JPS5823122B2 - distillation column - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in distillation columns.

The present invention has the greatest significance when applied to a main distillation column for petroleum products that distills crude oil or heavy oil to obtain various petroleum fractions in a petroleum refinery.

In the main distillation column of crude oil, it is recently possible to fractionate the crude oil into naphtha lighter fraction (a mixture of naphtha and lighter fractions), kerosene fraction, light gas oil fraction, heavy gas oil fraction and residual oil. It is often done.

In some cases, the naphtha fraction is divided into light naphtha and heavy naphtha and distilled from the main distillation column, or the light oil fraction is further divided and distilled.

When the naphtha lighter fraction is distilled all at once, it is common to separate light components from it and use a small distillation device called a splitter to divide it into light naphtha and heavy naphtha.

Since distillation of such crude oil is generally carried out under pressure near normal pressure, this main distillation column is usually called an atmospheric main distillation column.

FIG. 1 is a system diagram showing a typical flow surrounding an atmospheric main distillation column.

On the other hand, residual oil obtained by distilling crude oil in an atmospheric main distillation column and heavy oil, collectively called heavy oil, contain fractions useful as various lubricating oils, so in order to extract them, Heavy oil may be further distilled.

Distillation of heavy oil is carried out under reduced pressure to lower the boiling point in order to avoid deterioration and decomposition at high temperatures, so the main distillation column used for this purpose is called a vacuum main distillation column.

These main distillation columns, whether under normal pressure or reduced pressure, usually take out a plurality of fractions as side cuts from the middle of the column.

To further explain the atmospheric distillation of crude oil with reference to Figure 1, crude oil is preheated by exchanging heat with the distillate from the main distillation column, residual oil, and side reflux. It is heated to a predetermined temperature in a heating furnace and supplied to the atmospheric pressure main distillation column.

In the atmospheric main distillation column, no reboiler is used, and all of the heat required for distillation is given to the crude oil before it enters the main distillation column.

Therefore, each fraction in the crude oil, apart from the residual oil, is fed to the main distillation column mostly in the vapor state.

As is well known, gas-liquid contact means such as bubble cap trays, valve-type trays, and perforated trays are installed in the tower, and each fraction in the gaseous state is directed upward while the liquid is directed downward. By making contact here, the high-boiling components in the gas liquefy and the low-boiling components in the liquid vaporize. As a result of this process being repeated, the closer to the top of the tower the higher the content of low-boiling components, and the closer to the bottom of the tower the higher the content. Distillation is performed after the component distribution is changed so that the number of boiling point components increases.

In terms of temperature distribution, the temperature is lowest at the top of the column and highest at the raw material supply section.

The column top temperature is a temperature suitable for distilling the naphthalite fraction, which is the column top distillate, in the gas phase, and is obtained by adjusting the top reflux (column top reflux).

Most of the naphtha lighter fraction is condensed in a condenser and separated into light gas and LPG components and a naphtha fraction in a distillation device called a stabilizer.

If necessary, the naphtha fraction is divided into light and heavy.

As mentioned above.

Side-cut fractions such as kerosene, light gas oil and heavy gas oil are withdrawn from the main distillation column at respective appropriate locations.

However, each side-cut fraction is unavoidably mixed with low-boiling fractions, which is undesirable in terms of product use, so they are removed by using a stripper.

In the stripper, the side-cut fraction is heated by contacting it countercurrently with steam or by using a reboiler.
Drive off low-boiling fractions.

The driven off low-boiling fraction is returned to the main distillation column.

The residual oil fraction is supplied to the main distillation column in an almost liquid state,
Light components are removed by countercurrent contact with stripping steam introduced from the bottom of the column and exit from the bottom of the column.

In distillation operations, it goes without saying that so-called top reflux (top reflux), in which the top gas is condensed and a portion of it is returned to the first stage at the top of the column, is generally essential. In distillation operations that take a side cut fraction, such as in a distillation column, reflux is often divided into several parts and carried out not only at the top of the column but also in the middle of the column.

This is an operation called side reflux.
A considerable amount of liquid is extracted from the middle of the distillation column, cooled by applying heat to crude oil etc. via a heat exchanger, and then returned to several stages above the extraction stage.

This removes heat from the distillation column and reduces the burden of overhead reflux.

As will be clear from what will be described later, the use of side reflux is advantageous in avoiding an increase in the diameter of the distillation column and in more effectively utilizing the amount of heat removed from the column.

In the example shown in Figure 1, the top reflux is not performed through the gas condensation described above, but the liquid is extracted from several stages below the top of the tower in the same way as the side reflux, cooled (exchanged heat with crude oil), and then returned to the tower. It has returned to the first stage at the top.

