JPH0929001A - Device and process for distillation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control stably the colum top pressure of a distillation column. SOLUTION: A flow rate control valve 25 for controlling the opening degree based on the column top pressure of a distillation column 1 is set on an outlet side piping 24 of an air cooling type heat exchanger 2, and a bypass flow path 4 for directly flowing vapor from the distillation column 1 into a reduction container 3 not through the heat exchanger 2 is formed, and a differential pressure control valve 41 for controlling the opening degree based on the differential pressure between the upstream side and the downstream side is set on the bypass flow path 4. In this case, the flow rate of condensate on the outlet side of the air cooling type heat exchanger 2 is controlled based on the column top pressure of the distillation column 1, by which the heat transfer area of the air cooling type heat exchanger 2 is controlled. On the other hand, the amount of column top vapor flowing in the bypass flow path is controlled by the differential pressure control valve 41, and the condensation amount of vapor and the bypass passing amount of vapor are controlled by both of these actions to control the column top pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distillation apparatus and a distillation method used for petroleum refining, petrochemistry, general chemistry, etc., for cooling and condensing vapor from the top of a distillation column with an air-cooled heat exchanger.

[0002]

2. Description of the Related Art Conventionally, distillation apparatuses for continuous rectification have been
For example, it has been used in fields such as petroleum refining, petrochemistry, and general chemistry. In this type of distillation apparatus, for example, an air-cooling type heat exchanger is used to condense the overhead vapor, and in this case, as shown in FIGS. 3 to 5, the overhead vapor of the distillation column 50 is air-cooled. The condensate obtained by cooling and condensing in the type heat exchanger 51 is stored in the reflux container 52, and a part of the condensate is refluxed to the distillation column 50 via the pump 53 and the control valve 54, and the remaining Distillation is performed so that the condensate is taken out as a product through the control valve 55.

In such an apparatus, in order to stabilize the quality of the product, it is necessary to keep the top pressure of the distillation column 50 constant, and as a method of controlling the top pressure of the distillation column 50, For example, the following method is adopted.

One method is to control valve 5 as shown in FIG.
A pipe 56 connected to a seal gas supply means that includes an inert gas such as nitrogen as a seal gas and a pipe that includes a control valve 58 and connected to an exhaust gas combustion apparatus is connected to a reflux vessel 52. It is carried out in an apparatus in which the pressure at the top of the distillation column 50 is measured by a pressure gauge 59 and the openings of the control valves 57 and 58 are controlled based on this value. When the column top pressure of the column 50 becomes a predetermined value or less, a seal gas is supplied to the reflux container 52, and when the pressure value exceeds the predetermined value, the column gas is exhausted to the exhaust gas combustion apparatus to control the column top pressure to be constant.

As another method, as shown in FIG. 4, between the inlet side pipe of the air-cooled heat exchanger 51 and the reflux vessel 52,
Control valve 6 whose opening is controlled based on the top pressure of the distillation column
In a device in which a bypass flow path 61 including 2 is provided, the pressure of a gas phase portion in the reflux container 52 is measured by a pressure gauge 60, and the opening degrees of the control valves 57 and 58 are controlled based on this value. It will be implemented. In this method, when the pressure in the reflux container 52 is below a predetermined value, the seal gas is supplied to the reflux container 52, and when the pressure in the reflux container 52 exceeds the predetermined value, it is exhausted to the exhaust gas combustion device, and thus the reflux container 52 is discharged. While controlling the internal pressure to be constant, the amount of overhead vapor sent directly from the distillation column 50 to the reflux vessel 52 via the bypass flow passage 61 based on the overhead pressure of the distillation column 50 is adjusted. The top pressure is controlled to be constant.

