FR2458308A1 - PROCESS AND INSTALLATION FOR REMOVING OXIDABLE COMPONENTS OR POLLUTANTS FROM GASES, IN PARTICULAR AIR - Google Patents

Abstract

PROCESS FOR REMOVING OXIDIZABLE COMPONENTS IN GASES AND IN PARTICULAR IN AIR. SOLID AND IN PARTICULAR GASEOUS OXIDIZABLE COMPONENTS ARE REMOVED FROM THE AIR BY TREATMENT OF THE GAS THROUGH A BED OF ADSORBENT CAPABLE OF ACTING THE ROLE OF OXIDIZATION CATALYST AT HIGH TEMPERATURE, THIS ADSORBENT-CATALYZER AT EVERY TIME. SUITABLE BY RAISING THE TEMPERATURE TO A SUITABLE VALUE TO PERFORM CATALYTIC OXIDATION, THAT IS FROM 250 TO 350C. A PARTICULARLY INTERESTING ADSORBANT-CATALYST CONSISTS OF ALUMINA IMPREGNATED WITH COPPER CHROMITE. THIS METHOD IS INTERESTING IN THAT IT IS NOT NECESSARY TO HEAT THE HEATED AIR DURING NORMAL OPERATION BUT ONLY HEAT IS NEEDED TO BE PROVIDED, AT THE MOST DURING REGENERATION. A SIMPLE INSTALLATION FOR IMPLEMENTING SUCH A METHOD INCLUDES A REACTOR FILLED WITH ADSORBANT-CATALYST, A SUPPLY DUCT INTRODUCING THE AIR TO BE PURIFIED AND A COMBUSTION CHAMBER THAT CAN BE USED FOR REGENERATION AND POST-PURIFICATION SECTION WHICH CAN BE USED. REGENERATION SINCE THE AIR LEAVING THE REACTOR DURING REGENERATION MAY BE TOO POLLUTION TO BE ELIMINATED BY A CHIMNEY. IN ANOTHER MORE COMPLICATED BUT ADVANTAGEOUS IMPLEMENTATION, THE INSTALLATION INCLUDES SEVERAL REACTORS FILLED WITH ADSORBANT-CATALYST AND A CONTINUOUS REGENERATION TAKES PLACE IN ONE OF THE REACTORS, WHILE ADSORPTION IS CARRIED OUT IN THE OTHERS. SUCH AN INSTALLATION MAY OPERATE AUTOTHERMALLY OR EVEN EXOTHERMALLY, AND IN A MANNER TO PROVIDE USEABLE HEAT.

Description

METHOD AND INSTALLATION FOR REMOVING COMPONENTS OR POLLUTANTS

OXIDIZABLE

GAS AND IN PARTICULAR AIR.

  The present invention relates to a method for removing the oxidizable and particularly gaseous pollutant components contained in the currents

  gaseous and especially in the air.

  During the production processes of a great many

  sorting, such as printing works, dye or paint factories,

  food processing plants, processing plants

  chemicals and a large number of small workshops, it is clear that

  oxidizable volatile substances and gases; these products may be malodorous

  flammable and / or toxic. These substances are removed with air and, for economic reasons, are usually discharged directly

  in the atmosphere without prior purification.

  More and more severe recommendations and growing demands

  from the public, however, make it increasingly necessary to

  such drafts, even in cases where this was not required before. Purification of such drafts was expensive and

  technical problems because it involves dealing with large quantities of

  dyeing 100,000 Nm3 / h, which usually contains small quantities,

  less than about 1.6 g / Nm3 of substances to be removed.

  Known methods for purifying such streams of air can be broadly divided into four categories: - washing, adsorption, - thermal oxidation, and

- catalytic oxidation.

  Washing is done with water, often with chemicals that react with unwanted substances in the air stream. The disadvantage of such methods is, apart from their high price, the real problem of rendering the substances harmless.

  undesirable effects, is only partially solved since they are simply

transferred to water.

- - 245850B

  The adsorption is more generally carried out using active carbon.

  The biggest problem of this method is that the regeneration of the active carbon, necessary to make this process valid from the economic point of view,

  can not be done quite satisfactorily.

  Indeed, this regeneration must be carried out in an atmosphere without

  of oxygen, which is usually an atmosphere of superheated steam.

  Carbon must be freed from substances that tend to form

  polymerization products that clog the pores of carbon particles.

  Partial removal of these polymerization products can be achieved

  maintaining temperatures between 700 and 8000C in an atmosphere of

  Although oxygen-free, but at such temperatures, active carbon decomposition is observed. Other adsorbents, such as molecular sieves and refractory ceramic oxides, for example alumina, Al 2 O 3, can also be used. However, molecular sieves

  are considerably more expensive than the active carbon, and the

  The refractory properties offer a lower absorption capacity than active carbon. Such incombustible adsorbents are interesting in

  that they can be regenerated with air.

