FR2825648A1 - Supplying homogenous mixtures of different gases in very different proportions, for use in calibrating analyzers or testing exhaust catalysts, involves using static mixer - Google Patents

Abstract

The mixing chamber comprises a pipe connected to the main gas supply line, so that the gas flows along the pipe, and connected to the other gas supply lines via injectors, where the secondary gas flow is introduced into the main gas flow, and then into a static mixer in the extension to the pipe. An Independent claim is included for a device for synthesizing gaseous mixtures as above, with at least two gas supply lines, a flow regulator on each line, at least one computer-driven automatic controller to control the flow regulators and a mixing chamber into which the supply lines open. The injector is a jet injector producing an azimuthal flow effect at the periphery. The axis of the injector is at 90 deg with the axis of the pipe, an ejection end coaxial with the pipe and an azimuthal component of between 15 and 90. The static mixer has a first section forming a convergent part and then a divergent part; a second section with at least two contractions in the pipe, each obtained by radial crushing of the pipe in one direction, and out of phase with each other by 10 and 45 deg . A third section similar to the first comprises a convergence part and then a divergent part. The first and second sections of the mixer have a length of the order of an initial diameter, and each in pair of convergent then divergent parts the two parts have the same length at least a third of the initial diameter. The mixer does not have any elements protruding from the walls. The mixing chamber is surrounded by an external pipe with the injectors in the gap between the external pipe and the mixing chamber. The gases being mixed which have a risk of flammability are supplied in a different line.

Description

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DEVICE FOR SYNTHESIZING GAS MIXTURES AND
USE OF THIS DEVICE
TO TEST CATALYTIC COMPOSITIONS
The invention relates to a device for synthesizing gas mixtures that can automatically produce specific gas mixtures defined by the nature of the gases that compose them, their flow rate and the temperature.

 The gas mixture produced automatically and according to precise characteristics, both in nature of the gases, and the temperature or pressure of the mixture, is a known procedure for testing apparatuses or processes using these gas mixtures. This procedure is applied for example to test boilers or water heaters for which the gaseous mixtures used are particularly simple because they comprise only a few components.

 In other fields of application such as that of catalytic reactors for the treatment of automobile combustion exhaust gases, the gaseous mixtures to be created in order to be able to test the catalytic compositions are particularly difficult to produce, on the one hand because 'they include many different gases in very different proportions, secondly because during the operation of a motor vehicle, the composition of the exhaust gas varies significantly from one moment to another (start / deceleration or acceleration) as well as its temperature or flow rate. Gas mixing devices conventionally used to test boilers can not be used to replicate such complex mixtures as automotive exhaust. In addition, it may be important for some tests that the gas mixtures tested be perfectly homogeneous. This is the case, for example, when the gaseous mixture is passed through a catalyst pellet to be tested: if the composition of the mixture is not homogeneous, all the catalyst does not react. This homogeneity of the mixture is also important to control whether the composition of the desired gas is well obtained: this control is carried out using an analyzer whose probe is immersed in the gas mixture; a bad mix will lead to a wrong check.

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An object of the present invention is therefore to provide a mixing device for synthesizing a gas mixture comprising many different gases in very different proportions.

Another aim is to propose a device for synthesizing a gas mixture having a variable composition over time both in nature of the gases that compose it, in temperature or in total flow and specific to each gas.

Another object is to provide a mixing device for synthesizing a homogeneous gas mixture.

For these purposes, the invention relates to a device for the synthesis of gaseous mixtures comprising: at least two gas supply lines, at least two flow regulators each cooperating with the gas supply lines, at least one controller controlled by a computer for controlling the flow regulators; - a mixing chamber into which the gas supply lines open, said mixing chamber comprising: a pipe: connected to the supply gas flow line principal such that the gas forms a flow in the pipe,> connected to the secondary flow gas supply lines by at least one injector so that the secondary flow gases are introduced into the gas flow. main flow * a static mixer placed in the extension of the pipe.

The supply lines ensure the arrival of the gases to be mixed up to the mixing chamber. If certain fluids to be mixed are gaseous at ambient temperature, their supply lines are generally connected to the gas source by holders. On the other hand, if certain fluids are liquid at ambient temperature, their lines are connected to an evaporator making it possible to vaporize them and to convey them in gaseous form using a carrier gas such as nitrogen.

The evaporator is equipped with a temperature controller.

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 Supply lines are generally equipped with pneumatic and manual shut-off valves, as well as check valves and filters.

