ELECTROSTATIC SEPARATOR

Abstract

An electrostatic separator or precipitator through which an air stream to be cleaned of particles flows in a longitudinal direction includes at least one electrospray ionization source, which is supplied with a positive potential and can be implemented, for example, by the tips of a graphite fiber bundle, and a collector unit arranged downstream for particle separation and having parallel collector and driver plates. The ion flow from the corona zone is additionally homogenized and spread by an upstream collector element, in particular a collector grid, upstream of the at least one electrospray ionization source, so that high particle separation rates can be achieved with minimal ozone emissions. Alternatively, or in addition, the ion flow from the corona zone can be homogenized downstream of the at least one spray ionization source by one or more border counter-electrodes.

Claims

1. An electrostatic separator (10) through which a stream of particles to be cleaned flows in a longitudinal direction, comprising: a spray ionization source which is arranged within the air flow or multiple spray ionization sources (18a-d) which are arranged within the air flow in a matrix-like manner, which spray ionization source(s) is or are applied by a positive electric ionizer potential, a collector unit (12) arranged downstream of the at least one spray ionization source (18a-d) for particle deposition, having a plurality of electrically conductive collector and driver plates (38, 40), which are arranged substantially in parallel and through which the air flow flows and which are alternating with electrically negative collector or opposite positive driver potentials, wherein the at least one spray ionization source (18a-d) is approximately point-shaped, and that an upstream collector element (44) applied by an electrically negative potential is arranged in the flow path upstream of the at least one spray ionization source (18a-d).

2. Electrostatic separator (10) according to claim 1, wherein the upstream collector element (44) is formed as a collector grid.

3. Electrostatic separator (10) according to claim 2, wherein the collector grid of the upstream collector element (44) has a mesh number greater than or equal to the number of spray ionization sources.

4. Electrostatic separator (10) according to claim 1, wherein the at least one spray ionization source (18a-d) is formed by a metallically conductive fine needle tip or by a free fiber end of a conductive fiber or by a plurality of adjacent free fiber ends of a bundle of conductive fibers, wherein the conductive fibers are preferably graphite filaments and/or wherein the needle tip or the free fiber ends of the at least one spray ionization source (18a-d) are preferably arranged facing in the flow direction (28).

5. Electrostatic separator (10) according to claim 1, wherein at least one border counter-electrode (14a-d) is provided, each of which is associated with one of the one or more spray ionization sources (18a-d), which is arranged in the longitudinal direction between the associated spray ionization source (18a-d) and the collector unit (12) and at a longitudinal distance from the associated spray ionization source (18a-d), which has electrically conductive walls (30, 32) which extend substantially in the longitudinal flow direction and which delimit a flow channel upstream of the respective spray ionization source (18a-d) on all circumferential sides or at least in circumferential partial sections, wherein the electrically conductive walls (30, 32) of the facing border counter-electrode (14a-d) are applied by a negative border counter-electrode potential directed opposite the ionizer potential, and wherein the spray ionization source (18a-d) is centrally arranged with respect to the contour of the respectively associated border counter-electrode (14a-d) in a transverse plane.

6. Electrostatic separator (10) according to claim 5, wherein the face edges of the associated border counter-electrode (14a-d) facing the respective spray ionization source (18a-d) have a recess (34, 36) which is curved in an arc-shaped manner completely or in partial sections respectively, in such a way that an imaginary surface (22a-d) running through all or through at least two face edges of the border counter-electrode (14a-d) facing the spray ionization source (18a-d) with respect to the associated spray ionization source (18a-d) has a generally concave or specially a spherical-surface-shaped form.

7. Electrostatic separator (10) according to claim 5, wherein with respect to a clear span of a border counter-electrode (14a-d), wherein in the case of a rectangular-shaped border counter-electrode contour, including a square-shaped contour, the clear span d corresponds to the smaller of the side lengths, or in the case of an elliptical - including a circular - border counter-electrode contour, the clear span d corresponds to the smaller inner half diameter of the ellipse, and in any other shape the clear span d corresponds to the smallest inner diameter through the respective contour center of gravity, the height extension of the border counter-electrode (14a-d) is between 25% and 200% of the respective clear span d in the longitudinal direction-without considering optional arc-shaped incisions (34, 36); and/or the longitudinal distance of the spray ionization source (18a-d) from the frontmost facing edge regions of the associated border counter-electrode (14a-d) in upstream direction is between 25% and 400% of the clear span d.

8. Electrostatic separator (10) according to claim 1, wherein the upstream collector element (44) from the at least one spray ionization source (18a-d) has a distance in an upstream direction corresponding to 50% to 300%, preferably 75% to 150% of the longitudinal distance between the at least one spray ionization source (18a-d) and the associated border counter-electrode (14a-d).

