EP4673261A1

EP4673261A1 - Multi-stage filtration device

Info

Publication number: EP4673261A1
Application number: EP23730603.0A
Authority: EP
Inventors: Daniel-Ion MATEI
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-05-30
Filing date: 2023-05-30
Publication date: 2026-01-07
Also published as: WO2024248645A1

Abstract

Multi-stage filtration device (1) comprising at least two individual filtration devices (11), placed one over another in layers in a staggered manner and in a fluid connection, comprising: - a cathode structure (2) comprising: - a plurality of hollow longitudinal chambers (21) with a hydraulic diameter (dn, dn-1) dimensioned according to the mean particle size to be filtered at each stage (f1, f2,…fn); arranged in a parallel manner relative to each adjacent chambers (21) and comprising on their same lateral portion (a) a plurality of outlet perforations (12), equally spaced apart, - a clearance space (7) between each adjacent chamber (21) allowing passage of fluid flow between each device (11), - an anode structure (3) comprising: - a support structure (31), placed over said cathode structure (2) and comprising a plurality of inlet through-holes (13) arranged in an (x-z) array; each hole (13) is placed between two adjacent perforations (12), - each hole (13) is placed on a centerline (X) and each center of the holes (13) is arranged in an in-line manner on said centerline (X) - an electrical conductor (4) is placed along each centerline (X), each conductor (4) being connected through a common electrical conductor (5) to a power source (6) capable to generate an electric potential difference between the anode (3) and the cathode (2) when a predetermined charge (C1, C2) is applied to both (3, 2) such that an electrostatic ionizing field is created inside the chambers (21) for charging the particles with an electrostatic voltage and passage of flow in each stage (f1, f2,…fn), has a sinuous path through: - said holes (13) capable to separate flow into a plurality of vortices with a laminar flow, - said plurality of perforations (12) and space (7) into the chambers (21) of the next device (11) having another diameter (dn) which is smaller than the diameter (dn- 1) of the previous device (11) such that during the passage of said flow through each stage (f1, f2,…fn), charged particles are collected inside said chambers (21).

Description

MULTI-STAGE FILTRATION DEVICE

Description

Field of the invention

[0001] The present invention relates generally to the field of particle filtration devices which filter a range of particles having a mean particle size between about 0.01 pm and about 10 mm, suspended in a gas flow and particularly to a multi-stage filtration device having at least two individual filtration devices, placed one over another in layers, in a staggered manner and in a fluid connection for high-efficiency separation of various sizes and concentrations of particles suspended in gases, which require filtration, purification, separation, recovery, etc.

Background of the invention

[0002] Air pollution is assuming alarming dimensions from industries, automobiles and house hold fuel burning. Cement industry can be classified as highly air polluting industry emitting PM (“Particulate Matter” or particles) into the atmosphere. These particles can be solids (like dust) or liquids (like drops of water). Some common sources of PM are car exhaust, smoke from coal-fired power plants, pollen spores, and dust from construction sites. This pollutant in the form of PM (Particulate Matter) is required to be control by installing air pollution control equipments and filters. There are known devices and installations used for filtering relatively small particles or larger particles, in general using different physical principles such as inertial, interception, diffusion or electrostatic principles. Each principle is functionally linked to various parameters, such as the dynamics of the gas circulation or of atmospheric air, respectively if it is laminar or turbulent, the particles size, the concentration of particles in suspension and the electrical resistivity of the particles. Small particles (such as fine dust, ash, organic compounds or aerosols) are particles with a mean particle size between about 0.01 pm (PM2.5 - particles of less than 2.5 pm in diameter) and about 30 pm (PM30 - particles of less than 30 pm in diameter). Larger particles (such as sand, coarser particles) are particles with a mean particle size between about 0.1 mm and about 10 mm. Between these ranges are the medium sized particles.

[0003] For larger particles, the principle of inertial separation is generally applied, by creating vortices in the initial gas flow. A vortex (in fluid dynamics) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved; a mass of fluid (such as a gas) with a whirling or circular motion that tends to form a cavity or vacuum in the center of the circle and to draw particles, suspended in the fluid flow toward this cavity or vacuum, subject to its action. In this sense, the US patent 4008060 is known in the field, which describes a cyclone separator type device with a filter chamber construction with the vertical section of the walls in a triangular shape of a "V" for making the air pass therein along a more sinuous path compared to the known devices.

[0004] A cyclone separator is a known mechanical device that uses centrifugal force to separate particulate matter from a fluid mixture. It typically consists of a cylindrical chamber with a conical outlet and an inlet pipe that introduces the fluid mixture into the chamber. As the fluid enters the chamber, it is spun rapidly, causing the heavier particulate matter to be thrown to the outer wall of the chamber and fall to the bottom, where it is collected. The cleaner fluid exits the chamber through the conical outlet. Cyclone separators are commonly used in industrial settings to remove dust and other particulate matter from air or gas streams. According subsequent studies, collection efficiency is strongly dependent on particle size and efficiency has also been reported in terms of “cut point”, “cut size” or “cutoff aerodynamic diameter for cyclones” (i.e. the particle size where 50% of the targeted sized PM is captured by the filter and 50% are not or that particle size for which the collection (or grade) efficiency is 50%). It is an indicator of the size range of particles that can be collected. For particles significantly larger than this, collection efficiency approaches 100%. One important factor for an efficient cut point is the number of turns (5 to 10 for a typical cyclone device) and diameter of turns. A cyclone device is a simple dust control device. The most commonly used cyclone device is the Stairmand type cyclone device mentioned by Stairmand in 1951. Therefore, such a simple device will lead to a multiple number of vortices with small diameters and to good cut point efficiency. Physical properties like particle size and density are important for cyclone efficiency whereas chemical properties will affect the cyclone operation.