  Thermal oxidation is remarkable in that it is relatively simple and safe. However, it requires heating large quantities

  of air at a temperature between 700 and 800 ° C in a chamber

  bustion, which requires large amounts of energy. The air is general-

  heated by direct combustion with oil or possibly gas. Although it is possible to use some of the heat present in

  large amounts of air, this method remains expensive.

  Catalytic oxidation is distinguished from thermal oxidation in that oxidation does not take place in a combustion chamber but in a catalyst bed. The advantage of this process is that the catalytic oxidation takes place at a temperature between 250 and 3500C, so that the consumption

  energy is greatly reduced.

  The disadvantage of such catalytic oxidation is that certain types of catalysts are poisoned when they come in contact with certain

  substances such as H2S hydrogen sulfide and SO2 sulfur dioxide.

  It is particularly important to note that although the energy consumption required by catalytic oxidation is much lower than that required for thermal oxidation, it is still

  considerable when large air masses need to be heated.

  Given the small amounts of impurities indicated, the oxidation thereof is not sufficient to provide the amount of energy required

  t; 40 to the heating of the air masses.

  The present invention aims to overcome the drawbacks inherent in the known methods or to reduce them, and to provide a process for effectively purifying gases and air containing oxidizable pollutants, at the cost of significantly reduced energy consumption. compared to what is required for known catalytic and thermal oxidation processes. For this, (a) the gas is sent to a decontamination step between 0 ° and 250 ° C. through a bed of particulate absorbent having a large specific inner surface impregnated with an active material at elevated temperature, such as oxidation catalyst; and (b) intermittently regenerating this oxidizing catalyst adsorbent by raising the temperature to a value between 250 and 3500C to initiate catalytic oxidation of the accumulated contaminants on

and in the adsorbent-catalyst.

  This method is therefore particularly advantageous in that it makes it possible to treat the polluted air at its actual temperature and to send it to the stage

treatment without preheating.

  Most of the air masses to be purified thus passes through the adsorbent acting as high temperature oxidation catalyst

  for simplicity, this catalyst is hereinafter referred to as adsorbentcata-

  lyser - at the formation temperature, or perhaps at a slightly lower temperature given the heat loss, so that no energy is used to heat it. Optionally, the heat of the gases can be exploited before adsorption by passing them through a heat exchanger. During the passage, the polluting substances or most of them are adsorbed on the adsorbent-catalyst and

  the highly purified air can be released into the atmosphere.

  As the adsorbent-catalyst becomes more and more saturated with impure-

  a small part of these can be released into the atmosphere;

  when the concentration of undesirable substances has reached the maximum value

  If allowed or acceptable, the adsorbent-catalyst is regenerated by increasing the temperature so as to cause catalytic oxidation, generally between 250 and 350 ° C, at which temperature the oxidation of the contaminants present on the adsorbent-catalyst begins; during this step,

  the temperature can increase further.

  It is therefore necessary to provide heat only in the periods

  regeneration. In some cases it is possible to start the

  apart from being able to work practically without any

  their, or even to obtain a thermal gain, as it is explained more

far in the description.

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  As an adsorbent-catalyst, according to the invention, a porous ceramic support having a large specific internal surface (70 to 250 m 2 / g, and preferably 100 to 200 m 2 / g) is used. impregnated with a substance serving as a high temperature oxidation catalyst. The porous support itself plays the role of adsorbent but little or no that of oxidation catalyst. A variety of ceramic materials are particularly suitable for this purpose, such as oxides, in particular elements of groups II, III and IV of the Periodic Table. Such suitable materials are for example

  aluminum oxide, A1203, subsequently referred to as alumina, magnesium spinel

  sium aluminum, MgAl204, and silicon dioxide called silica.

  It has been found that gamma alumina is particularly suitable, but that also oxides of titanium and zirconium and similar ceramic oxides can be used. The support may comprise a mixture of

  two or more of these materials.

  The support, as described above, is advantageously impregnated with a

  material that acts as a high temperature oxidation catalyst.

  Such a material is, for example, a Group VIII metal of the Periodic Table (as described in "Handbook of Chemistry and Physics, 53rd Edition, 1972-73) and its compounds, in particular oxides and, especially, Other suitable materials are, for example, copper and the elements of groups Vb, VIb, and VIIb and their oxides, especially the oxides of copper, chromium, manganese,

of iron, vanadium and cerium.

  The indicated catalysts exhibit excellent catalytic activity and support the regeneration well. Surprisingly, however, it has been found that copper chromite, CuO, Cr 2 O 3, combines a high absorption capacity for the oxidizable polluting components of the air in question, with a high activity as a catalyst for oxidation. According to the invention, therefore, an adsorbent-catalyst comprising

  y-alumina impregnated with copper chromite.

  This adsorbent-catalyst is particularly advantageous in that it can adsorb large amounts of polymerizable compounds such as, for example, styrene. Many polluting compounds such as styrene,

  undergo partial polymerization after adsorption on this adsorbent.

  catalyst and copper chromite is able to accelerate this polymer

  authorization. Such polymerization helps to increase the adsorptivity

  tion and thus prolong the adsorption periods between the regenerations.

