NL2005456C2

NL2005456C2 - Push element for use in push-pull ventilation system, and method of applying push-pull ventilation using the same.

Info

Publication number: NL2005456C2
Application number: NL2005456A
Authority: NL
Inventors: Theo Oossanen
Original assignee: Theo Oossanen
Priority date: 2010-10-05
Filing date: 2010-10-05
Publication date: 2012-04-06

Description

Title: Push element for use in push-pull ventilation system, and method of applying push-pull ventilation using the same

Field of the invention 5 The present invention relates to the field of ventilation systems, and more in particular to a push element and a method for generating an air flow pattern that optimizes the capture efficiency of such systems.

Background 10 Process ventilation may be applied to transport air contaminants, such as heat, noxious or irritating fumes or vapors, suspended matter like dust, et cetera from a process location to elsewhere. In doing so, a process ventilation system may generally aim to remove contaminants from the process location at the highest possible concentration, i.e. to remove as much 15 contaminants with as little displaced and exhausted air as feasible, in order to optimize the capture efficiency of the system and to reduce the costs of running it.

A process ventilation system may generally include at least one exhaust point, e.g. a pull hood, at which air is pulled in to be removed from 20 the process location. In situations where it is impractical to dispose an exhaust point in the immediate vicinity of the source of the contamination, an air flow extending from or along the source to the exhaust point may be effected to aid the transport of contaminants from the source to the exhaust point. A process ventilation system that employs such a configuration 25 including a pull hood and a push air flow is commonly known as a ‘push-pull system’. In such a system, the push element used for emitting the push flow is of dominant importance to the operation of the process ventilation, since it conditions the initial geometry and air dynamics of the flow. Accordingly, it also determines to a large extent the system’s capture efficiency.

2

It is an object of the present invention to provide for a push element, suitable for use in a high-efficiency push-pull process ventilation system.

Summary of the invention 5 A first aspect of the present invention is directed to a push element suitable for use in a push-pull ventilation system. The push element may comprise a manifold including an air inlet and a first air outlet. The first air outlet may extend in a first direction, and include at least one air outlet opening. The manifold may be configured to emit an air curtain from the at 10 least one air outlet opening into an emission plane that extends parallel to the first direction. The push element may further include a guide blade including a first, substantially planar guide surface that extends substantially parallel to the emission plane, and that is disposed adjacent the first air outlet, such that, in operation, it borders on an onset of an air curtain 15 emitted from the at least one outlet opening.

The push element according to the present invention may be used as part of a variety of air ventilation or circulation systems, and for different purposes. One general purpose of the push element, however, may be described independently of the precise nature of the system in which it is 20 integrated. The push element may typically be installed in a gaseous, aerial atmosphere that, due to an industrial process performed therein, includes at least two discernable spatial zones. A first zone may be located relatively close to the process location, while a second zone may be located relatively distant therefrom. As a result of its proximity, the first zone may experience 25 the effects of the industrial process to a larger extent than the second zone.

The first zone may, for example, comprise warmer gas than the second zone in case the industrial process involves heating, or a larger content of contaminants given off by the industrial process. The push element may be employed to provide for a moving air curtain along a boundary between the 30 first and the second zone. Although the air curtain may have additional 3 functions, it may commonly at least serve to prevent gas present in the first zone from freely flowing into the second zone, and/or vice versa. That is, it may prevent warm gas in the first zone from flowing into and mixing with gas in the second zone, or prevent contaminants in the first zone from 5 spreading into the second zone. In this respect it is important that the generation of the moving air curtain itself does not cause or involve substantial mixing of gas from the first and second zones. The push element according to the present invention prevents such mixing at the generation stage of the curtain by means of the guide blade. The guide blade may be 10 disposed substantially at the boundary between the first and second zones, such that a first side thereof faces the first zone, and a second side thereof faces the second zone. Furthermore, the outlet of the push element may be located on either one of said sides of the guide blade, and adjacent thereto. In operation, the air outlet of the push element may emit an air curtain into the 15 atmosphere, in a direction substantially parallel to the adjacent side of the guide blade. The onset of the air curtain, having a relatively high velocity relative to the gaseous atmosphere, may thereby attempt to draw in or induce gas at its boundaries, i.e. both at its boundary facing the first zone and at its boundary facing the second zone, which would normally lead to the undesired 20 mixing. However, due to the presence of the guide blade, one of the boundaries of the onset of the air curtain is physically detached from gas in the adjoining atmosphere zone, and thus prevented from inducing gas therefrom. Below, several exemplary push-pull ventilation and air circulation systems that rely on this effect will be illustrated.

25 Another aspect of the present invention is directed to a method of using a push element according to the present invention in a push-pull ventilation system setup. The method may include performing, at a process location, a process by which air contaminants are produced, and providing a push element according to the present invention on a first side of the process 30 location. The method may further include providing a pull element on a 4 second, opposite side of the process location, wherein the pull element includes at least one exhaust inlet that faces the first air outlet of the first push element. The method may also include supplying pressurized air to the inlet of the manifold of the push element, such that an air curtain is emitted 5 from the at least one first air outlet opening thereof having an air speed in the range of 2.5-10 m/s, and preferably in the range of 5-10 m/s.

The first guide surface of the guide blade of the push element may preferably face the process location, or in terms of the above exposition: the first zone. In such a configuration the air curtain serves as a ‘contamination 10 accumulator and carrier’ that may induce contaminated air as it is generated and travels along the process location, towards the pull element. It has been observed that initial air curtain speeds in the range of 2.5-10 m/s (2.5 m/s for a relatively narrow spacing between the push and pull elements, e.g. < 1 m, and 10 m/s for a relatively large spacing, e.g. several meters) may generally 15 work satisfactorily in the sense that they provide for a sufficient degree of induction to have a significant, positive effect on the capture efficiency of the ventilation system. Higher initial air speeds may thereby provide for a greater induction rate, but also cause portions of the air curtain to eventually ‘overshoot’ the pull element. The optimal initial speed of the air curtain is 20 therefore to be determined with respect to a concrete application.

The construction and use of the push element according to the present invention, both alone and in different air ventilation and circulation systems, will be more fully understood from the following detailed description taken together with the accompanying drawings, which are meant to 25 illustrate and not to limit the invention.

