EP0040166A1 - Industrial chimney with forced draught - Google Patents

Abstract

The chimney comprises a central column (1) surrounded by an external wall (2) delimiting an annular space (3) which communicates with the interior of (1) by openings (4) just at the base of an outlet nozzle (1a). The combustion gases from the oven (5) are sent under pressure to (1) by a fan (5) while the air is forced into (3) by another fan (9). A pressure comparator (10) maintains the pressure in (3) slightly higher than that prevailing in (1) so that the air mixes in part with the gas to be evacuated by surrounding them with a sheath which delays condensation phenomena and diffusion into the surrounding atmosphere.

Description

The present invention refers to industrial chimneys intended for discharging gaseous products into the atmosphere which we want to get rid of, this term gaseous products including vapors and solid or liquid particles suspended in a gas. The most frequent case is that of combustion products from fireplaces, ovens and the like.

To minimize the annoyance and pollution that these products can cause, the corresponding chimneys should be as high as possible, which leads to expensive constructions.

To avoid this drawback, it has been proposed to reject the gases under pressure through a nozzle in the form of a high speed jet which rises very high in the atmosphere before being diluted. It has also been imagined to associate with the gaseous products to reject an auxiliary air current which drives them more or less efficiently. All these means have proven to be costly in energy and have given only fairly approximate results.

In accordance with the invention, in order to solve this problem, an auxiliary gas, such as air, is poured into the mass of gaseous products to be discharged, in a centripetal direction a short distance below the upper outlet of the chimney.

In a preferred embodiment, a forced draft chimney is used comprising an upper nozzle for evacuating gaseous products and the auxiliary gas is poured through openings provided at the base of this nozzle, under a slightly higher pressure. to that of said products in this area. The chimney can advantageously be provided for this purpose with double wall with central column for the flow of the products to be evacuated and annular space for the passage of the auxiliary gas.

• Fig. 1 est une coupe d'une cheminée suivant l'invention avec indication schématique de l'installation correspondante.
• Fig. 2 montre schématiquement comment se comporte cette cheminée en fonctionnement.

The appended drawing, given by way of example, will allow a better understanding of the invention, the characteristics which it presents and the advantages which it is capable of providing.

• Fig. 1 is a section through a chimney according to the invention with schematic indication of the corresponding installation.
• Fig. 2 schematically shows how this chimney behaves in operation.

The chimney shown in fig. 1 comprises a central column 1 established in any suitable manner, for example in bricks, and an outer wall 2 made for example of concrete, reinforced or unreinforced, and which surrounds the column 1 by providing an intermediate annular space 3. The column 1 is ends at the top with a part with the smallest diameter suitable for forming a nozzle or nozzle. In the embodiment shown, this part 1a is cylindrical, but it is perfectly possible to provide it converging over at least part of its height. As for the outer wall 2, it is connected to the column 1 towards the base of the part or nozzle 1a, as indicated in 2a.

The connection between the column 1 and the nozzle 1a is effected by a rounded part 1b immediately below which there are provided openings 4 which make the annular space 3 communicate with the interior of the column.

The hearth, oven or other device 5 which generates the gaseous products to be evacuated is connected to the base of the column 1 by a pipe 6 (shown diagrammatically by a single line) on which a blower fan 7 is inserted, so as to achieve what 'it was agreed to call the forced draw. Of course, the line 6 could also include any filtration, purification, cooling, dehumidification or other treatment devices that one could desire. For its part, the intermediate annular space 3 receives by a pipe 8 of the air discharged by a fan 9. A pressure comparator 10 is further provided connected to the respective pipes 6 and 8 by branches 11 and 12, this comparator acting on the fan 9 by means of any suitable connection, for example mechanical or electrical, which is shown diagrammatically by the broken line 13.

During operation, the fan 7 discharges the gaseous products to be discharged into the base of the column 1 under a certain overpressure. At the same time the fan 9 delivers air into the intermediate space 3 under a pressure that the pressure gauge 10 maintains very slightly greater than that generated by the fan 7. Under these conditions at the base of the nozzle l ' air from space 3 exits radially through the openings 4 in a centripetal direction and mixes with the mass of gaseous products which rises in column 1, the assembly being discharged at high speed through the nozzle la in which the pressure static is transformed into dynamic pressure, that is to say into kinetic energy.

• 1°) Du fait qu'une fraction de l'air se mélange aux gaz à évacuer, le jet qui sort de la tuyère la reste sans solution de continuité dans le sens transversal. En d'autres termes il n'y a pas de séparation entre une lame d'air extérieure et une masse centrale de produits gazeux.
• 2°) La gaine d'air presque pur qui adhère au jet central de produits gazeux est relativement sèche et isolante au point de vue thermique. Elle retarde donc considérablement les phénomènes de condensation qui n'apparaissent qu'à une hauteur notable au-dessus de la tuyère la.
• 3°) Du fait de la communication assurée entre l'espace 3 et la colonne 1 par les ouvertures 4 il se produit à l'entrée de la tuyère la un phénomène d'auto-régulation des pressions respectives de l'air et des produits gazeux à évacuer. En effet le débit de l'air à travers les ouvertures 4 est fonction non pas de la pression de refoulement du ventilateur 9, mais bien de la différence entre cette pression et celle de tirage forcé assurée par le ventilateur 7. Par conséquent les pertes de charges entre la sortie du ventilateur d'air 9 et le débouché desdites ouvertures 4 est également fonction de cette différence. Il en résulte que les petites erreurs de réglage du mano-compensateur 10 lors des variations d'allure du four 5 sont automatiquement compensées par ces pertes de charge. Si par exemple lors d'une réduction de cette allure et donc de la pression de tirage dans la colonne 1 le mano-comparateur 10 impose au ventilateur 9 une pression de refoulement trop forte, les pertes de charge interviennent efficacement pour limiter une trop importante augmentation du débit d'air.

