FR2663561A2 - Method for oxidising an oxidisable charge and its implementation - Google Patents

Abstract

Method for oxidising an oxidisable charge in gaseous phase by an oxidant gas, in which the charge is introduced through the pipe 1 and the oxidant gas through the pipe 2 into a mixing region 3 and the resultant mixture is made to flow through the central region of the reaction region 4, such that, in at least a first part of the said central reaction region, the gaseous mixture has a speed V1 and that, in at least another part of the said central region, following on from the said first part, the gaseous mixture has a speed Vf less than the said speed V1, and the reaction products formed are collected through the pipe 11. The variation in speed is obtained by using a central region of the reaction region having the overall shape of a nozzle or that of a venturi.

Description

The main patent application filed on September 12, 1989 has been described under
national registration number 89/12016 an oxidation process and a reactor
for the implementation of this process and in particular for the implementation of the
controlled oxidation reaction of an oxidizable charge with an oxidizing gas or a mixture
of gas containing at least one oxidizing gas, that is to say a gas allowing oxidation
of said charge.

The process according to this main patent is a process for oxidizing an oxidizable charge
in the gas phase with an oxidizing gas or a mixture of gases comprising at least one gas
oxidant into which the oxidizable charge and the oxidizing gas are introduced into a zone of
mixing, the gaseous mixture from the mixing zone is circulated in a reaction zone comprising a central zone and a peripheral zone, a loss is established
delta P1 load (A P1) in the central zone and delta P2 pressure drop (AP2)
in the peripheral zone, these pressure drops being such that one reacts
substantially all of the gas mixture from the mixing zone in said zone
central of said reaction zone and that the differential pressure drop delta
P2- delta Pl (P2 - AP1) is positive, and the reaction products are recovered
trained.

The reactor for implementing this process comprises at least one
mixture comprising means for supplying oxidizing gas and means
supply of oxidizable charge, at least one reaction member, following said audit
mixing member and located at a distance from it at most equal to the distance from
jamming of the flame, and at least one member for discharging the reaction products
connected to said reaction organ and whose main characteristic relates to a
embodiment of the reaction member making it possible to obtain a differential of
pressure drop between the central area of the reaction member and the peripheral area of said member.

 The design of this reactor makes it possible to prevent the conduction of the heat given off during the oxidation reaction, in particular in its first phase leading to a maximum, or peak, of temperature, from heating the gas mixer placed too strongly. upstream of the reaction member and risk causing an unwanted start of the oxidation reactions therein. This particular design also makes it possible to avoid excessive heat loss.

Even if it is possible, thanks to this particular design, to control these risks of unwanted starting, the fact of subjecting the mixer and in particular its part contiguous to the reaction organ, part which is sometimes called organ of ejection, at excessive temperatures can cause deformations of said member and require early replacement of the entire mixing member.

Thus, for the realization of the central zone of the reaction member, ceramic materials with a low coefficient of thermal conduction and thin walls are preferably used, in order to limit this conduction as much as possible and to ensure that the temperature profile obtained in the reaction member is such that the temperature peak is as far as possible from the end of the mixer.

One possibility for physically moving this temperature peak away from the end of the mixer adjoining the reaction member is to require the gases to have a very high linear speed, which allows them during the reaction induction period d oxidation and the time of rise to the temperature peak to move away enough from said end of the mixer.

However, another thermo-kinetic constraint of the oxidation reactions requires having a sufficiently long residence time, generally of the order of a few seconds, to allow the reactions to return to equilibrium, thermal or thermo - catalytic, to be carried out and with the mixture of gases thus produced to reach the equilibrium composition as provided for by the calculations of thermodynamics.

The process described in the main patent application and its implementation in the reactor of particular design described in this application allows, at least in part, to meet these two apparently contradictory constraints. However, according to this embodiment, the higher the speed of the gases, the more it is necessary to have a length of the significant reaction member, which can lead to very large pressure drops and furthermore risks enormously increasing the manufacturing cost of the reactor.

The object of the present addition is an improvement of the process described in the main patent application, and its implementation in a reactor designed so as to better respond to the two constraints mentioned above without leading to unacceptable pressure drops, or simply too important. The process according to the
this addition allows in particular to be able to work with speeds of
gases at the outlet of the relatively large mixer and therefore to keep the temperature peak away from the mixing element, without the need to increase
the length of the reaction organ, while limiting as much as possible
pressure losses.

The present invention provides an oxidation process as described in the main patent application, characterized in that in at least a first part of the central zone of the reaction zone, on the mixing zone side, the gas mixture is circulated at a speed V1 and in that in at least one subsequent part of said first part, on the discharge side of the reaction products, said gaseous mixture from said first part is circulated at a speed Vf lower than said speed V1.

Usually the speed V1 is about 2 to about 300 mxs-1, often this speed V1 is about 10 to about 200 mxs-1 and most often it is about 20 to about 150 mxs-1 and the speed Vf is usually about 0.05 to about 250 mxs-1, often this speed Vf is about 0.1 to about 100 mxs-1 and most often it is about 1 to 100 mxs-1.

