JP2007224204A - Distillation column and distillation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To heighten a treating capacity of an existing distillation column by suppressing flooding phenomena at the lower part of the distillation column without changing the internal structure of the lower part of the column in the distillation column of a fluid catalytic cracking apparatus or the like. <P>SOLUTION: The distillation column is constituted as follows. Two or more circulation pipes 7A and 7B for extracting a part of the bottom liquid of the distillation column for carrying out rectification and separation by introducing a gaseous feedstock hydrocarbon, and returning the extracted material to baffle trays 3 at different height positions at the lower part of the column are installed, and coolers 8 and 9 for cooling the bottom liquid flowing in the circulation pipes are also installed. When the number of the circulation pipes is N (N is an integer of ≥2), and the total amount of the bottom liquid flowing in all circulation pipes is 1, the bottom liquid flowing in one circulation pipe is regulated so as to be from 0.5 to 1.5 /N, and the bottom liquid is returned by cooling the bottom liquid from 350-400°C to 100-250°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a distillation column such as a fluid catalytic cracking apparatus or an ethylene plant. For example, the processing capability of an existing distillation column can be easily increased.

  A fluid catalytic cracker (FCC) is a device that produces high octane gasoline, cracked light oil, LPG, etc. by thermal cracking in the presence of a catalyst using heavy gas oil obtained from a vacuum distillation system as a raw material. The cracking apparatus is provided with a distillation column for converting the cracked oil produced by catalytic cracking into raw hydrocarbons and separating them into fractions such as high-octane gasoline, cracked light oil, and petroleum gas. .

In such a distillation column, as in a normal distillation column, the inside is filled with an internal for gas-liquid contact. In the present invention, the term “internal” is a general term for a gas-liquid contact member provided in a distillation column in which a tray and a packing (packing material) are combined, and there are various types depending on required performance.
For example, the tray includes a sheave tray, a valve tray, a slit tray, a bubble cap tray, a baffle tray, and the like. Packing is roughly divided into regular packing and irregular packing.

In general distillation, many trays are used, and packing is used to improve processing performance.
Among such internals, the internals in the lower part of the FCC distillation column are mainly composed of baffle trays.
The baffle tray includes a side-side tray, a disc & donut tray, and the like. A disc & donut tray is a disc in which a plurality of disc-shaped discs and a plurality of annular donuts are alternately stacked at intervals. One disc and one donut each have one. A stage is composed of a plurality of stages.

In addition, a raw material hydrocarbon inlet is provided below the baffle tray of the distillation column, from which the raw material hydrocarbon is fed into the distillation column in a gaseous state at a temperature of 500 ° C. or higher, and refluxed to flow down in the distillation column. The liquid and gas-liquid are brought into contact with each other to be separated into fractions.
In the following description, it is assumed that the internal at the lower part of the distillation column provided downstream of the FCC apparatus is a disk & donut baffle tray, but other internals may be used in the present invention, and the present invention is not limited thereto.

  In the above distillation column, if the feed amount of raw material hydrocarbons is increased to increase the processing amount, the circulation amount (load amount) of gas and liquid in the baffle tray increases. In the tray, the gas flow rate is remarkably increased, and flooding may occur in which the liquid does not flow downward.

In order to avoid this flooding phenomenon, it is conceivable to change the baffle tray at the lower part of the distillation column to packing which is an internal having higher processing capacity and separation performance.
However, in this method, when solid impurities such as catalyst powder due to the FCC unit contained in the raw material hydrocarbon are clogged in the packing, the operation of the distillation tower has to be stopped, and it takes time and labor to repair. There is.

  Therefore, the problem in the present invention is to suppress the flooding phenomenon in the lower part of the distillation column without changing the internal structure of the lower part of the distillation column, and to easily increase the processing capacity of the existing distillation column. There is to do.

To solve this problem,
The invention according to claim 1 is a distillation column that introduces a gaseous raw material hydrocarbon and separates by rectification,
This distillation column is provided with two or more circulation pipes for extracting a part of the column bottom liquid and returning it to different height positions at the bottom of the tower, and a cooler for cooling the column bottom liquid flowing through these circulation pipes. It is a distillation column characterized by that.

  The invention according to claim 2 is the distillation tower according to claim 1, wherein the lower part of the distillation tower is constituted by a baffle tray.

The invention according to claim 3 is a distillation method for rectifying and separating a raw material hydrocarbon using the distillation tower according to claim 1,
When the number of circulation pipes is N (N is an integer of 2 or more), and the total amount of tower bottom liquid flowing through all the circulation pipes is 1, the amount of tower bottom liquid flowing per circulation pipe is 0. It is a distillation method characterized by being 5 / N to 1.5 / N.

