JP5599634B2 - Rectification tower startup method - Google Patents

Description

  The present invention relates to a start-up of a rectifying column in which a hydrofinished product of a middle fraction and a hydrocracked product of a wax fraction contained in a synthetic oil produced by a Fischer-Tropsch synthesis reaction are supplied and fractionated. Regarding the method.

  In recent years, from the viewpoint of reducing environmental impact, clean liquid fuels that are low in sulfur and aromatic hydrocarbons and that are friendly to the environment have been demanded. From this point of view, as a technology that can produce fuel oil bases that are free of sulfur and aromatic hydrocarbons and are rich in aliphatic hydrocarbons, in particular, kerosene / light oil bases, Fischer uses carbon monoxide and hydrogen as raw materials. A method utilizing a Tropsch synthesis reaction (hereinafter sometimes referred to as “FT synthesis reaction”) has been studied (see, for example, Patent Document 1).

  Synthetic oil (crude oil) obtained by FT synthesis reaction (hereinafter sometimes referred to as “FT synthetic oil”) is a mixture mainly composed of aliphatic hydrocarbons having a wide carbon number distribution. From this FT synthetic oil, a naphtha fraction containing many components having a boiling point lower than about 150 ° C., a middle fraction containing many components having a boiling point of about 150 to about 360 ° C., and heavier than the middle fraction And a wax fraction containing a hydrocarbon component (boiling point above about 360 ° C.). Of these fractions, the middle fraction is the most useful fraction corresponding to the kerosene / light oil base, and it is desired to obtain this in a high yield. Therefore, in the upgrading process to obtain a fuel oil base material by fractionating and hydrotreating FT synthetic oil, the wax fraction produced together with a middle fraction in the FT synthesis reaction process is hydrocracked. It has been practiced to lower the molecular weight and convert it to a component corresponding to the middle distillate, thereby increasing the yield of the middle distillate as a whole.

  Specifically, as shown in FIG. 1, a crude wax fraction before hydrocracking obtained from FT synthetic oil by fractional distillation in the first fractionator 10 is a wax fraction hydrocracking apparatus 50 via a line 14. To be hydrocracked. Then, the hydrocracking product is supplied to the second rectification tower 20 via the line 51. On the other hand, the crude middle distillate before hydrorefining obtained from the FT synthetic oil by fractional distillation in the first fractionator 10 is supplied to the middle distillate hydrorefining apparatus 40 via the line 13 and hydrorefined. The hydrorefined product is combined with the hydrocracked product via the line 41 and supplied to the second rectification column 20. The hydrocracking product and hydrorefining product supplied to the second rectifying column 20 are fractionated, and an intermediate fraction serving as a kerosene / light oil base material is obtained from the line 22. Further, from the bottom of the second fractionator 20, a bottom oil composed of so-called “undecomposed wax” that has not been sufficiently decomposed in the hydrocracking of the wax fraction is extracted. Is recycled via line 24 to line 14 upstream of wax fraction hydrocracking apparatus 50 and again subjected to hydrocracking.

  Here, the hydrocracking product flowing out from the wax fraction hydrocracking apparatus 50 includes not only the hydrocarbon component whose molecular weight has been lowered to a predetermined value or less by hydrocracking, but also the aforementioned uncracked wax. . This undecomposed wax is a component having a high freezing point, and the hydrocracking product containing it is usually a solid or semisolid having no fluidity at normal temperature and pressure.

  By the way, when starting up the second rectification column 20 from a long-term shutdown state, the second rectification column 20 and piping connected thereto are at room temperature or a temperature close to room temperature. When the hydrocracking product of the wax fraction is supplied thereto, the temperature of the hydrocracking product is lowered to become a solid or semi-solid, and the second rectifying column 20 or a pipe connected thereto. There is a risk of problems such as blockage. Therefore, at the start-up of the rectifying tower 20, before supplying the hydrocracking product from the wax fraction hydrocracking apparatus 50 to the rectifying tower 20, a hydrocarbon oil that is liquid at room temperature and normal pressure from the outside. (Hereinafter sometimes referred to as “heated oil”), and heated and circulated, the hydrocracking product solidifies the second rectifying column 20 and the piping connected thereto. Preheating to a temperature that does not occur is performed.

After preheating the second fractionator 20 in this way, the hydrocracking product from the wax fraction hydrocracking device 50 and the hydrogen from the middle fraction hydrotreating device 40 are supplied to the second fractionator 20. The supply of the purified product is started, and the second rectification column 20 is operated. As a result, it is possible to prevent troubles such as clogging of the apparatus due to cooling and solidification of components having a high freezing point contained in the hydrocracking product in the second fractionator 20 or piping connected thereto. it can.
In addition, after the preheating of the second rectifying column 20 is completed, the heated oil is transferred to the slop tank through the discharge line 29 branched from the line 24.