[0005] The major disadvantage of such systems is their inability to efficiently separate very small particles with a very low mass, especially those in the category of PM1 - PM5.

Fine or smaller particles have a Brownian movement, also called Brownian motion or pedesis which is defined as the uncontrolled or erratic movement of particles in a fluid due to their constant collision with other fast-moving molecules. This pattern of motion typically consists of random fluctuations in a particle's position inside a fluid sub-domain, followed by relocation to another sub-domain. Brownian motion is caused by the structure and physics of fluids (i.e. liquids or gases). According to kinetic theory, all matter is in motion; atoms and molecules especially within liquids and gases are in constant vibrating motion. These particles will travel in straight lines until redirected by a collision. Particles within gases and liquids are constantly moving, colliding, and moving toward equilibrium. A common example of Brownian motion is dust particles floating in the air which have a random jittery movement. Brownian motion is the result of collisions between the small microscopic particles and the invisible but constantly moving water or air molecules surrounding them.

The fact that the jiggling movement of a particle exhibiting Brownian motion increases with temperature provided evidence that its motion could be explained by the kinetic molecular theory.

[0006] These fine or smaller particles with a Brownian movement are more likely to be influenced by an electrostatic charging, therefore more suitable to separate in an Electrostatic Precipitator, such as for example the prior art described in US7655076B2. If there are two objects/particles with different electrical charges, then an electrostatic field exists between the two objects/particles. An electrostatic field also forms around a single body/object/particle which is electrically charged with respect to its surroundings. The electrostatic field is due to the voltage on the wiring. An Electrostatic Precipitator is a device that removes suspended dust particles from a gas or exhaust by applying a high-voltage electrostatic charge which charge the particles to migrate toward the grounded collecting electrodes and collecting the particles on charged plates. The essential components of the electrode system consist of one or more discharge electrodes of relatively small diameter (such as wires) as well as collecting electrodes (such as plates or tubes). In general, the discharge electrodes are of negative polarity, whereas the collecting discharges are at ground potential and considered positive polarity. The particles are accelerated towards the collecting electrodes by Coulomb forces but inertial and viscous forces resist the motion. The electrostatic precipitation differs fundamentally from the fabric filtration and scrubbing processes in that the separation forces are electrical and are applied directly to the particles themselves, rather than indirectly through the gas stream. The electrical process has the inherent capability of capturing submicron particles at high efficiency with relatively low energy consumption and small pressure drop through the gas cleaning system.

[0007] However, the main disadvantages of such solution are:

- The linear movement of particles between the straight electrods/charged plates has a relative small contact or interaction time and distance (typically 2 m/s for about 40 mm), therefore a large number of particles may escape the electrostatic field. To improve capturing efficiency, given the short distance and relative small interaction time, the usual method is to increase the high voltage electrostatic charge. However, corona discharge or other radical molecules formation is invariably produced by strong electric fields associated with small diameter wires, needles, or sharp edges on an electrode. A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage.

The corona effect will occur in high voltage systems unless sufficient care is taken to limit the strength of the surrounding electric field. Corona discharge can cause an audible hissing or cracking noise as it ionizes the air around the conductors. This is common in high voltage electric power transmission lines. Ionized air is partially conductive. Electric discharge occurs due to the ionized air which results in corona. And if the conductors are close enough to each other, the air insulation breaks down and electric discharge occurs through a spark.

The minimum phase-neutral voltage at which corona starts to occur is called as critical disruptive voltage. And, the minimum phase-neutral voltage at which visual corona glow appears all along the conductors is called as visual critical voltage.

The lower the voltage, the safer is for maintaining low level radicals, but then efficiency to capture particles is decreasing.

- The large dimensions and concentrations of particles which are the object of the present invention, will form large deposits on the polarised electrods, thus reducing their effectiveness in capturing particles;

- Inflexibility of operating conditions, large space requirement, variation of removal efficiency with particle properties (e.g. resistivity of particles).

Summary of the invention

[0008] Efficient and cost-effective filtration devices that address these conventional inefficiencies are therefore needed.

[0009] The present invention provides a solution to the above-mentioned inherent problems associated with the known filtration devices. The main objective technical problem is to provide an improved and efficient filtration device which is able to collect a wide range of particle types, concentrations or sizes suspended in a gas flow. Another technical problem solved by the present invention is how to increase the interaction time of the particles, that need to be collected, with the electrostatic field in such a way that particles are strongly influenced by the field. [0010] The main purpose of the present invention is to remedy the above-mentioned drawbacks of the prior art by disclosing a multi-stage filtration device for filtering a wide range of particles having different concentrations or sizes, suspended in an initial gas flow which is able to collect said particles more efficiently by increasing the interaction time of the particles with the electrostatic field compared to the conventional inertial filtering devices or the electrostatic precipitators.

[0011] This purpose is achieved in accordance with the invention having the characteristics of the independent claim 1 .

[0012] Advantageous embodiments of the invention will appear from the dependent claims.