The invention according to claim 4 is a distillation method for rectifying and separating a raw material hydrocarbon using the distillation tower according to claim 1,
The temperature of the extracted column bottom liquid is 350 to 400 ° C., and this is cooled to 100 to 250 ° C. and returned to the distillation method.

  According to the present invention, a part of the column bottom liquid is divided into two or more and cooled, and then returned to different height positions, whereby the liquid load amount and gas in the internal such as the baffle tray at the bottom of the distillation column are returned. Both the load amount decreases and the flooding phenomenon does not occur even if the feed amount of the raw material hydrocarbon is increased.

For this reason, for example, the processing capacity of the existing distillation tower can be easily increased to about 15 to 20%. Also, a new distillation column can be provided with greater capacity without enlarging the column itself in preparation for future capacity enhancement.
Furthermore, since it is only necessary to make a slight modification to the existing distillation tower, it is not necessary to rebuild the equipment, and the increase in equipment costs can be suppressed.

FIG. 1 schematically shows an example of a distillation column of the present invention, and reference numeral 1 in the drawing indicates a distillation column main body (hereinafter sometimes referred to as a column main body).
The distillation column main body 1 is filled with an internal 2 such as packing, which is a gas-liquid contact means, in the same manner as a normal distillation column. Of the internal 2, the internal 2 at the bottom of the tower is constituted by a baffle tray 3.

  The baffle tray 3 is composed of a plurality of disk-shaped disks and a plurality of annular donuts stacked alternately in the vertical direction at intervals, with one disk and one disk. Each of these donuts constitutes one stage, and in this embodiment, the actual number of stages is six, and gas-liquid contact is performed in the space between the disk and the donut.

  In addition, an inlet 4 for introducing raw material hydrocarbons is provided at a position further below the baffle tray 3 below the distillation column main body 1, from which raw material hydrocarbons such as heavy light oil are heated at a temperature of 500 ° C. or higher. It is sent into the tower body 1 in the form of gas.

Furthermore, a drain outlet 5 for extracting the column bottom liquid is provided at the bottom of the tower body 1, and a pipe 6 is connected to the drain outlet 5, and heavy hydrocarbons are mainly formed from the drain outlet 5. A column bottom liquid having a temperature of 350 to 400 ° C. is withdrawn into the pipe 6.
In addition, one end of the circulation pipe 7 is connected to the middle of the pipe 6 so that a part of the tower bottom liquid is branched into the circulation pipe 7 and flows.

  The circulation pipe 7 branches in the middle to become a first circulation pipe 7A and a second circulation 7B, which are connected to different height positions of the baffle tray 3 of the tower body 1 and are extracted from the tower bottom liquid. The part is returned to a place where the height is different.

  Further, the first circulation pipe 7A is provided with a first heat exchanger 8, and the second circulation pipe 7B is provided with a second heat exchanger 9, and the tower cooled by the first heat exchanger 8 is provided. A part of the bottom liquid is returned to the intermediate stage of the baffle tray (between the third and fourth stages from the top in this embodiment), and a part of the bottom liquid cooled by the second heat exchanger 9 is recovered. The baffle tray is returned to the upper stage (between the first and second stages from the top in this embodiment).

  In addition, a pipe 11 for extracting heavy cycle oil (HCO) is provided at a position above the baffle tray 3 of the tower body 1, and a part of the heavy cycle oil extracted from the pipe 11 is provided in the heat exchanger 12. It is cooled and returned to the tower main body 1 from the pipe 13 to become a reflux liquid flowing down the internal 2 in the tower main body 1.

  Furthermore, a pipe 14 for extracting light cycle oil (LCO) is provided at an intermediate position of the tower body 1, and a part or the whole amount of the light cycle oil extracted therefrom is cooled by a heat exchanger 15, It is returned to the tower body 1 from the pipe 16 and becomes a reflux liquid flowing down the internal 2 in the tower body 1.

  In addition, a pipe 17 for extracting light cycle oil and naphtha is provided at the upper position of the tower body 1, and the light cycle oil and naphtha extracted from the pipe are cooled by a heat exchanger 18 and are It is returned to the main body 1 and becomes a reflux liquid flowing down the internal 2 in the tower main body 1.

  Further, gas is extracted from the pipe 20 from the top of the tower body 1, this gas is cooled by the heat exchanger 21, separated into gas and liquid in the gas-liquid separator 22, and the gas is discharged from the pipe 23. It is sent out of the system as petroleum gas, a part of the liquid is returned to the upper part of the tower body 1 through the pipe 24, and the remainder is extracted as FCC naphtha.

  As described above, in the distillation column of this example, two circulation pipes are installed, but in the same manner, two or more and N (N is an integer of 2 or more) can be installed. . However, when the number of installed circulation pipes is one, when the throughput of the raw material hydrocarbon is increased, a flooding phenomenon occurs in the baffle tray 3 and the operation of the distillation tower becomes impossible. It becomes impossible to cope with the increase.

