EP0316234B1 - Process and plant for the hydropyrolysis of heavy hydrocarbons by a plasma beam, in particular a h2/ch4 plasma - Google Patents

Description

The present invention relates to a process and an installation for hydropyrolysis of heavy hydrocarbons.

The hydropyrolysis of hydrocarbons, which mainly applies to the cracking of liquid hydrocarbons with a high number of carbons and / or comprising a significant proportion of aromatic constituents, consists in carrying out a thermal cracking in the presence of hydrogen by diluting the hydrocarbons in a phase hydrogenated gas at moderate pressure (a few bars to a few tens of bars).

The hydrogen present in excess during this reaction exerts a blocking effect on undesirable polymerization, condensation and aromatization reactions between two molecules of unsaturated hydrocarbons. The reactions involve essentially play free radicals (mainly ^H., But also ^{CH., CH₂., CH₃.),} A phenomenon characteristic of the hydropyrolysis relative to thermal cracking without hydrogen, the presence and the kinetics of recombination of these radicals free being essential parameters determining the efficiency and the yield of the hydropyrolysis reaction envisaged.

Hydropyrolysis cracking applies particularly well to the transformation of heavy residues comprising a high proportion of non-volatile aromatic components as well as a high proportion of residual materials (Ni, V, S) which make direct hydrogenation by catalysis difficult and expensive, in particular due to the rapid degradation of the catalyst due to the residual materials.

In particular, cracking by hydropyrolysis provides an almost complete conversion of these heavy residues with a high number of carbons into liquid and gaseous products.

FR-A-2 542 004 describes in particular a process and a device, assisted by electricity, for cracking by hydropyrolysis, in which an electric arc is produced between an anode and a distant cathode placed opposite, the hydrocarbons being injected in the form of a vortex flow around the arc column.

One of the difficulties encountered in this type of conversion, which is inherent in the role played by free radicals, consists in producing the highest possible amount of free radicals and in maintaining them in their free state for the duration of contact with the hydrocarbons, avoiding premature recombination reactions (mainly ^H. en H₂) before reaction, and mixing the as closely as possible these free radicals to the products to be converted before this recombination.

It is also necessary to increase as much as possible the surface area for exchange of free radicals with the products to be converted.

The aforementioned document proposes to produce a vortex flow of the hydrocarbons injected around the electric arc, in the vicinity of the anode (that is to say in the region of the electric arc richest in free radicals).

The injection of hydrocarbons is preferably done there tangentially or obliquely against the current of the arc jet, or by vortex sheathing the arc and striking the foot of the anode.

This flow mode, intended to improve the mixing of free radicals with the products to be converted, however limits the exchange zone to the region where the arc plasma is confined by the hydrocarbons injected around the arc column.

The turbulent nature of the flow and the interaction of the various gas streams also make it difficult to control the parameters of the reaction.

• d'assurer un mélange rapide et intime des deux phases réactives, avec pour conséquence un temps de réaction très court, et
• de conserver une proportion élevée de radicaux libres pendant toute la durée de réaction de craquage et d'hydrogénation.

One of the aims of the present invention is to overcome these difficulties, by proposing a method and an installation providing a large exchange surface between the hydrocarbons and the free radicals, which allows:

• ensure rapid and intimate mixing of the two reactive phases, with the consequence of a very short reaction time, and
• to maintain a high proportion of free radicals throughout the duration of the cracking reaction and hydrogenation.

• production et éjection d'un jet de plasma sous pression produit à partir d'un gaz plasmagène, générateur de radicaux libres H^.,
• injection, dans le jet de plasma ainsi produit, d'un gaz générateur de radicaux libres, notamment de radicaux H^., CH^., CH₂^. et CH₃^.,
• injection, dans le courant gazeux résultant, des hydrocarbures à hydropyrolyser pour les faire réagir avec le gaz générateur de radicaux libres,
• récupération des produits de l'hydropyrolyse ainsi obtenus.

