JP2000176202A - Operation of distillation column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a stable operation in the state where the maximum capacity of a distillation column is fully exhibited to be performed and also to use a relatively simple system to make the operation method advantageous even in installing cost by keeping the column differential pressure of the distillation column at a predetermined value. SOLUTION: The feed F to the distillation column is treated by the distillation column to separate it into a rundown overhead component (low boiling point component) D and a rundown bottom component (high boiling component) W. A part of the whole quantity flowing out from the top is returned to the distillation column as a reflux R. Furthermore, heat required for distillation is fed from a reboiler 5 installed in the bottom part. And, differential pressure ΔP is kept constant. That is, since the differential pressure ΔP depends on the flow rate of gas rising in the distillation column, the flow rate of gas is made constant. This is done by adjusting the heat fed to the reboiler 5 to a constant. And, when the ratio of the low boiling point component to the feed F is increased, the amount of heat fed is decreased, and on the contrary, when the ratio of the high boiling point component is increased, the amount of heat fed is increased and also the rundown overhead component D is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for operating a distillation column. More specifically, the present invention enables stable operation in a state where the maximum capacity of the distillation column is fully exhibited, and is advantageous in terms of equipment cost because a relatively simple system is used. The present invention relates to a method for operating a distillation column having excellent characteristics from the viewpoint of industrial implementation.

[0002]

2. Description of the Related Art Various methods are known for operating a distillation column, particularly for controlling the distillation column. For example, a preset reflux (R) / extraction overhead component (D)
There is a set point control method that controls to keep the ratio of the constant. Alternatively,
There is a model predictive control using a dynamic model of a process, and there is a method of controlling a large number of control variables at the same time. These methods have the feature that the state of the distillation column can be finely adjusted according to the fluctuations in the flow rate and composition of the feedstock, but the state of the distillation column can be disturbed due to the delay in following the adjustment to the fluctuations. It has nature. In particular, this possibility poses a serious problem when operating the distillation column with a load near its maximum capacity. That is, if the system is disturbed beyond the maximum capacity of the distillation column, it takes a long time to recover the system, during which time off-spec products must be discharged. That is, in the conventional method, it was difficult to perform a stable operation in a state where the maximum capacity of the distillation column was fully exhibited.

In addition, the above-mentioned conventional methods generally have a problem that a control system is complicated, a large amount of work is required until an optimum state is set, and equipment costs for installation and maintenance are high. .

[0004]

SUMMARY OF THE INVENTION Under such circumstances, the problem to be solved by the present invention is to enable a stable operation in a state where the maximum capacity of the distillation column is fully exhibited and to achieve a relatively simple operation. It is an object of the present invention to provide a method for operating a distillation column, which is advantageous in terms of equipment cost due to the use of the system, and has excellent characteristics, particularly from the viewpoint of industrial implementation.

[0005]

That is, the present invention relates to a method for operating a distillation column, and more particularly, to a method for operating a distillation column for maintaining a column pressure difference of the distillation column at a predetermined value.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The distillation column used in the present invention is not particularly limited, and examples thereof include a perforated plate and a continuous distillation column using a packing.

[0007] The present invention is characterized in that the column pressure difference of the distillation column is maintained at a predetermined value. The column pressure difference is a pressure difference between two points in the vertical direction of the distillation column. From the viewpoint of maintaining performance, it is preferable to maintain the pressure difference between the column bottom and the column top at a predetermined value.

The predetermined value of the column pressure difference is preferably a value of the column pressure difference corresponding to the maximum capacity of the distillation column, from the viewpoint of maximizing the maximum capacity of the distillation column. Here, the value of the column pressure difference corresponding to the maximum capacity of the distillation column can be determined as follows. That is, first, the tower differential pressure of the design maximum capacity is obtained. The column pressure difference may be obtained by a usual design method, and details thereof are described in “Chemical Engineering Handbook”
(Chemical Engineering Association). Next, the distillation column is actually operated near the designed maximum capacity, and while observing the state of the column, the column load is further increased gradually to increase the column differential pressure. By this operation, the maximum tower pressure difference that can be actually reached while maintaining the state of the tower normally is determined, and the tower pressure difference is defined as “tower pressure difference corresponding to the maximum capacity of the distillation column”.

Next, an example of a steady operation method will be described. (See FIG. 1. The symbols are those in FIG. 1.)

[0010] The feed (F) to the distillation column is treated in the distillation column, and separated into a top component (low boiling component) (D) and a bottom component (high boiling component) (W). A part of the total amount flowing out from the top of the column is returned to the distillation column as reflux (R). The amount of heat required for distillation is supplied by a reboiler (5) installed at the bottom of the column.