  When the adsorbent-catalyst acting as adsorbent is about to be saturated with impurities, which is easily realized that the purification becomes less efficient, the temperature is high to cause catalytic oxidation adsorbed impurities. The fact that some of the adsorbed substances could have been polymerized does not make the

difficult regeneration.

  During the regeneration, the temperature can be brought to a value of preferably between 250 and 350 ° C in a convenient manner. It is therefore possible to recycle hot gas from the regeneration or to directly add heat to the adsorbent-catalyst bed, for example by means of an electric heating element; but, in general, it is more practical to have upstream of the bed (with respect to the direction of flow of the polluted air) a

  combustion chamber supplied for example by oil or gas.

  The air leaving the adsorbent-catalyst bed during regeneration generally contains the undesirable compounds, unlike the air that leaves this bed during adsorption. According to the invention, it may be practical to subject this air to a post-purification. This postpurification can be carried out according to any of the main methods described

  above, that is, washing, adsorption, thermal oxidation or catalytic

  chosen, depending on the undesirable substances leaving the peni-

  regeneration. If these substances are oxidizable, it is more

  according to the invention that the post-purification is carried out by an oxy-

  catalytic dation. It is then possible to use another catalyst than that which serves as adsorbent-catalyst, but to make the installation and the

  as simple as possible, it is more

  to use the same catalyst as the adsorbent-catalyst used in the adsorption. It is advantageous to carry out the postpurification by catalytic oxidation because, under certain circumstances, the process can be carried out in an installation that consumes no energy from the outside, apart from that which is in the air to be purified, and

  which can even produce usable heat.

  The invention also describes an installation for implementing the above method. According to the invention, this installation comprises at least one reactor packed with an adsorbent bed acting as an oxidation catalyst at high temperature, a feed duct for introducing the gas to be treated, and in particular the air to purify in this reactor, a release duct for discharging the decontaminated gas (air) from the reactor,

  and means for performing intermittent regeneration of this adsorbent

  catalyst placed in the reactor. Optionally, the installation can be

  put means to achieve the post-purification of the gas (air) leaving the

  reactor during regeneration.

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  The periodic regeneration of the adsorbent-catalyst is preferably carried out in a combustion chamber associated with a burner, arranged

in the supply duct.

  According to the invention, the post-purification of the gas leaving the reactor

  the regeneration of the adsorbent-catalyst is preferably carried out in a second combustion chamber provided with a burner, disposed in a bypass of the discharge pipe and connected to a second reactor filled with

of oxidation catalyst.

  The post-purified air exiting the post-purification reactor may be either recycled to the vent or sent separately to a stack. Under certain circumstances, a part of it may be sent to the reactor comprising the adsorbent-catalyst. This is true when using a particularly advantageous system, implementing a plant comprising several reactors packed adsorbant catalyst and that we work so that one of the reactors is always

  in the regeneration stage, while the others adsorb impurities.

  Such an implementation is particularly interesting when the content

  organic material is greater than about 0.5 g / m 3 of hot gas,

  that it makes possible the use of the calorific value represented by the oxidizable substances to ensure heating, for example, so that the entire installation can become autothermic, or even

  exothermic. This is further illustrated later and such a facility

  according to the invention advantageously comprises at least two primary reaction chambers, each provided with an adsorbent-catalyst bed such as

  defined here, these reaction chambers being connected in parallel with a

  supply feed for the gas to be purified; a conduit from this supply line to a post-purification section; parallel vent lines from each of the reactors

  primary; parallel pipelines from each of the primary reactors

  mayors and going to the post-purification section; the post-section

  purification comprising a combustion chamber connected to a burner, a duct going from this combustion chamber to a secondary reactor filled with an oxidation catalyst bed and a release duct leaving

  this secondary reactor; this release duct leaving the secondary reactor

  The first branch includes a first bypass to remove the gases, a second bypass which is a recycle line from the combustion chamber to the secondary reactor and a third group of bypass to the primary reactors.

  Other advantages and features of the present invention are

  reading the following description and examples given

illustrative but non-limiting.

  Figures 1 and 2 are flow diagrams of two different implementations of an installation according to the invention allowing the realization of

  the process according to the invention.

  Figure 3 shows an experimental apparatus in which certain experiments are carried out to illustrate the process according to the invention; and Figures 4 and 5 are curves illustrating the results of such

experiences.

  In the installation illustrated in FIG. 1 (in which the auxiliary details such as pumps, valves and control means have been eliminated for clarity), the polluted air enters via a duct 10 into the unit of

  purification and passes through a chamber 12 connected to a burner 14.

  Most of the time, i.e., when the undesirable substances are adsorbed on the adsorbent, the burner 14 is not in operation and is only actuated when the adsorbent is to be regenerated. Then, the air enters a reaction chamber 16 in which there is an adsorbent-catalyst 18. The manner in which the adsorbent-catalyst 18

  is placed does not constitute a part of the invention.

