JP3673565B2 - Distillation apparatus and distillation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a distillation apparatus and a distillation method which are used in petroleum refining, petrochemistry, general chemistry, and the like, and cool and condense steam from the top of a distillation column with an air-cooled heat exchanger.
[0002]
[Prior art]
Conventionally, distillation apparatuses that perform continuous rectification have been used in fields such as petroleum refining, petrochemistry, and general chemistry. In this type of distillation apparatus, for example, an air-cooled heat exchanger is used to condense the overhead vapor. In this case, as shown in FIGS. 3 to 5, the overhead vapor of the distillation tower 50 is air-cooled. The condensate obtained by cooling and condensing in the heat exchanger 51 is stored in the reflux vessel 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 rest Distillation is carried out by taking out the condensate as a product through the control valve 55.
[0003]
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. As a method for controlling the top pressure of the distillation column 50, for example, The method is adopted.
[0004]
As shown in FIG. 3, one method includes a control valve 57 and a pipe connected to a seal gas supply means using an inert gas such as nitrogen as a seal gas, and a control valve 58 and connected to an exhaust gas combustion apparatus. A pipe 56 separated from the middle of the pipe is connected to the reflux vessel 52, and the top pressure of the distillation column 50 is measured with a pressure gauge 59, and the opening degree of the control valves 57 and 58 is controlled based on this value. In this method, when the top pressure of the distillation column 50 falls below a predetermined value, a sealing gas is supplied to the reflux vessel 52, and when the pressure value exceeds a predetermined value, exhaust gas is discharged to the exhaust gas combustion device. By doing so, the tower top pressure is controlled to be constant.
[0005]
In another method, as shown in FIG. 4, a regulating valve 62 whose opening degree is controlled based on the top pressure of the distillation column is provided between the inlet-side piping of the air-cooled heat exchanger 51 and the reflux vessel 52. And a bypass passage 61 provided with a pressure gauge 60 is used to measure the pressure in the gas phase portion in the reflux vessel 52, and the opening of the control valves 57 and 58 is controlled based on this value. It is what is done. In this method, when the pressure in the reflux container 52 is equal to or lower than a predetermined value, a seal gas is supplied to the reflux container 52, and when the pressure in the reflux container 52 exceeds a predetermined value, the exhaust gas is exhausted to the exhaust gas combustion device. While the internal pressure is controlled to be constant, the amount of overhead vapor sent directly from the distillation column 50 to the reflux vessel 52 via the bypass channel 61 is adjusted based on the overhead pressure of the distillation column 50, and as a result, The top pressure is controlled to be constant.
[0006]
In another method, as shown in FIG. 5, a control valve 63 for adjusting the flow rate of the top vapor flowing from the distillation column 50 to the air-cooled heat exchanger 51 is provided in the piping on the inlet side of the air-cooled heat exchanger 51. At the same time, the differential pressure for adjusting the amount of the top vapor directly sent from the distillation column 50 to the reflux vessel 52 based on the differential pressure between the top pressure of the distillation column 50 and the pressure in the reflux vessel 52 to the bypass channel 61. 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 a one-dot chain line in FIG. 5, a pressure equalizing pipe 64 is provided between the outlet of the air-cooled heat exchanger 51 and the reflux vessel 52, and thereby the air-cooled heat exchanger 51 and the air-cooled heat exchanger 51 are refluxed. It is also possible to prevent the condensate from staying in the pipe between the container 52 and the container 52.
[0007]
[Problems to be solved by the invention]
However, in the method shown in FIG. 3 described above, since the top pressure of the distillation column 50 is controlled using the seal gas, a large amount of seal gas is required. Further, when the top pressure of the distillation column 50 becomes low due to disturbance such as rain, for example, the seal gas is introduced into the reflux vessel 52 to compensate for this pressure drop. Therefore, the control response is poor, and during this time, the condensation is excessively advanced in the air-cooled heat exchanger 51, the tower top pressure becomes too low, and it takes several hours for the tower top pressure to stabilize. There was a problem.