[0013] The multi-stage filtration device for filtering a range of particles having a mean particle size between about 0.01 pm to about 10 mm, suspended in an initial gas flow according to the independent claim 1 comprises: at least two individual filtration devices, placed one over another in layers in a staggered manner and in a fluid connection, each of said at least two individual filtration devices comprising:

- a cathode structure comprising:

- a plurality of hollow longitudinal chambers, closed at their proximal longitudinal ends at a proximal side and at their distal longitudinal ends at a distal side, each of said chamber having a same and equal sized polygonal, oval or circular transversal cross-section, said polygonal, oval or circular transversal cross-section having a hydraulic diameter (d_n, d_n.-i) dimensioned according to the mean particle size to be filtered at each filtration stage (f1 , f2,...fn),

- each of said longitudinal chambers being arranged in a parallel manner relative to each adjacent longitudinal chambers such that all the proximal sides of each of the plurality of the longitudinal chambers are arranged on a first transversal plane and such that all the distal sides of each of the plurality of the longitudinal chambers are arranged on a second transversal plane and

- each of said longitudinal chambers comprising on their same lateral portion a plurality of outlet perforations, equally spaced apart from one another and from the proximal and distal sides, on a longitudinal direction,

- a clearance space is provided between each adjacent longitudinal chamber allowing passage of said initial gas flow between each of said at least two individual filtration devices,

- an anode structure comprising:

- an anode support structure, placed over said cathode structure and comprising a plurality of inlet through-holes arranged on said anode support structure in an (x-z) array to allow passage of the initial gas flow inside said longitudinal chambers and each inlet through-hole is placed between two adjacent outlet perforations,

- each inlet through-hole is further placed on a centerline, of each longitudinal chamber, which centerline connects a center of a portion (b) of said polygonal, oval or circular transversal cross-section which portion (b) is placed in contact with the anode support structure with each center of the inlet through-holes arranged in an in-line manner on said centerline at an equal distance (c),

- an electrical conductor is placed along each centerline or along a line which connects a center of each proximal and distal sides of each longitudinal chamber; each of said electrical conductors being connected through a common electrical conductor to a power source capable to generate an electric potential difference between anode and cathode structures when a predetermined charge is applied to both the anode structure and to the cathode structure such that an electrostatic ionizing field is created inside the longitudinal chambers for charging the particles with an electrostatic voltage and passage of said initial gas flow in each filtration stage (f1 , f2,...fn), has a sinuous path through:

- said inlet through-holes capable to separate said initial gas flow into a plurality of vortices with a laminar flow for capturing particles,

- further through said plurality of outlet perforations and through said clearance space into the plurality of hollow longitudinal chambers of the next individual filtration device having another hydraulic diameter (d_n) which is smaller than the hydraulic diameter (d_n.-i) of the longitudinal chambers of the previous individual filtration device such that during the passage of said initial gas flow through each filtration stage (f1 , f2,...fn), said charged particles are collected inside said longitudinal chambers.

Brief description of the drawings

[0014]

Fig 1 depicts a detailed perspective view of an individual filtration device according to an embodiment of the present invention;

Fig 2 depicts a detailed top view of the individual filtration device according to an embodiment of the present invention;

Fig 3 depicts a perspective view of an embodiment of a multi-stage filtration device with two filtration stages according to the present invention;

Fig. 4 depicts a front view of the embodiment of a multi-stage filtration device with two filtration stages according to the present invention;

Fig. 5 is a diagram which shows the efficiency of each known filtration device (Inertial, Electrostatic) compared to the efficiency of the multi-stage filtering device (1) of the present invention, according to the particle size.

Detailed description of embodiments of the invention

[0015] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and which only have an illustrative, not limiting value.

[0016] With reference to Figs.1 to 5, a multi-stage filtration device (1 ) for filtering a range of particles having a mean particle size between about 0.01 pm to about 10 mm, suspended in an initial gas flow according to the present invention is disclosed comprising at least two individual filtration devices (11 ), placed one over another in layers in a staggered manner and in a fluid connection. The individual filtration devices (11 ) are preferably arranged in a planar (as depicted in figs. 1 or 2) or in a closed structure manner, preferably a cylinder (as depicted in figs. 3 or 4) or a polyhedron with a hollow channel inside the cylinder or polyhedron to allow passage of the initial gas flow.

[0017] Each of the at least two individual filtration devices (11 ) comprises a cathode structure (2) and an anode structure (3). The cathode structure (2) may be placed over and above the anode structure (3) or over and below the anode structure (3) in a preferred embodiment of the present invention according to specific applications. The cathode structure (2) comprises a plurality of hollow longitudinal chambers (21 ).

[0018] A longitudinal direction is defined along a longitudinal axis of the cathode structure (2) or of the longitudinal chamber (21 ), oriented from the end of the cathode structure (2) or of the longitudinal chamber (21 ) that remains close to the position from which the cathode structure (2) or longitudinal chamber (21 ) is observed, called proximal longitudinal end of the cathode structure (2) or of each longitudinal chamber (21 ), to the end of the cathode structure (2) or longitudinal chamber (21 ) that is opposite to the proximal longitudinal end of the cathode structure (2) or of each longitudinal chamber (21 ) i.e. placed at the furthest distance from the proximal longitudinal end on the longitudinal direction, called distal longitudinal end of the cathode structure (2) or of each longitudinal chamber (21 ).

Each of the hollow longitudinal chambers (21 ) is closed at their respective proximal and distal longitudinal ends by a proximal side and respectively distal side. Each side is defined as a flat outer surface of the cathode structure (2) or of each longitudinal chamber (21 ) or of any part of the filtration device (1 ).

Taking into account the above definitions, then lateral sides/portions of the cathode structure (2) or of the longitudinal chambers (21 ) will be the left and right extremities/portions, considering the proximal and distal sides as defined above.

