EP0778332B1 - Process and apparatus for the visbreaking of heavy hydrocarbon feed - Google Patents

Abstract

Viscosity reduction process for a hydrocarbon-rich load in the liquid state, by bringing the load to a temperature which initiates cracking to at least part of the hydrocarbons present, then introducing hydrocarbons into the lower part of a maturer (3) in which it moves from bottom to top and is removed from the top to a fractionating unit. Inside the maturer, transverse to the direction of flow, are a number of annular discs (5) spaced apart and each with a central hole (6) which is coaxial with the maturer. The load to be treated is circulated from bottom to top using the central holes of different discs. Device for carrying out the above process, comprising a means of heating the load to a temperature suitable for cracking and a maturer containing at least one feed line to the bottom and at least one extraction line to the top. A number of annular discs are arranged inside the maturer, with their outside edges jointed to the inside face of the maturer and with a central passage coaxial to the maturer.

Description

The present invention relates to improvements brought to visbreaking processes and devices heavy loads of hydrocarbons.

We know that we designate by visbreaking a treatment of heavy hydrocarbon charges, consisting of bring these charges in the liquid state in an oven to a cracking temperature of the heaviest hydrocarbons and then introducing them into a ripener, in which, without further heating, they move at such a speed that at the temperature considered they have a time of sufficient stay to obtain the desired cracking of heavy molecules into lighter molecules. Cracking has for a reduction in the viscosity of the filler treated, hence the visbreaking terms, for the process implemented, and visbreaker, for the apparatus used.

The ripener is usually in the form of a cylindrical enclosure, which does not have any means of additional heating of the load and, the cracking being endothermic, the temperature of the load drops by a few tens of degrees between its entry into the ripener and its release. The temperature there is generally of the order of 400 to 500 ° C and the pressure of about 2 to 30 10 ⁵ Pascals. The residence time in the ripener is approximately 10 to 30 minutes. The severity, which depends on the residence time and the temperature of the ripener, is of the order of 20 minutes.

The treated charge is injected at the base of the ripener, while cracked products, including products gaseous possibly formed, are evacuated to the part upper towards a split assembly by atmospheric distillation, then by vacuum distillation.

The feedstock can be heavy crude oil, a residue from atmospheric distillation, which is little frequent, because there are other types of recovery, a vacuum distillation residue or a pitch of deasphalting.

The products resulting from visbreaking are, after fractionation, gaseous hydrocarbons and gas liquefied petroleum, petrol, diesel, distillate and the visbreaking vacuum residue.

The visbreaking vacuum residue is the last recoverable product and it must meet requirements severe stability and compatibility with others petroleum cuts to be able to be used as a base for fuel oil, which causes the operator to adjust the conditions of implementation of visbreaking, in particular the temperature, so as to comply with the imposed criteria.

A major problem encountered in the units of visbreaking resides in a non-homogeneous progression of the charge inside the ripener, effects of back mixing (in English, "back mixing") and vortices encountered in particular in the vicinity of the side walls of the ripener, in particular at the bottom thereof. These disturbances are further increased by the gases that form during cracking reactions, and the residence time of the charge in the ripener varies considerably, depending on the zones considered, in the same cross section. As a result, part of the load processed risks undergo an overcrowding, while another fraction will insufficiently cracked.

To remedy this drawback, it has been proposed, in EP-A-007 656, to have inside the ripener, transversely to the direction of flow of the charge at convert, a plurality of internal structures, for short "interne" (in English, "internals"), consisting of perforated trays, the openings in the trays may be circular and / or have the form of slots, the openings preferably representing between 1 and 30% of the surface of the plates.

Each tray thus produces, at the orifices that he understands and borrows the bubbles of the gases present, a charge mixing effect, and the patent application aforementioned European recommends the use of 1 to 20 trays of this type in the ripener.

As indicated in EP-A-0 138 247, the stability cracking products, however, prove to be insufficient, when using perforated trays of this type, in especially when large amounts of gaseous compounds, and significant amounts of coke appear, in use, with serious risks sealing the perforations of the plates. The result long and costly shutdown periods of the ripener, to clean the perforated trays and remove the coke present.

The present invention aims to avoid these drawbacks by proposing means suitable for ensuring a residence time more homogeneous charge in the ripener allowing to obtain better stability of the visbreaked residue and an increase in the conversion rate for products obtained from visbreaking.

The invention also aims to limit the phenomena of retromix associated with the treatment of a load of heavy hydrocarbons in the ripener of a set of visbreaking.