[0008]
The method shown in FIG. 4 is an improvement of the method shown in FIG. 3. In this method, the seal gas is used for pressure control of the reflux vessel 52, but the amount is smaller than the method of FIG. Again, sealing gas is necessary. Further, when the top pressure of the distillation column 50 becomes low during disturbance, the top pressure is increased by reducing the top vapor directly flowing to the reflux vessel 52 through the bypass passage 61 by the control valve 62. Although acting in the direction, excessive condensation may proceed in the air-cooled heat exchanger 51 serving as the main flow path for the top vapor of the tower, which may hinder the rise of the top pressure. That is, the amount of steam condensed in the air-cooled heat exchanger 51 is mainly governed by the heat transfer capacity of the air-cooled heat exchanger, and therefore the amount of condensed steam is expected when the air temperature is low and the capacity of the air-cooled heat exchanger becomes excessive. As a result, there is a risk that control of the tower top pressure becomes impossible even if the amount of steam in the bypass passage 61 is reduced.
[0009]
Further, 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 a large diameter through which vapor, which is a gas, passes. For this reason, the adjustment valve 63 provided in the pipe also needs to have a large diameter, which is expensive and heavy. In addition, the air-cooled heat exchanger 51 is installed on the uppermost frame so that the generated hot air does not hit other equipment. However, the control valve 63 needs to be located at a higher location upstream of it. It is also necessary to provide a large gantry for installing the heavy control valve 63 at a higher position than the upper gantry. For this reason, in addition to an increase in equipment costs, there is a disadvantage that when the control valve 63 is enlarged, it takes time to open and close and the responsiveness is poor.
[0010]
Further, for example, when the tower top pressure is lowered due to a disturbance, the opening degree of the control valve 63 is reduced in order to reduce the supply amount of the tower top steam to the air-cooled heat exchanger 51. When the regulating valve 63 is excessively throttled due to a delay or the like, the outlet side of the air-cooled heat exchanger 51 becomes negative pressure and a suction phenomenon occurs, and the condensate in the reflux vessel 52 is drawn into the air-cooled heat exchanger 51 at a stretch. Then, the inside of the heat exchanger becomes full and the condensing capacity is lost, and on the contrary, the top pressure suddenly fluctuates to a high level, so that the control of the top pressure of the distillation column 50 is stably performed. There was a risk that it would be difficult to do.
[0011]
When the pressure equalizing pipe 64 is provided as a countermeasure, when the outlet side of the air-cooled heat exchanger 51 becomes negative pressure, the hot steam in the reflux vessel 52 flows backward through the pressure-equalizing pipe 64 and the air-cooled heat exchanger 51 Hammering (steam liquefaction occurs intermittently) may occur due to sudden cooling on the outlet side and liquefaction, and this shock may damage the air-cooled heat exchanger 51.
[0012]
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]
[Means for Solving the Problems]
The invention of claim 1 condenses the vapor from the top of the distillation column with an air-cooled heat exchanger, stores the resulting condensate in a reflux vessel, and distills part of the condensate in the reflux vessel. In the distillation apparatus refluxed to the column, a pressure detection unit for detecting the top pressure of the distillation column, and provided between the outlet of the air-cooled heat exchanger and the reflux vessel, based on the detected pressure of the pressure detection unit A first control valve for controlling the flow rate of the condensate, and an air-cooled heat exchanger and a first control valve provided between the distillation column and the reflux vessel, and a part of the steam from the top of the distillation column A bypass passage for directly passing through the reflux vessel without intervening, and the flow rate of the steam based on the differential pressure between the upstream side and the downstream side of the bypass passage or the pressure in the reflux vessel. And a second control valve to be controlled.
[0014]
The invention of claim 2 condenses the vapor from the top of the distillation column with an air-cooled heat exchanger, stores the resulting condensate in a reflux vessel, and partially distills the condensate in the reflux vessel. In the distillation method for refluxing to the tower, 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 tower, and the vapor from the distillation tower A part of the water is directly passed into the reflux vessel while controlling the flow rate based on the differential pressure between the upstream side and the downstream side or the pressure in the reflux vessel without using an air-cooled heat exchanger. And
[0015]
When the top pressure of the distillation column decreases due to rainfall or the like, the first control valve as the first control system is throttled, and the condensate flow rate from the outlet side of the air-cooled heat exchanger to the reflux vessel decreases. . This increases the amount of condensate that accumulates in the air-cooled heat exchanger, and the number of air-cooled heat exchanger tube groups that contribute to condensation decreases, that is, the heat transfer area decreases. The amount of steam condensed is reduced and acts to increase the tower top pressure. Further, the opening of the second control valve as the second control system becomes small because the differential pressure between the tower top pressure on the upstream side and the pressure in the reflux vessel on the downstream side becomes small, and thereby the bypass flow. The amount of steam flowing through the passage is suppressed, and acts to increase the tower top pressure. That is, the tower top pressure is increased by the combined action of the first control system for reducing the flow rate of the condensate on the outlet side of the air-cooled heat exchanger and the second control system for reducing the flow rate of steam in the bypass channel. Will be allowed to.
