EP2322280A1

EP2322280A1 - Electrostatic filtration module and modular, two-stage, electrostatic filter

Info

Publication number: EP2322280A1
Application number: EP10190444A
Authority: EP
Inventors: Luigi Bontempi
Original assignee: Sabiana SpA
Current assignee: Sabiana SpA
Priority date: 2009-11-11
Filing date: 2010-11-09
Publication date: 2011-05-18
Anticipated expiration: 2030-11-09
Also published as: ITMI20091966A1; EP2322280B1

Abstract

Module for forming a two-stage electrostatic filter comprising a cathode stage (100) for collecting the particles and a polarization stage (200), in which said cathode stage (100) comprises a pair of flat side elements; the cathode side elements (110) and central elements (120) being parallel to each other and connected in pairs.

Description

The present invention relates to an electrostatic air filtration module and a two-stage electrostatic filter, in particular for air recirculating apparatus comprising said module.
It is known that in electrostatic air filters the air passes through an ionization zone or section comprising a high-potential electrode, where the suspended solid particles are ionized, and said ionized particles pass along paths which are bounded by walls having a sign opposite to that of the particles, which are thus attracted towards the said walls and stably deposited thereon.
The said electrostatic filters may be essentially of two types: so-called single-stage filters, in which the ionization section and the collection section are combined in a single section, and two-stage filters, in which the two sections are separate and arranged in succession. US2005/0051028 and W02009/059451 disclose electrostatic filters of the conventional type in which the anode components are all electrically connected to each other and to the positive pole. This means that any damage to an anode plate results in blockage of the entire filter.
US 4,119,416 also discloses and defines special dimensional ratios for the various parts and in particular the ratio between the distance of the polarization wire and ground and the relative distance between the anode and cathode surfaces.
In connection with two-stage filters EP 0,636,418 , in the name of the same present Applicants, also discloses a two-stage electrostatic filter for air recirculating apparatus comprising at least one ionization stage formed by facing parallel walls which have, arranged inside, a high-potential electrode able to generate an induction field which charges with a positive potential the walls of ionization cells and at least one precipitation stage formed by parallel walls, having a negative potential compared to the ionization potential, wherein said ionization and precipitation cells consist of at least one cathode element in the form of an "overturned U", the opposite ends of which are mechanically and electrically connected to a transverse support profile and which is provided internally with at least one partition extending parallel to the outer arms of the "U" along the length of the profile, but with a height less than that of said arms and able to cooperate with a U-shaped anode element arranged opposite it and mechanically fixed by means of insulating support members, further cathode elements being envisaged for modular expansion of the filter in the direction of the its width.
Although performing its function, this known filter has, however, limitations consisting in the limited possibility of increasing its performance by means of an increase in the filtration efficiency (= capacity of the filter to retain the particles) and the regularity of performance over time, without correspondingly increasing the energy consumption. The technical problem which is posed, therefore, is to provide a two-stage filter which can be formed from a minimum number of parts which can be easily produced and assembled together in a geometric configuration which can be realized and/or modified very easily depending on the specific requirements of the individual applications and which has a greater efficiency, but low energy consumption.
In connection with said problem the filter must also be simple to build and assemble, at little cost, and be able to be applied easily to purification apparatus and also be able to reduce the faults arising from handling of the ionization electrode, but at the same be suitable for achieving and obtaining high efficiency characteristics which are as constant as possible over time and with a small amount of maintenance. Said technical problems are solved according to the present invention by a module for forming a two-stage electrostatic filter comprising a cathode stage for collecting the particles and a polarization stage, said cathode stage comprising a pair of flat side elements of suitable length in the vertical direction and at least three further, flat, central elements of smaller length compared to the length of the side elements; the cathode side elements and central elements being parallel to each other and connected in pairs in the transverse direction by pairs of intermediate bridges; and said anode stage comprises at least four flat segments of suitable height in the vertical direction, arranged alternating with the anode elements in the transverse direction; said anode segments being connected together in pairs in the transverse direction by pairs of intermediate bridges; insulating elements for supporting the components of the cathode stage and anode stage; a high-potential electrode extending in the longitudinal direction and arranged between the two cathode side elements.
Further details may be obtained from the following description with reference to the accompanying drawings in which:

Figure 1: shows a schematic cross-sectional view of the basic elements forming a filter module according to the present invention;
Figure 2: shows an exploded view of the module of Fig. 1;
Figure 3: shows an exploded schematic view of a preferred embodiment of the particle collection stage according to the present invention;
Figure 4: shows an exploded schematic view of a preferred embodiment of the two stages, i.e. polarization stage and particle deposition stage;
Figure 5: shows a perspective of the filter according to Fig. 4 in the assembled condition;
Figure 6: shows a partial cross-section along the plane indicated by VI-VI in Fig. 5 and
Figure 7: shows a comparative graph of the efficiency results which can be obtained with a filter according to the prior art and a filter according to the present invention under different geometric operating conditions.

Assuming solely for the sake of convenience of the description and without any limiting meaning a set of three reference axes in a longitudinal direction X-X, transverse direction Y-Y and vertical direction Z-Z and referring, for the sake of brevity, to the higher potential elements as "anodes" and the lower potential elements as "cathodes", Figs. 1 and 2 show the structure of a base module for forming a two-stage filter according to the present invention.
In greater detail the said base module comprises:

a cathode stage 100 formed by:
- a pair of flat side elements 110 of suitable length C1 in the vertical direction and at least three further, flat, central elements 120 having a smaller length C2 than the length C1 of the side elements 110;
  said side elements 110 and central elements 120 being parallel to each other and connected in pairs in the transverse direction Y-Y by end bridges 131 and by pairs of intermediate bridges 132; said intermediate pairs defining a space 132a in the longitudinal direction X-X suitable for the insertion of support elements 300, as will become clearer below.
  It is envisaged moreover that said end bridges 131 are coplanar and, preferably, all connected together in the transverse direction Y-Y by a cross-piece 140 which is for example L-shaped as shown in Fig. 3 and which is in turn connected to the lower potential;
an anode stage 200 formed by:
- at least four flat segments 210 of suitable height in the vertical direction Z-Z and arranged alternating with the anode elements 120 in the transverse direction Y-Y;
  the anode segments 210 being in turn connected together in pairs in the transverse direction Y-Y by pairs of intermediate bridges 232 suitable for defining a space 232a in the longitudinal direction such as to allow the insertion of said support means 300;
a high-potential electrode 400 extending in the longitudinal direction X-X, arranged inside the base module and suitable for producing the positive charge of the anode elements 220;
support elements 300 substantially formed by a coil of insulating material, suitable for containing and supporting the various flat anode elements 110, 120 and cathode elements 210: the coil has projections 301 oppositely arranged in the vertical direction Z-Z for stable insertion with an interference fit inside the said seats 132a,232a defined by the cathode intermediate transverse bridges 132 and the anode transverse bridges 232.

Once the cathode stage 100 and the anode stage 200 have been joined together by means of the insulating supports 300, the base module is formed and geometrically stable for use.
According to a preferred embodiment of the base module for a modular electrostatic filter it is also envisaged that: if R indicates the radius of a virtual cylinder C, having a longitudinal axis coinciding with the polarization electrode 400, the following is obtained:

the cathode side elements 110 are tangential to the side surface of the cylinder C;
the free end of the cathode segments 120 is tangential to the side surface of the cylinder C.

It is envisaged, moreover, that, once the radius R has been defined as described above, the relative distances between the various elements of the module are as follows:

D1 = the distance in the vertical direction Z-Z between the end of the cathode segments 210 and the electrode 400; said distance D1 being between 0.33R and 0.57R, preferably between 0.41R and 0.49R;
D2 = the distance in the vertical direction Z-Z between the bottom end of the central cathode element 120 and bottom end of the anode elements 210; said distance D2 being between 0.40R and 0.60R, preferably between 0.49R and 0.54R;
D3 = the distance in the transverse direction Y-Y between the vertical anode elements 210 and the cathode segments 120; the distance D3 being between 0.41R and 0.57R, preferably between 0.48R and 0.56R.