9. Electrostatic separator according to claim 5, wherein the electrodes of the upstream collector element (44) are at least partially aligned in a longitudinal projection direction with preferably all or at least a part of the border counter-electrodes (14).

10. Electrostatic separator (10) according to claim 1, wherein the upstream collector element (44a, b) has one or more constant curvatures or protuberances with respect to the at least one spray ionization source (18a-d), which are kept as constant as possible from all points of the upstream collector element (44) to the at least one spray ionization source (18a-d).

11. Electrostatic separator (10) according to claim 1, wherein a plurality of spray ionization sources (18) are arranged in a matrix-like manner approximately in the centers of the rectangular meshes of an imaginary grid which consists of a grid row and a plurality of grid columns or of a plurality of grid rows and a grid column or of a plurality of grid columns and a plurality of grid columns, wherein all the row heights and all column widths do not deviate by more than ±50%, preferably not more than ±25%, from a uniform basic size.

12. Electrostatic separator (10) according to claim 1, wherein a fan unit (52) for forced air flow conveying through the electrostatic separator (10) is provided, which is arranged in the flow path upstream of the upstream collector element (44) and is protected from electrostatic charging by the upstream collector element (44).

13. Room ventilation unit (46), comprising an electrostatic separator (10) according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 shows a perspective oblique view of an electrostatic separator according to the invention with four spray ionization sources and corresponding border counter-electrode/collector units and an upstream-collector grid;

[0055] FIG. 2 shows a further embodiment of the invention with upstream collector electrodes;

[0056] FIG. 3 shows a schematic illustration of a decentralized room ventilation unit with an integrated electrostatic precipitator according to the invention, and

[0057] FIGS. 4a-c show examples of different border counter-electrode configurations. According to the illustration in FIG. 1, an electrostatic precipitator 10 according to the invention has as essential components a collector unit 12 which, in principle, consists of a number of collector plates 38 arranged in parallel to driving plates 40 (whereas, in the exemplary embodiment, collector plates are somewhat shorter than driver plates) (see FIG. 2).

[0058] This collector unit 12 is flowed through in a main flow direction (arrow 28) by an air flow to be cleaned of particles, this air flow generally being ensured by one or more fans (not shown in FIG. 1), for which purpose the electrostatic precipitator 10 is located within an air flow channel (also not shown in FIG. 1).

[0059] The collector unit 12 with its collector plates 38 at a negative potential electrostatically attracts particles (e.g., fine dust, pollutant particles, aerosols, etc.) from the air stream, which have been previously positively ionized, as a result of which the particles adhere to the collector plates 38 and thus can be removed from the air stream. The adhering particles can be removed, for example, by regular cleaning, mechanical knock-off or periodic air impact. Germs, bacteria or viruses adhering to deposited aerosol particles can also be deactivated - if they do not dry out anyway - by additional measures, such as UV light.

[0060] The collector plates 38 are connected to a negative voltage source - which can also be the ground potential - via a contact strip 26 and via corresponding counter-contact elements provided in a flow channel wall (voltage source and counter-contact elements are not shown).

[0061] Analogously, the driver plates 40 are connected to a positive potential of a corresponding voltage source via a contact strip 24 located above the contact strip 26. This is in general an average positive potential which lies between the negative potential of the collector plates 38 and the (high) positive potential of the spray ionization sources 18a-d (explained further below). The spray ionization potential would typically be too high for the driver plates 40, i.e., flashovers could occur between the plates 38, 40.

[0062] The positively ionized particles are produced according to the so-called Penney principle by positive corona discharges, for which one or more, in the exemplary, not limiting embodiment, four, approximately point-shaped spray ionization sources 18a-d are provided according to the invention.

[0063] In the exemplary, not limiting embodiment shown, it is a bundle or shell of thin, electrically conductive graphite fibers, which are acted upon by a high-resistance high-voltage source (not shown) with a positive high voltage of some kV. Alternatively, individual conductive fibers or needle-like metal tips or the like can also be used as spray ionization sources.

[0064] The spray ionization sources 18a-d (the totality of the spray ionization sources are also designated by the reference numeral 16) are mounted on a non-conductive support grid 20 in which high-voltage lines (not shown) for connecting the ionization sources 18a-d to one or more high-voltage sources are guided. The ionization current established by the corona discharge can be electronically controlled in one embodiment.

[0065] Within the scope of the invention it is advantageous if the ions are emitted as far as possible from one point, respectively, whereby it is understood that the term “point-shaped” is of course an idealized specification. At the thin tips of the spray ionization sources 18a-d-in cooperation with counter-electrodes as described further below - high electric field strengths are generated, which generate ions in a spatially narrowly limited are of the ionization sources 18a-d, typically of a few mm, of the so-called corona zone; whereby the boundary layer is also known as a so-called corona skin, ionizing gas molecules from the air flowing through. These ionized gas molecules then collide with the particles to be deposited, provided, that they have sufficient opportunity to interact with them, and ionize them, so that they can be correspondingly electrostatically deposited in the collector unit 12.

