EP0684427A1 - Rotating heat transfer and thermal purification device for gaseous effluents - Google Patents

Abstract

The rotary unit consists of a shell or cage (2) and a crown (1) containing a charge of a material with a large heat exchange surface, a drive to rotate the cage and crown relative to one another about a vertical axis, and at least one duct (5) for introducing the effluent gas into the cage and another (6) to remove it after treatment. The crown has at least one sector (A) to connect the inlet duct at any time with the central part of the cage, and a second sector (B) to connect it with the outlet duct. The central part of the crown has an aperture (8) for a thermal or catalytic reactor which burns off or converts pollutants contained in the gases passing through it. The charge of solid material can be in the form of cryogenic nodules. <IMAGE>

Description

The invention relates to a rotary transfer device for gaseous effluents, adapted to function as a heat exchanger and in addition, as a purifier with thermal effect.

The invention finds applications in particular in heat exchange systems or adapted to purify air loaded with substances such as volatile organic compounds (C.O.V), which can be oxidized and eliminated by thermal or catalytic incineration.

Heat treatment devices are generally very efficient and compact. Their most notable drawback is their high energy consumption, that which is necessary to bring the gases to be treated to oxidation temperatures (850 ° C. to 1100 ° C.), drawback reduced if the purification is carried out in the presence of catalysts at much lower temperatures (200 ° C to 450 ° C °).

For obvious economic reasons, it is necessary in all cases to recover as much as possible of the heat accumulated by the effluents as they pass through the thermal purifier. by means of heat exchangers placed downstream of it. In the case of an incineration in the presence of a catalytic bed, the effluents are heated prior to their incineration by passage through another heat exchanger placed upstream. The overall thermal efficiency depends on the efficiency of the exchangers. In practice, autothermal incinerators are produced for the purification of gases charged with at least 0.7 g / m3 of air.

A known process of heat exchange consists in circulating the gases to be purified between two masses capable of taking, storing and returning the heat. By passing through the first mass, the effluents heat up until they reach a temperature close to that necessary for the oxidation of polluting substances. They then pass through a combustion hearth (with or without flame) or else over a catalytic bed where they oxidize according to an exothermic reaction. Gas then cross the other mass to which they transfer their calories before being thrown out. The direction of flow is reversed periodically.

This periodic reversal has the main drawback of disturbing the regularity of treatment or its effectiveness. It also requires the interposition of valves adapted to effluent conduits, often of large section. If, in fact, the quality of treatment is chosen, it is necessary to prevent any mixing between polluted and cleaned gases during periods of cycle inversion and therefore stop treatment for a short period of time (a few seconds in when each cycle lasts several minutes). If the continuity of the treatment is imposed, it is necessary to accept the mixing of the flows at the moments of reversals of direction during the intercycles, and therefore a momentary loss of efficiency.

Another notable drawback of periodic inversion heat exchange devices is that the preheating chamber upstream of the hearth during one cycle is found downstream during the next cycle. This results, on the one hand, in a mixture in this enclosure at the intercycle, of polluted and purified effluents, and on the other hand a temperature variation of the enclosure during the duration of the following cycle.

A known technique used in particular in thermal power stations comprises the use of a rotating drum with a vertical or horizontal axis. The yield obtained is relatively low (of the order of 60 to 75%) owing to the fact that the flows of unequal temperatures which exchange heat, pass through the drum parallel to its axis and therefore are poorly separated from each other in adjacent traffic areas.

Another known technique of heat exchange involves the use of a cross-flow heat exchanger produced with plates or tubes, in which the heated effluents give up their calories continuously to the gases to be purified. This technique is expensive for medium or high flow rates, due to the significant heat exchange surfaces that it implies and the care that must be taken to obtain a perfect separation between the two flows.

By its arrangement, the device according to the invention makes it possible to carry out heat energy exchanges and possibly to thermally purify polluted effluents, avoiding the drawbacks of known techniques.

The device comprises an envelope or cage, a crown containing a charge of particulate solid materials chosen because they have a large heat exchange surface (silica, granite or lighter materials such as metallic or other cellular structures, or nodules cryogenic for negative temperatures, etc.) which is placed inside the cage. The crown is divided into several parts by an internal partitioning or else, as the case may be, it supports a certain number of baskets. Motor means are used to animate the crown and the cage in a rotational movement relative to each other about a vertical axis (either that the crown rotates, the cage being fixed, or that the crown on the contrary is fixed and the cage rotates around it).