JP 2004-323626 A

  However, in the case where the second rectifying column 20 is preheated by such a method, it is necessary to prepare a dedicated heating oil. This heat oil is in a liquid state at normal temperature and pressure, and it is necessary to be a special hydrocarbon oil that does not contain sulfur, aromatic hydrocarbons, etc. in consideration of mixing into products. In addition, after the preheating of the rectifying tower is completed, the heat oil is often used as a waste or in-house fuel without being used as a product, which is inefficient.

  The present invention has been made in view of the above circumstances, and can preheat the rectification tower without using a dedicated heating oil, and the used heating oil can be used as waste oil or in-house fuel. The objective is to provide a rectification tower startup method that can be used as a product.

  The rectifying tower start-up method of the present invention comprises a hydrocracked product obtained by hydrocracking a wax fraction contained in a Fischer-Tropsch synthetic oil and an intermediate fraction contained in the synthetic oil. This is a start-up method of a rectification column in which a hydrorefined product obtained by hydrorefining in a hydrorefining step is supplied and fractionated, and the hydrorefining supplied from a middle distillate hydrorefining step It has the preheating process which preheats the said rectification column using a product, It is characterized by the above-mentioned.

  In the rectification tower start-up method of the present invention, the preheating step includes a step of heating the hydrorefined product and supplying it to the rectification column, and extracting bottom oil from the bottom of the rectification column. It is preferable to comprise a step of heating and returning to the rectification column and a step of circulating the fraction distilled from the top of the rectification column to the rectification column.

  According to the start-up method of the present invention, the rectification tower can be preheated without using a special heating oil having special properties, and the hydrorefined product used for preheating can be used as waste oil or in-house. It can be used as a product without using it as a fuel, and the rectification tower can be started up efficiently.

It is a schematic block diagram of FT synthetic oil upgrading system. It is a block diagram which shows a part of FIG. 1 concretely.

Hereinafter, the present invention will be described in detail along examples of preferred embodiments.
[FT synthetic oil upgrading system]
FIG. 1 is a schematic configuration diagram of an FT synthetic oil upgrading system. First, the FT synthetic oil upgrading system will be described with reference to FIG.
The FT synthetic oil upgrading system in FIG. 1 is a first FT synthetic oil that is introduced from a FT synthesis reactor (not shown) via line 1 into a crude naphtha fraction, a crude middle distillate, and a crude wax fraction. The rectification column 10, the naphtha fraction hydrotreating apparatus 30 for hydrotreating the crude naphtha fraction introduced by the line 12, and the hydrofinishing and hydroisomerization of the crude middle fraction introduced by the line 13 A middle fraction hydrotreating apparatus 40 and a wax fraction hydrocracking apparatus 50 for hydrocracking the crude wax fraction introduced through the line 14. The “crude naphtha fraction”, “crude middle fraction”, and “crude wax fraction” obtained from the first fractionator 10 are the fractions not subjected to hydrorefining or hydrocracking, respectively. And oxygen-containing compounds such as olefins and alcohols, which are by-products of the FT synthesis reaction, in addition to saturated hydrocarbons.

Here, the FT synthetic oil is not particularly limited as long as it is synthesized by an FT synthesis reaction. However, from the viewpoint of increasing the yield of middle distillate, hydrocarbons having a boiling point of about 150 ° C. or higher are converted into the entire FT synthetic oil. It is preferable that 80 mass% or more is included on the basis of the mass.
The FT synthetic oil is usually produced by a known FT synthesis reaction method and is a mixture mainly composed of aliphatic hydrocarbons having a wide carbon number distribution, and can be obtained by appropriately fractionating this in advance. It may be a fraction.

The crude naphtha fraction is a component distilled at a temperature lower than about 150 ° C. in the first rectifying column 10, and the crude middle distillate is a temperature of about 150 ° C. or higher and about 360 ° C. or lower in the first rectifying column 10. The crude wax fraction is a component that is not distilled at about 360 ° C. in the first rectifying column 10 and is extracted from the bottom of the column.
Note that, here, as a preferred embodiment, an example is shown in which two cut points (that is, about 150 ° C. and about 360 ° C.) are set in the first rectifying column 10 and fractionation is performed into three fractions. For example, by setting one cut point, a fraction below the cut point is introduced into the middle distillate hydrotreating apparatus 40 from the line 13 as an intermediate fraction, and a fraction exceeding the cut point is designated as a wax fraction. It may be extracted from the line 14. Alternatively, three cut points are set in the first rectifying column 10, and four fractions, that is, a naphtha fraction, a middle fraction light component, a middle fraction heavy component, and a wax fraction four are selected. You may fractionate into fractions.