For connection of the circulation pipes in the present invention, there are a method of individually connecting the circulation pipes to the pipes 6, a method of connecting one circulation pipe to the pipes 6, and branching to N circulation pipes on the way. It is done.
Moreover, about the heat exchanger provided in circulation piping, you may arrange | position 1 each in each piping, and when branching one circulation piping into N circulation piping as mentioned above, it puts together before branching. One heat exchanger may be arranged.

Next, a distillation method using this distillation column will be described.
Gaseous raw material hydrocarbons having a temperature of 500 ° C. or higher such as heavy light oil are supplied from the inlet 4 of the distillation column main body 1.
This raw material hydrocarbon passes through the internal 2 packed in the column and moves upward, and is rectified by gas-liquid contact with the reflux liquid flowing down the internal 2, and the low-boiling components are converted into the column main body 1 The high boiling point component is separated on the lower side of the tower body 1 on the upper side of the column.

As a result, a column bottom liquid mainly composed of heavy hydrocarbons having a temperature of 350 to 400 ° C. is accumulated in the column bottom. This tower bottom liquid is extracted from the pipe 6, and a part thereof is sent to the first circulation pipe 7A and the second circulation pipe 7B through the circulation pipe 7, and the first and second heat exchangers 8, respectively. 10 is cooled to a temperature of 100 to 250 ° C. and returned to the middle stage and the upper stage of the baffle tray 3 of the tower body 1.
If the temperature of the bottom liquid after cooling is less than 100 ° C., it is excessively cooled, and if it exceeds 250 ° C., cooling is insufficient, and neither of them can increase the amount of oil flow. Not expected.

  At this time, assuming that the total flow rate of the column bottom liquid flowing through the pipes 7A and 7B is 1, the flow rate of the column bottom liquid flowing through the individual lines 7A and 7B is 0.5 / 2 to 1.5 / 2 (0. 25-0.75). Here, the denominator 2 means the number of pipes, and there is no particular limitation as long as the number of pipes is 2 or more, but 5 or less is preferable, and N (N is an integer of 2 or more) If so, it is set to 0.5 / N to 1.5 / N.

  If the flow rate per circulation pipe is less than 0.5 / N or exceeds 1.5 / N, the flow rate of the bottom liquid flowing in the specific circulation pipe will be excessive, resulting in the flow rate between the circulation pipes. There is no point in providing two or more circulation pipes to distribute and return the column bottom liquid, and the intended effect cannot be obtained.

  In such a distillation method, the column bottom liquid cooled to different positions in the middle stage and the upper stage of the baffle tray 3 is individually returned to an appropriate amount, as will be apparent from the examples described later. Both the liquid load amount and the gas load amount in the baffle tray 3 below the main body 1 are reduced, and the flooding phenomenon does not occur even if the supply amount of the raw material hydrocarbon is increased. For this reason, the processing capacity of the existing distillation tower can be increased.

  In this example, the internal 2 constituting the lower part of the tower body 1 is exemplified by using the baffle tray 3, but in the case of filling other internals, the amount of the raw material hydrocarbon is similarly treated. Can handle the increase.

Specific examples are shown below.
(Comparative Example 1)
Distillation was performed using the distillation column shown in FIG. The tower diameter is 2900 mm. However, the second circulation pipe 7B was directly connected to the pipe 6 without providing the first circulation pipe 7A and the first heat exchanger 8.

The feed amount of the raw material hydrocarbon was 20500 barrels / day. The operation was carried out with the flow rate of the column bottom liquid flowing through the second circulation pipe 7B being 176940 kg / hour and the cooling temperature in the second heat exchanger 9 being 235 ° C.
Under these operating conditions, the liquid load on the baffle tray 3 was 290 m ³ / hour and the gas load was 9.70 m ³ / hour.
At this time, the flooding phenomenon in the baffle tray 3 was not recognized.

(Comparative Example 2)
In Comparative Example 1, the feed amount of the raw material hydrocarbon was increased to 25,000 barrels / day. The flow rate of the bottom liquid flowing through the second circulation pipe 7B was 216667 kg / hour, and the cooling temperature was the same as in Comparative Example 1.
Under these operating conditions, the liquid load on the baffle tray 3 was 352 m ³ / hour and the gas load was 11.4 m ³ / hour.
At this time, a severe flooding phenomenon was observed in the baffle tray 3 of the tower body 1, and the distillation treatment became impossible.

