EP1436362B2 - Hydrodesulfurisation method comprising a stripping section and a vacuum fractionation section - Google Patents

Abstract

The invention concerns a facility and a process for hydrodesulphurizing gas oil or vacuum distillate comprising at least one hydrodesulphurization reaction section, at least one stripping section and at least one fractionation section in which the fractionation section comprises at least one fractionation column operated under moderate vacuum.

Description

PRIOR ART:

Conventional hydrodesulfurization processes for gas oils or vacuum distillates comprise an oven generally located between the H 2 S stripper and the main fractionator. The presence of this furnace makes it possible to raise the temperatures after the stripping and to obtain an effective fractionation in the fractionation column situated downstream. On the other hand, the presence of this furnace generates important energy consumptions and represents an investment and an important operating cost both in absolute and in relation to the whole process.

The US Patent 3,737,260 discloses a gas oil hydrodesulphurization process comprising a hydrodesulfurization reaction section, a separation of the effluent of this section into a gaseous fraction and a first high temperature and high pressure liquid fraction, a partial condensation of said vapor phase into a fraction comprising essentially hydrogen and a second liquid fraction, stripping of the H 2 S and light hydrocarbons of the first and second liquid fractions by means of the previously treated hydrogen, separation of the stripped hydrocarbons into a naphtha and a diesel fuel and recycling said naphtha to the condensation stage.

The request for WO 98/42804 discloses a composition comprising paraffinic, naphthenic and alkylbenzene fractions and processes for producing such composition. One of the processes described comprises a heavy molecule cracking reactor in the presence of hydrogen followed by a gas / liquid separation, a stripping and a vacuum fractionation after reheating the stripped effluent by means of an oven .

The US Patent 4,808,289 discloses a process for hydrotreating residues comprising mixing said residue with lighter hydrocarbons from a separator flask, sending said mixture to a series of reactors operated as a bubbling bed, separating in a separator flask from effluent obtained in 2 gaseous and liquid fractions, the fractionation of the liquid in an atmospheric distillation tower into a naphtha and a residue, then a vacuum fractionation of this residue into a gas, a naphtha and a vacuum residue

OBJECT OF THE INVENTION:

The present invention relates to a process for hydrodesulfurization of gas oil or vacuum distillate, preferably vacuum gas oil and / or vacuum distillates, comprising at least one hydrodesulfurization reaction section, at least one stripping section and at least one a fractionation section in which the main fractionating column is operated under a moderate vacuum. The method according to the invention makes it possible to reduce the amount of heat to be supplied to the charge of the fractionation section and thus to operate said section at moderate temperature levels. The method according to the invention therefore makes it possible to desulphurize a gas oil and or a vacuum distillate without the need to implant a furnace between the stripping section and the fractionation section, which represents a significant economic advantage over the processes of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process according to claim 1 for hydrodesulfurization of gas oil or vacuum distillate, preferably vacuum gas oil and / or vacuum distillates, comprising at least one hydrodesulfurization reaction section, at least one section of stripping and at least one fractionation section in which the main fractionating column is operated under a moderate vacuum. The plant used in the process according to the invention also comprises a hot separator flask.

In the process and the plant according to the invention, the hydrodesulfurization reaction section may comprise one or more reactors arranged in series or in parallel, for example two reactors arranged in series. Each reactor of the reaction section comprises at least one catalyst bed. The catalyst can be used in a fixed bed or in an expanded bed, or in a bubbling bed. In the case of a catalyst implemented in fixed bed, it is possible to have several catalyst beds in at least one reactor.

Any catalyst known to those skilled in the art can be used in the process according to the invention, for example a catalyst comprising at least one element selected from the elements of Group VIII of the periodic table (Groups 8, 9 and 10 of the new periodic classification) and possibly at least one element selected from Group VIB elements of the Periodic Table (Group 6 of the new Periodic Table).

The operating conditions of this hydrodesulfurization reaction section are generally within the operating condition ranges described in the prior art. These operating conditions that can be used in hydrotreatment are well known to those skilled in the art:

The temperature is typically between about 200 and about 460 ° C.

The total pressure is typically between about 1 MPa and about 20 MPa, typically between 2 and 20 MPa, preferably between 2.5 and 18 MPa, and most preferably between 3 and 18 MPa.

The overall hourly space velocity of liquid charge for each catalytic step is typically from about 0.1 to about 12, and generally from about 0.4 to about 10.

The purity of the hydrogen used in the process according to the invention is typically between 50 and 99.9.

The amount of hydrogen relative to the liquid feed is typically from about 50 to about 1200 Nm3 / m3.

The fractionation and stripping sections may be equipped with any type of stripping column at any pressure or moderate vacuum fractionation known to those skilled in the art. Steam is used to carry out said stripping. The vacuum column is also preferably fed by means of any stripping gas, preferably steam.

