JPS58223402A - Operating method of distillation column - Google Patents

Abstract

PURPOSE:To improve an operating characteristic and to economize the energy in the entire part of a device by installing an internal reflux flowmeter for measuring an internal reflux rate separately from an overflush meter. CONSTITUTION:An internal reflux flowmeter is installed to measure or monitor an iternal reflux rate directly and to regulate the heat load (the quantity of the heat recovered from a distillation column) of each reflux. As a result, the reflux rate at the column top is decreased while the adequate gas-liquid ratio is assured on each tray and the optimum recovery of heat by the reflux in the intermediate side part is made possible. More specifically, the reflux liquid from the tray T' is drawn out with a pipe 10' and part thereof is fed as side flow through the pipe 10 to a side stripper and the rest is returned through a pipe 36 and a flowmeter 37 and a pipe 38 to the tray T.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the method of operating a distillation column having intermediate reflux and top reflux or top reflux.

Generally, in petroleum refining and chemical industries, during distillation,
For the purpose of recovering the heat of condensation from which an internal reflux liquid is obtained, a distillation column is used which has a reflux at the middle part and a reflux at the top of the column or a reflux at the top of the column. That is, from one or more places on the middle column wall of the distillation column,
The internal liquid is discharged and heat exchanged between it and other fluids, such as the feedstock for the distillation column, through a heat exchanger, and the above condensation heat necessary for distillation is transferred to other fluids. After being recovered as a fluid, it is returned to the distillation column.

In addition, such operations are also carried out at the top of the column, for example, after heat-exchanging the distillate from the top of the column to form a condensate, a part of it is refluxed to the top of the column (top reflux), Chirui extracts the internal liquid from the tray near the top of the column, exchanges heat with other fluids via a heat exchanger, and then refluxes it back to the top of the column (reflux on the top side). It is being done.

However, it is important to know how much heat should be recovered in the middle part side reflux, or how to maintain the mutual ratio when heat recovery in the middle part side reflux is performed at two or more places. Whether it is suitable depends on the properties of each raw material oil, product specifications, etc. The above conditions are often obtained when processing feedstock oil whose properties are the same as or close to the design conditions of the distillation column, but when processing feedstock oil whose properties differ from the design conditions, it is necessary to control the reflux on the intermediate side. Furthermore, there are no clear indicators regarding the control of column top reflux or column top side reflux in relation to intermediate section reflux, and the current situation is that it has traditionally relied on the long experience and intuition of operators. . Therefore, when changing the type of distillation raw material or changing the throughput, it is extremely difficult to operate the distillation column appropriately, and it is necessary for experienced operators to properly operate the distillation column by trial and error. The conditions are determined. However, even in this case, it is difficult to find the optimal conditions for the reflux on the middle part side, and in reality, some parts are used more than necessary due to concerns that the purification and distillation efficiency will deteriorate due to insufficient internal reflux liquid volume. The reality is that internal reflux is used, which impedes economical operation of the distillation column.

The present invention has been completed as a result of intensive research to overcome the above-mentioned difficulties and develop an economical operating method.

That is, according to the present invention, there is reflux on the middle part side, and
In a distillation column having column top reflux or column top side reflux, the amount of internal reflux liquid from the tray above the tray where the intermediate reflux is returned to the distillation column, preferably from the tray immediately above, is measured using a flowmeter. In addition to direct measurement, based on the internal reflux volume measurement information, the amount of heat removed or recovered from the distillation column via the intermediate reflux and the overhead reflux or the top reflux is controlled, thereby controlling the amount of heat removed or recovered from the distillation column. Provided is a method for operating a distillation column, characterized in that the gas-liquid ratio is adjusted.

The present invention uses a flowmeter to measure the amount of internal reflux liquid in the distillation column.

more directly and control the amount of heat removed or recovered from the distillation column via the mid-side reflux and the overhead reflux or the overhead reflux in conjunction with the measurement information, thereby controlling the This method adjusts the air-liquid ratio appropriately, and unlike conventional methods, it does not rely on the experience or intuition of experts.
This enables economical operation of the distillation column.

The present invention is characterized in that the amount of internal reflux in the distillation column is directly measured using a flow meter. After weighing, there are two methods: one is to circulate the distillate again to the plate, or the other is to install a flow rate measuring means inside the distillation column and read the flow rate outside the column.Measurement. The target internal reflux liquid is not particularly limited as long as it is an internal reflux liquid that flows down from a tray above the tray where the middle section side reflux is returned to the distillation column, but it is usually 1 to 3 times lower than the tray above that tray.
The internal reflux liquid flows down from a shelf at the upper level, preferably from a shelf immediately above the shelf. The number of points for measuring the flow rate of the internal reflux liquid may be one or a plurality of points, and preferably, the number should match the number of points for measuring the flow rate of the internal reflux liquid.

