FR2648471A1 - Multichannel reactor made of ceramic material comprising means for creating turbulence in the fluid in contact therewith - Google Patents

Abstract

A multichannel reactor made of ceramic material, its method of manufacture and its use are described. The reactor comprises a first pyrolysis section A including a plurality of plates 10 which are substantially mutually parallel. Each of these plates contains a plurality of substantially parallel channels 6 connected to means 8 for feeding a hydrocarbon-containing charge and to means 22 for discharging the effluents produced. The plates are arranged such that they define between them passages 11 for the flow of a pyrolysis fluid in contact with the outer face of the channels. More precisely, the reactor comprises, on at least part of at least one face of these channels, means 4 made of ceramic material capable of promoting turbulence in the fluid in contact with the said face. The effluents are then cooled in a second, quenching section. Application to steam cracking and to pyrolysis of gas containing methane.

Description

The invention relates to a multichannel reactor made of ceramic material allowing turbulent flow of one or more fluids passing through it and the method for manufacturing this reactor. It also relates to the use of this reactor.

This invention applies in particular to the process of steam cracking of conventional petroleum charges, naphtha or. ethane for example, and to the process for pyrolysis of gases containing methane into hydrocarbons of higher molecular weight as described in patent applications EP 229,093, EP 226,487 and
FR 2584 733. It can be applied to hydrocarbon feedstocks in general liable to contain sulfur, nitrogen and even chlorine such as dichloroethane.

The reactions involved in these applications involve quantities of heat which must be supplied for a short time and therefore it is advantageous to be able to have a reactor capable of delivering a high thermal flux.

The patents mentioned above provide a solution by describing monolithic type reactors having a so-called honeycomb structure which make it possible to improve the ratio of exchange surface area to reaction volume thanks to the presence of juxtaposed channels of low ceramic material. diameter.

However, the use of such an extruded and densified material at high temperature produces a reactor whose walls are very smooth and the heat transfer takes place under unsatisfactory conditions which imply to overcome these drawbacks, higher thermal levels.

In the long run, we can note a weakening of the device, in addition to the higher operating cost.

The technical problem to be resolved therefore consists in increasing the heat transfer at the level of the walls in contact with the fluids circulating along or against these walls, in order to economically improve the selectivity of the reactions of both steam cracking and pyrolysis of gas containing methane.

The Applicant therefore proposes a multi-channel reactor allowing better overall heat transfer, which makes possible shorter residence times in the reaction chamber, and improved selectivity.

This reactor according to the invention, of elongated shape comprises a first section called pyrolysis or cracking section and a second cooling section comprising cooling means cooperating with the first section.

This first section comprises a plurality of plates which are substantially parallel to each other, each of which comprises a plurality of channels which are substantially parallel to each other, connected to means for supplying a first gaseous fluid (a hydrocarbon charge for example) to said inlet end and to means for discharging the first fluid having passed through the channels at the outlet end, each of said channels having an internal face in contact with the first fluid flowing therein, and an external face, said plates being arranged in such a way that they determine between them at least one passage for the circulation of a second gaseous fluid (pyrolysis or heating fluid for example) in contact with the external face of said channels, said passage being connected at a first end to means d supply of this second gaseous fluid and at a second end to means for evacuating the second gaseous fluid, the means for evacuating acution of the first fluid being connected to the cooling means of the second section.

The reactor is characterized in that it comprises, on at least part of at least one face of said channels, means made of ceramic material adapted to promote the turbulence of the fluid in contact with said face.

According to a characteristic of the invention when the first gaseous fluid is a hydrocarbon feed and when the second gaseous fluid is a fluid suitable for the pyrolysis of the feed, the turbulence means are arranged on at least part of the internal face of the channels in contact with the load.

According to a preferred characteristic leading to very interesting results, the turbulence means can be arranged on at least part of the internal face and on at least part of the external face of the channels. Whatever the face covered with the channels, the turbulence means can be arranged substantially perpendicular to the axis of the channels. They are generally 1 to 100 mm apart from each other.