 The supply lines are equipped with flow regulators to set the values of the flow rates of the gases to be mixed. These are usually mass flow controllers. If a fluid to be mixed is liquid at room temperature and must be vaporized, flow regulators are placed both on the liquid supply line of the evaporator and on the gas supply line of the evaporator. . For these lines, it is generally expected, after the evaporator, the introduction of a conductor cord to prevent condensation of the vaporized liquid during transport. Flow controllers are controlled by a controller controlled by a computer. Thus, for each flow controller, the computer calculates the flow setpoint, reads the actual value resulting from this setpoint, opens the valve of the associated controller, checks that the measured value complies with the setpoint applied. The calculator is linked to: - instructions concerning the gas mixture to be carried out (nature of the gases, proportion, flow rate of the final mixture, temperature) and which are characteristic of the mixture to be reproduced, - databases on the properties of the gases to be mix: phase diagram, flammability risk alone or mixed.

 Depending on the instructions given, the computer controls the PLCs that control the flow controllers.

 The supply lines can be equipped with a thermal oven, controlled by the computer, for setting the temperature of the gases to be mixed; the lines are then generally thermostated.

 Several supply lines can join to form a single line, for example when it comes to lines carrying gas whose flow or temperature are close. In the case where lines meet and where the temperature of the gases must be fixed, it is then preferable to place the thermal oven on the final line in which several gases are present. However, it is preferable that gases whose mixture presents risks of flammability are introduced by different supply lines.

 The gas supply lines open into the mixing chamber, which includes a pipe and a static mixer. Supply lines are differently connected to driving according to the nature of the

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 flow rates of the gases that are conveyed there. Thus, the supply line that conveys the main flow gas (i.e. the largest flow gas) flows into the mixing chamber so that this main flow gas forms a flow in the pipe. This flow can be advantageously obtained by the introduction of the main gas tangentially in the pipe, for example by an injection pipe opening tangentially into the pipe. The secondary flow gas supply line (s) (i.e. those having a flow rate less than the main flow rate) opens (s) into the mixing chamber pipe via at least one injector so that the secondary flow gases are introduced into the flow of the main gas. Injector means a port for access to the pipe of the mixing chamber. This orifice may be located at the edge or in the middle of the pipe.

 It can be any type of injector. It preferably has a calculated form for the injection of a low flow gas. For example, it may be an injector opening in the middle of the pipe and injecting at least one secondary flow gas axially in the pipe. It may also be a jet injector having an effect to flow azimuthal (called "swirl" in English) periphery. This effect allows the creation of a turbulence promoting shear mixing. An injector whose injection axis has an angle of 900 with the axis of the pipe, a coaxial ejection end to the pipe and an azimuthal component between 15 and 900 is particularly recommended. It may for example be the injector described in the patent application EP-A-0 474 524. It may also be a plurality of jet injectors, for example arranged in the same cross section of driving in the form of a crown. Several injectors such as those mentioned above can be used simultaneously to introduce different secondary flow gases into the main flow gas stream. Thus, according to one particular embodiment of the invention: the main flow gas is introduced into the pipe by an injector opening tangentially into the pipe, part of the secondary gases (preferably oxygenated gas, if an oxygenated gas is a secondary flow gas), are injected axially in the center of the pipe, and - the other part of the secondary gases are injected by a plurality of injectors all arranged in the same cross section of the pipe in the form of a

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 crowned. These secondary gases can be premixed, the premix obtained then being introduced into the injectors placed in the form of a ring; these gases can also be introduced separately into different injectors of the ring.

 Generally, the shape of the straight sections of the injectors is circular, but it has been observed that the triangular or rhombic shapes can make it possible to obtain better mixtures.

 The mixing chamber also comprises a static mixer placed in the extension of the pipe, that is to say after the injector connected to the secondary flow gas supply lines in the direction of gas flow. This combination of a static mixer and the pipe makes it possible to achieve the goal set by the present invention when none of these latter devices taken separately allowed it.

 According to the preferred embodiment of the invention, the static mixer present downstream of the injector is a pipe consisting successively of: a first section consisting of at least one concatenation of a convergent part and then of a divergent part the pipe, then - a second section comprising at least two successive radial deformations of the pipe, each deformation. creating a continuous tightening and loosening of the pipe, and. being obtained by radially crushing a straight section of the pipe between two parallel straight lines tangential to the section of the pipe, and the successive deformations being offset relative to each other by an angle of between 10 and 45, then - a third section consisting of at least one concatenation of a convergent part then of a divergent part.

 In the remainder of the description, initial diameter is understood to mean the diameter of the pipe at the beginning of the first section, if this pipe is round.