[0016]
When the pressure at the top of the column rises, the reverse of the above occurs, the opening of the first control valve increases, increases the flow of condensate from the outlet side of the air-cooled heat exchanger to the reflux vessel, and increases the heat transfer area. It increases and acts in the direction of condensing and reducing the pressure at the top of the tower, and the opening of the second control valve in the bypass passage is increased to increase the amount of steam flowing from the tower top to the reflux vessel. Acts in the direction of decreasing pressure. That is, the tower top pressure is obtained by the combined action of both the first control system for increasing the liquid flow rate of the condensate on the outlet side of the air-cooled heat exchanger and the second control system for increasing the flow rate of steam in the bypass channel. Will be reduced.
[0017]
And when it shakes so that a column top pressure may fall or raise greatly, said operation | movement will be repeated alternately and the column top pressure of a distillation column will be converged on predetermined pressure.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Examples 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 top of the distillation column is connected to the inlet side of the air-cooled heat exchanger 2 (the upper end of a side frame described later) by a pipe 11. The air-cooling type heat exchanger 2 supports the pipe line 22 extending in the horizontal direction by the side frame 21 so as to have a plurality of stages (usually 4 to 6 stages), and from the uppermost line 22 to the lowermost line. Up to the pipe line 22 is connected so as to form a bent path through a flow path inside the side frame 21, and a fan 23 that blows air toward the pipe line 22 is disposed below the pipe line 22. Composed. On the outlet side of the air-cooled heat exchanger 2, that is, on the lower part of the side frame 21, a pipe 24 having a flow rate adjusting valve 25 that is a first adjusting valve is connected. It is extended to near the bottom. The distillation column 1 is provided with a pressure gauge 12 that constitutes a pressure detection unit for detecting the top pressure of the column, and the flow rate control valve 25 is connected to the control unit 13 based on the pressure detection value of the pressure gauge 12. The opening degree is controlled (first control system).
[0019]
Further, a bypass flow for flowing the steam directly to the top portion of the reflux vessel 3 without passing through the air-cooled heat exchanger 2 and the control valve 25 from the pipe 11 for sending the steam from the distillation column 1 to the air-cooled heat exchanger 2. Road 4 is branched. The bypass flow path 4 is provided with a differential pressure regulating valve 41 as a second regulating valve, and the differential pressure regulating valve 41 detects a differential pressure between the upstream side and the downstream side. The opening degree is controlled (second control system) by the control unit 43 based on the differential pressure detection value of the meter 42.
[0020]
A pipe 31 for extracting the condensate in the reflux container 3 is connected to the bottom of the reflux container 3, and this pipe 31 is connected, for example, near the top of the distillation column 1 via a pump 32 and a control valve 33. In addition to being connected, it branches between a pump 32 and a control valve 33 into a product extraction pipe 34 having a control valve 35.
[0021]
In the distillation apparatus having such a configuration, most of the steam from the top of the distillation column is sent to the air-cooled heat exchanger 2 via the pipe 11, and in the air-cooled heat exchanger 2, the fan 23 from the lower side is used. The duct 22 is cooled by blowing air, whereby the steam passing therethrough is cooled and condensed and liquefied. The obtained condensate is fed to the vicinity of the bottom of the reflux vessel 3 through the pipe 24 while the amount of liquid fed is adjusted by the flow rate control valve 25. Subsequently, a part of this condensate is refluxed to the vicinity of the top of the distillation column 1 through the pipe 31, the pump 32 and the control valve 33, and the remaining condensate is passed through the pipe 34 and the control valve 35 branched from the pipe 31. Taken out as a product.