Brief description of the drawings

Fig. 1 is a schematic cross-sectional side view of a conventional push-pull process ventilation system installed on opposite sides of an open 30 surface treatment tank; 5

Fig. 2 is a schematic cross-sectional side view of a first exemplary embodiment of a push-pull process ventilation system according to the present invention, installed on opposite sides of an open surface treatment tank; 5 Fig. 3 is a schematic perspective view of the push element of the process ventilation system shown in Fig. 2;

Fig. 4 is a schematic cross-sectional side view of a second exemplary embodiment of a push-pull process ventilation system according to the present invention, installed on opposite sides of a surface treatment bath, 10 wherein the push element includes two air outlets that are separated by a guide blade;

Fig. 5 is a schematic cross-sectional side view of a third exemplary embodiment of a process ventilation system according to the present invention, including two push elements that are arranged on opposite sides of 15 an open surface treatment tank;

Fig. 6 is a schematic cross-sectional side view of a fourth exemplary embodiment of a process ventilation system according to the present invention, including an exhaust hood disposed above an open surface treatment tank; and 20 Fig. 7 schematically illustrates in two cross-sectional side views a fifth exemplary embodiment of an air circulation system according to the present invention, the system including at least two push elements that have been arranged adjacent an entrance and/or exit opening of a heated process chamber.

25

Detailed description

Push-pull process ventilation systems are known in the art and in common use in industries where contaminants or pollutants need to be removed from a process location within a working environment. By way of 30 example, Fig. 1 shows a schematic side view of a conventional push-pull 6 process ventilation system 1 installed on opposite sides 8, 8’ of an open surface treatment tank 6. The tank 6, which in the depicted setup defines the process location, may for example comprise molten zinc for hot-dip galvanizing metal objects, such as scaffolding elements or steel sheet car body 5 panels. As the zinc in the tank 6 is maintained in its molten state, metal fumes may continuously arise from the open surface of the tank. The fumes may contain contaminants like fine zinc-dust particles and simple zinc compounds, e.g. zinc oxide, which are considered harmful to the health of workers working in the vicinity of the tank 6.

10 To remove the noxious fumes from the process location, the installed push-pull system 1 includes a push element 2 and a pull element 4. The push element 2 is disposed on a first side 8 of the tank 6, not too far above the open surface thereof. It is configured to generate an air jet 12 in the form of a curtain. The air jet 12 is directed across the open surface of the tank 15 6 and towards the pull element 4, disposed on the opposite, parallel side 8’ thereof. Accordingly, once the air jet 12 is emitted by the push element 2, it travels across the surface of the tank 6, accumulating contaminants and transferring them to the pull element 4, which eventually collects the air jet 12 and the contaminants captured therein.

20 Upon emission from the push element 2, the air jet 12 has a velocity in the direction of the pull element 4 that is significantly larger than that of the comparatively stationary environmental air 10 above the tank 6. As a result the air jet 12 will drag along and suck in such environmental air 10 as it travels, a process called induction. Induction of environmental air 10 by the 25 air jet 12 causes the velocity of the air jet to diminish gradually, and the overall mass of air moving towards the pull element 4 to increase; i.e. the air jet 12 grows wider (cf. Fig. 1). The ratio between the mass flow of air (jet air including induced environmental air) moving across the tank 6 and the mass flow of the air jet upon its generation at the push element 2 is called the 30 induction rate (Dutch: “het inductievoud”).

7

As indicated in Fig. 1, induction of environmental air 10 may take place both at the lower 12a and the upper boundary 12b of the air jet 12. While induction at the lower boundary 12a may be considered advantageous, induction at the upper boundary is typically undesirable. The reason for this 5 is as follows. The air jet 12 may be considered to divide the environmental air 10 above the tank 6 into a lower zone 10a below the air jet 12, and an upper zone 10b above it. The environmental air 10 in the lower zone 10a, which extends between the open surface of the tank 6 and the lower boundary 12a of the air jet 12, includes high concentrations of contaminants as a result of 10 the noxious fumes that continuously emerge from the tank 6. The air jet 12 produces a depression in this lower zone 10a, and so generates a recirculating flow of highly contaminated air, part of which is induced by the air jet 12. Induction of environmental air 10 at the lower boundary 12a of the air jet 12 thus ‘enriches’ the air jet 12, i.e. increases its contaminant concentration. In 15 contrast, the environmental air 10 in the upper zone 10b may include relatively low levels of contaminants since it is effectively shielded from contact with the open surface of the tank 6 by the air jet 12. Nevertheless, a significant amount of relatively clean environmental air 10 is induced at the upper, free boundary 12b of the air jet 12. This induction at the upper 20 boundary 12b causes a decrease in contaminant concentration in, i.e. dilution of, the air jet 12, and hence a decrease in the capture efficiency of the ventilation system 1. From a practical point of view, the induction of relatively clean environmental air 10 from the upper zone 10b translates into the demand that more air be displaced, and eventually exhausted by the pull 25 element 4, in order to maintain the overall contamination content of the environmental air 10 at a desired level.

Fig. 2 schematically illustrates a first exemplary embodiment of a push-pull process ventilation system 100 according to the present invention that mitigates the aforementioned problem. The ventilation system 100 30 includes a push element 120 and a pull element 140. The push element 120 is 8 schematically depicted in more detail in a perspective view in Fig. 3. For ease of comparison, the ventilation system 100 is depicted as installed on opposite sides 108, 108’ of an open surface treatment tank 106 similar to that shown in Fig. 1. One skilled in the art will appreciate, however, that the ventilation 5 system 100 according to the present invention is not limited to applications involving such a treatment tank 106. The treatment tank 106 may therefore be taken to represent any process location from which contaminants like noxious fumes and suspended matter are to be removed. Exemplary alternative process locations may include metalworking locations for hot or 10 cold rolling metal from which the fumes of rolling emulsions need to be removed, and production lines in the food processing industry from above which water vapor and/or aromatic substances are to be exhausted.

First, the general construction of the ventilation system 100, and in particular the push element 120 thereof, will be described with reference to 15 both Fig. 2 and 3. The operation of the ventilation system 100 will be discussed directly there after.

The push element 120 may include a manifold 122. The manifold 122 may typically be shaped to follow a contour or side of a process location 106. This may often imply that the manifold 122 is elongate and generally 20 straight for reasons of space efficiency, although in principle it may have any suitable shape. In the embodiment of Figs. 2 and 3, the manifold 122 comprises a tube that extends in an axial or longitudinal direction X between a first end and a second end. The manifold 122 may define an interior plenum 124, and include an air inlet 126 and a (first) air outlet 128a. Pressurized air 25 may be supplied to the plenum 124 via the air inlet 126, and be emitted from the plenum 124 via the air outlet 128a, so as to form an air curtain 112.