In the present invention, as is clear from the above, while measuring or monitoring the amount of internal reflux liquid using a flow meter, the liquid is removed or recovered from the distillation column via the intermediate reflux and the top reflux or the top reflux. It controls the amount of heat, and by controlling the amount of heat removed or recovered, the amount of internal reflux liquid is controlled within an appropriate range while being measured or monitored with a flow meter. The gas-liquid ratio in the tray can be easily and reliably adjusted to the required range for effective distillation, making it possible to operate the distillation column in a very simple and effective manner.

The amount of heat removed or recovered through various refluxes as described above is usually controlled by controlling the amount of reflux.

In the present invention, when controlling the heat recovery from the distillation column through various types of reflux as described above, the amount of heat recovered through the middle section side reflux is increased, and the column top reflux or column top side reflux is adjusted accordingly. In addition, when heat is recovered through a plurality of intermediate refluxes, control should be performed to reduce the amount of heat removed or recovered through the intermediate refluxes. It is preferable to control so as to increase the amount of heat recovered through the reflux on the intermediate part side (the one near the bottom of the column).

That is, when heat recovery is performed by various types of reflux as described above, it is desirable to avoid heat recovery by reflux on the low temperature side as much as possible, and recover heat through reflux on the high temperature side as much as possible.

Recovery of high-temperature heat is advantageous compared to recovery of low-temperature heat in that it allows for more effective use of heat; When performing heat exchange with the high temperature side reflux, a higher temperature gradient can be achieved, making it possible to downsize the heat exchange device and bring other fluids to a higher temperature □ . Further, when heat is removed or recovered through each reflux as described above, care must be taken so that the properties of each product obtained from the distillation column do not deviate from the product specifications.

Next, specific methods and effects of the present invention will be explained using a crude oil atmospheric distillation column, which is a central equipment in the petroleum refining industry, as an example.

The crude oil atmospheric distillation column converts crude oil into gas and light naphtha.

This equipment separates heavy naphtha, kerosene, light gas oil, heavy gas oil, residual oil, etc., and usually has 3 to 4 types of side streams and 2 to 3 types of side reflux. FIG. 1 shows a typical atmospheric distillation apparatus. Crude oil passes through a pipe 1, is pressurized by a pump 2, and then undergoes heat exchange with product oil in a heat exchanger 4 before being transferred to a heating furnace 6. will be introduced in 290℃ to 380℃ in heating furnace 6
After being heated to a certain temperature, the tube 7 is also introduced into the flash zone 8 of the atmospheric distillation column 9. Inside the distillation column 9, a gas-liquid contact device such as a valve tray and side stream extraction equipment are installed, and the side stream is extracted from a pipe 10 and introduced into a side stripper 12. Steam 1 Hydrocarbon vapors and steam that are not condensed in the distillation column 9 are extracted from the distillation column 9 through a pipe 15VC and transferred to an air-cooled heat exchanger 1.
6 and a cooler 16 using cooling water, most of the hydrocarbon vapor and steam are condensed, and then separated into gas, hydrocarbon liquid, and condensed water (wastewater) in a tower top tank 20. The hydrocarbon liquid in the top tank 2o is extracted by the top reflux pump 22, and becomes top reflux passing through a pipe 23 and top distillate passing through a pipe 24.

A dedicated pump may be installed separately from the tower top reflux pump 22 to extract the tower top distillate oil.

Condensate water (waste water) is withdrawn through pipe 25 and gas is withdrawn through pipe 26.

Each side stream introduced into the side stripper 12 is connected to a pipe 13
After light components are removed by stripping steam introduced into the bottom of the column, they are extracted through a pipe 14 and sent out of the system as intermediate oil.

At the bottom of the distillation column 9, the stripping steam flows into the tube 2.
7 and the light components in the residual oil flowing down from the flash zone 8 are removed.

The residual oil from which the light components have been removed is extracted through a pipe 28,
It is sent out of the system as residual oil.

Generally, an atmospheric distillation column is often provided with one to three side reflux facilities in addition to the top reflux. The reflux on each side is extracted from the distillation column 9 through a pipe 29, and is pressurized by a side reflux pump 30.
After the heat is recovered in a heat exchanger 32 with the crude oil, it passes through a flow rate control valve 34 and is returned to the distillation column 9 through a pipe 35. The side reflux withdrawal tray is usually 3 to 6 stages below the upper side reflux withdrawal tray, and the position of the return to the distillation column is usually
It is above the side reflux withdrawal tray and below the side flow withdrawal tray. A flow rate control valve 34 is installed to control the side return flow @1. Furthermore, instead of the top reflux, side reflux equipment may be provided at the top of the distillation column. FIG. 2 shows an explanatory diagram of the reflux at the top of the column. This column top side reflux is carried out by extracting the liquid inside the pipe 29 from a shelf near the column top and pumping it into the pump 3.
After cooling in the heat exchanger 39 via 0, the flow rate control valve 34
and is returned to the top of the distillation column via pipe 35.