[0022]
Here, in the first control system described above, the flow rate of the condensate in the pipe 24 on the outlet side of the air-cooled heat exchanger 2 is adjusted according to the change in the top pressure of the distillation column 1, so that the air-cooled heat exchanger 2, the number of stages of the pipe line 22 that contributes 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. On the other hand, in the second control system, the gas directly flows from the distillation column 1 to the reflux vessel 3 through the bypass channel 4 according to the pressure difference between the top pressure of the distillation column 1 and the pressure in the gas phase portion of the reflux vessel 3. Since the flow rate of the steam is adjusted, a large fluctuation in the top pressure of the tower can be suppressed, and the change in the propagation surface of the air-cooled heat exchanger 2 due to the adjustment of the amount of condensed steam can be achieved by adjusting the steam flow rate of the bypass passage 4. In other words, the amount of overshoot is suppressed, and the control of these two systems is combined to suppress a rapid change in the tower top pressure so that the tower top pressure becomes a constant value.
[0023]
If the top pressure of the distillation column 1 becomes lower than a predetermined value during a disturbance such as rain, for example, the amount of steam condensed in the air-cooled heat exchanger 2 is larger than the amount of steam generated from the distillation column 1. In this case, the opening degree of the flow rate adjustment valve 25 that is the first control system is reduced, and the flow rate of the condensate is reduced. 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-cooled heat exchanger 2 (the portion indicated by A in the figure). Since the heat transfer area (the part indicated by B in the figure), that is, the area of the part contributing to the heat exchange of the pipe line 22 is reduced, the amount of steam condensation in the air-cooled heat exchanger 2 is suppressed, and the tower top pressure is increased. Acts on direction.
[0024]
On the other hand, since the differential pressure between the pressure at the top of the bypass channel 4 and the pressure inside the reflux vessel 3 at the downstream side is small, the differential pressure regulating valve 41 as the second control system has its opening degree. Is reduced, the amount of steam flowing from the distillation column 1 to the reflux vessel 3 via the bypass channel 4 is suppressed, and acts to increase the column top pressure.
[0025]
Since the first and second control systems work together, the efficiency is high, and it is possible to suppress an abrupt pressure change due to mutual influence.
[0026]
When the tower top pressure is greatly reduced, the tower top pressure may increase excessively due to the above-described action. 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 full line 22. The liquid is reduced, the cooling capacity of the air-cooled heat exchanger 2 is restored, and the amount of steam directly flowing from the bypass flow path 4 to the reflux vessel 3 is increased to act to reduce the tower top pressure. Then, the above control of pressure increase and decrease is repeated, and the tower top pressure converges to a predetermined pressure.
[0027]
In the present invention, the flow control valve 25 is provided on the outlet side of the air-cooled heat exchanger 2, and the differential pressure control valve 41 is provided in the bypass flow path 4, so that the top vapor or the condensate continuously flows in the system. The flow is stable, and a sudden large change in the opening of the flow rate control valve 25 or the differential pressure control valve 41 can be suppressed. Therefore, a sudden change in the top pressure can be prevented, so that the control of the top pressure can be stabilized. It can be carried out.
[0028]
In the air-cooled 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 solution is fed to the bottom of the reflux vessel 3 as it is. On the other hand, since the hot vapor | steam more than a condensation temperature is sent into the reflux container 3 via the bypass flow path 4, the condensate in the reflux container 3 is heated by this vapor | steam, and it heats up, The surface layer part is It rises until the boiling temperature is reached. For this reason, the surface layer portion of the condensate in the reflux vessel 3 is in an equilibrium state, whereby the pressure in the reflux vessel 3 becomes more stable, and as a result, the control of the tower top pressure is performed more stably.
[0029]
As described above, in the above-described embodiment, the flow control valve 25 is provided on the outlet side of the air-cooled heat exchanger 2, and the amount of the condensate liquid fed to the reflux vessel 3 is changed according to the tower top pressure. Since the heat transfer area of the air-cooled heat exchanger 2 can be adjusted to adjust the amount of condensation of the top vapor, the top pressure can be controlled with good responsiveness. Further, since the flow rate adjusting valve 25 is provided for adjusting the amount of the condensate fed, even if the adjusting valve 25 is excessively throttled, the outlet side of the air-cooled heat exchanger 2 becomes a negative pressure and the condensate is refluxed. There is no risk of suction from the container 3 and backflow to the inlet side of the air-cooled heat exchanger 2, and as a result, the tower top pressure can be stabilized.
