JP2011256156A - Temperature control method for distillation column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature control method for a distillation column which enables the stable temperature control of a distillation column, hardly gives a loss of hydrocarbon fraction and is highly efficient.SOLUTION: In a facility for treating a product generated by naphtha cracking, the method controls the temperature of a distillation column 12 of a distillation facility which separate and eliminate heavy substances from the C5 fraction obtained by separating the naphtha-cracked product. In the temperature control method, the temperature of the column base of the distillation column 12 is controlled so that the amount of 5C hydrocarbon in a discharge liquid from the column base of the distillation column 12 becomes at most 3 wt.%. Since the temperature of the column base does not change greatly even when the temperature at the middle stage of the distillation column 12 made a sudden change, by controlling the temperature of the column base, the stable temperature control of the distillation column 12 becomes possible and the temperature control of the distillation column 12 with a small loss of hydrocarbon fraction and high efficiency can be performed.

Description

  The present invention controls the temperature of a distillation column of a distillation facility that separates and removes heavy matter from a C5 fraction obtained by separating the naphtha decomposition product in a processing facility that processes the naphtha decomposition product generated by the decomposition of naphtha. On how to do.

  Ethylene, propylene, butadiene, benzene, toluene, xylene and the like, which are basic products of the petrochemical industry, are produced by separating and purifying naphtha decomposition products generated by thermal decomposition of naphtha in a processing facility. The C5 fraction produced in this separation and purification process includes isoprene, piperylene, cyclopentadiene, amylene and the like as useful components. Further, dicyclopentadiene produced by dimerization of cyclopentadiene is also included. These useful components are separated by distilling the C5 fraction in a plurality of distillation columns. For example, paragraphs 0003 and 0004 of Patent Document 1 (JP-A-5-301828) describe that dicyclopentadiene, isoprene, and the like are isolated from this C5 fraction by distillation.

  Usually, in a distillation column, the temperature in the column is adjusted by a reboiler arranged near the bottom of the column. The control of the temperature in the tower is generally performed by monitoring the temperature of the portion where the temperature change in the tower is likely to occur and controlling the temperature to be within an appropriate range. Here, as the part where the temperature change in the tower is likely to occur, a part having a temperature gradient in the tower, that is, a part having a large composition change is selected. Also in the distillation separation process of the C5 fraction in the above naphtha decomposition product processing equipment, the temperature of the middle stage of the distillation tower is usually monitored as a part having a large temperature gradient, and the temperature is controlled to be within a certain range. Is done.

  However, according to the study by the present inventors, when the operation of the distillation column is continued for a certain period of time, the temperature of the middle stage of the distillation column that is monitored rises rapidly, and the temperature and pressure control device for the distillation column is accordingly increased. As a result, the phenomenon that the temperature of the distillation column becomes uncontrollable has occurred. This rapid increase in temperature has been found to occur suddenly. Further, while the distillation column is not controllable, the heavy material is not sufficiently separated, leading to a problem that off-spec products are included in products manufactured during that time.

JP-A-5-301828

  An object of the present invention is to provide a distillation column temperature control method capable of stably controlling the temperature of a distillation column for separating and removing heavy substances from a C5 fraction and capable of performing distillation with high efficiency.

  In view of the above problems, the inventors of the present invention, in a distillation column that separates and removes heavy matter from a C5 fraction obtained by separating naphtha decomposition products in an ethylene plant, what causes the rapid temperature change in the middle stage of the distillation column? It was examined whether it was caused by. As a result, if the distillation column feed liquid (C5 + C10 fraction) contains impurities (for example, water) that azeotrope with the heavy substances, the heavy substances in the distillation column feed liquid and the impurities azeotrope to form a tray. The liquid composition on the tray changed into the upper part of the tray, and the temperature at the temperature control point installed at the bottom of the tray (middle of the distillation column) was thought to be a cause of a sudden rise of 40-50 ° C. . And even when there is a sudden change in the temperature of the middle stage, there is no significant change in the tower bottom temperature (the bottom bottom effluent temperature). Therefore, the C5 fraction and heavy matter are removed by controlling the tower bottom temperature. As a result of examining whether it can be separated, it was found that separation is possible. The present inventors have completed the present invention based on the findings.

  That is, the temperature control method for a distillation column according to the present invention (Claim 1) is a method for treating heavy water from a C5 fraction obtained by separating the naphtha decomposition product in a processing facility for processing the naphtha decomposition product generated by naphtha decomposition. In the method for controlling the temperature of the distillation column of the distillation facility for separating and removing the mass, the distillation column is adjusted so that the content of hydrocarbon having 5 carbon atoms in the bottom effluent of the distillation column is 3% by weight or less. The column bottom temperature is controlled.

