Title of Invention	ELECTROSTATIC PRECIPITATOR
Abstract	An Electrostatic Precipitator comprising: one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen; one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen); one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entrainment) and the collecting electrode parts ( being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire, volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts).

Title of Invention

ELECTROSTATIC PRECIPITATOR

Abstract

An Electrostatic Precipitator comprising: one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen; one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen); one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entrainment) and the collecting electrode parts ( being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire, volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts).

Full Text	This invention relates to Electrostatic Precipitator for separating dust particles from dust laden gas. PRIOR ART Before this invention, in the known art, Electrostatic Precipitators were used for separating dust particles contained in a gas stream by charging the dust particles with the help of high voltage DC electricity and collecting the dust particles on collecting electrodes and discharge electrodes. The discharge electrodes are usually connected to a high voltage negative DC electric power source normally with rated voltage of 70 KV to 105 KV( peak) and rated current of around 300 micro- amperes ( A) per square metre of collecting electrode surface area. The discharge electrodes may be connected to a high voltage positive DC electric power source also.The collecting electrodes are earthed.The combination of collecting electrodes and discharge electrodes are called field of an Electrostatic Precipitator. The Electrostatic Precipitator is like a condenser. The surface of collecting electrode contain positive charge induced by the negative charge on the discharge electrode. The outline of an Electrostatic Precipitator in the known art is shown in the figure-1 to 3, in which, casing (20) houses the electrical field (19). The electrical field (19) consists of collecting electrodes (24) and discharge electrodes(25). The casing (20) consists of roof (at the top) and two side walls.The casing is open at the inlet side and outlet side and at the bottom side.At the inlet side from where dust laden gas enters the Electrostatic Precipitator is the inlet funnel(17). The inlet funnel (17) is a transition piece between the inlet duct (16) which is having a lesser cross-sectional area and the casing (20) which is having a bigger cross-sectional area. The dust laden gas enters through the inlet duct (16) to the inlet funnel(17) to the casing (20). The dust laden gas coming out from casing (20) enters the outlet funnel (22), and from outlet funnel (22) to outlet duct (23). Outlet duct (23) is having lesser cross-sectional area and casing is having a bigger cross-sectional area. The outlet funnel is a transition piece between casing (20) and outlet duct (23).At the bottom of the casing (20) is fitted the hopper (26) which has the shape of an inverted pyramid. The dust collected on the collecting electrodes and discharge electrodes when rapped fall on the hopper (26) and is discharged from the bottom of the hopper (26). Electrical field (19) may consist of one or more fields. Each field has a number of collecting electrode curtains (24) arranged parallel to the side wall of the casing.These curtains divide the volume of the casing of that field into a number of gas passages as shown in figure-2. Space is kept in between any two adjacent fields for movement of men during repair/ maintenance work whenever necessary. As shown in figure-1, the gas enters into the field (19) from inlet funnel (17) and passes through the gas passages and enters the next field (if the Electrostatic Precipitator has more than one field ) and in this way when the gas leaves the last field it enters the outlet funnel (22). Each gas passage has its inlet side and outlet side open so that gas enters and leaves the gas passage un-obstructed.Also the bottom side of the gas passage is open so that when the electrodes are rapped the dislodged dust fall to the hopper un-obstructed.The gas passages consisting of curtains of collecting electrodes (24) have discharge electrodes(25) placed along the central axis of the gas passage as shown in figure-3. The discharge electrodes charge the dust particles and majority of the dust particles present in the gas stream is collected on the 2 collecting electrodes and a small portion is collected on the discharge electrodes. The gas flows parallel to the collecting electrode surface.As the gas flows through the gas passages in the electrical field, the dust particles continue to get separated from the gas stream and the dust concentration of the gas in the gas stream get progressively reduced. The efficiency of this Electrostatic Precipitator and its sizing can be determined by the following two equations. One equation is where =Efficiency Inlet dust concentration- Outlet dust concentration Inlet dust concentration W =Migration velocity (m/ sec.), which is velocity component of dust particle moving towards collecting Electrode in an Electrostatic Precipitator. It depends on the size of the particle, viscosity of the medium and voltages of charging field and collecting field. V= Gas flow rate expressed in cubic metre per second (m3/sec.) A= Total collecting electrode surface area of the Electrostatic Precipitator (m ) Total collecting electrode surface area of the Precipitator = No. of field x No. of Gas Passage x[ Height of collecting electrode x Length of collecting electrode curtain in a field (along gas flow)] x 2 (because there two surfaces of collecting electrode in a gas passage) Inlet dust concentration = Quantity of dust present in unit volume of the gas (gm/m3) before the gas enters the Electrostatic Precipitator Outlet dust concentration = Quantity of dust present in unit volume of the gas (gm/m3 or, mg/ m3) after gas leaves the Electrostatic Precipitator. where, =Efficiency W= Migration Velocity (m/sec.) It is the velocity component in which the dust particle moves towards the collecting electrode in an Electrostatic Precipitator. v = velocity of flow of gas inside the Electrostatic Precipitator (m/sec.) L = Field length (m) This is the total length of collecting electrodes [ by adding length of collecting electrodes (along flow) of all the fields) d = Discharge Distance (m) This is the distance between the centre of a collecting electrode row and centre of adjacent discharge electrode row. If we know the gas flow rate (V), inlet dust concentration of the gas at the inlet of the Electrostatic Precipitator, the migration velocity (W), and the required dust concentration of the gas at the outlet of the Electrostatic Precipitator, we can find out the total required collecting electrode surface area of the Electrostatic Precipitator to obtain the required outlet dust concentration by applying any one of the above two equations, where discharge distance is generally kept 0.15 m or, 0.2 m and gas velocity is generally chosen any thing between 0.3 m/ sec. to 1.4 m/ sec. When the collecting electrode surface area is known, the whole Electrostatic Precipitator can be designed. The above mentioned two equations are same equation expressed in two different forms, which can be easily shown. These two equations are called Deutsch Anderson equation and Deutsch equation respectively. From these equations we see that if dust laden gas is passed through an Electrostatic Precipitator, when the gas passes over a given collecting electrode surface area, the outlet dust concentration of the gas gets accordingly reduced. In other words, we can say that when dust laden gas is passed over a given collecting electrode surface area the dust particles get separated from the dust laden gas stream. The quantity of dust separated or the outlet dust concentration of the gas in an Electrostatic Precipitator can be found out from these equations. These equipments are used for separating dust from dust laden gas in various industries for air pollution control and other purposes. 4 DISTINGUISHING FEATURES a) In the Electrostatic Precipitator as described in this invention when dust laden gas stream crosses one discharge electrode screen at inlet side, one collecting electrode screen, and one discharge electrode screen at the outlet side, all the dust particles present in the gas stream get separated from the entire volume of the gas passing through migration distance area. Whereas in case of an Electrostatic Precipitator of prior art (including US patent No.5603752 & 5922111), the dust particles present in the gas get separated from a certain depth of gas stream from collecting electrode surface (here we call it migration distance area) as elaborated in the invention part and as a result the dust concentration of the gas stream get progressively reduced as the gas passes through the gas passages of the precipitator and so the gas has to travel a long distance through the precipitator to achieve a given outlet dust concentration, and a large collecting electrode surface area, as per Deutsch equation or Deutsch Anderson equation, is required. In case of US patent No. 5603752, from the fact that a plurality of dust collecting electrode group is required, it can be understood that dust concentration of the gas get progressively reduced as the gas passes through successive dust collecting electrode groups and dust particles are not separated from the entire volume of the gas when it crosses a single dust collecting electrode group. Requirement of dust collecting electrode in this type of Electrostatic Precipitator is 30 % to 40 % in weight of dust collecting electrode required in case of a prior type precipitator. The collecting electrode surface area required in an Electrostatic Precipitator as described in the present invention will be 10 to 15 times smaller compared to precipitators of prior art. b) In the electrostatic Precipitator of this invention, the collecting electrode screen is made of collecting electrode parts, trays and collectors as shown in Fig. 10 to Fig. 15 and individual collecting electrode parts are shown in Fig. 13. Whereas the dust collecting electrodes of US patent No. 5603752 is made of commercially available chains and of US patent No. 5922111 are made of pipes. c) In the Electrostatic Precipitator of this invention the discharge electrodes are made of plates whose longitudinal edges are having saw tooth shape as shown in Fig. 17. Whereas discharge electrodes of US patent No. 5603752 are made of rectangular metal plates, the longitudinal edges of each plate form semi-circles, with a series of saw tooth portions having tips protruding from between each pair of semi-circles. The discharge electrodes of US patent No. 5922111 are pin like positively charged discharge electrodes centrally located within the collecting electrodes. 4a DISADVANTAGE The followings are the disadvantages of an existing type of Electrostatic Precipitator (prior to this invention). a) Migration velocity is the central point in the basic equations and, =1-e-(wl/vd) where, A= Total Collecting Electrode Surface Area (m2) V= Gas flow rate (m3/ sec.) W= Migration velocity (m/ sec.) L= Field length (m) v = Velocity of gas flow (m/sec.) d = Discharge Distance (m) (The above equations are known as Deutsch Anderson equation and Deutsch equation respectively on which the theory of existing type of Electrostatic Precipitator is founded ). But the migration velocity concept has some flaws which are discussed in the following lines. Collection of dust particles on the electrodes inside an electrostatic precipitator take place due to force of attraction between two oppositely charged bodies, one being the charged dust particle and the other being the opposite charge on the surface of the collecting electrode. If, the force of attraction =F, charge on collecting electrode and discharge electrode = Q1 and Q2 respectively, the distance between the charged dust particle and the collecting Thus, force between any particular charged dust particle and the collecting electrode being F, velocity changes with time due to the acceleration associated with the force. Also, as the distance between the dust particle and the collecting electrode changes (reduces), the force also increases resulting into higher velocity of the dust particle moving towards the collecting electrode. Thus a particular migration velocity cannot exist. b) In an Electrostatic Precipitator, the separation of the dust particles from a gas stream takes place gradually, so a large collecting electrode surface area is required. This requires a large number of discharge electrodes also. To accommodate such a large collecting electrode area, the casing (the enclosure box or housing of collecting electrodes and discharge electrodes) becomes very large. To give structural strength to such a big casing, large quantity of steel material is required. Also, a big supporting structure, large hoppers, inlet funnel, out funnel, bottom dust conveying system etc. are required. Thus the total cost of the electrostatic Precipitator becomes very large. c) Since for the Electrostatic precipitator a large collecting electrode surface area is required, current requirement is also very high (considering a current rating of 300 micro-ampere per square metre of collecting electrode surface area). 5 So the power consumption of an Electrostatic Precipitator is very high. d) The Electrostatic Precipitator occupies a large space. So, it becomes very difficult to accommodate an Electrostatic Precipitator, particularly when retrofitting in an existing plant, where space available is limited. OBJECT OF THE INVENTION The object of the invention is given below. a) To build a new type of Electrostatic Precipitator which will separate dust particles from a gas stream. b) This new type of Electrostatic Precipitator will be small sized compared to existing type of Electrostatic Precipitators. c) This new type of Electrostatic Precipitator will contain smaller and less number of components compared to existing type of Electrostatic Precipitator and so will be cheap. d) The running cost of this Electrostatic Precipitator will be less due to less Electric power consumption. INVENTION This invention -" Electrostatic Precipitator (based on Migration Distance concept) is described in the following chapters starting from the development of Migration Distance concept. Let us consider an existing type of Electrostatic Precipitator in which the discharge electrodes are charged with high voltage negative DC electricity and the collecting electrodes are earthed or grounded. The surface of the collecting electrode contains positive charge (induced by the negative charge on the discharge electrodes). When the dust particles come in contact with (or pass near) the negatively charged discharge electrodes, they get negatively charged and then these negatively charged dust particles get attracted by the positive charge on the surface of the collecting electrodes. Due to attraction of a charged dust particle and opposite charge on the collecting electrode surface, a force is exerted on the dust particle, which pulls the dust particle towards the collecting electrode. When the distance between the charged dust particle and the collecting electrode is small (within a particular range), the force of attraction is greater than the pull on the dust particle exerted by the flowing gas due to aerodynamic forces. In this condition dust particle is separated from the gas stream and ultimately get collected on the collecting electrode. Let us consider an existing type of Electrostatic Precipitator with: Collecting Electrode surface area = A (square metre) 6 Gas flow rate = V, (m3/sec.) Treatment time = t1, (sec.) [ The treatment time is the time taken by the gas flow or a dust particle (if not collected during its travel) to cross the entire electrical field from entry to exit of an Electrostatic Precipitator.] Let the inlet dust concentration of the gas = C1 gms/m3 . (This means one cubic metre of gas contains C1 gms of dust particles before the gas stream enters the Electrostatic Precipitator.) Let us assume that all the dust particles in a charged Electrostatic Precipitator within a particular range of distance (say from 0 to % metre) from the collecting electrode surface will be separated from the gas stream for ultimately collection on the collecting electrode. Now collecting electrode surface area for unit quantity of gas flow ( 1 m / sec. gas flow) This is [ A1 (square metre)] also called specific collection area. [ Let the cross-sectional area of the chamber of the Electrostatic Precipitator is divided into 'V number of sub-areas with each having equal area. Then gas passing through one such sub-area of the cross-section of the Electrostatic Precipitator will pass over In t1 sec. unit volume of gas passes over A1 square metre of collecting electrode surface area. .".In 1 sec. unit volume of gas passes over square metre of collecting electrode surface area. If we consider a very small interval of time At sec, such that, At > 0 Then, if we consider all the dust particles present in the flowing gas within a range of distance (from 0 to % metre) from the collecting electrode surface are separated from the gas stream and ultimately get collected on the collecting electrode surface, then for unit flow of gas, in the first At sec. all the dust particles in the volume 7 will get separated from the gas stream. Dust particles separated from gas in first At sec. which is the dust concentration after first At sec. travel of the gas through the electrical field of the Electrostatic Precipitator. Similarly, for 1 m3 of gas, dust particles separated from the gas in second At sec. 8 .'