The device comprises at least one conduit for the introduction of effluents into the cage and at least one conduit for the evacuation of effluents out of the cage. The crown comprises at least a first sector for communicating at any time the introduction conduit with the central part of the cage, where a first heat transfer takes place between the effluents and the charge in the crown. The crown also has a second sector making it possible to communicate at any time the central part of the cage with the discharge pipe, where a second heat transfer takes place between effluents and the charge in the crown.

The rotation of the crown brings the mass of material which has been heated (respectively cooled) by effluents towards the second angular zone where it heats (respectively cools) a second gaseous effluent.

The device can be used only as a heat exchanger and in this case, it has a primary effluent circulation circuit including the introduction pipe and a pipe arranged in the central zone of the crown, this primary circuit communicating with a first source of effluents. It also includes a secondary effluent circulation circuit including the evacuation pipe, located on either side of the second sector, this secondary circuit communicating with a second source of effluents.

One of the two primary or secondary circuits is connected to a source of hot effluents, the other circuit being connected to a source of cooler effluents.

The device can be used both as a heat exchanger and as an incinerator for polluted effluents. In this case, the introduction conduit is connected to a source of effluents containing polluting substances. The first sector and the second sector communicate directly with each other via the central part of the cage. A thermal reactor is arranged in this central part to burn the polluting substances in the effluents channeled by the first angular zone.

Preferably, a catalytic bed thermal reactor chosen is used to cause an exothermic reaction in the presence of polluting substances.

The device may include additional means (burner, fuel injector) for raising the temperature prevailing in the reactor if necessary, as well as other mechanical or chemical means for treating the mass in the crown.

The device according to the invention with its rotary drum has great advantages:
- It allows to perform under a small volume, treatment and heat exchange functions. Due to its compactness, the pressure drops are very reduced.

• a) les pertes thermiques sont faibles. Du fait de la symétrie cylindrique du dispositif et de la rotation de la couronne intérieure, les échanges thermiques s'effectuent en continu ce qui ne nécessite aucune inversion de sens des flux et permet la régularité du débit épuré. Les inversions de sens éventuelles sont de toute façon progressives, ce qui favorise un rendement élevé.
• b) La forte dilatation consécutive à l'élévation de température entraîne, on le sait, une augmentation de la vitesse d'écoulement et par conséquent des pertes de charge. On peut noter à cet égard que l'agencement et la forme du dispositif permettent de raccourcir beaucoup la portion de circuit où les effluents sont à une température élevée et donc de diminuer les dépenses d'énergie de l'installation de traitement.
• c) Du fait de sa compacité, la surface périphérique de la cage par où s'effectuent les échanges thermiques avec l'extérieur, est relativement réduite, et les pertes thermiques sont par conséquent plus faibles et plus faciles à minimiser.
• d) La zone la plus chaude est au centre et la couronne qui fonctionne comme récupérateur d'énergie, est interposée entre cette zone et la périphérie de la cage. De ce fait, la température extérieure de l'enveloppe est relativement faible (moins de 100°C en pratique), ce qui simplifie le calorifugeage extérieur. On obtient ainsi une forte concentration de la chaleur et une récupération optimale des dissipations par la masse thermique placée dans la couronne.

In its configuration where the hottest reaction zone is in the center of the cage, and the colder zones are at the periphery,

• a) the heat losses are low. Due to the cylindrical symmetry of the device and the rotation of the inner ring, the heat exchanges are carried out continuously which does not require any reversal of the direction of flow and allows the regularity of the purified flow. Any reversals of direction are in any case progressive, which promotes high efficiency.
• b) The strong expansion following the rise in temperature leads, as is known, to an increase in the flow speed and consequently to pressure losses. It may be noted in this regard that the arrangement and the shape of the device make it possible to greatly shorten the portion of the circuit where the effluents are at a high temperature and therefore to reduce the energy expenditure of the treatment installation.
• c) Due to its compactness, the peripheral surface of the cage through which the heat exchanges with the outside take place, is relatively reduced, and the heat losses are consequently lower and easier to minimize.
• d) The hottest area is in the center and the crown, which functions as an energy recuperator, is interposed between this area and the periphery of the cage. Therefore, the outside temperature of the envelope is relatively low (less than 100 ° C in practice), which simplifies the external insulation. A high concentration of heat is thus obtained and an optimal recovery of dissipations by the thermal mass placed in the crown.

In practice, the device according to the invention, in its version with catalytic bed reactor in the central zone, can operate in an autothermal manner with effluents loaded with 400 mg of VOCs per m3.