According to a particularly advantageous embodiment of the invention, the turbulence means on the internal face of the channels may for example be beads of thickness such that the ratio of the section of these beads on the section of the unitary channel is between 0, 1 and 0.8 and preferably between 0.3 and 0.6.

Furthermore, the thickness of the turbulence means on the external face of the channels can represent 30 to 500% of the thickness of the turbulence means on the internal face of these channels.

The channels are advantageously juxtaposed and generally have a unit cross section between 9 and 900 mm2 and preferably between 25 and 100 mm2.

The distance between plates is usually at least 1 mm, for example from 1 to 50 mm and preferably from 5 to 15 mm.

According to the embodiment described above, the reactor may include a second section where the cooling means constitute a direct quenching of the effluents leaving the channels of the first section, the cooling gases (quench in English) being able to be introduced co -current with effluents when brought into contact with them.

According to another preferred embodiment, the reactor can comprise a second section known as indirect quenching, with a plurality of plates substantially parallel to each other, each of them having a plurality of channels substantially parallel to each other communicating by an inlet at the end. of exit of the plates of the first section where circulates the first fluid (the load, for example). The plates of the second section are arranged, like those of the first section, in such a way that they determine between them a passage for the circulation of a third so-called cooling fluid allowing the indirect quenching of the effluents leaving the first section . The passage of the second section is not communicating with the passage of the first section by means of a watertight partition. However, it has an inlet and an outlet respectively connected to supply means and to means for discharging the third fluid.

The channels of the second section in which the effluents circulate once pyrolyzed comprise, on at least part of at least one of their face (internal or external), means adapted to promote the turbulence of the gaseous fluid in contact with this face such as those already described above.

The load, the heating fluid and the cooling fluid are those described in patent applications EP 229 093 and EP 226 487. The load and the heating or cooling fluid can circulate co-current and / or against current or even cross currents. In the case of a co-current and / or counter-current circulation, the beads are advantageously perpendicular to the flow of the fluids and advantageously parallel to one another.

In the case of cross-current circulation, the beads are advantageously perpendicular to the flow of each of the fluids, the beads located on the load side then being perpendicular to the beads on the heating fluid side.

All the combinations of arrangement of the beads are possible, for example one can fix, on the same level - two internal and external beads (see Figure 2a) on the flat sheet (la) and two internal and external beads on the corrugated sheet (lob ) - two internal and external beads on the corrugated sheet or on the flat sheet - two beads inside the channels, on the charge circulation side - two beads outside the channels, on the heating fluid side - and any other combination of these various provisions.

The internal and external beads of a given channel can be on the same plane but they can also be on different planes.

The reactor with direct quenching of the effluents can be manufactured according to the steps below 1) A plurality of channel plates is produced in the following way a) at least one extra-thickener made of ceramic fiber is created in a given direction over at least part at least one side of a first piece of fiber fabric of ceramic material. For example, the additional thickness may be a bead produced by the buttonhole technique (flanges for example produced in chain stitches) or by sewing a ceramic fiber bead on a sheet of fabric made of ceramic material b) channels are formed for example by waving this first piece of fabric by fixing it on a second piece of fabric made of ceramic material, so that the axis of said channels makes an angle of 10 to 170 with respect to the direction of the extra thickness c ) at least one means for feeding a first gaseous fluid (for example petroleum charge) is sewn at a first end of the said channels formed. and at least one evacuation means at a second end of said channels d) depositing silicon carbide on the pieces of fabric thus formed under conditions such that said fabrics are stiffened, and e) assembling said plates in a enclosure in such a way that the circulation passages of a second fluid (pyrolysis fluid for example) contiguous to the channels are produced and means for supplying the second fluid are connected to the between these passages and means for evacuating this fluid at the outlet of these passages 2) Cooling means are connected either at the end of the channels or at the outlet of these passages depending on whether the channels or the passages are adapted to the circulation of the load to be treated.