This is one way to use heat more effectively, and its function as a top reflux is no different from conventional technology.

By the way, the cross-sectional area required for a distillation column is determined by the amounts of liquid and gas that flow countercurrently through the column and come into contact with each other, the so-called sum of the column internal liquid load and vapor load.

This internal load varies significantly depending on the vertical force direction of the distillation column.

Since it is the liquid load force that has a greater influence on fluctuations in the load inside the tower, if we can represent this schematically, we can use the second
As shown in the figure.

In the case of simple distillation without side cuts, the amount of reflux in the column decreases as the temperature rises from the top of the column toward the raw material supply section, so the load is large at the top, as shown in Figure 2A. It gradually becomes smaller towards the bottom.

When a part of the liquid is extracted as a product by performing a side cut, the reflux in the column below the stage from which the liquid was extracted is reduced by that amount, and becomes as shown by the broken line in FIG. 2B.

Furthermore, in a distillation column provided with side reflux, part of the heat within the column is removed, and as a result, the reflux in the column above the column is reduced compared to a case without side reflux.

The degree of this reduction is proportional to the rate of flux.

- Between the stage for taking out the side reflux and the stage for returning it, the amount of circulation becomes large, and the liquid load becomes significantly large.

The situation is as shown in Figure 2C, where the shaded area in the figure is the amount of liquid reflux in the column that has been reduced by adopting side reflux, and the double shaded area is on the contrary, the amount that has increased in the column. This is the internal fluid reflux amount.

Needless to say, the cross-sectional area required for the distillation column, in other words, the column diameter, is controlled by the maximum load, so in the cases of Figure 2 A and B, the load at the top of the column is the standard, and the second Diagram C
In this case, the standard is the force that has the greater load on either the tower top or side reflux section.

It will be easily understood from FIG. 2C that the diameter of the column can be reduced by employing the side reflux described above.

It will also be appreciated that the in-column load varies significantly from side to side in the vertical direction of the column due to side cut and also due to side reflux.

The diameter of the distillation column may be determined in part depending on the magnitude of the load.

However, if the outer shell of the tower is to be made with many irregularities, it will require higher costs and a longer construction period, which is actually disadvantageous from an industrial perspective.

Traditionally, Trakuri-type distillation columns have only been built for special distillations where the load near the top of the shell is much lower than that below.

circle.

Therefore, distillation columns, especially atmospheric main distillation columns for crude oil, have necessarily been constructed with large margins.

Needless to say, this means wasted space.

In addition, distillation columns generally require distillation operations or associated equipment.

In particular, when side-cutting is performed, as mentioned above, it is desirable to remove low-boiling components contained in the side-cut fraction, and a device such as a side stripper should be provided.

Traditionally, such auxiliary equipment was constructed separately from the distillation column.
Piping was also required to go back and forth between the two.

The inventors of the present invention have focused on the fact that there is unused space within the distillation column, and in order to make effective use of this space and reduce construction costs, the inventors of the present invention have attempted to install attached equipment in this space in order to make effective use of it and reduce construction costs. The present invention was conceived based on the idea of incorporating the following.

Therefore, the distillation column of the present invention separates a mixture of a plurality of liquid components based on the difference in their boiling points, and separates at least one type of side cut fraction. It is characterized in that equipment for processing the distilled fraction is housed in a portion where the amount of material refluxing in the column is small, occupying a part of the horizontal cross section of the column.

As may be clear from Sagi's description, a preferred embodiment of the invention is that the distillation column is equipped with at least one side reflux facility, and the side reflux stream does not circulate through the facility for treatment of the fraction. It is provided in the section.

According to the present invention, construction work for equipment for treating fractions, including foundation work, becomes unnecessary.

Moreover, piping work between the main distillation column and the processing equipment can be significantly reduced.

Since the fraction processing equipment can be housed in the space that was previously wasted within the distillation column, there is no need to increase the column diameter itself.

These benefits greatly contribute to reducing plant construction costs and shortening the construction period.

Furthermore, the present invention is extremely useful when attempting to construct a distillation plant on limited land.

Let's go back to the atmospheric main distillation column for crude oil and consider the points mentioned above.

The load in the column varies depending on the properties of the crude oil, mainly its distillation curve.

In other words, how much of the total fraction other than residual oil, in other words, the fraction supplied in gaseous form to the main distillation column, is contained in the crude oil, and what is the proportion of each fraction obtained by distillation? It depends.

However, in any case, the in-column loads vary widely from section to section of the column.

As mentioned above, this is due to side cut and side reflux, and how the load changes depending on the part of the column depends on the amount ratio of each distillate except for residual oil, as well as which reflux. It depends on how much heat is removed.