The invention finally aims to reduce the formation of coke in visbreaking processes and devices.

The Applicant has, in fact, established that by having in the ripener, transverse to the direction of displacement of the treated load, of the annular discs spaced from each other, whose edges are joined or not with the internal faces of the side walls of the maturer, we obtain simultaneously a more significant load, and therefore a reduction significant coke formed, and better stability of the visbreaking vacuum residue.

The invention therefore relates to a method of visbreaking of a heavy load of hydrocarbons in the state liquid, in which this charge is brought to a temperature likely to cause cracking of at least one part of the hydrocarbons present, then is introduced to the lower part of a ripener in which it is moves from bottom to top, to be evacuated to the part superior of this ripener towards a unit of fractionation, this process being characterized in that, at inside the ripener, transverse to the direction displacement of the load to be treated, is arranged a plurality of annular discs spaced from each other, each having a substantially circular central passage coaxial with the ripener, the treated charge flowing from bottom to high in the ripener using the central passages different annular discs.

By forcing the load to move from bottom to top along the axis of the ripener, the annular discs have for main effect of limiting a radial dispersion of this charge.

Advantageously, the edges of the annular discs are contiguous with the adjoining internal faces of the walls side of the soaker.

Preferably, for a cylindrical ripener having a axial length from 8 meters to 14 meters, and a diameter between 1.5 and 2.5 meters, from 3 to 10 discs regularly spaced annulars will be arranged between the bottom and upper part of the ripener.

Advantageously, the central passage of each disc annular will represent at least 30% of the surface of the disc and preferably between 30 and 65% of this surface.

In order to avoid the formation of dead zones between the annular discs, these discs are preferably perforated, the orifices thus formed in the discs being distributed substantially evenly on their surface and occupying between about 5 and 30% of this surface. The orifices will have a diameter large enough to to prevent possible coking which would risk them shut off. In particular, they will have a diameter of at least 30 millimeters and preferably between 30 and 100 millimeters.

Preferably, the orifices of the annular discs contiguous perforated will be offset laterally by relation to others, in order to avoid the phenomena of foxing that could occur if the orifices of consecutive discs were arranged opposite.

The invention naturally also relates to a heavy load visbreaking device of hydrocarbons in the liquid state, of the type comprising a means of heating the load to a temperature likely to cause cracking of at least some of the hydrocarbons, and a ripener comprising, in its part lower, at least one load supply line preheated and, at the top, at least one line evacuation of the treated load to a fractionation of this charge, this device being characterized in that inside the ripener, transverse to the direction of movement of the load to be treated, is arranged a plurality of annular discs spaced from each other, whose edges are preferably contiguous with the contiguous internal faces of the side walls of the soaker which each have a circular central passage substantially coaxial at ripener.

The attached drawing, which is not limiting, illustrates a form of implementation of the invention.

The single figure in this drawing is a schematic view visbreaking equipment in accordance with this invention.

• une ligne 1 d'amenée de la charge lourde, à l'état liquide, d'hydrocarbures à traiter ;
• un four 2, que traverse la ligne 1 et qui préchauffe la charge lourde à une température propre à assurer le craquage d'au moins une partie des hydrocarbures qu'elle contient ;
• un maturateur 3, se présentant sous la forme d'une enceinte cylindrique fermée, disposée verticalement, qui est alimentée à sa base par la ligne 1 et qui est équipée à sa partie supérieure d'une ligne 4 d'évacuation des produits de craquage de la charge vers une unité de fractionnement.

In this drawing, we find the usual elements of a visbreaking unit, namely:

• a line 1 for feeding the heavy load, in the liquid state, of hydrocarbons to be treated;
• an oven 2, which the line 1 crosses and which preheats the heavy load to a temperature suitable for cracking at least part of the hydrocarbons it contains;
• a ripener 3, in the form of a closed cylindrical enclosure, arranged vertically, which is supplied at its base by line 1 and which is equipped at its upper part with a line 4 for evacuating cracked products from the load to a fractionation unit.

In accordance with the invention, annular discs 5, having a central circular passage 6, are arranged at the interior of the ripener 3, perpendicular to its axis. These discs 5, 8 in number, for example, for a 12 meter high ripener, are spaced so substantially regular to each other, from the bottom of the ripener 3 to the top of it. Their edges are in contact with the inside of the walls side of the soaker and the circular passages 6 represent at least 35% of the surface of the disc.