It is however very important to note that in reality the air which leaves the openings 4 preferentially flows against the wall of the nozzle 1a, so that at the exit of this one there is in the presence of a jet gaseous whose periphery is almost exclusively constituted by air. This conformation has many advantages:

• 1 °) Because a fraction of the air mixes with the gases to be evacuated, the jet which leaves the nozzle remains it without solution of continuity in the transverse direction. In other words, there is no separation between an external air space and a central mass of gaseous products.
• 2) The almost pure air duct which adheres to the central jet of gaseous products is relatively dry and thermally insulating. It therefore considerably delays the condensation phenomena which only appear at a significant height above the nozzle 1a.
• 3 °) Due to the communication ensured between the space 3 and the column 1 by the openings 4 it occurs at the inlet of the nozzle la a phenomenon of self-regulation of the respective pressures of the air and the gaseous products to be evacuated. Indeed, the air flow through the openings 4 is not a function of the discharge pressure of the fan 9, but rather of the difference between this pressure and that of forced draft provided by the fan 7. Consequently the losses of loads between the outlet of the air fan 9 and the outlet of said openings 4 is also a function of this difference. As a result, the small adjustment errors of the pressure compensator 10 during variations in the shape of the oven 5 are automatically compensated by these pressure drops. If for example during a reduction of this speed and therefore of the drawing pressure in column 1 the pressure comparator 10 imposes on the fan 9 a too high discharge pressure, the pressure drops intervene effectively to limit an excessive increase air flow.

We can also note that the presence of air in very slight overpressure in space 3 avoids all seepage through the joints of column 1 (especially when it is made of bricks). In addition, the wall of this column is subjected on its two faces to almost equal pressures and runs no risk of bursting. As for the outer wall 2, even if it has slight leaks, this is immaterial since it is then air which escapes towards the outside.

We have schematically represented in FIG. 2 the general appearance of the gas jet 14 leaving a chimney according to the invention. This has a height H. The jet 14 of combustion gases or the like and the peripheral air rises first vertically, then gradually tilts under the effect of the wind (indicated by arrow 15). The horizontal plume 16 only appears at a height h above the nozzle la, so that from this point of view everything happens as if we were dealing with a conventional chimney of height H + h. It should also be noted that due to the delay in condensation, the jet 14 is at first perfectly transparent and practically invisible. It only takes the usual white color very gradually, for example at the level indicated in 14a. We could also increase this action of the auxiliary air by pre-treating it by heating and / or dehydration before discharging it into space 3.

It should also be noted in this regard that the auxiliary air is automatically heated by heat exchange with the wall of the column 1. This has the double advantage of reducing the energy required to obtain a determined temperature of this air at the outlet of the openings 4, on the other hand, to avoid excessive heating of said wall in the case of very hot gaseous products.

It should moreover be understood that the above description has been given only by way of example and that it in no way limits the field of the invention from which one would not depart by replacing the execution details described by all other equivalents. The auxiliary gas could be other than atmospheric air. We could treat it before sending it to space 3. Although it is particularly advantageous to make this space 3 over the entire height of the chimney to the nozzle la, we could, if necessary, reduce it to a sort of groove surrounding the openings 4 and that a pipe parallel to the column 1 would connect to the fan 9.

Claims (5)

1. Chimney for the evacuation into the atmosphere of combustion gases or the like, in which, in order to raise the plume of smoke or vapor, air is blown into the area of the upper outlet thereof ci so as to produce a jet which surrounds the stream of gaseous products to be discharged over at least part of its periphery, characterized in that it comprises means so that air or other auxiliary gas is discharged into said stream of gaseous products to be evacuated in a centripetal direction a short distance below its upper outlet. 2. Chimney according to Reveudication 1, of the type comprising a central column for the flow of the gaseous products to be evacuated and an outer wall which surrounds this column by providing an annular space in which the air intended to be mixed with these products passes. the upper outlet of said chimney, and of the kind also with forced draft in which the upper end is shaped as a nozzle, characterized in that it comprises at the base of this nozzle (la) radial discharge openings (4) which communicate the annular space (3) with the interior of the central column (1), the auxiliary gas being discharged into this space so as to be in overpressure relative to the gaseous products to be evacuated at said openings. 3. Chimney according to claim 2, characterized in that the outer wall (2) is connected to the central column (1) immediately above the injection openings (4) and below the nozzle. 4. Chimney according to any one of the preceding claims, characterized in that it comprises means (mano-comparator 10) for automatically adjusting at its base the discharge pressure of the auxiliary gas to a value slightly greater than that of blowing gaseous products to be removed. 5. Chimney according to any one of the preceding claims, characterized in that the auxiliary gas is treated before discharging it into the gaseous products to be discharged so as to lower its relative and / or absolute humidity and to reduce and / or delay the formation of the vapor plume above the outlet of said chimney.

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