Figure 3 shows an example of the normal pressure main distillation column, with the internal load in the column similar to Figure 2, and the solid line indicates the liquid load,
Each dotted line indicates the steam load.

In this example, crude oil is fractionated into naphthalene fraction, kerosene fraction, light gas oil fraction, heavy gas oil fraction, and residual oil, and in addition to the top reflux, a light gas oil fraction extraction section is also used. Side reflux is provided at two locations: the heavy gas oil distillate extraction section.

In this figure, the following operations are performed in each section indicated by symbols A to G.

A... Top reflux circulates B...
・Fractional distillation C between naphtha lighter fraction and kerosene fraction...
・Fractional distillation D between kerosene lighter fraction and light gas oil fraction...
・Light diesel oil side reflux circulates E...
Fractional distillation of light gas oil lighter fraction and heavy gas oil fraction F...Heavy gas oil side reflux is circulated G.
...To explain the phenomenon in the fractionation tower between the lighter fraction of heavy gas oil and residual oil, heated crude oil is flashed to the bottom of the tower, and vapor and liquid are separated.

Crude oil usually enters with a slight overflush;
While the steam rises in the column, its overflash condenses at G and falls to the bottom of the column.

In G, the temperature in the upper part is low and the amount of condensed liquid increases, so the liquid load increases upward from the lower blade.

At the same time, evaporation of the lighter fraction of heavy gas oil occurs, so the steam load also increases from the lower part to the upper part.

In part F, heavy light oil side reflux is circulating, so the liquid load increases, but there is almost no difference between the upper and lower parts of this part.

− As part of the force and steam condenses due to reflux,
The steam load decreases slightly from the bottom to the top.

Similarly, at E, where the light oil fraction and heavy gas oil fraction are fractionated, and at D, where the light gas oil side reflux is circulated, the liquid load and vapor load are low for the reasons described for G and F. Change.

C, where the kerosene lighter fraction and light gas oil fraction are fractionated, B, where the naphtha lighter fraction and kerosene fraction are fractionated, and A, where the top reflux circulates, are the same as G and F. A significant change in fluid load occurs.

Needless to say, since there is a temperature gradient that decreases toward the top of the column, the liquid load at the top of each section is large, and furthermore, B and C
There is a difference depending on the amount of extraction between A and A, and there is an increase in load depending on the reflux ratio.

Top reflux is 9. Since the temperature drops considerably and returns to the top of the column, the phenomenon of steam load at A is significant, and this influence also extends to B, resulting in the change in steam load as shown in the figure.

As mentioned above, the liquid load changes greatly in the part z-h-"(z-h-") bounded by the side-cut distillate extraction section, the side-reflux extraction section, and the return section. The liquid load in the area where the liquid is applied is large, and can reach more than 10 times that in the area without it.

Gravity and the amount of vapor in the column above the raw material supply section correspond to the sum of the amount of reflux in the column in each section and the amount of fraction distilled from above that section.

The sum naturally differs from part to part, but in terms of volumetric flow rate, even the part with the highest volume does not reach twice the volume of the part with the lowest volume.

Therefore, although there is no difference in the liquid load shown in Figure 2C, the internal load of each part, which is the sum of the liquid load and vapor load mentioned above, is determined by the circulation of side reflux. There is no change in the fact that the part that is present is significantly larger than the part that is not.

The normal pressure main distillation column for crude oil has a processing capacity of 15,900 kiloliters/day (a column for 100,000 barrels has an inner diameter of about 5.7 m, 31,800 kiloliters) and a torr/day (20,000 barrels).
It is a gigantic facility with a capacity of 8,000 barrels per day (1,000 barrels per day) and an effective tower height of 45 to 50 meters.

Therefore, effective use of the space within this wide tower is of great significance.

FIG. 4 is a detailed view of a part of the column illustrating an embodiment of the present invention, in which cytosl-IJ is located inside the shell 1 of the main distillation column and on the side of the main distillation apparatus 2. An example is shown in which the collar 3 is accommodated.

The side cut fraction extracted from the main distillation apparatus 2 is supplied to the top 31 of the Cytos t-IJ tube 3 through a line 4.

It is convenient to provide a control valve (not shown) in the withdrawal line 4, and as shown in the figure, if the side cut fraction is taken out of the column once and then sent to the side stripper 3, the column A control valve can be installed in the middle of the line 4 located outside.

The supply of the side cut fraction to the side stripper 3 is as follows:
Although gravity is used in FIG. 4, the use of a control valve involves fluid pressure loss, so if necessary, a pump may be used to supply the fluid.

Steam is introduced into the side stripper 3 from the bottom 32 line 6.

The removed low-boiling components are discharged through paper line 7 to appropriate stages within main distillation apparatus 2.