In the case of an elongate manifold 122, as shown in Figs. 2 and 3, an air inlet 126 may be provided at one or both the respective end(s) of the manifold. Alternatively, the ends of the manifold 122 may be closed, and an 30 air inlet 126 may be provided along a longitudinal portion of the manifold 122.

9

The air inlet 126 may for example include a continuous, elongate air inlet slot, or a plurality of discrete, spaced apart air inlet openings. An elongate manifold 122 with an air inlet 126 located at one or both of its ends may be attractive for reasons of constructional simplicity. However, when the 5 manifold 122 is relatively long, the supply of pressurized air via distant air inlets 126 may easily give rise to pressure variations within the plenum 124. These pressure variations may correspond to non-uniform air emission conditions along the longitudinal direction X of the manifold 122, which is generally undesirable. It may therefore be preferable to equip a long manifold 10 122 with an air inlet 126 that extends along the longitudinal direction X of the manifold 122.

The air outlet 128a may extend along the longitudinal direction Xof the manifold 122, and comprise at least one air outlet opening 130a provided in a wall thereof. In one embodiment, the at least one air outlet opening may 15 take the form of a continuous, elongate air outlet or emission slot (not shown). In another, preferred embodiment, the air outlet 128a may include a plurality of aligned, longitudinally spaced apart air outlet openings 130a or nozzles.

See Fig. 3.

Various aspects of the geometry of the push element 120 as a whole 20 may be purposefully related to the geometry of the air outlet opening(s) 130a of the air outlet 128a, as will be elucidated below. To this end, the air outlet opening(s) 130a may be associated with a characteristic dimension D that may be held to be normative for other dimensions of the push element 120. In embodiments where the air outlet 128a includes an elongate emission slot, D 25 may be taken to be the width (in Fig. 1 measured in the Z-direction) of that slot. Similarly, in embodiments where the air outlet 128a comprises a plurality of air outlet openings 130a, the characteristic dimension D may be taken equal to an (effective) average diameter of the air outlet openings 130a of said plurality.

10

Different air outlet openings 130a of the air outlet 128a may be identical in shape, but need not be. In the embodiment of Fig. 3, for example, the air outlet openings 130a are all of a substantially circular cross-section, but it is contemplated that one or more of them may have a different shape in 5 other embodiments, e.g. elliptical, square or otherwise. In either case, the plurality of air outlet openings 130a may be associated with a typical average air outlet opening diameter D in the range of 2-25 mm.

The air outlet openings 130a may be regularly, in particular equidistantly, spaced along the longitudinal direction X. The center-to-center 10 spacing of the air outlet openings 130a may thereby be characterized by an average center-to-center distance d. In a preferred embodiment of the push element 120, the average center-to-center distance d may be in a range of 2D-8D, and preferably in a range of 2D-4D. An average center-to-center distance d in the aforementioned ranges helps to ensure that the air outlet opening-15 density (i.e. the number of such openings per unit of length) is sufficiently large to effect the formation of a continuous or closed air curtain 112 at a relatively short distance from the air outlet openings 130a.

To determine the direction in which air is emitted from an air outlet opening 130a, each air outlet opening may be provided at the downstream 20 end of a respective air outlet channel 132a. In a constructionally simple embodiment, an air outlet channel 132a may be provided in a wall of the manifold 122, for example in the form of a bore or passage, such that a length of the channel 132a corresponds to the thickness of the manifold wall in which it is provided. See for example the embodiment of Figs. 2 and 3. In an 25 alternative embodiment, one or each air outlet channel may be provided for in the form of a separate nozzle, pipe or conduit, an upstream end of which is in fluid communication with the plenum 124, and a downstream end of which defines the respective air outlet opening 130a. Independent of the specific embodiment chosen, an air outlet channel 132a, or at least a downstream end 30 portion thereof, may preferably have a length that is equal to or larger than 11 D, and extend in a second or emission direction Ythat is substantially perpendicular to the first direction X along which the air outlet 128a extends. Accordingly, at least immediately prior to being emitted from the air outlet openings 130a, air for an air curtain 112 is guided by the air outlet channels 5 132a into in the desired emission direction Y.

The X/Y-plane into which an air curtain 112 is to be emitted, i.e. the (infinitely extending) plane having a small but finite thickness in which the onset or initial portion of an emitted air curtain may be considered to extend during operation, is referred to in this text as the emission plane. Given 10 uniform emission conditions along a length of an air outlet 128a, an air curtain 112 emitted from the outlet into a fully homogenous atmosphere or environment would develop symmetrically relative to this emission plane. In Figures 2 and 3, a small portion of an emission plane Ea associated with an air curtain 112 is shown to indicate its location and orientation.

15 The push element 120 may further comprise a guide blade 134.

The guide blade 134 may be connected to the manifold 122, and extend along the entire length of the air outlet 128a thereof. It may additionally extend from the manifold 122 into the Y direction into which the air curtain 112 is to be emitted. An (elongate) connection between the guide blade 134 and the 20 manifold 122 may preferably be airtight, so that air on one side of the guide blade is prevented from flowing to the other side thereof via the connection.

The guide blade 134 may provide for a (first) guide surface 136a. The guide surface 136a may preferably be substantially planar, as in the embodiment of Figs. 2 and 3, although it is contemplated it may be somewhat 25 curved in alternative embodiments. The guide surface 136a may extend substantially in parallel with the emission plane Ea in which the air outlet 128a is configured to emit the air curtain 112. In addition, it may preferably be disposed adjacent the at least one air outlet opening 130a of the air outlet 128a, such that, in operation, it faces and borders on the onset or initial 30 portion of an air curtain 112 emitted there from.

12 A distance S between the first guide surface 136a and the emission plane Ea in which the air curtain 112 is to be emitted, may preferably be in the range of 1D-3D. Larger separations S might easily negate the desired effects of the guide surface 136a, as will be clarified below.

5 A distance W over which the guide surface 136a extends in the emission direction Y beyond or past the air outlet opening(s) 130a of the air outlet 128a, may be at least 5D, and preferably at least ΙΟΖλ Such an extension may effect a high induction rate adjacent the first guide surface 136a, which in the situation shown in Fig. 2 may causes the air curtain 112 to 10 have a high contamination content at the end of the guide blade 134.