As another method, as shown in FIG. 5, a control valve for adjusting the flow rate of overhead vapor flowing from the distillation column 50 to the air-cooling heat exchanger 51 is provided in a pipe on the inlet side of the air-cooling heat exchanger 51. 63 is provided, and the distillation column 50 is provided in the bypass channel 61.
Based on the differential pressure between the top pressure of the column and the pressure in the reflux vessel 52, the apparatus is provided with a differential pressure control valve 64 for adjusting the amount of the top vapor sent directly from the distillation column 50 to the reflux vessel 52. In this method, the top pressure of the distillation column 50 and the pressure in the reflux vessel 52 are controlled to be constant. Further, as shown by the alternate long and short dash line in FIG. 5, a pressure equalizing pipe 64 is provided between the outlet of the air-cooling heat exchanger 51 and the reflux vessel 52, whereby the air-cooling heat exchanger 51 and the air-cooling heat exchanger 51 and the reflux Container 5
It is also performed to prevent the condensate from staying in the pipe between the two.

[0007]

However, in the method shown in FIG. 3 described above, a large amount of seal gas is required because the top pressure of the distillation column 50 is controlled by using the seal gas. In addition, the distillation column 5 can be used when there is a disturbance such as rainfall.
When the column top pressure of 0 becomes low, the seal gas is introduced into the reflux vessel 52 to compensate for this drop in pressure, but there is a delay depending on the volume of this column top system, so the control response is high. However, there was a problem that during this time, the condensation in the air-cooling heat exchanger 51 proceeded too much, the column top pressure became too low, and it took several hours for the column top pressure to stabilize.

The method shown in FIG. 4 is an improvement of the method shown in FIG. 3, and since the sealing gas is used to control the pressure of the reflux container 52 in this method, the amount thereof is smaller than that of the method shown in FIG. Seal gas is still necessary although it is less. Further, when the top pressure of the distillation column 50 becomes low during disturbance, the top vapor flowing directly to the reflux container 52 via the bypass flow passage 61 is reduced by the control valve 62, so that the top pressure rises. However, there is a case where excessive condensation proceeds in the air-cooled heat exchanger 51, which serves as a main flow path for the overhead vapor, to hinder the rise of the overhead pressure. That is, since the amount of steam condensed in the air-cooled heat exchanger 51 is mainly controlled by the heat transfer capacity of the air-cooled heat exchanger, the amount of condensed steam is expected when the atmospheric temperature is low and the capacity of the air-cooled heat exchanger becomes excessive. There is a risk that the above-mentioned pressure will increase and the pressure at the top of the column will decrease, and even if the amount of vapor in the bypass channel 61 is reduced, control of the pressure at the top of the column will become impossible as a result.

Furthermore, the method shown in FIG. 5 is superior to the previous two methods in that no seal gas is used, but the pipe diameter from the distillation column 50 to the air-cooled heat exchanger 51 is large so that vapor, which is gas, can pass through. Since the diameter is large, the adjustment valve 63 provided in the pipe also needs to have a large diameter, which is expensive and heavy. Moreover, the air-cooling type heat exchanger 51 is installed on the uppermost pedestal so that the generated hot air does not hit other devices, but the control valve 63 needs to be located at a high position further upstream, It was also necessary to provide a large pedestal for installing the heavy control valve 63 at a higher place than on the upper pedestal.
For this reason, there is a drawback that the facility cost increases, and that if the control valve 63 becomes large, it takes time to open and close, and the responsiveness is poor.

Further, for example, when the top pressure becomes low due to disturbance, the opening amount of the control valve 63 is made small in order to reduce the supply amount of the top vapor to the air-cooling heat exchanger 51. When the control valve 63 is excessively throttled due to a delay in response or the like, a suction phenomenon occurs due to negative pressure on the outlet side of the air-cooling heat exchanger 51, and the condensate in the reflux container 52 suddenly enters the air-cooling heat exchanger 51. Then, the heat exchanger is filled with liquid and the condensing capacity is lost. On the contrary, the pressure at the top of the column suddenly fluctuates to a higher level.
There was a possibility that it would be difficult to stably control the column top pressure of.

If a pressure equalizing tube 64 is provided as a countermeasure against this, when the outlet side of the air-cooling type heat exchanger 51 becomes a negative pressure, the hot steam in the reflux container 52 flows back through the pressure equalizing tube 64 and the air-cooling type heat exchange is performed. Hammering (intermittent vapor liquefaction) may occur due to sudden cooling and liquefaction on the outlet side of the vessel 51, and this impact may damage the air-cooled heat exchanger 51. there were.

