JPH0199603A - Distillation column control method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for controlling a distillation column.

[Conventional technology]

The distillation operation uses the boiling point difference between the components of a mixture to separate them, and is a repeated operation of evaporation and condensation. For this reason, a distillation column that performs a distillation operation generally has a raw material supply section on the side of the column, a condenser at the top of the column, a reboiler at the bottom of the column, and steam is used as a heating source.

The control of such a distillation column is a cascade control system that controls the amount of raw material fed to the distillation column, controls the bottom temperature and controls the amount of reboiler steam, and the bottom temperature controls the amount of heating such as steam to the boiler. It is a cascade control system, and a cascade control system of reflux tank liquid level control - reflux amount control, reflux ratio control - side cut flow rate control, bottom liquid level, etc. are controlled. Each control is controlled individually or in cascade control.

Japanese Patent Publication No. 5B-7321 describes the internal temperature of the column near the pinch point and the amount of energy supplied to the reboiler in the control system of a distillation apparatus where the pinch point at stable time is close to the raw material feed position. It is described that these are detected and used as the iA adjustment control signal for the raw material feed amount.

[Problem that the invention seeks to solve]

In distillation columns, stabilizing the temperature inside the column is an important control point. The bottom temperature of the column is determined by the pressure inside the column and the composition distribution.

In a multi-component continuous distillation system, the biggest factor in temperature control is the increase or decrease in the catch-up amount due to the increase or decrease in the boiler heating flow rate. Therefore, the bottom temperature control 1' is a system in which temperature control is performed by analog, and the fluctuation factors of the composition and feed flow rate are controlled by increasing and decreasing the side cut flow rate by controlling the reflux ratio.

The main factors that fluctuate the bottom temperature are boiler heating amount, feed amount, feed composition, feed preheat amount, and side cut withdrawal amount. It was found that the disturbance factors in the control system were changes in feed composition and preheating amount.

This variation in feed composition causes a variation in the composition distribution within the column, which ultimately results in disturbances in the bottom temperature of the column. On the other hand, fluctuations in the amount of preheating directly result in fluctuations in the amount of evaporation, resulting in disturbances in the bottom temperature and the reflux amount. Furthermore, fluctuations in the reflux amount disturb the composition distribution in the column, resulting in fluctuations in the bottom temperature of the column.

The main cause of variation in side-cut flow rate is variation in feed composition, but variation in reflux amount due to variation in heating amount becomes a variation in side-cut meteor under reflux ratio control, and becomes a double factor. This is the main cause of mutual interference between the tower bottom temperature control system and the reflux ratio control system.

In addition, due to these fluctuations, if the amount extracted from the bottom of the column by distillation is less than the total amount extracted from the top and side cuts, for example, 30% or less, light active ingredients may be extracted from the oil extracted from the bottom of the column. This resulted in a decrease in yield.

An object of the present invention is to provide a method for controlling a distillation column that can easily correct fluctuations caused by disturbances.

[Means for solving problems]

As a result of various research conducted by the present inventors to solve the above-mentioned problems, we found that the feed meter is the dominant factor in determining the amount of heating in the distillation column, and that a correction mechanism should be added to absorb other fluctuation factors. He realized that it was possible to stabilize the control system and completed the present invention.

That is, the present invention provides a method for controlling a distillation column in which a mixture of a plurality of liquid components is separated based on the difference in boiling points and the amount of bottom extraction is small. This is a distillation column control method that controls the supply amount of the heat source, detects fluctuations in the bottom temperature and reflux ratio, and corrects the supply amount of the heat source for heating the column bottom based on this signal.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 shows an example of an embodiment of the present invention.

In Fig. 1, 1 is a distillation column, 2 is a raw material feed line, 3 is a heat source supply line for heating the bottom reboiler, 4 is a top steam extraction line, 5 is a high-boiling fraction extraction line, and 6 is a column Bottom circulation line, 7 is reboiler, 8 is feed flow meter,
9 is a feed amount adjustment valve, 10 is a control calculation device, 11
is a reflux line, 12 is a reflux rate adjustment valve, 13 is a reflux flowmeter, 14 is a condenser, 15 is a low boiling point distillate extraction line, 16 is a heat source supply amount adjustment valve for heating the bottom reboiler, 17 is a bottom of the column Thermometer, 18 is a side force/7t fraction extraction line, 19 is a side cut flow meter, 20 is a side cut flow ffi adjustment valve, and aSb, c, d, and e are signal lines.