  The temperature control method for a distillation column according to claim 2 is the method according to claim 1, wherein the temperature of the bottom effluent is measured and controlled so that the bottom effluent temperature is in a range of 150 to 170 ° C. The tower bottom temperature is controlled.

  The temperature control method for a distillation column according to claim 3 is the method according to claim 1, further comprising a reboiler for heating a part of the bottom effluent and returning it to the distillation column. The tower bottom temperature is controlled by measuring the temperature and controlling the return fluid temperature to be in the range of 160 to 190 ° C.

  In the present invention, when the temperature of the distillation column for separating and removing heavy substances from the C5 fraction is controlled, the column bottom temperature of the distillation column is controlled. Since the bottom temperature does not change greatly even when there is a sudden change in the middle temperature of the distillation tower, controlling the bottom temperature enables stable temperature control of the distillation tower, thereby allowing distillation to be performed. It can be performed with high efficiency.

  As a method of controlling the tower bottom temperature, it is preferable to apply a method of measuring the temperature of the tower bottom effluent and controlling the tower bottom effluent temperature in the range of 150 to 170 ° C. In this case, there is no need to install a thermometer in the distillation column.

  Further, as another method for controlling the tower bottom temperature, a method of measuring the temperature of the return fluid at the outlet of the reboiler and controlling the return fluid temperature in the range of 160 to 190 ° C. may be applied. Good. In this case, it is not necessary to install a thermometer in the distillation column.

It is a systematic diagram explaining embodiment of the temperature control method of the distillation tower of this invention. 3 is a graph showing a temperature change in the distillation column in Example 1. FIG. 6 is a graph showing a temperature change in a distillation column in Comparative Example 1.

  The distillation tower temperature control method of the present invention is a distillation facility for separating and removing heavy substances from a C5 fraction obtained by separating the naphtha decomposition product in a processing facility for processing the naphtha decomposition product generated by the decomposition of naphtha. In the method for controlling the temperature of the distillation column, the bottom temperature of the distillation column is controlled so that the content of hydrocarbon having 5 carbon atoms in the bottom effluent of the distillation column is 3% by weight or less. It is characterized by this.

  Here, the processing equipment for naphtha decomposition products means that naphtha is thermally decomposed at a high temperature, methane, ethane, ethylene, propylene, butane, butadiene, hydrocarbons having 5 carbon atoms, benzene, xylene, other off-gas, heavy This refers to the entire facility that produces quality oil and separates and acquires these. As the processing equipment for the naphtha cracking product, for example, a naphtha cracking furnace, a heat recovery device such as a cracking gas quenching section, a desulfurization equipment, a distillation separation equipment or the like is used, but the naphtha cracking product according to the present invention is used. As long as the treatment equipment includes a distillation equipment for the C5 fraction, the whole treatment equipment for the naphtha decomposition product may be used.

  The C5 fraction obtained by separating the naphtha decomposition product is a mixture of components having a boiling point in the range of 5 hydrocarbons contained in the naphtha decomposition product obtained by thermally decomposing naphtha. Specifically, it is a mixture of substances having a boiling point in the range of 9 to 60 ° C. Examples of the C5 fraction include pentane, isoprene, 2-methylbutane, and cyclopentadiene. As a method for producing the C5 fraction, for example, the heavy ending oil having 9 or more carbon atoms is removed from the naphtha decomposition product, and the olefins having 1 to 4 carbon atoms and the like are separated from the remainder (in the present specification, And a method of separating a substance having a boiling point of 60 ° C. or higher. The cracked gasoline contains C5 (carbon number 5) to C8 (carbon number 8) aliphatic hydrocarbon, C6 (carbon number 6) to C8 (carbon number 8) aromatic hydrocarbon, and the like. Note that a small amount of hydrocarbons having C4 (carbon number 4) or less or C9 (carbon number 9) or more is included due to the separation mechanism.

  This C5 fraction is subjected to a process for producing by separating and purifying the substance contained in the C5 fraction. As a part of the process, first, a distillation process for removing heavy substances from the C5 fraction by distillation is performed. The distillation tower temperature control method of the present invention is a temperature control method for a distillation tower of distillation equipment in the distillation step. The heavy material removed here refers to those having a higher boiling point than the C5 fraction, and mainly the C10 (carbon number 10) fraction. As the configuration of the distillation equipment, for example, a reboiler using a 1.5 MPaG vapor as a heating source is provided at the bottom of a vertical distillation tower provided with a shelf, and a distillation tower provided with a condenser is used at the top. It is done. The distillation column may be a single distillation column or a plurality of distillation columns configured in parallel.

