JPH06158059A - Method for start-up of fractionator - Google Patents

Abstract

PURPOSE:To provide an improved method for starting up a fractionator smoothly and quickly. CONSTITUTION:A fractionator, which distills a liq. mixture contg. components having different boiling points into fractions, is started up by delivering an intermediate fraction between the overhead and the bottom fractions of the fractionator to at least one of side reflux systems installed in the fractionator to allow the fraction to stay there, introducing the liq. mixture at an elevated temp. into the fractionator simultaneously with the start-up of the side reflux system where the intermediate fraction is staying, and thereby causing a forced internal reflux in the fractionator before a spontaneous internal reflux occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a start-up method for a fractionator, and more specifically, to prevent coloring and impurities from the top fraction and side cut fraction,
The present invention relates to a fractionator start-up method that is improved so that the fractionator starts up quickly and smoothly.

[0002]

2. Description of the Related Art A fractionator is a distillation column for distilling a raw material liquid consisting of an extremely large number of components having different boiling points and fractionally distilling it into a plurality of fractions having a desired distillation property. More specifically, the fractionator is a column having a function of vertically stacking a plurality of single distillation columns, and the liquid and the vapor are countercurrently contacted with each other in the column so that the vapor having a high boiling point is condensed. Redistillation and partial condensation are performed while evaporating the liquid with a low boiling point that flows down from the upper stage by the heat of condensation, and the side reflux is refluxed and the desired side cut fraction is towered if necessary. It is a distillation column for extracting a plurality of fractions from a multi-component raw material liquid by extracting it from the middle of the process and heating it once. As described above, since the fractionator has a complicated function, its start-up method is technically difficult and requires considerable skill and knowledge.

[0003] Crude oil, which is almost similar to petroleum as it is extracted from an oil field, is a typical multi-component feed oil, and the crude oil is fractionally distilled into low-to-high-boiling fractions such as naphtha, kerosene, gas oil, and heavy oil. The crude oil atmospheric distillation column is an example of a typical fractionator. Therefore, taking the crude oil atmospheric distillation column as an example, a conventional fractionator start-up method will be described. FIG. 1 is a typical schematic flow sheet of the essential part of a crude oil atmospheric distillation apparatus including a crude oil atmospheric distillation column. The crude oil atmospheric distillation column 10 (hereinafter, abbreviated as the column 10 for simplicity) comprises a TPA (Top Pump Around) series 12, in order from the top.
MPA (Middle Pump Around) Series 14, BPA (Bot
Tom Pump Around) sequence 16 has three side reflux sequences. Each side-reflux system consists of a pump and a cooler, draws high-temperature liquid from the accumulator tray of the tower 10, cools it, returns it to the tower 10, and condenses vapor by the cooling heat into the tower. Creating an internal reflux. This side reflux is included in both the case of returning all to the tower 10 and the case of extracting a part and returning the rest to the tower 10.

In the steady operation, the crude oil is heated to a predetermined temperature in the heating furnace 17 and then fed into the crude oil feeding section of the tower 10, and the naphtha distillation is carried out from the top line 18 of the tower 10 by fractional distillation. , A kerosene fraction from the first side stream line 20, a diesel oil fraction from the second side stream line 22, and a light oil fraction from the third side stream line 24, respectively, and from the bottom line 26. The heavy oil fraction has been extracted. In this example, the MPA is extracted from the side stream line where the side cut fraction is extracted.
Although the BPA series reflux liquid is extracted, the side reflux liquid and the side cut fraction may be extracted from different extraction pipes.

The kerosene fraction, the diesel oil fraction, and the gas oil fraction withdrawn are light strips having a low boiling point due to steam stripping in side strippers 28, 30, and 32 provided near the column 10, respectively. After the components are removed and cooled by a heat exchanger (not shown), they flow out of the system and enter each storage tank. The heavy oil fraction discharged from the bottom of the column is cooled by the heat exchanger, then similarly flows out of the system, and enters the storage tank.

The internal structure of the fractionator is constructed in various forms depending on the properties of the raw material liquid and the product fraction. For example, the internal structure of a crude oil atmospheric distillation column is the feed of crude oil. It is divided into upper and lower parts. A large number of horizontal trays and a large number of downcomers that let the liquid flow down from the upper tray to the lower tray are provided in the upper portion, and a small number of trays for stripping with water vapor are provided in the lower portion. Only. The upper trays are classified into horizontal trays (trays) for gas-liquid contact such as valve cap trays, valve trays, and perforated plate trays, and accumulator trays for extracting side reflux. Each is provided as needed.