  However, it is always advantageous to arrange it so that the

  pressure drop in the reactor 16 is as low as possible.

  The air flow then leaves the reaction chamber 16 through the pipe which divides in two: namely a pipe 22 going to a chimney and a

  pipe 30 leading to a post-purification section. The means

  10-22 are those which are necessary for carrying out the process according to the invention. During normal operation, that is to say during adsorption, the purified gas passes directly from the reactor 16 through the ducts 20 and 22 to a chimney. During the regeneration, the burner 14 is actuated and the air entering the chamber 12 is heated, preferably at a temperature of between 250 and 450 ° C., so that the adsorbent-catalyst bed 18 consisting of Preferably porous elements of y-alumina impregnated with copper chromite, exerts an oxidizing catalytic activity, and burns adsorbed oxidizable impurities. During this operation, the air exiting the reactor 16 can also be sent to the chimney via the conduits 20. and 22 but it is preferable to direct these air currents through the conduit 30 to the post-purification section, the stream of purified air exits through a conduit 40 to a conduit 42 opening into the conduit

22 or the chimney.

  The post-purification shown in FIG. 1 is carried out by catalytic oxidation. The stream of air is heated directly in a combustion chamber 32 with the aid of the burner 34 to the desired temperature, then sent to a reaction chamber 36 packed with a catalyst 38. With the help of this catalyst of oxidation 38, undesired components of the air are removed to the required level. The oxidation catalyst 38 placed in the reaction chamber 36 can be chosen independently of the adsorbent-catalyst 18 located

  in reactor 16, but in practice it is quite interesting to use

  to use the same adsorbent-catalyst comprising copper chromite / alumina,

  in the reactor 16 and in the reaction chamber 36.

  An encrypted Example, which is provided in Example 1 below, further illustrates the mode of action of the invention in an installation such as

shown in Figure 1.

  Another implementation of the installation is shown in Figure 2 which is also very simplified: a number of details, such as blowers, pumps, valves, and control devices, have been completely omitted since they have not no direct connection in the invention and that their

  use and their operation are obvious to the specialist.

  The polluted air enters the installation via a pipe 10, which is

  is aimed between two conduits 42 and 44. A small amount of air passes through the conduit 42 to the post-purification section. The largest part in line 44 takes the derivations 461, 4611, and so on. from

  to several reactors containing adsorbent-catalyst 18.

  The plant illustrated in the drawing comprises six reactors called: 48, 48, 48, 48, 48, and 48. The number of reactors determines the length of the regeneration period with respect to the length of the adsorption period in the reactors. reactors. The number of reactors 461, etc., depends, for example, on the amount of air to be treated and its degree of pollution. The purified air leaves the reactors via conduits 501, 501, etc., which

  join a common conduit 22 which directs the purified air to a chimney.

  In practical operation, five reactors are still in phase

  adsorption and a reactor is subjected to regeneration.

  The air used for the regeneration is conveyed to the reactors 48I, etc., from a conduit 52 provided with branches 541, 5411, etc. going to separate reactors. A series of other conduits 561, 5611, etc. drives the air from the reactors in a common duct 58 which directs the air towards a

post-purification section.

  From the duct 58, the air leaving a reactor in which the adsorbent

  bant-catalyst 18 is regenerated, flows into a combustion chamber 60 disposed in the conduit 58 and is connected to a burner 62; these two elements normally function only when the installation is started and, during normal operation, the air passes directly through them without there being

  heating. From the combustion chamber 60, which is therefore in normal operation

  and simply a member of the conduit 58, the air flows through the remainder of the conduit 58 to a junction point 64 in which a desired amount of hot recirculating air is added through the conduit 66. In this way, a flow of inlet having the temperature is obtained in a duct 68

  required for a reaction chamber 76 containing an oxidation catalyst.

  The purified air stream is led from the chamber 76 to a conduit 70 at the junction 72. Before reaching this point, a portion of the recycle stream

  takes the conduit 66 and another part takes the conduit 74.

  The purified stream of air from the chamber 76 has a considerable temperature (400 to 500 ° C), so that the portion of gas leaving the system

  through conduit 74 can generally be used to effect heating.

  At the junction 72, the hot purified air is mixed with the polluted air from

  duct 42 and forms the stream of air that takes the duct 52 and goes

  to one of the reactors 481, etc. used during the regeneration.

  The installation shown in Figure 2 is particularly interesting.

  in that the burner 62 is used only when the system is started. During normal industrial operation, there is therefore no

  energy consumption in the burner, nor anywhere else.

  On the contrary, it is possible to use in the installation the calorific value of the substances present in the polluted air since the heat in the air stream 72 is generally used, either in the form of air

  hot for steamers, or to heat water.

  The conduit 66 of the recycling, moreover, is of particular interest. If it did not exist, the temperature in the reaction chamber (o the catalyst

  may be an oxidation catalyst and conveniently the same as the adsorbent

  catalyst 18), would vary greatly and in a complex manner, as described below. By appropriately controlling the amount of recycle air in line 66 and the amount of air going into the reactor to be regenerated, for example 48II, the temperature in reaction chamber 76 can be kept relatively constant, one side is interesting about the use of air in duct 74 serving

  heating and, on the other hand, may be important for the catalyst.