The properties (particularly distillation properties) of the overhead distillate oil and the middle distillate oil depend on the amount of internal reflux liquid in the distillation column 9, and the larger the amount of internal reflux liquid, the better the properties of the distillate product obtained.

However, depending on the distribution of the internal reflux liquid amount in the column,
The distribution of the amount of internal reflux in the cardinal direction is different from distillation with side reflux, as the amount of internal reflux is too large for some distillate products, while it is too small for other distillate products. is an important operating variable for the tower. The distribution of the amount of internal reflux liquid can be controlled to a considerable extent by changing the ratio of heat load (amount of heat recovered from the distillation column) between the top reflux and the side reflux.

On the other hand, the side reflux exchanges heat with the crude oil, but the extraction temperature of the side reflux increases as the extraction position moves toward the bottom of the distillation column, so it is better to increase the heat load ratio of the side reflux at the bottom to reduce the temperature in the high temperature section. Heat recovery can be achieved, which is advantageous in terms of heat recovery for the entire device.

In addition, in order to maintain the efficiency of the tray, it is generally desirable that the tray for gas-liquid contact installed in the vaporization tower 9 be operated within a predetermined gas-liquid ratio range corresponding to the structure of the tray. .

However, in conventional distillation columns, although there are examples in which an overflash meter is installed in the flash zone to measure the amount of overflash, there is no equipment to directly measure the amount of internal reflux at other locations, so it is not suitable for It is not possible to determine the heat load ratio of the overhead reflux and the reflux on each side, resulting in energy loss due to applying more reflux than necessary in some areas, and product properties due to tray operation with an inappropriate gas-liquid ratio. has been forced to deteriorate.

In the present invention, in order to solve the above-mentioned operational defects, an internal reflux liquid meter is installed to directly measure the internal reflux liquid amount, separate from the overflash meter, to improve operability. At the same time, it achieves energy savings for the entire device.

The most effective place to measure the amount of internal reflux is the internal reflux from the tray directly above the tray that returns the middle section reflux to the distillation column; Any other location may be used as long as it is a shelf above the shelf. The internal reflux liquid is withdrawn in its entirety from the distillation column 9 through a pipe 36, together with or separately from the side stream, and after its flow rate is measured with a flowmeter 37, it is returned to the distillation column 9 through a pipe 38.

FIG. 3 shows a detailed view of the tray equipped with a flow meter for measuring the amount of internally recirculated liquid. In this figure, the middle part side reflux is pipe 3.
5, the flowmeter is returned to the shelf T.
It is configured to measure the amount of liquid flowing back to the shelf T from the shelf T' directly above the shelf T'.

That is, the reflux liquid from the tray T' is withdrawn through the pipe 10', a portion of which is sent through the pipe 10 as a side stream to the side stripper 12, and the remainder is passed through the pipe 36 and the flow meter 37. It is returned to the shelf T by the pipe 38.

As mentioned above, in a distillation apparatus in which heat exchange is performed between the middle part side reflux and the crude oil, the middle part side reflux is located at the bottom19. From the viewpoint of effective use of heat in the high temperature section, the amount of heat recovered is as much as possible from the distillation column by increasing the ratio of the heat load of the reflux on the lower middle section, that is, the high temperature middle section reflux. Aiming for heat recovery is advantageous in terms of overall heat recovery.

However, if the heat load of the reflux on the lower intermediate section side is increased too much, the amount of internal reflux liquid at the top of the column will decrease, resulting in deterioration of product properties, and in extreme cases, it may not be possible to secure the specified side flow rate. .

In the case of the present invention, the internal reflux liquid volume meter is installed to directly measure or monitor the internal reflux liquid volume, and at the same time adjust the heat load of each reflux (the amount of heat recovered from the distillation column). It is possible to reduce the amount of liquid refluxed at the top of the column while controlling the amount and ensuring an appropriate gas-liquid ratio in each tray, and it is also possible to recover heat by optimum reflux on the intermediate side. Particularly when a large number of crude oil types are processed separately, such as in a crude oil atmospheric distillation column, it becomes possible to easily set operating conditions according to the properties of the crude oil when switching crude oil types, resulting in a significant improvement in operability.

Next, in the case where 100,000 barrels/day of Middle Eastern heavy crude oil is processed by the distillation treatment system shown in the drawing, by changing the heat load of the middle section side reflux, the heat load of the column top reflux is Specific examples will be shown regarding the increase in heat recovery and changes in the properties of each distillate when changing. Table 1 shows the crude oil types and product yields.

