JP2011256157A - Pressure control method for distillation column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure control method for a distillation column, which enables safe and inexpensive distillation of C5 fraction.SOLUTION: In a facility for treating a product generated by naphtha cracking, the method controls the pressure of a distillation column 12 of a distillation facility by introducing a pressure control gas to the distillation column 12, which separates and eliminates heavy substances from the C5 fraction obtained by separating the product generated by naphtha. For the pressure control gas, a gas containing no hydrocarbon having at least C5 (carbon number 5), which is present in the treating facility, is used. Since a gas, present in the treating facility, is used as the pressure control gas, the cost is lower than the case using an external gas, and since nitrogen is prevented from mixing into the treating facility with the external gas, the safety is guaranteed.

Description

  The present invention relates to a distillation column 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. The present invention relates to a method for controlling the pressure of the distillation column by introducing a pressure control gas.

  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. Isoprene, piperylene, cyclopentadiene, amylene and the like are included as useful components in the C5 fraction produced in the separation and purification process in this processing facility. 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. In distillation using a distillation tower, a reboiler is generally provided near the bottom of the tower to adjust the temperature in the tower. In general, an external gas such as hydrogen or nitrogen gas is introduced into the distillation column from the outside of the naphtha decomposition product processing equipment to adjust the pressure in the column.

  In the processing facilities for such naphtha decomposition products, explosion accidents have occurred in the past. That is, in 1990, an explosion accident occurred at Shell's ethylene plant cryogenic gas separator in BERRE, France. AIChE investigated and examined the explosion, and summarized that the cause of the accident was that nitrogen oxide condensed in the heat exchanger of the cryogenic gas separator, which reacted with the dienes and exploded. It has also been pointed out that if naphtha cracking equipment is mixed with nitrogen, it will come into contact with water vapor in the naphtha pyrolysis furnace and become oxide (nitrogen oxide), which may cause a similar explosion. (Non-patent documents 1 to 3). Accumulation of nitric oxide has also been found in the cryogenic gas separator of Texas Union Carbide, USA.

  For this reason, when an external gas containing nitrogen gas is used as the pressure control gas of the distillation column for distilling the C5 fraction as described above, the external gas enters into various processing apparatuses connected to the distillation tower, Risk of explosion. Therefore, the recovery destination of the off-gas (containing nitrogen) of the distillation column is limited, and in some cases, it is burned with fuel or flare, resulting in a loss of valuable hydrocarbon fraction. In addition, when using a nitrogen-free gas provided as an utility from the outside as the pressure control gas, the cost is high, and it is a big problem in a large-scale facility such as a naphtha decomposition product processing facility. It was.

JACQUES KOHLER, "COLD BOX EXPLOSION AT SHELL STEAM CRACKER IN BERRE, FRANCE", AIChE Spring National Meeting, Houston (1991) ARTHUR J. BAUMGARTNER, TIMM E. PAXSON et al., "Feedstock Contaminants in Ethylene Plants-an Update", AIChE Spring National Meeting, Houston (1991) Journal of High Pressure Gas Association Vol. 24, No. 11, 41-50 (1960)

  An object of this invention is to provide the pressure control method of the distillation column which can perform distillation of C5 fraction safely at low cost.

  As a result of intensive studies, the present inventors have found that in the distillation tower for separating and removing heavy substances from the C5 fraction of the naphtha decomposition product treatment equipment, the pressure control gas for the distillation tower is present in the treatment equipment for the naphtha decomposition product. By using a gas that does not contain hydrocarbons of C5 or higher, it is possible to prevent nitrogen gas having a dangerous concentration or more from being mixed into the naphtha decomposition product processing equipment in this distillation process, and to safely remove C5 fraction at low cost. As a result, it was found that the distillation can be performed, and the present invention has been completed.

  That is, the pressure control method for a distillation column according to the present invention (Claim 1) uses 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 a method for controlling the pressure of a distillation column by introducing a pressure control gas into a distillation column of a distillation facility for separating and removing heavy substances, a hydrocarbon of C5 or higher existing in the processing facility is used as the pressure control gas. It is characterized by using a gas that does not contain.

