EP0778331B1 - Process and apparatus for the visbreaking of heavy hydrocarbon feed - Google Patents

Abstract

Viscoreduction process for a hydrocarbon-rich load in the liquid state, in which this load is brought to a temperature which provokes cracking at least part of the hydrocarbons present, is then introduced 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. An inert gas is injected into the maturer in the hydrocarbon load, at least at the base of the unit near its side walls. The gas is injected towards the top along the side walls of the maturer and circulates from bottom to top along the walls, in the same direction as the hydrocarbon load. Also claimed is device for carrying out the above process. Preferably the gas is injected into the maturer at several different levels next to the side walls, by injectors arranged in a coronet. The gas is injected into the hydrocarbon load after it is heated, upstream of the maturer in the direction of flow of the load. For a flow of hydrocarbons of between 75 and 200 t/h, the gas flow is between 0.2 and 3 t/h, preferably between 0.5 and 2 t/h.

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 of the charge in the ripener is approximately 10 to 30 minutes. The severity, depending 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 interns made up of trays perforated, the openings in the trays can 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.

Document FR-A-2 528 444 proposes a method of thermal cracking of hydrocarbon oils in which a fluid, such as water vapor, can be introduced tangentially in the lower part of the ripener (see page 6, lines 8 to 17) through nozzles. This introduction aims to rotate the load of hydrocarbons.

However, the rotation drive of the load requires very high vapor flow rates, which implies a limitation of the space available for charging in the ripener and therefore a reduction in its residence time which is detrimental to visbreaking.

The present invention aims to avoid these drawbacks by proposing means suitable for ensuring a residence time more homogeneous charge in the ripener and a better stability of the visbreaker.

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 injecting a gas such as water vapor or nitrogen in the ripener, co-current, at least near the bottom and side walls of it, we get simultaneously a better conversion of the load, and therefore a significant reduction in coke formed, and better stability of the residue under visbreaking.

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, and in which a gas, preferably inert, is injected inside the ripener into the charge of hydrocarbons, at least at the base of the ripener, at near its side walls. This process is characterized in that the gas is injected upwards along the walls side of the soaker and flows from bottom to top along of said walls, co-current with the hydrocarbon charge.

Gas (water vapor, nitrogen, hydrogen, refinery or other), moving from bottom to top at proximity of the walls of the soaker, thus limiting the formation of dead zones and back mixes at the level of the bottom and side walls, and the residence time of different threads of hydrocarbon fluid inside of the ripener will tend to homogenize and approximate the average residence time of the load.

In addition, the gas produces a stripping effect on the load products, which facilitates the separation of light products (liquefied petroleum gas, petrol, diesel, etc ...), obtained by conversion in the ripener.

In addition to the injection planned at the base of the near the side walls, other injections may be provided, always in the vicinity of the side walls, different levels in the ripener, to further minimize more back mixes and coke production.

The injection of gas, according to the invention, upwards and in the vicinity of the ripener walls requires only low gas flow, which in particular makes it possible to avoid disadvantages encountered during the implementation of the process of document FR-A-2 528 444 mentioned previously.

For a charge flow of between 75 and 200 t / h, the flow rate of the injected gas will advantageously be between 0.2 and 3 t / h and preferably between 0.5 and 2 t / h.

Preferably the gas, superheated and at a pressure greater than that of the ripener, will be injected annually at the different injection levels, but the gas can also be introduced into the supply line of the charge charge to crack, upstream of the charge.

The invention also relates to a device for visbreaking of a heavy load of hydrocarbons in the state liquid, of the type comprising a means for heating the charge up to a temperature suitable for causing cracking of at least part of the oil, and a ripener comprising, in its lower part, at least one preheated load supply line and part thereof upper, at least one load evacuation line processed to a fractionation unit for this charge, this device being characterized in that it comprises a means injection of a gas, preferably inert, into the charge of hydrocarbons to be treated, the injection means being arranged in a location such that the injected gas moves co-current of the charge, inside the ripener, at less at the base of it, near the inner side of its side walls.

The gas injection means may include nozzles regularly distributed injection systems connected to a source gas under pressure and arranged annularly, either along the lower part of the internal face of the walls of the ripener, or according to the bottom thereof.