  The distillation conditions for removing the heavy matter from the C5 fraction can be appropriately selected according to the supply amount of the C5 fraction as a raw material, the specifications of the equipment, and the like. The tower top pressure is preferably 0.01 to 0.1 MPaG, and the reflux ratio is preferably about 0.01 to 1.

  The temperature control of the distillation column is performed by controlling the column bottom temperature of the distillation column. Specifically, the tower bottom temperature is controlled in a temperature range in which the content of C5 hydrocarbons (C5 hydrocarbons) in the tower bottom effluent is 3% by weight or less, preferably 2% by weight or less. Such a column bottom temperature varies depending on the distillation column, but is usually in the range of 150 to 170 ° C.

  In addition, when the tower bottom temperature of a distillation tower cannot be measured, the temperature of a tower bottom effluent may be measured and it may be controlled so that this temperature may be in the range of 150-170 degreeC. However, in this case, when the flow rate of the bottom effluent changes greatly, it may not be possible to perform good temperature control. That is, the temperature of the bottom effluent falls (ΔT) during the time t until the bottom effluent flowing out from the bottom flows through the bottom line and reaches the installation position of the thermometer. When the flow rate of the column bottom effluent changes, the flow velocity flowing through the column bottom line changes. As a result, the time t changes and the degree of temperature drop (ΔT) also changes. For this reason, when the flow rate of the column bottom effluent changes greatly, it is greatly affected by this temperature drop (ΔT), and good temperature control may not be performed. In such a case, the outlet temperature of the reboiler to which the tower bottom effluent is supplied (the temperature of the return fluid at the outlet of the reboiler) is measured and controlled so that the outlet temperature is in the range of 160 to 190 ° C. May be.

  In the present invention, it is preferable to control the pressure of the distillation column by introducing into the distillation column a gas not containing C5 or higher hydrocarbons (pressure control gas) present in the naphtha decomposition product processing facility. . The pressure control gas may be a gas discharged at any location in the processing facility for the naphtha decomposition product, but it is necessary to be a gas that does not contain C5 or higher hydrocarbons. It is preferable to use those generated from facilities that handle hydrocarbons having 4 or less carbon atoms. Here, the gas not containing hydrocarbons of C5 or higher in the processing equipment is specifically preferably a gas containing hydrocarbons of C4 or lower, for example, C5 from which heavy substances in the processing equipment are removed. An off gas or the like separated from a distillation apparatus for removing low boilers from the fraction is more preferably used.

  The C5 fraction from which the heavy substances have been removed is then subjected to a separation and purification process of useful substances contained in the C5 fraction after the above-mentioned low-boiling substances and the like are removed as necessary. Production of hydrocarbon products takes place.

  Next, the present invention will be described more specifically with reference to FIG. FIG. 1 is a system diagram illustrating an embodiment of a temperature control method for a distillation column according to the present invention. All the devices in FIG. 1 constitute part of the processing equipment for naphtha decomposition products.

[Decomposition system 1]
In the cracking system 1, naphtha and steam for diluting the naphtha are introduced into a naphtha cracking furnace (ethylene cracker), and the naphtha is thermally decomposed.

[Rapid cooling system 2]
The naphtha cracked product produced in the cracking system 1 is introduced into the quenching system 2, where heavy oil and cracked gasoline are separated and removed. The separated cracked gasoline is supplied to the front distillation system 10 described later. The gas after separation of the cracked gasoline and heavy oil is supplied to the next compression system 3.

[Compression system 3]
The gas flowing out of the quenching system 2 is supplied to the compression system 3 and compressed by a gas compressor, and part or all of the gas is washed with caustic soda or the like as necessary, and further condensed water generated by the compression. Are separated.

[Deep cooling system 4]
The compressed gas that has flowed out of the compression system 3 is introduced into the deep cooling system 4 and cooled to separate hydrogen.

[Low temperature purification system 5]
The compressed gas that has flowed out of the deep cooling system 4 is introduced into the low temperature purification system 5, and methane, ethylene, and ethane are fractionated.

[High-temperature purification system 6]
The fraction from which methane, ethylene and ethane have been removed by distillation in the low-temperature purification system 5 is introduced into the high-temperature purification system 6, and propylene, propane, butane and butadiene are fractionated.