[0007] The tower 10 is generally a very large device having about 50 trays, and the tower capable of processing 100,000 barrels of crude oil per day has a diameter of about 5 to 7 m and a height of about 40.
m is near. During steady operation, the tower top temperature is about 100-120 °
It is in the range of C and the temperature at the crude oil feeding part is about 340 to 3
In the range of 60 ° C, the temperature gradient is large. Careful startup is required to start up the complex and large tower 10 as described above. Otherwise, not only the operational problem that it is difficult to settle the operating conditions of the tower 10 to a steady state, but also as the temperature of the tower 10 rises,
The tower body and its internal structure thermally expand, but due to the large absolute amount of the thermal expansion and the difference in the thermal expansion amount depending on the location, various mechanical influences are exerted on the tower 10 itself and the crude oil atmospheric distillation apparatus. This is because it occurs everywhere.

To start up the above-described tower 10 by a conventional method, first, circulating oil is circulated before warming up the crude oil to warm the tower 10 to a predetermined temperature. In the warm-up process, a slightly heavy oil, for example, an oil in which a light gas oil fraction and a heavy oil fraction are mixed in a ratio of about 6: 4 is used as a circulating oil, and the circulating oil is heated to about 200 ° C in a heating furnace. Then, the crude oil is introduced into the crude oil feeding section of the tower 10. With regard to the introduced circulating oil, a light oil fraction is vaporized to some extent, and the rest flows down the lower part of the tower as it is and flows out from the bottom of the tower. The introduced circulating oil warms up the tower body, while the circulating oil cools down, so it is fed again into the heating furnace 17 to raise the temperature, and the temperature is returned to the original temperature of about 200 ° C. Circulate to tower 10. At the final stage of the circulation process, the temperature at the exit of the heating furnace is about 250 ° C. By warming up in this way,
In the tower 10, the temperature of the tower body finally rises to about 250 ° C. at the crude oil feeding part and about 70 ° C. at the top of the tower.

When the tower 10 is warmed up, the crude oil heated to about 250 ° C. is gradually introduced into the tower 10 to replace the circulating oil in the circulation passage with the crude oil. The temperature of the crude oil heating furnace is gradually increased to increase the amount of vapor component that is separated into gas and liquid at the crude oil inlet. While continuing this process, the liquid component flowing down from the upper part of the tower, that is, the internal reflux flow rate, gradually increases. When the side-reflux fraction is collected in the accumulator tray, the side-reflux series is activated, the side-reflux fraction is gradually extracted from the tower 10, and cooled to the side-reflux in the tower 10. Start the cycle of returning.

When the heating furnace outlet temperature of crude oil is gradually raised to the steady-state operating temperature, the temperature inside the tower including the tower top temperature becomes close to the set temperature in the steady operation. Further, as the temperature distribution of the column 10 approaches the steady operating condition, the side cut fraction is distilled out to the side stripper and can be withdrawn. continue,
If the flow rate of crude oil is gradually increased to the steady operation flow rate and finally the steady operation state is reached, the start-up of the tower 10 is completed.

[0011]

However, the conventional start-up method has various problems to be improved. First, it is extremely difficult to start up a large-sized fractionator safely and smoothly while adjusting the overall operating state in a well-balanced manner as described above. For example, it is actually extremely difficult to smoothly raise the column top temperature and settle it to a steady condition. In many cases, the flux was suddenly refluxed and, conversely, was drastically reduced. Further, therefore, the properties of the extracted distillate fluctuate, and the amount of slop that cannot be sent to the next treatment step increases.

Secondly, it took a long time to bring the column 10 into a steady state after the crude oil was charged.
Since the crude oil atmospheric distillation apparatus including the tower 10 is an apparatus constructed by investing a very large amount of money, it becomes less economical as the apparatus cannot be operated in a steady state for a long time. In addition, since various operations are required to start up the tower 10, a large number of operators must be attached to the tower 10 during that time, and it takes a long time to start up in order to save labor costs. .

