EP0605821A1 - Exhaust gases extraction hood - Google Patents

Abstract

In order to further develop an exhaust gases extraction hood for extracting contaminated air or other gases in particular from elongated sources (10), the hood being bounded by two mutually parallel end faces (6) and having a lateral surface (7) running therebetween, in which at least one stabilised swirling flow is maintained, in such a way that said hood can be used for any lengths and which furthermore can be used advantageously as "overhead hood" without being connected to an exhausting area, can moreover be produced simply and economically, is easy to maintain and can be constructed so that it is operationally reliable, it is proposed that the exhaust gases extraction hood is provided between its end plates (6) with sink pipes (4) which are aligned at right angles to the axis of said end plates or radially to the lateral surface (7) and have sink openings concentric to the lateral surface (7), the sink pipes (4) introduced into the hood being linked to an exhausting system. <IMAGE>

Description

The invention relates to an exhaust gas detection hood for detecting contaminated air or other gases, in particular from elongated sources, in which the hood is delimited by two mutually parallel end faces and has a jacket running between them, in which at least one stabilized swirl flow is maintained.

For the removal of ascending or escaping exhaust gases from a source of air-polluting substances located in a hall Often a ridge ventilation with at least one longitudinal roof rider is provided in the ridge of the hall, which is provided with air outlets opening outwards. Roof attachments of this type are known in a wide variety of forms, and the individual embodiments are essentially concerned with ensuring that indoor air is unaffected by the weather. In such systems, these emerging contaminants initially pass into the air in the hall and are released into the free atmosphere with the air in the hall, possibly considerably diluted. This involves an air change that can possibly be tolerated in hot factories, but which leads to drafts and creates additional heating problems in halls without significant heat sources, and which generally does not allow the exhaust air to be cleaned. For this reason, in addition to encapsulating the source (direct suction), attempts have already been made to cover the base area of the source with a detection hood, which is then to take up and remove the contaminants emerging from the source. This extraction must be aligned with the work process so that the extraction hoods used for extraction capture the released air pollution as completely as possible. Such suction hoods, however, lead to considerable air flows that are difficult to manage; since these air flows have to be cleaned in downstream separators in order to comply with the requirements for keeping the air clean. Investment costs and the operation of such separators increase with the size of the air streams, so that, in particular, large-area extraction hoods entail considerable consequential costs because of the downstream separators. Hood designs in which suction is only carried out in the edge area to reduce the extracted air flow can be operated with a lower air flow, but their detection suffers in particular if the air pollution occurs intermittently or if it is released with high kinetic initial energy.

From DE-OS 39 01 859 is now a detection hood for contaminated Air is known which produces a suction air flow along a horizontal plane, the hood extending between two end faces providing a suction area, the width of which is given by the distance between the two end faces. The height of the inflow opening, which also extends over the entire width of the hood, can be designed as desired. It is essential here that both end faces are connected by a cylindrical partial casing which completes the housing of the hood, the inflow opening being smaller in height than the diameter of this casing. A pure swirl flow is formed in this hood, which, in compliance with the laws of potential flow, has a circumferential speed that is relatively high compared to the entry speed of the intake air. The dynamic pressure directly associated with the high peripheral speed allows the static pressure in the area of the inflow opening to drop because of the constancy of the total pressure, so that the desired effect of suctioning off and detecting the impurities released in the area of the inflow opening is ensured. With such a hood, suction air currents can be generated, provided the width of the hood does not exceed a dimension dependent on the swallowing capacity of the frontal depressions. In addition, such an exhaust gas detection hood requires a suction area that limits the flow in order to force the desired defined suction flow, which, however, is not possible in free space.

This is where the invention comes in, which is based on the task of further developing a generic exhaust gas detection hood in such a way that it can be used for any lengths , can advantageously be used as an "overhead hood". In addition, the hood should be simple and economical to manufacture, easy to maintain and reliable.

The solution to the problem is described in the features of the license plate contained in the main claim; advantageous further developments and preferred embodiments describe the subclaims.