  In the naphtha fraction hydrotreating apparatus 30, the crude naphtha fraction is hydrorefined by a known method, and the olefins contained in the naphtha fraction are converted to saturated hydrocarbons by hydrogenation, and also contain alcohols and the like. Oxygen compounds are converted to saturated hydrocarbons and water by hydrodeoxygenation.

  In the middle distillate hydrotreating apparatus 40, the olefins and oxygen-containing compounds contained in the crude middle distillate are converted into saturated hydrocarbons by a known method, as in the naphtha distillate hydrotreating apparatus 30. . At the same time, in order to improve the low temperature characteristics (low temperature fluidity) of the produced oil as a fuel oil base material, at least a part of the normal paraffin mainly constituting the crude middle distillate is hydroisomerized and converted to isoparaffin. The

  In the wax fraction hydrocracking apparatus 50, the crude wax fraction is hydrocracked by a known method using a hydrocracking catalyst and converted into a component corresponding to the middle fraction. At this time, oxygen-containing compounds such as olefins and alcohols contained in the crude wax fraction are converted into paraffin. At the same time, hydroisomerization of normal paraffin, which contributes to the improvement of the low temperature characteristics (low temperature fluidity) of the produced oil as the fuel oil base, also proceeds.

  On the other hand, a portion of the crude wax fraction is excessively hydrocracked and converted to a hydrocarbon corresponding to a naphtha fraction having a lower boiling point than hydrocarbons having a boiling range corresponding to the target middle fraction. . In addition, hydrocracking of some of them proceeds further and is converted into gaseous hydrocarbons having 4 or less carbon atoms such as butanes, propane, ethane, and methane.

  The FT synthetic oil upgrading system in FIG. 1 is a gas mainly composed of hydrocarbons having 4 or less carbon atoms from a naphtha fraction that has passed through the naphtha fraction hydrotreating device 30 downstream of the naphtha fraction hydrotreating device 30. The naphtha stabilizer 60 which discharges a gaseous hydrocarbon from the line 62 connected to the tower top, and the naphtha tank 70 which stores the naphtha fraction from which the gaseous hydrocarbon was removed in this way are provided. Here, the naphtha fraction flowing out from the naphtha fraction hydrotreating apparatus 30 is introduced into the naphtha stabilizer 60 through the line 31, and the naphtha fraction from which the gaseous hydrocarbons have been removed in the naphtha stabilizer 60 is introduced into the naphtha fraction through the line 61. It is introduced into the tank 70 and stored.

  A part of the naphtha fraction hydrorefined in the naphtha fraction hydrotreating apparatus 30 is recycled to the line 12 upstream of the naphtha hydrotreating apparatus 30 through the line 32. Hydrorefining of the crude naphtha fraction is a reaction with a large exotherm, and when only the crude naphtha fraction is hydrorefined, the temperature of the naphtha fraction excessively increases in the naphtha fraction hydrorefining apparatus 30. There is a risk. Therefore, the crude naphtha fraction is diluted by recycling a part of the naphtha fraction after the hydrorefining to prevent the excessive temperature rise.

  In the downstream of the middle distillate hydrotreating apparatus 40 and the wax distillate hydrocracking apparatus 50, the hydrotreating product from the middle distillate hydrotreating apparatus 40 and the hydrogen from the wax fraction hydrotreating apparatus 50. A chemical distillation product is supplied, and a second rectifying column 20 for fractionating these mixtures is installed. In the second fractionator 20, a light fraction is extracted from the line 21, and an intermediate fraction that is a kerosene / light oil base material is extracted from the line 22. The hydrorefined product of the middle distillate hydrotreating apparatus 40 is supplied to the second rectification tower 20 via a line 41, and the hydrocracking product from the wax fraction hydrocracking apparatus 50 is sent via a line 51. The second rectification column 20 is supplied. The hydrotreating product from the middle distillate hydrotreating apparatus 40 and the hydrocracking product from the wax fraction hydrocracking apparatus 50 supplied to the second fractionator 20 are mixed by line blending. Or may be mixed by tank blending, and the mixing method is not particularly limited.

  Further, in this example, the middle fraction is obtained as a single fraction in the second fractionator 20 and is introduced into the middle fraction tank 90 through the line 22 and stored. As appropriate, a plurality of fractions, for example, a kerosene fraction and a light oil fraction, may be fractionated and introduced into a plurality of tanks for storage.

  The bottom oil of the second rectifying column 20 is mainly composed of an undecomposed wax fraction, that is, a wax fraction that has not been sufficiently decomposed in the wax fraction hydrocracking step. The bottom oil is recycled to the line 14 upstream of the wax fraction hydrocracking device 50 via the line 24, and is supplied to the wax fraction hydrocracking device 50 to undergo hydrocracking again. Thereby, the middle distillate yield can be improved.