• la Fig.1 montre une vue en coupe schématique d'un premier mode de réalisation du dispositif, avec une couronne tournante;
• la Fig.2 montre une vue schématique en coupe simplifiée d'un deuxième mode de réalisation du dispositif avec une cage susceptible de tourner autour de la couronne;
• la Fig.3 montre une vue éclatée du tambour tournant pour illustrer schématiquement les circulations des effluents à l'intérieur du tambour rotatif; et
• la Fig.4 montre schématiquement un mode de réalisation du tambour rotatif utilisé comme échangeur de chaleur; et
• la Fig.5 montre un mode de réalisation où le dispositif est utilisé pour un usage mixte comme incinérateur de substances polluantes dans des effluents, et échangeur de chaleur; et
• la Fig.6 montre schématiquement le tambour tournant et sa zone centrale.

Other characteristics and advantages of the device according to the invention will appear on reading the following description of nonlimiting exemplary embodiments, with reference to the appended drawings where:

• Fig.1 shows a schematic sectional view of a first embodiment of the device, with a rotating crown;
• Fig.2 shows a schematic view in simplified section of a second embodiment of the device with a cage capable of rotating around the crown;
• Fig.3 shows an exploded view of the rotating drum to schematically illustrate the flow of effluents inside the rotating drum; and
• Fig.4 schematically shows an embodiment of the rotary drum used as a heat exchanger; and
• Fig.5 shows an embodiment where the device is used for mixed use as an incinerator of polluting substances in effluents, and heat exchanger; and
• Fig.6 schematically shows the rotating drum and its central area.

According to the embodiment of Fig.1, 2, 3, the device comprises a drum DR consisting of a crown 1 with a vertical axis arranged inside a metal outer casing or cage 2 of cylindrical shape for example. The cage comprises a first arm 3 and a second arm 4 to which are connected respectively a conduit 5 for supplying the gaseous effluents to be purified, and a conduit 6 for discharging these same effluents after treatment. The crown 1 is provided with an internal partition consisting of a set of straight or curved blades 7 regularly distributed. A first angular sector A delimited by one or more blades, channels the effluents coming from the conduit 5 towards the central zone 8 of the cage (flow Fe in FIG. 3). A second angular sector B communicates the central zone 8 of the cage with the evacuation duct 6 (flow Fs in FIG. 3).

The crown can also be arranged to serve as a support for a certain number of baskets.

Inside the crown (between the blades or in the baskets), an active mass M is made up of a material with a large heat exchange surface.

They may be ceramic or metallic balls, turnings or machining chips, loose or structured packing, a honeycomb structure with regular or irregular honeycombs such as honeycombs, metallic knitted fabrics or ceramic etc. Advantageously, a honeycomb structure such as that described in patent FR 2,564,037 of the applicant is used.

The crown load can also consist of stones. In the case of a negative heat transfer, cryogenic nodules are used.

Seals 9 are arranged between the cage and the crown to ensure vertical sealing and isolate the two spaces upstream and downstream from the central zone or transit zone 8 from each other, so that all the effluents are practically channeled towards it. These seals 9 are arranged so that the residual pressure drop between the crown 1 and the cage 2, is at least equal to the pressure drop experienced by the gases in the main circuit passing through the device.

Other seals (not shown) of the lip or brush type, with annular hydraulic seal with baffling in an oil bath, etc., are arranged so as to provide the perimeter seal (horizontally).

The circular configuration of the crown 1 and the cage 2, as well as the preferably curved shape of the vanes 7, are particularly well suited to withstand strong and frequent temperature variations, while ensuring satisfactory guidance of the flows passing through the device.

The cage 2 and the crown 1 are driven by motor means (not shown) with a slow rotational movement relative to one another.

The cage 2 also has at least one opening in its side wall in each of the angular sectors C, D intermediate between sectors A and B, where conduits 10, 11 open connected to suction means 13 (Fig.4). The peripheral gas leaks between the crown 1 and the cage 2, are sucked through the conduits 10, 11 (return flow Fr of FIG. 3) and reinjected into the supply duct 5 (incoming flow Fe).

In one of the two intermediate angular sectors C, D (Fig. 3), the cage 2 can also include openings into which one or more conduits 13 (Fig. 1-2) open to perform other functions. It may involve injecting a chemical inhibitor to avoid a parasitic chemical reaction such as polymerization, or else the formation of plugs. It can be a mechanical action: suction or blowing in order to clean the crown load, etc.

According to one embodiment, the cage 2 is fixed (Fig. 1) and the crown 1 is driven in rotation.