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  Indeed, certain catalysts and in particular the supports, can undergo sintering or their activity can decrease if the temperature rises beyond a level threshold too high; but this can be effectively prevented by the regulation of the recycled amount. Moreover, the post-purification carried out in the chamber 76 may become insufficient if the temperature becomes too low, in this case it is also possible to control the

amount of recycled air.

  An encrypted example illustrates the operation of the installation of the

  Figure 2 and is provided in Example 2 below.

  Figure 3 depicts a small pilot unit in which some

  none are done with polluted air. The atmospheric air is sent into the installation via a duct 90. The quantity of air is determined by a flow meter 78 and is controlled by means of a valve 80. The leaving air

  the flow meter takes a duct 82 to a cylindrical preheating element

  drique 84 comprising an electric coil. By controlling this coil, it is possible to adjust the temperature to a required value, heated air leaving the system through the conduit 10. A conduit 88 directs a polluting liquid to a pump 92 which, via a conduit 94, sends the liquid in the conduit 10 in which there is evaporation. The conduit 19 conveys the air, now polluted to a reactor 16. In the upper part of the reactor, there is a heating coil 96, which allows

  a temperature adjustment of the polluted gas. In the lower part

  the reactor is an adsorbent-catalyst 18 placed in a cylindrical bed 18 450 mm in height and 73 mm in diameter, corresponding

  to the inner diameter of the reactor. In the axis of the bed is a thermal well.

  mic 98 crossing the bed from top to bottom. In this heat sink, we dis-

  provides a thermoelement mbbile to know the temperature at various depths of the catalyst bed. The stream leaving the catalyst bed is discharged from this reactor via line 20. A conduit 22 and a valve

  control 100 allow to direct a part of the current towards a sec-

  analysis in a continuous hydrocarbon analyzer.

  This hydrocarbon analyzer is a flame ionization analyzer of the

  type "Beckmann Model 400 Hydrocarbon Analyzer".

  The present invention will be better understood by means of the

  following examples given for illustrative purposes.

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EXAMPLE 1 This example illustrates the purification plant of FIG.

  used to decontaminate off-gas from the styrene-containing polymer preparation. In the reaction chamber 16, there are 22 m 3 of particulate adsorbent having a size of 3 to 6 mm.

  The adsorbent comprises γ-alumina impregnated with 20% CuO, Cr 2 O 3.

  The amount of catalyst in the reactor 36 depends on the volume of air during

  regeneration. In this example, it is stipulated that it is possible to reduce

  reduce the volume of air to 10 to 20% of the volume during normal operation.

  In this way, the volume of catalyst in the reactor 36 is reduced to 3 m 3.

  The catalyst is identical to the adsorbent-catalyst 18 located in the reactor 16: 45 000 Nm3 / h are sent to the purification plant of a release gas having a styrene content of 0.25 g / Nm3. The styrene content in the decontaminated gas released from the stack gradually increases with time from an initial value close to zero. After operation

  about 40 hours, the styrene content of the decontaminant gas reached

  Viron 10 mg / Nm3. At this time, about 20g of styrene was adsorbed per kg

  adsorbent. Regeneration usually takes 2 to 3 hours.

  The adsorbed styrene has a certain calorific value, which causes

  the increase of the temperature of the adsorbent during the regeneration.

  In extreme cases, the temperature may be so high that the adsorbent has adsorption properties, for example, a loss of specific surface area, and / or loss of its catalytic properties, for example as a result of sintering. Effective regeneration can be achieved to ensure adsorbent temperature below 850OC, by reducing the volume of

  air at 6,000 Nm3 / hour. The air stream is sent into the post-section

  The temperature in the combustion chamber 12 is maintained at 2500 ° C. by means of the burner 14. After 45 minutes, the volume of air

  is raised to 10,000 Nm3 / h, and the temperature is raised to 270C.

  After another 45 minutes, the burner 14 is stopped and the volume of air is raised to 20,000 Nm 3 / h. 45 minutes later, regeneration can be considered complete. The volume of the air is increased to 45,000 Nm3 / hour,

  and this air is directed by the ducts 40,42 towards the chimney.

  During the entire regeneration, the inlet temperature in the reactor 30

  is maintained at 3000C, possibly with the aid of the burner 34. A cycle of ad-

  sorption and regeneration lasts about 42 h q and the total energy consumption corresponding to 310 kg of oil, of which 110 kg are used in the burner 12 and 200 in the burner 34; in this regard, it may be noted that the off-gas from reactor 16 during regeneration has a

certain calorific interest.

EXAMPLE 2-

  This example relates to the installation shown in Figure 2.

