Tower-bottom temperature

The reboiler duty increases, to restore the tower-bottom temperature... 

Reducing reflux saves reboiler duty. Also, the lower pressure will reduce the tower-bottom temperature, and this also cuts the reboiler energy requirement. For most distillation towers, the energy cost of the reboiler duty is the main component of the total operating cost to run the tower. 

There are two ways to answer this question. Let s first look at the reboiler. As the tower-top temperature shown in Fig. 4.1 goes down, more of the lighter, lower-boiling-point alcohol is refluxed down the tower. The tower-bottom temperature begins to drop, and the steam flow to the reboiler is automatically increased by the action of the temperature recorder controller (TRC). As the steam flow to the reboiler increases, so does the reboiler duty (or energy injected into the tower in the form of heat). Almost all the reboiler heat or duty is converted to vaporization. We will prove this statement mathematically later in this chapter. The increased vapor leaving the reboiler then bubbles up through the trays, and hence the flow of vapor is seen to increase, as the reflux rate is raised. 

A. Heat 9000 lb/h of water from the 100°F feed temperature to the tower-bottom temperature of 220°F. 

This means that when the once-through thermosyphon reboiler is working correctly, the reboiler outlet temperature, and the tower bottoms temperature, are identical. If the tower-bottom temperature is cooler then the reboiler outlet temperature, then something has gone wrong with the thermosyphon circulation. 

The reboiler outlet temperature is always higher than the tower-bottom temperature. 

Water in reflux tends to get trapped in the tower, if the tower-bottom temperature is above the boiling point of water, at the tower s operating pressure. The water trickles down the tower and revaporizes off of the hot reboiler tubes. As the water may be saturated with corrosive salts and gases, reboiler tube corrosion can be rapid. In almost every petroleum refinery service, refluxing water is a quick route to reboiler tube leaks. 

Calculate the average alpha values (K of each component divided by HKK value). The average tower alpha A of each component = (Ai A2 A3)L 3. These A s are the tower top, the tower average temperature, and the tower bottom temperature AjS, all of which are used here to calculate the tower average A S. 

More efficient utilization of heat. In the first-stage towers of the Manhattan District plants, where most of the heat was consumed, heat flowed from the tower bottom temperature of... 

The tower top temperature and gross volume of overhead vapors are not high enough to force the moisture in the feed to be evaporated overhead. The tower bottom temperature and boil-up rate are too high to permit all... 

If the premature flooding problem was really attributable to excessive vaporization of cycle oil by the hot reactor vapors, then desuperheating the vapor external to the fractionator ought to mitigate the problem. I discussed the possibility with a colleague who suggested the modification shown in Figure 8-3. Cooled slurry oil from the pumparound return line is sprayed into the reactor vapor line. The slurry oil does not start to vaporize until it is healed to 680 F (i.e., the tower bottoms temperature). Hence, if... 

To answer this fundamental question, we should realize that reducing the tower pressure will also reduce both the tower-top temperature and the tower-bottom temperature. So the change in these temperatures, by themselves, is not particularly informative. But if we look at the difference between the bottom and top temperatures, this difference is an excellent indication of fractionation efficiency. The bigger this temperature difference, the better the split. For instance, if the tower-top and tower-bottom temperatures are the same for a 25-tray tower, what is the average tray efficiency (Answer 100 percent + 25 = 4 percent.)... 

There are two ways to answer this question. Let s first look at the reboiler. As the tower-top temperature shown in Fig. 7.1 goes down, more of the lighter, lower-boiling-point alcohol is refluxed down the tower. The tower-bottom temperature begins to drop, and the steam flow to the reboiler is automatically increased by the action of the... 

Heat the feed from 180°F to the 250°F tower bottoms temperature. 

As the amount of liquid overflowing the draw pan increases, and the amount of liquid flowing to the reboiler decreases, the tower bottoms temperature will start to approach the tray temperature. For example, with valve A wide open, I had observed the following temperatures ... 

Temperature difference In distillation, the tower bottom temperature minus the tower top temperature. 

Reducing reflux saves reboiler duty. Also, the lower pressure will reduce the tower-bottom temperature, and this also cuts the reboiler... 

But if valve A is opened, and the feed to the reboiler is coming from the bottom of the tower, then the reboiler outlet temperature must be hotter than the tower bottoms temperature. This temperature difference would be quite small if we had essentially a pure component (like butane) as the tower bottoms product. But with a wide boiling... 

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