A reactor according to the invention with an indirect quenching of the effluents can be manufactured in the following way, a plurality of plates are produced in accordance with steps a, b, c and d, then said plates are assembled in an enclosure so that creates the circulation passages for the second fluid, contiguous to the channels, a watertight ceramic barrier is inserted in the passages at a point such that two non-communicating parts are obtained, a first part of the passages suitable for the circulation of a pyrolysis fluid and a second part of the passages adapted to the circulation of a cooling fluid; means for supplying a first fluid (charge) are connected to the end of the channels, means for discharging the treated fluid at the other end of the channels are means for supplying the pyrolysis fluid to the inlet of the first part of the passages, means for evacuating the pyrolysis fluid at the exit from the first part of the passages, means for supplying the cooling fluid to the entry of, the second part of the passages and means for evacuation of the cooling fluid at the outlet of the second part of the passages.

Any refractory ceramic material for fabrics and swirls resistant to the maximum temperature of the heat transfer fluid can be used in the context of the present invention. Preferably, fibers of the alumina silica type will be used.

To maintain the shape of each of the plates after stitching, for example of the two layers of fabric, the assembly can be advantageously stiffened by depositing with a brush phenolic resin for example. It is then placed in an oven at 120 "C for 2 hours.

The supply and exhaust manifolds are then formed and sewn at one and at the other of the ends of each plate. They are then stiffened in the same way and the whole is then subjected to the deposition of silicon carbide.

This deposition is generally carried out as follows: the woven plate is introduced into an oven in which methyltrichlorosilane (MTS) and hydrogen circulate in a volume ratio H21MTS included, preferably from 6 to 8. This oven is usually heated by induction between 1200 and 1300 "C at atmospheric pressure or under slight vacuum.

The presence of the beads on the internal and external faces of the channels creates turbulence during the passage of the fluids. This turbulence makes it possible to significantly increase the global transfer coefficient and therefore to work, with the same amount of heat supplied, with lower thermal levels.

The invention will be better understood in view of the attached FIGS. 1 to 4, illustrating some embodiments of the reactor, among which - FIGS. 1 a and 1b represent two embodiments of beads adapted to create turbulence in the flow fluids in the canals.

- Figure 2 shows without limitation several embodiments of channels.

According to FIG. 1a, a cord 2 of ceramic fiber is sewn onto a sheet 1 of ceramic material at an infinity of stitches 3 thus creating a suitable means 4 causing turbulence in the flow of the fluids in contact with it. this.

This means or bead can be produced according to the buttonhole technique (fig. 1 b) or, on the 2 faces of the ply 1, a winding of wire 5 of ceramic material is sewn on the two internal and external faces of the ply 1.

The plies thus produced are arranged in such a way that one of these plies is flat, the other lb is in wavy shape and that the beads 4 are advantageously perpendicular to the channels 6 (FIG. 2a). A seam at an infinity of stitches 7 in contact with the two plies 1 and 1b freezes at the level of a unitary plate 10 the configuration of these channels. That of FIG. 2a is preferred because it has good geometry in terms of thermal performance and ease of manufacture.

Figures 2b, 2c and 2d show examples of channel configuration from 2 or 3 layers of ceramic fabric.

FIG. 3 shows a multi-channel assembly comprising a pyrolysis zone (A) and an indirect quenching zone (B) making it possible both to cool the pyrolysis effluents very quickly and to recover energy. The reactor described below illustrates, without limitation, the implementation of a process for pyrolysis of a gas containing methane. The mixture or charge constituted by the hydrocarbon charge to be treated and optionally by steam is preheated, in a preheating zone not shown in the figure.

- This preheating zone can either be of the conventional type, such as a convection system, or be constituted by a multi-channel type heat exchanger system, according to the technology described for the pyrolysis zone, the heat transfer fluid passing through this preheating zone which can advantageously be constituted by the heat transfer fluid coming from the outlet of the pyrolysis zone. On leaving this preheating zone, the mixture enters via the line (8) into the pyrolysis zone (A) where it is distributed by means of the distributor (C) in the plurality of reaction channels (6) containing beads ( 4) and supported by the unitary plates (10), such as those described in FIG. 2a.