  On the other hand, the light fraction discharged from the top of the second fractionator 20 is sent to the line 31 via the line 21 and supplied to the naphtha stabilizer 60.

[Middle distillate hydrotreating process]
Next, with reference to FIG. 2, the configuration and operation around the middle distillate hydrotreating apparatus 40 will be described in detail.

The middle distillate hydrotreating step is a step of hydrotreating and hydroisomerizing the middle distillate obtained by the FT synthesis reaction in the middle distillate hydrotreating device 40. In the FT synthesis reaction, in addition to saturated hydrocarbons as main products, oxygen-containing compounds such as olefins and alcohols containing carbon monoxide-derived oxygen atoms are by-produced, and FT synthetic oil is fractionated. These by-products are also contained in the middle distillate obtained. Hydrorefining in the middle distillate hydrorefining step includes the reaction of hydrogenating the olefins to convert them to saturated hydrocarbons (paraffin hydrocarbons), and hydrodeoxygenating the oxygen-containing compounds to obtain saturated hydrocarbons and water. Mainly includes the reaction to convert to As a catalyst effective for this hydrorefining, a catalyst having a metal component having hydrogenation ability as an active site is used.
On the other hand, the hydroisomerization in the middle distillate hydrotreating process is a reaction for converting normal paraffin, which is the main component of the middle distillate, into isoparaffin. As a catalyst effective for this hydroisomerization, a catalyst comprising a metal component having hydrogenation-dehydrogenation ability and a solid acid component is used. The normal paraffin is first dehydrogenated by the action of the metal component to become an olefin. This olefin is skeletal isomerized by the action of the solid acid component, and further hydrogenated by the action of the metal component to be converted to isoparaffin.
In the middle distillate hydrorefining step, both a catalyst effective for hydrorefining and a catalyst effective for hydroisomerization may be used. In general, a catalyst effective for hydroisomerization is hydrogen. Therefore, it is efficient and preferable to use a catalyst effective for hydroisomerization.

  Although the form of the middle distillate hydrotreating apparatus 40 according to the present invention is not limited, it is preferably a fixed bed continuous flow reactor. The reactor may be a single reactor or a plurality of reactors arranged in series or in parallel. Moreover, the catalyst bed provided in a reactor may be single, and may be divided into plurality.

The catalyst charged in the middle distillate hydrorefining apparatus 40 is a catalyst generally used for hydrorefining and / or hydroisomerization in petroleum refining or the like, that is, hydrogenation (-dehydrogenation to an inorganic carrier). A catalyst on which an active metal having an ability is supported can be used.
As the active metal constituting the catalyst, one or more metals selected from the group consisting of metals of Group 6, Group 8, Group 9 and Group 10 of the periodic table of elements are used. Specific examples of these metals include noble metals such as platinum, palladium, rhodium, ruthenium, iridium and osmium, or cobalt, nickel, molybdenum, tungsten, iron, etc., preferably platinum, palladium, nickel, Cobalt, molybdenum and tungsten are preferable, and platinum and palladium are more preferable. These metals are also preferably used in combination of a plurality of types, and preferable combinations in that case include platinum-palladium, cobalt-molybdenum, nickel-molybdenum, nickel-cobalt-molybdenum, nickel-tungsten and the like. Here, the periodic table of elements refers to a periodic table of long-period elements based on the provisions of IUPAC (International Pure and Applied Chemical Association).

  Examples of the inorganic carrier constituting the catalyst include metal oxides such as alumina, silica, titania, zirconia, and boria. These metal oxides may be one kind or a mixture of two or more kinds or a composite metal oxide such as silica alumina, silica zirconia, alumina zirconia, alumina boria and the like. The inorganic carrier is a composite metal oxide having solid acidity such as silica alumina, silica zirconia, alumina zirconia, alumina boria, etc. from the viewpoint of efficiently proceeding hydroisomerization of normal paraffin simultaneously with hydrorefining. Preferably there is. The inorganic carrier may contain a small amount of zeolite. Furthermore, the inorganic carrier may contain a binder for the purpose of improving the moldability and mechanical strength of the carrier. Preferred binders include alumina, silica, magnesia and the like.

  The content of the active metal in the catalyst is preferably about 0.1 to 3% by mass as a metal atom based on the mass of the support when the active metal is the above-mentioned noble metal. When the active metal is a metal other than the above-mentioned noble metal, the metal oxide is preferably about 2 to 50% by mass based on the mass of the support. When the content of the active metal is less than the lower limit, hydrorefining and hydroisomerization tend not to proceed sufficiently. On the other hand, when the content of the active metal exceeds the upper limit value, the dispersion of the active metal tends to decrease, and the activity of the catalyst tends to decrease, and the catalyst cost increases.

