FR2622894A1 - METHOD AND INSTALLATION OF HYDROPYROLYSIS OF HEAVY HYDROCARBONS BY PLASMA JET, IN PARTICULAR OF H2 / CH4 PLASMA - Google Patents

Abstract

The installation allowing the implementation of this method comprises: - a plasma torch 100, for producing and ejecting a pressurized plasma jet produced from a plasma gas 210, generator of free radicals H, - an intermediate stage 200 comprising means for injecting, into this plasma jet, a gas 220 which generates free radicals, in particular H, CH, CH2 and CH3 radicals, - a convergent-divergent 310, 320 at the level of the constriction of which the hydrocarbons 320 are injected into the resulting downstream gas stream, - means 400, 500 for collecting, downstream, the products of hydropyrolysis. The convergent-divergent, in particular, makes it possible to ensure an excellent mixing of the two reactive phases, sufficient cooling of the plasma avoiding coking and, by the acceleration of the flow that it provides, a slowing down of the recombination reactions of the radicals. free.

Description

The present invention relates to a method and an installation

  hydropyrolysis of heavy hydrocarbons.

  The hydropyrolysis of hydrocarbons, which is mainly applied to the cracking of high-carbon liquid hydrocarbons and / or comprising a significant proportion of aromatic constituents, consists in carrying out thermal cracking in the presence of hydrogen by diluting the hydrocarbons in a single phase. gaseous hydrogenated pressure

  moderate (a few bars to a few dozen bars).

  The hydrogen present in excess during this reaction,

  exerts a blocking effect on unwanted polymeric

  condensation and aromatization between two molecules.

  unsaturated hydrocarbons. Reactions

  partly free radicals (mainly H, but also CH, CH 2, CH 3 '), a phenomenon characteristic of hydropyrolysis compared to thermal cracking without hydrogen, the presence and the kinetics of recombination of

  these free radicals being essential parameters determining

  the efficiency and performance of the hydro-

pyrolysis envisaged.

  Hydropyrolytic cracking is particularly applicable to the processing of heavy residues comprising a high proportion of nonvolatile aromatic components as well as a high proportion of residual materials (Ni, V, S) which make catalytic direct hydrogenation difficult and costly, in particular because of the rapid deterioration

  catalyst due to residual materials.

  In particular, hydropyrolysis cracking provides substantially complete conversion of these heavy residues to

  high number of carbons in liquid and gaseous products.

  FR-A-2 542 004 describes in particular an electrolytic assisted cracking process and apparatus, in which an electric arc is produced between a remote anode and a cathode placed opposite, the hydrocarbons being injected in the form of a flow

  swirl around the arch column.

  One of the difficulties encountered in this type of conversion, and which is inherent in the role played by free radicals, consists in producing the highest possible quantity of free radicals and keeping them in their free state during free radicals. the duration of the contact with the hydrocarbons, avoiding the premature reactions of recombination (essentially H 'in H2) before reaction, and to mix as closely as possible these free radicals with the

  products to be converted before this recombination.

  It is also necessary to increase the surface area as much as possible

  free radical exchange with the products to be converted.

  The aforementioned document proposes to make a whirlpool flow of hydrocarbons injected around the electric arc, in the vicinity of the anode (ie in the

  region of the electric arc the richest in free radicals).

  The injection of hydrocarbons is preferably made tangentially or obliquely against the current of the jet of the arc, or by vortex sheathing the bow and striking the foot of

1 anode.

  This flow mode, intended to improve the mixture 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 different gaseous currents make it difficult to

  control of the parameters of the reaction.

  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 hydrocarbons and free radicals, which allows: to ensure a rapid and intimate mixing of the two reactive phases, resulting in a very short reaction time, and - maintaining a high proportion of free radicals

  throughout the duration of the cracking reaction and

  génation. For this purpose, the process of the present invention proposes to carry out the hydropyrolysis of hydrocarbons by the following steps: production and ejection of a jet of plasma under pressure produced from a plasmagene gas, generator of free radicals H ' injection into the plasma jet thus produced of a radical-generating gas. free radicals, in particular radicals H ', CH', CH2 'and CH3', - injecting, into the resulting gas stream, hydrocarbons to be hydropyrolysed to react with the free-radical generating gas, - recovering the products of hydropyrolysis thus obtained. Very advantageously, the generator gas of radicals

  free is injected radially into the plasma jet.