The dotted line (M) is approximately half the length of the pyrolysis zone (A); the coolant inlet line (9) reaches the zone (A) at an intermediate point located between (M) and (C) at a distance from the start of the pyrolysis zone (A) representing 5 to 50% of the total length of this zone and preferably 20 to 40% of the length of this zone; this heat transfer fluid is preferably constituted by combustion fumes coming for example from a burner not shown in the figure.

These fumes penetrate into the zone (A) and are distributed in the plurality of passages (11) defined between the unitary plates (1 0); they preferably run through these series of passages (11) against the flow of the reaction mixture circulating in the channels (6) in the part of the zone (A) located between the smoke inlet (9) and their upper outlet (12 ), and circulate cocurrently with the reaction mixture between the inlet (9) and the lower smoke outlet (13).

The smoke outlet lines (12) and (13) include flow control systems (14) and (15), such as, for example butterfly valves, making it possible to adjust the respective smoke flow rates between the outlets (12) and (13).

In the particular case where it is desired that the arrival of heat transfer fluid takes place at the start of the zone (A), the latter may then not include an arrival (9), or else the latter may be closed, the fluid inlet is then carried out by the line (9a) and the fluid path is carried out completely co-current with the reaction mixture, and its outlet is made by the single line (13), 3), the output (12) then being deleted.

In the most general case described above, the fumes exiting through lines (12) and (13) are grouped together and returned by line (16) to the preheating zone (by convection for example).

The sealing of the passages (11) by sealed ceramic sealing devices (17) makes it possible to delimit the pyrolysis (A) and quenching (B) zones whose channels are continuous (channels (6)) for the load. and the effluents, passages (11) and (19) defined below).

The cooling fluid preferably enters the quenching zone (B) through the line (18) located at the very beginning of the exchanger, and circulates in passages (19) parallel to the channels (6), co-current of the effluents reactive, and leaves the exchanger by the line (20). We can. if necessary, reverse the direction of circulation of the cooling fluid which, in this case, enters the exchange zone (B) by line 20 and, after having cooled the reaction effluents with "countercurrent", leaves (B) by line 18.

The reaction effluents thus cooled are collected in zone (E) and collected by line 21. Depending on the nature of the charges treated, these effluents can, if necessary, undergo a second quenching by direct addition of cold fluid, according to a process known. The subsequent effluent treatments are part of the prior art and are outside the scope of the present invention.

- Figure 4 shows an exploded perspective of a module of the first section or pyrolysis zone (A) of the pyrolysis zone - quenching zone assembly. In this figure, for reasons of clarity, the charge distributor (C> described in FIG. 3 is not represented nor the beads (4) of turbulence on the channels. The designations used for the various elements are those of the figure 3.

In this figure, the path of the load to be treated is represented by the arrows (8); the charge enters the pyrolysis zone (A), is distributed in the plurality of unit channels (6) in the plates (10) and passes longitudinally through the pyrolysis zone (A) in these multichannels (6) to leave the zone (A) by these same multichannels in (22); these multichannels (6) continue in the quenching zone not shown in the figure, which is immediately adjacent to the zone (A). These channels (6) are shown in a configuration where the vertices of the undulations taken on two consecutive plates are in the same horizontal plane.

These vertices could also be arranged opposite one another on this same plane.

They could also be offset by half a wavelength. The path followed by the heat transfer fluid is represented by the arrows (line 9) located opposite the orifices (23); the heat transfer fluid enters (A) through the orifices (23) located in the first half of the zone (A) it is distributed in the plurality of passages (11), part of this fluid flows through these channels against the current the charge flowing in the channels (6) and leaves (A) through the orifices (24) connected to the line (12); The other part of this fluid circulates in the passages (11) co-current with the load and leaves (A) through the orifices (25).

The reactor according to the invention and in particular that which has been described above can implement an improved pyrolysis process. It is indeed possible to add to the preheated gas containing methane the effluent of a plasma torch supplied with a plasma gas as described in patent application EP 226487. It is also possible to add to the preheated gas according to this same request at least one initiating reagent chosen from the group formed by oxygen, ozone and hydrogen peroxide, in suitable proportions relative to the amount of reactive gas introduced into the reaction zone.