This injection means may also include a conduit substantially toroidal in shape, connected to a gas source under pressure and fitted with regularly distributed orifices gas evacuation, this duct being arranged in the vicinity from the bottom of the ripener, coaxial to it.

The injection means may also include a line for introducing this gas into the heavy load of hydrocarbons downstream of the load heating means and upstream of the ripener, in the direction of circulation of the charge.

Several means of injecting gas into the load of identical or different hydrocarbons can naturally be expected at different levels of the ripener, in the vicinity of the internal face of the walls of this one.

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 quelle 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 d'évacuation 4 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;
• a furnace 2, which the line 1 crosses and which preheats the heavy load to a temperature suitable for cracking at least part of the hydrocarbons which it contains;
• a ripener 3, in the form of a closed cylindrical enclosure, arranged vertically, which is fed at its base by line 1 and which is equipped at its upper part with a discharge line 4 for cracking products of the load to a fractionation unit.

According to the invention, a means of injecting a preferably inert gas in the hydrocarbon feed is provided inside the ripener 3, in the vicinity of the bottom of it and near its side walls. In the in the case of the drawing, this injection means comprises a toroidal shape 5, arranged coaxially to the side walls of the ripener, at the bottom thereof, and supplied with gas under pressure through a line 6. This conduit 5 includes regularly spaced orifices which let the gas escape under pressure to the upper part of the ripener 3, at co-current of the hydrocarbon charge. This limits the dead volumes of this ripener and the feedbacks from the charge, while avoiding the formation of coke and ensuring stripping of light cracking products present in the ripener.

The use of conduit 5 is advantageous compared to using nozzles such as that described in document FR-A-2 528 444 in connection with FIGS. 3A and 3B, because it avoids a modification of the reactor and therefore greater complexity of implementation.

As indicated above, several similar devices gas injection can be provided at different levels in the ripener, to optimize the effect of this gas.

We could also use injection nozzles regularly arranged, opening inside the ripener from the side walls and / or the bottom and supplied from a source of pressurized gas.

We could alternatively inject gas from preferably inert under pressure in line 1, downstream of the oven 2 and upstream of the ripener 3, in the direction of circulation of the load, by line 7 represented in broken lines in the drawing.

In the case where the gas used is water vapor under pressure, it will naturally be necessary to take into account calories and water which are thus introduced into the ripener and adjust the conditions accordingly operative of it.

Under analogous processing conditions, the process according to the invention makes it possible to obtain a vacuum residue visoreduction of greatly improved stability, such as it will emerge from the examples below.

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

Under conditions of equal severity, the stripping of light products of cracking by the injected gas allows to increase the stability of the visbreaking residue. In retaining the same stability value, it is thus possible increase the charge conversion rate by increasing the temperature of the ripener.

This is apparent from the comparative examples below.

Example 1

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

This example illustrates a usual cracking process by visbreaking, without using an auxiliary gas, 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: 520 ° C.

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

It is operated at a temperature of 425 ° C and under a pressure of 8.10 ⁵ Pascals. The feed rate is around 100 t / h and its average residence time is around 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 charge is heated in the oven to a temperature of the order of 450 ° C and the ripener is operated at a temperature of 430 ° C under a pressure of 8.10 ⁵ Pascals.

The ripener is equipped, in accordance with the invention, with a pressurized steam distributor, consisting of a toric duct with a diameter of 30 millimeters, having regularly distributed injection ports, facing upwards . This distributor rests on the bottom of the ripener and is arranged coaxially to the side walls. The superheated steam is injected at a pressure of 11.10 ⁵ Pascals and at a flow rate of 0.5 t / h, while the flow rate of the charge is 100 t / h. The charge residence time is around 15 minutes. We therefore operate under severity conditions roughly analogous to those of Example 1.

As before, the visbreaking effluent is fractionated in an atmospheric distillation column, taken in a vacuum distillation column. The results obtained are collated in Table 1 below.

We see that the production of gas is reduced, that gasoline and liquefied petroleum gas (LPG) production increases slightly, while diesel production significantly increases and that decreases the amount of residue visbreaking vacuum (R.S.V.R).

The viscosity of the visbreaking residue is unchanged, but its stability is improved and production decreased sediment.