  The fraction after propylene, propane, butane and butadiene are fractionally distilled in the high-temperature refining system 6 is supplied to the fore-end system 10 described later together with cracked gasoline discharged from the quenching system 2.

[Preliminary system 10]
The cracked gasoline flowing out from the quenching system 2 contains C9 or more hydrocarbons, and the fraction flowing out from the high temperature refining system 6 contains C6 or more and C8 or less hydrocarbons. A mixture of the cracked gasoline and the fraction from the high-temperature refining system 6 is introduced into the de-C5 tower 11, and the C5 fraction is separated and discharged from the top of the tower. The remaining fraction from which the C5 fraction has been separated is discharged from the bottom of the column and supplied to a hydrogenation system, intermediate distillation system, dealkylation system, purification system, etc. (not shown), and benzene, crude benzene, tar, methane, Ethane, raffinate, etc. are produced.

  An example of the composition of the C5 fraction (hereinafter sometimes referred to as “crude C5 fraction”) flowing out from the top of the de-C5 tower 11 is as follows.

<Composition of crude C5 fraction>
C5 hydrocarbon: 65 to 90 vol%
Hydrocarbons having 4 or less carbon atoms: 0 to 10 vol%
Hydrocarbons having 6 or more carbon atoms: 0 to 30 vol%

  This crude C5 fraction is supplied to the distillation equipment of the fore-end system 10. This distillation equipment includes a distillation column 12, an outflow line 19 for flowing out the bottom effluent (column bottom fraction) of the distillation column 12, a reboiler supply line 19a branched from the outflow line 19, and a bottom effluent. A reboiler 13 for heating a part, a return line 19b for returning a return fluid flowing out from the reboiler 13 to the distillation column, a condenser 14 for cooling the tower top effluent gas, and a drum for gas-liquid separation of the condenser effluent fluid 15, a return pump 16 for returning a part of the condensate flowing out of the drum 15 to the distillation column 12, a tower top discharge pump 17 for discharging the remainder of the condensate, and the gas separated by the drum 15 And a gas discharge line 18 for discharging.

  The crude C5 fraction is introduced into the distillation column 12, and heavy matter is removed from the bottom as a bottom effluent (a bottom fraction). A part of the tower bottom effluent is supplied to the reboiler 13, heated, and then returned to the distillation tower 12 as a return fluid.

  The C5 fraction from which the heavy matter has been separated flows out from the top of the column, is cooled by the condenser 14, and is then gas-liquid separated in the drum 15. A part of the liquid accumulated in the drum 15 is returned to the distillation column 12 via the pump 16. The remainder of the liquid accumulated in the drum 15 is discharged by the pump 17 as a refined C5 fraction (top fraction). This purified C5 fraction contains useful components such as isoprene, piperylene, dicyclopentadiene and amylene. These useful components are separated and purified in a later step (not shown). The gas separated in the drum 15 is discharged from the gas discharge line 18.

  In the present embodiment, in this distillation facility, the bottom temperature of the distillation column 12 is set so that the content of hydrocarbons having 5 carbon atoms in the bottom effluent of the distillation column 12 is 3% by weight or less. Control. As an example of a method for controlling the tower bottom temperature, a thermometer is installed in the distillation column 12, and the tower bottom temperature is controlled based on the measurement result of the thermometer. Further, when it is difficult to install a thermometer in the distillation column 12, a thermometer may be installed in the outflow line 19, and the tower bottom temperature may be controlled based on the measurement result of the thermometer. . Further, a thermometer may be installed in the return line 19b of the reboiler 13, and the tower bottom temperature may be controlled based on the measurement result of the thermometer. Based on the measurement result of at least one of these thermometers, the temperature of the reboiler 13, the supply flow rate of the bottom effluent to the reboiler 13, the temperature of the condenser 14, and the return of the condensate in the drum 15 to the distillation column 12. The column bottom temperature can be controlled by changing the amount and the like.

  This embodiment is an example of the present invention, and the present invention is not limited to the above embodiment. For example, in the distillation facility shown in FIG. 1, it is a preferred embodiment to control the pressure in the distillation column 12 by supplying a pressure control gas into the distillation column 12. In this case, as the pressure control gas, it is preferable to use a gas that does not contain C5 or higher hydrocarbons, which exists in the processing equipment for the naphtha decomposition product. Thus, the cost can be reduced by using the gas existing in the processing facility of the naphtha decomposition product as the pressure control gas as compared with the case of using the external gas from the outside of the processing facility. In addition, even if the gas present in the naphtha decomposition product processing facility is put in the processing facility, nitrogen is kept below the hazardous concentration in the entire processing facility. Therefore, nitrogen gas is recycled in the naphtha decomposition furnace by recycling. It is possible to prevent the above-described nitric oxide from being formed, and it is safe.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited at all by these Examples.