The pull element 140 of the ventilation system 100 may be disposed on a side 108’ of the open surface treatment tank 106 opposite to that on which the push element 120 is installed, and be of a conventional design. The pull element 140 may in particular include an exhaust hood or a similar 15 device.

With regard to the configuration of the installed ventilation system 100 as shown in Fig. 2, it is noted that the guide surface 136a of the guide blade 134 faces the process location 106, such that the air outlet 128a of the push element 120 is disposed at a level between the first guide surface 136a 20 and the surface of the tank. In addition, it deserves mentioning that both the air outlet 128a of the push element 120 and an exhaust inlet 142 of the pull element 140 may generally be located relatively close to, e.g. within a vertical distance of about 50 cm of, a surface level of the tank 106. The push element 120 may thereby be oriented such that the direction Y into which an air 25 curtain 112 is to be emitted extends substantially parallel to said surface level of the tank 106; see Fig. 2. Alternatively, the direction Y may be made to extend downwards towards the surface of the tank 106, so as to include an angle there with, for example in the range of 20-45 degrees. To promote the smooth circulation of (contaminated) air, the space between just downstream 13 of the air outlet openings 130a of the air outlet 128a and the open surface of the treatment tank 106 may preferably be free of any physical obstacles.

Now that the general construction of the push-pull ventilation system 100 according to the present invention has been described in some 5 detail, attention is invited to the operation thereof.

Referring in particular to Fig. 2. During operation, the air inlet 126 of the manifold 122 of the push element 120 may normally be connected to a source of pressurized air, e.g. an air pump. The source may supply the pressurized air to the plenum 124, from which it may subsequently be 10 emitted via the air outlet 128a in the form of an air curtain 112. It is understood that the air pressure that is maintained in the plenum is related to the speed at which the air is emitted from the outlet opening(s) 130, and that a greater spacing between the push element 120 and the pull element 140 may generally require a greater initial air speed, and hence a greater air 15 pressure in the plenum, for the ventilation system 100 to work properly.

Typical initial air speeds of the air curtain 112 may be in the range of 2.5-10 m/s, and preferably in the range of 5-10 m/s. In case the air outlet 130 includes a plurality of spaced apart air outlet openings 130, the distance from the air outlet openings 130 at which the air curtain 112 becomes continuous 20 or closed may depend largely on the average center-to-center-spacing d between them. Generally, the smaller the spacing d, the sooner the air curtain becomes continuous.

In the orientation of Fig. 2, the guide surface 136a of the guide blade 134 roofs over the onset or initial portion of the air curtain 112 much 25 like a lean-to roof. Provided it is positioned close enough to the air outlet 128a, it prevents the initial portion of the air curtain 112 from inducing environmental air 110 at its upper boundary 112b. At the same time, the first guide surface 136a may prevent air recirculating in the lower zone 110a from escaping through gaps in between individual air jets emitted from respective 30 air outlet openings 130, which jets have not yet fused together to form a 14 continuous curtain 112. Both effects of the first guide surface 136a promote enrichment of the air curtain in contaminants, and thus enhance the capture efficiency of the ventilation system 100.

A drawback associated with the first exemplary embodiment of the 5 ventilation system 100 illustrated in Fig. 2 is that the air curtain 112 may still induce relatively clean environmental air 110 from the upper zone 110b once it has left from underneath the first guide surface 136a. The cause of the induction lies at least partly in the velocity difference between the moving air curtain 112 and the comparatively stationary environmental air 110.

10 The issue may be addressed by providing the manifold 122 of the push element 120 with two air outlets 128a, 128b, as shown in the second embodiment of the ventilation system 100 of Fig. 4. The two air outlets 128a, 128b may extend in parallel, and each be of a similar or identical construction as described above. Each air outlet 128a, 128b may for example include a 15 plurality of longitudinally spaced apart air outlet openings 130a, 130b. The air outlet openings 130a, 130b may all be connected to the same plenum 124, and be configured such that pressurized air supplied there to via an air inlet 126 is emitted from both the first and second air outlets 128a, 128b into a second direction Y that is substantially perpendicular to the first direction X 20 along which the outlets 128a, 128b extend. Hence, the first and second air outlets 128a, 128b may be configured to emit two initially parallel curtains of air 112, 113. The guide blade 134 of the push element 120 may be connected to the manifold 122, at a position in between the first and second air outlet 128a, 128b, and extend there from in the second direction Y. In operation, the 25 guide blade 134 may thus extend in between the onsets of the respective air curtains 112, 113. A first, preferably planar guide surface 136a of the guide blade 134 may thereby flank a portion of the upper boundary 112a of the (onset of the) first air curtain 112, while a second, preferably planar guide surface 136b of the guide blade 134, facing away from the first guide surface 30 136a, may flank a portion of the lower boundary 113a of (the onset of) the 15 second air curtain 113. Accordingly, the guide blade 134 may ensure that the onset of the upper air curtain 112b merely induces clean, environmental air 110 from the upper zone 110b, while the onset of the lower air curtain 112a merely enriches itself through induction of contaminated air from the lower 5 zone 110a. Beyond the guide blade 134, the upper boundary 112b of the lower air curtain 112 may border on the lower boundary 113a of the upper air curtain 113. Due to the fact that the air of the respective curtains 112, 113 may move at approximately the same speed in approximately the same direction at both boundaries 112b, 113a, further induction at these 10 boundaries may remain limited. Compared to the situation of Fig. 2, the air curtain 112 may thus be subject to less dilution, which enables it to deliver air with a relatively high contamination content to the exhaust hood 140 at the opposite side 108’ of the open surface treatment tank 106.