In a frequent implementation of the process of the present invention, the speed ratio Vî: Vf is usually from about 2 1 to about 50 1 and often this ratio is from about 5: 1 to about 25: 1 and , in the most frequent case, this ratio is from approximately 8 1 to approximately 20 1.

The process of the present invention can be implemented in reactors, the reaction member of which has a particular shape and characteristics making it possible to easily obtain the desired speeds of the gas mixture in the various zones of said reaction member. The circulation of the gas mixture at a speed V1 in at least a first part of the central zone of the reaction zone can be obtained by regulating, for a given reaction member, the flow rate and / or the pressure of the gases introduced into the mixing member, the speed Vf then essentially being a function of the respective overall dimensions of the sections of the various parts of the reaction member.

The invention will be better understood from the description of a few embodiments given purely by way of illustration but in no way limiting, which will be made of it below with the aid of the appended figures, in which similar bodies are designated by the same figures. and letters of reference.

In FIG. 1, curve 1 represents the temperature profile (T "C on the ordinate), along the axis XX '(length L on the abscissa) of a reactor, such as that shown diagrammatically in FIG. 6 and which corresponds to a reactor as described in the main patent application, in the central zone of the reaction member, from the inlet E to the outlet F of said member; point M is the point corresponding to the maximum This temperature profile, represented by curve 1 in FIG. 1, is the temperature profile for the reaction of methane oxidation, by air, in the presence of water vapor. This profile was recorded using 20 thermocouples arranged regularly throughout the reaction member at a distance from each other equal to Lg / 20 for a reaction member of length Lg. In this FIG. 1, curve 2 represents the temperature profile obtained for the methane oxidation reaction with l air, in the presence of water, using a reactor such as that shown diagrammatically in FIG. 2; point M 'is the point corresponding to the maximum temperature. The reactor used to draw the temperature profile represented on curve 1 had a reaction member comprising a lining formed using a plurality of identical thin monoliths each comprising a plurality of channels, each channel having a section of Sm surface. This reactor had a reaction member of the same length as that of the reactor used to draw curve 1 and the experiment was carried out while keeping the overall residence time in the reaction member identical to that which one had chosen to draw curve 1 with the reactor shown diagrammatically in FIG. 6, that is to say while keeping the same reaction volume. From the determination of the location of the temperature peak M, in the case of the use of the reactor shown diagrammatically in FIG. 6, it is possible, taking into account the gas flow rate, to determine the time necessary to reach this peak. using a reactor such as that shown diagrammatically in FIG. 2 having the same reaction volume as that shown diagrammatically in FIG. 6 and having served to determine the time necessary to reach the temperature peak, it is then possible to calculate the location of the temperature peak M 'in this reactor as shown diagrammatically in FIG. 2.

- Figure 2 shows, in an axial section, a reactor for implementing the method according to a first embodiment of the present invention.

- Figure 3 shows, in an axial section, a reactor for implementing the method according to a second embodiment of the present invention.

- Figure 4 shows, in an axial section, a reactor for implementing the method according to a third embodiment of the present invention.

- Figure 5 shows, in an axial section, a reactor for implementing the method according to another embodiment of the present invention.

- Figure 6 shows, in an axial section, a reactor for implementing the method according to the main patent application.

In FIG. 2, there is shown, according to a first embodiment of the invention, a vertical, cylindrical reactor R, of elongated shape, of axis XX 'comprising an external wall 8 of steel, a sleeve of refractory concrete 9 and a ceramic fiber sleeve 10 and substantially in its center a mixing member 3 surrounded by a sealed metal casing 13 and into which is introduced by line 1 an oxidizable charge and by line 2 an oxidizing gas, said mixing zone being constituted by the stacking of a series of monoliths 6 of small thickness, made of hard ceramic, with offset mesh and crossed channels; this reactor comprises a reaction member 4, having the overall shape of a nozzle, and formed by the superposition of a series of monoliths 7 of small thickness, each comprising a plurality of channels of substantially square section, said monoliths being superimposed on so that a plurality of channels 12, juxtaposed and substantially parallel, is formed, at least part of which opens into the member 5 for discharging the reaction products through the pipe 11. The overall shape of the nozzle of the member of reaction implies that the gas velocity in the throat of the nozzle of length Lg1 is greater than in the part of length Lg3, following the divergence of length Lg2, and connecting this divergence to the device for discharging the products formed The channels 12, in this first embodiment of the method of the invention, each have a surface section and of substantially constant shape over the entire length of the reaction member.