Passing the column to a moderate vacuum, that is to say included in the flash zone between 0.05 bar and 0.95 bar (1 bar = 0.1 MPa), preferably between 0.1 bar and 0.90 bar, more preferably between 0.1 bar and 0.7 bar and more preferably between 0.15 bar and 0.5 bar, can significantly reduce the heat to be brought to the load of this column for vaporizing the light fraction resulting from hydrocarbon conversion reactions in the hydrodesulfurization reactor.

The plant used in the process according to the invention comprises a hot separator flask. The additional heat required for this vaporization may possibly be provided by increasing the temperature of said separator tank relative to the current practice which corresponds to a temperature generally between 240 ° C and 280 ° C. Generally this increase is less than 60 ° C, preferably less than 50 ° C, more preferably less than 40 ° C. This mode of operation also differs significantly from that of the prior art in which the temperature of the hot flask is set for the operation of the H2S stripper column. The temperature of said separator flask is between 280 ° C and 350 ° C, preferably between 300 ° C and 340 ° C and very preferably between 300 ° C and 330 ° C.

This rise in temperature is then used to distil a maximum of naphtha in the stripper so as to send to the main fractionation column compounds whose boiling point is generally greater than about 100 ° C. The absence of light compounds in the vacuum column thus makes it possible to obtain complete condensation of the overhead product with a very moderate vacuum (for example 0.1 to 0.5 bar abs).

Any other method of supplying additional heat other than a furnace may, however, be envisaged in the method according to the invention, in particular those known to those skilled in the art, such as, for example, an additional heat exchanger.

In the process according to the invention, the temperature of the vacuum system is generally governed by the condensing temperature of the water coming from the stripping steam of the column. The complete condensation of hydrocarbons and water vapor makes it possible to use a very simple vacuum system that consumes little energy.

At the energy level, this process therefore makes it possible to gain most often about 2/3 of the energy consumption of the furnace used in the processes of the prior art. The remaining 1/3 is transferred to the furnace of the reaction loop.

At the equipment level this process saves the furnace as well as many cooling exchangers usually necessary before collecting products from the process. The vacuum column operates under a moderate vacuum, that is to say between 0.05 bar and 0.95 bar flash zone (1 bar = 0.1 MPa). These vacuum operations do not induce significant additional cost. Another notable simplification is the preferred possibility of eliminating the lateral strippers of this column, because the extraction of a large quantity of naphtha in the stripper makes it possible to obtain kerosene and diesel fractions having the correct flashpoint specification, generally understood. between 50 and 70 ° C.

The Figure 1 describes one of the possible embodiments of the method according to the invention. This embodiment is particularly well suited to the case where the conversion of the charge in the hydrodesulphurization reaction section is limited to less than 50% (ie less than 50% by weight of the charge is converted into this section), preferably less than 30%.

The feed, for example a vacuum gas oil comprising hydrocarbons with boiling points between 370 and 565 ° C, is fed via line 1. The hydrogen, preferably in excess of the feed, is fed via line 3 and compressor 4 and then line 5, and mixed with the charge 1 before being admitted into a charge-effluent exchanger (6) via line 2. The exchanger 6 preheats the load by means of the effluent from the hydrodesulphurization reactor 10. After this exchange, the feedstock is fed via line 7 into an oven that makes it possible to reach the temperature level necessary for the hydrodesulfurization reaction, and then the hot feed is sent via the line 9, in the hydrodesulfurization section 10, constituted by at least one hydrodesulfurization reactor comprising at least one hydrodesulphurization catalyst.

The effluent from the reactor 10 is then sent to the exchanger 6, then via the line 12 to the separator tank 13. A gaseous fraction is separated in this flask and recovered via the line 14. The desulfurized liquid fraction is recovered in the bottom via line 27. Said gaseous fraction comprises unreacted hydrogen, the hydrogen sulphide (H2S) formed during the reaction, as well as generally light hydrocarbons resulting from the conversion of the hydrocarbons of the charge into the reaction section. hydrodesulfurization. After cooling in an exchanger 15 and an air condenser 17, this fraction is fed, via the line 18, into a flash balloon allowing both a gas-liquid separation and a decantation of the aqueous liquid phase. The liquid hydrocarbon phase is recycled via lines 20 and 26 to the liquid effluent from the flask 13 and mixed with this liquid effluent before being sent via line 28 to the stripping column (stripper) 29.

The gaseous fraction from the flash tank 19 is sent via line 21 to an amine absorber or a washing column 22 for removing at least a portion of the H 2 S, and then the gaseous fraction containing hydrogen is recycled. via lines 23 and 25 to the hydrodesulphurization reactor, after compression by means of the compressor 24 and mixing with the load 1.

Stripper 29 is preferably fed with stripping steam via line 32. At the top of the stripper, a gaseous fraction (generally called acid gas) is recovered via line 30 and via line 31 a naphtha having a dot of final boiling most often above 100 ° C. The liquid recovered at the bottom of the stripper via the line 33 is sent via the fractionation column 34, without it being necessary to reheat it in an oven or exchanger.