The side cut fraction from which low boiling point components have been removed is taken out to the product line 5 from the side stripper bottom 32.

The cross-sectional shape of the side stripper 3 is arbitrary, and the fifth
It may be as shown in Figure A or as shown in Figure B.

However, when housing it in the tower 1, attention must be paid to thermal stress.

The main distillation device 2 and the side stripper 3 have different internal temperatures, so if the side stripper 3 is provided in contact with the outer shell of the column, the part facing the shell 1c and the part separated from the main distillation device 2 are Distortion occurs due to the temperature difference between.

This is because there is a risk of causing damage to the device.

To avoid this problem and ensure that all side walls of the side stripper are at approximately the same temperature, it is possible, for example, to move the side stripper 3 away from the column shell 1 and install it in an independent device, as shown in FIG. Alternatively, a partition plate 8 may be placed between the side stripper 3 and the main distillation apparatus 2 so that the fluid in the main distillation apparatus 2 surrounds the side stripper 3 without causing a short circuit.

6 and 7A and 7B show an embodiment in which the side stripper 3 is located in the center of the main distillation apparatus 2.

This eliminates the problem of thermal distortion mentioned above.

In addition, when the temperature difference between the main distillation apparatus 2 and the side stripper 3 is large, heat insulation may be provided between the two.

The crude oil atmospheric pressure main distillation column with the structure shown in Figure 3 has a throughput capacity of 4.
, 770 kiloliters/day (30,000 barrels/day) to refine the crude oil listed in the table to obtain the product also listed in the table.

The cross-sectional area of the column required by each part of the main distillation apparatus and the cross-sectional area required by the stripper of each sidecut fraction was calculated.

The results are as follows.

In the above example, it can be seen that even if the side stripper is accommodated in the tower, there is still room.

As you can understand from the previous explanation, the required cross-sectional area of the main distillation column, in other words, the size of the extra space, is
Rather than the difference between heavy and light crude oil, it is determined by the yield of each fraction excluding residual oil, the side cut ratio, and how side reflux is taken.

In most cases, there is still sufficient space to accommodate the side stripper within the tower, as illustrated above.

Therefore, in some cases, not only side strippers,
For example, a splitter could be included for redistilling the overhead distillate.

Furthermore, there is a possibility that it can be used as a place to install a heat exchanger.

Although the present invention has been explained above using an example of an ordinary pressure main distillation column for crude oil, which is a typical application target, the present invention is not limited to this, and the present invention is not limited to this. Regarding distillation columns and other types of distillation equipment, if the side cut fraction is separated, especially if side reflux is performed, it is necessary to accommodate the attached equipment by taking advantage of the difference in the load inside the column. It should be understood that this can be achieved by

Moreover, various modifications are possible to the present invention, and those skilled in the art will be able to implement them as necessary.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a typical example of an atmospheric main distillation column for crude oil and related equipment. FIGS. 2A, B, and C are diagrams schematically illustrating the situation in which the amount of liquid load in the distillation column changes in the vertical direction of the column, comparing it in relation to side cut and side reflux. . FIG. 3 is a diagram similar to FIG. 2, showing changes in liquid load and vapor load in each part of the atmospheric-pressure main distillation column in FIG. 1. 4 and 5A and 5B are detailed views of a portion of a tower showing an embodiment of the present invention, FIG. 4 being a longitudinal sectional view;
5A and 5B are cross sections of the I-1 section in FIG. 4. 6 and 7A and B are views similar to FIGS. 4 and 5A and B showing another embodiment of the invention. 1...Outer shell of the distillation column, 2...Main distillation apparatus, 3...Side stripper.

Claims (1)

[Claims] 1. Separating a mixture of a plurality of liquid components based on the difference in boiling points,
In a distillation column that separates at least one type of side cut fraction, the distillation fraction is placed inside the outer shell of the column and in a part of the column with a small load so as to occupy a part of the horizontal cross section of the column. A distillation column characterized in that it houses treatment equipment. 2. The distillation column according to claim 1, wherein the distillation column is equipped with at least one side reflux equipment, and the equipment for treating the fraction is provided in a part where the side reflux stream is not circulated. 3. The distillation column according to claim 1, wherein the object of distillation is petroleum. 4. The distillation column according to claim 3, wherein the petroleum is crude oil and the main distillation column is operated under pressure near normal pressure. 5. The distillation column according to claim 3, wherein the petroleum is heavy oil and the main distillation column is operated under reduced pressure. 6. The distillation column according to claim 1, wherein the equipment for treating the fraction is a distillation device using gas-liquid contact. 7. The distillation column according to claim 6, wherein the distillation device is a Cytos t-IJ tube.