Example 1
Distillation was performed using the distillation column shown in FIG. That is, in addition to the structures of Comparative Examples 1 and 2, the first circulation pipe 7A and the first heat exchanger 8 were provided.
The feed amount of the raw material hydrocarbon is 25,000 barrels / day, which is the same as in Comparative Example 2.
The flow rate of the column bottom liquid flowing through the first circulation pipe 7A was set to 52093 kg / hour, and the cooling temperature by the first heat exchanger 8 was set to 200 ° C.

Moreover, the flow rate of the bottom liquid flowing through the second circulation pipe 7B was set to 139670 kg / hour, and the cooling temperature in the second heat exchanger 9 was set to 235 ° C.
Under these operating conditions, the liquid load on the baffle tray 3 was 214 m ³ / hour and the gas load was 10.3 m ³ / hour.
In Example 1, no flooding phenomenon was observed, and a continuous distillation operation was possible even at a treatment amount increased by about 20% compared to Comparative Example 1.

(Comparative Example 3)
Although it is the same structure as Comparative Example 1, that is, a structure in which only the second circulation pipe 7B and the second heat exchanger 9 are provided, this is an example in which the amount of heat removal is greatly increased.
That is, the operation was performed with the flow rate of the column bottom liquid flowing through the second circulation pipe 7B being 142666 kg / hour and the cooling temperature in the second heat exchanger 9 being 150 ° C.
Under these operating conditions, a severe flooding phenomenon occurred. In addition, there was a problem that the recovery rate of LCO and HCO, which are part of products recovered from the upper part of the distillation column, was reduced, and a function that was satisfactory as a distillation column was not obtained, such as the need for reheating.

(Example 2)
The same structure as in Example 1 was used except that the amount of oil passing through the first circulation pipe 7A and the second circulation pipe 7B was changed.
That is, the flow rate of the bottom liquid flowing through the first circulation pipe 7A is 88503 kg / hour, the cooling temperature is 200 ° C., the flow rate of the bottom liquid flowing through the second circulation pipe is 117670 kg / hour, and the cooling temperature is 235. It was operated at ℃.

Under these operating conditions, no flooding phenomenon was observed, and continuous operation was possible. Further, the liquid load amount in the baffle tray 3 is 190 m ³ / hour, and the gas load amount is 10.1 m ³ / hour. Compared to the first embodiment, the liquid load amount and the gas load amount can be surpassed. It can be seen that this is a more preferable condition. That is, it can be seen that the condition where the flow rate distribution ratio between the first circulation pipe 7A and the second circulation pipe 7B is closer to one is more preferable than the one is biased to one side.

FIG. 2 shows the relationship between the liquid load amount and the gas load amount on the baffle tray 3 in Comparative Examples 1 to 3 and Examples 1 and 2 described above.
Reference symbol A indicates that of Comparative Example 1, B indicates that of Comparative Example 2, C indicates that of Example 1, D indicates that of Example 2, and E indicates that of Comparative Example 3.

  From this graph, it can be seen that the operation in which the occurrence of the flooding phenomenon in the baffle tray 3 is prevented is impossible even if only one of the liquid load amount and the gas load amount is reduced. On the other hand, when the load amounts of both the liquid and the gas can be reduced in a balanced manner (Example 1 and Example 2), the occurrence of flooding can be prevented and the processing amount can be increased. Recognize.

  Table 1 shows a comparison of operating conditions, operating results, and the like in Comparative Examples 1, 2, and 3 and Examples 1 and 2 described above.

It is the schematic block diagram which showed typically an example of the distillation tower of this invention. It is a graph which shows the result of a specific example.

Explanation of symbols

1 ·· Tower body 2 ·· Internal 3 ·· Baffle tray 6 ·· Pipe 7A ··· First circulation pipe 8 ·· First heat exchanger 7B ··· Second circulation pipe 9, Second heat exchanger.

Claims (4)

A distillation column for rectifying and separating gaseous raw material hydrocarbons,
This distillation column is provided with two or more circulation pipes for extracting a part of the column bottom liquid and returning it to different height positions at the bottom of the tower, and a cooler for cooling the column bottom liquid flowing through these circulation pipes. A distillation column characterized by   The distillation column according to claim 1, wherein the lower portion of the distillation column is constituted by a baffle tray. A distillation method for rectifying and separating raw material hydrocarbons using the distillation tower according to claim 1,
When the number of circulation pipes is N (N is an integer of 2 or more), and the total amount of tower bottom liquid flowing through all the circulation pipes is 1, the amount of tower bottom liquid flowing per circulation pipe is 0. A distillation method characterized by being 5 / N to 1.5 / N. A distillation method for rectifying and separating raw material hydrocarbons using the distillation tower according to claim 1,
The temperature of the extracted column bottom liquid is 350-400 degreeC, This is cooled and returned to 100-250 degreeC, The distillation method characterized by the above-mentioned.

Images