  25 000 Nm3 / h are sent into this installation of a stream of air emanating from the furnaces of an offset printing installation. The polluted air contains S 1.5g of hydrocarbons per Nm3 and has a temperature of 110 ° C. Hydrocarbons, which constituted the solvents for printing inks, comprise about 20% aromatic hydrocarbons of 80% aliphatic hydrocarbons

  and provide a boiling point of between about 240 and 2700C.

  The total quantity of polluted drying air is sent into the installation via line 10. A partial flow of v0 Nm3 / h for regeneration is derived via line 42. The remaining 25,000 - v0 Nm3 / hr 44 to reactors 48 which are in the adsorption phase and are distributed at a rate of (25 000 v) / 5 Nm3 / h to each

  of these five reactors. Each reactor 48 contains 1500 kg of the same adsorbent

  catalyst than that described in Example 1. The post-reactor 76 is

  purification also contains 1500 kg of the same adsorbent-catalyst.

  The duration of the adsorption period is limited by two facts - in the first place, it must not be too long for the concentration of hydrocarbons in the air stream leaving an adsorption reactor

does not exceed a permitted value.

  - Second, there must not be more than 15g of adsorbed hydrocarbons

per kg of adsorbent-catalyst.

  With this value, the maximum temperature in the adsorbent-catalyst does not

does not pass 800 to 8500C.

  By determining the duration of the adsorption period at 175 minutes, a quantity of 12.8 g of hydrocarbons is adsorbed per kg of adsorbent-catalyst, so that the maximum temperature in this adsorbent-catalyst does not exceed the value. sought during regeneration, namely a value of which one is

  sure it does not destroy the catalyst. During adsorption, the concentration

  In the decontaminant gas fed to the stack, the hydrocarbon flow is approximately 2 mg / Nm3 for the first 100 min and amounts to 5 mg / Nm3 at the end of

  adsorption. Since the number of reactors is six, the regeneration period

is 35 (175: 5) minutes.

  If v1 represents the quantity of air sent via line 52 to the regeneration, v2 represents the amount of air recycled in line 66 after reactor 76, T1 is the temperature in line 52 going to reactors 48, T2 is the temperature in the duct 58 leaving the reactors 48, T3 is the temperature in the duct 68 going into the reactor 76,

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  Table I, below, shows how the regeneration of adsorption occurs.

in a reactor 48. -

During the first 12 minutes of the regeneration, a temperature in the duct 54 in question of about 31 ° C. is obtained by mixing 1000 Nm 3 / h (v 1) of contaminated air coming from the duct 42 with 2000 Nm 3 / h (v 1 -v ) hot air

  decontaminated from the conduit 70 at the junction 72.

  At the temperature obtained, the hydrocarbons adsorbed in the inlet layer

  reactor 48 in question, are in combustion due to the catalytic properties

  lytic catalyst-adsorbent. Hydrocarbons from polluted gases used for regeneration oxidize with some of the adsorbed hydrocarbons. The remaining adsorbed hydrocarbons are desorbed as a result of the increase in temperature and entrained with the flow of air to reactor 76 where oxidation takes place. 5 to 10 minutes after the start of the regeneration, the hydrocarbon concentration of the air stream rose to a maximum of 2 to 3 g / Nm3. In the first 15 to 20 minutes, when

  the hydrocarbon content in the air of the duct 58 is important, the temperature

  The temperature is relatively low. To ensure sufficient oxidation in

  At reactor 76, the air stream must be heated to at least 260 ° C.

  For this, hot air is recycled into the reactor via line 66.

  The temperature of the stream of air from the reactor 76 must have a constant value of about 418 ° C. despite the temperature variations in the conduit 58. This is particularly due to the fact that the catalyst in the reactor 76 has a certain capacity in the reactor. As a thermal buffer and that, on the other hand, the hot air is recycled through the conduit 66. The temperature in the conduit 74 is almost constantly 418 ° C. The volume of the decontaminated air in the duct 74 is identical to 20 minutes after the beginning of the regeneration, the addition of hot air from the duct 70 to the junction point 72 is stopped and, at the same time, the amount of polluted air in the conduit 42 is increased. The rest of the regeneration is carried out with hot polluted air at 130 ° C., at a rate of 4000 Nm3 / h. The recycling in the reactor 76 can be reduced to 3500 Nm3 / h since the temperature of the air at the outlet of the reactor 48 in question began to rise. This temperature will reach a maximum of about 600 ° C after 25 minutes of regeneration. At the same time, the temperature of the air stream

  decontaminated outgoing reactor 76 will also reach a maximum of

  The hydrocarbon content in line 58 falls below

  mg / Nm3 after 15 to 20 minutes of regeneration.

  The burner 62 does not come into operation during the regeneration, it is used only when starting the installation so that it

14 2458308

  there is no energy consumption to heat the air during operation

  of the installation, which is a great advantage.

  The stream of decontaminated hot air leaving the system through line 74 has large amounts of heat. By cooling the air stream to 1300C, it is possible to use a quantity of heat corresponding to the value

  heat of 27 kg of oil per hour.