In FIG. 3, there is shown, according to a second embodiment of the invention, a vertical, cylindrical reactor R, of elongated shape, of axis XX ′ comprising a reaction member 4, having the overall shape of a nozzle, and formed by the superposition of three successive linings each produced using a series of monoliths 7 of small thickness, each comprising a plurality of channels of substantially square section, said monoliths being superimposed so that the a plurality of channels 12, juxtaposed and substantially parallel, are formed in each lining 12, at least part of which opens into the member 5 for discharging the reaction products via the conduit 11. The first lining, on the mixing member side, of length L1 substantially equal to the length Lg1 of the throat of the nozzle, comprises a plurality of channels each having a surface section S1. The second lining, subsequent to said first lining, of length L2 slightly larger than the length Lg2 of the diverging portion of the nozzle, comprises a plurality of channels each having a surface section S2 greater than SI. The third and last lining, on the discharge member side, of length L3, comprises a plurality of channels each having a surface section S3 greater than S2. In this embodiment of the invention, the channels 12 have a shaped section substantially constant over the entire length of the reaction member, but whose individual surface area is smaller near the mixing member than near the discharge member. In this embodiment, the overall shape of the nozzle of the reaction member implies that the speed of the gases in the throat of the nozzle of length Lg1 is greater than in the part of length Lg3, following the divergence of length
Lg2, and connecting this diverging point to the device for evacuating the products formed. Furthermore, according to this embodiment, the progressive increase in the dimension of the free spaces in the reaction device since the charge entered the zone central of the reaction member (4) up to the outlet of the reaction products formed, at the level of the discharge member (5) of said products, allows progressive control of the oxidation kinetics with the consequence of a reduction in the maximum temperature reached during the reaction.

In Figure 4, there is shown, according to a third embodiment of the invention, a vertical cylindrical reactor R, of elongated shape, axis XX 'comprising a reaction member 4, having the overall shape of a nozzle, and formed by the superposition of three successive linings. This embodiment differs from that shown in FIG. 3 only in that the first lining has a length L1 less than the length of the neck of the nozzle. In this embodiment, the sum of the lengths of the first two linings is substantially equal to the length of the neck of the nozzle, the third lining extending from the start of the diverging portion of the nozzle to the level of the member (5) d evacuation of reaction products.

Usually, these embodiments of the invention, as shown diagrammatically in FIGS. 3 and 4, correspond to the case where the oxidizable charge and at least one oxidizing gas are introduced into a mixing zone under pressure and with a flow rate such that the speed of the gas mixture at the outlet of the mixing zone is equal to Vî, this gas mixture is circulated at speed V1 in said first part of the central zone of the reaction zone comprising at least one lining adapted to define a multiplicity of spaces having passages the cross section of which has a surface S1, said layers having in at least one direction a dimension at most equal to the flame jamming distance, said first part of the central zone having a overall surface 8g1, then the gas mixture, coming from said first part, is circulated at a speed Vf, in at least one other part, subsequent to said first part and comprises as long as at least one lining adapted to define a multiplicity of spaces having passages whose cross section has an area Ss greater than or equal to S1, said passages having in at least one direction a dimension at most equal to the flame jamming distance , said part of the central zone having a global surface Sgf greater than Sg-1. It is usually preferred to use an embodiment in which the central zone of the reaction member comprises three parts of respective lengths Lg1, Lg2 and Lg3, the first part having an overall surface 8g1 substantially constant over its entire length, the third part having a surface overall Sg2, greater than Sg1, substantially constant over its entire length and the second part connecting said first part to said third part having an increasing area from the value Sg1 to the value Sg2, said central zone thus having the shape of a nozzle and the length Lg2 being such that the angle alpha (a) of said nozzle is approximately 15 to 120 degrees of angle.

In the embodiments shown diagrammatically in FIGS. 3 and 4, the central zone of the reaction member has, near the mixing member, the shape of a nozzle, the cross section of which has, at its connection to the mixing member (3) and over a length Lg1, an area Sgl less than or equal to approximately the area S of the section of the mixing member at said connection, then over a length Lg2 the area of the section increases , substantially regularly, up to a value
Sg2 equal to approximately 1.5 to 500 times Sg1, preferably from 2 to 200 times Sg1, and most often from 5 to 100 times Sg1, and is then kept substantially constant over a length Lg3, the sum Lg of the lengths Lg1, Lg2 and Lg3 preferably being substantially equal to the length of said central zone of said reaction member. It would not be departing from the scope of the present invention in the case where the length Lg3 is equal to zero. Usually, the first lining of the reaction member has characteristics of length L1 and surface area S1 of passage section such that for the oxidation reaction considered the maximum temperature is reached at a distance from the mixing member to the less substantially equal to the value of the length
L1, independently of the value of the length Lg1, preferably this maximum will be reached at a distance between the value of the length LI and the value of the sum of the lengths L1 + L2. The length Lg2 is usually such that the angle nozzle alpha (<i) is from about 15 to about 120 degrees of angle, this angle most often being from about 20 to about 90 degrees of angle and preferably from about 30 to about 60 degrees d 'angle. The length Lg3 will preferably be chosen so that the total residence time in the reaction member is sufficient to reach equilibrium. It is possible to keep constant and equal to Sg2 the surface of the section of the nozzle over a length Lg4, then to decrease or gradually increase this section until it has a value Sg3 such that the ratio of these surfaces
Sg2: Sg3 is for example from approximately 0.2: 1 to approximately 5: 1, this variation is carried out over a length Lg5. The sum of the lengths Lg4 + Lg5 usually being equal to the length Lg3 defined above. It is sometimes desirable to obtain, at the outlet of the reaction member, gases having a relatively high speed; in this case, it is possible to reduce the surface area of the section of the nozzle close to the discharge member for the reaction products and one can, in this case, optionally choose to then keep this section constant, for example over a length Lg6 such that the sum of the lengths Lg4 + Lg5 + Lg6 is equal to the length Lg3 defined above.