The distance from the proximal longitudinal end to the distal longitudinal end of the cathode structure (2) or of the longitudinal chamber (21 ) defines the length of the cathode structure (2) or the length of the longitudinal chamber (21).

[0019] Each chamber (21 ) has a same and equal sized polygonal, oval or circular transversal cross-section (A) being versatile for a wide range of applications where space and airaulic specifications require different construction shapes. The transverse axis passes through the cathode structure (2) or through the longitudinal chamber (21 ) or through any part of the filtration device (1 ) always perpendicular to the relevant section on the longitudinal axis.

Preferably, the polygonal transversal cross-section (A) is a V-shaped triangle.

The polygonal, oval or circular transversal cross-section (A) of each longitudinal chamber (21 ) has a hydraulic diameter (d_n, d_n.i) dimensioned according to the mean particle size to be filtered at each filtration stage (f 1 , f2,...fn). A hydraulic diameter is a commonly used term when handling flow in non-circular tubes/conduits. The hydraulic diameter transforms non-circular ducts into pipes of equivalent diameter for the purpose of pressure drop and fluid flow rate calculations. For example, the hydraulic diameter for a square duct is calculated as 4 times the flow area divided by the “wetted” perimeter of the conduit. The “wetted” perimeter of a non-circular tube or conduit is the area of the tube/conduit in contact with the fluid (such as air or gas) that it carries.

Each individual filtration device (11 ) has longitudinal chambers (21 ) with different hydraulic diameters per filtration stage (f 1 , f2, ...fn), calibrated to remove firstly the larger particles and then to remove smaller particle sizes. The first individual filtration device (11 ) has chambers (21 ) with a hydraulic diameter (d_n.-i) greater than another hydraulic diameter (d_n) of the longitudinal chambers (21 ) of the second individual filtration device (11 ) and so on...For example, larger particles require a large hydraulic diameter which is usually found at the longitudinal chambers (21 ) of the first individual filtration device (11 ), in the first filtration stage (f1 ). The second individual filtration device (11 ) is similar except that the longitudinal chambers (21 ) have a much smaller hydraulic diameter, for smaller particle sizes. The layers of individual filtration devices (11 ) may be placed one over another in a similar manner for even smaller hydraulic diameters.

[0020] Each longitudinal chamber (21 ) is arranged in a parallel manner relative to each adjacent longitudinal chambers (21 ) in such a way that all the proximal sides of each of the plurality of the longitudinal chambers (21 ) are arranged on a first transversal plane. Also, all the distal sides of each of the plurality of the longitudinal chambers (21 ) are arranged on a second transversal plane. Each longitudinal chamber (21 ) has on their same lateral portion (a), i.e. either the right portion or the left portion, but never on different lateral portions (e.g. left-right or right-left), a plurality of outlet perforations (12), equally spaced apart from one another and from the proximal and distal sides, on a longitudinal direction. The outlet perforations (12) are preferably circular or oval through-holes. An embodiment of a preferred example of the present invention is a multi-stage filtration device (1 ) comprising a first individual filtration device (11 ) with longitudinal chambers (21 ) having a hydraulic diameter of about 70 mm and outlet perforations (12) with a diameter of about 25 mm. A second individual filtration device (11 ) with longitudinal chambers (21 ) of the multi-stage filtration device (1 ) has preferably a hydraulic diameter of the longitudinal chambers (21 ) of about 15 mm and outlet perforations (12) with a diameter of about 10 mm.

[0021] A clearance space (7) is provided between each adjacent longitudinal chambers (21 ) allowing passage of the initial gas flow between each of at least two individual filtration devices (11 ). The cathode structure (2) is preferably made from a conductive material or a conductive material covered with an insulating material to prevent power surges.

[0022] Each of the individual filtration devices (11 ) further comprises an anode structure (3) with an anode support structure (31 ), placed over the cathode structure (2). The anode structure (3) comprises a plurality of inlet through-holes (13) arranged on the anode support structure (31 ) in an (x-z) array to allow passage of the initial gas flow inside the cathode’s longitudinal chambers (21 ). Each inlet through-hole (13) is placed between two adjacent outlet perforations (12) and preferably at an equal distance from each adjacent outlet perforations (12). Further, the inlet through- holes (13) are preferably circular or oval through-holes.

[0023] The polygonal transversal cross-section (A) of the longitudinal chambers (21 ) is preferably a triangular (V-shaped) cross-section (A) with its base in contact with the anode support structure (31 ) and with its vertex oriented towards the next anode support structure (31 ) of the next individual filtration device (11 ). The V-shaped triangular cross-section is preferred because this shape allows the formation of vortices of different hydraulic diameters inside the longitudinal chambers (21 ) due to its corners.

[0024] Each inlet through-hole (13) is further placed on a centerline (X) of each longitudinal chamber (21 ), which centerline (X) connects a center of a portion (b) of the polygonal, oval or circular transversal cross-section (A), which portion (b) is placed in contact with the anode support structure (31 ), with each center of the inlet through-holes (13) arranged in an in-line manner on the centerline (X), at an equal distance (c). This distance (c) is preferably less than about 40 mm.