The present invention has been made under such circumstances, and an object thereof is to provide a distillation apparatus and a distillation method capable of stabilizing the top pressure of the distillation column.

[0013]

According to a first aspect of the present invention, the vapor from the top of the distillation column is condensed by an air-cooling heat exchanger, the obtained condensate is stored in a reflux container, and In a distillation apparatus for refluxing a part of the condensate to the distillation column, a pressure detection unit that detects the top pressure of the distillation column, and is provided between the outlet of the air-cooled heat exchanger and the reflux container,
A first control valve that controls the flow rate of the condensate based on the pressure detected by the pressure detection unit, and is provided between the distillation column and the reflux vessel, and a part of the vapor from the top of the distillation column is air-cooled. A bypass flow passage for directly communicating with the reflux container without passing through the heat exchanger and the first control valve, and provided in the bypass flow passage,
A second control valve for controlling the flow rate of the steam based on the pressure difference between the upstream side and the downstream side or the pressure in the reflux container.

According to a second aspect of the present invention, the vapor from the top of the distillation column is condensed by an air-cooled heat exchanger, the obtained condensate is stored in a reflux container, and a part of the condensate in the reflux container is stored. In the distillation method of refluxing to the distillation column, the condensate condensed by the air-cooled heat exchanger is fed into the reflux container while controlling the flow rate based on the top pressure of the distillation column, and the distillation column A part of the steam from is directly flowed into the reflux vessel while controlling the flow rate based on the pressure difference in the upstream side and the downstream side or the pressure in the reflux vessel without passing through the air-cooled heat exchanger. It is characterized by

When the top pressure of the distillation column is lowered due to rainfall or the like, the first control valve as the first control system is throttled to flow the condensate from the outlet side of the air-cooled heat exchanger to the reflux vessel. Is less. As a result, the amount of condensate accumulated in the air-cooled heat exchanger increases, and the number of conduits that contribute to condensation in the group of air-cooled heat exchanger conduits decreases, that is, the heat transfer area decreases. The amount of vapor condensed is reduced, which acts to increase the overhead pressure. Further, the opening degree of the second control valve as the second control system becomes small because the differential pressure between the upstream pressure on the upstream side and the internal pressure of the reflux container on the downstream side becomes small, whereby the bypass flow rate is reduced. The amount of steam flowing through the channel is suppressed, and the column top pressure is increased.
That is, the tower top pressure is increased by the combined action of the first control system that reduces the liquid flow rate of the condensate on the outlet side of the air-cooling heat exchanger and the second control system that reduces the flow rate of the vapor in the bypass passage. Will be made.

When the column top pressure rises, the above is reversed, the opening of the first control valve becomes large, and the flow rate of the condensate from the outlet side of the air-cooling heat exchanger to the reflux vessel is increased to increase the transmission. It acts to increase the heat area to promote condensation and reduce the overhead pressure, and increase the opening of the second control valve in the bypass channel to increase the vapor flowing from the overhead side to the reflux vessel. It works to reduce the overhead pressure. That is, the overhead pressure is obtained by the combined action of both the first control system that increases the liquid flow rate of the condensate on the outlet side of the air-cooling heat exchanger and the second control system that increases the flow rate of the vapor in the bypass passage. Will be reduced.

When the top pressure of the distillation column swings so as to largely decrease or rise, the above-mentioned action is repeated alternately and the top pressure of the distillation column converges to a predetermined pressure.

[0018]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a distillation apparatus for carrying out the method of the present invention. In the figure, 1 is a distillation column, and the column top is connected to the inlet side (upper end of a side frame described later) of the air-cooled heat exchanger 2 by a pipe 11. The air-cooling type heat exchanger 2 supports a pipeline 22 extending horizontally by a side frame 21 in a plurality of stages (usually 4 to 6 stages) in the vertical direction, and the pipeline 22 from the uppermost stage to the lowermost stage. The conduit 22 is connected via a flow path inside the side frame 21 so as to form a bent path, and the conduit 2 is provided below the conduit 22.
2, a fan 23 for blowing air is provided.
The outlet side of the air-cooled heat exchanger 2, that is, the side frame 21.
A pipe 24 provided with a flow rate control valve 25 that is a first control valve is connected to the lower part of the, and the tip end thereof is extended to the vicinity of the bottom of the reflux container 3. Further, the distillation column 1 is provided with a pressure gauge 12 which serves as a pressure detection unit for detecting the pressure at the top of the distillation column.
The opening degree is controlled (first control system) via the control unit 13 on the basis of the pressure detection value.