As shown in Figs. 3 to 6 with the base module for electrostatic filter according to the invention, it is possible to provide a two-stage modular filter comprising:

an ionization stage 2000 formed by a frame 2010 of insulating material having, arranged inside, the electrode 400 formed by a continuous wire extending in the longitudinal direction X-X so as to be arranged with parallel sections which have a constant interaxial distance equal to 2R in the transverse direction Y-Y;
a stage 1000 for collecting the ionized particles, formed by a plurality of base modules extending as required in the longitudinal direction X-X and arranged alongside each other in the transverse direction Y-Y.

Preferably the base modules are connected together by a pair of L-shaped cross-pieces 140 for connection to the lower potential and inserted inside insulating end-pieces 1010 suitable for connection to and engagement with the frame 2010 of the polarization stage 1000.
Said end-pieces have special guide seats 1010a suitable for insertion, in the longitudinal direction X-X, of the ends of the anode segments 110 and cathode segments 210 in order to obtain the correct interaxial distance in the transverse direction.
According to a preferred embodiment, said cathode elements 210 and anode elements 110 are assembled together individually in order to form modules which are electrically insulated so that any malfunctioning or short-circuiting of one of the modules does not alter the electric field of the entire filter, adversely affecting the overall operating performance thereof.
It has been established during tests that, with the filtration module and modular filter according to the present invention, it is possible to obtain a high degree of efficiency and reliability with lower energy consumption and high degree of reliability and ease of maintenance for normal cleaning operations.

As shown, in fact, in Fig. 7 it is possible to establish that the efficiency (continuous line A) which can be obtained with a filter provided according to the teachings of the present invention which has:
useful deposition area = 5.40 m²;
R = 12 mm; D1 = 5.5 mm; D2 = 6.5 mm ; D3 = 2.5 mm
and with the characteristics shown in the table below

Novel filter type with proportions as per patent (version 1)
Pressure Drop Pa	2
Temp	35
Relative Humidity (ur) %	16.4
Diethyl sebacate exil (dehs)	0.5
Recorded throughput m3/h	1050
Nominal throughput m3/h	1200
Power supply	7330
Current	0.22 mA

is far superior to that of a filter provided according to the teachings of EP 0,636,418 (broken line B) and with the characteristics as shown in the table below

Existing (old) filter type
Pressure Drop Pa	8
Temp	35
Relative Humidity (ur) %	16.4
Diethyl sebacate exil (dehs)	0.5
Recorded throughput m3/h	1050
Nominal throughput m3/h	1200
Power supply	7330
Current	0.35 mA

From the same Fig. 7 it is also possible to establish (dot-dash line C) that a filter designed with the structure according to the present invention and with
same deposition area = 5.40 m2;
but with dimensional ratios
R = 12 mm; D1 = 7.5 mm; D2 = 4.5 mm ; D3 = 2.5 mm different from those envisaged by the present invention and with the characteristics as shown in the table below

Novel filter type with different proportions (version 2)
Pressure Drop Pa	2
Temp	35
Relative Humidity (ur) %	16.4
Diethyl sebacate exil (dehs)	0.5
Recorded throughput m3/h	1050
Nominal throughput m3/h	1200
Power supply	7330
Current	0.30 mA

produces a limited increase in efficiency and a simultaneous increase in current consumption, thus demonstrating that the efficiency has been surprisingly increased without having to resort to a banal increase in the deposition areas.

As shown in Fig. 5 it is also envisaged that the end side cathode elements in the transverse direction Y-Y are formed by means of elements 1110 folded in the manner of a Z in order to provide support surfaces for the cross-pieces 140 for electrical connection to the lower potential and to the frame 2010 of the polarization stage.
It is envisaged moreover that said cathode and anode elements are preferably made by folding sheet metal parts so as to limit the need for special mechanical machining equipment and therefore resulting in lower production costs.
Although described in connection with certain constructional forms and certain preferred examples of embodiment of the invention, it is understood that the scope of protection of the present patent is defined solely by the following claims.