  The reaction temperature of the middle distillate hydrotreating apparatus 40 in the example of this embodiment is 180 to 400 ° C, preferably 280 to 350 ° C, more preferably 300 to 340 ° C. Here, the reaction temperature is the average temperature of the catalyst layer in the middle distillate hydrotreating apparatus 40. If the reaction temperature is equal to or higher than the lower limit temperature, the middle distillate is sufficiently hydrorefined and hydroisomerized. Moreover, the lifetime reduction of a catalyst is suppressed.

  The pressure (hydrogen partial pressure) in the middle distillate hydrotreating apparatus 40 is preferably 0.5 to 12 MPa, and more preferably 1 to 5 MPa. If the hydrorefining equipment pressure is 0.5 MPa or higher, the crude middle distillate is sufficiently hydrorefined and hydroisomerized, and if it is 12 MPa or lower, the equipment cost for increasing the pressure resistance of the equipment is suppressed. it can.

Preferably the liquid hourly space velocity in the middle distillate hydrotreating apparatus 40 (LHSV [liquid hourly space velocity ]) is 0.1 to 10 ^-1, and more preferably 0.3 to 3.5 ^-1 . If LHSV is 0.1 h ⁻¹ or more, the reactor volume does not need to be excessive, and if it is 10 h ⁻¹ or less, the middle distillate is efficiently hydrorefined and hydroisomerized.

  The hydrogen gas / oil ratio in the middle distillate hydrotreating apparatus 40 is preferably 50 to 1000 NL / L, and more preferably 70 to 800 NL. Here, “NL” means the hydrogen capacity (L) in the standard state (0 ° C., 101325 Pa). If the hydrogen gas / oil ratio is 50 NL / L or more, the middle distillate is sufficiently hydrorefined and hydroisomerized. If it is 1000 NL / L or less, no equipment for supplying a large amount of hydrogen gas is required. In addition, an increase in operating costs can be suppressed.

[Wax fraction hydrocracking process-recycling process]
Next, the wax fraction hydrocracking process and each downstream process in the upgrading system will be described in more detail with reference to FIG.

(Wax fraction hydrocracking process)
In the wax fraction hydrocracking process, as shown in FIG. 2, the wax fraction was supplied from the bottom of the first rectifying column (not shown), possibly via an intermediate tank (not shown), through the line 14. The crude wax fraction is hydrocracked in the wax fraction hydrocracking apparatus 50 to obtain a hydrocracked product containing undecomposed wax. Unless otherwise specified, hydrocracking products mean those containing undecomposed wax. The hydrocracked product is subjected to gas-liquid separation by a first gas-liquid separator 55 and a second gas-liquid separator 57 described later, and the liquid component is supplied to the second rectification column 20. The bottom oil of the second rectification tower 20 containing undecomposed wax as a main component is returned to the line 14 upstream of the wax fraction hydrocracking apparatus 50 through the line 24, and the crude wax fraction in the mixing tank (not shown). And is supplied to the wax fraction hydrocracking apparatus 50 and hydrocracked again.

Examples of the hydrocracking catalyst used in the wax fraction hydrocracking apparatus 50 include a support in which a metal belonging to Groups 8 to 10 of the periodic table is supported as an active metal on a carrier containing a solid acid.
Suitable supports include crystalline zeolites such as ultrastable Y-type (USY) zeolite, Y-type zeolite, mordenite and beta zeolite, and amorphous composite metals having heat resistance such as silica alumina, silica zirconia, and alumina boria. What is comprised including 1 or more types of solid acids chosen from an oxide is mentioned. Further, the carrier is more preferably composed of USY zeolite and at least one solid acid selected from silica alumina, alumina boria and silica zirconia. USY zeolite, alumina boria and / or silica More preferably, it contains alumina.

  USY zeolite is obtained by ultra-stabilizing Y-type zeolite by hydrothermal treatment and / or acid treatment, and in addition to the fine pore structure called micropores having a pore diameter originally possessed by Y-type zeolite of 2 nm or less, New pores having a pore diameter in the range of 10 nm are formed. The average particle size of the USY zeolite is not particularly limited, but is preferably 1.0 μm or less, more preferably 0.5 μm or less. In the USY zeolite, the silica / alumina molar ratio (the molar ratio of silica to alumina) is preferably 10 to 200, more preferably 15 to 100, and still more preferably 20 to 60.

  Moreover, it is preferable that a support | carrier is comprised including 0.1-80 mass% of crystalline zeolite and 0.1-60 mass% of amorphous complex metal oxides which have heat resistance.

