. Due to the low operating pressure, it is necessary to provide expensive compression capacity to permit recovery of these light hydrocarbons in subsequent equipment. 

In the atmospheric distillation process (Figure 2.1), heated crude oil is separated in a distillation column (distillation tower, fractionating tower, atmospheric pipe still) into streams which are then purified, transformed, adapted, and treated... 

The high temperatures applied to the bottom of the tower stills damaged them so that they had to be replaced frequently. This was relatively expensive. As a result, special coke stills were used. Similar to the tower stills but smaller, the bottoms of these stills were cheaper to replace. The crude oil was reduced in the tower still to about 20° to 25° API gravity and transferred to the atmospheric coke still. This still was then heated rapidly to effect the cracking and coking. The entire coking operation required about 40 hours (55). Twenty-five years ago, a major part of petroleum coke was made in such shell stills. 

When crude oil comes into a refinery, it is processed in an atmospheric pipe still. The side stream of the pipe still is rich with light gas oil. Fluid catalytic cracking units, or catcrackers, split this gas oil into smaller, more useful molecules (Figure 11-9). Fluid catalytic cracking units use the following equipment during operation ... 

Vacmun crude still— A vacuum tower that processes the bottoms from an atmospheric pressure distillation of crude oil. 

In two stage units, it is often economical to distill more gas oil in the vacuum stage and less in the atmospheric stage than the maximum attainable. Gas formed in the atmospheric tower bottoms piping at high temperatures tends to overload the vacuum system and thereby to reduce the capacity of the vacuum tower. The volume of crude vaporized at the flash zone is approximately equal to the total volume of distillate products. Of course, the vapor at this point contains some undesirable heavy material and the liquid still contains some valuable distillate products. The concentration of heavy ends in the vapor is reduced by contact with liquid on the trays as the vapor passes up the tower. This liquid reflux is induced by removing heat farther up in the tower. 

A 500-ml, three-necked, round-bottom flask is equipped with a condenser, a dropping funnel, and a thermometer in the reaction mixture. In the flask is placed a mixture of 85% hydrazine (115 ml, 118 g) and 225 ml of 95% ethanol with a few boiling chips. The solution is brought to reflux (mantle) and cinnamaldehyde (100 g, 0.76 mole) is added dropwise over about 30 minutes followed by an additional 30 minutes of refluxing. A still head is attached to the flask and volatiles (ethanol, water, hydrazine hydrate) are slowly distilled at atmospheric pressure until the pot temperature reaches 200° (about 3 hours). Hereafter, phenylcyclopropane is collected over the range 170-180°. When the pot temperature exceeds 250°, the recovery is complete. The crude product (55-65 g) is washed twice with 50-ml portions of water and dried (anhydrous potassium carbonate). Distillation under vacuum through a short column affords the product, bp 60°/13 mm, 79-80°/37 mm, n f 1.5309, about 40 g (45%). 

Caustic that is added downstream of the crude oil desalter. Caustic is injected downstream of the desalter to control overhead corrosion. Natural chloride salts in crude decompose to HCl at typical unit temperatures. Caustic reacts with these salts to form sodium chloride. Sodium chloride is thermally stable at the temperature found in the crude and vacuum unit heaters. This results in sodium chloride being present in either atmospheric or vacuum resids. Most refiners discontinue caustic injection when they process residue to the FCC unit. It can still be present in purchased feedstocks, however. 

Result The recovery of different fractions of petroleum distillate under atmospheric pressure was more than under reduced pressure because at lower pressure the vapour pressure of lighter molecule of crude oil increased so that they were siphoned out from the system without being condensed. Whereas a combination of distillation of lighter fraction under normal atmospheric pressure followed by the distillation of heavier contents under reduced pressure showed an improvement in the recovery of petroleum products. Recovery of distillates was still more when crude oil was first sonicated and then distilled under normal and reduced pressures. The viscosity of distillate increased with sonication whereas there was a decrease in value of density. 

The asphaltic residuum from atmospheric distillation amounts to roughly one-third (U.S. average) of the crude charged. This material is sent to vacuum stills, which recover additional heavy gas oil and deasphalting feedstock from the bottoms residue. 

A. 2-Methyl-2-nitropro]f)ane. To a well-stirred suspension of 650 g. (4.11 moles) of potassium permanganate in 3 1. of water, contained in a 5-1. three-necked flask fitted with a reflux condenser, a mechanical stirrer, a thermometer, and a 250-ml. dropping funnel, is added dropwise and with stirring over a 10-minute period, 100 g. (1.37 moles) of i-butylamine (Note 1). When the addition is complete, the reaction mixture is heated to 55° over a period of approximately 2 hours, and then the reaction mixture is maintained at 55° with continuous stirring for 3 hours. The dropping funnel and reflux condenser are replaced by a stopper and a still head fitted for steam distillation and the product is steam distilled from the reaction mixture (Note 2). The liquid product is separated from the denser water layer and then diluted with 250 ml. of ether and washed successively with two 50-ml. portions of aqueous 2M hydrochloric acid and with 50 ml. of water. After the ethereal solution has been dried over anhydrous magnesium sulfate, the solution is fractionally distilled at atmospheric pressure to remove the ether. The residual crude product (Note 3) amounts to 106-128 g. and is sufficiently pure for use in the next step. In a typical run, distillation of 124 g. of the crude product afforded 110 g. (78%) of the pure 2-methyl-2-nitrobutane as a colorless liquid, b.p. 127-128°, d 1.3992. The material slowly solidifies on standing to a waxy solid, m.p. 25-26° (Note 4). 

Two years later Gay-Lussac and J.-B. Biot made a daring balloon ascension to study the behavior of a magnetic needle and the chemical composition of the atmosphere at high altitudes. On another occasion, when Gay-Lussac alone had reached an elevation of 7016 meters and wished to ascend still higher, he threw overboard some small objects to lighten the balloon. A shepherdess in the field was astonished to see a white wooden chair fall from the sky into some bushes, and the peasants who heard her story were at a loss to explain why, if the chair had come direct from Heaven, the workmanship on it should be so crude (3). 

A. Purification of phenanthrene. 1. By azeotropic distillation.2 A mixture of 300 g. of commercial phenanthrene (Note 1), 90 g. of maleic anhydride, and 600 ml. of xylene, contained in a 2-1. round-bottomed flask, is heated under reflux for 20 hours (Note 2). The initially yellow solution rapidly turns to a dark brown on heating. This solution is cooled to room temperature and filtered by suction to remove any insoluble adduct. The filtrate is then extracted with two 100-ml. portions of dilute sodium hydroxide, and the basic extracts are discarded. The organic phase is next washed with water and saturated sodium chloride solution, and finally is filtered through a layer of anhydrous magnesium sulfate. The excess xylene is removed by distillation, first at atmospheric pressure then the final portions are removed at reduced pressure. The residue, while still hot, is poured into a large mortar and, after solidification, is powdered to a convenient size. The yield of crude phenanthrene is 230-240 g. 

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