In order to flow steam directly from the distillation column 1 to the air-cooling heat exchanger 2 through the pipe 11, without passing through the air-cooling heat exchanger 2 and the control valve 25, to the top portion of the reflux container 3. The bypass flow path 4 is branched. A differential pressure control valve 41, which is a second control valve, is interposed in the bypass flow path 4, and the differential pressure control valve 41 detects differential pressure between the upstream side and the downstream side thereof. The opening degree is controlled (second control system) by the control unit 43 based on the differential pressure detection value of the total 42.

At the bottom of the reflux container 3, a pipe 31 for extracting the condensate in the reflux container 3 is connected, and this pipe 31 is connected to a distillation column 1 via a pump 32 and a control valve 33.
Is connected to, for example, the vicinity of the top of the tower, and is branched between the pump 32 and the regulating valve 33 into a pipe 34 for taking out a product, which is provided with a regulating valve 35.

In the distillation apparatus having such a structure, most of the vapor from the top of the distillation column is sent to the air-cooled heat exchanger 2 through the pipe 11, and in the air-cooled heat exchanger 2, the steam from the lower side is supplied. The duct 22 is cooled by the air blown by the fan 23, whereby the steam passing therethrough is cooled and condensed and liquefied. Then, the obtained condensate is sent to the vicinity of the bottom of the reflux container 3 through the pipe 24 while the amount of the sent liquid is adjusted by the flow rate adjusting valve 25. Next, a part of the condensate is refluxed to the vicinity of the top of the distillation column 1 via the pipe 31, the pump 32, and the control valve 33, and the remaining condensate is branched from the pipe 31 to the pipe 3.
4. The product is taken out through the control valve 35.

In the first control system described above, the flow rate of the condensate in the pipe 24 on the outlet side of the air-cooling heat exchanger 2 is adjusted according to the change in the top pressure of the distillation column 1, so that the air-cooling system is used. In the heat exchanger 2, the number of stages of the pipe lines 22 contributing to heat exchange changes, whereby the amount of vapor condensed in the air-cooled heat exchanger 2 is adjusted and the top pressure of the distillation column 1 is controlled. It On the other hand, in the second control system, the top pressure of the distillation column 1 and the reflux container 3
Since the flow rate of the steam that directly flows from the distillation column 1 to the reflux container 3 through the bypass flow path 4 is adjusted according to the pressure difference between the gas phase portion and By adjusting the flow rate of the steam in the bypass passage 4, the so-called overshoot of the change in the transmission surface of the air-cooled heat exchanger 2 due to the adjustment of the amount of condensation of the steam is suppressed, and the control of these two systems is combined. The top pressure is controlled so as to be a constant value by suppressing a rapid change in the top pressure.

Now, for example, when the top pressure of the distillation column 1 becomes lower than a predetermined value during disturbance such as rainfall, that is, the amount of vapor condensed in the air-cooled heat exchanger 2 is smaller than the amount of vapor generated from the distillation column 1. When the number is larger, the opening degree of the flow rate control valve 25, which is the first control system, becomes smaller and the flow rate of the condensate becomes smaller. As a result, for example, as shown in FIG. 2, the condensate begins to accumulate in the pipe 24 and the lowermost pipe line 22 of the air-cooling heat exchanger 2 (the portion indicated by A in the figure), and the condensate of the air-cooling heat exchanger 2 Since the heat transfer area (the portion indicated by B in the figure), that is, the area of the portion of the conduit 22 that contributes to heat exchange, decreases, the air-cooled heat exchanger 2
In this case, the amount of vapor condensation in the column is suppressed, and the column top pressure is increased.