The two air outlets 128a, 128b of the push element 120 may be 15 mutually identical, but need not be. It is contemplated that in an advantageous embodiment the second air outlet 128b may comprise more and/or larger outlet openings 130b, or in case of emission slots: a wider emission slot, than the first air outlet 128a. When the second air outlet 128b is fitted with a larger (effective) air outlet opening area per unit of length of 20 the air outlet than the first air outlet 128a, while both air outlets 128a, 128b are connected to the same plenum 124, the second air outlet 128b may, during operation, emit more air per unit of length than the second air outlet 128a. As a result of its larger air mass, the air curtain 113 emitted by the second air outlet 128b may carry a larger impulse than air curtain 112 25 emitted by the first air outlet 128a, which may make the former harder to slow down by induction of environmental air 110. The larger impulse (per unit of air outlet length) of the upper air curtain 113 may be useful in configurations where the spacing between the push element 120 and the pull 140 is relatively large, and the upper air curtain 113 proves to be more prone 30 to losing velocity due to induction of environmental air 110 than the lower air 16 curtain 112. In such cases, the larger impulse of the upper air curtain 113 may ensure that the velocity of the upper air curtain 113 does not significantly fall behind that of the lower curtain 112 in the course of crossing the process location 106, which in turn could cause the lower curtain 112 to 5 stagnate (by induction) as well.

It is understood that instead of providing a single push element 120 according to the present invention with two air outlets 128a, 128b, as shown in Fig.4, it is possible to use two push elements 120 each with a single air outlet 128a, for example by disposing the two push elements on top of each 10 other, with their guide blades 134 back-to-back and their guide surfaces 136a facing away from each other. In such a case, the manifolds of the two push elements may be in fluid communication; in case they are not, care must be taken to ensure that both air curtains are generated at substantially the same air speed in order to optimally counteract induction at their mutual 15 boundary beyond their guide blades.

Above, a first and second exemplary embodiment of a push-pull ventilation system 100 according to the present invention have been described with reference to Figs.2-4. Both embodiments feature a single push element 120 that is configured to effect an air flow that is directed to a pull 20 element 140. It is contemplated, however, that the push element 120 according to the present invention may alternatively be employed in air ventilation or circulation systems to generate air flows that are not (linearly) directed to an exhaust point of such a system, while still exercising a favorable influence on the operation thereof. A few examples of such 25 alternative systems will be described below with reference to Figs. 5-7.

Fig. 5 schematically illustrates a third embodiment of a ventilation system 100 according to the present invention. The third embodiment may encompass the first or second embodiment as described with reference to Fig. 2 and 4 respectively, and additionally include another, second push element 30 120’ according to the present invention. The two push elements 120, 120’ of 17 the third embodiment of Fig. 5 may be arranged on opposite sides 108, 108’ of the process location 106. The second push element 120’ may in particular be disposed adjacent, e.g. above or on top of, the pull element 140, such that an angle a included between a line extending from the air outlet 128a of the first 5 push element 120 to the exhaust inlet 142 of the pull element 140 (or in Fig. 5: any substantially horizontal line), and the emission plane of the second push element 120’ (or in Fig. 5: any plane parallel to the guide blade 134’), is in the range of 10-45 degrees, and preferably in the range of 15-30 degrees. By emitting an air curtain 112’ from the air outlet 128a’ underneath the guide 10 blade 134’, air is induced at the onset of the air curtain 112’. The resulting flow pattern, schematically shown in Fig. 5, ensures that air that can be exhausted or sucked in at the pull element 140 is primarily supplied from over the open surface of the treatment tank 106. Accordingly, exhaustion of environmental air 110 from upper zone 110b by the pull element 140, which 15 might disadvantageously dilute the overall exhausted mass of air, is kept to a minimum.

Fig. 6 schematically illustrates a fourth exemplary embodiment of a ventilation system 100 according to the present invention. It may comprise a pull element 140, for example in the form of an exhaust hood, that is disposed 20 adjacent to, e.g. overhead of, a process location 106. In Fig. 6 the process location 106 is again depicted as an open surface treatment tank, but it is contemplated that the ventilation system 100 has wide range of applications, including use as a (domestic) cooker hood, or as an industrial exhaust hood disposed overhead a melting furnace for metals. One or more preferably 25 opposite portions of a circumferential edge 144 of an exhaust inlet 142 of the pull element 140 may be lined with push elements 120 according to the present invention. In the depicted embodiment, the push elements 120 are of the type having two air outlets, as first discussed in relation to the second embodiment of the push-pull ventilation system 100 of Fig. 4. In the 30 embodiment of Fig. 6, however, the push elements 120 may not be configured 18 to emit air curtains 112, 113 in a direction towards the exhaust inlet 142 of the pull element 140, but instead each be oriented such that the second direction Y into which they are configured to emit an air curtain 112, 113 extends or faces away from the exhaust inlet 142 and towards the process 5 location 106. The air curtains 112, 113 may thus effectively shield a portion of the imaginary surface via which environmental air 110 might otherwise be sucked in towards the exhaust inlet 142 of the pull element.

The fourth embodiment of the present invention addresses a particular problem associated with conventional overhead exhaust hoods 140, 10 namely that they require a relatively high exhaust flow rate to effect a sufficient level of suction. This is partly due to the fact that they tend to suck in large amounts of relatively clean environmental air 110 from aside. The air curtains 112, 113 generated by the push elements 120 provided on the exhaust hood 140 prevent this, allowing the exhaust hood to operate at a 15 lower exhaust flow rate. Furthermore, when exhausting heated fumes, local differences in density of the fumes may cause lighter portions of the fumes to rise quickly towards the exhaust inlet 142. These lighter portions may temporarily fill the inlet 142 with a heated ‘air cushion’. The air cushion may block the exhaust inlet 142 from access by denser fumes, and cause them to 20 be diverted and escape past the exhaust hood 140. The air curtains 112, 113 counteract such escape by inducing fumes that flow towards the peripheral edge of the exhaust inlet, and circulating them back into the space between the exhaust hood 140 and the process location 106.

With regard to the fourth exemplary embodiment, it is noted that 25 the one or more push elements 120 provided alongside the exhaust inlet 142 need not necessarily comprise a guide blade 134. It may be sufficient for them to generate an air curtain that substantially extends away from the exhaust inlet 142 and towards the process location 106. The fourth embodiment may thus generally be described as a ventilation system 100 for use at a process 30 location 106 at which air contaminants are produced. The ventilation system 19 100 may comprise a pull element 140 to be disposed adjacent, for example above, the process location 106 and include an exhaust inlet 142 that is to face said process location. The ventilation system may further comprise at least one air push element 120, disposed on a circumferential edge 144 of the 5 exhaust inlet 142, and oriented such that an air outlet thereof faces away from the exhaust inlet 142. The push element 120 may have a conventional construction, or be constructed in accordance with a push element according to the present invention.

