Distillation towers side streams

Separation of the oxide and the organic byproducts is accomplished by distillation in two towers. Feed from the saponifier contains oxide, aldehyde, dichloride, and water. In the first tower, oxide and aldehyde go overhead together with only small amounts of the other substances the dichloride and water go to the bottom and also contain small amounts of contaminants. Two phases will form in the lower section of this tower this is taken off as a partial side stream and separated into a dichloride phase which is sent to storage and a water phase which is sent to the saponifier as recycle near the top of that vessel. The bottoms are a waste product. Tower pressure is 20 psig. Live steam provides heat at the bottom of this column. 

Figure 3.13. Crude oil vacuum tower. Pumparound reflux is provided at three lower positions as well as at the top, with the object of optimizing the diameter of the tower. Cooling of the side streams is part of the heat recovery system of the entire crude oil distillation plant. The cooling water and the steam for stripping and to the vacuum ejector are on hand control.

The bottoms of the CD, also known as atmospheric residue, are charged to a second fired heater where the typical outlet temperature is about 750-775°F. From the second heater, the atmospheric residue is sent to a vacuum tower. Steam ejectors are used to create the vacuum so that the absolute pressure can be as low as 30-40 mm Hg (about 7.0 psia). The vacuum permits hydrocarbons to be vaporized at temperatures below their normal boiling point. Thus, the fractions with normal boiling points above 650°F can be separated by vacuum distillation without causing thermal cracking. In this example (Fig. 18.14), the distillate is condensed into two sections and withdrawn as two sidestreams. The two side-streams are combined to form cracking feedstocks vacuum gas oil (VGO) and asphalt base stock. 

In 1992, a rather unusual furfural plant was built. With a front end according to the AGRIFURANE process described in chapter 10.2, the back end was designed as shown in Figure 112. The filtered reactor condensate containing 5 % furfural, 1.7 % acetic acid, 0.17 % formic acid, and various low boilers was introduced into an extraction tower 1 fed with chloroform at the top. On the way downwards, the heavy chloroform (density 1.498 g/cc at room temperature) picked up the furfural, and in view of the poor solubility of chloroform in water, it formed a chloroform/furfural extract at the bottom. This extract entered a distillation column 2 removing the chloroform as the head fraction. From a buffer tank 3, this chloroform was recycled to the extraction tower 1. The sump fraction of the distillation column 2 consisted of furfural, polymers, waxes, and some low boilers. This fraction was introduced into a distillation column 4, which yielded a head fraction of low boilers, a side stream of furfural, and a sump fraction of polymers and waxes. 

FIGURE 11.4-17. Processflow for a rectification tower with a liquid side stream. Sec. 11.4 Distillation With Reflux and McCabe-Thiele Method... 

Packie s (2) classic paper was the first to disclose criteria for defining fractionation between atmospheric tower distillate streams. Figure 2.6 is Packie s curve for fractionation between the overhead fraction and the adjacent side-stream. 

Fio. 16-22. Gap and overlap of top and side-stream products from topping towers. (Packie, Tram. A.I.Ch.E.) See discussion for. application to cracking-plant fractionators. 1. For overhead and top stream only. 2. Solid curves for no steam. Dotted curves for the maximum stripping steam generally used. 3. Numbers on curves represent degrees Fahrenheit difference in 50 per cent distillation points of the overhead and top side-stream products. 

The atmospheric distillation column in a refinery is highly complex system because of the interactions between the main column with different side strippers and draw streams where the study of this complex system will be more difficult. However, the decomposition of the complex column into a series of simple columns ease and simplify its study. There are a number of advantages of decomposing a complex tower, namely ... 

Feed from the Toluene tower is preheated (1) by the MX tower distillate product and then enters the MX tower (2) at approximately the middle tray. The MX tower overhead is totally condensed using heated water firom the gas fired reboiler (3). Steam is produced in the condenser (4) and dehv-ered to a utility header. Flow of water into the shell side of the condenser is manipulated by a level controller. The condensed MX tower overhead material is collected in an accumulator (5). A level controller manipulates the reflux to the tower to maintain the accumulator level. The overhead product flow is set externally, either by an advanced controller or manually. At the bottom of the MX tower the flow is divided into two streams. One of the streams is circulated through the gas fired reboiler, where it is partially vaporized and then returned to the MX tower. The vaporization rate is set... 

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