  The carrier can be produced by molding a carrier composition containing the solid acid and the binder and then baking the carrier composition. The blending ratio of the solid acid is preferably 1 to 70% by mass and more preferably 2 to 60% by mass based on the total amount of the carrier. Moreover, when a support | carrier is comprised including USY zeolite, it is preferable that the mixture ratio of USY zeolite is 0.1-10 mass% on the basis of the mass of the whole support | carrier, and is 0.5-5 mass%. It is more preferable. Furthermore, when the carrier is configured to contain USY zeolite and alumina boria, the blending ratio of USY zeolite to alumina boria (USY zeolite / alumina boria) is preferably 0.03 to 1 in terms of mass ratio. Moreover, when a support | carrier is comprised including USY zeolite and silica alumina, it is preferable that the compounding ratio (USY zeolite / silica alumina) of USY zeolite and silica alumina is 0.03-1.

  The binder is not particularly limited, but alumina, silica, titania and magnesia are preferable, and alumina is more preferable. The blending amount of the binder is preferably 20 to 98% by mass, and more preferably 30 to 96% by mass based on the mass of the entire carrier.

  The shape of the molded carrier is not limited, and examples thereof include a spherical shape, a cylindrical shape, and a deformed cylindrical shape having a three-leaf / four-leaf cross section. Moreover, there is no restriction | limiting in particular also about the particle diameter, However, It is preferable that it is 1 micrometer-10 mm from practicality.

  The firing temperature of the carrier composition is preferably in the range of 400 to 550 ° C, more preferably in the range of 470 to 530 ° C, and even more preferably in the range of 490 to 530 ° C.

  Specific examples of the metals in Groups 8 to 10 of the periodic table include cobalt, nickel, rhodium, palladium, iridium, platinum, and the like. Among these, it is preferable to use a metal selected from nickel, palladium and platinum alone or in combination of two or more. These metals can be supported on the above-mentioned carrier by a conventional method such as impregnation or ion exchange. The amount of metal to be supported is not particularly limited, but the total amount of metals is preferably 0.1 to 3.0% by mass with respect to the mass of the carrier.

  The hydrogen partial pressure in the wax fraction hydrocracking apparatus 50 is, for example, 0.5 to 12 MPa, and preferably 1.0 to 5.0 MPa.

The liquid space velocity (LHSV) in the wax fraction cracking hydrocracking apparatus 50 is, for example, 0.1 to 10.0 h ⁻¹ , and preferably 0.3 to 3.5 h ⁻¹ . The ratio of the hydrogen gas to the wax fraction (hydrogen gas / oil ratio) is not particularly limited, but is, for example, 50 to 1000 NL / L, and preferably 70 to 800 NL / L.

  Examples of the reaction temperature (catalyst bed weight average temperature) during normal operation of the wax fraction hydrocracking apparatus 50 include 180 to 400 ° C, preferably 200 to 370 ° C, more preferably 250 to 350 ° C, and still more preferably. Is 280-350 ° C. When the reaction temperature exceeds 400 ° C., hydrocracking proceeds excessively, and the yield of the target middle distillate tends to decrease. In addition, the hydrocracking product may be colored to restrict use as a fuel base material. On the other hand, when the reaction temperature is lower than 180 ° C., the hydrocracking of the wax fraction does not proceed sufficiently, and the yield of the middle fraction tends to decrease. The reaction temperature is controlled by adjusting the set temperature at the outlet of the heat exchanger 18 provided in the line 14.

  During normal operation of the wax fraction hydrocracking apparatus 50, the total hydrocracking with a boiling point of 25 ° C. or more and 360 ° C. or less of hydrocarbon components contained in the hydrocracking product is 25 ° C. or more. It is preferable to operate the hydrocracking apparatus 50 so that the amount is preferably 20 to 90% by mass, more preferably 30 to 80% by mass, and still more preferably 45 to 70% by mass, based on the mass of the product. If the content of the specific hydrocarbon component is within such a range, the degree of progress of hydrocracking is appropriate, and the yield of middle distillate can be increased.

(Gas-liquid separation process)
In this example, the hydrocracking product in the wax fraction hydrocracking step is introduced into a gas-liquid separator provided in two stages and separated into gas and liquid. That is, in the hydrocracking process, unreacted hydrogen gas and wax fraction are separated into a gaseous component composed of gaseous hydrocarbons produced by excessive hydrocracking and a liquid component composed of liquid hydrocarbons.
A heat exchanger (not shown) for cooling the hydrocracking product is preferably installed in the line 52 connected to the outlet of the wax fraction hydrocracking apparatus 50. The hydrocracked product cooled by this heat exchanger is separated into a gas component and a liquid component by the first gas-liquid separator 55. The temperature in the first gas-liquid separator 55 is preferably about 180 to 300 ° C. That is, the liquid component separated in the first gas-liquid separation device 55 is a heavy oil component made of hydrocarbons that are in a liquid state at the temperature, and contains a large amount of undecomposed wax fraction. The heavy oil component is supplied from the bottom of the first gas-liquid separator 55 to the second rectification tower 20 via the line 53 and the line 51.