Fig. 7 schematically illustrates a fifth exemplary embodiment of a 10 ventilation or air circulation system 100 according to the present invention. The embodiment concerns an integration of one or more push elements 120 with a heated process chamber 150, such as a drying tunnel or a muffle furnace, having at least one entrance and/or exit opening 156 via which objects to be processed may be inserted into and/or removed therefrom.

15 Fig. 7A illustrates a general problem of such process chambers 150: heating inside the chamber may causes the air therein to warm up, expand and rise. When there is an opening 156 via which the interior of the chamber 150 is in open fluid communication with exterior environmental air 110, the heating may sustain a circulating air current that transports heated air 152 20 out of the chamber 150, while drawing cold environmental air in 154. The circulating current may represent a significant loss of heat/energy, and may additionally facilitate the undesired escape of noxious fumes.

The fifth exemplary embodiment of the present invention, shown schematically in Fig. 7B, overcomes or mitigates the problem associated with 25 conventional heated process chambers 150. It may include two push elements 120 that are arranged on opposite sides of the opening 156 of the process chamber 150. Each of the push elements 120, 120’ may be oriented to emit an air curtain 112 - or in the depicted embodiment: two air curtains 112, 113 -towards a side of the opening 156 opposite the one on which it is disposed, 30 while the emission planes in which the two push elements 120, 120’ are 20 configured to emit the respective air curtains 112, 112’, 113, 113’ extend substantially parallel to each other without coinciding. That is to say that the air curtains are not emitted in directions that would cause head-on ‘collisions’ between them, which collisions would result in local turbulence that could 5 promote the mixing of warm 152 and cold air 154 instead of counteract it. In operation, the correct orientation of the push elements 120, 120’ may result in two at least partially overlapping air curtains that reduce the effective opening 156 via which air may be exchanged freely between the process chamber and the environment.

10 With regard to the terminology used in this text, it is noted that the word ‘substantially’, where a quantitative interpretation is appropriate, may be construed to mean ± 15% of the relevant quantity. In cases there the relevant quantity implicitly concerns an angle, ‘substantially’ may be interpreted to mean ± 15°. For example, a description stating that the first 15 guide surface may be substantially parallel to the emission plane may be construed to mean that an angle included by the first guide surface and the emission plane may be in the range of 0-15°.

Although illustrative embodiments of the present invention have been described above, in part with reference to the accompanying drawings, it 20 is to be understood that the invention is not limited to these embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Reference throughout this specification to "one embodiment" or "an embodiment" means that a 25 particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, it is noted 30 that particular features, structures, or characteristics of one or more 21 embodiments may be combined in any suitable manner to form new, not explicitly described embodiments.

22

List of elements 1 conventional push-pull ventilation system 2 push element 4 pull element 5 6 open surface treatment tank 8, 8’ parallel, opposite sided of open surface treatment tank 10 environmental air 10a,b zone of environmental air below (a) and above (b) the air jet 12 air jet 10 12a,b lower (a) and upper (b) boundary of air jet 100 air ventilation or circulation system according to present invention 106 open surface treatment tank 108, 108’ opposite first and second sides of open surface treatment tank 15 110 environmental air 110a,b zone of environmental air below (a) and above (b) the air curtain 112 lower or inner air curtain 112a,b lower (a) and upper (b) boundary of air curtain 112 113 upper or outer air curtain 20 113a,b lower (a) and upper (b) boundary of air curtain 113 120 push element 122 manifold 124 plenum 126 air inlet 25 128a,b first (a) and second (b) air outlet 130 air outlet opening 132 air outlet channel 134 guide blade 136a, b first (a) and second (b) guide surface 30 140 pull element, e.g. an exhaust hood 23 142 exhaust inlet 144 circumferential edge of exhaust inlet 150 heated process chamber, e.g. drying tunnel or muffle furnace 152 warm air at low density 5 154 cold air at high density 156 entrance/exit opening of process chamber d average center-to-center distance between air outlet openings D characteristic dimension of air outlet opening(s) of first air outlet 10 Ea,b first (a) and second (b) emission plane S perpendicular distance between guide surface and air outlet W distance by which the first guide surface extends beyond the air

outlet opening(s) of the first air outlet, seen in the direction of air curtain emission Y

15 X first direction / longitudinal direction of manifold Y second direction / air curtain emission direction, perpendicular to

direction X

Claims

1. Een push-element (120) geschikt voor gebruik in een push-pull-ventilatiesysteem (100), omvattende: 5. een verdeler (122) omvattende een luchtinlaat (126) en een eerste luchtuitlaat (128a), waarbij de eerste luchtuitlaat zich uitstrekt in een eerste richting (X) en ten minste één eerste luchtuitlaatopening (130a) omvat, en waarbij de verdeler is ingericht voor het vanuit de ten minste ene eerste uitlaatopening emitteren van een luchtgordijn (112) 10 in een eerste emissievlak (Ea) dat zich parallel aan de eerste richting uitstrekt; en - een geleidingsblad (134) omvattende een eerste, in hoofdzaak vlak geleidingsoppervlak (136a) dat zich parallel aan het eerste emissievlak uitstrekt, en dat nabij de eerste luchtuitlaat (128a) is opgesteld, 15 zodanig dat het, in bedrijf, grenst aan een aanzet van het luchtgordijn (112) dat wordt geëmitteerd vanuit de ten minste ene eerste uitlaatopening (130a).A push element (120) suitable for use in a push-pull ventilation system (100), comprising: 5. a distributor (122) comprising an air inlet (126) and a first air outlet (128a), the first air outlet extending in a first direction (X) and including at least one first air outlet opening (130a), and wherein the distributor is adapted to emit an air curtain (112) in a first emission plane (Ea) from the at least one first outlet opening extending parallel to the first direction; and - a guide sheet (134) comprising a first, substantially flat guide surface (136a) extending parallel to the first emission surface, and arranged near the first air outlet (128a) such that, in operation, it is adjacent to a onset of the air curtain (112) emitted from the at least one first outlet opening (130a).