To this end, the process of the present invention proposes carrying out the hydropyrolysis of hydrocarbons by the following steps:

• production and ejection of a pressurized jet of plasma generated from a plasma gas, free radical generator ^H. ,
• injection, into the plasma jet thus produced, of a gas generating free radicals, in particular H radicals ^. , CH ^. , CH₂ ^. and CH₃ ^. ,
• injection, into the resulting gas stream, of hydrocarbons to be hydropyrolyzed to make them react with the gas generating free radicals,
• recovery of the hydropyrolysis products thus obtained.

The gas generating free radicals is injected radially into the plasma jet.

The gas stream is non-vortex at the point of injection of the hydrocarbons, and it is accelerated prior to the injection of the hydrocarbons.

Indeed, it has been observed that the creation of a vortex in the flow (as envisaged by the aforementioned FR-A-2 542 004, but in another configuration) due to the injection of the gas generating radicals free in the plasma jet downstream of the torch outlet confined the plasma jet on the axis, thus increasing its inhomogeneity; this inhomogeneity results in a very poor spraying of the charge, which flows in large drops along the wall of the installation downstream of the injection point.

On the contrary, the radial injection of the gas generating free radicals does not create any vortex and allows a very fine spraying of the charge ensuring a very superior plasma / hydrocarbon mixture.

• une torche à plasma, pour produire et éjecter un jet de plasma sous pression produit à partir d'un gaz plasmagène,
• un étage intermédiaire comprenant des moyens pour injecter périphériquement et radialement par une pluralité d'orifices, dans ce jet de plasma, un gaz générateur de radicaux libres, notamment de radicaux H^., CH^., CH₂^. et CH₃^.,
• des moyens pour injecter, dans le courant gazeux aval résultant, les hydrocarbures à hydropyrolyser,
• des moyens pour recueillir, en aval, les produits de l'hydropyrolyse.

The invention also relates to a hydropyrolysis installation, comprising:

• a plasma torch, for producing and ejecting a jet of pressurized plasma produced from a plasma gas,
• an intermediate stage comprising means for inject peripherally and radially through a plurality of orifices, into this plasma jet, a gas generating free radicals, in particular H radicals ^. , CH ^. , CH₂ ^. and CH₃ ^. ,
• means for injecting, into the resulting downstream gas stream, the hydrocarbons to be hydropyrolyzed,
• means for collecting, downstream, the hydropyrolysis products.

In a preferred embodiment, there is provided, downstream of the intermediate stage, a convergent-divergent oriented in the axis of the plasma jet, the injection of hydrocarbons being carried out at this convergent-divergent.

This convergent-divergent allows to obtain all the advantages mentioned above, ensuring an excellent mixture of the two reactive phases and a cooling of the flow which causes a slowdown of the recombination reactions of free radicals.

• la figure 1 est une représentation schématique d'une unité de conversion incorporant l'installation d'hydropyrolyse de la présente invention,
• la figure 2 est une vue partielle montrant la structure de cette installation,
• la figure 3 est une vue en coupe de la zone d'injection des hydrocarbures et de la zone de réaction de l'installation de la figure 2 ,
• les figures 4 et 5 sont des vues en plan, respectivement en coupe selon les lignes IV-IV et V-V de la figure 3. Elles présentent des détails qui n'apparaissent pas sur la figure 3.

Other characteristics and advantages of the invention will appear on reading the detailed description below of an embodiment of the invention, with reference to the appended drawings, in which:

• FIG. 1 is a schematic representation of a conversion unit incorporating the hydropyrolysis installation of the present invention,
• FIG. 2 is a partial view showing the structure of this installation,
• FIG. 3 is a sectional view of the hydrocarbon injection zone and of the reaction zone of the installation of FIG. 2,
• FIGS. 4 and 5 are plan views, respectively in section along the lines IV-IV and VV of FIG. 3. They present details which do not appear in FIG. 3.

In Figure 1, there is shown schematically a conversion unit implementing the installation of the present invention.