Thus, by using a reaction member comprising several successive linings each having channels of unit section of increasing surface in the direction of flow of the charge and by adopting working conditions allowing a variation of speed of the gases in the reaction member and for example a relatively narrow overall passage section at the start of the reaction zone, overall section of
surface for example roughly equivalent to that of the mixing member at
its connection to the reaction member or to that of the ejection member (not
shown in the figures) gases out of the mixer, then flaring
progressively the internal part, as shown in FIGS. 3 and 4,
the location of the temperature peak in the reactor is very far removed and
so we minimize the risk of overheating of the mixing element and we thus reduce
the risks of deformation of said organ and those of deterioration of the materials which
constitute. The implementation of the method of the present invention allows to be able
no more preheating the gases that are introduced into the mixing element, without risk
excessive for this one since the temperature peak is, thanks to this process and its
implementation, clipped and relatively distant from the end of the mixing member, which allows improved conversion while maintaining a safety margin
more than enough. The ejection member can be any member chosen from those well known to those skilled in the art. Most often, this ejection member is a simple grid and it has a cross section of surface roughly equivalent to that of the organ of
mixture at its connection with it.

Without being limiting, the shape of the nozzle will preferably be such that, at the start of the reaction zone, its section has a passage surface Sg1 approximately
equivalent to the surface of the gas ejection member outside the mixer, this in order to
minimize turbulence at this level.

In an advantageous embodiment, the central zone of the reaction zone comprises a catalyst in at least a subsequent part of the part in
which the gas mixture has a speed V1.

In this advantageous embodiment, the reaction member may, for example in at least part of its volume and over at least part of the length Lg2 and / or over at least part of the length Lg3, comprise at least a catalyst such as for example one of the catalysts well known to those skilled in the art for promoting endothermic reactions returning to equilibrium.

This catalyst can be supported by the walls of the channels of the monolith (s), or else by particulate elements as described in the main patent application. By way of nonlimiting examples of catalysts, mention may be made of those comprising a support, for example of alumina or of silica, on which, for example, copper chloride and potassium chloride, oxide have been deposited of vanadium optionally combined with potassium sulphate, cerium, lanthanum, or a cerium or lanthanum compound, chromium, a group VIII metal such as, for example, nickel and iron, or a chromium or d compound a group VIII metal such as for example a nickel or iron compound, bismuth phosphomolybdate, or cobalt molybdate. The catalyst can also include metal oxides such as silver and / or copper oxides and porous silicon carbide coated with silver. In a particularly advantageous form, it will be possible to have several catalysts of different compositions, each of them being placed in the reaction zone at the place where its composition is best suited to favor, for example, the desired endothermic reaction (s).

According to another embodiment of the present invention, the oxidizable charge and at least one oxidizing gas are introduced into a mixing zone, then this gaseous mixture is circulated in the central zone of the reaction member, said central zone having the shape of a venturi (FIG. 5) comprising a convergent and a divergent separated by a neck, preferably substantially rectilinear, said zone comprising one or more packings adapted to define a multiplicity of spaces having passages whose cross section has in the first of them a surface S1 and in the last of them a surface Ss greater than or equal to S1, said passages having in at least one direction a dimension at most equal to the flame jamming distance, said zone having a section at its connection to the mixing member with a surface area substantially equal to that of said member at said connection, a section at the level of the neck of the surfa this overall less than that of the mixing member at its connection to said venturi and a section at the end of the divergent whose overall surface is greater than that of said neck,
The introduction of the charge and the oxidizing gas being carried out under a pressure and with a flow rate such that the speed of the gas mixture at the level of the venturi neck is equal to
V1, said gaseous mixture then having, at the outlet of the divergent portion of said venturi, a speed Vf lower than said speed V1.