  On the other hand, the gas component separated in the first gas-liquid separation device 55 is introduced into the heat exchanger (cooling device) 56 through the line 59 from the top of the first gas-liquid separation device 55 and cooled. At least a portion is liquefied. The effluent from the heat exchanger 56 is introduced into the second gas-liquid separator 57. The inlet temperature of the second gas-liquid separator 57 is set to about 90 to 130 ° C. by cooling with the heat exchanger 56.

  In the second gas-liquid separation device 57, the gas component and the liquid component liquefied by cooling in the heat exchanger 56 are separated. The separated gas component is extracted from the top of the second gas-liquid separator 57 by the line 19. A heat exchanger is installed in the line 19 (not shown), and the gas component is preferably cooled to about 40 ° C. Thereby, a part of the light hydrocarbon in the gas component is liquefied and returned to the second gas-liquid separator 57. The remaining gas component is mainly composed of hydrogen gas containing gaseous hydrocarbons, and is supplied to the middle distillate hydrotreating apparatus 40 or the naphtha distillate hydrotreating apparatus 30 (not shown) for hydrogenation. As reused.

  On the other hand, a liquid component is extracted from the line 54 connected to the bottom of the second gas-liquid separator 57. This liquid component is a light oil component made of lighter hydrocarbons which is liquid at the temperature of the second gas-liquid separator 57 which is lower than that of the first gas-liquid separator 55. The light oil component is supplied to the second rectification tower 20 through the line 51 together with the heavy oil component from the first gas-liquid separator 55.

  In this way, by installing the gas-liquid separation device in two stages and adopting the method of cooling in two stages, a component having a high freezing point contained in the hydrocracking product of the wax fraction hydrocracking process (especially undecomposed) The wax fraction) is solidified by cooling, and troubles such as device clogging can be prevented. In this example, the gas-liquid separation process has two stages, but may have three stages or more.

(Fractionation process)
Next, of the cracked products in the wax fraction hydrocracking step, the liquid component separated in the gas-liquid separation step as described above is supplied to the second rectifying column 20 through the line 51. Further, the hydrofinished middle fraction flowing out from the middle distillate hydrotreating apparatus 40 is separated from the gas mainly composed of hydrogen gas in the gas-liquid separation apparatus 45, and the hydrocracking product is generated by the line 41. And is fed to the rectification column 20. An intermediate fraction (kerosene / light oil fraction) is obtained from the line 22 connected to the center of the rectifying column 20, and a light fraction is obtained from the line 21 connected to the upper part of the rectifying column 20. From the bottom of the column, heavy hydrocarbons mainly containing undecomposed wax remaining in the hydrocracking product are recovered.

(Recycling process)
Next, in the recycling process, the entire amount of the bottom oil obtained in the fractionation process is re-supplied to the wax fraction hydrocracking process through the line 24. Since this bottom oil contains the undecomposed wax remaining in the cracked product from the wax fraction hydrocracking step, hydrogen is re-supplied to the wax fraction hydrocracking step to generate hydrogen. The chemical decomposition can be advanced, and the yield of the final middle distillate can be further increased.

[Startup method of rectification tower]
Next, a startup method of the second rectifying column 20 will be described with reference to FIG.

  At the start-up of the second rectification column 20, first, the operation of the middle distillate hydrotreating apparatus 40 is started. Specifically, the crude middle distillate supplied from the center of the first rectifying column (not shown) is supplied to the middle distillate hydrotreating apparatus 40 via the line 13 to perform hydrotreating. The operating condition may be an operating condition in the normal operation of the apparatus described above. However, at the start of the operation of the process, the supply of the crude middle distillate starts at a low supply rate (LHSV) and is gradually increased as in the start of the operation of a general apparatus.

  The hydrorefined product flowing out from the middle distillate hydrorefining apparatus 40 is gas-liquid separated in the gas-liquid separation apparatus 45. The gas component separated here is mainly composed of hydrogen gas that has not been reacted in hydrorefining. On the other hand, the liquid component (hydrorefined product) obtained here is obtained by converting olefins and oxygen-containing compounds into paraffin hydrocarbons by hydrorefining, and further, at least one of normal paraffins as a main component of the crude middle distillate. Part is a hydrocarbon oil converted to isoparaffin by hydroisomerization. The hydrorefined product is a liquid at normal temperature and pressure, and is a paraffin hydrocarbon substantially free of sulfur, aromatic hydrocarbons, and naphthene hydrocarbons, and is suitable for preheating of the second rectification column 20. Hydrogen oil.