This conversion unit comprises a plasma torch 100, which is of a conventional type of plasma projection torch. As can be seen in detail in FIG. 2 which shows the lower part of this torch, it comprises a cathode 101 of the hot cathode type in thoriated tungsten, placed in the axis of a nozzle-anode 102 comprising a channel axial 103 at the outlet of which the plasma jet will be projected, at a temperature between 2000 and 3500 K, for example of the order of 3250 K.

A cooling jacket 104 makes it possible to limit the temperature of the anode so as to allow the latter to be kept at its optimum operating temperature.

This torch 100 is supplied with plasma gas (FIG. 1) by a pipe 110 connected to reserves 120 of hydrogen and argon by means of a series of valves V and sensors of flow rate D, pressure P and temperature T. Depending on the setting of valves V, the plasma torch operates continuously, both with an argon-hydrogen mixture (for example, at around 10% argon) as with pure hydrogen.

Finally, a direct current generator 130 makes it possible to supply the torch 100 with the desired voltages and intensities, for example in a range going from 300 V / 400 A to 1200 V / 100 A, the output voltage being regulated, for example by semiconductors controlled in phase.

The installation then comprises an intermediate stage 200 for injecting the gas generating free radicals. This stage 200, which will be described in more detail below with reference to FIGS. 2 to 5, makes it possible to inject at the outlet of the anode a gas which can be either hydrogen or natural gas (essentially methane ), to enrich by free radicals such as ^H. or CH ^. (and possibly CH₂ ^. or CH₃ ^. ) the plasma projected by the torch into this intermediate stage. Hydrogen and methane are brought to the intermediate stage 200 by a line 210 connected to reserves 220 by means of valves V and means for measuring the flow rate D, the pressure P and the temperature T of the gases. injected.

Downstream of this intermediate stage, there is provided a stage 300 for injecting the charge to be cracked, this injection taking place at the level of the throttle of a convergent-divergent, also described below with reference to FIGS. 2 to 5, which has the function of accelerating the flow and avoiding making it swirling at the injection point.

The charge to be hydropyrolyzed is brought to this stage 300 by a line 350 connected to the reservoir 360 containing this charge, in liquid form; the tank 360 is possibly preheated to a temperature slightly lower than the boiling or decomposition temperature of the charge, by a heating tape 361 so that all the constituents of the charge are in liquid form (even those which could solidify at a temperature close to room temperature) and have a viscosity sufficiently reduced to allow their nebulization at the time of injection.

Finally, the reservoir 360 is pressurized, for example by a gas 362, such as natural gas or methane, to allow the charge to be injected under pressure into the stage 300.

Furthermore, in addition to this pressurization of the hydrocarbons to be injected, the injection of the charge at the location of the throttle of the convergent-divergent creates a suction of liquid allowing a very effective injection, due to the vacuum produced at this location by plasma flow.

Downstream of stage 300, the mixed constituents react at the outlet of the convergent-divergent in a stage 400 forming an actual reactor, the gaseous and liquid reaction products being collected, separated and analyzed by circuits 500 of conventional type which will not described in detail. A probe 410 also makes it possible to take a sample and measure its temperature at the very heart of the reactor 400.

We will now describe in more detail, with reference to Figures 2 to 5, the characteristic elements of the present invention.

At the outlet of the torch 100, the game of plasma is projected into a mixing chamber 230 supplied in addition with gas generating free radicals by a series of orifices 240, preferably radial, connected to the gas supply line 210 (usually hydrogen, or a mixture of hydrogen and methane).

One can for example provide six injection holes with a diameter of 1.5 mm for a gas flow rate of the order of 40 Nl / min.

As indicated above, it is important that the injection is carried out radially into the plasma jet, to avoid the creation of a vortex.

The injection of cold gas (at a temperature close to room temperature) has the effect of lowering the temperature of the plasma set at the anode outlet (where the temperature of the argon / hydrogen mixture or of pure hydrogen is between 2000 and 3500 K, for example of the order of approximately 3250 K as indicated above) at a temperature remaining below approximately 2800 K in the lower part of the chamber 230.