.After 2 At sec. from beginning, dust contained in 1 m3 of the gas 9 After t1 sec. from beginning of the flow of the gas in the Electrostatic Precipitator, the particular 1 m3 of gas has passed through the Precipitator for such small 10 interval of time of At sec. duration. Therefore, dust concentration of the 1 m3 of gas after t1 sec. or the outlet dust concentration of the gas at the outlet of the precipitator 11 which is Deutsch Anderson equation. Since Deutsch Anderson equation is true, and by assuming that all the dust particles within distance % metres from collecting electrode surface in a charged Electrostatic Precipitator are separated from the gas stream for ultimately collection on the collecting electrode, we arrive at the Deutsch Anderson equation, our assumption that the dust particles within a distance of % metres from the surface of collecting electrodes of a charged Electrostatic Precipitator will get separated from the gas stream and ultimately get collected on the collecting electrode is true. Here % has numerically the same value as that of migration velocity in Deutsch equation or Deutsch Anderson equation. This shows that consideration of migration distance is sufficient to arrive at the result experimentally found true by operation of existing Electrostatic Precipitators designed according to Deutsch equation or Deutsch Anderson equation. Above forms the basis of the Migration Distance concept of Electrostatic Precipitators. This can be said in the following way. The dust particles present in a dust laden gas stream in a charged Electrostatic Precipitator within a given distance from the collecting electrode surface (where this distance will be called Migration Distance and which has the same numerical value as that of the Migration Velocity in Deutsch equation or Deutsch Anderson equation) will be separated from the gas stream and ultimately get collected on the collecting electrodes. This concept will be called Migration distance concept. Based on this migration distance concept, a new type of Electrostatic Precipitator can be constructed in which the dust laden gas can be passed in such a way that while it flows in the chamber of the Electrostatic Precipitator (of the new type) it passes through the discharge electrode screen (where the discharge electrode screen is charged by connecting it to a high voltage DC negative power source), whereby the dust particles get charged and then the dust laden gas is passed through the collecting electrode screen in such a way that the total flow (i.e., the whole gas volume ) has to cross the collecting electrode screen and passes very near to the collecting electrodes ( where the collecting electrode screen is earthed or grounded ), so that the whole gas volume and all the dust particles present in the gas stream passes near the collecting electrode surface within the migration distance ( from collecting electrode surface ), and as a result all the dust particles get separated from the gas stream and ultimately get collected on the collecting electrodes. 12 SUMMARY OF THE INVENTION An Electrostatic Precipitator (subject of this invention, which is described below), based on migration distance concept, will require 10 to 15 times smaller collecting electrode surface area compared to Electrostatic Precipitators of prior art, for which quantity of collecting electrode surface area required is determined with the help of Deutsch equation or Deutsch Anderson equation. An Electrostatic Precipitator comprising: one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen; one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen); one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entratnment) and the collecting electrode parts (being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts). When dust laden gas enters the precipitator, it enters from the inlet duct (12). Gas flows from inlet duct to inlet funnel (9) and from inlet funnel to casing (15), through inlet gas distribution screen (8). 12a The casing houses the electrical field consisting of the collecting electrode screen and discharge electrode screens. When the gas enters the casing from inlet gas distribution screen, the gas passes through electrical field comprising of negatively charged discharge electrode screen (at inlet side) comprising discharge electrode frame (5) and discharge electrodes (4), earthed or grounded collecting electrode screen comprising collecting electrode part (1), tray (2) and collector (3) and negatively charged discharge electrode screen (at outlet side) comprising discharge electrode frame (5) and discharge electrodes (4). Since trays divide the height of collecting electrode part into many parts, the falling dust particles do not achieve a high velocity, which help to avoid re-entrainment of dust particles in the gas stream. Also due to particular arrangement of collecting electrodes the gas flow become such that around collecting electrode surface there will be no gas flow and this will help to prevent re-entrainment of dust particles in the gas stream. See Fig. 18. The whole body of the Electrostatic Precipitator is earthed as a result the collecting electrodes, which are directly supported on the precipitator casing, are also earthed. Discharge electrode frames with the discharge electrodes are suspended through insulators (6) so that the charge on the discharge electrodes does not go to the earth. See Fig. 19. Collecting electrodes are suspended from roof and are spring (7) supported. These electrodes are rapped by electromagnetic rappers, mounted on the roof for dislodging dust particles collected on the collecting electrodes. Since these electrodes are mounted on springs, the shock of rapping is not transmitted to the body of the precipitator. The discharge electrode frames with the discharge electrodes, which are suspended from roof through insulators, are also mounted on springs. Discharge electrodes are also rapped by electromagnetic rappers, mounted on roof for dislodging dust collected on the discharge electrodes. These rappers are insulated from the discharge electrode frames and discharges by putting insulators. When the dust particles are separated from the dust-laden gas in the electrical field, the clean gas enters the outlet funnel (11) through outlet gas distribution screen (10) and from outlet funnel to outlet duct (13). The inlet gas distribution screen (8) and outlet gas distribution screen (10) are provided for evenly distribution of the gas in the precipitator chamber. Hopper (14) is provided for collecting the dust dislodged from collecting electrodes and discharge electrodes. 12b BRIEF DESCRIPTION OF FIGURES A brief description of the figures is given in the following lines. Figure-1 to figure-9 shows existing type of Electrostatic Precipitators (used prior to this invention). Figure-1 This figure shows an existing type of Electrostatic Precipitator (used prior to this invention). Figure-2 This figure shows collecting electrodes in the form of curtains, gas passage and gas flow direction. Figure-3 This figure shows collecting electrode curtains, gas passages formed by collecting electrode curtains and discharge electrodes placed at the central axis of the gas passage. Figure-4 This figure shows discharge electrode. Figure-5 This figure shows collecting electrodes, discharge electrodes in a gas passage and high voltage DC negative electric power supplied to a discharge electrode. Collecting electrodes are earthed (or grounded). Figure-6 This figure shows collecting electrodes (earthed or grounded), discharge electrode connected to high voltage DC negative power source. Positive end of the high voltage DC power source is grounded. Figure-7 This figure shows collecting electrodes forming a gas passage and discharge electrodes placed in the central axis of the gas passage, gas flow direction by an arrow mark. Figure-8 This figure shows a gas passage formed by two collecting electrode curtains and a discharge electrode in the central axis of the gas passage. Figure-8a This figure shows collecting electrode curtains forming a gas passage. Collecting electrodes are earthed. Figure-9 This figure shows a gas passage formed by two collecting electrodes and discharge electrodes placed in the central axis of the gas passage. 13 Figure-10 to figure-19 shows new type of Electrostatic Precipitator based on migration distance concept. Figure-10 This figure shows two discharge electrode screens and one collecting electrode screen. Figure-11 This figure shows a collecting electrode screen (in plan view) Figure-12 This figure shows one collecting electrode and two collectors (front elevation). Figure-13 This figure shows collecting electrode part. Figure-14 This figure shows a sectional view of tray. Figure-15 This figure shows a collector with anti-sneakage guards. Figure-16 This figure shows discharge electrodes mounted on discharge electrode frame. Figure-17 This figure shows a discharge electrode. Figure-18 This figure shows a collecting electrode. Figure-19 This figure shows a new type of Electrostatic Precipitator based on migration distance concept. DETAIL DESCRIPTION OF FIGURES, CONSTRUCTION AND OPERATION Detailed description of figures and construction and operation is given in the following lines. Figure-1 to figure-9 shows existing type of Electrostatic Precipitator (used prior to this invention). Figure-1 This figure shows an existing type of Electrostatic Precipitator (used prior to this invention). (16) - Inlet duct (17) -Inlet funnel (18) - Inlet gas distribution screen 14 (19) - Electrical field consisting of collecting electrodes and discharge electrodes (20) - Casing which houses collecting electrodes and discharge electrodes (21) - Outlet gas distribution screen (22) - Outlet funnel (23) - Outlet duct (26) - Hopper In this Precipitator, dust laden gas enters through the inlet duct (16) to inlet funnel (17). Inlet funnel is a transition piece from inlet duct to casing. Inlet duct is having less cross-sectional area where gas flows at a velocity of around 15 to 20 m/sec. Casing is having bigger cross-sectional area where gas flows at a velocity of around 0 o 5 to 1 m/sec. So, the inlet funnel is having a cross-sectional area, which is in increasing order from inlet side to outlet side i.e., along the direction of gas flow. From inlet funnel (17) the dust laden gas goes to casing (20) through inlet gas distribution screen (18). The inlet gas distribution screen is a perforated sheet i.e., having a large number of holes all over its length and breadth. The inlet gas distribution screen distributes the gas uniformly through out the cross-section of the casing of the precipitator. The casing is like a hollow box. It houses the collecting electrodes and discharge electrodes. When the dust laden gas enters the casing (20) the gas comes to the electrical field (19), consisting of collecting electrodes and discharge electrodes. Here the dust particles are separated from the dust laden gas. The dust particles get separated from the gas stream (when the dust particles are within migration distance area) and get collected on the collecting electrodes. Collecting electrodes are rapped so that the dust particles collected on the surface of the collecting electrodes get dislodged and fall on the hopper (26). Discharge electrodes are also rapped to keep the discharge electrodes clean which help in better charging of the dust particles of the gas stream. The clean gas leaves electrical field (19) and casing (20) and goes to outlet funnel (22) through outlet gas distribution screen (21). From outlet funnel (22) the gas goes to outlet duct (23). The outlet gas distribution screen is normally perforated sheet or plain sheets having gap in between them, which help in distributing the gas through out the cross-section of the casing of the precipitator. The outlet funnel is a transition piece from casing to outlet duct .The outlet duct is having less cross-sectional area (compared to casing), where gas flows at a velocity of around 15 to 20 m/sec. So, the outlet funnel is having a cross-sectional area, which is in decreasing order from inlet side to outlet side i.e., along the direction of the gas flow. Figure-2 This figure shows collecting electrodes in the form of curtains, gas passage formed by two adjacent collecting electrode curtains and gas flow direction. (24) - Collecting electrode (G.P.) - Gas passage -> - The arrow shows the direction of gas flow. 15 Figure-3 This figure shows collecting electrode curtains, gas passage formed by collecting electrode curtains and discharge electrodes placed at the central axis of the gas passage. (24) - Collecting electrode (25) - Discharge electrode -> - The arrow shows gas flow direction Figure-4 This figure shows a discharge electrode. (25) - Discharge electrode Figure-5 This figure shows collecting electrodes, discharge electrodes in a gas passage, high voltage rectified DC negative electric power supplied to a discharge electrode. Collecting electrodes are earthed or grounded. (24) - Collecting electrode (25) - Discharge electrode (+) - Shows positive charge on the collecting electrode surface (-) - Shows negative charge on discharge electrode Figure-6 This figure shows collecting electrode (earthed or grounded), discharge electrode connected to high voltage DC negative power source. Positive end of the high voltage DC power source is earthed or grounded. (24) - Collecting electrode (25) - Discharge electrode A black dot with an encircled (-) sign shows an arbitrarily chosen dust particle with a negative charge and the arrow with the black dot signifies that the negatively charged dust particle is moving towards the positive charge on the surface of the collecting electrode. The encircled (+) sign near collecting electrode shows the positive charge on the surface of the collecting electrode. The encircled (-) sign near the discharge electrode shows negative charge on the discharge electrode. Figure-7 This figure shows collecting electrodes forming a gas passage and discharge electrodes placed in the central axis of the gas passage, gas flow direction by the arrow mark. (24) - Collecting electrode (25) - Discharge electrode d -Discharge distance. (This is the distance between the centre of a row of collecting electrode and the centre of an adjacent row of discharge electrode). W - migration velocity -> - The arrow shows gas flow direction 16 Figure-8 This figure shows a gas passage formed by two collecting electrode curtains and a discharge electrode placed in the central axis of the gas passage. Collecting electrodes are earthed. (24) - Collecting electrode (25) - Discharge electrode (+) - Positive charge on collecting electrode surface (-) -Negative charge on discharge electrode Figure-8a This figure shows collecting electrode curtains forming a gas passage. Collecting electrodes are earthed. (24) - Collecting electrode Figure-9 This figure shows a gas passage formed by two collecting electrodes and discharge electrodes placed in the central axis of the gas passage, the migration distance area is showmtiy the shaded area. (24) - Collecting electrode (earthed) (25) - Discharge electrode (+) - Positive charge on the collecting electrode surface (-) -Negative charge on the discharge electrode (G.P.) - Gas passage (D.P.) - An arbitrarily chosen dust particle (black dot is dust particle, associated with (-), a negative charge) -> -The arrow shows gas flow direction Shaded area - Shows migration distance area as described in the "invention" of the new type of Electrostatic Precipitator Figure-10 to figure-19 shows new type of Electrostatic Precipitator based on migration distance concept. Figure-10 This figure shows two discharge electrode screens and one collecting electrode screen of new type of Electrostatic Precipitator based on migration distance concept A discharge electrode screen (at the inlet side) consisting of (4) - Discharge electrodes mounted on discharge electrode frame (5) - Discharge electrode frame (-) -Negative charge on discharge electrode 17 A collecting electrode screen consisting of (1) - Collecting electrode part (trays, collectors and anti-sneakage guards are not shown for clarity of figure) (+) - Positive charge on the collecting electrode surface Shaded area - Shaded area shows migration distance area (D.P.) - An arbitrarily chosen dust particle carrying a negative charge (the dust particle shown by black dot with a minus sign showing negative charge on this dust particle) ( % ) - The migration distance A discharge electrode screen (at the outlet side) consisting of (4) - Discharge electrode mounted on discharge electrode frame (5) - Discharge electrode frame (-)-Negative charge on discharge electrode -> - The arrow shows the direction of gas flow. The space between two discharge electrodes (mounted on discharge electrode frame) is clear passage for passing gas un-obstructed (which can be understood from the other view of the discharge electrodes mounted on discharge electrode frame as shown in figure-16). When the dust laden gas passes through the discharge electrode screen (at the inlet side), all the dust particles present in the gas stream either touches or passes very near to the discharge electrode thereby getting negatively charged. When these negatively charged dust particles pass through the collecting electrode screen, they pass through the migration distance area and they are separated from the gas stream and get collected on the collecting electrodes. The discharge electrode screen (on the outlet side) is provided to get a migration distance area on the outlet side of the collecting electrode screen. Figure-11 This figure shows a collecting electrode screen (in plan view). (1) & (2) - Colleting electrode part (1) and tray (2) (3), (3A) & (3B) - Collector (3), anti-sneakage guards (3A) & (3B) Here collecting electrode part (1) and tray (2) are collectively called collecting electrode. Figure-12 This figure shows one collecting electrode consisting of collecting electrode part (1) tray (2) and two collectors. (1) - Collecting electrode part (2) -Tray (3) -Collector Figure-13 This figure shows collecting electrode part (1). Figure-14 This figure shows a sectional view of tray (2). 