 In general, the sequences of a convergent part and of a diverging part in the first section of the static mixer have a length of the order of an initial diameter, a length corresponding to the part of the pipe between two points where it has a diameter equal to the initial diameter and between which it converges and diverges. The two convergent and divergent parts generally have the same length. The diameter

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 The minimum of these sequences of convergent and divergent portions at the most convergent point of the pipe is usually at least one-third of the original diameter value. In the third section of the static mixer, the same rules are applied to the convergent part and divergent part sequences as for the first section. In the same first or third section, the static mixer may comprise several successive sequences of a convergent portion and a divergent portion. This is for example the case when it is desired to mix fluids having a low Reynolds number.

In the second section, each deformation leads to a pipe having in the cross-section of the crushing a section of ellipsoidal shape (if the pipe at the beginning of the second section is round). Two successive deformations must be offset relative to each other by an angle between
10 and 45, preferably between 25 and 450, this angle corresponding to the angle formed between the directions of the crushing lines of each deformation. The number of tightenings must be adapted to the nature of each mixture of fluids and to the subsequent use of the mixture, considering the fact that the greater the number of tightenings, the greater the pressure drop of the mixed fluids.

 In general, a tightening is carried out so that the minimum diameter of the pipe at the cross-section of the crushing is at least one third of the value of the initial diameter. The length of a tightening may be for example of the order of the initial diameter.

 Preferably, the static mixer does not comprise an element forming an intrusion into its wall and penetrating into its pipe (such as fins) to form an obstacle to the passage of fluids, especially if the mixer makes it possible to treat fluids containing dust which may be deposited on these intrusive elements, or if the mixer can treat fluids whose temperature is desired to control, or if the mixer must treat corrosive gases.

 The device according to the invention makes it possible to mix gases having flow rates of between 10 l / min and 800 l / min and main / secondary flow ratios of between 1 and 50. These flow rates can change over time to values such that the value of the total flow decreases or increases by 30%.

It was found that a perfectly homogeneous mixture of different fluids could be obtained regardless of the value of these flows. The quality control of the mixture is carried out using a probe analyzing, at the end of the pipe, the

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 composition of the gas mixture along the entire length of a diameter of the pipe. By perfectly homogeneous mixing is therefore meant a mixture for which the composition is identical over the entire length of this diameter.

 According to a variant, the assembly of the pipe and the static mixer may be surrounded by an external pipe having means for injecting a fluid into the interstice delimited by this external pipe and the outer wall of the pipe chamber. mixed. The fluid is injected into this gap against the current of the fluids to be mixed. The countercurrent fluid is generally an inert gas, preferably nitrogen. The temperature of this fluid corresponds to that at which it is desired to maintain the gas mixture. This variant using an inert gas to counteract the fluids to be treated makes it possible to regulate the temperature of the gases during mixing effectively. The temperature can be maintained or changed very quickly; thus, this implementation makes it possible to vary the temperature of +/- 5 C per second for a temperature range between 60 and 600 C.

 The present invention also relates to the use of the preceding device for testing catalytic compositions. This device makes it possible to produce gaseous mixtures representative of industrial applications and which are subjected to catalytic treatments. The mixture at will of these gases makes it possible to test catalytic compositions.

 In this context, the invention relates more particularly to a device for testing catalytic compositions using reactions with gas mixtures comprising: at least two gas supply lines, at least two flow regulators each cooperating with gas supply lines, - at least one controller controlled by a computer for controlling the flow rate regulators, - a mixing chamber in which the gas supply lines open, said mixing chamber comprising: a pipe:> connected to the main flow gas supply line so that this gas forms a flow in the pipe,

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 connected to the secondary flow gas supply lines by at least one injector so that the secondary flow gases are introduced into the flow of the main flow gas, a static mixer placed in the extension of the pipe an analyzer placed at the outlet of the mixing chamber; a reaction chamber comprising means for contacting the gas mixture with the catalyst to be tested; an analyzer for the gas mixture leaving the reaction chamber.

 The test device corresponds to the previously described mixing device to which is added: a first gas analyzer making it possible to control the nature of the gas mixture at the outlet of the mixing chamber; a reaction chamber in which the catalyst to be tested is brought into contact with the gas mixture produced in the mixing chamber; - a second gas analyzer making it possible to control the nature of the gas mixture at the outlet of the reaction chamber in order to analyze the effectiveness of the catalyst tested; in comparison with the nature of the gas mixture at the outlet of the mixing chamber.