According to the solution, the hood is provided with sink tubes which are aligned radially to the jacket surface and have sink openings concentric to the jacket surface, the sink tubes inserted into the hood being connected to a suction system. Characterized in that each of the end faces has two flow sinks and in that further flow sinks are provided at intervals therefrom, which are introduced radially into the partial cylinder, the sink pipes being provided with inflow openings which are coaxial with the cylinder producing the hood, flow conditions are created which ensure a continuous swirl flow over the entire width of the exhaust gas detection hood. These sink pipes are connected to suction systems, via which the air to be extracted is sucked out of the center of the stabilized swirl flow in such a way that this flow is maintained in a stable manner. These sink tubes each represent a double sink, since the inflow openings coaxial to the cylinder are open on both sides.

According to one embodiment, the cross section of the jacket is partially cylindrical; In another embodiment, it is polygonal, and in both forms the partial area corresponding to the outflowing flow can be drawn in to the central axis of the exhaust gas detection hood. In the case of the partially cylindrical shape, the spiral formation of at least this partial area is advantageous; in the case of the polygonal shape, the last section of the polygon lying in the direction of the flow is advantageously bent inwards, so that in both cases the desired restriction of the flow before entry is reached in the area of the suction opening.

In an advantageous development, the inflow openings of the flow sinks expediently have conventional inlet nozzles provided with curves, which are inserted into the end faces or the sink pipes. These rounded inlet nozzles reduce the inflow losses of each of these sinks and thus reduce the energy required to promote the extracted air flow.

The suction systems can be provided individually for each of these sink pipes, it being advantageous if the connections are made via flexible connecting lines. With the multitude of connections to be provided, the suction devices can also be set up in groups. Alternatively, all or some of the sink pipes combined in groups are connected to a suction device. In this case, a common suction channel is provided for all drain pipes or for the drain pipe group. In order to ensure the uniformity of the sink suction and to limit the pressure loss in the suction channel, the channel cross-section is designed such that the cross-section increases by a certain amount each time one of the sink pipes is introduced, this cross-sectional increase being such that the Flow velocity in the entire suction channel is essentially the same. The sink tubes are advantageously arranged at equidistant distances from the respectively adjacent or opposite the respective adjacent end wall. This arrangement provides a symmetry which allows the individual suction flows of the individual sinks (end faces) or double sinks (sink pipes) to be compared with one another in a simple manner.

In a preferred embodiment, the outer surface of the hood is formed by two penetrating cylinders, the penetration being such that the center points of the cylinders lie outside the respective other cylinder and that the openings of the cylinders complement one another to form a suction opening. Such an exhaust gas detection hood does not require an additional flow guide surface and it can easily be used as an "overhead hood". Since it can be extended to any length due to the additional sinks, it also allows exhaust gases or gases from elongated sources to be effectively captured and extracted. The source is advantageously parallel to the axis of the exhaust gas detection hood and symmetrical to a vertical plane running through its center. The jacket surrounding the hood volume is formed by two penetrating cylinders, which are equally open in the lower area of each of these cylinders, the air flowing into the suction opening is forced into a double swirl flow, the two swirl flows being afflicted in opposite directions and mutually stabilize. The arrangement of the two hoods, which are arranged in mirror image to one another, is important, the two swirling currents being superimposed in the area of penetration. With these opposing swirl flows it is achieved that the required suction flow is formed on both sides of the center plane of the hood arrangement. The opposing swirl flows in the two hoods, which are due to inflow asymmetries, run at a higher rotational speed than the suction speed, so that the dynamic pressure of the swirl flow can lower the static pressure in the inflow area and force the inflow out of the room. The inflow is mirror-symmetrical to the longitudinal axis and extends essentially over the entire length of the exhaust gas detection hood.