18 Figure-15 This figure shows a collector (3) with anti-sneakage guards (3A) & (3B). The anti-sneakage guards do not allow the dust laden gas to cross the collecting electrode screen bypassing migration distance area. Figure-16 This figure shows discharge electrodes mounted on a discharge electrode frame. (4)-Discharge electrode (5) - Discharge electrode frame The space between two discharge electrodes is a clear passage for flow of gas. Figure-17 This figure shows a discharge electrode (4). Figure-18 This figure shows a collecting electrode screen (for clarity of figure the trays and collectors are not shown). (1) - Collecting electrode part (N.G.) - This shows the area near the collecting electrode surface, where there is no gas flow or very little gas flow. Shaded area - here the shaded area shows a layer of dust particles collected on collecting electrode surface. -> - The arrow shows the gas flow direction Figure-19 This figure shows the new type of Electrostatic Precipitator based on migration distance concept. (12) - Inlet duct (9) - inlet tunnel (8) - Inlet gas distribution screen (15) - Casing which houses the discharge electrode screens and collecting electrode screen The discharge electrode screen (inlet side) consisting of (4) - Discharge electrodes mounted on discharge electrode frame (5) - Discharge electrode frame The collecting electrode screen consisting of (1) -Collecting electrode part (part of collecting electrode) (2) -Tray (part of collecting electrode) (3) - Collector The discharge electrode screen (outlet side), consisting of (4)-Discharge electrodes mounted on discharge electrode frame 19 (5)-Discharge electrode frame (10) - Outlet gas distribution screen (11) - Outlet funnel (13) - Outlet duct (6) -Insulator (7) -Spring (14) - Hopper The dust laden gas enters through the inlet duct (12). From the inlet duct the dust laden gas goes to the inlet funnel (9) through the inlet gas distribution screen (8). The inlet funnel is a transition piece from inlet duct to casing. The inlet duct is having less cross-sectional area where gas flows at a velocity of around 15 to 20 m/sec. The casing is having bigger cross-sectional area where gas flows at a velocity of around 0 o 5 to 1 m/sec. So, the inlet funnel has cross-sectional area in increasing order from inlet side to outlet side (along the direction of gas flow). The inlet gas distribution screen is made of perforated sheet (i.e., having holes through out its length and breadth). The dust laden gas goes from inlet funnel to casing through the inlet gas distribution screen (8). The inlet gas distribution screen helps in evenly, distributing the gas through out the cross-section of the casing of the precipitator. When the dust laden gas enters the casing, the gas comes to electrical field consisting of discharge electrode screens and collecting electrode screen. The discharge electrode screen consists of discharge electrodes (4) and discharge electrode frame (5). The collecting electrode screen consist of collecting electrode part (1), tray (2), collectors (3) and anti-sneakage guards (3A) & (3B). When the dust laden gas enters the electrical field, it first crosses (the inlet side) discharge electrode screen. When the dust laden gas crosses the discharge electrode screen, the dust particles either touch or pass very near to the discharge electrodes thereby get negatively charged. These negatively charged dust particles, when reach the migration distance area, are separated from the gas stream and get collected on the collecting electrodes. The collecting electrode screen is made in such a manner that all the gas (while crossing the collecting electrode screen) has to pass through the migration distance area. Thus while the dust laden gas passes through the collecting electrode screen, all the dust particles get separated from the gas stream and ultimately get collected on the collecting electrodes. The dust particles get deposited on the collecting electrode part (1). When the collecting electrode screen is rapped, the dust particles get dislodged from the collecting electrode part and fall on the trays. The trays are inclined surfaces. The dust particles, which fall on the trays, slide down and enter the collectors. From the collectors the dust particles fall to the hopper (14). The discharge electrodes are rapped to keep it clean for better charging of the dust particles. In a collecting electrode screen, the collecting electrode parts (1) are arranged in two rows. In the front row i.e., which row of collecting electrode parts (1) the gas stream crosses first (or in the inlet side according to gas flow direction), the collecting electrode parts are arranged in such a manner that a gap of size equal to a collecting electrode part is kept in between any two adjacent collecting electrode parts of this row. Thus we see that, in the front row of collecting electrode parts of the collecting electrode screen, there is one collecting electrode part and then one gap of size equal to the size of a collecting electrode part. Thus the gaps and the collecting electrode parts are alternately arranged. In the collecting "electrode screen, behind the front row of collecting electrode parts, the back row of collecting electrode parts 20 are arranged in such a manner that exactly behind a gap of front row, one collecting electrode part is kept in the back row. In the back row also, the collecting electrode parts and gaps are alternately arranged. This is shown in figure-18. In this figure, trays are not shown for clarity of figure. The plane of collecting electrode parts, in both the rows of collecting electrode parts of the collecting electrode screen, are perpendicular to the direction of gas flow in the precipitator before the gas flow reaches the collecting electrode screen. When the gas stream flows through the collecting electrode screen, the gas passes through the opening or gap (between the collecting electrode parts), of the front row of collecting electrode parts and then exits through the opening or gap (between the collecting electrode parts) of the back row of collecting electrode parts. This is shown in figure-18. Here (1) shows collecting electrode part, the arrow shows the direction of gas flow, the shaded area shows layer of dust particles collected on collecting electrode part. The area marked (N.G.) shows the zone where there is no gas flow or very little gas flow. Due to this no gas flow zone near the surface of the collecting electrode part, the re-entrainment of dust particles is minimized. Collecting electrodes are suspended from roof and are spring ( 7) supported. These electrodes are rapped by electromagnetic rappers, mounted on the roof for dislodging dust collected on the collecting electrodes. Since the electrodes are mounted on springs, the shock of rapping is not transmitted to the body of the precipitator. The discharge electrode frames with the discharge electrodes are suspended from the roof of the casing with the help of insulators and springs, which is shown in figure-19. Since the discharge electrode frames are suspended from the roof of the casing through the insulators, the charge contained by the discharge electrodes does not go to the casing, which is earthed or grounded. Since the springs are provided for supporting the discharge electrode frame, so when the discharge electrode frames are rapped for dislodging the dust particles collected on the discharge electrodes, the shock of rapping is not transmitted to the casing. Discharge electrodes are also rapped by electromagnetic rappers, mounted on the roof for dislodging dust collected on the discharge electrodes. When the gas stream crosses the electrical field consisting of discharge electrode screen and collecting electrode screen, the dust particles are separated from the gas stream. The separated dust particles fall on the hopper (14). The clean gas leaving the casing (and the electrical field) goes to the outlet funnel (11) through the outlet gas distribution screen (10). The outlet funnel is a transition piece from casing to outlet duct (13). Outlet duct is having less cross-sectional area where gas flows at a velocity of around 15 to 20 m/sec. The outlet funnel is having its cross-sectional area in decreasing order from inlet side to outlet side in the direction of gas flow. Thus the dust laden gas is cleaned from the dust and the clean gas leaves the precipitator through the outlet duct and the separated dust particles are collected on the hopper. 21 WORKING / OPERATION The working of new type of Electrostatic Precipitator based on migration distance concept is described in the following lines. Let us consider figure-19. At first the dust laden gas enters the inlet duct (12). From inlet duct the gas enters the inlet funnel (9). In the inlet funnel there is inlet gas distribution screen (8). The dust laden gas coming out from the inlet funnel enters the casing (15) through the inlet gas distribution screen (8), which uniformly distributes the gas through out the cross-section of the precipitator when the gas reaches the casing. In the casing the gas passes through the electrical field consisting of discharge electrode screen and collecting electrode screen. The discharge electrode screen consists of discharge electrode frame (5) and discharge electrodes (4). The discharge electrodes are charged with high voltage DC negative electricity. This high voltage DC negative electricity charges all the dust particles of the gas stream, which crosses the discharge electrode screen. Due to this high voltage DC negative electrical charge on the discharge electrodes (4), positive charge is induced on the collecting electrode surface, which is earthed. This positive charge on the surface of the collecting electrodes pulls the negatively charged dust particles. When the distance between the positive charge on the collecting electrode surface and the negatively charged dust particle is within a given range (which is migration distance), the pull between the positive charge on the surface of the collecting electrode and negatively charged dust particle become more than the aerodynamic force exerted on the dust particle by the flowing gas stream. Due to this the flowing gas stream can no longer carry that dust particle with the flow and the dust particle move towards the collecting electrode surface and gets separated from the flowing gas stream. The movement of the dust particle towards the collecting electrode surface continues and ultimately the dust particle gets collected on the collecting electrode part (1). The collecting electrodes are rapped intermittently to dislodge dust particles deposited on the collecting electrode surface. When the collecting electrode is rapped, the dust particles dislodge from the collecting electrode part (1) and fall on the trays (2). The dust particles, which fall on the tray, slide down the tray and goes to the collector (3). From the collector the dust particles fall down to the hopper (14). Discharge electrodes are also rapped intermittently to keep them clean for better charging of the dust particles. When the gas stream flows through the collecting electrode screen, the gas passes through the opening or gap (between the collecting electrode parts), of the front row of collecting electrode parts and then exits through the opening or gap (between the collecting electrode parts) of the back row of collecting electrode parts. This is shown in figure-18. Advantages: This new type of Electrostatic Precipitator (based on migration distance concept) will have the following advantages over the existing type of electrostatic precipitators. In this precipitator, where the gas stream crosses two discharge electrode screens and one collecting electrode screen, all the gas and the dust particles pass through migration distance 22 area and all the dust particles are separated from the gas stream and collected on the collecting electrodes. Thus the requirement of collecting electrode surface area and number of discharge electrodes is less and one electrical field consisting of two discharge electrode screens and one collecting electrode screen is sufficient for separating all the dust particles contained in the gas stream. This has been shown in figure-10. So, the size of this precipitator is small. Whereas in case of an existing type of Electrostatic Precipitator, the gas stream has to travel a long distance along the gas passages of the precipitator and since the outer portions of the gas stream in the gas passage passes through the migration distance area, so dust particles are separated from the outer portion of the gas stream passing through each gas passage. So, a large collecting electrode surface area and consequently a large number of discharge electrodes are required. A big casing is required to house these large number of electrodes and big and a number of hoppers are required below this big casing. This that the dust particles from the outer portion of the gas stream is separated in the precipitator) has been shown in figure-9. Also since the rated current supplied to the Electrostatic Precipitator is proportional to the collecting electrode surface area of the precipitator, due to having much less collecting electrode surface area, the new type of Electrostatic Precipitator will have much less current consumption compared to the existing type of precipitators. So, this new type of Electrostatic Precipitator will be cheap both in cost of equipment and running cost due to consumption of less power. THE CONSTRUCTIONAL IMPROVEMENT OVER EXISTING PRECIPITATORS In the existing type of Electrostatic Precipitators (prior to this invention), the precipitators were designed or sized (and constructed) on the basis of Deutsch Anderson equation or Deutsch equation. So, for a given gas flow rate (V, expressed in m3/sec), inlet dust concentration (expressed in gm/m3), outlet dust concentration (expressed in gm/m3) and migration velocity (expressed in m/sec.) a given quantity of collecting electrode surface area would have to be provided, which has to be calculated with the help of Deutsch equation or Deutsch Anderson equation. This required a very large collecting electrode surface area and consequently a large number of discharge electrodes. To house this large collecting electrode surface area and large number of discharge electrodes, a large casing also would have to be provided. To collect the dust in the hopper below the casing (below the collecting electrodes and the discharge electrodes) a number of large hoppers were required to be provided. Thus the cost of the precipitator would become very high. Also in designing these precipitators, current rating of high voltage DC (negative) power to the discharge electrodes used to be kept proportional to the collecting electrode surface area (approximately 300 A per square metre of collecting electrode surface area). This caused very high electric power consumption for the precipitator. 23 Thus the Electrostatic Precipitator was large in size, having many components (like big casing, large hoppers, large collecting electrode surface area, large number of discharge electrodes etc.) with large weight, requiring costly civil foundation and high running cost due to high current rating of the power source (for large collecting electrode surface). This is apparently so, because the precipitator had to be provided with a big collecting electrode surface area which was arrived at by calculating with the help of Deutsch equation or Deutsch Anderson equation. The precipitator had to be provided with a large number of fields, each field having a large number of gas passages, collecting electrodes with big height and big length, with the gas flow parallel to the collecting electrode surface in each gas passage. But the actual reason for all these were wrong consideration that the dust particles move with a given velocity component (called migration velocity) towards the collecting electrode surface and the collecting electrode surface area had to be determined by calculating as per Deutsch Anderson equation or Deutsch equation. Actually, when the dust laden gas passes through a region (within a given distance from collecting electrode surface area, which we call here migration distance and which has numerically the same value as that of the migration velocity), the dust particles in the gas stream get separated from the gas and ultimately get collected on the collecting electrode surface. In the existing type of precipitators, while the gas flows through a gas passage (with the discharge electrodes placed in the central axis of the gas passage), the gas stream flows parallel to the collecting electrode surface (as shown in figure-9), the dust particles get separated from the gas stream in the migration distance area (in the figure the shaded area). Thus the dust particles get separated within a given depth of the gas stream in the gas passage (within a distance from the collecting electrode surface which is equal to migration distance and is numerically equal to the value of migration velocity). So, for an existing type of Electrostatic Precipitator, it takes a much longer time to get a major portion of the dust contained in the gas to be separated. In the new type of Electrostatic Precipitator (the this invention), the collecting electrode is designed in such a manner that the dust laden gas has to cross a single collecting electrode screen and while crossing the collecting electrode screen, the total gas has to pass through the region which is within migration distance from the collecting electrode surface. Thus one screen of collecting electrode is sufficient to separate all the dust particles present in the dust laden gas. So the precipitator has less collecting electrode surface area and consequently has fewer number of discharge electrodes, a single hopper, a small casing and ultimately the size of the precipitator is small. Due to having smaller collecting electrode surface area, power consumption of this precipitator is also less. In case of existing type of Electrostatic Precipitators (prior to this invention), when the collecting electrodes are rapped, the dust particles deposited on the collecting electrodes fall from the whole height of the collecting electrode, the velocity of the falling dislodged dust particles being high causes re-entrainment of dust particles in the gas stream. 24 Whereas in case of new type of Electrostatic Precipitator, the whole height of the collecting electrode is divided into many parts by trays, which allow the dislodged dust (during rapping) to fall a small vertical height only. Thus re-entrainment of dust particles in the gas stream is less. In case of existing type of Electrostatic Precipitator, gas flows throughout the cross-section of the gas passage, thus near the collecting electrode surface also. So, during rapping, some re-entrainment of the dust particles would take place. Whereas in case of new type of Electrostatic Precipitator, there is no gas flow region in front of the collecting electrode part surfaces, where there is no gas flow or very little gas flow. So, re-entrainment of dust particles, when rapping takes place, is less in this type of precipitator. 25 I CLAIM : 1. An Electrostatic Precipitator comprising: one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen; one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen); one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entrainment) and the collecting electrode parts ( being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts). 2. An Electrostatic Precipitator as claimed in claim 1, where migration distance areas are created in front of the collecting electrode surfaces on both the front side and the back side of the collecting electrode screen, and when dust laden gas passes through the collecting electrode screen, as shown in the accompanying drawings, the dust laden gas has to pass through the migration distance area where all the dust particles are separated from the gas stream and ultimately collected on the collecting electrode. Thus the dust particles are separated from the dust laden gas and we get clean gas. 3. An Electrostatic Precipitator as claimed in claim 1, as shown in the accompanying drawings, where the trays divide the height of the collecting electrode parts into many 26 parts thus the falling dust particles (dislodged from collecting electrode parts) do not achieve a high velocity minimizing re-entrainment of dust particles in the gas stream; where the arrangement of collecting electrode parts in the collecting electrode screen in the front row and back row guides the gas flow in such a manner that the gas flow does not touch the dust layer adhering to the collecting electrode part surfaces, minimizing re-entrainment of dust particles in the gas stream; where the dust particles dislodged from collecting electrode part surfaces (coming from the trays) fall through collectors (vertical pipes) without coming in contact with gas flow minimizing re-entrainment of dust particles in the gas stream. 4.An Electrostatic Precipitator substantially as hereinbefore described and illustrated with reference to the accompanying drawings. An Electrostatic Precipitator comprising: one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen; one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen); one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entrainment) and the collecting electrode parts ( being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire, volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts).