 In a preferred embodiment, the gas mixture analyzer leaving the mixing chamber and the computer controlling the controller that controls the flow regulators are coupled so as to adjust the composition of the gas mixture. This coupling makes it possible to avoid drifts due for example to the clogging of the device.

 The catalytic composition test device may in particular be used to simulate an automobile engine exhaust gas composition and to test various depolluting catalysts.

 The present invention finally relates to the use of the preceding device for calibrating analyzers. This device makes it possible to produce gaseous mixtures, to subject these gaseous mixtures to precise catalytic treatments, the exact result of which is known on gaseous mixtures. By controlling the gas mixture compositions before and after catalytic treatment with analyzers, it is therefore possible to calibrate the analyzers.

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 Figures 1 and 2 illustrate the mixing chamber of the device according to the invention. In these figures, a linear duct (1) with a diameter of 60 mm, one end of which is closed, is recognized. At the closed end of this pipe (1), a pipe (2) of diameter 10 mm and tangent to the pipe (1) penetrates tangentially into the pipe (1). The main flow fluid is injected through this conduit (2). In addition, at this closed end of the pipe (1), a pipe (3) penetrates axially into the pipe (1). The end of this duct (3), which enters the pipe (1), is pierced with a hole (4) for the injection of a secondary fluid axially to the pipe (1) via a pipe (41) . At this same end of the duct (3), the duct (3) is also radially pierced with 8 holes (5) of diameter 4 mm for the injection of secondary fluids, mixed or separately, radially in the pipe (1).

 The pipe (1) continues with a static mixer composed of: - a first section, 60 mm long, consisting of a converging section (6) passing from an initial diameter of 60 mm to a minimum diameter of 20 mm and a diverging section (7) passing from the minimum diameter of 20 mm to a maximum diameter of 60 mm, - a second section consisting of: a first portion of length 60 mm comprising a radial deformation (8) of minimum section 20 mm, and. a second portion of length 60 mm comprising a radial deformation (9) of minimum diameter 20 mm, this second deformation being obtained by crushing the cross section of the pipe between two parallel straight lines whose direction makes an angle of 450 with the direction of the two parallel straight lines leading to the first deformation, - a third section consisting of a converging section (10) passing from an initial diameter of 60 mm to a minimum diameter of 20 mm and a diverging section (11). ) from a minimum diameter of 20 mm to a maximum diameter of 60 mm.

Example

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The device of the invention is used to reproduce a time varying automobile combustion exhaust gas mixture. The desired mixture must have the following composition and flow rate characteristics:

<Tb>
<tb> Product <SEP> bit rate <SEP> minimum <SEP> (llmin) <SEP> rate <SEP> maximum <SEP> (limine)
<tb> N2 <SEP> of <SEP> flow <SEP> main <SEP> 10 <SEP> 500
<tb> 02 <SEP> 0, <SEP> 1 <SEP> 100
<tb> CO <SEP> 0, <SEP> 25 <SEP> 12, <SEP> 5
<tb> H2 <SEP> 0, <SEP> 25 <SEP> 12, <SEP> 5
<tb> CO2 <SEP> 0, <SEP> 5 <SEP> 100
<tb> S020, <SEP> 0010, <SEP> 005
<tb> N2 <SEP> of <SEP> debit <SEP> secondary <SEP> 0, <SEP> 009 <SEP> 0, <SEP> 045
<tb> NO <SEP> 0, <SEP> 005 <SEP> 0, <SEP> 125
<tb> N02 <SEP> 0, <SEP> 005 <SEP> 0, <SEP> 125
<tb> NH3 <SEP> 0, <SEP> 01 <SEP> 0, <SEP> 2
<tb> H20 <SEP> 0, <SEP> 5 <SEP> 15
<tb> CH4 <SEP> 0, <SEP> 001 <SEP> 5
<tb> C3Ha <SEP> 0, <SEP> 00025 <SEP> 1, <SEP> 25
<tb> C3H6 <SEP> 0, <SEP> 00075 <SEP> 3, <SEP> 75
<tb> C7Ha <SEP> 0, <SEP> 001 <SEP> 5
<tb> C1oH22 <SEP> 0, <SEP> 001 <SEP> 5
<Tb>

These flow variations are performed according to a defined motor cycle.

 In order to be mixed in gaseous form, the liquid hydrocarbons and H 2 O are each vaporized at a temperature of 300 ° C. in a stream of nitrogen. The flow rate of each of the currents obtained is controlled by a flow regulator, then these streams are mixed in an isolated common supply line so as to avoid condensation of the vaporized products. This line joins two other supply lines: that of the main flow nitrogen and that of S02 and CO2, which forms the main supply line, which enters the mixing chamber of Figure 1 by the duct ( 2). This is the main flow gas.