[0030]
The pipe 24 on the outlet side of the air-cooled heat exchanger 2 is a pipe for condensate flow, and has a pipe diameter that is smaller than that of the pipe 11 on the inlet side of the air-cooled heat exchanger 2 that is a pipe for steam. Since it is small, the control valve 25 attached to the outlet side pipe 24 can be smaller than the control valve attached to the inlet side pipe. In addition, since the control valve 25 is installed at a position near the top of the reflux vessel 3, which is lower than the air-cooled heat exchanger 2, an inlet-side control valve that must be installed higher than the air-cooled heat exchanger 2 is installed. Compared to the case, the installation is easy, and a large pedestal or the like is not required, so that the equipment cost can be greatly reduced.
[0031]
In the above, in order to set the differential pressure between the top pressure of the distillation column and the pressure in the reflux vessel to a predetermined value, the differential pressure between the upstream side and the downstream side of the differential pressure control valve is detected, and the detected value is However, in the present invention, instead of detecting the differential pressure, the pressure in the gas phase portion in the reflux vessel is detected, and the differential pressure control valve is detected based on the detected value. The degree of opening may be adjusted. When adjusting the differential pressure control valve based on the pressure in 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, and the liquid surface temperature (pressure) of the reflux container is reduced. On the contrary, if the pressure in the reflux container is too low, the opening degree of the differential pressure adjustment valve 41 is increased, and as a result, the pressure in the reflux container is controlled to be constant. Under such conditions, the tower top pressure is controlled to be constant.
[0032]
【The invention's effect】
According to the present invention, the outlet valve of the air-cooled heat exchanger is provided with a control valve that is controlled based on the tower top pressure of the distillation tower, and the differential pressure between the tower top pressure and the reflux vessel pressure is provided in the bypass channel. Alternatively, since a differential pressure control valve that is controlled based on the pressure in the reflux vessel is provided, the amount of condensate sent from the air-cooled heat exchanger is adjusted according to the tower top pressure, and the air-cooled heat exchanger By adjusting the heat transfer area, it is possible to control the amount of condensation of the top steam in the air-cooled heat exchanger, and depending on the differential pressure between the top pressure and the pressure in the reflux vessel or the pressure in the reflux vessel The amount of steam flowing through the bypass channel can be directly controlled, and the change in the top pressure of the distillation column can be controlled with good responsiveness by the combined action of both controls. In addition, there is no risk of negative pressure on the outlet side of the air-cooled heat exchanger, so there is no concern about condensate flow or backflow, and the steam and condensate flow continuously and stably in the system. Can be stably controlled, and the quality of the distilled product can be stabilized. Furthermore, since the first control valve is provided in a thin pipe for liquid circulation on the outlet side of the air-cooled heat exchanger, it can be small in size with good responsiveness, and it is easy to install because the installation place is low. In addition, there is no need for a large mounting stand at a high place, and the equipment cost can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a distillation apparatus for carrying out the distillation method of the present invention.
FIG. 2 is an explanatory diagram for explaining the operation of an air-cooled heat exchanger.
FIG. 3 is a configuration 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]
DESCRIPTION OF SYMBOLS 1 Distillation tower 2 Air-cooling type heat exchanger 25 Flow control valve 3 Reflux vessel 4 Bypass flow path 41 Differential pressure control valve

Claims (2)

In a distillation apparatus for condensing the vapor from the top of the distillation column with an air-cooled heat exchanger, storing the resulting condensate in a reflux vessel, and refluxing part of the condensate in the reflux vessel to the distillation column ,
A pressure detector for detecting the top pressure of the distillation column;
A first control valve that is provided between the outlet of the air-cooled heat exchanger and the reflux vessel and controls the flow rate of the condensate based on the detected pressure of the pressure detector;
A bypass flow provided between the distillation column and the reflux vessel, for directly passing a part of the vapor from the top of the distillation column to the reflux vessel without passing through the air-cooled heat exchanger and the first control valve. Road,
A second control valve that is provided in the bypass flow path and controls the flow rate of the steam based on the differential pressure between the upstream side and the downstream side or the pressure in the reflux vessel;
A distillation apparatus comprising: In the distillation method of condensing the vapor from the top of the distillation column with an air-cooled heat exchanger, storing the resulting condensate in a reflux vessel, and refluxing a part of the condensate in the reflux vessel to the distillation column. ,
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 tower, and a part of the vapor from the distillation tower is cooled by air-cooling heat. A distillation method characterized by flowing directly into a reflux vessel while controlling a flow rate based on a differential pressure between the upstream side and the downstream side or a pressure in the reflux vessel without using an exchanger.

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