In the embodiment shown diagrammatically in FIG. 5, the venturi comprises three packings each formed by the superposition of a series of monoliths 7 of small thickness, each comprising a plurality of channels of substantially square section,
said monoliths being superimposed so that a plurality of
juxtaposed and substantially parallel channels 12 at least part of which opens out
in the member 5 for discharging the reaction products via the line 11. These
monoliths each have an overall surface section which goes in
decreasing from an overall surface value preferably substantially equal to
that of the overall surface S of the mixing member at its connection to
the reaction organ up to a value Sg4 lower than S. The reduction in the surface
overall of the section is performed over a length Lg7 such that the beta angle (, 8) of the
converge, preferably around 30 to 120 degrees of angle. The venturi neck has
preferably a substantially constant overall surface section equal to Sg4 over
a length Lg8 such that the sum of the lengths Lg7 + Lg8 is substantially equal to the length Lg1 defined above. It would not go beyond the scope of the present invention
in the case where the length Lg7 is substantially equal to the length Lg1, the length
Lg8 then being substantially equal to zero.The divergent part of the venturi usually has to
its end a section whose overall surface Sg5 is greater than that of said neck and
is preferably at least equal to that of the mixing member in terms of its
connection to the reaction device. The increase in the overall surface of the section
is performed over a length Lg9 such that the gamma angle (y) of the divergent is
preferably about 15 to 120 degrees of angle. The sum of the lengths Lg1 + Lg9 can
be equal to or less than the length Lg of the reaction organ. In the case where the
sum of the lengths Lg1 + Lg9 is less than the length Lg of the
reaction, the overall cross-sectional area at the end of the divergent venturi can
be kept substantially constant and equal to Sg5 over a length Lg3 such that the
sum of the lengths Lg1 + Lg9 + Lg3 is equal to the length Lg of the
We would not go outside the framework of this other embodiment by retaining
constant the value Sg5 of the global surface of the section at the end of the venturi on
a length Lg4, then gradually decreasing or increasing this surface until it has a value Sg6 such that the ratio of these surfaces Sg5: Sg6 is
for example from about 0.2: 1 to about 5 1, this variation being carried out on a
length Lg5. The sum of the lengths Lg4 + Lg5 is usually equal to the
length Lg3 defined above. It is sometimes desirable to obtain, at the end of
the reaction organ, gases having a relatively high speed and in this case one
may decrease the overall area of the reaction organ section near
the reaction products discharge device, which amounts to carrying out a second
converge opening directly into the discharge device for the reaction products or extending over a length Lg6 with a substantially constant overall surface section up to the discharge device for the reaction products, this length Lg6 usually being such that the sum lengths Lg4 + Lg5 +
Lg6 is equal to the length Lg3 defined above. It is likewise possible, as in the previous embodiment, to introduce at least one catalyst, for example into at least part of the reaction volume of the central zone of the reaction member and in particular over at least part of the length Lg8 and / or over at least part of the length Lg9 and / or Lg3.

In the various embodiments of the present invention, the reaction member has a section, of any shape, defined by a closed curve such as for example a circle, an ellipse or a polygon such as a rectangle or a square. In the case where this member has the shape of a nozzle, the latter has a cross section whose overall surface area Sg1 is smaller near the mixing member than near the discharge member where it is equal to Sg2. In the embodiments shown diagrammatically in FIGS. 3 and 4, the nozzle has a substantially square section.

The process of the present invention can thus be implemented in a reactor whose central zone of the reaction member has for example the shape of a nozzle or that of a venturi. This central zone can comprise s successive parts, each part comprising a lining having passages whose section has, in each of them, a constant surface throughout said central zone, or according to another embodiment each part comprises a lining presenting passages whose section has, in each of them, an increasing surface, from one to the other, from the first to the last. Usually s is a positive integer greater than or equal to 2.

In the case where the passages have a larger surface section on the discharge member side than on the mixing member side, the central zone of the reaction member is most often such that the first part, on the mixing member side, has a lining adapted to define a multiplicity of spaces having passages the cross section of which has a surface S1, said passages having in at least one direction a dimension at most equal to the flame jamming distance which may result from the oxidation of said charge , and the last part of which, on the discharge member side, comprises a lining adapted to define a multiplicity of spaces having passages the cross section of which has an area Ss greater than S1, said passages having at least one dimension in at least one direction equal to the flame jamming distance that may result from the oxidation of said charge.

Usually, the central zone of the reaction member comprises successive parts, each comprising a lining adapted to define a multiplicity of spaces having passages whose section has an increasing surface, from one part to the next, from the first part. until the last part. Preferably, the number s is a positive integer from 2 to 10 and most often from 3 to 6. The surfaces S1 and Ss are usually such that the ratio Ss: S1 is from approximately 100 1 to approximately 4 1 and frequently from about 50 1 to about 4 1 and most often from about 25 1 to about 10 1. In a frequent embodiment, the central zone of the reaction member comprises three successive parts.

In this most frequent case where the central zone comprises three successive parts, the first part, on the mixing member side, comprises over a length L1 a lining adapted to define passages the section of which has a surface S1, the second part, subsequent to said first part comprises over a length L2 a lining adapted to define passages whose section has a surface S2 and the third and last part, on the discharge member side, comprises over a length L3 a lining adapted to define passages whose section has a surface S3, said surfaces S1, 52 and S3 being such that the ratio S3: SI is from approximately 100 1 to approximately 4: 1, and the ratio S2: S1 is from approximately 50: 1 to approximately 1, 2: 1.