In these two cases, the advantages inherent in the reactor according to the invention (better selectivity, working at a lower average temperature in the pyrolysis reactor. Shorter residence times) are found to be exalted.

The following examples illustrate the invention without limiting its scope.

Exernple 1 (comparative)
The pyrolysis of a natural gas is carried out, the composition in molar percentage of which is as follows methane: 94.10 ethane: 5.04 propane: 0.74 butane: 0.12
Each volume of gas is mixed with one volume of hydrogen. This mixture is preheated to 600 "C and then cracked under the following conditions
The reactor is formed by three parallel plates 20 mm apart as shown in Figure 4.

Each plate has 5 channels with a cross section of 100 mm2 and a length of 900 mm.

The internal and external walls of the channels do not have beads. Sealed barriers are inserted in the passage between the plates so as to have a pyrolysis zone of 600 mm and an indirect quenching zone of 250 mm.

7.5 m3 / h of 50/50 mixture of natural gas and hydrogen are injected. The heat is supplied by combustion gases at 1370 "C circulating between the co-current plates and introduced 50 mm from the inlet end of the reactor. The effluent at the end of the pyrolysis zone is at 1200" C .

The quenching zone is supplied with air as the coolant. At the exit from the quenching zone, the effluent gases are at 350 "C.

The effluent gases are then cooled to room temperature. A gas phase and a liquid phase are obtained.

The coke deposited in the channels during the pyrolysis is eliminated by combustion with air circulating in the channels after having of course stopped the charge flow.

The CO2 produced makes it possible to determine the quantity of coke deposited on the internal wall of the channels.

The main products formed are acetylene, ethylene, benzene and coke.

Under the pyrolysis conditions described above, the conversion rate of natural gas is 28.6%.

For 100 moles of natural gas converted, we obtain
15.75 moles of acetylene,
11.70 moles of ethylene,
2.40 moles of benzene, and
16.30 carbon atoms.

Example 2
The same test is repeated using plates identical to that of Example 1 but having on the internal faces of the channels of the beads formed by sewing a bead of ceramic fiber of thickness such that the ratio of the section of the beads on the section of the unitary channel is 0.38 and on the external faces of the beads whose thickness represents 130% of the thickness of the beads of the internal faces.

The distance between two beads is 20 mm. The beads are distributed over the entire length of each channel. They are perpendicular to the axis of the channels.

The operating conditions are the same as those of Example 1 except for the combustion gas temperature which is 1320 "C. The effluent at the end of the pyrolysis zone is at 1170" C. The natural gas conversion rate is 29.2%. For 100 moles of natural gas converted, we obtain
14.25 moles of acetylene,
12.75 moles of ethylene,
3.30 moles of benzene, and 13.90 carbon atoms.

Claims (14)