Full Text

This invention relates to Electrostatic Precipitator for separating dust particles from dust laden gas.
PRIOR ART
Before this invention, in the known art, Electrostatic Precipitators were used for separating dust particles contained in a gas stream by charging the dust particles with the help of high voltage DC electricity and collecting the dust particles on collecting electrodes and discharge electrodes. The discharge electrodes are usually connected to a high voltage negative DC electric power source normally with rated voltage of 70 KV to 105 KV( peak) and rated current of around 300 micro- amperes ( A) per square metre of collecting electrode surface area. The discharge electrodes may be connected to a high voltage positive DC electric power source also.The collecting electrodes are earthed.The combination of collecting electrodes and discharge electrodes are called field of an Electrostatic Precipitator. The Electrostatic Precipitator is like a condenser. The surface of collecting electrode contain positive charge induced by the negative charge on the discharge electrode.
The outline of an Electrostatic Precipitator in the known art is shown in the figure-1 to 3, in which, casing (20) houses the electrical field (19). The electrical field (19) consists of collecting electrodes (24) and discharge electrodes(25). The casing (20) consists of roof (at the top) and two side walls.The casing is open at the inlet side and outlet side and at the bottom side.At the inlet side from where dust laden gas enters the Electrostatic Precipitator is the inlet funnel(17). The inlet funnel (17) is a transition piece between the inlet duct (16) which is having a lesser cross-sectional area and the casing (20) which is having a bigger cross-sectional area. The dust laden gas enters through the inlet duct (16) to the inlet funnel(17) to the casing (20). The dust laden gas coming out from casing (20) enters the outlet funnel (22), and from outlet funnel (22) to outlet duct (23). Outlet duct (23) is having lesser cross-sectional area and casing is having a bigger cross-sectional area. The outlet funnel is a transition piece between casing (20) and outlet duct (23).At the bottom of the casing (20) is fitted the hopper (26) which has the shape of an inverted pyramid. The dust collected on the collecting electrodes and discharge electrodes when rapped fall on the hopper (26) and is discharged from the bottom of the hopper (26).
Electrical field (19) may consist of one or more fields. Each field has a number of collecting electrode curtains (24) arranged parallel to the side wall of the casing.These curtains divide the volume of the casing of that field into a number of gas passages as shown in figure-2. Space is kept in between any two adjacent fields for movement of men during repair/ maintenance work whenever necessary.
As shown in figure-1, the gas enters into the field (19) from inlet funnel (17) and passes through the gas passages and enters the next field (if the Electrostatic Precipitator has more than one field ) and in this way when the gas leaves the last field it enters the outlet funnel (22). Each gas passage has its inlet side and outlet side open so that gas enters and leaves the gas passage un-obstructed.Also the bottom side of the gas passage is open so that when the electrodes are rapped the dislodged dust fall to the hopper un-obstructed.The gas passages consisting of curtains of collecting electrodes (24) have discharge electrodes(25) placed along the central axis of the gas passage as shown in figure-3. The discharge electrodes charge the dust particles and majority of the dust particles present in the gas stream is collected on the
2