[0066] This secondary ionization of the particles to be deposited by the gas ions is carried out in a substantially larger volume than the corona discharge itself.

[0067] Within the scope of the present invention, it has been recognized that it is important for optimum deposition performance with minimal ozone emissions to initially generate the gas ions in a volume that is as small as possible (because ozone is only present there due to high ozone generating field strengths) and then distributed as uniformly and homogeneously as possible through the gas volume flow in order to achieve optimum flow cross-sections between gas ions and particles, wherein a focus of the present invention lies at the upstream air volume.

[0068] For this purpose, on the one hand, to one (preferably each) spray ionization source a border counter-electrode 14a-d is assigned, which has walls 30, 32 located at a negative potential with respect to the spray ionization source 18a-d, which walls 30, 32, for the respective spray ionization source 18a-d, delimit an (section-by-section) flow channel and which are spaced apart from this spray ionization source.

[0069] When the border counter-electrodes 14a-d are rectangular shaped as shown in FIG. 1, the opposite walls of the wider side are denoted by 30 and the ones of the narrower side are denoted by 32.

[0070] Due to the in totality overall rectangular grid-like structure of the border counter-electrodes 16, the narrow side walls 32 of the individual border counter-electrodes 18a-d are each formed by a common narrow side wall 32 for adjoining border counter-electrodes (i.e., except for the outermost narrow sides).

[0071] The positive gas ions are drawn through these border counter-electrodes 14a-d and are ideally fanned out over the entire flow channel available, so that optimum effective cross-sections between gas ions and particles are achieved.

[0072] Furthermore, it has been recognized that the homogenization of the gas ion current is then almost optimal if the distances between the spray ionization source 18a-d and the associated border counter-electrode 14a-d are as constant as possible. Therefore, the spray ionization sources 18a-d are arranged approximately centrally or centered with respect to the contour of the border counter-electrodes 14a-d or with respect to the flow channels defined by these definite flow channels. “Approximately” is intended to be within the scope of the invention that design-related deviations of typically a few percent to about 10% or 20% are tolerable.

[0073] In case of a rectangular grid, as it is appropriate for an aerodynamically ideal covering of the overall flow cross-section (in particular of a rectangular flow cross-section) when a plurality of spray ionization sources 18a-d are provided, the distances between the idealized point-shaped or punctiform spraying source 18a-d and the facing edges of the walls 30 that are relevant to the electric field of the border counter-electrodes 14a-d vary in a relatively strong way in the case of an assumed “straight” design of these facing edges, despite the central arrangement of the spray ionization sources 18a-d. That is to say, in case of a “straight” design of the facing edges, the distance to the respective center of the front edges would be different than to the corners.

[0074] Therefore, in the embodiment according to FIG. 1, it is provided that the walls 30, 32 of the border counter-electrodes have rounded incisions 34, 36, which are defined by the intersection curves of a virtual sphere (or a spherical segment, if only one side is considered) 22a-d with the respective spray ionization source 18a-d in the imaginary center point. As a result of this, a uniform spacing of the spray ionization sources 18a-d to the border counter-electrodes 14a-d is realized and thus, an ion distribution which is as uniform or homogeneous as possible is achieved, wherein in practice some field distortions are unavoidable, for example by the superposition of the electric fields emanating from the collector electrode and driver plates.

[0075] In a more general embodiment, the contour of the incisions 34, 36 can be formed in the border counter-electrode walls 30, 32 such that the virtual surface is concave at least from the perspective of the spray ionization source.

[0076] In the context of the present invention, as an alternative or in addition to the above-described measures taken downstream of the spray ionization sources, a further upstream collector element 44 is seen upstream, which in FIG. 1 is represented only schematically as a grid 44 with eight meshes, but which can also have other shapes.

[0077] The aforementioned upstream collector element or grid 44 is also placed to or applied by a negative potential, e.g., the ground potential, and thus provides for a fanning and homogenization of the gas ion currents upstream of the spray ionization sources 18a-d

[0078] The longitudinal distance of the upstream collector element 44 from the spray ionization sources 18a-d is preferably selected to be approximately as long as the distance of the border counter-electrodes 18a-d from the spray ionization sources 18a-d in order to achieve a uniform current distribution in both directions. The ideal distance is not neces-sarily the same in both directions, since the field properties of the border counter-electrodes and of the upstream collector element 44 are generally different. If necessary, the ideal distance may be determined experimentally. The spacing of the mesh or grid 44 shown in FIG. 1 can therefore be varied; in particular, it is conceivable to arrange the grid 44 approximately equidistant to the border counter-electrodes 14a-d, i.e. as far as the upstream part of the imaginary spherical surfaces 22a-d.