2. Het push-element volgens conclusie 1, waarbij de eerste 20 luchtuitlaat (128a) een veelvoud aan eerste luchtuitlaatopeningen (130a) omvat die op afstand van elkaar zijn voorzien langs de eerste richting (X)2. The push element according to claim 1, wherein the first air outlet (128a) comprises a plurality of first air outlet openings (130a) spaced apart along the first direction (X)

3. Het push-element volgens conclusie 2, waarbij de verdeler (122) een buis omvat die zich uitstrekt in de eerste richting (Z) van een eerste einde tot 25 aan een tweede einde, waarbij de luchtinlaat (126) is voorzien aan het eerste en/of tweede einde, en waarbij de eerste luchtuitlaatopeningen (130a) van de eerste luchtuitlaat (128a) zijn voorzien in een wand van de buis.The push element according to claim 2, wherein the distributor (122) comprises a tube extending in the first direction (Z) from a first end to a second end, wherein the air inlet (126) is provided at the first and / or second end, and wherein the first air outlet openings (130a) of the first air outlet (128a) are provided in a wall of the tube.

4. Het push-element volgens conclusie 2 of 3, waarbij de eerste luchtuitlaatopeningen (130a) van de eerste luchtuitlaat (128a) in hoofdzaak dezelfde vorm hebben, en onderling equidistant zijn geplaatst.The push element according to claim 2 or 3, wherein the first air outlet openings (130a) of the first air outlet (128a) have substantially the same shape and are mutually equidistant.

5. Het push-element volgens een van de conclusies 2-4, waarbij de eerste luchtuitlaatopeningen (130a) van de eerste luchtuitlaat (128a) in hoofdzaak rond zijn.The push element according to any of claims 2-4, wherein the first air outlet openings (130a) of the first air outlet (128a) are substantially round.

6. Het push-element volgens een van de conclusies 2-5, waarbij een 10 gemiddelde centrum-tot-centrum afstand (d) van de eerste luchtuitlaat openingen (130a) van de eerste luchtuitlaat (128a) ligt in het bereik 2D-8D, en bij voorkeur in het bereik 2D-4D, waarbij D een gemiddelde diameter van de eerste luchtuitlaatopeningen is.6. The push element according to any of claims 2-5, wherein an average center-to-center distance (d) of the first air outlet openings (130a) of the first air outlet (128a) is in the range 2D-8D , and preferably in the range 2D-4D, where D is an average diameter of the first air outlet openings.

7. Het push-element volgens een van de conclusies 2-6, waarbij elk van de eerste luchtuitlaatopeningen (130a) van de eerste luchtuitlaat (128a) is voorzien aan het einde van een respectief eerste luchtuitlaatkanaal (132a) dat zich in hoofdzaak uitstrekt in het eerste emissievlak (Ea), en waarbij een lengte van elk eerste luchtuitlaatkanaal gelijk is aan of groter is dan D, 20 waarbij D een gemiddelde diameter van de eerste luchtuitlaatopeningen is.The push element according to any of claims 2-6, wherein each of the first air outlet openings (130a) of the first air outlet (128a) is provided at the end of a respective first air outlet channel (132a) that extends substantially in the first emission surface (Ea), and wherein a length of each first air outlet channel is equal to or greater than D, wherein D is an average diameter of the first air outlet openings.

8. Het push-element volgens een van de conclusies 1-7, waarbij het eerste geleidingsoppervlak (136a) zich over een afstand (W) van ten minste 5D, en bij voorkeur ten minste 10D, uitstrekt voorbij de ten minste ene eerste 25 luchtuitlaatopening (130a) in een richting (Y) waarin de verdeler (122) is ingericht om het luchtgordijn (122) te emitteren, waarbij D een karakteristieke afmeting is van de ten minste ene eerste luchtuitlaatopening (130a) van de eerste luchtuitlaat (128a).8. The push element according to any of claims 1-7, wherein the first guide surface (136a) extends over the at least one first air outlet opening over a distance (W) of at least 5D, and preferably at least 10D (130a) in a direction (Y) in which the distributor (122) is arranged to emit the air curtain (122), wherein D is a characteristic dimension of the at least one first air outlet opening (130a) of the first air outlet (128a).

9. Het push-element volgens een van de conclusies 1-8, waarbij een afstand (S) tussen het eerste geleidingsoppervlak (136a) en het eerste emissievlak (Ea) ligt in het bereik 1D-3D, waarbij D een karakteristieke afmeting is van de ten minste ene eerste luchtuitlaatopening (130a) van de 5 eerste luchtuitlaat (128a).The push element according to any of claims 1-8, wherein a distance (S) between the first guide surface (136a) and the first emission surface (Ea) is in the range 1D-3D, where D is a characteristic dimension of the at least one first air outlet opening (130a) of the first air outlet (128a).

10. Het push-element volgens een van de conclusies 1-9, waarbij: - de verdeler (122) voorts een tweede luchtuitlaat (128b) omvat die zich in hoofdzaak parallel aan de eerst luchtuitlaat (128a) uitstrekt en die 10 ten minste één tweede luchtuitlaatopening (130b) omvat, en waarbij de verdeler is ingericht voor het vanuit de ten minste ene tweede luchtuitlaatopening emitteren van een luchtgordijn (113) in een tweede emissievlak (Eb) dat zich parallel aan het eerste emissievlak (Ea) uitstrekt; en 15. het geleidingsblad (134) is geplaatst tussen het eerste emissievlak (Ea) en het tweede emissievlak (Eb), en voorts een tweede, in hoofdzaak vlak geleidingsoppervlak (136b) omvat dat zich parallel aan het tweede emissievlak (Eb) uitstrekt en dat nabij de tweede luchtuitlaat (128b) is opgesteld, zodanig dat het, in bedrijf, grenst aan een aanzet van een 20 luchtgordijn (113) dat wordt geëmitteerd vanuit de ten minste ene tweede uitlaatopening (130b).The push element according to any of claims 1-9, wherein: - the distributor (122) further comprises a second air outlet (128b) which extends substantially parallel to the first air outlet (128a) and which has at least one comprises second air outlet opening (130b), and wherein the distributor is adapted to emit an air curtain (113) from the at least one second air outlet opening in a second emission plane (Eb) extending parallel to the first emission plane (Ea); and 15. the guide sheet (134) is disposed between the first emission plane (Ea) and the second emission plane (Eb), and further comprises a second, substantially flat guide surface (136b) extending parallel to the second emission plane (Eb) and which is arranged near the second air outlet (128b), such that, in operation, it borders on an onset of an air curtain (113) that is emitted from the at least one second outlet opening (130b).