A crude raw material to be distilled is supplied to the distillation column 1 via a raw material feed line 2, and is fractionated into a low-boiling fraction and a high-boiling fraction within the column. As the distillation column 1, a sieve tray, a bubble cap, a packed column, etc. can be used. A bottom Va ring line 6 is provided at the bottom of the distillation column 1, and a part of the bottom circulation line 6 is heated by a heat source supplied via a heat source supply line 3 for heating the bottom reboiler. A reboiler 7 is provided, by means of which heat is supplied. As the heat source, a heat medium may be used in addition to steam, and other heat sources such as combustion gas or an electric heater may also be used.

The low-boiling fraction is taken out from the top vapor extraction line 4 and condensed in the condenser 14, and a part of it is sent as a reflux fraction to the upper part of the distillation column 1 via the reflux line 11.

On the other hand, the remainder passes through the low-boiling fraction extraction line 15 and is recovered as a product. Further, the high boiling point fraction is extracted through a high boiling point fraction extraction line 5.

In such a configuration, the flow rate detected by the feed 21t meter 8 of the raw material feed line 2 is sent to the control calculation device 10 via the signal line a, and the flow rate is detected by the bottom thermometer 17 provided in the bottom circulation line 6. The temperature detected by the flow meter 13 provided in the reflux line 11 is sent to the control calculation device 10 through the signal line C, and the ti mold detected by the flow meter 13 provided in the reflux line 11 is sent to the control calculation device IO through the signal line d. The instruction obtained through calculation processing is sent to the bottom reboiler heating heat source supply amount adjustment valve 16 via a signal line, and the supply amount of the heating heat source to the bottom reboiler is adjusted to correct the temperature inside the distillation column. It is.

Furthermore, for controlling the flow rate of the side cut distillate extraction line 18, a reflux flow meter 1 provided in the reflux line 11 is used.
It is preferable to perform a comparison calculation between the flow rate detected in step 3 and the side-cut flow rate set value to prevent the side-cut pump from running dry and to operate at a low reflux ratio.

In addition, especially when the amount of high-boiling fraction extracted is very small, the high-boiling fraction extracted from high-boiling fraction extraction line 5 is circulated to raw material feed line 2 in order to stabilize the composition in the column. It is preferable to do so.

The (D fdl ?3'W method of the present invention) can be implemented in combination with other control methods as appropriate.

〔Example〕

This is a preliminary distillation column that performs pretreatment to extract active ingredients from petroleum-based feedstock oil and coal-based feedstock oil, and the temperature is 40 to 50℃ from the top of the column.
Nearby distillate, 50 to 1 from the side cut distillate extraction line
The control method of the present invention was used for a distillation column that extracts a fraction at around 60°C and a fraction at around 180 to 220°C from the bottom of the column. The results are shown in FIGS. 2, 3, 4, and 5, respectively, comparing the bottom temperature, reflux ratio, and gas chromatography analysis values of active ingredients in the bottom oil with conventional results. In the figure (1
) shows the control method according to the conventional method, and (2) shows the control method according to the present invention. In FIGS. 2 and 3, the dotted lines indicate coal-based feedstock oil, and the solid lines indicate petroleum-based feedstock oil.

In addition, the dotted lines in Figures 4 and 5 indicate the distillate amount at 180°C,
The solid lines indicate the gas chromatography analysis values of each active ingredient in the bottom oil.

As is clear from Figures 2 to 5, according to the control method of the present invention, the bottom temperature and reflux ratio are stabilized, and both the variation in gas chromatography analysis value and concentration of active ingredients in the bottom oil are reduced. And stable.

〔Effect of the invention〕

According to the control method of the present invention as described in detail above, since mutual interference can be prevented, it is possible to automatically follow increases and decreases and changes in composition, and a stable operating state can be maintained.

[Brief explanation of the drawing]

FIG. 1 is an example in which the control method of the present invention is applied to a distillation column. Figure 2 shows the fluctuations in the bottom temperature of the tower, Figure 3 shows the fluctuations in the reflux ratio, Figure 4 shows the results when petroleum-based feedstock is used, and Figure 5 shows the fluctuations when coal-based feedstock is used. 180℃CUT
It shows the variation in the distillation amount and the gas chromatography analysis value of the active ingredient in the bottom oil.・・−・−−1−−−Distillation column, 2 ・・−・−・
...-raw material feed line, 3-----... heat source supply line for heating the bottom reboiler, i o ---
−・・・・・Control calculation device Fig. 5 (
1) 180℃ CUT distillation amount - Active ingredient amount - Number of days elapsed

Claims (1)

[Claims] In a method for controlling a distillation column in which a mixture of multiple liquid components is separated based on the difference in boiling point and the amount of bottom extraction is small, the amount of heat source supplied for heating the bottom of the column is controlled according to a signal of the amount of raw material fed into the column. 1. A method for controlling a distillation column, the method comprising controlling the column bottom temperature and detecting fluctuations in the reflux ratio, and correcting the supply amount of a heat source for heating the column bottom based on this signal.