Frequently the S3: S1 ratio will be from about 50: 1 to about 4: 1 and most often it will be from about 25: 1 to about 10: 1 and the S2: S1 ratio will frequently be from about 25: 1 to about 1.5: 1 and most often it will be from about 10: 1 to about 2: 1.

Preferably in the process of the present invention, the gas mixture is circulated in the central zone of the reaction zone under conditions such that for the oxidation reaction considered the maximum temperature is reached in the zone of maximum speed at a point between the middle of said zone and its end located on the side of the evacuation zone.

Most often, in the case where the central zone of the reaction member comprises several packings having cross-sections of variable surface area, the conditions of speed and dimensions (in particular length L1 of the first packing and surface S1 of the section passages of this first lining) will be chosen so that for the oxidation reaction considered, the maximum temperature is reached at a distance from the mixing member at least substantially equal to the value of the length L1. more often, the characteristics of length L1 and L2 and surface area S1 and S2 of passage section of the first two linings will be such that the maximum temperature is reached at a distance from the mixing member substantially between the value of the length L1 and the value of the sum of the lengths LI + L2.

'' As well in the case of the nozzle as in that of the venturi, it may be advantageous, depending on the length and surface characteristics of passage sections of the first two linings, that for the oxidation reaction considered the maximum temperature is reached at a distance from the mixing member substantially between approximately 0.8 times and approximately 1 time the value of the length Lg; this choice has several advantages: - the temperature peak is generally pushed relatively far from the mixer, especially if the overall surface area of the section of the reaction zone is relatively small and therefore the speed of the gases relatively large, - at level of the temperature peak, there will thus be a thickness of the second lining forming a sleeve (10), produced using a refractory and heat insulating material, relatively large, thus minimizing the heat losses at this level, - finally, the passage section being constricted at the level of the temperature peak, the capacity to store heat will be reduced, the gases carrying a maximum of this towards the continuation of the reactor for the reactions of return to equilibrium.

As specified above, the temperature peak is preferably reached in the zone where the gases have the maximum speed, but it would not be departing from the scope of the present invention in the event that this peak is only reached in a subsequent zone. at said maximum speed zone. Usually, in one case as in the other, the temperature peak is reached in the zone comprising the second packing both in the case of the nozzle and in the case of the venturi. We can thus distinguish for example in the case of the nozzle two embodiments: the first in which the portion of smaller section of the nozzle comprises over its entire length one or more linings having characteristics of dimension, surface of the passage sections and length such as for the reaction of oxidation considered and under the chosen conditions of gas speed the maximum temperature is reached in said part and the second in which the part of smaller section of the nozzle comprises over its entire length one or more linings having characteristics of dimensions, area of passage sections and lengths such that for the oxidation reaction considered, the maximum temperature is att eint in one of the subsequent parts of said part and therefore is not reached in said part.

In the case of the venturi, the latter preferably comprises over its entire length one or more packings having characteristics of dimension, surface area of the passage sections and lengths such as for the oxidation reaction considered and under the chosen conditions of gas velocity, the maximum temperature is reached at a point located after the middle of the neck in the direction of flow of the reacted charge and preferably at a point located at a distance greater than 0.8 times the length of the neck from the start of it in the direction of flow of the load.

The conditions for implementing the method are, in this case, most often chosen so that the temperature peak is reached before the end of the neck situated on the side of the discharge member.

Overall, the method according to the present invention is particularly advantageous.

Thus, according to the present invention, in particular in the case of a central reaction zone the member of which has channels of increasing cross-sectional area in the direction of gas flow, when passing from the mixing zone to the reaction zone, we go from the point of view of the kinetics of the oxidation reactions to a situation of almost complete blockage of the progress of the oxidation reactions, in particular in the case of powder mixers, since the powder of controlled particle size has precisely this role, to a situation of controlled progress of these reactions. This allows on the one hand, by the presence of even fine channels at the beginning of the reaction organ, to limit the pressure drop of the together, on the other hand, from a kinetic point of view, the oxidation reactions are limited, or even totally controlled by wall effects, which is much less the case for return to equilibrium reactions such as steam reforming tea rmique. It is therefore clear that it is possible, in part, to limit the exothermic oxidation reactions by considerably increasing the wall effects since the average size of the channels is smaller and simultaneously to allow more time for the endothermic reactions to return to l So, in terms of free space, we go from a situation where the average size of the spaces (in terms of average surface area of passage section) is usually of the order of a few tens of square microns to a situation where the average size of the spaces is of the order of a few square millimeters. The process of the present invention, implemented under the conditions described above, therefore makes it possible to control the kinetics of the oxidation reactions in the reaction zone by having free spaces of relatively small dimensions at the start of this zone. increasing the dimensions of these spaces throughout this area. Such an embodiment makes it possible to obtain what one might call a "progressive loosening" of the kinetics of the oxidation reactions.