11. Een systeem, omvattende: - een proceslocatie (106) voor het uitvoeren van een proces waarbij 25 luchtverontreinigende stoffen worden geproduceerd; - een eerste push-element (120) volgens een van de conclusies 1-10, opgesteld aan een eerste zijde (108) van de proceslocatie; en - een pull-element (140), opgesteld aan een tweede, tegenoverliggende zijde (108’) van de proceslocatie, waarbij het pull-element ten minste één afvoerinlaat (142) omvat die is gekeerd naar de eerste luchtuitlaat (128a) van het eerste push-element.A system, comprising: - a process location (106) for performing a process in which air pollutants are produced; - a first push element (120) according to any of claims 1-10, arranged on a first side (108) of the process location; and - a pull element (140) arranged on a second, opposite side (108 ') of the process location, the pull element comprising at least one discharge inlet (142) facing the first air outlet (128a) of the process location first push element.

12. Een systeem, omvattende: 5. een proceslocatie (106) voor het uitvoeren van een proces waarbij luchtverontreinigende stoffen worden geproduceerd; - een eerste push-element (120), in het bijzonder volgens een van de conclusies 1-10, opgesteld aan een eerste zijde (108) van de proceslocatie; en 10. een pull-element (140), opgesteld aan een tweede, tegenoverliggende zijde (108’) van de proceslocatie, waarbij het pull-element ten minste één afvoerinlaat (142) omvat die is gekeerd naar de eerste luchtuitlaat (128a) van het eerste push-element; en - een tweede push-element (120’) volgens een van de conclusies 1-10, 15 opgesteld aan de tweede zijde nabij het pull-element, en zodanig georiënteerd dat een hoek (a) die wordt ingesloten tussen een lijn die zich vanaf de luchtuitlaat (128a) van het eerste push-element uitstrekt naar de afvoerinlaat van het pull-element, en het eerste emissievlak van het tweede push-element ligt in het bereik van 10-45 graden, meer 20 in het bijzonder in het bereik van 15-30 graden.A system, comprising: 5. a process location (106) for performing a process producing air pollutants; - a first push element (120), in particular according to any one of claims 1-10, arranged on a first side (108) of the process location; and 10. a pull element (140) disposed on a second, opposite side (108 ') of the process location, the pull element comprising at least one discharge inlet (142) facing the first air outlet (128a) of the first push element; and - a second push element (120 ') according to any of claims 1-10, 15 arranged on the second side near the pull element, and oriented such that an angle (a) is enclosed between a line extending from the air outlet (128a) of the first push element extends to the discharge inlet of the pull element, and the first emission surface of the second push element is in the range of 10-45 degrees, more particularly in the range of 15-30 degrees.

13. Een ventilatiesysteem voor gebruik op een proceslocatie (106) waar luchtverontreinigende stoffen worden geproduceerd, omvattende: - een pull-element (140) dat nabij, bijvoorbeeld boven, de proceslocatie 25 (106) dient te zijn geplaatst en dat een afvoerinlaat (142) omvat die naar de proceslocatie dient te zijn gekeerd; en - ten minste één push-element (120) volgens een van de conclusies 1-10, opgesteld aan een omtreksrand (144) van de afvoerinlaat (142), en zodanig georiënteerd dat de eerste luchtuitlaat (128a) is afgekeerd van 30 de afvoerinlaat (142).A ventilation system for use at a process location (106) where air pollutants are produced, comprising: - a pull element (140) that is to be positioned near, for example, the process location (106) and that a discharge inlet (142) ) that must be turned to the process location; and - at least one push element (120) according to any of claims 1-10, arranged on a peripheral edge (144) of the discharge inlet (142), and oriented such that the first air outlet (128a) faces away from the discharge inlet (142).

14. Een systeem, omvattende: - een proceskamer (150) die een inwendige ruimte definieert voor het uitvoeren van een proces in een verwarmde luchtatmosfeer, en die ten 5 minste één opening (156) omvat via welke de inwendige ruimte in open fluïdumcommunicatie is met een omgeving van de proceskamer; - twee push-elementen (120, 120’) volgens een van de conclusies 1-10, opgesteld aan tegenovergestelde zijden van de opening, waarbij elk van de push-elementen is ingericht voor het emitteren van een luchtgordijn 10 richting een zijde van de opening die tegenover de zijde ligt waaraan het respectieve push-element zelf is opgesteld, en waarbij de respectieve eerste emissievlakken, in welke de push-elementen zijn ingericht om de luchtgordijnen te emitteren, zich in hoofdzaak parallel aan elkaar uitstrekken zonder samen te vallen. 15A system, comprising: - a process chamber (150) defining an internal space for performing a process in a heated air atmosphere, and comprising at least one opening (156) through which the internal space is in open fluid communication with an environment of the process chamber; - two push elements (120, 120 ') according to any of claims 1-10, arranged on opposite sides of the opening, each of the push elements being adapted to emit an air curtain 10 towards one side of the opening which faces the side on which the respective push element itself is arranged, and wherein the respective first emission surfaces, in which the push elements are arranged to emit the air curtains, extend substantially parallel to each other without coinciding. 15

14. Een werkwijze, omvattende: - het op een proceslocatie (106) uitvoeren van een proces waarbij luchtverontreinigende stoffen worden geproduceerd; - het verschaffen van een push-element (120) volgens een van de 20 conclusies 1-10 aan een eerste zijde (108) van de proceslocatie; - het verschaffen van een pull-element (140) aan een tweede, tegenoverliggende zijde (108’) van de proceslocatie, waarbij het pull-element ten minste één afvoerinlaat (142) omvat die is gekeerd naar de eerste luchtuitlaat (128a) van het push-element; en 25. het toevoeren van perslucht aan de luchtinlaat van de verdeler van het push-element, zodanig dat een luchtgordijn (112) wordt geëmitteerd vanuit de ten minste ene eerste luchtuitlaatopening (130a) daarvan met een luchtsnelheid in het bereik van 2.5-10m/s, en bij voorkeur in het bereik van 5-10m/s.A method comprising: - performing a process at a process location (106) wherein air pollutants are produced; - providing a push element (120) according to any of claims 1-10 on a first side (108) of the process location; - providing a pull element (140) on a second opposite side (108 ') of the process location, the pull element comprising at least one discharge inlet (142) facing the first air outlet (128a) of the process location push element; and 25. supplying compressed air to the air inlet of the push element distributor such that an air curtain (112) is emitted from its at least one first air outlet opening (130a) at an air speed in the range of 2.5-10m / s, and preferably in the range of 5-10 m / s.