The anode support structure (31 ) is preferably made from an insulating material, preferably ceramic or different composites which are compatible with the environment of the filtration process (for example, in case of high temperatures or acid environment), for example, plastic or any suitable electrostatic isolator material. [0025] An electrical conductor (4) is placed along each centerline (X) or along a line (X’) which connects a center of each proximal and distal sides of each longitudinal chamber (21 ). Each electrical conductor (4) is then connected through a common electrical conductor (5 - not shown) to a power source (6 - not shown). This power source (6) is capable to generate an electric potential difference between the anode

(3) and the cathode (2) structures when a predetermined charge (C1 , C2) is applied to both the anode structure (3) and to the cathode structure (2). Thus, an electrostatic ionizing field is created inside the longitudinal chambers (21 ) for charging the particles travelling inside the chambers (21 ), with an electrostatic voltage. The electrical conductor (4) is preferably an electrical wire (4) placed over or inside each of the inlet through-holes (13) or a needle type anode (4) placed inside each inlet through-hole (13) or a wire mesh (4) placed on the interior surface of the insulation material of the anode support structure (31 ). The anode electrical wire (4) is preferably made of conductive materials such as metals (e.g. Copper, Aluminum, Steel, etc.) and shall be placed in such way to encourage particle charging, as close to the center of the air/gas passage and at equal distances from the cathode’s longitudinal chambers (21 ). The preferred location of the anode electrical conductor

(4) is along the line (X’) which connects a center of each proximal and distal sides of each longitudinal chamber (21 ). Each electrical connector (4), preferably an electrical wire (4) is fastened to each center of the proximal and distal sides of each longitudinal chamber (21 ) by fastening means, preferably by screws. The electrical wire (4) placed in the middle of each longitudinal chamber (21 ) will allow creation of an electrostatic ionizing field with an enhanced particle capturing efficiency. The common electrical conductor (5) is preferably made from a conductive material, preferably Copper, Aluminum or Steel covered with an insulating material. The different layers of individual filtration devices (11 ) have a space between them because each individual filtration device (11 ) has a different voltage applied thereon according to the hydraulic diameter (d_n, d_n.-i) of each longitudinal chamber (21 ) of each individual filtration device (11 ). Therefore, an electric potential difference will be generated between different individual filtration devices (11 ). Each individual filtration device (11 ) is isolated from the other individual filtration devices (11 ).

[0026] Passage of the initial gas flow in each filtration stage (f1 , f2,...fn), has a sinuous path through the inlet through-holes (13) separating the initial gas flow into a plurality of vortices with a laminar flow. The vortices are created inside the plurality of longitudinal chambers (21 ) with minimum energy loss, as air/gas flow is laminar in the extremity of the vortices, due to low Reynolds number at minimum speed. Reynolds number (Re) is used to determine whether a flow will be laminar or turbulent. If Re is high (> 2100), inertial forces dominate viscous forces and the flow is turbulent; if Re is low (< 1100), viscous forces dominate and the flow is laminar. However, at low enough Reynolds number (critical Reynolds number of less than 1100) is an example of a laminar flow with vortex structures or vortices. The critical Reynolds’s number is different for every shape of the cross-section of the longitudinal chambers (21 ). The vortices created inside the longitudinal chambers (21 ) will inertially separate the larger particles with mass, while the smaller particles will be transported in the vortices and delayed along their way, by extending the distance that a particle has to travel between two adjacent outlet perforations (12) to exit through these outlet perforations (12) and through the clearance space (7) and enter into the next individual filtration device (11 ). Each inlet through-hole (13) is placed between two adjacent outlet perforations (12) and preferably at an equal distance from each adjacent outlet perforations (12), because this is the best position to allow formation of a maximum vortex circuit.

[0027] Known devices charge the particles to migrate toward the grounded collecting electrodes/charged plates and thus collecting the particles on charged plates. The linear movement of particles between the straight electrods/charged plates has a relative small contact or interaction time and distance (typically 2 m/s for about 40 mm), therefore a large number of particles may escape the electrostatic field. If the particle traveling between these plates has a mass, it will also have speed and therefore will be less influenced by the electrostatic field. The interaction time of the particle with the electrostatic field is very important in this case. For example, for particles of about 10 pm to about 15 pm, the interaction time will be 20 milliseconds which is an insufficient interaction time for this size of particles to be captured and therefore these particles will escape. For particles of about 0.1 pm to about 2 pm, this 20 milliseconds time is sufficient and has a very good capturing efficiency. The question arising from this analysis is how to extend this particle travel distance of about 40 mm to catch more particles of different sizes.

[0028] The present invention uses the effect of the laminar flow with vortices that can extend the travel distance of a particle by multiplying the hydraulic diameter (d_n, d_n.-i) with the mathematical constant IT that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159. Preferably, the number of turns of each vortex in the present invention is of about 3 to 4 turns between two adjacent outlet perforations (12). During the passage of the initial gas flow in each filtration stage (f1 , f2,...fn), the particles to be filtered are passed through the longitudinal chambers (21 ). A predetermined charge (C1 , C2) is applied to both the anode structure (3) and to the cathode structure (2) such that an electrostatic ionizing field is created inside the longitudinal chambers (21 ) for charging the particles with an electrostatic voltage. Thus, the travel distance of the particles and the interaction time of the particles with the electrostatic field are considerably higher, resulting in a cluster of charged particles with mass that can be collected inertially.

If the ultrafine powder particles of about 0.1 pm to about 2 pm escape through the outlet perforations (12) of an individual filtration device (11 ), the particles will enter into the next individual filtration device (11 ) which has longitudinal chambers (21) with another hydraulic diameter (d_n) which is smaller compared to the hydraulic diameter (d_n.i) of the longitudinal chambers (21 ) of the previous individual filtration device (11 ).