Claims

Module for forming a two-stage electrostatic filter comprising a cathode stage (100) for collecting the particles and a polarization stage (200), in which said cathode stage (100) comprises:
- a pair of flat side elements (110) of suitable length (C1) in the vertical direction and at least three further, flat, central elements (120) of smaller length (C2) compared to the length of the side elements (110);
characterized in that

- said cathode side elements (110) and central elements (120) of the cathode stage (100) are parallel to each other and connected in pairs in the transverse direction (Y-Y) by pairs of intermediate mechanical bridges (132);
and said anode stage (200) comprises:
- at least four flat segments (210) of suitable height in the vertical direction (Z-Z), arranged alternating with the anode elements (120) in the transverse direction (Y-Y);

- the anode segments (210) being connected together in pairs in the transverse direction (Y-Y) by pairs of intermediate mechanical bridges (232);

- insulating elements (300) for supporting the components (110,210) of the cathode stage (100) and anode stage (200);

- a high-potential electrode (400) extending in the longitudinal direction (X-X) and arranged between the two cathode side elements (110);
in that

- said intermediate pairs of mechanical bridges (132,232) define a space (132a,232a) in the longitudinal direction (X-X) suitable for the insertion of support elements (300);
in that

- said cathode elements and anode elements are formed by means of folding; and
in that

- said cathode side elements (110) and central elements (120) are connected together by mechanical end bridges (131).
Module according to Claim 1, characterized in that said end bridges (131) are coplanar and all connected together in the transverse direction (Y-Y) by a cross-piece (140) connected to the lower potential.
Module according to Claim 1, characterized in that the cathode side elements (110) are tangential to the side surface of a virtual cylinder (C) of radius R which has a longitudinal axis coinciding with the polarization electrode (400).
Module according to Claim 3, characterized in that the free end of the central cathode segment (120) is tangential to the side surface of the said cylinder (C).
Module according to Claim 3, characterized in that the distance D1 in the vertical direction (Z-Z) between the end of the anode segments (210) and the electrode (400) is between 0.33R and 0.57R.
Module according to Claim 5, characterized in that said distance D1 is preferably between 0.41R and 0.49R.
Module according to Claim 3, characterized in that the distance D2 in the vertical direction (Z-Z) between the bottom end of the central cathode element (120) and the bottom end of the cathode elements (210) is between 0.40R and 0.60R.
Module according to Claim 7, characterized in that said distance D2 is preferably between 0.49R and 0.54R.
Module according to Claim 3, characterized in that the distance D3 in the transverse direction (Y-Y) between the vertical anode elements (110) and the cathode segments (120) is between 0.41R and 0.57R.
Module according to Claim 9, characterized in that said distance D3 is preferably between 0.48R and 0.56R.
Module according to Claim 1, characterized in that said support elements (300) are formed by a coil of insulating material which has projections (301) oppositely arranged in the vertical direction (Z-Z) for insertion with an interference fit inside the said seats (132a,232a) defined by the pairs of cathode transverse bridges (132) and anode transverse bridges (232).
Two-stage, modular, electrostatic filter comprising an ionization stage (2000) and a stage (1000) for collecting the ionized particles, characterized in that it comprises at least one electrostatic filtration module according to Claim 1.
Filter according to Claim 12, characterized in that the ionization stage (2000) is formed by a frame (2010) which is made of insulating material and inside which the polarization electrode (400) is arranged and the stage (1000) for collecting the ionized particles is formed by a plurality of modules extending as required in the longitudinal direction (X-X) and arranged alongside each other in the transverse direction (Y-Y).
Filter according to Claim 12, characterized in that said polarization electrode is formed by a continuous wire (400) extending in the longitudinal direction (X-X) so as to be arranged with parallel sections having a constant interaxial distance equal to 2R in the transverse direction (Y-Y).
Filter according to Claim 12, characterized in that the cathode elements (110,120) of the base modules are rigidly connected together by a pair of cross-pieces (140) for connection to the lower potential.
Filter according to Claim 12, characterized in that it has insulating end-pieces (1010) suitable for connection and relative engagement between the frame (2010) of the ionization stage (2000) and the collection stage (1000).
Filter according to Claim 16, characterized in that said end-pieces (1010) have guide seats (1010a) suitable for insertion of the ends of the anode segments (110) and cathode segments (210).
Filter according to Claim 12, characterized in that said cathode elements (210) and anode elements (110) are assembled together individually forming electrically insulated modules.
Filter according to Claim 12, characterized in that the cathode end side elements in the transverse direction (Y-Y) are formed by means of elements (1110) folded in the form of a "Z" and arranged opposite each other.