collecting electrodes and a small portion is collected on the discharge electrodes. The gas flows parallel to the collecting electrode surface.As the gas flows through the gas passages in the electrical field, the dust particles continue to get separated from the gas stream and the dust concentration of the gas in the gas stream get progressively reduced.
The efficiency of this Electrostatic Precipitator and its sizing can be determined by the following two equations.
One equation is

where =Efficiency
Inlet dust concentration- Outlet dust concentration
Inlet dust concentration
W =Migration velocity (m/ sec.),
which is velocity component of dust particle moving towards collecting Electrode in an Electrostatic Precipitator. It depends on the size of the particle, viscosity of the medium and voltages of charging field and collecting field. V= Gas flow rate expressed in cubic metre per second (m3/sec.) A= Total collecting electrode surface area of the Electrostatic Precipitator (m )
Total collecting electrode surface area of the Precipitator = No. of field x No. of Gas Passage x[ Height of collecting electrode x Length of collecting electrode curtain in a field (along gas flow)] x 2
(because there two surfaces of collecting electrode in a gas passage)
Inlet dust concentration
= Quantity of dust present in unit volume of the gas (gm/m3) before the gas enters the Electrostatic Precipitator
Outlet dust concentration
= Quantity of dust present in unit volume of the gas (gm/m3 or, mg/ m3) after gas leaves the Electrostatic Precipitator.

where, =Efficiency

W= Migration Velocity (m/sec.)
It is the velocity component in which the dust particle moves towards the collecting electrode in an Electrostatic Precipitator. v = velocity of flow of gas inside the Electrostatic
Precipitator (m/sec.)
L = Field length (m)
This is the total length of collecting electrodes [ by adding length of collecting electrodes (along flow) of all the fields)
d = Discharge Distance (m)
This is the distance between the centre of a collecting electrode row and centre of adjacent discharge electrode row.
If we know the gas flow rate (V), inlet dust concentration of the gas at the inlet of the Electrostatic Precipitator, the migration velocity (W), and the required dust concentration of the gas at the outlet of the Electrostatic Precipitator, we can find out the total required collecting electrode surface area of the Electrostatic Precipitator to obtain the required outlet dust concentration by applying any one of the above two equations, where discharge distance is generally kept 0.15 m or, 0.2 m and gas velocity is generally chosen any thing between 0.3 m/ sec. to 1.4 m/ sec. When the collecting electrode surface area is known, the whole Electrostatic Precipitator can be designed.
The above mentioned two equations are same equation expressed in two different forms, which can be easily shown. These two equations are called Deutsch Anderson equation and Deutsch equation respectively.
From these equations we see that if dust laden gas is passed through an Electrostatic Precipitator, when the gas passes over a given collecting electrode surface area, the outlet dust concentration of the gas gets accordingly reduced. In other words, we can say that when dust laden gas is passed over a given collecting electrode surface area the dust particles get separated from the dust laden gas stream. The quantity of dust separated or the outlet dust concentration of the gas in an Electrostatic Precipitator can be found out from these equations. These equipments are used for separating dust from dust laden gas in various industries for air pollution control and other purposes.
4

DISTINGUISHING FEATURES
a) In the Electrostatic Precipitator as described in this invention when dust laden
gas stream crosses one discharge electrode screen at inlet side, one collecting
electrode screen, and one discharge electrode screen at the outlet side, all the
dust particles present in the gas stream get separated from the entire volume of
the gas passing through migration distance area.
Whereas in case of an Electrostatic Precipitator of prior art (including US patent No.5603752 & 5922111), the dust particles present in the gas get separated from a certain depth of gas stream from collecting electrode surface (here we call it migration distance area) as elaborated in the invention part and as a result the dust concentration of the gas stream get progressively reduced as the gas passes through the gas passages of the precipitator and so the gas has to travel a long distance through the precipitator to achieve a given outlet dust concentration, and a large collecting electrode surface area, as per Deutsch equation or Deutsch Anderson equation, is required.
In case of US patent No. 5603752, from the fact that a plurality of dust collecting electrode group is required, it can be understood that dust concentration of the gas get progressively reduced as the gas passes through successive dust collecting electrode groups and dust particles are not separated from the entire volume of the gas when it crosses a single dust collecting electrode group. Requirement of dust collecting electrode in this type of Electrostatic Precipitator is 30 % to 40 % in weight of dust collecting electrode required in case of a prior type precipitator.
The collecting electrode surface area required in an Electrostatic Precipitator as described in the present invention will be 10 to 15 times smaller compared to precipitators of prior art.
b) In the electrostatic Precipitator of this invention, the collecting electrode screen
is made of collecting electrode parts, trays and collectors as shown in Fig. 10 to
Fig. 15 and individual collecting electrode parts are shown in Fig. 13.
Whereas the dust collecting electrodes of US patent No. 5603752 is made of commercially available chains and of US patent No. 5922111 are made of pipes.
c) In the Electrostatic Precipitator of this invention the discharge electrodes are
made of plates whose longitudinal edges are having saw tooth shape as shown
in Fig. 17.
Whereas discharge electrodes of US patent No. 5603752 are made of rectangular metal plates, the longitudinal edges of each plate form semi-circles, with a series of saw tooth portions having tips protruding from between each pair of semi-circles.
The discharge electrodes of US patent No. 5922111 are pin like positively charged discharge electrodes centrally located within the collecting electrodes.
4a

DISADVANTAGE
The followings are the disadvantages of an existing type of Electrostatic Precipitator (prior to this invention).
a) Migration velocity is the central point in the basic equations
and, =1-e-(wl/vd)
where, A= Total Collecting Electrode Surface Area (m2)
V= Gas flow rate (m3/ sec.)
W= Migration velocity (m/ sec.)
L= Field length (m)
v = Velocity of gas flow (m/sec.)
d = Discharge Distance (m)
(The above equations are known as Deutsch Anderson equation and Deutsch equation respectively on which the theory of existing type of Electrostatic Precipitator is founded ).
But the migration velocity concept has some flaws which are discussed in the following lines. Collection of dust particles on the electrodes inside an electrostatic precipitator take place due to force of attraction between two oppositely charged bodies, one being the charged dust particle and the other being the opposite charge on the surface of the collecting electrode. If, the force of attraction =F, charge on collecting electrode and discharge electrode = Q1 and Q2 respectively, the distance between the charged dust particle and the collecting

Thus, force between any particular charged dust particle and the collecting electrode being F, velocity changes with time due to the acceleration associated with the force. Also, as the distance between the dust particle and the collecting electrode changes (reduces), the force also increases resulting into higher velocity of the dust particle moving towards the collecting electrode. Thus a particular migration velocity cannot exist.
b) In an Electrostatic Precipitator, the separation of the dust particles from a gas stream takes
place gradually, so a large collecting electrode surface area is required. This requires a large
number of discharge electrodes also. To accommodate such a large collecting electrode area,
the casing (the enclosure box or housing of collecting electrodes and discharge electrodes)
becomes very large. To give structural strength to such a big casing, large quantity of steel
material is required. Also, a big supporting structure, large hoppers, inlet funnel, out funnel,
bottom dust conveying system etc. are required. Thus the total cost of the electrostatic
Precipitator becomes very large.
c) Since for the Electrostatic precipitator a large collecting electrode surface area is required,
current requirement is also very high (considering a current rating of 300 micro-ampere per
square metre of collecting electrode surface area).
5

So the power consumption of an Electrostatic Precipitator is very high.
d) The Electrostatic Precipitator occupies a large space. So, it becomes very difficult to accommodate an Electrostatic Precipitator, particularly when retrofitting in an existing plant, where space available is limited.
OBJECT OF THE INVENTION
The object of the invention is given below.
a) To build a new type of Electrostatic Precipitator which will separate dust particles from a gas
stream.
b) This new type of Electrostatic Precipitator will be small sized compared to existing type of
Electrostatic Precipitators.
c) This new type of Electrostatic Precipitator will contain smaller and less number of
components compared to existing type of Electrostatic Precipitator and so will be cheap.
d) The running cost of this Electrostatic Precipitator will be less due to less Electric power
consumption.
INVENTION
This invention -" Electrostatic Precipitator (based on Migration Distance concept) is described in the following chapters starting from the development of Migration Distance concept.
Let us consider an existing type of Electrostatic Precipitator in which the discharge electrodes are charged with high voltage negative DC electricity and the collecting electrodes are earthed or grounded.
The surface of the collecting electrode contains positive charge (induced by the negative charge on the discharge electrodes).
When the dust particles come in contact with (or pass near) the negatively charged discharge electrodes, they get negatively charged and then these negatively charged dust particles get attracted by the positive charge on the surface of the collecting electrodes.
Due to attraction of a charged dust particle and opposite charge on the collecting electrode surface, a force is exerted on the dust particle, which pulls the dust particle towards the collecting electrode. When the distance between the charged dust particle and the collecting electrode is small (within a particular range), the force of attraction is greater than the pull on the dust particle exerted by the flowing gas due to aerodynamic forces. In this condition dust particle is separated from the gas stream and ultimately get collected on the collecting electrode.
Let us consider an existing type of Electrostatic Precipitator with: Collecting Electrode surface area = A (square metre)
6

Gas flow rate = V, (m3/sec.) Treatment time = t1, (sec.)
[ The treatment time is the time taken by the gas flow or a dust particle (if not collected during its travel) to cross the entire electrical field from entry to exit of an Electrostatic Precipitator.]
Let the inlet dust concentration of the gas = C1 gms/m3 .
(This means one cubic metre of gas contains C1 gms of dust particles before the gas stream
enters the Electrostatic Precipitator.)
Let us assume that all the dust particles in a charged Electrostatic Precipitator within a particular range of distance (say from 0 to % metre) from the collecting electrode surface will be separated from the gas stream for ultimately collection on the collecting electrode.
Now collecting electrode surface area for unit quantity of gas flow ( 1 m / sec. gas flow)

This is [ A1 (square metre)] also called specific collection area.
[ Let the cross-sectional area of the chamber of the Electrostatic Precipitator is divided into 'V number of sub-areas with each having equal area. Then gas passing through one such sub-area of the cross-section of the Electrostatic Precipitator will pass over

In t1 sec. unit volume of gas passes over A1 square metre of collecting electrode surface area.
.".In 1 sec. unit volume of gas passes over square metre of collecting electrode surface area.
If we consider a very small interval of time At sec, such that, At > 0

Then, if we consider all the dust particles present in the flowing gas within a range of distance (from 0 to % metre) from the collecting electrode surface are separated from the gas stream and ultimately get collected on the collecting electrode surface, then for unit flow of gas, in the first At sec. all the dust particles in the volume
7

will get separated from the gas stream.
Dust particles separated from gas in first At sec.

which is the dust concentration after first At sec. travel of the gas through the electrical field of the Electrostatic Precipitator.
Similarly, for 1 m3 of gas, dust particles separated from the gas in second At sec.