According to another embodiment (Fig.2), it is the crown 1 which is fixed and the cage 2 driving with it the conduits 5, 6, which can rotate around its axis. In the central area 8 of the cage 2, is disposed an intermediate cover 14 with selective openings. This cover 14 rotates at the same time as the cage 2 and serves to guide the incoming flow (Fe in FIG. 3) towards the central zone 8 and the outgoing flow towards a converging chamber 15 from which a discharge chimney starts. 16 arranged to be able to follow the rotation of the cage 2.

Depending on the mass of the ring, which depends on the nature of the load M with a large heat exchange surface or the applications and / or the volume of effluents to be treated, one chooses the embodiment of FIG. 1 or for that of Fig. 2.

According to a first embodiment (Fig. 4), the central zone 8 is used as a flow exchange zone for the evacuation or the admission of effluents.

Through the angular sector A, a stream of hot effluents Fc is channeled towards the central zone 8. The effluents cede their thermal energy to the load M. In the central zone 8, they are channeled by a pipe 17 towards the outside ( flow Fs1). A another conduit 18 is used to channel towards the zone B a flow of cooler gases Ff. These cold gases passing through the angular zone B, are then in contact with the particles which have been previously heated during their passage in the zone A and exit through the conduit 6 at a higher temperature (flow Fs2).

The operation is identical for a reverse heat transfer. The flow of cold gas admitted via line 5 cools the mass M in the angular sector A of the crown. Via line 18, a warmer gas flow is admitted which, crossing the angular zone B, is then in contact with the particles which have been cooled during their passage through the zone A and emerge through the line 6 at a lower temperature.

According to the embodiment of Fig.5, the device is used for a mixed use of heat exchange and incineration of gaseous effluents loaded with polluting substances such as VOC compounds for example. The crown 1 also contains a charge M of a material with a large heat exchange surface, as defined above. The incineration of polluting substances is carried out in a reactor 19 placed in the central zone 8 of the cage 2. Preferably, the reactor 19 is of the catalytic bed type. The effluents to be purified are introduced at a relatively low temperature (from 200 ° C. to 400 ° C. for example. The reaction is exothermic and it is regulated so as to release enough energy to substantially compensate for the heat dissipation. A proportion of 0 , 4 mg of VOC per m3 of effluent is sufficient for autothermal operation.

In certain cases, if the content of polluting compounds VOC is insufficient, the device is connected by an injection tube 20, a reservoir 21 of natural gas or LPG to improve the calorific value of the admitted effluents. A by-pass circuit 22 controlled by a valve 23 allows part of the hot gases to be removed without passing them through the exchanger. A burner 24 can be arranged upstream of the drum T, to heat at start-up if necessary the incoming effluents, so as to reach an auto-thermal operating point.

After crossing reactor 19, the polluting compounds (VOCs) are transformed by the reaction into various combustion products: CO2, H2O, N2 mainly, SOx and NOx in trace amounts.

The high temperature gases from the reactor 19 pass through the part M2 of the charge M located in the angular zone B of the ring and give it a good part of their calories. The rotation of the crown 1 relative to the cage 2, gradually brings the heated elements to the angular zone A where they can in turn yield to the incoming gases via the supply duct 5, part of the accumulated heat energy.

The desired oxidation can also be obtained by placing direct heating means of a known type in the central zone of the crown, making it possible to bring the effluents to a temperature of the order of 850 ° C. to 1100 ° C.

Example of use

The polluted air (or the discharge to be incinerated) is sent (Fig. 6) to the load M1 in the angular sector A of the device, a hot zone where an increasing temperature gradient is established on the outside (temperature T '' 1) towards the interior (temperature T'1) around an average temperature T1 (T'1>T1>T''1). The heated air passes into the distribution zone E. If the temperature of the heated air is lower than the catalytic activity temperature, it can be provided in this zone E, a thermal back-up. The air then passes over the catalyst in the reactor 19 and the polluting compounds VOCs are transformed into combustion products (CO2, H2O, SO2, N2 and NOx). The gases then pass through the mass M2 of the angular sector B which they heat to an outlet temperature of the filling mass equal to T2, very close to T'1, apart from the thermal losses.

• lorsqu'on ne veut pas récupérer les composés polluants COV,
• lorsque la teneur en composés COV est suffisament élevée pour éviter un appoint thermique important en E, la chaleur d'incinération catalytique équilibrant les pertes thermiques. Cette limite avec le système ainsi décrit, se situe au niveau de 400 mg/m3 d' hydrocarbures.