It is advantageous if the two outer edges of the jacket, which delimit the suction opening, are provided with guide surfaces directed into the interior of the cylinders, which narrow the flow cross-section of both cylinders in approximately the same way. This constriction of the swirl flows into the areas of their transitions into the inflow opening, which is known per se from DE-OS 39 01 859, accelerates the swirl flow on the one hand and the asymmetry of the inflow on the other enlarged and thus favors the formation of the swirl flow; this narrowing is made equally on both sides. A reduction in the radius of the swirl flow available by about 25%, which is provided here on both sides, has proven to be advantageous. This can be done by simple diaphragms attached to the corresponding edges of the partial shells of the hood and directed towards the respective center of the partial hood. Another possibility results from the fact that instead of these diaphragms, the edges of the partial shells delimiting the inflow opening are introduced into the swirl flow region with increased and / or increased edging or with increasing curvature, thus causing the flow to be restricted. These flow restrictions are advantageously designed so that they correspond to the upper surfaces of the source, whereby the exhaust gas detection hood can be adapted to the sources so that the "secondary air intake" is kept within limits. It is advantageous if the guide surfaces directed into the interior of the cylinder can be placed against the boundary surfaces of the source.

In a preferred embodiment, the exhaust gas detection hood is arranged to be adjustable in height and is preferably provided with an adjustment drive. Their connecting pieces are connected to the suction lines or to the suction channel. It goes without saying that it is irrelevant for the function of the suction hoods whether they are connected to rigid suction tubes or to flexible suction lines. The rigid suction pipes are telescopically pushed into one another when the height of the hood changes, for example, or they can be pivoted to compensate for the height difference. In the case of flexible suction lines, a certain amount of height difference can be bridged with their flexibility in a simple manner, although increased pipe friction and an associated increased pressure drop have to be accepted.

To generate an effective suction flow via the stabilized Swirl flow means that the flow sinks of the outer of the sink pipes, which are arranged opposite one another in pairs, and those of the associated end faces of the exhaust gas detection hood or the adjacent sink pipes are significant, the flow sinks being coaxial with one another. It is primarily a question of the inflow speed of the air into the flow sinks, for reasons of continuity the air flow entering the flow sinks must correspond to the air flow that enters the hood through the inflow opening, the entry speed into the hood due to the superimposed high swirl speed (relative ) can be kept small. The swirl currents develop safely and without interference if the two partially cylindrical housing walls of the suction hood each guide the flow at least over 270 °. If the flow in the area of the edge opposite the inflow surface or the plane of symmetry is also narrowed (ie its speed is increased), the stability increases further. It is advantageous if the constriction is carried out by a straight or a diaphragm rounded in accordance with the flow in such a way that the radius of the flow is reduced by about 25%. This diaphragm also achieves a "pre-direction" of the air flowing in to the inlet opening from the side facing away from the inflow surface, so that the formation and the stability of the swirl flow are also favored from this side.

Fig. 01:

Schema-Darstellung eines Haubenstückes mit angedeuteter Strömung;

Fig. 02:

Querschnitt einer Haube mit spiraligem Mantel;

Fig. 03:

Querschnitt einer Haube mit polygonalen Querschnitt;

Fig. 04:

Längs-Ansicht einer Abgaserfassungs-Haube mit Abluft-Sammelkanal;

Fig. 05:

Querschnitt durch eine Abgaserfassungs-Haube mit doppelter Drallströmung.

The essence of the invention is explained in more detail with reference to Figures 1 and 2; show

Fig. 01:

Schematic representation of a hood section with indicated flow;

Fig. 02:

Cross section of a hood with a spiral jacket;

Fig. 03:

Cross section of a hood with polygonal cross section;

Fig. 04:

Longitudinal view of an exhaust gas detection hood with exhaust air collecting duct;

Fig. 05:

Cross section through an exhaust gas detection hood with double swirl flow.