The fractionation column 34 is operated under vacuum. This is usually a moderate vacuum (for example about 0.25 bar in flash zone). The operation of the column under a moderate vacuum considerably reduces the heat to be supplied to the charge of this column to vaporize the fraction having a boiling point below 370 ° C. The additional heat is preferably provided by an increase in the temperature of the hot separator tank (13) relatively moderate compared to the current practice (for example about 310 ° C instead of 270 ° C). This vacuum column is also fed with stripping steam via line 44.

The overhead fraction recovered via the line 35 is essentially free of light products and after cooling via the aerocondenser 36, this fraction can be easily condensed under a moderate vacuum: about 0.1 to 0.7 bar abs, preferably about 0 , 1 to 0.5 bar absolute (1 bar = 0.1 MPa). For example, it will be possible to operate with a temperature at the outlet of the air condenser (36) of 52 ° C., ie 0.14 bar of vapor pressure of the water.

In the vacuum separation and maintenance section 37, the details of which are not shown because they are known to those skilled in the art, it is possible to separate an aqueous liquid fraction and a hydrocarbon fraction which one does not wish to recover. via line 38. The product obtained line 38 is for example constituted by sections naphtha and / or kerosene and / or gas oil having an initial boiling point greater than 100 ° C. Said section 37 also includes equipment for generating a partial vacuum and maintain it in the column, any equipment known to those skilled in the art can be used, for example an ejector and a condenser or a vacuum pump.

The intermediate fraction from the fractionation column via the line 39 is cooled, for example by means of an exchanger (40) and an air condenser (42), and then recovered via the line 43. a gas oil fraction having a final boiling point of less than 370 ° C.

The heavy fraction from the fractionation column via the line 45 is also cooled by means of, for example, the exchanger 46 and the aerocondenser 48. The fraction thus obtained via the line 49 is a hydrotreated vacuum gas oil with cooling points. adjacent to the initial charge (eg, initial and final boiling points of 370 ° C and 565 ° C respectively).

According to another preferred mode of operation, it is possible to recover via line 38 a fraction ranging from naphtha to light gas oil (for example having a boiling point of less than 370 ° C.), and via line 49 a diesel fraction. additional heavy product (eg having an initial boiling point above 370 ° C). In this case, the fractionation column does not include intermediate fractionation and lines 39 to 43 are absent.

Claims (9)

1. Hydrodesulphurisation method implemented in a hydrodesulphurisation installation for gas oil or distillate under vacuum, including:

   - a hydrodesulphurisation section including et least one hydrodesulphurisation reactor,

   - at least one supply (1, 2) supplying said hydrodesulphurisation reaction section with the load,

   - at least one supply (3, 5, 2) supplying said hydrodesulphurisation section with a gas including hydrogen,

   - a load-effluent exchanger (6) which enables the preheating of the load by means of the effluent from the hydrodesulphurisation reactor,

   - a furnace (8) situated upstream of said hydrodesulphurisation section,

   - at least one separating vessel (13) situated downstream of the hydrodesulphurisation section and enabling the separation of the effluent coming from said section into a gaseous fraction (14) and a desulphurised liquid fraction (27),

   - at least one stripping column (29) supplied by said desulphurised liquid fraction (27, 28) and by the stripping vapour (32),

   - at least one fractionating column (34) supplied by the liquid fraction (33) coming from the stripping column (32), without the introduction of a furnace between said stripping section and said fractionating section,

   - at least one vacuum-generating and vacuum-maintaining section (37),

   wherein said hot separating vessel is operated at a temperature of between 280°C and 350°C and the fractionating section includes a fractionating column operated at a pressure of between 0.05 and 0.95 bar.
2. Hydrodesulphurisation method according to Claim 1, wherein said fractionating section enables the separation of the desulphurised liquid effluent coming from the stripping section into at least 2 fractions: one fraction making the transition from naphtha to light gas oil and a heavy gas oil fraction.
3. Hydrodesulphurisation method according to one of Claims 1 or 2, wherein the reaction section includes 2 hydrodesulphurisation reactors in series.
4. Hydrodesulphurisation method according to one of Claims 1 to 3 further including a means (22) for removing at least a part of the H₂S formed in the hydrodesulphurisation section and present in said gaseous phase.
5. The installation according to Claim 4, wherein said removal means (22) is an amine absorber or a washing column.
6. Hydrodesulphurisation method according to one of Claims 1 to 5, wherein said hot separating vessel is operated at a temperature of between 300°C and 340°C.
7. Hydrodesulphurisation method according to one of Claims 1 to 6, wherein the fractionating section includes a fractionating column operated at a pressure of between 0.10 and 0.90 bar.
8. The hydrodesulphurisation method according to one of claims 1 to 7, wherein the hydrodesulphurisation reaction section includes at least one reactor loaded with at least one hydrodesulphurisation catalyst.
9. The method according to claim 8, wherein said catalyst includes at least one element selected from the elements of Group VIII and the elements of Group VIB of the periodic table.

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