By the way, in order to start up the tower 10 quickly, how quickly the temperature distribution in the tower is shifted to the set temperature distribution for steady operation, and for that purpose, the tower 1
It is necessary to increase the temperature rising rate of the crude oil introduced to zero. Therefore, an attempt was made to increase the temperature rising rate of the crude oil heating furnace outlet temperature for quick start-up, but it became more difficult to adjust the operation of the tower 10, and the overhead fraction and side
Impurities are mixed in the cut fraction to give a black color, or the distillation properties fluctuate, and it is difficult to distill a fraction that satisfies the specified product specifications after introducing crude oil. As a result, the time required to shift to steady operation becomes longer and the amount of rejected product specifications increases, which has no effect of reducing the time required for startup.

In view of the above circumstances, an object of the present invention is to provide a fractionator start-up method improved so that the fractionator can be started up smoothly and promptly.

[0015]

The present inventor has studied the cause of the above-mentioned problem and found that the cause is the following fact. That is, the crude oil introduced into the tower 10 at the time of start-up is gas-liquid separated in the crude oil inlet, the vapor component rises to the upper part of the column, the liquid component flows to the lower part of the column, and flows out from the bottom of the column. The vapor component rising in the upper part of the column rises upward as it is because there is no liquid component in the upper part of the column as in the steady operation. While rising, it is gradually cooled by the tower body having a low temperature, is condensed and flows down in the tower, and the liquid is accumulated in the accumulator tray. When the liquid is collected, the side reflux series is activated to gradually generate internal reflux. If such a state change is progressed in a well-balanced manner, it is possible to smoothly shift to steady operation. However, the operator recognizes the state change inside the tower through various instruments and follows the state change to operate many devices.
It is impossible in reality.

In addition to this, when the temperature rise rate of crude oil is increased in order to shorten the start-up time, a large amount of crude oil is vaporized into vapor and entrained with heavy oil components having a high boiling point or impurities. Rise to the top of the tower. Moreover, since the internal reflux for capturing the heavy oil fraction by vapor-liquid contact with vapor for mass transfer or for capturing the impurities has not yet been generated, the heavy oil fraction or the impurities rises as it is near the top of the column, While increasing the top temperature, it is cooled and liquefied there and mixed in the fraction withdrawn from it,
Reject the fraction. From the above, we focused on the fact that the early generation of internal reflux is extremely important for solving the problem.

Based on the above findings, in order to achieve the above object, the start-up method of the fractionator according to the present invention is to feed a multi-component raw material liquid having different boiling points into the fractionator to obtain a plurality of distillation liquids. When starting the process of fractional distillation into fractions, an intermediate fraction between the overhead fraction and the bottom oil fraction of the fractionator is added to at least one of the side reflux series provided in the fractionator. Is fed and allowed to stay, the temperature of the raw material liquid is raised and sent to the fractionator, and before and after that, the side-reflux series in which the middle distillate is retained is activated, and the inside of the fractionator is naturally It is characterized by including a step of generating a forced internal reflux before the occurrence of the reflux.

The method of the present invention is not particularly limited as long as it is a fractionator having a side reflux series,
It can be applied to any of pressurized, normal pressure and depressurized fractionators. In the present specification, the natural internal reflux means that the heavy component in the vapor generated from the raw material liquid is a top reflux or a side reflow while the mass transfer is accompanied by the natural interaction between the components in the fractionator. A flow that is condensed by heat exchange with the liquid cooled by the flux and flows from the upper tray to the lower tray. On the other hand, forced internal reflux means that the above-mentioned middle distillate, which has been pre-filled in at least one of the side reflux series, is forced to flow from the upper tray to the lower tray, and the same action as natural internal reflux is performed. It is a thing.

The point at which the middle distillate is introduced to produce the forced internal reflux is preferably the side reflux series near the top of the column. This is because the effect of forced internal reflux is the widest. Preferably, the middle distillate is filled so as to fill the flow path of the side reflux series. This is because the forced internal reflux can be smoothly generated in the tower at the same time when the side reflux series is activated. Further, the intermediate fraction to be charged is an intermediate component having a lower boiling point than the bottom oil fraction and a higher boiling point than the top fraction, and for example, in a crude oil atmospheric distillation column, kerosene, light oil, or a mixture thereof. Although it is an oil, the kerosene fraction is most desirable from the viewpoint of achieving the object of the method of the present invention. Further, preferably,
A fraction close to a normal side-reflux fraction is put into each side-reflux series, and each side-reflux series is activated almost at the same time to force the internal reflux to flow down the column. This is because the forced internal reflux closest to the natural internal reflux is generated.