The second rectifying column 20 and the pipes connected to the second rectifying column 20 are preheated by such a hydrorefined product as follows (preheating step).
The hydrorefined product obtained as described above is heated from the line 41 by the heat exchanger 28 and supplied to the second rectification column 20. Light components in the supplied hydrorefining product are extracted from the top of the second rectifying column 20, and liquefied hydrocarbons are stored in the reflux drum 31 through the heat exchanger 30 for cooling. Is done. The liquefied hydrocarbon in the reflux drum 31 is refluxed to the second rectification column 20 through the line 25.
On the other hand, tower bottom oil is extracted from the bottom of the second rectifying tower 20, heated by the heat exchanger 28 via the lines 24, 27 and 51, and returned to the second rectifying tower 20. In this way, preheating of the second fractionator 20 and piping connected to the second rectification column 20 is performed using the hydrorefined product.

  As described above, preheating of the second rectifying column 20 and piping connected thereto proceeds, and the temperature of the second rectifying column 20 and piping connected thereto increases. This preheating is performed until at least the temperature of the feed oil supply stage (hydrorefined product supply stage) to the second fractionator 20 reaches about 120 ° C. or higher. By setting the temperature of the feed oil supply stage (hydrorefined product supply stage) to the second rectifying column to about 120 ° C. or higher, the hydrocracking product containing undecomposed wax is then converted into the second rectifying column. Even when supplied to 20, the wax fraction solidifies in the piping around the inlet of the second rectifying column 20 or the like or in the second rectifying column 20, thereby preventing the apparatus from being blocked. At this stage, preheating of the second rectification column 20 is completed.

  When the preheating of the second rectifying column is completed, the operation of the wax fraction hydrocracking process is started, and the supply of the hydrocracking product containing undecomposed wax to the second rectifying column 20 is started. Specifically, the crude wax fraction supplied from the bottom of the first rectifying tower (not shown) is supplied to the wax fraction hydrocracking apparatus 50 to perform hydrocracking. The operating conditions of the wax fraction hydrocracking apparatus 50 are preferably the normal operating conditions of the above-mentioned apparatus, but the crude wax fraction is the same as at the start of the middle distillate hydrotreating process. Supply starts at a low supply rate (LHSV) and gradually increases. The hydrocracking product containing the undecomposed wax flowing out is gas-liquid separated in the first gas-liquid separation device 55 and the second gas-liquid separation device 57 provided in two stages in this example, The liquid component joins with the middle distillate hydrorefining product flowing in via the line 41, heated by the heat exchanger 28, and supplied to the second fractionator 20.

By starting supply of the hydrocracking product containing undecomposed wax to the second rectifying column 20 and continuing this, the temperature profile of the second rectifying column 20 is brought closer to that of normal operation. As one guideline, at the stage where the temperature of the middle distillate extraction stage to which the line 22 is connected in the second rectifying column 20 has risen to the temperature in normal operation, the wax fraction hydrocracking apparatus 50 for the column bottom oil is used. Recycle upstream of and start extracting middle distillate from line 22. Also, extraction of naphtha fraction will be started. Thus, the start-up of the second rectification tower 20 is completed.
As described above, the hydrorefined product used for preheating the second rectification column 20 does not need to be recovered and discarded, and is used as part of the product as it is.

  According to the above-mentioned method, it is usually possible to prepare a heating oil having a specific property that had to be procured in the past, and the used hydrorefined product is not disposed of by disposal or combustion. It can be used as a part of the product and can efficiently start up the rectification column. This makes it possible to reduce the cost required for rectification tower startup.

  The start-up method of the rectifying column of the present invention is not limited to the above-described preferred embodiment, and various modifications can be made within a range that does not impair the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 1st rectification tower 20 2nd rectification tower 40 Middle distillate hydrorefining apparatus 50 Wax distillate hydrocracking apparatus

Claims (2)

Hydrocracked product obtained by hydrocracking the wax fraction contained in Fischer-Tropsch synthetic oil, and obtained by hydrotreating the middle fraction contained in the synthetic oil in the middle distillate hydrorefining step. A rectification column start-up method in which a hydrorefined product is fed and fractionated,
A rectifying tower start-up method comprising a preheating step of preheating the rectifying column using a hydrorefining product supplied from a middle distillate hydrotreating step. The preheating step
Heating the hydrorefined product and supplying it to the rectification column;
Extracting the bottom oil from the bottom of the rectifying column, heating and returning it to the rectifying column;
Refluxing a fraction distilled from the top of the rectifying column to the rectifying column;
The rectification tower start-up method according to claim 1, comprising:

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