[0029] Stairmand (1951 ) and Barth (1956) first developed the “static particle theory” for the analysis of cyclone device collection efficiency. Since then, this static particle theory based upon a force balance analysis has been adopted by many other researchers in their theoretical analyses for characterizing cyclone performance. Basically the “static particle theory” suggested that force balance (centrifugal force Fc = drag force FD) on a particle yields a “critical particle” or “cut point”, “cut size” or “cutoff aerodynamic diameter for cyclones”, which has 50% chance to be collected and 50% chance to penetrate the cyclone. The diameter of the critical particle or cut size is d50. The critically sized particle (d50) is smaller than the smallest particle, which is collected, and larger than the largest particle that penetrates the cyclone. The critical particle with diameter of d50 is theoretically suspended in the outer vortex due to the force balance. The force balance on the particle gives the particle a 50% chance to be collected and a 50% chance to penetrate. In fact, d50 is the critical separating diameter. If a particle is larger than d50, for example if the cut size d50 is 2 pm and a particle size is of more than 2 pm, it will move towards the wall and collected, whereas, if a particle is smaller than the d50, for example smaller than 2 pm, it will move towards the inner vortex and escape the filter. Particle moves from the interface of inner vortex and outer vortex towards the cyclone wall, once the particle hits the wall, it will be collected.

According to the Stairmand equation:

Where: q = Efficiency of the cyclone separator

Ci = A constant that depends on the dimensions of the cyclone separator

Dp = Particle size (in microns)

Vi = Inlet velocity (in m/s)

V₂ = Outlet velocity (in m/s) the smaller particles can be captured inertially, with more than 50% efficiency, if the cut size d50 is smaller than the particle size. The smaller the cut size d50 in a cyclone separator, the better is its dust separation performance.

This equation is based on experimental data and is valid for certain ranges of operating conditions. It is generally used to evaluate the efficiency of a cyclone separator for a single particle size and is not suitable for multi-modal particle size distributions.

Note that the constant Ci is a function of the cyclone geometry, and it is obtained by experiments.

[0030] One of the problems in calculation of inertial separation efficiency is the effect of flow characteristics. In general, transportation of particles in gases is performed at relatively high speeds (more than 10 m/s up to 40 m/s), therefore the flow type is turbulent in large diameters (more than 100 mm up to 1000 mm).

According to the present invention, the initial gas flow having for example, a speed of about 10 to 30 m/s is separated into a plurality of laminar gas flows with a designed speed for example, 1 to 4 m/s, in order to create small vortices with a very good efficiency (higher than 90%) for the addressed particle sizes. For different applications, diameters of the inlet through-holes (13) and of the outlet perforations (12) are correlated with the vortex diameter and may be calculated for each stage of filtration (f 1 , f2, ...fn).

[0031] The charger (i.e. power source (6)) applies an electrical predetermined charge (C1 , C2) to the anode structure (3) and to the cathode structure (2), according to ionization requirements depending on the use conditions. The electrical predetermined charge (C1 , C2) is chosen so that will create an electrostatic effect but without ionization of the air/gas and may preferably be a continuous electrical charge, DC or AC, in pulsing/alternative sessions manner.

For example, in a classic Direct Current (DC), a positive predetermined charge (C1 ) of 10 kV is applied to the anode structure (3) and a negative predetermined charge (C2) of -10kV is applied to the cathode structure (2). The electrical potential difference generated between the anode (3) and the cathode structures (2), perceived by the particles will be 20 kV, therefore the air/gas flow will be ionized with effective 20 kV, particles will be charged and passed over the next stage of filtration (f 1 , f2,..fn) with a pre-charged value between 0 kV to 10 kV, interacting in a field of +/- 10kV. Particles initially with 0 kV, will be attracted by the positive field, and charged positive, air speed and vortex turns will move them over to the cathode structure (2) and be influenced by the negative attraction and eventually slowing the transportation speed of particles, resulting in an agglomeration effect. This agglomeration of smaller particles or cluster of particles increases the specific weight of the cluster and improves the collection efficiency in the inertial vortex. One important requirement is that the electrostatic ionizing field should be stronger enough compared to the inertial force of a particle. If the particle has inertial force, it is desired to collect that particle using the inertial principle and not the electrostatic principle. Particles which have more inertial force to escape this attraction, on each turn of the vortex will eventually move to the next stage of filtration (f1 , f2, ..fn) through the outlet perforations (12) and through the clearance space (7), having a pre-charge which will increase with the new field interaction from the next individual filtration device’s (11 ) anode structure (3). The process will be repeated on smaller hydraulic diameters of the vortices formed in the longitudinal chambers (21 ) of the next individual filtration device (11 ).

[0032] Thus, a synergistic effect is attained which combines both the inertial and the electrostatic effect on the particles. The inertial effect is therefore encouraged by the electrostatic effect by delaying the smaller particles along their path between two adjacent outlet perforations (12) to increase the interaction time of the smaller particles with the electrostatic ionizing field and to create clusters of particles with a critical mass that can be collected inertially.

[0033] In order to increase the electrostatic efficiency, a higher voltage is required. This may result in excessive ionization and shortcuts, especially when ionization conditions are influenced by high temperatures or humidity.

On the other side, decreasing the voltage of the electrostatic chargers, will lead to lowering the particle charge, thus decreasing capturing efficiency.

An alternative solution, in a preferred embodiment of the present invention may be to alternate the predetermined charges (C1 , C2) on the cathode (2) and on the anode (3) structures in such way that the electric potential difference will be only half, as follows:

- when positive electrical voltage is applied over the anode structure (3), a zero electrical voltage is on the cathode structure (2);

- when negative electrical voltage is applied over the cathode structure (2), zero electrical voltage is on the anode structure (3).

In this way, the electric potential difference is half of the total amount, but the particles will be influenced by the total amount of charge.