1.- Multichannel ceramic reactor having an inlet and an outlet, comprising a first so-called pyrolysis (A) or cracking section and a second cooling section (B) comprising cooling means cooperating with the first section, the first section comprising a plurality of plates (10) substantially parallel to each other and having an inlet end and an outlet end, each of these plates comprising a plurality of channels (6) substantially parallel to each other connected to supply means ( 8) in a first gaseous fluid (a hydrocarbon feed for example) at said inlet end and to means for discharging (21) the first fluid having passed through the channels at the outlet end, each of said channels having a face internal in contact with the first fluid flowing therein and an external face, said plates were arranged in such a way that they determine at least between them a passage (11) for the circulation of a second gaseous fluid, (pyrolysis or heating fluid for example) in contact with the external face of said channels, said passage being connected at a first end to supply means (9 ) in this second gaseous fluid and at a second end to means for discharging (13) the second gaseous fluid, the means for discharging the first fluid being connected to the cooling means of the second section, said reactor being characterized in that that it comprises on at least part of at least one face of said channels, means (4) of ceramic material adapted to promote turbulence of the fluid in contact with said face. 2.- Reactor according to claim 1 wherein the first gaseous fluid is a hydrocarbon feed, the second gaseous fluid a fluid suitable for the pyrolysis of the petroleum feed and in which said turbulence means are arranged on at least part of the face internal channels in contact with the load. 3.- Reactor according to claim 1 wherein said turbulence means (4) are arranged on at least part of the internal face and on at least part of the external face of the channels (6 !. 4. Reactor according to one of claims 1 to 3 wherein the channels have an axis of symmetry, said turbulence means are arranged substantially perpendicular to the axis of the channels. 5. Reactor according to one of claims 1 to 4 wherein said turbulence means are spaced from 1 to 100 mm from each other. 6.- Reactor according to one of claims 1 to 5 wherein the section  2, 2 unit of said channels is from 9 to 900 nm, preferably from 25 to 100 mm. 7.- Reactor according to one of claims 1 to 6 wherein the plates are arranged at a distance of at least 1 min. 8. Reactor according to one of claims 1 to 7 in which the turbulence means on the internal face of said channels have a thickness such that the ratio of their section to the section of the unitary channel is between 0.1 and 0, 8. 9. Reactor according to claim 8 wherein the thickness of said turbulence means on the external face of the channels represents 30 to 500% of the thickness of the turbulence means on the internal face of the channels. 10.- Reactor according to one of claims 1 to 9 wherein said channels are juxtaposed. 11.- Reactor according to one of claims 1 to 10 wherein the second section (B) comprises a plurality of plates substantially parallel to each other, each of these plates having a plurality of channels (6) substantially parallel to each other communicating by a inlet at the outlet end of the plates of the first section (A) where the first fluid circulates, said channels (6) of the plates of the second section having an internal face and an external face, said plates of the second section being arranged in such a way that they determine between them a passage (19) for the circulation of a third so-called cooling fluid, the passage (19) of the second section being non-communicating (17) with the passage (11) of the first section and having an inlet and an outlet connected respectively to supply means (18) and to discharge means (21) of said third fluid, the reactor being characterized in that the channels (6 ) of this second section comprise, on at least part of at least one of their faces, means (4) adapted to promote the turbulence of the gaseous fluids in contact with said face, such as those defined in claims 1 to 10 . 12 - Process for manufacturing the reactor according to one of claims 1 to 10 characterized in that 1) a plurality of channel plates are produced in the following manner a) at least one extra thickness of ceramic fiber is created in a given direction on at least a part of at least one face of a first piece of fabric of ceramic fibers. b) channels are formed for example by waving this first piece of fabric by fixing it on a second piece of fabric made of ceramic material, so that the axis of said channels makes an angle of 10 to 170 with respect to the direction of the extra thickness. c) at least one means for feeding a first gaseous fluid (petroleum charge, for example) is sewn at a first end of said channels formed and at least one discharge means at a second end of said channels. d) silicon carbide is placed on the pieces of fabric thus formed under conditions such that the said fabrics are stiffened, and e) the said plates are assembled in an enclosure in such a way that the circulation passages are produced d '' a second fluid (pyrolysis fluid for example), contiguous to the channels and means for supplying the second fluid are connected to the inlet of these passages and means for discharging this fluid at the outlet of these passages 2) cooling means are connected either, at the end of the channels, or at the outlet of these passages depending on whether the channels or the passages are adapted to the circulation of the load to be treated. 13 - Process for manufacturing the reactor according to claim 12 in which a plurality of plates are produced in accordance with steps a, b, c and d, then said plates are assembled in an enclosure so that the circulation passages are produced of the second fluid, contiguous to the channels, a watertight ceramic barrier is inserted in the passages at a point such that two non-communicating parts are obtained, a first part of the passages suitable for the circulation of a pyrolysis fluid and a second part of the passages adapted to the circulation of a cooling fluid and means for supplying a first fluid (charge) are connected to the end of the channels, means for discharging the treated fluid to the other end of the channels, means for supplying the pyrolysis fluid at the inlet of the first part of the passages, means for discharging the pyrolysis fluid at the outlet of the first part of es passages, means for supplying the coolant at the inlet to the second part of the passages and means for discharging the coolant at the outlet from the second part of the passages. 14 - Use of the reactor according to one of claims 1 to 11 in a process of steam cracking of an oil charge or in a process of pyrolysis of gas containing methane.