Usually, the dimension of the various passages in the central zone of the reaction member remains less than about 10-2 meters (m), this dimension is most often from about 5x10-5 to about 2x10-3 m and preferably from about 10-4 to about 10-3 m. In terms of cross-sectional area these spaces will thus have a surface area usually of about 0.0025 to about 100 mm2 and more often about 0.01 to about 4 mm2.

In addition, when this action of “progressive loosening” of the kinetics of the oxidation reactions is cumulated with the speed effect by choosing operating conditions such that the speed V1 is very high and that the speed Vf is relatively low, the temperature peak is moved as far away from the mixer as possible without greatly increasing the pressure drops nor excessively the total length of the reactor.

The oxidation process applies in particular to the oxidation of a charge of hydrocarbons, and for example of a charge of saturated aliphatic hydrocarbons such as methane and the effluents of the catalytic steam reforming process,
Orthoxylene, naphthalene, benzene, methanol, methane-toluene mixtures, and ethylene-hydrochloric acid mixtures. As the oxidizing gas, for example, air or oxygen-enriched air can be used, without notable disadvantages, and in particular without excessive formation of soot. The process of the present invention is in particular applicable to the controlled oxidation of a hydrocarbon feedstock by a gas mixture comprising oxygen, in order to produce a gas mixture, usable for the synthesis of ammonia or the synthesis of alcohols, including hydrogen and carbon monoxide. Usually, the reactive gases are preheated so that the temperature of the mixture at the entrance of the reaction zone is about 300 "C at around 800 "C and most often around 350" C to around 750 "C. The molar ratios of oxidizing gas to oxidizable charge which are recommended, and for example the molar ratio of oxygen / methane, are usually from approximately 0.5 1 to approximately 0.75 1. The residence time of the reactive gases in the zone The reaction time is usually from about 2 milliseconds to about 10 seconds, and preferably from about 50 milliseconds to about 1 second.

Example
Oxidation of a methane charge is carried out in the presence of water vapor, with air in a vertical reactor R of tubular shape (FIG. 3) comprising an outer casing 8, metallic, supporting the pressure, two inlets 1 and 2 for gases and an outlet 1 1 for effluents.

Inside said envelope and substantially at its center, a gas mixer is placed, itself surrounded by a sealed metallic envelope 13, cylindrical 10-1 m high and 4x10-2 m in diameter (I 'together forms the mixing member 3).

This mixer is formed by discs 6 stacked on each other comprising crossed channels of the SULZER type; these discs and the free space surmounting them are filled with alumina powder with a particle size between 5x10'5 m and 10-4 m (50 to 100 µm (micrometer)).

In the mixing member, at its upper end, two conduits make it possible to supply the two fluids (methane + water vapor on one side by the conduit 1, air on the other by the conduit 2).

The cylindrical envelope surrounding the mixer is terminated by a hopper retaining the alumina powder placed on a grid (not shown in Figure 3) having 16 holes 4x10-5 m in diameter arranged inside a central square 10-2 m side. This grid plays the role of the member for ejecting the gases from the mixing member in the reaction member.

The gases leaving the mixing member penetrate through the central grid into the reaction part 4 which is constituted by the stacking of 50 square unitary pieces in mullite zirconia with a section of variable overall surface area, but of the same thickness equal to 10- 2 m. We first find a stack of 12 pieces of 10-2 m side with 100 square holes of 0.25x10'3 m side, then 10 pieces of variable overall dimensions ranging from 1.2 to 4.8x1 0-2 m side with a pitch of 0.4x10-2 m comprising an increasing number of holes, in proportion to the overall dimensions, said holes having 0.5x10-3 m side, then 28 pieces of 5x10-2 m side having 1296 holes squares of 10-3 m side.

The metal casing 13, surrounding the mixer, and the monoliths 7, of the reaction part 4, are enclosed in an alumina fiber sleeve with an external diameter of 14 × 10 −2 m. This fiber sleeve 10 is surrounded by a refractory concrete sleeve 9 connecting with the metal wall 8 forming the outer envelope of the reactor R. The alumina fibers used to manufacture the sleeve have an average diameter of 3 × 10 -6 m and an average length of 150x10-6 m. The apparent density of the sleeve measured after 10 hours of operation of the reactor is 0.3 and the average dimension of the fiber spaces is 6 × 10 -6 m.