For example, by applying the alternative electrical voltage as described above, the voltage gradient will be 20 kV, same as in the previous example, but the difference interacting with the particle is 40 kV. The voltage gradient is the potential difference between two points, divided by the distance between them.

[0034] In another preferred embodiment of the present invention, an inlet airflow distribution system (not shown) is preferably placed in the proximity of the inlet through-holes (13) that will secure that the initial air/gas flow will pass through each inlet through-hole (13) with the same speed. The inlet airflow distribution system may be shaped as a conical element when placed in the middle of the cylinder or polyhedron shaped multi-stage filtration device (1 ) and preferably shaped as an inclined plate or a lamination panel when placed in the proximity of the inlet through- holes (13) of the planar shaped multi-stage filtration device (1 ). The multi-stage filtration device (1 ) of the present invention has large air/gas flow passage channels thus, will not oppose resistance to air/gas compared to other types of known filtering devices. The higher permeability will allow the passage of the air/gas flow straight to the contact area with the first individual filtration device (11 ), without a uniform distribution of the initial air/gas flow over the entire surface of the contact area (i.e. of the anode structure (3)). To compensate this effect, it is necessary to take a compensatory measure by adding an inlet airflow distribution system or by changing the cross-sectional geometry of the holes if for example, a panel filter with holes is used for this purpose. The initial air/gas flow’s speed through the holes of the inlet airflow distribution system must be constant and relatively low compared to the transport speed of the particles, therefore the high-speed air/gas flow transported on the ventilation ducts to the multi-stage filtration device (1 ) will have to be evenly distributed over the entire surface of the inlet airflow distribution system.

This can be achieved for example, by adding a lamination panel with several slots or a conical element with holes or an inclined plate that could be placed over the last individual filtration device (11 ), described according to the present invention.

[0035] In yet another preferred embodiment of the present invention an automated or manual discharge system for the filtered particles, collected in the longitudinal chambers (21 ) of each individual filtration device (11 ) is preferably connected to the multi-stage filtration device (1 ). After each of the individual filtration device (11 ) collects the filtered particles in its longitudinal chambers (21 ), the multi-stage filtration device’s (1 ) efficiency is starting to decrease. The cleaning of the known devices is very difficult to achieve if not impossible to do, thus, the filters are being discarded and replaced. This fact contributes to a good amount of pollution, as industrial wastes, which causes major damage to human, plants or animal lives and significantly contributes to climate change. The solution according to the present invention can be used for a longer period of time because the cleaning of the longitudinal chambers (21 ) can be easily done with an automated or manual discharge system, such as pipe-line scrapers, surface wipes or rubber blades. By discharging the filtered particles during operation of the multi-stage filtering device (1 ), the maximum filtration performance of the device (1 ) is preserved over time, without diminishing it due to the particles accumulated in the longitudinal chambers (21 ).

[0036] Fig. 5 is a diagram which shows the efficiency of each known filtration device (Inertial, Electrostatic) compared to the efficiency of the multi-stage filtering device (1) of the present invention, according to the particle size. It can be noted that efficiency of the known electrostatic device decreases as the particle size increases while efficiency of the known inertial device increases only if the particle size increases. The efficiency of the multi-stage filtering device (1 ) of the present invention is relatively constant of 87% to 100%, due to the synergistic effect of the combined electrostatic and inertial effects.

[0037] The multi-stage filtering device (1 ) according to the present invention, may be used in a wide range of industrial applications, such as: powder, sand or chips separation, smoke or ash capture. Also, it can be used in harshest environmental conditions where extreme temperatures or acid formation is not avoidable (such as chimneys, exhaust gas ducts, combustion automotive or aircrafts engines etc.).

[0038] In conclusion, there are various advantages of the present invention which include:

- the energy required for the fluid flow to pass through all the layers of individual filtration devices (11 ) is very low, which leads to reduced electricity consumption, because the pressure loss during this passing is below 100 Pa; - the electric potential difference between the anode (3) and the cathode (2) structures avoids the formation of "corona" discharges and the formation of ozone due to its relatively low value;

- the path length of the particles through the longitudinal chambers (21 ) in the electrostatic ionizing field is tens of times longer than in the case of known electrostatic filter devices, which allows a much more efficient collection of small, fine particles and increase of the agglomeration effect which favours a good inertial separation of the particles inside the longitudinal chambers (21 );

- by discharging the accumulated filtered particles during operation, the functioning of the multi-stage filtering device (1 ) does not need to be temporarily halted to clean it and therefore the difficult technical problems of access inside the collecting chambers and interruption of filtration are avoided;

- by using an automatic discharge/cleaning system, the multi-stage filtering device (1 ) according to the present invention can function for longer periods of time without interruption;

- the compact and efficient multi-stage filtering device (1 ), proposed by the present invention can alone replace the groups of known filtering devices, specialized separately on large and small particle sizes.

[0039] What has been described and illustrated herein is an example of the disclosure along with some of its optional features. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. The scope of the disclosure is intended to be defined by the following claims.