[Example 1]
The operation was carried out using the naphtha decomposition product treatment facility of FIG. As operating conditions for the distillation column 12, the pressure at the top of the column was 0.04 MPaG, and the supply amount of the crude C5 fraction was 15 t / h. Further, a thermometer was installed in the return line 19b of the reboiler 13, the reboiler outlet temperature (return fluid temperature) was measured, and the reboiler outlet temperature was controlled to be 174 ° C. for operation. Thermometers were also installed at the middle stage of the distillation column 12 (upper part of the lowermost tray) and the bottom of the column to measure the temperature. The composition of the crude C5 fraction (feed solution to the distillation column 12) discharged from the top of the de-C5 column 11 at the start of operation was as shown in Table 1.

  One week after the start of operation, separation performance and operation stability were confirmed. Specifically, the composition of the crude C5 fraction (feed liquid to the distillation column 12), the composition of the purified C5 fraction flowing out from the drum 15, and the composition of the bottom effluent of the distillation column 12 were measured. The results are shown in Table 2. Moreover, the time-dependent change of the measured value of said two thermometers installed in the middle stage and tower bottom part of the distillation column 12 was plotted in FIG. In addition, this Table 2 shows the confirmation result of the separation performance when 6 hours have passed since the start of the confirmation of the operational stability in FIG.

  As is clear from FIG. 2, by controlling the temperature based on the measurement result of the reboiler outlet temperature, the temperature at the bottom of the tower is stabilized, and the middle stage in which the composition changes greatly according to the change in the composition of the feed liquid. It was confirmed that the temperature of was also stable. Moreover, as shown in Table 2, C5 hydrocarbons in the column bottom effluent at this time accounted for 1.8% by weight of the total, and it was confirmed that heavy substances were well separated.

[Comparative Example 1]
The operation was performed in the same manner as in Example 1 except that the temperature of the middle thermometer was controlled to 55 ° C., and the separation performance and operation stability were confirmed one week after the start of operation. These results are shown in Table 3 and FIG. Specifically, as shown in FIG. 3, the separation performance was confirmed when 21 hours had elapsed since the start of the confirmation of the operational stability (at the time when the vertical line in FIG. 3 was drawn). Table 3 shows the confirmation results of the separation performance at this point.

  As is clear from FIG. 3, it was confirmed that there was a period in which the temperature of the middle stage of the distillation column 12 increased rapidly. Further, along with the sudden rise in the temperature of the middle stage, the control device for the distillation column 12 worked in the direction of lowering the temperature, but thereafter, the temperature of the middle stage thermometer could not be kept within a certain range, and accordingly, the bottom temperature of the tower It was confirmed that the temperature changed drastically and the temperature of the distillation column 12 as a whole could not be controlled. Further, when this temperature control is impossible, as shown in Table 3, the C5 hydrocarbon in the bottom effluent is 11% by weight of the total, and the separation from the heavy matter is not sufficient. all right.

DESCRIPTION OF SYMBOLS 1 Decomposition system 2 Rapid cooling system 3 Compression system 4 Deep cooling system 5 Low temperature purification system 6 High temperature purification system 11 De-C5 tower 12 Distillation tower 13 Reboiler 14 Condenser 15 Drum

Claims (3)

In a method for controlling the temperature of a distillation tower of a distillation facility for separating and removing heavy substances from a C5 fraction obtained by separating the naphtha decomposition product in a processing facility for processing a naphtha decomposition product generated by the decomposition of naphtha,
A temperature control method for a distillation column, comprising controlling the column bottom temperature of the distillation column so that the content of hydrocarbon having 5 carbon atoms in the bottom effluent of the distillation column is 3% by weight or less. .   2. The temperature at the bottom of the tower is measured according to claim 1, and the bottom temperature is controlled by controlling the temperature at the bottom of the tower to be in the range of 150 to 170 ° C. Temperature control method for distillation tower. In claim 1, a reboiler for heating a part of the bottom effluent and returning it to the distillation column is provided,
The temperature control of the distillation column is characterized in that the temperature of the return fluid at the outlet of the reboiler is measured and controlled so that the temperature of the return fluid is in the range of 160 to 190 ° C. Method.

Images