FIG. 1 shows a highly schematic section of an exhaust gas detection hood in a perspective view with an end plate 6 and a jacket 7 which extends from the end plate 6 in the axial direction and which has a cylindrical cross section in the example shown. The end plate 6 is provided (here :) with a sink pipe 3 arranged centrally to the jacket 7, which has an inlet nozzle 3.1, which represents the flow sink and with which exhaust air is taken over in the center of the exhaust gas detection hood and thus a swirl flow is excited. Because of the limited effect of such a sink flow in the axial direction, a sink pipe 4 is guided axially into the flow through the jacket 7 at a distance from the end plate 6 and is provided with two mutually directed inlet nozzles 4.1, which are coaxial with the inlet nozzles 3.1 of the end plates 6 lie. These inlet nozzles 4.1 of the axial sink pipes 4 likewise produce a sink flow, as indicated by the dashed arrows, which stimulates a swirl flow, also indicated by the dashed arrows, with a proportion of air corresponding to the air flowing into the flow sink through the inflow opening 8 of the exhaust gas detection system. The hood is sucked in again, as indicated by dashed arrows. By an apron 9.1 directed into the interior of the exhaust gas detection hood, the swirl flow is forced inward before entering the area of the inflow opening 8 and thereby accelerated, so that the dynamic pressure increases and the static pressure required for the inflow of air from the Outside space is responsible, because of the constant total pressure drops.

The swirl flow is not tied to a cylindrical shape of the exhaust gas detection hood. As FIG. 2 shows, hoods with a spiral-shaped jacket 7 'can be used in the same way, the flow (indicated by dashed lines) over the entire path is pushed inside. The acceleration is distributed over the path covered by the jacket 7. The end plate 6 is here (shown for better illustration with a circularly delimited upper part) beyond the suction opening 8, both ends of the jacket 7 being provided with aprons 9.2 which, together with the protruding end plate 6, limit the inflow region to the outside. In FIG. 3, the casing 7 ″ is designed as a polygon (shown here as a hexagon). With this design of the jacket 7, the exhaust gas detection hood is able to generate and guide a swirl flow (shown in dashed lines). Here, too, it is possible, for example by bending the last section of the polygon in the direction of flow, to force the swirl flow inwards and thus accelerate it before entering the area of the suction opening 8. The end plate 6 is expediently adapted to the polygon, it being able to protrude in the region of the inwardly bent section. In this embodiment, too, the two ends of the jacket 7 can be provided with aprons which — as in the case of the spiral jacket 7 ′ - are directed outwards and, together with the projection of the end plate 6, limit the inflow region.

FIG. 4 shows a longitudinal view of an exhaust gas detection hood with the jacket 7, which extends between the two end plates 6. The axial sink tubes 3 for the end plates are guided centrally into these end plates and are provided with inlet nozzles 3.1 on the inflow side. Between the end plates 6 there are also radially inserted sink tubes 4 at equal distances from the end plates 6 or from one another, which are provided coaxially with the inlet nozzles 3.1 of the axial sink tubes 3 with inlet nozzles 4.1. Each of the radial sink tubes 4 has two inlet nozzles 4.1, which are directed towards each other. The axial drain pipes 3, like the radial drain pipes 4, are connected via the connecting lines 3.2 and 4.2 to an exhaust air collecting duct 2, which in turn is connected to the exhaust air connector 1 is connected to an exhaust air extraction system (not shown). A proportion of fresh air corresponding to the air sucked out via the inlet nozzles of the sink pipes is sucked in through the suction opening 8, an inward-facing apron 9.1 pushing the air into the area of the suction opening 8 of the swirl flow inward and accelerating it.

FIG. 5 shows a special application of the exhaust gas detection hood: Here two opposing swirl flows are generated in a hood which is provided with two end plates, one of which can be seen in the section shown. Between these end plates 6 extends the jacket 7, which is formed here from two penetrating cylinders, these mutually penetrating cylinders being open in the range of the angle, which is in the range from 90 ° to 145 °. Otherwise, the end plates 6 are provided with the axial sink pipes 3 and radial sink pipes 4 are introduced into the swirl flow, all sink pipes being provided with the corresponding inlet nozzles 3.1 and 4.1, respectively, which have one or two (not shown in more detail) exhaust air collecting duct / channels are connected. The two swirl flows which are formed by the inflow of the extracted air into the inflow openings of the sink pipes are in opposite directions, the direction of flow being advantageously chosen such that both swirl flows in the area of the suction opening 8 are directed away from the latter. Both edges of the common casing 7 are expediently provided with inward-facing skirts 9.1, which force both swirl flows inwards and accelerate them before they enter the area of the suction opening 8. The two coats can also be formed spirally inwards - as indicated by dashed lines. The end plates 6 can - as shown - be designed so that their contour represents an envelope of the common jacket 7. It goes without saying that this end plate 6 can also be shaped according to the contour of the common casing 7.