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 The oxygen enters the mixing chamber of Figure 1 through the hole (4) of the conduit (3) (secondary flow).

The gaseous products CO, H2, NH3, the gaseous hydrocarbons, the secondary flow nitrogen are introduced through the same supply line into the conduit (3) through four of the holes (5) of the conduit (3) (secondary flow). )
NO is introduced by the other four holes (5) of the duct (3) (secondary flow).

 The different supply lines for products to be mixed are all equipped with flow controllers controlled by PLCs. The controllers are controlled by a computer programmed to implement the composition and flow rates of the table above to reproduce the engine cycle.

 The control of the homogeneity of the mixture is carried out using an analysis sampling probe placed at the output of the dynamic mixer and analyzing at this point the composition of the fluid over the entire length of the diameter of the dynamic mixer. During the production of this mixture of variable composition over time, it is found that at any time the mixture obtained is homogeneous, that is to say that the composition of the mixture is identical over the entire length of a diameter. .

Claims (15)

 1. Device for synthesizing gaseous mixtures comprising: - at least two gas supply lines, - at least two flow regulators each cooperating with the gas supply lines, - at least one controller controlled by a computer for controlling the flow regulators; - a mixing chamber into which the gas supply lines open, said mixing chamber comprising: * a pipe:> connected to the main flow gas supply line so that this gas forms a flow in the pipe,> connected to the secondary flow gas supply lines by at least one injector so that the secondary flow gases are introduced into the flow of the main flow gas, a static mixer placed in the extension of the pipe. 2. Device according to claim 1, characterized in that the injector is a jet injector having an azimuthal flow effect at the periphery. 3. Device according to claim 2, characterized in that the axis of the injector has an angle of 90 with the axis of the pipe, a coaxial ejection end to the pipe and an azimuthal component between 15 and 90 4. Device according to any one of the preceding claims, characterized in that the static mixer is a pipe successively consisting of: - a first section consisting of a convergent portion and a divergent portion, and - a second section comprising at least two constrictions of the pipe, each constriction being obtained by radially crushing the pipe in one direction, and <Desc / Clms Page number 13>  . said constrictions being offset relative to each other by an angle of between 10 and 45, then - a third section consisting of at least one concatenation of a converging part and then of a diverging part. 5. Device according to claim 4, characterized in that the first and second sections of the static mixer have a length of the order of an initial diameter, this length corresponding to the portion of the pipe between two points where it has a diameter equal to the initial diameter and between which it converges then diverges. 6. Device according to one of claims 4 or 5, characterized in that the two parts converging and diverging of a sequence of a convergent portion and a divergent portion of the pipe have the same length. 7. Device according to one of claims 4 to 6, characterized in that the minimum diameter of a concatenation of a convergent portion and a divergent portion of the pipe at the most convergent point of this sequence is to at least one third of the value of the initial diameter. 8. Device according to any one of the preceding claims, characterized in that the static mixer has no element forming an intrusion into its wall. 9. Device according to any one of the preceding claims, characterized in that the mixing chamber is surrounded by an outer pipe having means for injecting a fluid into the gap defined by this outer pipe and the wall. external mixing chamber. 10. Device according to any one of the preceding claims, characterized in that the gases whose mixture presents risks of flammability are introduced by different supply lines. <Desc / Clms Page number 14> 11. Use of the device according to any one of claims 1 to 10 for testing catalytic compositions.  12. Use of the device according to any one of claims 1 to 10 for the simulation of a motor vehicle exhaust gas composition. 13. A device for testing catalytic compositions employing reactions with gas mixtures comprising: at least two gas supply lines, at least two flow regulators each cooperating with the gas supply lines, at least one controller controlled by a computer for controlling the flow regulators; - a mixing chamber into which the gas supply lines open, said mixing chamber comprising: a pipe: connected to the supply line of the main flow gas so that this gas forms a flow in the pipe, connected to the secondary flow gas supply lines by at least one injector so that the secondary flow gases are introduced into the flow main flow gas, * a static mixer placed in the extension of the pipe, - an analyzer - a reaction chamber comprising m means for contacting the gas mixture with the catalyst to be tested.  an analyzer of the gas mixture leaving the reaction chamber. 14. Device according to the preceding claim, characterized in that the gas mixture analyzer leaving the mixing chamber and the computer controlling the controller that controls the flow regulators are coupled to adjust the composition of the gas mixture. . 15. Use of the device according to claim 13 or 14 for calibrating the analyzers.