8
.'.After 2 At sec. from beginning, dust contained in 1 m3 of the gas

9

After t1 sec. from beginning of the flow of the gas in the Electrostatic Precipitator, the particular 1 m3 of gas has passed through the Precipitator for such small
10
interval of time of At sec. duration.

Therefore, dust concentration of the 1 m3 of gas after t1 sec. or the outlet dust concentration of the gas at the outlet of the precipitator
11

which is Deutsch Anderson equation.
Since Deutsch Anderson equation is true, and by assuming that all the dust particles within distance % metres from collecting electrode surface in a charged Electrostatic Precipitator are separated from the gas stream for ultimately collection on the collecting electrode, we arrive at the Deutsch Anderson equation, our assumption that the dust particles within a distance of % metres from the surface of collecting electrodes of a charged Electrostatic Precipitator will get separated from the gas stream and ultimately get collected on the collecting electrode is true. Here % has numerically the same value as that of migration velocity in Deutsch equation or Deutsch Anderson equation. This shows that consideration of migration distance is sufficient to arrive at the result experimentally found true by operation of existing Electrostatic Precipitators designed according to Deutsch equation or Deutsch Anderson equation.
Above forms the basis of the Migration Distance concept of Electrostatic Precipitators. This can be said in the following way.
The dust particles present in a dust laden gas stream in a charged Electrostatic Precipitator within a given distance from the collecting electrode surface (where this distance will be called Migration Distance and which has the same numerical value as that of the Migration Velocity in Deutsch equation or Deutsch Anderson equation) will be separated from the gas stream and ultimately get collected on the collecting electrodes. This concept will be called Migration distance concept.
Based on this migration distance concept, a new type of Electrostatic Precipitator can be constructed in which the dust laden gas can be passed in such a way that while it flows in the chamber of the Electrostatic Precipitator (of the new type) it passes through the discharge electrode screen (where the discharge electrode screen is charged by connecting it to a high voltage DC negative power source), whereby the dust particles get charged and then the dust laden gas is passed through the collecting electrode screen in such a way that the total flow (i.e., the whole gas volume ) has to cross the collecting electrode screen and passes very near to the collecting electrodes ( where the collecting electrode screen is earthed or grounded ), so that the whole gas volume and all the dust particles present in the gas stream passes near the collecting electrode surface within the migration distance ( from collecting electrode surface ), and as a result all the dust particles get separated from the gas stream and ultimately get collected on the collecting electrodes.
12

SUMMARY OF THE INVENTION
An Electrostatic Precipitator (subject of this invention, which is described below), based on migration distance concept, will require 10 to 15 times smaller collecting electrode surface area compared to Electrostatic Precipitators of prior art, for which quantity of collecting electrode surface area required is determined with the help of Deutsch equation or Deutsch Anderson equation.
An Electrostatic Precipitator comprising:
one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen;
one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen);
one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entratnment) and the collecting electrode parts (being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts).
When dust laden gas enters the precipitator, it enters from the inlet duct (12). Gas flows from inlet duct to inlet funnel (9) and from inlet funnel to casing (15), through inlet gas distribution screen (8).
12a

The casing houses the electrical field consisting of the collecting electrode screen and discharge electrode screens.
When the gas enters the casing from inlet gas distribution screen, the gas passes through electrical field comprising of negatively charged discharge electrode screen (at inlet side) comprising discharge electrode frame (5) and discharge electrodes (4), earthed or grounded collecting electrode screen comprising collecting electrode part (1), tray (2) and collector (3) and negatively charged discharge electrode screen (at outlet side) comprising discharge electrode frame (5) and discharge electrodes (4).
Since trays divide the height of collecting electrode part into many parts, the falling dust particles do not achieve a high velocity, which help to avoid re-entrainment of dust particles in the gas stream.
Also due to particular arrangement of collecting electrodes the gas flow become such that around collecting electrode surface there will be no gas flow and this will help to prevent re-entrainment of dust particles in the gas stream. See Fig. 18.
The whole body of the Electrostatic Precipitator is earthed as a result the collecting electrodes, which are directly supported on the precipitator casing, are also earthed.
Discharge electrode frames with the discharge electrodes are suspended through insulators (6) so that the charge on the discharge electrodes does not go to the earth. See Fig. 19.
Collecting electrodes are suspended from roof and are spring (7) supported. These electrodes are rapped by electromagnetic rappers, mounted on the roof for dislodging dust particles collected on the collecting electrodes. Since these electrodes are mounted on springs, the shock of rapping is not transmitted to the body of the precipitator.
The discharge electrode frames with the discharge electrodes, which are suspended from roof through insulators, are also mounted on springs. Discharge electrodes are also rapped by electromagnetic rappers, mounted on roof for dislodging dust collected on the discharge electrodes. These rappers are insulated from the discharge electrode frames and discharges by putting insulators.
When the dust particles are separated from the dust-laden gas in the electrical field, the clean gas enters the outlet funnel (11) through outlet gas distribution screen (10) and from outlet funnel to outlet duct (13).
The inlet gas distribution screen (8) and outlet gas distribution screen (10) are provided for evenly distribution of the gas in the precipitator chamber.
Hopper (14) is provided for collecting the dust dislodged from collecting electrodes and discharge electrodes.
12b

BRIEF DESCRIPTION OF FIGURES
A brief description of the figures is given in the following lines.
Figure-1 to figure-9 shows existing type of Electrostatic Precipitators (used prior to this invention).
Figure-1
This figure shows an existing type of Electrostatic Precipitator (used prior to this invention).
Figure-2
This figure shows collecting electrodes in the form of curtains, gas passage and gas flow direction.
Figure-3
This figure shows collecting electrode curtains, gas passages formed by collecting electrode curtains and discharge electrodes placed at the central axis of the gas passage.
Figure-4 This figure shows discharge electrode.
Figure-5
This figure shows collecting electrodes, discharge electrodes in a gas passage and high voltage DC negative electric power supplied to a discharge electrode. Collecting electrodes are earthed (or grounded).
Figure-6
This figure shows collecting electrodes (earthed or grounded), discharge electrode connected to high voltage DC negative power source. Positive end of the high voltage DC power source is grounded.
Figure-7
This figure shows collecting electrodes forming a gas passage and discharge electrodes
placed in the central axis of the gas passage, gas flow direction by an arrow mark.
Figure-8
This figure shows a gas passage formed by two collecting electrode curtains and a discharge
electrode in the central axis of the gas passage.
Figure-8a
This figure shows collecting electrode curtains forming a gas passage. Collecting electrodes
are earthed.
Figure-9
This figure shows a gas passage formed by two collecting electrodes and discharge electrodes
placed in the central axis of the gas passage.
13

Figure-10 to figure-19 shows new type of Electrostatic Precipitator based on migration distance concept.
Figure-10
This figure shows two discharge electrode screens and one collecting electrode screen.
Figure-11
This figure shows a collecting electrode screen (in plan view)
Figure-12 This figure shows one collecting electrode and two collectors (front elevation).
Figure-13
This figure shows collecting electrode part.
Figure-14
This figure shows a sectional view of tray.
Figure-15
This figure shows a collector with anti-sneakage guards.
Figure-16
This figure shows discharge electrodes mounted on discharge electrode frame.
Figure-17
This figure shows a discharge electrode.
Figure-18
This figure shows a collecting electrode.
Figure-19
This figure shows a new type of Electrostatic Precipitator based on migration distance
concept.
DETAIL DESCRIPTION OF FIGURES, CONSTRUCTION AND OPERATION
Detailed description of figures and construction and operation is given in the following lines.
Figure-1 to figure-9 shows existing type of Electrostatic Precipitator (used prior to this invention).
Figure-1
This figure shows an existing type of Electrostatic Precipitator (used prior to this invention).
(16) - Inlet duct
(17) -Inlet funnel
(18) - Inlet gas distribution screen
14

(19) - Electrical field consisting of collecting electrodes and discharge electrodes
(20) - Casing which houses collecting electrodes and discharge electrodes
(21) - Outlet gas distribution screen
(22) - Outlet funnel
(23) - Outlet duct
(26) - Hopper
In this Precipitator, dust laden gas enters through the inlet duct (16) to inlet funnel (17). Inlet funnel is a transition piece from inlet duct to casing. Inlet duct is having less cross-sectional area where gas flows at a velocity of around 15 to 20 m/sec. Casing is having bigger cross-sectional area where gas flows at a velocity of around 0 o 5 to 1 m/sec. So, the inlet funnel is having a cross-sectional area, which is in increasing order from inlet side to outlet side i.e., along the direction of gas flow.
From inlet funnel (17) the dust laden gas goes to casing (20) through inlet gas distribution screen (18). The inlet gas distribution screen is a perforated sheet i.e., having a large number of holes all over its length and breadth. The inlet gas distribution screen distributes the gas uniformly through out the cross-section of the casing of the precipitator. The casing is like a hollow box. It houses the collecting electrodes and discharge electrodes. When the dust laden gas enters the casing (20) the gas comes to the electrical field (19), consisting of collecting electrodes and discharge electrodes. Here the dust particles are separated from the dust laden gas. The dust particles get separated from the gas stream (when the dust particles are within migration distance area) and get collected on the collecting electrodes. Collecting electrodes are rapped so that the dust particles collected on the surface of the collecting electrodes get dislodged and fall on the hopper (26). Discharge electrodes are also rapped to keep the discharge electrodes clean which help in better charging of the dust particles of the gas stream.
The clean gas leaves electrical field (19) and casing (20) and goes to outlet funnel (22)
through outlet gas distribution screen (21). From outlet funnel (22) the gas goes to outlet duct
(23).
The outlet gas distribution screen is normally perforated sheet or plain sheets having gap in
between them, which help in distributing the gas through out the cross-section of the casing
of the precipitator.
The outlet funnel is a transition piece from casing to outlet duct .The outlet duct is having less cross-sectional area (compared to casing), where gas flows at a velocity of around 15 to 20 m/sec. So, the outlet funnel is having a cross-sectional area, which is in decreasing order from inlet side to outlet side i.e., along the direction of the gas flow.
Figure-2
This figure shows collecting electrodes in the form of curtains, gas passage formed by two
adjacent collecting electrode curtains and gas flow direction.
(24) - Collecting electrode
(G.P.) - Gas passage
-> - The arrow shows the direction of gas flow.
15

Figure-3
This figure shows collecting electrode curtains, gas passage formed by collecting electrode
curtains and discharge electrodes placed at the central axis of the gas passage.
(24) - Collecting electrode
(25) - Discharge electrode
-> - The arrow shows gas flow direction
Figure-4
This figure shows a discharge electrode. (25) - Discharge electrode
Figure-5
This figure shows collecting electrodes, discharge electrodes in a gas passage, high voltage
rectified DC negative electric power supplied to a discharge electrode. Collecting electrodes
are earthed or grounded.
(24) - Collecting electrode
(25) - Discharge electrode
(+) - Shows positive charge on the collecting electrode surface
(-) - Shows negative charge on discharge electrode
Figure-6
This figure shows collecting electrode (earthed or grounded), discharge electrode connected to high voltage DC negative power source. Positive end of the high voltage DC power source is earthed or grounded.
(24) - Collecting electrode
(25) - Discharge electrode
A black dot with an encircled (-) sign shows an arbitrarily chosen dust particle with a negative charge and the arrow with the black dot signifies that the negatively charged dust particle is moving towards the positive charge on the surface of the collecting electrode. The encircled (+) sign near collecting electrode shows the positive charge on the surface of the collecting electrode. The encircled (-) sign near the discharge electrode shows negative charge on the discharge electrode.
Figure-7
This figure shows collecting electrodes forming a gas passage and discharge electrodes
placed in the central axis of the gas passage, gas flow direction by the arrow mark.
(24) - Collecting electrode
(25) - Discharge electrode
d -Discharge distance.
(This is the distance between the centre of a row of collecting electrode and the centre of an adjacent row of discharge electrode). W - migration velocity -> - The arrow shows gas flow direction
16