Claims (18)

Exhaust gas detection hood for detecting contaminated air or other gases, in particular from elongated sources, in which the hood is delimited by two mutually parallel end faces and has a jacket running between them, in which at least one stabilized swirl flow is maintained, characterized in that the exhaust gas detection hood is located between its end plates (6) is provided with sink tubes (4) oriented at right angles to its axis or radially to the lateral surface (7), which have sink openings concentric to the lateral surface (7), the sink tubes (4) inserted into the hood being connected to a suction system are. Exhaust gas detection hood according to claim 1, characterized in that the cross section of the jacket (7) is partially cylindrical. Exhaust gas detection hood according to Claim 2, characterized in that the cross section of the jacket (7 ') is of spiral design at least in a partial region corresponding to the outflowing flow. Exhaust gas detection hood according to claim 1, characterized in that the cross section of the jacket (7 '') is polygonal. Exhaust gas detection hood according to claim 4, characterized in that the shape of the polygonal casing (7 '') is drawn in towards the axis at least in a partial area corresponding to the escaping flow. Exhaust gas detection hood according to one of claims 1 to 5, characterized in that the inflow openings for the flow sinks have customary rounded inlet nozzles (3.1; 4.1) which are inserted into the end faces (6) or the sink pipes (4). Exhaust gas detection hood according to one of Claims 1 to 5, characterized in that the suction system for the sink pipes (3; 4) comprises a number of suction devices which corresponds to the number of sink pipes (3; 4) and which is connected to the sink pipes assigned to them via preferably flexible connecting lines are, is formed. Exhaust gas detection hood according to one of claims 1 to 5, characterized in that the suction system for the sink pipes (3; 4) is formed by at least one central suction device, each of which works on an exhaust air collecting duct (2) and the sink pipes (3; 4 ) are connected to this suction channel (2). Exhaust gas detection hood according to claim 8, characterized in that an enlargement of the cross section of the exhaust air collecting duct (2) is provided at least at each junction of one of the sink pipes (3; 4), the enlargement of the cross section is preferably such that the flow velocity in the suction channel (2) is essentially constant. Exhaust gas detection hood according to one of Claims 1 to 9, characterized in that adjacent sink tubes (4) are at equal distances from one another and from the end walls (6). Exhaust gas detection hood according to one of claims 1 to 10, characterized in that the outer surface (7) of the exhaust gas detection hood is formed by two penetrating cylinders, the penetration being such that the centers of the cylinders lie outside the respective other cylinder and that the openings of the Cylinder (7) add up to a suction opening (8). Exhaust gas detection hood according to Claim 11, characterized in that the jacket (7) of the exhaust gas detection hood is opened in the lower region to the suction opening (8), preferably both cylinders being opened equally far. Exhaust gas detection hood according to claim 11 or 11, characterized in that the two outer edges of the jacket (7) which delimit the suction opening are provided with guide surfaces (9.1) which face the interior of the two penetrating cylinders and which have approximately the flow cross section of both cylinders (7) narrow in the same way. Exhaust gas detection hood according to Claim 13, characterized in that the exhaust gas detection hood is arranged in such a way that the guide surfaces (9.1) directed into the interior of the cylinders (7) delimit the top of the source (10) Areas correspond. Exhaust gas detection hood according to claim 14, characterized in that the guide surfaces (9.1) directed into the interior of the cylinders (7) can be placed against the boundary surfaces of the source (10). Exhaust gas detection hood according to one of claims 1 to 15, characterized in that the exhaust gas detection hood is arranged adjustable in height and is preferably provided with an adjustment drive. Exhaust gas detection hood according to claim 16, characterized in that the suction lines (1) or the sink pipe connections (4.2) to the exhaust air collecting duct (2) are flexible. Exhaust gas detection hood according to claim 17, characterized in that the suction lines (1) are designed as telescopic lines.

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