TABLE I

EXAMPLE 3

  In the first experiment with the experimental installation represented

  In Figure 3, air polluted with styrene is used. The adsorbent-cata-

  lyser is composed of y-alumina impregnated with copper chromite, as described

  above, in the form of beads of 3 to 6 mm in diameter.

  4.4 Nm3 / h of air containing 0.22 g is introduced into the catalyst bed

  styrene by Nm3 and having a temperature of 50 ° C. The amount of adsorbent

  catalyst is 1.67 kg, corresponding to 1.8 liter. Styrene content

  in the outlet stream of the reactor is measured in a hydrogen analyzer.

  carbides in ppm by volume of methane equivalents, hereinafter referred to as C ,.

  It can be noted that 100 mg of styrene per Nm 3 corresponds to 179 ppm by volume of C 1. In the first 30 hours of the adsorption period, the content of

  styrene in the decontaminated air is less than 20 ppm by volume of IC.

  After 40 hours of operation, this content is 30 ppm by volume of C, and after 45 hours, this content reached 50 ppm by volume of CI. We stop

  then the adsorption period and starts the regeneration.

  Number of minutes since start of Regeneration 0-12 12-20 20-25 25-30-30 30-35 Vo. (Nm3 / h) ....... 1000 4000 4000 4000 4000 4000 v, (Nm3 / h) ....

  . 3000 4000 4000 4000 4000 4000 v2 (Nm3 / h) ....... 4000 3500 3500 3500 3500 3500 Tl (OC) ....... 318 130 130 130 130 130..DTD: T2 (OC) ....... 290 300 450 600 450 350

T3 (Oc) .......

  Concentration of hydrocarbons in line 58 (g / Nm ') ....... max. 2-3 1-0.02 <0.01 '0.01 <0.01 <0.01

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  The air flow is reduced to 1.1 Nm3 / h. while the temperature of this cou-

  rant entering the catalyst bed is raised to 3000C. The adsorbed material at the inlet of the bed comes into combustion at about 2800C, then a hot zone descends through the bed. This hot zone reaches its highest temperature of 700C, at a depth of about 150 mm. The hot zone reaches the reactor outlet in about 1 hour. The styrene content of the eliminated air

  the reactor at the beginning of the regeneration is 30 ppm / volume of Ci.

  During the first 17 minutes of the regeneration period, the styrene content is greater than 1000 ppm by volume of Ci, which is the upper limit that can be measured by the hydrocarbon analyzer. After about min, the styrene content decreases again to less than 1000 ppm by volume of C1 and during the next 10 minutes this styrene content falls

  at 20 ppm by volume of Ci. Regeneration lasts a total of 50 minutes.

  The experiment is repeated three times and the result is as described above. Calculations made on the experimental data show that the adsorption capacity under the conditions used is about 25 g / kg of adsorbent-catalyst. After a 45 hour adsorption operation, a sample of a few grams of adsorbent catalyst is taken and analyzed. This sample contains 33 g of organic carbon per kg. The sample is then heat treated at 2000C in nitrogen. After being held at this temperature for 2 hours, the sample is again analyzed. The carbon content

  organic is 15 g / kg of adsorbent-catalyst. It is assumed that this quantity

  organic carbon content corresponds to styrene adsorbed in a more

or less polymerized.

EXAMPLE 4

  In this series of experiments, comprising four separate tests, the reactor contains 1.6 liter (1.5 kg) of the adsorbent-catalyst arranged in one

  bed 40 cm high. The stream of air entering the adsorbent bed

  catalyst in all experiments is 4.0 Nm3 / h. This air stream is polluted by a mixture of hydrocarbons having a boiling point included

  between 240 and 270C, usually used in offset printing "Heatset".

  The temperature and hydrocarbon content in the air stream at the inlet (Z = O) of the adsorbent-catalyst bed are indicated in FIG.

Table II below.

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TABLE II

  The hydrocarbon concentration in the reactor outlet stream is determined in a hydrocarbon analyzer as ppm by volume of C1. Figure 4 shows graphically the hydrocarbon concentration in ppm by volume of C1 versus time, expressed in hours, for the four experiments. The graph bears a line that corresponds to the concentration of 20 mg C1par Nm3, which is frequently the maximum limit allowed for a

  current released into the atmosphere.

  From Figure 4, it can be seen that the adsorption capacity in the temperature range studied depends strongly on the temperature since a small increase or decrease of the temperature causes a strong

  decreasing or increasing, respectively, the adsorption capacity.

  Before being subjected to the series of experiments, the adsorbent-catalyst was used in 10 cycles of adsorption and regeneration in which the maximum temperature during the regenerations was between 900 and 920C; the limit of 800 to 8500C previously fixed thus provides a good margin of safety. During the ten subsequent adsorption and regeneration cycles, the adsorption capacity is determined. No signs of reduction are observed

  notable adsorption capacity.