To resist these high temperature values, the cylinder 250 constituting the wall of the mixing chamber can be formed from an external piece 251 of copper provided with a sleeve 252 formed of a material limiting the transfer of heat to the room. made of copper, for example a 5 mm thick boron nitride sleeve.

The stage 300 for injecting the liquid charge essentially comprises a convergent-divergent 310,320 forming a throttle 330 at the level of which the liquid charge is injected.

To achieve as fine a spray as possible, the charge is preferably injected through a plurality of orifices 340 (for example three in number, arranged radially at 120 °), with a radial orientation and perpendicular to the axis nozzle.

The homogeneity of the injection of the charge through these orifices is obtained by a distributor interposed between the orifices injection line and supply line for the liquid charge.

The holes have for example a diameter of 1.5 mm for a nozzle diameter at the location of the neck of 3 mm and an angle at the top of the diverging point of 16 °. The piece constituting the convergent-divergent can be made of copper, or else of stainless steel to have a higher wall temperature.

Furthermore, a bore 370 makes it possible to introduce a thermocouple making it possible to measure the temperature approximately in the vicinity of the wall at the level of the constriction.

The depression produced at the constriction of the convergent-divergent and the suction of the resulting charge make it possible to divide and nebulize very finely the injected charge (which correlatively increases the exchange surface), the shape of the convergent- divergent favoring an intimate mixture of hydrocarbons within the plasma rich in free radicals.

Claims (10)

1. A process for the hydropyrolysis of heavy hydrocarbons, characterised by the steps of:

- production and ejection of a jet of plasma under pressure produced from a plasmagenic gas which generates free H^. radicals,

- injection radially into the jet of plasma thus produced, of a gas which generates free radicals, inter alia H^., CH^., CH₂^. and CH₃^. radicals,

- injection, into the resulting stream of gas which is non-turbulent at this point (330), of the hydrocarbons for hydropyrolysis, in order to cause them to react with the free radical generating gas,

- recovery of the resulting hydropyrolysis products.

2. The process of claim 1, wherein the stream of gas is accelerated prior to the injection of the hydrocarbons.

3. The process of claim 1 or 2, wherein the temperature of the plasma jet at the point (230) where the free radical generating gas is injected is between 2000 and 3500 K approximately.

4. The process of any one of claims 1 to 3, wherein the free radical generating gas is hydrogen or a mixture comprising hydrogen and methane.

5. The process of any one of claims 1 to 4, wherein the hydrocarbons for hydropyrolysis are injected into the stream of gas via a plurality of injection orifices (340) distributed circumferentially and uniformly.

6. The process of any one of claims 1 to 5, wherein the temperature of the stream of gas at the point (330) where the hydrocarbons for hydropyrolysis are injected is less than 2800 K approximately.

7. An installation for the hydropyrolysis of heavy hydrocarbons, characterised by:

- a plasma torch (100) for producing and ejecting a jet of plasma under pressure produced from a plasmagenic gas,

- an intermediate stage (200) comprising a mixing chamber (230) in which a free radical generating gas is injected peripherally and radially through a plurality of orifice points (240) into said plasma jet, inter alia H^., CH^., CH₂^. and CH₃^. radicals,

- means for injecting the hydrocarbons for hydropyrolysis into the resulting downstream flow of gas,

- means (400, 500) for collecting the hydropyrolysis products downstream.

8. The installation of claim 7 further comprising:

- downstream of the intermediate stage a convergent-divergent element (310,320) oriented along the axis of the plasma jet, injection of the hydrocarbons being effected at the said convergent-divergent element.

9. The installation of claim 8, wherein the hydrocarbons for hydropyrolysis are injected at the constriction (330) of the convergent-divergent element.

10. The installation of claim 8 or 9, wherein the hydrocarbons for hydropyrolysis are injected into the convergent-divergent element through a plurality of orifices (340) distributed circumferentially and uniformly.

Images