In the present invention, the tower pressure difference (ΔP) is kept constant by the following method. That is, since the tower pressure difference (ΔP) mainly depends on the flow rate of the gas rising in the distillation column, the flow rate of the gas may be kept constant.
This is performed by adjusting the amount of heat supplied to the reboiler (5). That is, the amount of heat supplied to the reboiler (5) is adjusted to be constant by increasing or decreasing the flow rate of the feed (F). When the feed (F) decreases, the amount of heat supplied to the reboiler is increased. When the proportion of the low-boiling component in the feed (F) increases, the supplied calorific value is decreased. Conversely, when the proportion of the high-boiling component in the feed (F) increases, the supplied caloric value decreases. The extraction overhead component (D) is adjusted in advance in accordance with the ratio of the low-boiling components in the feed together with the increase in. In addition, the ratio of reflux (R) / extraction overhead component (D) is maintained at a certain value or more so that the extraction overhead component (D), which is a product, can maintain a certain quality or more. Then, the operation is performed within a range where these items are satisfied, and if necessary, feed (F) to the distillation column is performed.
Restrict the flow rate. Therefore, it is desirable to measure the composition of the feed (F) intermittently. The tower pressure difference (Δ
Automatic control in which the amount of heat supplied to P) and the reboiler (5) is linked may be employed. Thus, a method for operating the distillation column that maintains the pressure difference of the distillation column at a predetermined value is realized.

As described above, since the present invention is operated while maintaining the column pressure difference of the distillation column at a predetermined value, the state of the column may be disturbed beyond its maximum capacity due to feed conditions and the like. Absent. Therefore, high-load operation very close to the maximum capacity of the distillation column, which is difficult to realize by the ordinary control method, can be performed stably and safely.

In the present invention, the distillation column is operated while maintaining the column pressure difference at a predetermined value, but the predetermined value may be set intermittently.

The process of the present invention is particularly useful in distillation columns where the composition and throughput of the feed do not vary appreciably and can be optimally applied to distillation columns in large petrochemical plants where long-term continuous steady operation is required. .

[0015]

Example 1 Using a distillation column (column diameter: 3100 mm, tray type), a mixture of ethane and ethylene was used as a distillation column feed, ethylene was recovered from the top of the column, and ethane was recovered from the bottom of the column. The flow rate of the distillation column feed was 50 to 70 T / h. By adjusting the amount of heat supplied to the reboiler, the pressure difference between the top and bottom of the tower was maintained at a constant value of 0.2 kg / cm ² . This value is
This is a value determined by a method for determining a column pressure difference corresponding to the maximum capacity of the distillation column. The results are shown in FIG. The vertical axis in FIG. 2 is the tower pressure difference, and the horizontal axis is the recovery flow rate of ethylene from the top of the tower. From FIG. 2, it can be seen that the conventional (100
%), A stable operation is performed at an extremely high load of about 103%.

Comparative Example 1 The distillation column was controlled in the same manner as in Example 1, except that the distillation column was controlled by the above-mentioned conventional method (method using a dynamic model of the process). The results are shown in FIG. The load is lower than in the first embodiment.

[0017]

As described above, according to the present invention, stable operation can be performed in the state where the maximum capacity of the distillation column is fully exhibited, and equipment cost is reduced because a relatively simple system is used. It is possible to provide a method for operating a distillation column, which is advantageous and has excellent characteristics, particularly from the viewpoint of industrial implementation.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a specific example of the method of the present invention.

FIG. 2 is a diagram showing results of Example 1 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Distillation tower 2 Cooler 3 Drum 4 Pump 5 Reboiler F Distillation tower feed D Extraction top component W Extraction bottom component

Continued on front page F term (reference) 4D076 BB01 DA02 EA13Y EA14Y 5H316 AA02 BB01 BB07 BB11 DD02 DD12 EE02 EE34 FF02 GG15 HH04

Claims (4)

[Claims] 1. A method for operating a distillation column, wherein the pressure difference of the distillation column is maintained at a predetermined value. 2. The method according to claim 1, wherein the predetermined value of the column pressure difference is a value of the column pressure difference corresponding to the maximum capacity of the distillation column. 3. The method according to claim 1, wherein the column pressure difference is a pressure difference between the bottom and the top of the distillation column. 4. The method according to claim 1, wherein the pressure difference of the distillation column is maintained at a predetermined value by adjusting the amount of heat supplied to the reboiler.