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 455 ° C, then is introduced into the ripener equipped with an injection ring of water vapor identical to that of Example 2. The The ripener is operated at a temperature of 434 ° C. The water vapor pressure and flow conditions in the ripener are the same as in Example 2.

The charge flow and its average residence time in the ripener remain the same as in Example 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, and we see that, if the quantity of gas is substantially equal to that of Example 2, the quantity gasoline and liquefied petroleum gas, as well as that distillate, is increased, while the amount of diesel significantly increases, and that of vacuum residue of visbreaking decreases significantly.

The viscosity of the residue under vacuum increases slightly compared to Examples 1 and 2 and its stability is identical to that of Example 1, despite the more severe conditions of visbreaking. Products obtained after fractionation (% by weight) Example 1 Example 2 Example 3 Gas 0.64 0.42 0.44 Petrol + LPG 5 5.3 5.5 Diesel 12.3 13.7 14.3 Distillate 10.9 10.3 10.8 RSVR 71.2 70.2 68.9 RSVR stability - stability ( ) + ++ + - sediments ( ) (ppm) 850 500 800 Viscosity of RSVR (10 ^-6 m ² / s at 100 ° C) 40,000 50,000 70,000

These results therefore clearly illustrate the advantage of injecting a gas in the co-current of the charge processed.

Claims (10)

1. Process for the visbreaking of a heavy hydrocarbon feed in the liquid state in which this feed is brought to a temperature capable of causing the cracking of at least a proportion of the hydrocarbons present, is then introduced into the lower portion of a maturation unit (3) in which it moves from bottom to top and is evacuated at the upper portion of this maturation unit (3) in the direction of a fractionation unit, and in which a gas, preferably an inert gas, is injected into the hydrocarbon feed inside the maturation unit (3), at least at the base of the maturation unit (3) in the vicinity of its lateral walls, characterised in that the gas is injected upward along the lateral walls of the maturation unit (3) and circulates from bottom to top along said walls in a co-current with the hydrocarbon feed.
2. Process according to claim 1, characterised in that the gas is injected into the maturation unit (3) at several different levels, in the vicinity of the internal face of the lateral walls.
3. Process according to one of claims 1 and 2, characterised in that the gas is injected into the maturation unit (3) by injection means arranged in a ring.
4. Process according to claim 1, characterised in that the gas is injected into the hydrocarbon feed after heating of this feed, upstream of the maturation unit (3) in the direction of flow of the feed.
5. Process according to one of claims 1 to 4, characterised in that, for a flow rate of feed in the maturation unit of between 75 and 200 t/h, the flow rate of gas is between 0.2 and 3 t/h and preferably between 0.5 and 2 t/h.
6. Device for the visbreaking of a heavy hydrocarbon feed in the liquid state of the type comprising a means (2) for heating the feed to a temperature capable of causing the cracking of at least a proportion of the hydrocarbons, a maturation unit (3) comprising, at its lower portion, at least one preheated feed supply line (1) and, at its upper portion, at least one line (4) for evacuation of the treated feed to a fractionation unit for this charge, and a means (S) for injection of a gas, preferably an inert gas, into the hydrocarbon feed to be treated, the injection means (5) being arranged inside the maturation unit (3) at least at the base thereof in the vicinity of the internal face of its lateral walls, characterised in that this injection means (5) has upwardly turned injection orifices to allow the gas to escape toward the upper portion of the maturation unit (3).
7. Device according to claim 6, characterised in that the gas injection means comprises evenly distributed injection nozzles connected to a source of gas under pressure and arranged annularly, either round the lower portion of the internal face of the lateral walls of the maturation unit (3) or round the base thereof.
8. Device according to claim 6, characterised in that the gas injection means comprises a conduit (5) of substantially toric shape connected to a source of inert gas under pressure and equipped with inert gas evacuation orifices, this conduit (5) being arranged in the vicinity of the base of the maturation unit (3), coaxially thereto.
9. Device according to claim 6, characterised in that the gas injection means comprises a line (7) for introduction of this gas into the heavy hydrocarbon feed downstream of the heating means (2) and upstream of the maturation unit (3) in the direction of circulation of the feed.
10. Device according to one of claims 6 to 9, characterised in that it comprises a plurality of means for injection of gas into the maturation unit (3) arranged at different levels thereof.

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