This application of the device is particularly advantageous:

• when we don't want to recover VOC pollutants,
• when the content of VOC compounds is high enough to avoid significant thermal back-up in E, the catalytic incineration heat balancing the thermal losses. This limit with the system thus described is at the level of 400 mg / m3 of hydrocarbons.

Claims (18)

1) Rotary transfer device applied to gaseous effluents, characterized in that it comprises an envelope or cage (2), a ring (1) containing a charge (M) of solid materials having a large heat exchange surface, which is arranged inside the cage, and motor means for animating the crown and the cage with a rotational movement relative to each other about a vertical axis, at least one conduit (5, 18) for the introduction of effluents into the cage (2) and at least one conduit (6, 17) for the evacuation of effluents out of the cage, the crown (1) comprising at least a first sector (A ) to communicate at any time the introduction conduit (5) with the central part (8) of the cage (2), where a first heat transfer takes place between the effluents and the charge (M1) in the crown (1), and at least a second sector (B) of the crown to communicate at any time the central part (8) of the cage with the evacuation circuits, where a second heat transfer takes place between effluents and the charge (M2) in the crown. 2) Device according to claim 1, characterized in that it comprises a primary effluent circulation circuit including the introduction pipe (5) and a pipe (17) disposed in the central zone of the crown (1), this primary circuit communicating with a first source of effluents, and a secondary circuit for circulation of effluents (6, 18) including the discharge pipe (6), located on either side of the second sector (B), this secondary circuit communicating with a second source of effluents. 3) Device according to claim 2, characterized in that one of the two primary or secondary circuits is connected to a source of hot effluents, the other circuit being connected to a source of cooler effluents. 4) Device according to claim 1 or 2, characterized in that the first source delivers effluents charged with polluting substances, the first sector (A) and the second sector (B) communicate directly with each other via the central part (8) of the cage (2), a thermal reactor (19) being disposed in this central part for burning the polluting substances charging the effluents channeled through said first angular zone (A). 5) Device according to claim 4, characterized in that the thermal reactor (19) contains a catalyst chosen to cause an exothermic reaction in the presence of polluting substances. 6) Device according to claim 4, characterized in that the reactor (19) contains heating means for burning said polluting substances. 7) Device according to one of claims 4 to 6, characterized in that it comprises means for raising the temperature prevailing in the reactor (19). 8) Device according to the preceding claim, characterized in that the means for raising the temperature comprise means (20,21) for injecting fuel. 9) Device according to one of the preceding claims, characterized in that it comprises means (11,12) for sucking effluents in at least one sector (C1, C2) of the crown (1) intermediate between the first and the second heat transfer sector. 10) Device according to one of the preceding claims, characterized in that it comprises means (13) for communicating the interior of the crown with mechanical or aeraulic means for cleaning the mass (M). 11) Device according to one of the preceding claims, characterized in that it comprises means (13) for communicating the interior of the crown with means for injecting chemical substances. 12) Device according to one of the preceding claims, characterized in that the drive means are associated with the crown (1), the cage (2) being fixed. 13) Device according to one of the preceding claims, characterized in that the crown (1) is fixed, the drive means are associated with the cage (2) which is movable relative to the crown, and the circuits (5, 6) inlet and outlet are attached to the cage and rotate with it. 14) Device according to one of the preceding claims, characterized in that the mass (M) consists of cryogenic nodules. 15) Device according to one of the preceding claims, characterized in that the crown is divided into several angular zones by an internal partitioning (7). 16) Device according to one of the preceding claims, characterized in that the crown is arranged to serve as a support for several baskets containing the load (M). 17) Application of the device according to one of claims 1 to 16, to the heat exchange between two gas flows via a mass (M) of a material provided with a large heat exchange surface , moved by continuous rotation of a crown (1) of vertical axis, to be successively brought into thermal contact with the two flows. 18) Process for the continuous purification of gaseous effluents loaded with polluting substances, characterized in that it comprises: the establishment of a permanent circulation of effluents to be purified on the one hand between conduits (5) for supplying effluents and the central part (8) of a cage containing a crown (1) which is loaded with a mass (M) of a material having a large heat exchange surface, via a first sector (A) of the crown, the cage and the crown being able to rotate relative to one another, and other part between the central part (8) of the cage and means for discharging effluents via a second sector (B) of the crown, the central part of the crown comprising a thermal reactor (19) for burning the polluting substances; and - the preheating of the effluents by the thermal energy accumulated by the mass (M) in contact with the effluents leaving the reactor, the effluents crossing during the journey a first zone at a temperature sufficient for the incineration of polluting substances and a second zone d 'heat exchange where they give up at least part of the heat acquired in crossing the first zone.

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