On the other hand, the differential pressure control valve 41 which is the second control system.
Is small because the pressure difference between the column top pressure on the upstream side of the bypass flow passage 4 and the internal pressure of the reflux container 3 on the downstream side is small, so that the opening degree becomes small, and the distillation tower 1 passes through the bypass flow passage 4 As a result, the amount of steam flowing to the reflux container 3 is suppressed, and the column top pressure is increased.

Since the first and second control systems work together, efficiency is high, and sudden pressure changes due to mutual influences can be suppressed.

When the column top pressure is greatly reduced, the above action may cause the column top pressure to rise excessively. In that case, the rise of the condensate in the air-cooled heat exchanger 2 is suppressed as the pressure rises, and the first and second control valves 25 and 41 are opened to condense from the line 22 which is full. The amount of liquid decreases, the cooling capacity of the air-cooled heat exchanger 2 is restored, and the amount of vapor flowing directly from the bypass flow path 4 to the reflux container 3 also increases, which acts to decrease the overhead pressure. Then, the above control of pressure increase and pressure decrease is repeated, and the column top pressure converges to a predetermined pressure.

In the present invention, since the flow rate adjusting valve 25 is provided on the outlet side of the air-cooling heat exchanger 2 and the differential pressure adjusting valve 41 is provided in the bypass flow passage 4, the overhead vapor or the condensate is
It continuously and stably flows in the system, and abrupt large changes in the openings of the flow rate control valve 25 and the differential pressure control valve 41 are suppressed. Therefore, abrupt changes in the column top pressure can be prevented. Can be stably controlled.

Further, in the air-cooling type heat exchanger 2, for example, the condensate accumulated in the lowermost pipe line 22 is always cooled by the fan 23, so that the condensate is supercooled to a temperature lower than the condensing temperature. The liquid is sent to the bottom of the reflux container 3 at this temperature. On the other hand, the bypass flow path 4 is introduced into the reflux container 3.
Since hot steam above the condensation temperature is sent via
The condensate in the reflux container 3 is heated by this vapor and rises in temperature, and the surface layer portion rises to almost the boiling temperature.
For this reason, the surface layer portion of the condensate in the reflux container 3 is in an equilibrium state, whereby the pressure in the reflux container 3 is more stable, and as a result, the control of the overhead pressure is more stable.

As described above, in the above-described embodiment, the flow rate control valve 25 is provided on the outlet side of the air-cooling type heat exchanger 2, and the amount of the condensate to be sent to the reflux vessel 3 is changed according to the column top pressure. As a result, the heat transfer area of the air-cooled heat exchanger 2 can be adjusted to adjust the condensation amount of the overhead vapor, so that the overhead pressure can be controlled with good response. In addition, the flow control valve 25
Is provided in order to adjust the amount of condensate to be sent, so even if the control valve 25 is excessively throttled, the air-cooled heat exchanger 2
There is no possibility that the outlet side becomes negative pressure and the condensate is sucked from the reflux container 3 all at once and flows backward to the inlet side of the air-cooling heat exchanger 2, and as a result, the overhead pressure can be stabilized.

The pipe 24 on the outlet side of the air-cooled heat exchanger 2
Is a condensate flow passage pipe, and has a smaller pipe diameter than the inlet side pipe 11 of the air-cooling heat exchanger 2 which is a vapor flow passage pipe, and is therefore a control valve attached to the outlet side pipe 24. As the valve 25, a smaller valve than the control valve attached to the inlet side pipe can be used. Moreover, since the control valve 25 is installed near the upper part of the reflux container 3 which is lower than the air-cooling heat exchanger 2, an inlet-side control valve which must be installed at a position higher than the air-cooling heat exchanger 2 is installed. As compared with the case where it is carried out, the installation is easy and a large pedestal at a high place is not necessary, so that the equipment cost can be significantly reduced.