Table 1 (crude oil type and product yield) Gas and LPG 2vo1% light naphtha
14 〃 Heavy naphtha 7 〃 Kerosene 10 〃 Light gas oil 13 〃 Heavy gas oil 6 〃 Residual oil 48〃 Next, when using the conventional general reflux heat load on the middle part side (
Case 1) and the operating state of the distillation column when, according to the present invention, the heat load of the third intermediate section side reflux, which has the highest temperature, is increased and the heat load of the top reflux, which has the lowest temperature, is reduced (case 2) are shown in Table 2, and the product distillation properties in both cases are shown in Table 2.
Shown in 3.

In addition, when changing this operating state from Case 1 to Case 2, the amount of internal reflux liquid could be determined by the flow meter, so it was possible to avoid a decrease in efficiency of the tray due to insufficient amount of internal reflux liquid. However, the operating conditions could be easily changed.

Table 2 (Operating status when changing the reflux heat load on the intermediate section side)
Case 1 Case 2 Heat load of reflux (106 kcal/tar) Top reflux 7 2B, 0 22.0
1st side reflux 17.6 1
7.6 Second side reflux 1. ,0
1.0 Third side reflux
4.0 10.02, Furnace heat load (10'kc
al/hr) 50.8 44.8 First side reflux section 13.7 0.6
Second side reflux section 43,1 28
．． 0 Third side reflux section 19.2
6.1 Since Table containing heat of condensation of product and steam -
3 (Changes in product distillation properties when changing the reflux heat load on the middle part side) In this example, when processing Middle Eastern heavy crude oil,
This figure shows how the increase in heat recovery and product properties change when the side reflux heat load is changed. Case 1 in Tables 2 and 3 is a case in which the heat load of the third side reflux of the intermediate part side reflux is 4,000,000 kcal/hr, and Case 2 is a case where the heat load of the third side reflux of the middle part side reflux is 4,000,000 kcal/hr. This is a case where the heat load is 10,000,0OOkal/hr. As is clear from Table 2, by changing the operating state of Case 1 to Case 2, 6,000,000 k
It is possible to reduce the load on the heating furnace by as much as 1/hr and save a large amount of thermal energy. As shown in item 3 in Table 2, the amount of internal reflux liquid immediately above the first side reflux decreased to 0 in terms of crude oil ratio due to the increase in the heat load of the third side reflux.
．． On the other hand, as shown in Table 3, the distillation properties of the product do not change significantly even if the heat load of the third side reflux is increased. By employing the present invention as described above, it becomes possible to quickly and accurately grasp the amount of internal reflux liquid, thereby greatly contributing to improving the operability of the distillation column and saving energy.

As described above, according to the present invention, it is extremely easy to set the operating conditions to maintain the internal reflux liquid amount at an appropriate value, and it is also possible to achieve highly efficient heat recovery, resulting in a significant reduction in operating costs. becomes.

[Brief explanation of drawings]

FIG. 1 is a flow sheet for explaining the present invention, FIG. 2 is an explanatory diagram of column top side reflux, and FIG. 3 is a flow sheet for explaining the present invention.
FIG. 3 is a detailed view of the vicinity of a shelf provided with a flow meter. 2...crude oil pump, 4...crude oil heat exchanger, 6...heating furnace, 9...normal pressure distillation column, 12...・Side stripper, 16...
...Air-cooled tower top heat exchanger, 18...Top cooler, 2゜...Top tank, 2-bed top reflux pump, 3
0... Side reflux pump, 32... Side reflux/crude oil heat exchanger, 34... Flow rate adjustment valve, 37...
...Flowmeter, 39...Heat exchanger. Patent applicant: Chiyoda Corporation Patent attorney: Toshiaki Ikeura

Claims (3)

[Claims] (1) In a distillation column that has an intermediate reflux and also has an overhead reflux or an overhead reflux, a shelf above the shelf where the intermediate reflux is returned to the distillation column, preferably a shelf directly above it. The amount of internal reflux liquid from the stage is directly measured using a flowmeter, and based on the information on the measurement of the amount of internal reflux liquid, it is removed or recovered from the distillation column via intermediate reflux and column top reflux, or column top reflux. A method for operating a distillation column, characterized by controlling the amount of heat and thereby adjusting the gas-liquid ratio in the plates of the distillation column. (2) The method of claim 1, in which the amount of heat recovered via the intermediate reflux is increased and the amount of heat removed or recovered via the overhead reflux or the top reflux is correspondingly reduced. (3) The method according to claim 2, in which heat is recovered through a plurality of middle section side refluxes, and the amount of heat recovered through the middle section side reflux on the high temperature side among these middle section side refluxes is increased. .