[0079] In principle, other types of upstream collector elements, such as, for example, an only edge-side ring or a wire harness, are also conceivable.

[0080] Furthermore, in accordance with the preferred embodiment of the border counter-electrodes, a non-planar configuration of the upstream collector element, e.g. with cup-like bulges, is also conceivable in order to keep the distance between the collector element and the spray ionization source as constant as possible.

[0081] In FIG. 1, two variants of the upstream collector element are indicated by dashed lines (and only in partial regions), namely on the one hand a first curved variant 44a, in which the wire-like electrodes of the collector element are curved approximately corresponding to the border counter-electrodes and thus a more uniform distance from the spray ionization source is ensured (in this embodiment, the elongated central strut of the collector element is then preferably waived). Alternatively, in a second variant 44b the upstream collector element can be designed in a manner similar to the border counter-electrodes, namely as a metallic strip with a certain longitudinal extent, in each of which an arc-shaped cut-out is embedded.

[0082] FIG. 2 shows an embodiment of an electrostatic precipitator 10 which can be realized in a technically particularly simple manner, in which a border counter-electrode 30 is formed by means of two opposite walls from an extension of the outermost collector plates 38 of the collector unit 12, wherein these walls 30 can be formed either straight or with the above-described round incisions (not shown). In this further embodiment, a collector grid 44 as an upstream collector element is also provided upstream of the spray ionization source 18a.

[0083] FIG. 3 schematically illustrates how an electrostatic precipitator 10 according to the invention could be integrated into a decentralized room ventilation unit 46, whereby—as initially mentioned—alternative uses, e.g. for “stand-alone” air cleaners for residential spaces or for a wide variety of further applications in a similar configuration, are of course also possible and intended.

[0084] In this case, an ionization/counter-electrode unit is shown schematically as a “black box” 54 adjacent to the collector unit 12, an upstream collector grid 44 according to the invention being provided upstream and again upstream of which an axial fan 52 is arranged.

[0085] The elements mentioned are arranged sequentially in a tube in a wall outlet 56, which extends between a room-side air inlet/air outlet 48 and an outside air inlet air outlet 50.

[0086] In this configuration, the upstream collector grid 44 additionally also protects the electron-ics of the fan 52, or the control thereof, from excess voltage damage by eventual discharges of ion-current-induced electrostatic charges.

[0087] In FIGS. 4a-c, various variants of border counter-electrode configuration on the example of an electrostatic filter having, for example, a total of six spray ionization sources 18 in a 2×3 (or depending on the designation 3×2) matrix are shown schematically (in contrast, the example of FIG. 1 has a 1×4 or 4×1 configuration). The respectively thicker lines are intended to indicate guide plates with border counter-electrodes 14, which have thinner lines.

[0088] In FIG. 4a, all cell boundaries are provided with border counter-electrodes, whereas in FIG. 4b this is the case only in the case of the longitudinal side electrodes, and in the case of FIG. 4c only in the case of the outer boundaries.

[0089] It can also be seen from the schematic representation of FIGS. 4a-c that the electrostatic filter 10 can be scaled or matched very easily to different cross-sectional areas, since this is assembled modularly from individual cells, wherein the individual cell is optimized in each case with respect to the electrostatic deposition properties, and virtually any cross-sectional areas can be covered with these cells, without the performance of the individual cells having to be re-engineered.

LIST OF REFERENCE SIGNS

[0090] 10 Electrostatic precipitator [0091] 12 Collector unit [0092] 14a-d Border counter-electrodes [0093] 16 Totality of border counter-electrodes (grid) [0094] 18a-d Spray ionization sources [0095] 20 Support grid [0096] 22a-d Imaginary spherical surfaces [0097] 24 Driver plate contact row [0098] 26 Collector plate contact row [0099] 28 Arrow indicating direction of flow [0100] 30 Longitudinal side walls border counter-electrodes [0101] 32 Narrow-side walls of border counter-electrodes [0102] 34 Cut-in border-counter-electrode walls (longitudinal side) [0103] 36 Cut-in border-counter-electrode walls (narrow side) [0104] 38 Collector plates [0105] 40 Driver plates [0106] 44 Upstream collector grid [0107] 44a First option for upstream collector grid [0108] 44b Second option for upstream collector grid [0109] 46 Decentralized room ventilation unit with electrostatic precipitator [0110] 48 Room-side air inlet/air outlet [0111] 50 Outer air inlet/air outlet [0112] 52 Axial fan [0113] 54 Ionization/border counter-electrode unit [0114] 56 Wall passage