Figure-8
This figure shows a gas passage formed by two collecting electrode curtains and a discharge
electrode placed in the central axis of the gas passage. Collecting electrodes are earthed.
(24) - Collecting electrode
(25) - Discharge electrode
(+) - Positive charge on collecting electrode surface (-) -Negative charge on discharge electrode
Figure-8a
This figure shows collecting electrode curtains forming a gas passage. Collecting electrodes
are earthed.
(24) - Collecting electrode
Figure-9
This figure shows a gas passage formed by two collecting electrodes and discharge electrodes placed in the central axis of the gas passage, the migration distance area is showmtiy the shaded area.
(24) - Collecting electrode (earthed)
(25) - Discharge electrode
(+) - Positive charge on the collecting electrode surface
(-) -Negative charge on the discharge electrode
(G.P.) - Gas passage
(D.P.) - An arbitrarily chosen dust particle (black dot is dust particle, associated with (-), a
negative charge)
-> -The arrow shows gas flow direction
Shaded area - Shows migration distance area as described in the "invention" of the new
type of Electrostatic Precipitator
Figure-10 to figure-19 shows new type of Electrostatic Precipitator based on migration distance concept.
Figure-10
This figure shows two discharge electrode screens and one collecting electrode screen of new
type of Electrostatic Precipitator based on migration distance concept
A discharge electrode screen (at the inlet side) consisting of
(4) - Discharge electrodes mounted on discharge electrode frame
(5) - Discharge electrode frame
(-) -Negative charge on discharge electrode
17

A collecting electrode screen consisting of
(1) - Collecting electrode part (trays, collectors and anti-sneakage guards are not shown for clarity of figure)
(+) - Positive charge on the collecting electrode surface Shaded area - Shaded area shows migration distance area
(D.P.) - An arbitrarily chosen dust particle carrying a negative charge (the dust particle shown by black dot with a minus sign showing negative charge on this dust particle) ( % ) - The migration distance
A discharge electrode screen (at the outlet side) consisting of
(4) - Discharge electrode mounted on discharge electrode frame
(5) - Discharge electrode frame
(-)-Negative charge on discharge electrode
-> - The arrow shows the direction of gas flow.
The space between two discharge electrodes (mounted on discharge electrode frame) is clear passage for passing gas un-obstructed (which can be understood from the other view of the discharge electrodes mounted on discharge electrode frame as shown in figure-16).
When the dust laden gas passes through the discharge electrode screen (at the inlet side), all the dust particles present in the gas stream either touches or passes very near to the discharge electrode thereby getting negatively charged. When these negatively charged dust particles pass through the collecting electrode screen, they pass through the migration distance area and they are separated from the gas stream and get collected on the collecting electrodes. The discharge electrode screen (on the outlet side) is provided to get a migration distance area on the outlet side of the collecting electrode screen.
Figure-11
This figure shows a collecting electrode screen (in plan view).
(1) & (2) - Colleting electrode part (1) and tray (2)
(3), (3A) & (3B) - Collector (3), anti-sneakage guards (3A) & (3B)
Here collecting electrode part (1) and tray (2) are collectively called collecting electrode.
Figure-12
This figure shows one collecting electrode consisting of collecting electrode part (1) tray (2)
and two collectors.
(1) - Collecting electrode part
(2) -Tray
(3) -Collector
Figure-13
This figure shows collecting electrode part (1).
Figure-14
This figure shows a sectional view of tray (2).
18

Figure-15
This figure shows a collector (3) with anti-sneakage guards (3A) & (3B).
The anti-sneakage guards do not allow the dust laden gas to cross the collecting electrode
screen bypassing migration distance area.
Figure-16
This figure shows discharge electrodes mounted on a discharge electrode frame.
(4)-Discharge electrode
(5) - Discharge electrode frame
The space between two discharge electrodes is a clear passage for flow of gas.
Figure-17
This figure shows a discharge electrode (4).
Figure-18
This figure shows a collecting electrode screen (for clarity of figure the trays and collectors
are not shown).
(1) - Collecting electrode part
(N.G.) - This shows the area near the collecting electrode surface, where there is no gas
flow or very little gas flow.
Shaded area - here the shaded area shows a layer of dust particles collected on collecting
electrode surface.
-> - The arrow shows the gas flow direction
Figure-19
This figure shows the new type of Electrostatic Precipitator based on migration distance
concept.
(12) - Inlet duct
(9) - inlet tunnel
(8) - Inlet gas distribution screen
(15) - Casing which houses the discharge electrode screens and collecting electrode screen
The discharge electrode screen (inlet side) consisting of
(4) - Discharge electrodes mounted on discharge electrode frame
(5) - Discharge electrode frame
The collecting electrode screen consisting of
(1) -Collecting electrode part (part of collecting electrode)
(2) -Tray (part of collecting electrode)
(3) - Collector
The discharge electrode screen (outlet side), consisting of (4)-Discharge electrodes mounted on discharge electrode frame
19

(5)-Discharge electrode frame
(10) - Outlet gas distribution screen
(11) - Outlet funnel
(13) - Outlet duct
(6) -Insulator
(7) -Spring
(14) - Hopper
The dust laden gas enters through the inlet duct (12). From the inlet duct the dust laden gas goes to the inlet funnel (9) through the inlet gas distribution screen (8). The inlet funnel is a transition piece from inlet duct to casing. The inlet duct is having less cross-sectional area where gas flows at a velocity of around 15 to 20 m/sec. The casing is having bigger cross-sectional area where gas flows at a velocity of around 0 o 5 to 1 m/sec. So, the inlet funnel has cross-sectional area in increasing order from inlet side to outlet side (along the direction of gas flow). The inlet gas distribution screen is made of perforated sheet (i.e., having holes through out its length and breadth). The dust laden gas goes from inlet funnel to casing through the inlet gas distribution screen (8). The inlet gas distribution screen helps in evenly, distributing the gas through out the cross-section of the casing of the precipitator. When the dust laden gas enters the casing, the gas comes to electrical field consisting of discharge electrode screens and collecting electrode screen. The discharge electrode screen consists of discharge electrodes (4) and discharge electrode frame (5). The collecting electrode screen consist of collecting electrode part (1), tray (2), collectors (3) and anti-sneakage guards (3A) & (3B).
When the dust laden gas enters the electrical field, it first crosses (the inlet side) discharge electrode screen. When the dust laden gas crosses the discharge electrode screen, the dust particles either touch or pass very near to the discharge electrodes thereby get negatively charged. These negatively charged dust particles, when reach the migration distance area, are separated from the gas stream and get collected on the collecting electrodes. The collecting electrode screen is made in such a manner that all the gas (while crossing the collecting electrode screen) has to pass through the migration distance area. Thus while the dust laden gas passes through the collecting electrode screen, all the dust particles get separated from the gas stream and ultimately get collected on the collecting electrodes. The dust particles get deposited on the collecting electrode part (1). When the collecting electrode screen is rapped, the dust particles get dislodged from the collecting electrode part and fall on the trays. The trays are inclined surfaces. The dust particles, which fall on the trays, slide down and enter the collectors. From the collectors the dust particles fall to the hopper (14). The discharge electrodes are rapped to keep it clean for better charging of the dust particles.
In a collecting electrode screen, the collecting electrode parts (1) are arranged in two rows. In the front row i.e., which row of collecting electrode parts (1) the gas stream crosses first (or in the inlet side according to gas flow direction), the collecting electrode parts are arranged in such a manner that a gap of size equal to a collecting electrode part is kept in between any two adjacent collecting electrode parts of this row. Thus we see that, in the front row of collecting electrode parts of the collecting electrode screen, there is one collecting electrode part and then one gap of size equal to the size of a collecting electrode part. Thus the gaps and the collecting electrode parts are alternately arranged. In the collecting "electrode screen, behind the front row of collecting electrode parts, the back row of collecting electrode parts
20

are arranged in such a manner that exactly behind a gap of front row, one collecting electrode part is kept in the back row. In the back row also, the collecting electrode parts and gaps are alternately arranged. This is shown in figure-18. In this figure, trays are not shown for clarity of figure. The plane of collecting electrode parts, in both the rows of collecting electrode parts of the collecting electrode screen, are perpendicular to the direction of gas flow in the precipitator before the gas flow reaches the collecting electrode screen.
When the gas stream flows through the collecting electrode screen, the gas passes through the opening or gap (between the collecting electrode parts), of the front row of collecting electrode parts and then exits through the opening or gap (between the collecting electrode parts) of the back row of collecting electrode parts. This is shown in figure-18.
Here (1) shows collecting electrode part, the arrow shows the direction of gas flow, the shaded area shows layer of dust particles collected on collecting electrode part. The area marked (N.G.) shows the zone where there is no gas flow or very little gas flow. Due to this no gas flow zone near the surface of the collecting electrode part, the re-entrainment of dust particles is minimized.
Collecting electrodes are suspended from roof and are spring ( 7) supported. These electrodes are rapped by electromagnetic rappers, mounted on the roof for dislodging dust collected on the collecting electrodes. Since the electrodes are mounted on springs, the shock of rapping is not transmitted to the body of the precipitator.
The discharge electrode frames with the discharge electrodes are suspended from the roof of the casing with the help of insulators and springs, which is shown in figure-19. Since the discharge electrode frames are suspended from the roof of the casing through the insulators, the charge contained by the discharge electrodes does not go to the casing, which is earthed or grounded. Since the springs are provided for supporting the discharge electrode frame, so when the discharge electrode frames are rapped for dislodging the dust particles collected on the discharge electrodes, the shock of rapping is not transmitted to the casing. Discharge electrodes are also rapped by electromagnetic rappers, mounted on the roof for dislodging dust collected on the discharge electrodes.
When the gas stream crosses the electrical field consisting of discharge electrode screen and collecting electrode screen, the dust particles are separated from the gas stream. The separated dust particles fall on the hopper (14). The clean gas leaving the casing (and the electrical field) goes to the outlet funnel (11) through the outlet gas distribution screen (10). The outlet funnel is a transition piece from casing to outlet duct (13). Outlet duct is having less cross-sectional area where gas flows at a velocity of around 15 to 20 m/sec. The outlet funnel is having its cross-sectional area in decreasing order from inlet side to outlet side in the direction of gas flow. Thus the dust laden gas is cleaned from the dust and the clean gas leaves the precipitator through the outlet duct and the separated dust particles are collected on the hopper.
21