In the reactor as described above and operating under 4MPa, methane and water vapor are introduced through line 1, and through air line 2 in proportions such that the gas mixture has the composition following molar: CH4 = 450 H2O = 900 2 = 290
N2 = 1130
The total gas flow rate at the conditions of entry into the reactor is 4.1 m3xh-1 (cubic meter per hour). Under these conditions, the calculated gas velocity (taking into account the flow rate and the total passage surface) at the level of the gas inlet in the central zone of the reaction member is 23.3 mxs-1 ( meter per second) and the gases have substantially the same speed at the end of the throat of the nozzle. The gas speed calculated at the outlet of the central zone of the reaction member is 1.4 mxs-1 . The temperature of the gas mixture at the inlet of the mixing member is 480 C. At the outlet 1 1 of the reactor, a gas is recovered at a temperature of 890 "C, the molar composition of which is, after condensation of 1 the next
CH4 = 15
N2 = 1130 2 = 0
H2 = 903
CO = 256 Cl2 = 179
After 5 hours of operation, the thermal conditions are stabilized and the reaction could be carried out for 600 hours without any problem. The pressure drop differential (AP2- aP1), measured after 5 hours of operation, is 0.1 MPa. During this operation, the temperature of the metal wall of the reactor measured on its external face did not exceed 1500C. After stopping the test and dismantling the various elements forming the reactor, there were no cracks in the concrete layer, no deterioration, neither of the fibrous sleeve, nor of the various ceramic parts. Furthermore, during this test, it was possible to measure a coke content equal to approximately 8 milligrams of coke per cubic meter of gas (brought back to normal temperature and pressure) at the outlet 1 1 of the reactor. These results show that it is possible, without major problem, to work with gases having a higher inlet temperature and to obtain a better conversion with a reduction in the formation of coke compared to what was obtained with the reactor according to main demand.

Claims (10)

1 - Oxidation process according to claim 15 or 16 of the main application characterized in that in at least a first part of the central zone of the reaction zone, on the mixing zone side, the gas mixture is circulated at a speed V1 and in that in at least one subsequent part of said first part, side of the reaction product discharge zone, said gas mixture from said first part is circulated at a speed Vf lower than said speed V1. 2 - Method according to claim 1 wherein the speed V1 is from about 2 to about 300 mxs-1 and the speed Vf is from about 0.05 to about 250 mxs-1. 3 - Method according to claim 1 or 2 wherein the speed ratio VI: Vf is from about 2 1 to about 50 1. 4 - Method according to one of claims 1 to 3 wherein the oxidizable charge and at least one oxidizing gas are introduced into a mixing zone under pressure and with a flow rate such that the speed of the gaseous mixture at the outlet of the zone mixture is equal to V1, this gaseous mixture is circulated at speed V1 in said first part of the central zone of the reaction zone comprising at least one lining adapted to define a multiplicity of spaces having passages whose cross section has a surface SI, said passages having in at least one direction a dimension at most equal to the flame jamming distance, said first part of the central zone having a global surface Sg1, then the gas mixture, originating from said, is circulated first part, at a speed Vf, in at least one other part, subsequent to said first part and comprising at least one lining adapted to define a multiplicity of spaces pr showing passages whose cross-section has a surface Ss greater than or equal to S1, said passages having in at least one direction a dimension at most equal to the flame jamming distance, said part of the central zone having an overall surface Sgf greater than Sg1. 5 - The method of claim 4 wherein the central region of the reaction member comprises three parts of respective length Lg1, Lg2 and Lg3, the first part having an overall surface Sg1 substantially constant over its entire length, the third part having a overall surface Sg2, greater than 8g1, substantially constant over its entire length and the second part connecting said first part to said third part having an increasing surface from the value Sg1 to the value Sg2, said central zone thus having the shape of a nozzle and the length Lg2 being such that the angle alpha (a) of said nozzle is approximately 15 to 120 degrees of angle. 6 - Method according to one of claims 1 to 3 wherein the oxidizable charge is introduced and at least one oxidizing gas in a mixing zone, then this gas mixture is circulated in the central zone of the reaction member, said central zone having the shape of a venturi comprising a convergent and a divergent separated by a neck, said zone comprising one or more linings adapted to define a multiplicity of spaces having passages of which the section has in the first of them a surface S1 and in the last of them a surface Ss greater than or equal to S1,  said passages having in at least one direction a dimension at most equal to the flame jamming distance, said zone having a section at its connection to the mixing member with an overall surface area substantially equal to that of said member at said connection, a section at the neck of the overall surface less than that of the mixing member at its connection to said venturi and a section at the end of the divergent whose overall surface is greater than that of said neck, the introduction of the charge and of the oxidizing gas being carried out under a pressure and with a flow rate such that the speed of the gas mixture at the level of the neck of the venturi is equal to V1, said gaseous mixture then having at the outlet of the diverging portion of said venturi a lower speed Vf at said speed Vî. 7 - Method according to one of claims 4 to 6 wherein the central area of the reaction member comprises linings having passages whose section has, in each of them, a constant surface throughout said central area . 8 - Method according to one of claims 4 to 6 wherein the central region of the reaction member comprises linings having passages whose section has, in each of them, an increasing surface, from one to one other, from the first to the last. 9 - Method according to one of claims 4 to 8 wherein the gas mixture is circulated in the central zone of the reaction zone under conditions such that for the oxidation reaction considered the maximum temperature is reached in the zone maximum speed at a point between the middle of said zone and its end located on the side of the evacuation zone. 10 - Method according to one of claims 1 to 9 wherein the central zone of the reaction zone comprises a catalyst in at least a subsequent part of the part in which the gas mixture has a speed V1.