[0020]

[Function] The middle distillate is preliminarily charged into at least one of the side reflux series of the fractionator, and then the side reflux series is started before and after the raw material solution is injected, whereby natural internal reflux Prior to occurrence, a forced internal reflux can be generated that can act much like a natural internal reflux. When the internal reflux is formed, fluctuations in operating conditions in the tower are suppressed, and settling of operating conditions is facilitated. Further, even if the rate of temperature rise of crude oil is significantly increased, the heavy components in the vapor or impurities are captured by the internal reflux, so that the overhead fraction and the side cut fraction are prevented from being colored and the impurities are prevented from being mixed. be able to.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail based on an embodiment with reference to FIG. 1 already described. As shown in the flow sheet of FIG. 1, in order to carry out the method of the present invention, a kerosene feed system is newly provided, which is connected to the suction side of the naphtha reflux pump 40 from the kerosene storage tank 36 via the pump 38, and the valve 44 is provided. Close and open valve 42. Before the crude oil heated in the heating furnace 17 is started to be fed into the tower 10, the pump 38 and the naphtha reflux pump 40 are started in advance, and the naphtha reflux pump 40 is pumped from the kerosene storage tank 36 via the pump 38.
To send kerosene to the TPA series 12. TPA series 1
2 is filled with kerosene and is also fed into the tower 10, and is forced to flow down in the tower to be retained in the accumulator tray 46 for extracting the side reflux of the TPA 12.

Almost at the same time when the crude oil whose temperature has been raised in the heating furnace 17 is introduced into the tower 10, the cooling medium is flown into the cooler 50 to bring it into an operating state, and then the TPA series 12 pump 48 is started to turn the TPA series 12 Get up and running. As a result, the tray 52 that has returned the reflux and the accumulator tray 46
A forced internal reflux is formed between and. Gradually but much more rapidly than in the past, the side reflux flow rate of the TPA series 12 is increased. The kerosene introduced repeats heat exchange and mass transfer with the vapor component in the crude oil in the tower, and finally distills out from the kerosene stripper 28.

As described above, since the side-reflux system of the TPA 12 is established and the forced internal reflux is formed before the establishment of the natural internal reflux, there is no change in the operating conditions as in the conventional method, and smooth operation is possible. Can be brought to a steady state. Further, the heavy fraction in the vapor component separated from the crude oil is replaced with the light fraction by the formed internal reflux, and the impurities are captured, so that the distilled fraction is colored or the impurities are mixed. This prevents the fractionator from starting up faster than the conventional startup method.

Alternatively, as in the case of the TPA series 12, kerosene is fed into the tower 10 via the MPA series 14 and the MPA series 14 is operated, whereby the MPA series 14 is operated.
It is also possible to establish a forced internal return between the return tray 54 of the series 14 and the accumulator tray 56 of the MPA series 14 before the occurrence of natural internal return.

Example A column 10 was started up according to the method of the present invention using the crude oil atmospheric distillation apparatus shown in FIG. The crude oil atmospheric distillation apparatus including the tower 10 used in the method of this example has a daily amount of about 85.0.
It has a processing capacity of 00 barrels (about 563 KL / HR). Fig. 2 shows when crude oil is fed into the tower 10 (indicated by the arrow "A")
FIG. 2A is a graph showing the operation results from the start to the steady operation shift (indicated by the arrow “B”). FIG. 2B shows the temperature at the top of the tower 10 (broken line) and the outlet temperature of the heating furnace (solid line) with respect to the elapsed time including the warm-up of the tower 10 by circulating oil.

First, the circulating oil heated in the heating furnace according to the temperature / time curve shown in FIG.
The tower 10 was warmed up by circulating in the second stage at a temperature of about 200 ° C. at a furnace exit temperature of ° C. The temperature was gradually raised from the temperature of the second stage, and the outlet temperature of the circulating oil heating furnace immediately before the crude oil was finally fed was raised to about 350 ° C. Before introducing crude oil, prepare about 120 KL of kerosene as described above.
The PA series 12 and the tower 10 were filled, and the entire TPA series 12 including the accumulator tray 46 was filled and retained. At the heating furnace outlet temperature at the time of arrow "A", 350 °
The crude oil heated to C was introduced to start the replacement of the circulating oil.
At the same time, the pump 48 of the TPA series 12 is started, and is cooled to a predetermined temperature by a cooler 50 in which a cooling medium is flown, and FIG.
As shown in (a), the kerosene which was squeezed was circulated while the flow rate was increased with the passage of time. At the same time, the feed rate of crude oil is increased as shown in FIG. 2 (a).
At the time point of arrow "B" after 7 hours, it was possible to shift to the steady operation with the crude oil flow rate of 400 KL / HR. According to the method of this embodiment,
As shown by the broken line in FIG. 2 (b), the fluctuation of the column top temperature did not occur. Nine hours after sending the crude oil, products such as naphtha were started to be sent. It was confirmed that the product was neither colored black nor contained impurities.