  In experiment 2, the adsorption period is completed after 6 h

  of operation and regeneration is initiated. At this time, the adsorbent

  calculated catalyst adsorbed a total of 39g of hydrocarbons, cor-

  corresponding to 26 g / kg. The progress of regeneration, which is carried out with clean air is shown in Figure 5. Time counts from

  the beginning of the regeneration is represented in minutes on the abscissa.

  The left ordinate shows the methane equivalent content in the air stream leaving the reactor, the right ordinate the temperature measured at various depths (Z) in the adsorbent-catalyst bed. As the length of the bed is 40 cm, Z = 0 corresponds to the bed entrance layer

  and Z = 40 at the exit layer of this bed.

  Experience Temperature Hydrocarbon Content, No. (OC) (g / Nm3)

1,155 1.40

2,125 1.40

3,122 0.78

4,100 0.91

  The temperature at the Z = O level is identical to the temperature of the air stream used for the regeneration. The temperature at level Z = 40 is identical to

  the temperature of the air stream leaving the reactor.

  From Figure 5, it can be seen that the temperature of the regeneration air during the first 10 minutes is about 290 ° C and that the temperature

  the remaining time of regeneration is about 100C.

  We also see that the highest temperature presented in the bed,

  namely about 930 ° C is observed at a depth of 10 cm.

  Corresponding regenerations with smaller amounts of adsorbate show that about 15g of hydrocarbons per kg of adsorbent

  maximum temperature in the bed of about 8250C.

  The hydrocarbon concentration in the outgoing air decreases, as well as

  as shown in the figure, at less than 10 ppm by volume of Ci after about 20 minutes.

  Regeneration is complete in about 30 minutes. During the last 10 minutes

  regeneration, the adsorbate is completely oxidized on the adsorbent

  lyst. During the entire regeneration period, generally half of the adsorbate is oxidized on the adsorbent-catalyst, while the remainder

  is entralné with the current of air towards the post-purification section.

  Of course, the present invention is not limited to the examples

  and modes of implementation mentioned above; it is likely to

  Many variants accessible to those skilled in the art, depending on the applications

  visages and without departing from the spirit of the invention.

18 2458308

Claims (9)

  1. A process for removing the oxidizable components of polluted gases, in particular polluted air, characterized in that the polluted gas is sent at a temperature between 0 and 250 ° C. through a bed of particulate adsorbent comprising a porous ceramic support having a surface area of   significant and impregnated with an effective high-temperature material.   as an oxidation catalyst, this adsorbent-catalyst being   regenerated by oxidation at certain intervals, by increasing the temperature   to a value between 250 and 3500C so as to initiate oxidation.   catalytic deposition of accumulated contaminants on and in the adsorbent   lyst. 2. Method according to claim 1, characterized in that one uses   y-alumina impregnated with copper chromite as catalyst adsorber.   3. A process according to claim 1 or 2, characterized in that the gases leaving the adsorbent-catalyst during the regeneration by oxidation at a post-purification.   4. A process according to claim 3, characterized in that the post-   purification is carried out by catalytic oxidation.   5. A process according to claim 4, characterized in that the same catalyst is used in the post-purification that the adsorbent-catalyst put   in the adsorption and regeneration according to claim 1.   6.- Installation for carrying out the process according to claim 1, characterized in that it contains at least one reactor (16) having a bed (18) of adsorbent which at high temperature also constitutes a catalyst of active oxidation, a supply pipe (10) introducing the gas to be treated into the reactor and a relief pipe (20) discharging the purified gas from the reactor, means (12, 14) for intermittent regeneration of the adsorbent -catalyst in the reactor (16) and, optionally, means (32-42) for postpurification of the gas leaving the reactor, during regeneration.   7.- Installation according to claim 6, characterized in that the   means for ensuring the regeneration of the adsorbent-catalyst   take a combustion chamber (12) connected to a burner (14).   8.- Installation according to claim 6, characterized in that the means for ensuring the post-purification of the gas leaving the reactor (16) during regeneration comprises another combustion chamber (32) connected to a burner (34) and connected by a bypass (30) to the disengagement tube (20), another reactor (36) comprising an oxidation catalyst (38)   and a conduit from this reactor to a chimney or vent   (22) from the first reactor (16).   9.- Installation according to claim 6, characterized in that it comprises at least two réadtion rooms (48I, 48II, etc.) lined with adsorbent-catalyst material (18) and connected in parallel, a supply duct ( 10) which divides on one side into a conduit (42) to a post-purification section and, on the other side, into a conduit (44; 46I, 46II, etc.) to the reactors (48, 48, etc.), bypass lines from these reactors ranging from (50Z, 50II, etc 22) to a stack, ie (56I, 56II, etc. 58) to the post-purification section which includes a chamber of combustion (60) associated with a burner (62), a conduit therethrough to a reactor (76) lined with an oxidation catalyst and a stripping duct from the reactor (76) with partially 74) outside the system, partially (52; 541, 54II, etc.) to the reactors (48I, 481I, etc.) and partially in a recycle conduit (66) to the duct (56, 68) between the combustion chamber (60) of the   post-purification and the reactor (76) thereof.