Each disc 5 is crossed by perforations 7 forming regularly spaced orifices on its surface. These ports allow passage to the treated charge, including the gases formed and / or injected, transversely to the disc, thus avoiding the formation of dead zones between the contiguous discs. The openings 7 of the contiguous discs do not are not arranged opposite, but are offset angularly with respect to each other, in view avoid foxing phenomena. They occupy approximately 30% of the surface of the discs, on which they are regularly distributed.

Under similar processing conditions, the discs annulars according to the invention allow to obtain a visually reduced stability vacuum residue greatly improved, as will emerge from the examples below.

We know, in fact, that a visbreaking unit is controlled using stability as a benchmark of the visbreaking vacuum residue, for its use as fuel oil, because if the stability is not greater at a certain threshold, fuel oil can present problems of use, due to the formation of sediments by precipitation of asphaltenes.

Various variants of the device can be designed according to the invention without departing from the scope of the request.

In particular, in one embodiment, a central rod removable by the top of the ripener, penetrates into it through the central passages of the annular discs.

This rod also supports "internals" additional spaced apart, whose surface transverse is such that these "interns" can pass to the through central passages of the discs, so that be removed, but is greater than 5% of the surface transverse of the ripener.

These additional "interns" are for example solid discs, possibly perforated. The different "internal" can be arranged to form a alternation between solid discs and annular discs. Each full disc is for example positioned at a distance between one third and two thirds of the distance separating two consecutive annular discs, and preferably halfway between these.

The following comparative examples show that the residue visbreaking vacuum obtained by the process according to the invention has improved stability. They illustrate furthermore the advantages of this process.

Example 1

• densité :   1,0375 ,
• viscosité
  (10^-6 m²/s à 100°C):   3500 ,
• teneur en souffre
  (% en poids):   3,86 ,
• teneur en carbone
  Conradson (% en poids):   19,6 ,
• teneur en asphaltènes
  (% en poids) :   12,1 ,
• point de coupe
  (°C) :   520°C.

This example illustrates a usual cracking process by visbreaking, without the use in the ripener of the annular discs according to the invention, of a vacuum distillation residue having the following characteristics:

• density: 1.0375,
• viscosity
  (10 ^-6 m ² / s at 100 ° C): 3500,
• sulfur content
  (% by weight): 3.86,
• carbon content
  Conradson (% by weight): 19.6,
• asphaltenes content
  (% by weight): 12.1,
• cutting point
  (° C): 520 ° C.

This vacuum residue is heated to a temperature of around 440 ° C in a visbreaking unit oven, then is introduced into a visbreaking ripener not modified in accordance with the present invention. This ripener has a diameter of 2.5 meters and a height of 14 meters.

It is operated at a temperature of 425 ° C and under a pressure of 8.10 ⁵ Pascals. The load flow rate is 100 t / h and its average residence time is 18 minutes.

At the outlet of the soaker, the visbreaking effluent is fractionated in a distillation column atmospheric and then in a distillation column under empty.

The products obtained after fractionation and their quantities are indicated in Table 1 below.

Example 2

The same vacuum distillation residue as in Example 1 is again subjected to a visbreaking treatment under conditions of identical severity. The load is heated in the oven to a temperature of the order of 440 ° C and one operates in the ripener at a temperature of 425 ° C under a pressure of 8.10 ⁵ Pascals. The charge rate remains the same as before.

The ripener was modified in accordance with the invention and it has six annular discs, separated from each other others at a distance of 2 meters, the lowest disc being located 2.5 meters from the bottom. These discs are made of steel and have a thickness of 3 millimeters. They are willing coaxially with the ripener and they each have a circular central passage with a diameter of 1.5 meters and holes of 90 millimeters in diameter are distributed regularly on their surface. The six discs are identical and angularly offset by 20 °, so that the holes of two contiguous discs are not arranged opposite.

As before, at the exit of the ripener, the visbreaking effluent is fractionated in a column atmospheric distillation then in a column of vacuum distillation.

The nature of the products obtained and the quantities respective are collated in Table 1 below.

Example 3

With the same vacuum distillation residue as in Example 1, a visbreaking treatment is carried out under conditions of increased severity compared to Examples 1 and 2.

The residue is heated in the oven to 448 ° C, then is introduced into the ripener equipped with six discs annulars identical to that of Example 2. The ripener is maintained at a temperature of 434 ° C. The conditions of pressure as well as the flow rate of the charge and its time average stay in the ripener are the same as in the Examples 1 and 2.

We therefore operate with more severe conditions marked only in Examples 1 and 2.