  Very advantageously, the gaseous stream is non-ferrous

  at the point of injection of hydrocarbons, and it is

  accelerated before the injection of hydrocarbons.

  Indeed, it has been found that the creation of a vortex in the flow (as envisioned in FR-A-2 542 004 mentioned above, but in another configuration) due to the injection of the radical generating gas free in the plasma jet downstream of the outlet of the torch contained the jet of plasma 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 other hand, the radial injection of the free-radical generating gas does not create any vortex and allows a very fine spraying of the charge ensuring a mixture.

  plasma / hydrocarbons much higher.

  The invention also relates to a hydropyrolysis plant, comprising: a plasma torch, for producing and ejecting a jet of pressurized plasma produced from a plasmagen gas, an intermediate stage comprising means for

4 2622894

  injecting, in this plasma jet, a gas generating free radicals, in particular radicals H ', CH', CH2 and CH3 '; - means for injecting, in the resulting downstream gas stream, the hydrocarbons to be hydropyrolyzed, - means to collect, downstream, the products of hydropyrolysis. 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 performed at this convergent-divergent level.

  This convergent-divergent makes it possible to obtain the whole

  advantages mentioned above, by ensuring an excellent

  slow mixing of the two reactive phases and a cooling of the flow which causes a slowing of

  -, recombination reactions of free radicals.

  Other features and advantages of the invention

  will appear on reading the detailed description

  BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a conversion unit incorporating the hydropyrolysis plant 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 the reaction zone of the installation of FIG. 2; FIG. and 5 are plan views, respectively

  in section along the lines IV-IV and V-V of Figure 3.

  FIG. 1 diagrammatically shows 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 tungsten cathode type, placed in the axis of an anode nozzle 102 comprising a channel axial output 103 which will be projected plasma jet at a temperature between 2000 and 3500 K, for example of the order of 3250 K. A cooling jacket 104 can limit the temperature of the anode so as to allow maintaining

  this at its optimum operating temperature.

  This torch 100 is supplied with plasma gas (FIG. 1) by a line 110 connected to hydrogen and argon reserves 120 via a series of valves V and flow rate sensors D, P and With the setting of the valves V, the plasma torch runs continuously, with an argon-hydrogen mixture (by

  approximately 10% argon) with pure hydrogen.

  Finally, a DC generator 130 makes it possible to supply the torch 100 with the desired voltages and intensities, for example in a range 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 free-radical generating gas. This stage, 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 may be either hydrogen or natural gas (essentially methane). , allowing to enrich in free radicals such as H or CH (and optionally CH2 or CH3 ') the plasma projected by the torch in this intermediate stage. Hydrogen and methane are fed to the intermediate stage 200 via a line 210 connected to reserves 220 via 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 being made at the level of the constriction of a convergent-divergent, also described hereinafter with reference to FIGS. 5, which has the function of accelerating the flow and avoiding

  to make it swirl at the injection site.

  The charge to be hydropyrolyzed is brought to this stage 300 by a pipe 310 connected to the tank 320 containing this charge, in liquid form; the tank 320 is optionally preheated to a slightly

  below the boiling or decomposition temperature

  the load, by a heating tape 321 so that all the components of the load are

  in liquid form (even those that could solidify

  at a temperature close to room temperature) and have a sufficiently reduced viscosity to allow

  their nebulization at the time of injection.

  Finally, the tank 320 is pressurized, for example by a gas 322, such as natural gas or methane, for

  allow the pressure to be injected under pressure into the stage300.

  Moreover, besides this pressurization of the hydrocarbons to be injected, the injection of the charge at the point of the throat of the convergent divergent creates a suction of liquid allowing a very efficient injection, because of the depression carried out there by the flow of the plasma. Downstream of the stage 300, the mixed constituents react at the outlet of the convergent-divergent in a stage 400 forming the reactor itself, the gaseous and liquid products of reaction being collected, separated and analyzed by circuits 500 of conventional type which do not will not be described in detail. A probe 410 also makes it possible to take a sample and measure its temperature in the very heart of the

reactor 400.

  The characteristic elements of the present invention will now be described in more detail with reference to FIGS. 2 to 5. At the outlet of the torch 100, the plasma clearance is projected into a mixing chamber 230 fed by free radical-generating gas by a series of orifices 240, preferably radial, connected to the feed pipe 210. gas (usually hydrogen, or a mixture of hydrogen and methane). For example, six injection orifices can be provided.

  diameter 1.5 mm for a gas flow of the order of 40 Nl / min.