  The pressure control method for a distillation column according to claim 2 is characterized in that, in claim 1, the gas that does not contain C5 or more hydrocarbons present in the processing equipment contains C4 or less hydrocarbon gas. It is.

  The pressure control method for a distillation column according to claim 3 is the method according to claim 1 or 2, wherein the gas not containing hydrocarbons of C5 or higher present in the processing facility removes light boiling substances from the C5 fraction in the processing facility. It is an off-gas separated from the distillation apparatus for carrying out.

  In the present invention, a gas not containing hydrocarbons of C5 or higher, which is present in the processing equipment, is used as the pressure control gas of the distillation column for separating and removing heavy substances from the C5 fraction, so that it is less expensive than the case of using an external gas. In addition, if the gas does not contain C5 or higher hydrocarbons in the processing facility, the nitrogen concentration can be kept below the hazardous concentration in the entire processing facility, and the generation of nitrogen oxides above the hazardous concentration does not occur. , Safe.

  The pressure control gas which does not contain C5 or higher hydrocarbons present in this treatment facility is preferably a gas containing hydrocarbon gas of C4 or less in the treatment facility for naphtha cracked products, Particularly preferred is an off-gas separated from the distillation apparatus for removing water.

It is a systematic diagram explaining embodiment of the pressure control method of the distillation column of this invention.

  The present invention is obtained by separating the naphtha decomposition product in a processing facility for treating the naphtha decomposition product generated by the decomposition of naphtha (sometimes referred to as “processing facility” in this specification). In a method for controlling the pressure of a distillation column by introducing a pressure control gas into a distillation column of a distillation facility that separates and removes heavy matter from a C5 fraction, C5 is present in the processing facility as the pressure control gas. This is a pressure control method for a distillation column, wherein a gas not containing hydrocarbons having 5 or more carbon atoms is used.

  Here, the naphtha decomposition product processing equipment produced by the decomposition of naphtha is methane, ethane, ethylene, propylene, butane, butadiene, hydrocarbons having 5 carbon atoms, benzene, by thermally decomposing naphtha at a high temperature. , Xylene, other off-gas, heavy oil, etc., and the equipment that separates and acquires these. As the processing equipment for this naphtha decomposition product, for example, a naphtha cracking furnace, a heat recovery device such as a cracked gas quenching section, a desulfurization equipment, a distillation separation equipment, etc. are used. Any apparatus may be used as long as it includes equipment for separating the C5 fraction and processes the naphtha decomposition product as a whole.

  The C5 fraction obtained by separating the naphtha decomposition product is a mixture of components contained in the naphtha decomposition product obtained by thermally decomposing naphtha and having a boiling point in the range of 5 carbon atoms. 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 lower or C9 (carbon number 9) or higher is included in 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 pressure control method of the present invention is a distillation tower pressure control method for 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.

  In the present invention, the pressure in the distillation column is controlled by “a gas that does not contain hydrocarbons of C5 or higher and exists in the processing equipment for naphtha decomposition products” (pressure control gas). This pressure control gas may be a gas discharged at any location in the processing equipment for the naphtha decomposition product, but it is necessary to be a gas not containing C5 or higher hydrocarbons. It is preferable to use one generated from a facility that handles hydrocarbons. Here, the gas that does not contain C5 or higher hydrocarbons present in the processing equipment is specifically a gas that is present in the processing equipment and further contains C4 or lower hydrocarbons. Off-gas etc. which are separated from a distillation apparatus for removing low boilers from the C5 fraction from which the mass has been removed are 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 pressure 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 decomposition system 1, naphtha and steam for diluting the naphtha are introduced into the naphtha decomposition furnace, 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 fraction: 65 to 90 vol%
C4 fraction or less: 0 to 10 vol%
C6 or higher fraction: 0 to 30 vol%
This crude C5 fraction is introduced into the first distillation column 12, and a distillation step (first distillation step) for removing heavy substances is performed. The details of the distillation step for removing this heavy material are as described above.