As in these examples, the effluent from the ripener is fractionated in an atmospheric distillation column, then in a vacuum distillation column.

The products obtained are listed in Table 1 below. Products obtained after fractionation (% by weight) Example 1 Example 2 Example 3 Gas 0.64 0.50 0.55 Petrol + LPG 5.00 5.50 5.80 Diesel 12.30 13.70 14.70 Distillate 10.90 11.10 11.75 RSVR (vacuum residue) 71.20 69.20 67.20 RSVR stability - stability ( ) + ++ + - sediments ( ) (ppm) 850 500 800 Viscosity of RSVR (cst at 100 ° C) 40,000 63,000 102,000

It can be seen that the quantities of gas and residue under vacuum obtained with the ripener according to the invention of Example 2 are lower than those obtained with the standard technique (Example 1) and that the higher amounts of petrol and distillate. Above all, there is a very marked increase in the amount of diesel.

The viscosity of the visbreaking vacuum residue (R.S.V.R.) of Example 2 (process according to the invention) is higher than that of the vacuum residue obtained according to the prior art method. In addition, stability is better for the residue from treatment with ripener according to the invention.

For example 3, the conversion is further improved and results in an increase in the quantities of gasoline, distillate and diesel. The viscosity of the vacuum residue significantly increases compared to Examples 1 and 2 and its stability is identical to that of Example 1, despite the more severe conditions of visbreaking.

These results therefore clearly illustrate the advantages of the process according to the invention.

Claims (12)

1. A process for the visbreaking of a heavy hydrocarbon charge in the liquid state, in which this charge is brought to a suitable temperature for inducing the cracking of at least one portion of the hydrocarbons present, then it is introduced at the lower part of a soaking vessel (3) in which it moves from the bottom upwards, so as to be removed at the upper part of this soaking vessel towards a fractionating unit, said process being characterised in that, inside the soaking vessel (3), transversely to the direction of movement of the charge to be treated, there is provided a plurality of annular discs (5) which are spaced apart and which each comprise a central circular passage (6) substantially coaxial to the soaking vessel (3), the treated charge circulating from the bottom upwards in the soaking vessel using the central passages of the different annular discs (6).
2. A process according to claim 1, characterised in that the edges of the annular discs are contiguous with the inner contiguous surfaces of the side walls of the soaking vessel.
3. A process according to either of claims 1 and 2, characterised in that the volumes of the soaking vessel (3) separated by the annular discs (5) are also in communication with one another via orifices (7) in these discs used by the treated charge, including the gases formed.
4. An apparatus for the visbreaking of a heavy hydrocarbon charge in the liquid state, of the type comprising a means (2) for heating the charge to a suitable temperature for inducing the cracking of at least one portion of the hydrocarbons, and a soaking vessel (3) comprising, in its lower part, at least one line (1) for supplying preheated charge and, in its upper part, at least one line (4) for removing the treated charge towards a fractionating unit for said charge, said apparatus being characterised in that inside the soaking vessel (3), transversely to the direction of movement of the charge to be treated, there is provided a plurality of annular discs (5) which are spaced apart and the edges of which are preferably contiguous with the inner contiguous surfaces of the side walls of the soaking vessel and which each comprise a central circular passage (6) substantially coaxial to the soaking vessel (3).
5. An apparatus according to claim 4, characterised in that the annular discs (5) are regularly spaced apart.
6. An apparatus according to either of claims 4 and 5, characterised in that the circular passage (6) of the annular discs (5) represents at least 30 % of the surface of the disc and, preferably, between 30 and 65 % of this surface.
7. An apparatus according to any one of claims 4 to 6, characterised in that the annular discs (5) are perforated with orifices (7).
8. An apparatus according to claim 7, characterised in that the orifices (7) are regularly spaced apart on the surface of each annular disc (5).
9. An apparatus according to either of claims 7 and 8, characterised in that the orifices (7) occupy between 5 and 30 % of the surface of the annular discs (7) [sic].
10. An apparatus according to any one of claims 7 to 9, characterised in that the orifices (7) have a diameter of at least 30 mm and, preferably, of between 30 and 100 mm.
11. An apparatus according to any one of claims 6 to 9, characterised in that the corresponding orifices (7) of the contiguous discs are offset laterally with respect to one another.
12. An apparatus according to any one of claims 4 to 10, in which the soaking vessel (3) is of an axial length of between 8 and 14 metres and a diameter of between 1.5 and 2.5 metres, characterised in that it comprises between 3 and 10 annular discs (5).

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