Conventional Example The column 10 was started up in a conventional manner using the same crude oil atmospheric distillation equipment as in the examples. FIG. 3 is a graph showing the operation results when the tower 10 is started up by the conventional method, from when the crude oil is fed (indicated by the arrow “A”) to after the steady operation transition (indicated by the arrow “B”). Indicates. Fig. 3 (a) shows the crude oil flow rate (broken line) and TPA with respect to the elapsed time after the crude oil is fed.
The flow rate (solid line) of the series is shown, and FIG. 3B shows the tower top temperature (broken line) and the furnace outlet temperature (solid line) with respect to the elapsed time including the warm-up of the tower 10 by the circulating oil.

Up to the time of feeding crude oil, the procedure is the same as that of the embodiment, but after feeding crude oil, the temperature at the top of the column fluctuates greatly and reaches a temperature of more than 200 ° C. at the maximum. Did not settle. The reason why the temperature of the top of the tower rose sharply was that the vapor component in the crude oil rose to the vicinity of the top of the tower, and the TPA series 12 was tried to start in order to lower the temperature of the top of the tower. I couldn't start because there was no. Even after the TPA series 12 was started up, the flow rate changed significantly, and it was not easily settled. It was 16 hours after the crude oil was fed at the time of arrow "B" that the steady operation could be achieved at the crude oil flow rate of 400 KL / HR.

As described above, the start-up according to the method of this embodiment enables the same tower 10 to be operated 9 hours faster than the conventional method, and to perform a smooth operation very smoothly, without causing any trouble such as coloring of the product. I was able to move. Also,
No troubles such as coloring of the product and mixing of impurities occurred.

[0030]

EFFECTS OF THE INVENTION According to the present invention, at the time of feeding the heated raw material liquid to the fractionator and starting the fractional distillation, at least one of the side-reflux series provided in the fractionator is started. An intermediate fraction between the overhead fraction and the bottom oil fraction of the fractionator is fed and allowed to stay, and a forced internal reflux is generated before the occurrence of natural internal reflux, whereby the fractionator is converted. It is possible to start up quickly and smoothly, and it is possible to prevent troubles such as coloring and contamination of products such as naphtha and kerosene. According to the method of the present invention, the time required for the start-up of the fractionator can be shortened, so that the operating rate of the device can be increased and the labor cost of the operator specially required for the start-up can be reduced.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a main part of a crude oil atmospheric distillation apparatus including a crude oil atmospheric distillation column.

2 is a graph showing an operation result when the crude oil atmospheric distillation column of FIG. 1 is started up by the method of the present invention, and FIG. 2 (a) is a circulation flow rate (solid line) of TPA series with respect to elapsed time and crude oil Fig. 2 (b) shows the inflow flow rate (broken line).
Indicates the column top temperature (broken line) and heating furnace outlet temperature (solid line) with respect to elapsed time.

3 is a graph showing an operation result when the crude oil atmospheric distillation column of FIG. 1 is started up by a conventional method.
(A) shows the circulating flow rate of the TPA series (solid line) and the feed rate of crude oil (broken line) with respect to elapsed time, and FIG.
Indicates the column top temperature (broken line) and heating furnace outlet temperature (solid line) with respect to elapsed time.

[Explanation of symbols]

 10 crude oil atmospheric distillation column 12 TPA series 14 MPA series 16 BPA series 17 heating furnace 36 kerosene storage tank 38 pump 40 naphtha reflux pump

Claims (1)

[Claims] 1. When starting a process of feeding a multi-component raw material liquid having different boiling points into a fractionator and fractionally distilling it into a plurality of fractions, a side-reflux series provided in the fractionator is used. An intermediate fraction between the top fraction and the bottom oil fraction of the fractionator is fed to at least one of them and allowed to stay therein, and the raw material liquid is heated and fed to the fractionator. Along with that, a step of activating a side-reflux series in which the middle distillate is retained and generating a forced internal reflux before the occurrence of natural internal reflux in the fractionator is included. How to start up the sessionator.