In the above, in order to make the differential pressure between the top pressure of the distillation column and the pressure in the reflux vessel a predetermined value, the differential pressure between the upstream side and the downstream side of the differential pressure control valve is detected and Although the opening of the differential pressure control valve is adjusted based on the detected value, in the present invention, instead of detecting the differential pressure, the pressure of the gas phase portion in the reflux container is detected, and the difference based on the detected value is detected. The opening of the pressure control valve may be adjusted. When adjusting the differential pressure control valve based on the pressure of the gas phase portion in the reflux container, if the pressure in the reflux container is too high, the differential pressure control valve 41 is throttled to adjust the liquid surface temperature (pressure) of the reflux container. When the pressure in the reflux container is too low, the opening degree of the differential pressure control valve 41 is increased, and as a result, the pressure in the reflux container is controlled to be constant. Under these conditions, the column top pressure is controlled to be constant.

[0032]

According to the present invention, the outlet side pipe of the air-cooled heat exchanger is provided with a control valve which is controlled based on the top pressure of the distillation column, and the bypass channel is provided with the top pressure and the inside of the reflux vessel. Since a differential pressure control valve that is controlled based on the pressure difference from the pressure or the pressure in the reflux vessel is installed, the amount of condensate sent from the air-cooling heat exchanger is adjusted according to the tower top pressure to perform air cooling. By adjusting the heat transfer area of the heat exchanger, it is possible to control the amount of condensation of the overhead vapor in the air-cooled heat exchanger, and also the differential pressure between the overhead pressure and the pressure in the reflux vessel or the pressure in the reflux vessel. It is possible to directly control the amount of vapor flowing through the bypass flow passage in accordance with the pressure of 1, and the change in the top pressure of the distillation column can be controlled with good responsiveness by the cooperation of both controls. In addition, since there is no risk of negative pressure on the outlet side of the air-cooled heat exchanger, there is no concern of stopping or backflow of the condensate, and steam and condensate flow continuously and stably in the system. Can be stably controlled, and the quality of the distilled product can be stabilized. Further, since the first control valve is provided in the thin pipe for liquid circulation on the outlet side of the air-cooled heat exchanger, it may be a small one with good responsiveness, and since the installation location is low,
It is easy to install and does not require a large installation base or the like at a high place, and the equipment cost can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a distillation apparatus for carrying out a distillation method of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of the air-cooled heat exchanger.

FIG. 3 is a block diagram of a conventional distillation apparatus.

FIG. 4 is a configuration diagram of a conventional distillation apparatus.

FIG. 5 is a configuration diagram of a conventional distillation apparatus.

[Explanation of symbols]

 1 Distillation tower 2 Air-cooled heat exchanger 25 Flow rate control valve 3 Reflux container 4 Bypass flow path 41 Differential pressure control valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kachu Nishimoto 11 Minamihamacho, Chita City, Aichi Prefecture, Idemitsu Kosan Co., Ltd. (72) Nobuo Matsuyama 11th Minamihama Town, Chita City, Aichi Prefecture

Claims (2)

[Claims] 1. The vapor from the top of the distillation column is condensed by an air-cooled heat exchanger, the obtained condensate is stored in a reflux container, and a part of the condensate in the reflux container is stored in the distillation column. In a reflux distillation apparatus, a pressure detection unit that detects the top pressure of the distillation column, and is provided between the outlet of the air-cooled heat exchanger and a reflux container, and condenses based on the pressure detected by the pressure detection unit. A first control valve for controlling the flow rate of the liquid is provided between the distillation column and the reflux vessel, and a part of the vapor from the top of the distillation column is passed through the air-cooled heat exchanger and the first control valve. A bypass flow path for directly flowing into the reflux container without being provided, and the bypass flow path, which is provided in the bypass flow path and controls the flow rate of the steam based on the pressure difference between the upstream side and the downstream side or the pressure in the reflux container. A second control valve, and a distillation apparatus comprising: 2. The vapor from the top of the distillation column is condensed by an air-cooled heat exchanger, the obtained condensate is stored in a reflux container, and a part of the condensate in the reflux container is stored in the distillation column. In the reflux distillation method, the condensate condensed by the air-cooled heat exchanger is fed into the reflux vessel while controlling the flow rate based on the top pressure of the distillation column, and at the same time, one of the vapors from the distillation column The part is directly flowed into the reflux container while controlling the flow rate based on the pressure difference between the upstream side and the downstream side or the pressure inside the reflux container without passing through the air-cooled heat exchanger. Distillation method.