Claims

1. Multi-stage filtration device (1 ) for filtering a range of particles having a mean particle size between about 0.01 pm to about 10 mm, suspended in an initial gas flow, said multi-stage filtration device (1 ) comprising at least two individual filtration devices (1 1 ), placed one over another in layers in a staggered manner and in a fluid connection, each of said at least two individual filtration devices (1 1 ) comprising:

- a cathode structure (2) comprising:

- a plurality of hollow longitudinal chambers (21 ), closed at their proximal longitudinal ends at a proximal side and at their distal longitudinal ends at a distal side, each of said chamber (21 ) having a same and equal sized polygonal, oval or circular transversal cross-section (A), said polygonal, oval or circular transversal cross-section (A) having a hydraulic diameter (d_n, d_n.-i) dimensioned according to the mean particle size to be filtered at each filtration stage (f1 , f2,...fn),

- each of said longitudinal chambers (21 ) being arranged in a parallel manner relative to each adjacent longitudinal chambers (21 ) such that all the proximal sides of each of the plurality of the longitudinal chambers (21 ) are arranged on a first transversal plane and such that all the distal sides of each of the plurality of the longitudinal chambers (21 ) are arranged on a second transversal plane and

- each of said longitudinal chambers (21 ) comprising on their same lateral portion (a) a plurality of outlet perforations (12), equally spaced apart from one another and from the proximal and distal sides, on a longitudinal direction,

- a clearance space (7) is provided between each adjacent longitudinal chamber (21 ) allowing passage of said initial gas flow between each of said at least two individual filtration devices (1 1 ),

- an anode structure (3) comprising:

- an anode support structure (31 ), placed over said cathode structure (2) and comprising a plurality of inlet through-holes (13) arranged on said anode support structure (31 ) in an (x-z) array to allow passage of the initial gas flow inside said longitudinal chambers (21 ) and each inlet through-hole (13) is placed between two adjacent outlet perforations (12),

- each inlet through-hole (13) is further placed on a centerline (X), of each longitudinal chamber (21 ), which centerline (X) connects a center of a portion (b) of said polygonal, oval or circular transversal cross-section (A), which portion (b) is placed in contact with the anode support structure (31 ), with each center of the inlet through-holes (13) arranged in an in-line manner on said centerline (X) at an equal distance (c),

- an electrical conductor (4) is placed along each centerline (X) or along a line (X’) which connects a center of each proximal and distal sides of each longitudinal chamber (21 ); each of said electrical conductors (4) being connected through a common electrical conductor (5) to a power source (6) capable to generate an electric potential difference between anode (3) and cathode (2) structures when a predetermined charge (C1 , C2) is applied to both the anode structure (3) and to the cathode structure (2) such that an electrostatic ionizing field is created inside the longitudinal chambers (21 ) for charging the particles with an electrostatic voltage and passage of said initial gas flow in each filtration stage (f1 , f2,...fn), has a sinuous path through:

- said inlet through-holes (13) capable to separate said initial gas flow into a plurality of vortices with a laminar flow for capturing particles, - further through said plurality of outlet perforations (12) and through said clearance space (7) into the plurality of hollow longitudinal chambers (21 ) of the next individual filtration device (11 ) having another hydraulic diameter (d_n) which is smaller than the hydraulic diameter (d_n.-i) of the longitudinal chambers (21 ) of the previous individual filtration device (11 ) such that during the passage of said initial gas flow through each filtration stage (f1 , f2,...fn), said charged particles are collected inside said longitudinal chambers (21 ).

2. Multi-stage filtration device (1 ) according to claim 1 wherein each inlet through- hole (13) is placed between two adjacent outlet perforations (12), preferably at an equal distance from each adjacent outlet perforation (12).

3. Multi-stage filtration device (1 ) according to claim 1 or 2 wherein said polygonal transversal cross-section (A) is preferably a triangular (V-shaped) cross-section (A) with its base in contact with the anode support structure (31 ).

4. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 3 wherein the at least two individual filtration devices (11 ) are arranged in a planar or in a closed structure manner, preferably a cylinder or a polyhedron, with a hollow channel inside the cylinder or polyhedron to allow passage of the initial gas flow.

5. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 4 wherein said electrical conductor (4) is preferably an electrical wire (4) placed over or inside each of said inlet through-hole (13) or inside said longitudinal chambers (21 ) or a needle type anode (4) placed inside each inlet through-hole (13) or a wire mesh (4).

6. Multi-stage filtration device (1 ) according to claim 5 wherein said electrical conductor (4) is made from a conductive material, preferably Copper, Aluminum or Steel.

7. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 6 wherein said common electrical conductor (5) is made from a conductive material, preferably Copper, Aluminum or Steel covered with an insulating material.

8. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 7 wherein said anode support structure (31 ) is made from an insulating material, preferably ceramic, plastic or any suitable electrostatic insulating material.

9. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 8 wherein said cathode structure (2) is made from a conductive material or a conductive material covered with an insulating material.

10. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 9 wherein an inlet airflow distribution system is preferably placed in the proximity of said inlet through-holes (13).

11. Multi-stage filtration device (1 ) according to claim 10 when dependent on claim 4 wherein the inlet airflow distribution system is preferably shaped as a conical element when placed in the hollow channel of the cylinder or polyhedron shaped multi-stage filtration device (1 ) and preferably shaped as an inclined plate or a lamination panel when placed in the proximity of said inlet through-holes (13) of the planar shaped multi-stage filtration device (1 ).

12. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 11 wherein said outlet perforations (12) and/or said inlet through-holes (13) are preferably circular or oval through-holes.

13. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 12 wherein an automated or manual discharge system for the filtered particles is preferably connected to the filtration device (1 ).

14. Multi-stage filtration device (1 ) according to claim 13 wherein said automated or manual discharge system has preferably pipe-line scrapers, surface wipes or rubber blades.

15. Multi-stage filtration device (1 ) according to any of the preceding claims 1 to 14 wherein the electrical predetermined charge (C1 , C2) is preferably a continuous electrical charge, DC or AC, in pulsing/alternative sessions manner.