  As mentioned above, it is important that injection

  radially in the plasma jet, to

ter the creation of vortices.

  Injection of the cold gas (at a temperature close to ambient temperature) has the effect of lowering the

  temperature of the plasma play at the outlet of the anode (where the temperature

  the argon / hydrogen mixture or pure hydrogen is between 2000 and 3500 K, for example of the order

  approximately 3250 K as indicated above) at a temperature of

  remaining less than approximately 2800 K less than

of room 230.

  To withstand these high temperature values, the cylinder 250 constituting the wall of the mixing chamber may be formed of an outer piece 251 copper provided with a sleeve 252 formed of a material limiting the heat transfer to the room in copper, for example a sleeve in

  boron nitride 5 mm thick.

  The injection stage 300 of the liquid charge essentially comprises a convergent-divergent 310,320 forming a throat 330 at 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 nozzle axis.

  The homogeneity of the injection of the charge through these orifices is obtained by a distributor interposed between the injection orifices and the supply line of the liquid charge. The holes have for example a diameter of 1.5 mm for a nozzle diameter at the point of the neck of 3 mm and an angle at the apex of the divergent of 16. The part constituting the convergent-divergent can be made of copper, or of stainless steel to have a higher wall temperature. Moreover, a bore 350 makes it possible to introduce a thermocouple making it possible to measure approximately the temperature in the vicinity of the wall at the level of the constriction. The depression carried out at the level of the constriction of the convergent-divergent and the suction of the load which results from it allow to divide and nebulize very finely the injected charge (which correspondingly increases the exchange surface), the shape of the convergent- divergent favoring an intimate mixture of hydrocarbons within the plasma rich in

free radicals.

Claims (14)

  1. A method of hydropyrolysis of heavy hydrocarbons, characterized by the steps of: producing and ejecting a jet of plasma under pressure produced from a plasma gas, generating free radicals H ', injection, in the plasma jet thus produced, a gas generating free radicals, especially radicals H ', CH', CH 2 'and CH 3 -,   injection, in the resulting gas stream, of hydrocarbons   hydropyrolysers to react with the gen- free radicals,   recovery of the products of hydropyrolysis thus obtained.   2. The process of claim 1, wherein the gaseous stream is non-swirling at the injection point (330) of the hydrocarbons.   3. The process of one of claims 1 and 2, wherein   the gas stream is accelerated prior to the injection of the hydrocarbons.   4. The process of one of claims 1 to 3, wherein   the free radical generating gas is injected radially in the plasma jet.   The process of one of claims 1 to 4, wherein   the temperature of the plasma jet at the point (230) for injecting the free-radical generating gas is between 2000 and About 3500 K.   The process of one of claims 1 to 5, wherein   the free radical generating gas is hydrogen or a   mixture comprising hydrogen and methane.   The process of one of claims 1 to 6, wherein   the hydrocarbons to be hydropyrolysed are injected into the gas stream through a plurality of distributed injection ports (340)   circumferentially in a uniform manner.   The process of one of claims 1 to 7, wherein   the temperature of the gaseous stream at the injection point (330) of the hydrocarbons to be hydropyrolysed is less than about 2800 K. 1 0 E c 2622894 9. A hydropyrolysis plant for heavy hydrocarbons, characterized by: - a plasma torch (100), for producing and ejecting a   pressure plasma jet produced from a plasma gas   magene, - an intermediate stage (200) comprising means for injecting, in this plasma jet, a gas generating free radicals, in particular radicals H ', CH 2' and CH 3 ', - means for injecting into the gas stream downstream, hydrocarbons to be hydropyrolysed, means (400,500) to collect, downstream, the products of hydropyrolysis.   The installation of claim 9, further comprising: - downstream of the intermediate stage, a convergent-divergent (310,320) oriented in the axis of the plasma jet, the injection   hydrocarbons being carried out at this convergent-   diverge. The plant of claim 10, wherein the hydrocarbons to be hydropyrolysed are injected at the level of   the constriction (330) of the convergent-divergent.   12. The installation of one of claims 10 and 11,   wherein the hydropyrolysed hydrocarbons are injected into the convergent-divergent through a plurality of orifices   (340) circumferentially distributed uniformly.   13. The installation of one of claims 9 to 12, in   wherein the intermediate stage comprises a mixing chamber (230) in which the free-radical generating gas is peripherally injected through a plurality of orifice points (240).   14. The installation of claim 13, wherein the free radical generating gas is injected radially. in the mixing chamber.