  The crude C5 fraction separated from the heavy substances, which flows out from the top of the first distillation column 12, is introduced into the second distillation column 13 to remove a low boiling point product of C4 or less (first step). 2 distillation step) is performed. The low boiling point C4 or lower is discharged from the top of the column, and the C5 fraction (hereinafter sometimes referred to as “purified C5 fraction”) is discharged from the bottom of the column. 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).

  In addition, as a pressure control gas of said 1st distillation column 12, the gas which does not contain the C5 or more hydrocarbon which exists in the processing equipment of this naphtha decomposition product is used. For example, low boiling point C4 or less flowing out from the top of the second distillation column 13, hydrogen flowing out from the deep cooling system 4, methane, ethylene and ethane flowing out from the low temperature refining system 5, high temperature refining system 6 One or more selected from propylene, propane, butane, butadiene, and other gases that do not contain C5 or higher hydrocarbons (methane, ethane, etc.) generated downstream from the hydrogenation system. be able to. 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. In addition, when using the low-boiling thing which flows out from the top of the 2nd distillation column 13 as pressure control gas, it is cheaper compared with the case where the said hydrocarbon product manufactured in this processing equipment is used. is there.

  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]
In the naphtha decomposition product treatment facility shown in FIG. 1, the operation is performed using a low boiling point C4 or less discharged from the top of the second distillation column 13 as the pressure control gas of the first distillation column 12. went. The operating conditions of the first distillation column 12 were as follows. Further, the composition of the crude C5 fraction flowing out from the top of the de-C5 tower 11 was as shown in Table 1.
Supply amount of crude C5 fraction: 10t / h
Column bottom temperature: 160 ° C
Tower top pressure: 0.04 MPaG
Reflux ratio: 0.033

  One week after the start of operation, the composition of the top fraction flowing out from the top of the first distillation column 12 was analyzed. The results are shown in Table 2.

  As shown in Table 2, the top fraction of the first distillation column 12 was mainly composed of C5 or lower hydrocarbons. As described above, according to Example 1, it was confirmed that the operation of the distillation tower can be performed safely at low cost without introducing gas from the outside.

[Comparative Example 1]
A static simulation model of the processing equipment for naphtha decomposition products similar to that in Example 1 was constructed on a computer. Except for using those as the pressure control gas in the first distillation column 12, was added N ₂ of 0.1 parts by weight of the crude C5 fraction 100 parts by weight in Table 1, Example 1 As a condition for operating in the same manner as above, the composition of the top fraction of the first distillation column 12 was calculated. The results are shown in Table 3. As shown in Table 3, 0.09 wt% of the composition of the top fraction of the first distillation column 12 became nitrogen.

  In the study of AIChE, it is said that if ppm order nitrogen accumulates in the cryogenic separator of the treatment facility, there is a risk of explosion (Non-patent Document 3). For this reason, the top fraction of the first distillation column 12 is recovered in a system for thermally decomposing and separating naphtha (that is, the compression system 3 in FIG. 1), and nitrogen having a dangerous concentration or more is mixed as a recycle gas. It was also found that dangerous concentrations of nitric oxide can accumulate.

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 10 Pre-distillation system 11 De-C5 tower 12 Distillation tower 13 Distillation tower

Claims (3)

A pressure control gas is supplied to 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 the naphtha decomposition product generated by the decomposition of naphtha. In the method of introducing and controlling the pressure of the distillation column,
A pressure control method for a distillation column, characterized in that a gas not containing C5 or higher hydrocarbons present in the processing facility is used as the pressure control gas.   2. The pressure control method for a distillation column according to claim 1, wherein the gas that does not contain C5 or higher hydrocarbons present in the processing equipment contains C4 or lower hydrocarbon gas.   In Claim 1 or 2, the gas which does not contain C5 or more hydrocarbons present in the processing facility is an off-gas separated from a distillation apparatus for removing light boiling substances from a C5 fraction in the processing facility. A pressure control method for a distillation column,

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