WORKING / OPERATION
The working of new type of Electrostatic Precipitator based on migration distance concept is described in the following lines.
Let us consider figure-19. At first the dust laden gas enters the inlet duct (12). From inlet duct the gas enters the inlet funnel (9). In the inlet funnel there is inlet gas distribution screen (8). The dust laden gas coming out from the inlet funnel enters the casing (15) through the inlet gas distribution screen (8), which uniformly distributes the gas through out the cross-section of the precipitator when the gas reaches the casing. In the casing the gas passes through the electrical field consisting of discharge electrode screen and collecting electrode screen. The discharge electrode screen consists of discharge electrode frame (5) and discharge electrodes (4). The discharge electrodes are charged with high voltage DC negative electricity. This high voltage DC negative electricity charges all the dust particles of the gas stream, which crosses the discharge electrode screen. Due to this high voltage DC negative electrical charge on the discharge electrodes (4), positive charge is induced on the collecting electrode surface, which is earthed. This positive charge on the surface of the collecting electrodes pulls the negatively charged dust particles. When the distance between the positive charge on the collecting electrode surface and the negatively charged dust particle is within a given range (which is migration distance), the pull between the positive charge on the surface of the collecting electrode and negatively charged dust particle become more than the aerodynamic force exerted on the dust particle by the flowing gas stream. Due to this the flowing gas stream can no longer carry that dust particle with the flow and the dust particle move towards the collecting electrode surface and gets separated from the flowing gas stream. The movement of the dust particle towards the collecting electrode surface continues and ultimately the dust particle gets collected on the collecting electrode part (1).
The collecting electrodes are rapped intermittently to dislodge dust particles deposited on the collecting electrode surface.
When the collecting electrode is rapped, the dust particles dislodge from the collecting electrode part (1) and fall on the trays (2). The dust particles, which fall on the tray, slide down the tray and goes to the collector (3). From the collector the dust particles fall down to the hopper (14). Discharge electrodes are also rapped intermittently to keep them clean for better charging of the dust particles.
When the gas stream flows through the collecting electrode screen, the gas passes through the opening or gap (between the collecting electrode parts), of the front row of collecting electrode parts and then exits through the opening or gap (between the collecting electrode parts) of the back row of collecting electrode parts. This is shown in figure-18.
Advantages:
This new type of Electrostatic Precipitator (based on migration distance concept) will have the following advantages over the existing type of electrostatic precipitators.
In this precipitator, where the gas stream crosses two discharge electrode screens and one collecting electrode screen, all the gas and the dust particles pass through migration distance
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area and all the dust particles are separated from the gas stream and collected on the collecting electrodes.
Thus the requirement of collecting electrode surface area and number of discharge electrodes is less and one electrical field consisting of two discharge electrode screens and one collecting electrode screen is sufficient for separating all the dust particles contained in the gas stream. This has been shown in figure-10.
So, the size of this precipitator is small.
Whereas in case of an existing type of Electrostatic Precipitator, the gas stream has to travel a long distance along the gas passages of the precipitator and since the outer portions of the gas stream in the gas passage passes through the migration distance area, so dust particles are separated from the outer portion of the gas stream passing through each gas passage. So, a large collecting electrode surface area and consequently a large number of discharge electrodes are required. A big casing is required to house these large number of electrodes and big and a number of hoppers are required below this big casing. This that the dust particles from the outer portion of the gas stream is separated in the precipitator) has been shown in figure-9.
Also since the rated current supplied to the Electrostatic Precipitator is proportional to the collecting electrode surface area of the precipitator, due to having much less collecting electrode surface area, the new type of Electrostatic Precipitator will have much less current consumption compared to the existing type of precipitators. So, this new type of Electrostatic Precipitator will be cheap both in cost of equipment and running cost due to consumption of less power.
THE CONSTRUCTIONAL IMPROVEMENT OVER EXISTING PRECIPITATORS
In the existing type of Electrostatic Precipitators (prior to this invention), the precipitators were designed or sized (and constructed) on the basis of Deutsch Anderson equation or Deutsch equation.
So, for a given gas flow rate (V, expressed in m3/sec), inlet dust concentration (expressed in gm/m3), outlet dust concentration (expressed in gm/m3) and migration velocity (expressed in m/sec.) a given quantity of collecting electrode surface area would have to be provided, which has to be calculated with the help of Deutsch equation or Deutsch Anderson equation. This required a very large collecting electrode surface area and consequently a large number of discharge electrodes. To house this large collecting electrode surface area and large number of discharge electrodes, a large casing also would have to be provided. To collect the dust in the hopper below the casing (below the collecting electrodes and the discharge electrodes) a number of large hoppers were required to be provided. Thus the cost of the precipitator would become very high. Also in designing these precipitators, current rating of high voltage DC (negative) power to the discharge electrodes used to be kept proportional to the collecting electrode surface area (approximately 300 A per square metre of collecting electrode surface area). This caused very high electric power consumption for the precipitator.
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Thus the Electrostatic Precipitator was large in size, having many components (like big casing, large hoppers, large collecting electrode surface area, large number of discharge electrodes etc.) with large weight, requiring costly civil foundation and high running cost due to high current rating of the power source (for large collecting electrode surface).
This is apparently so, because the precipitator had to be provided with a big collecting electrode surface area which was arrived at by calculating with the help of Deutsch equation or Deutsch Anderson equation. The precipitator had to be provided with a large number of fields, each field having a large number of gas passages, collecting electrodes with big height and big length, with the gas flow parallel to the collecting electrode surface in each gas passage.
But the actual reason for all these were wrong consideration that the dust particles move with a given velocity component (called migration velocity) towards the collecting electrode surface and the collecting electrode surface area had to be determined by calculating as per Deutsch Anderson equation or Deutsch equation.
Actually, when the dust laden gas passes through a region (within a given distance from collecting electrode surface area, which we call here migration distance and which has numerically the same value as that of the migration velocity), the dust particles in the gas stream get separated from the gas and ultimately get collected on the collecting electrode surface.
In the existing type of precipitators, while the gas flows through a gas passage (with the discharge electrodes placed in the central axis of the gas passage), the gas stream flows parallel to the collecting electrode surface (as shown in figure-9), the dust particles get separated from the gas stream in the migration distance area (in the figure the shaded area). Thus the dust particles get separated within a given depth of the gas stream in the gas passage (within a distance from the collecting electrode surface which is equal to migration distance and is numerically equal to the value of migration velocity). So, for an existing type of Electrostatic Precipitator, it takes a much longer time to get a major portion of the dust contained in the gas to be separated.
In the new type of Electrostatic Precipitator (the this invention), the collecting electrode is designed in such a manner that the dust laden gas has to cross a single collecting electrode screen and while crossing the collecting electrode screen, the total gas has to pass through the region which is within migration distance from the collecting electrode surface. Thus one screen of collecting electrode is sufficient to separate all the dust particles present in the dust laden gas. So the precipitator has less collecting electrode surface area and consequently has fewer number of discharge electrodes, a single hopper, a small casing and ultimately the size of the precipitator is small. Due to having smaller collecting electrode surface area, power consumption of this precipitator is also less.
In case of existing type of Electrostatic Precipitators (prior to this invention), when the collecting electrodes are rapped, the dust particles deposited on the collecting electrodes fall from the whole height of the collecting electrode, the velocity of the falling dislodged dust particles being high causes re-entrainment of dust particles in the gas stream.
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Whereas in case of new type of Electrostatic Precipitator, the whole height of the collecting electrode is divided into many parts by trays, which allow the dislodged dust (during rapping) to fall a small vertical height only. Thus re-entrainment of dust particles in the gas stream is less.
In case of existing type of Electrostatic Precipitator, gas flows throughout the cross-section of the gas passage, thus near the collecting electrode surface also. So, during rapping, some re-entrainment of the dust particles would take place.
Whereas in case of new type of Electrostatic Precipitator, there is no gas flow region in front of the collecting electrode part surfaces, where there is no gas flow or very little gas flow. So, re-entrainment of dust particles, when rapping takes place, is less in this type of precipitator.
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I CLAIM :
1. An Electrostatic Precipitator comprising:
one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of
the dust-laden gas when the gas stream crosses the discharge electrode screen;
one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen);
one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entrainment) and the collecting electrode parts ( being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts).
2. An Electrostatic Precipitator as claimed in claim 1, where migration distance
areas are created in front of the collecting electrode surfaces on both the front side and the
back side of the collecting electrode screen, and when dust laden gas passes through the
collecting electrode screen, as shown in the accompanying drawings, the dust laden gas
has to pass through the migration distance area where all the dust particles are separated
from the gas stream and ultimately collected on the collecting electrode. Thus the dust
particles are separated from the dust laden gas and we get clean gas.
3. An Electrostatic Precipitator as claimed in claim 1, as shown in the accompanying
drawings, where the trays divide the height of the collecting electrode parts into many
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parts thus the falling dust particles (dislodged from collecting electrode parts) do not achieve a high velocity minimizing re-entrainment of dust particles in the gas stream;
where the arrangement of collecting electrode parts in the collecting electrode screen in the front row and back row guides the gas flow in such a manner that the gas flow does not touch the dust layer adhering to the collecting electrode part surfaces, minimizing re-entrainment of dust particles in the gas stream;
where the dust particles dislodged from collecting electrode part surfaces (coming from the trays) fall through collectors (vertical pipes) without coming in contact with gas flow minimizing re-entrainment of dust particles in the gas stream.
4.An Electrostatic Precipitator substantially as hereinbefore described and illustrated with reference to the accompanying drawings.
An Electrostatic Precipitator comprising:
one negatively charged discharge electrode screen, comprising a discharge electrode frame and discharge electrodes (mounted on discharge electrode frame) at the inlet side (i.e., at the up stream side of the collecting electrode screen), which charges the dust particles of the dust-laden gas when the gas stream crosses the discharge electrode screen;
one negatively charged discharge electrode screen similar to one described above at the outlet side (i.e., at the down stream side of the collecting electrode screen);
one earthed or grounded collecting electrode screen comprising the trays (being inclined surfaces on which dust particles, dislodged from collecting electrode part due to rapping, fall and slide down along the trays and enter the collectors through the openings on the collectors where the trays are connected to the collectors), the collectors (being vertical pipes through which dust particles, coming from trays, fall without coming in contact with the gas flow and thus minimizing re-entrainment) and the collecting electrode parts ( being thin rectangular plates with stiffeners at the middle which provide strength and rigidity to the collecting electrode parts and create high charge density areas due to their curvature, and these collecting electrode parts are arranged in two rows- front row and back row with each row of collecting electrode parts arranged in such a manner that there is a gap of size equal to that of a collecting electrode part between any two adjacent collecting electrode parts of that row and just behind a collecting electrode part of front row there is a gap in the back row and just behind a gap in the front row there is a collecting electrode part in the back row and when the dust laden gas crosses collecting electrode screen, this arrangement guides the gas to pass in front of the surface of collecting electrode parts in such a manner that the dust laden gas passes in front of surfaces of collecting electrode part within a distance from collecting electrode part surfaces which is less than migration distance resulting into all the charged dust particles getting separated from the entire, volume of the gas passing through migration distance area, where the migration distance area being the space in front of collecting electrode part surfaces up to a distance of migration distance from collecting electrode part surfaces and under the influence of charged discharge electrodes in front of the surfaces of collecting electrode parts).

Documents:

00032-cal-1999-abstract.pdf

00032-cal-1999-claims.pdf

00032-cal-1999-correspondence.pdf

00032-cal-1999-description(complete).pdf

00032-cal-1999-drawings.pdf

00032-cal-1999-form-1.pdf

00032-cal-1999-form-2.pdf

00032-cal-1999-letters patent.pdf

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Patent Number

206904

Indian Patent Application Number

32/CAL/1999

PG Journal Number

20/2007

Publication Date

18-May-2007

Grant Date

16-May-2007

Date of Filing

18-Jan-1999

Name of Patentee

DHURJATI PRASAD GHOSH

Applicant Address

OF DEWANBATI ,GARDARAJA P.O-BISHNUPUR DT-BANKURA

Inventors:

#	Inventor's Name	Inventor's Address
1	DHURJATI PRASAD DAS	OF DEWANBATI ,GARDARAJA P.O-BISHNUPUR DT-BANKURA

PCT International Classification Number

B03C- 3/36,3/76

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA