Patent Publication Number: US-6902604-B2

Title: Electrostatic precipitator with internal power supply

Description:
BACKGROUND AND SUMMARY 
   The invention relates to electrostatic precipitators, including for diesel engine electrostatic crankcase ventilation systems for blowby gas for removing suspended particulate matter including oil droplets from the blowby gas. 
   Electrostatic precipitators, including for diesel engine electrostatic crankcase ventilation systems, are known in the prior art. In its simplest form, a high voltage corona discharge electrode is placed in the center of a grounded tube or canister providing an annular ground plane around the electrode. A high DC voltage, such as several thousand volts, e.g. 15 kV, on the center discharge electrode causes a corona discharge to develop between the discharge electrode and the interior surface of the tube providing a collector electrode. As the gas containing suspended particles flows between the discharge electrode and the collector electrode provided by the wall of the tube, the particles are electrically charged by the corona ions. The charged particles are then precipitated electrostatically by the electric field onto the interior surface of the collecting tube. 
   Electrostatic precipitators have been used in diesel engine crankcase ventilation systems for removing suspended particulate matter including oil droplets from the blowby gas, for example so that the blowby gas can be returned to the fresh air intake side of the diesel engine for further combustion, thus providing a blowby gas recirculation system. 
   In known electrostatic precipitators, the high voltage power supply is placed outside the collector section, either remotely mounted or mounted directly to the collector in some manner. In either of these configurations, a high voltage electrode rod or lead must pass-through an insulator section to deliver the high voltage to the corona producing discharge electrode assembly. The insulator may also be heated to prevent moisture and contaminant accumulation on the insulating surface, thereby reducing the insulating properties of such section. 
   The present invention eliminates the need for the noted high voltage pass-through of a high voltage lead through the noted insulator. In the present invention, the high voltage power supply is disposed internally of such insulator, and in the preferred embodiment is in the hollow interior of the corona discharge electrode assembly. This eliminates the need for any external high voltage cables or connections and eliminates the need for the high voltage pass-through of a high voltage lead through the insulator. 
   The present invention relates to improvements arising during continuing development efforts related to the subject matter of U.S. Pat. No. 6,221,136, incorporated herein by reference. The drawings and specification of the &#39;136 patent are set forth below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     U.S. Pat. No. 6,221,136 
       FIG. 1  is a schematic cross sectional view of a compact electrostatic precipitator made according to the invention of the &#39;136 patent. 
       FIG. 2  is a sectional view taken on horizontal line  2 — 2  in FIG.  1 . 
       FIG. 3A  is a schematic sectional view of a modified form of the electrode support and high voltage shield used with the precipitator of FIG.  1 . 
       FIG. 3B  is a further modified form of a electrode support and high voltage shield used with the precipitator of FIG.  1 . 
       FIG. 4  is a transverse sectional view of a precipitator made according to the &#39;136 invention but having a rectangular configuration. 
       FIG. 5  is a schematic representation of an ultrasonic generator used for introducing aerosols into the electrostatic precipitator in the invention of the &#39;136 patent. 
       FIG. 6  is a cross sectional view of a modified compact precipitator using a different style of electrode assembly from that shown in FIG.  1 . 
       FIG. 7  is sectional view taken on line  7 — 7  in FIG.  6 . 
       FIG. 8  is a sectional view of a still further modified form of a electrostatic precipitator of the compact electrostatic precipitator of the invention of the &#39;136 patent. 
       FIG. 9  is a sectional view taken on the line  9 — 9  in FIG.  8 . 
       FIG. 10  is a schematic block diagram of a blowby gas recirculation system used in a diesel engine. 
       FIG. 10A  is a modified recirculation system similar to that shown in FIG.  10 . 
       FIG. 11  is a further modified block diagram of a blowby gas recirculation system used in a diesel engine. 
       FIG. 12  is a block diagram similar to  FIG. 11  with a controlled flow restrictor on the outlet of the intercooler. 
       FIG. 13  is a cross sectional view of a modified support for the electrode wire. 
       FIG. 14  is a vertical sectional view of a further modified compact electrostatic precipitator. 
       FIG. 15  is a sectional view taken on line  15 — 15  in FIG.  14 . 
       FIG. 16  is a cross sectional view of a modified support for the electrode wire as it would be taken along the line  15 — 15  of FIG.  14 . 
       FIG. 17  is a cross sectional view of a modified support for the electrode wire as would be taken along the line  17 — 17  of FIG.  14 . 
       FIG. 18  is a flat layout of a cylindrical electrode support unrolled to a flat surface to reveal a modified pattern for the electrode wire supported on the electrode surface. 
     Present Invention 
       FIG. 19  is a sectional view showing an electrostatic precipitator in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   U.S. Pat. No. 6,221,136 
     FIG. 1  is a schematic cross-sectional view of an electrostatic precipitator  10  made according to the invention of the &#39;136 patent. A housing  12  has a discharging electrode assembly  14  to produce the corona discharge. The high voltage DC power supply  16  applies a high voltage (several thousand volts), to the electrode assembly  14  on a wire surrounded by an insulator bushing  18 . The bushing  18  is surrounded by a high voltage shield  20 , made of suitable conducting material. 
   An electric heater  22  is in contact with the insulator bushing  18  to keep the insulator bushing at a sufficiently high temperature to prevent vapor condensation and particle deposition on the bushing  18 . 
   Gas containing suspended droplets and other particulate matter from a source  23  is directed to flow through an inlet opening  24  of the housing  12  and passes through a porous medium  26  in the inlet. The porous medium  26  is a relatively inefficient droplet collector to keep out large contaminants, so that most of the droplets in the aerosol are carried by the gas into the electrostatic electrode region or chamber  28  above. 
   The input gas then flows around the electrode assembly  14  to expose the droplet particles in the gas to the high electric field around the electrode assembly. The discharge electrode assembly  14  includes a central rigid support  30  for two support discs  32  and  34  on opposite ends of the central support. The upper disc  32  may be attached to the insulator bushing  18  and thus support the discs  32  and  24  from the housing  12 . A plurality of holes  35  (see  FIG. 2 ) are formed in each disc  32  and  34  and a fine metal wire,  36  is strung between them. The sectional view  FIG. 2 , through the compact electrostatic precipitator electrode  14  shows there are eight holes in each of the support discs. A fine metal wire  36  is threaded through the holes to form eight straight, parallel discharge electrodes  36 . By way of example, if the distance between the two support discs is 8 inches, the fine wire electrode  36  extending between them will each be 8 inches in length for a total discharge electrode length of 64 inches. More holes can be used in the support discs  32  and  34  to create more discharge electrodes, or fewer holes can be used if less length of the discharge electrodes is needed. With the above mentioned distance of 8 inches between the support disks, an electrode circle diameter of 3 inches, the diameter of the housing  12  is approximately 5 inches, and its length, approximately 10 inches. Using the conventional design of a single discharge electrode in the center of a tube, the total length of the electrostatic precipitator is more than 64 inches. The advantage of the present electrode design in reducing the size of the precipitator and making it compact over the conventional design thus becomes obvious. 
   The gas (aerosol) flows around the wires  36  and ions are produced in the corona discharge. The ions collide with the droplets to cause the droplets to be charged. The charged droplets are then carried by the gas flow through an electrically conducting, grounded porous medium  40  as the gas flows to an outlet  42 . The droplets are collected by electrostatic precipitation onto the grounded collecting elements in-the medium. 
   The clean gas then flows out of the annular space  41  between the porous medium  40  and the outer housing  12  to the outlet  42 . The collected oil droplets flow down the inside surface of the porous medium  40  as a thin film which is returned by gravity to an oil reservoir or sump  44 . 
   As shown in  FIG. 1 , all parts of the system are grounded except for the high voltage electrode assembly and the high voltage shield  20 . 
   Using a thin wire of a uniform diameter in the above electrode arrangement, and in other embodiments disclosed, it is important to keep the distance between each wire segment and the adjacent collector electrode the same for all the wire segments on the support structure. By keeping the distance uniform and using the same high voltage potential on all the wire segments, a uniform corona discharge can be maintained. This will insure that all particles flowing through the device will be charged uniformly and to the same maximum possible extent to insure high collection efficiency for the device. 
   In designing an electrostatic precipitator using the above electrode assembly, the spacing, S, between the wire segments must bear a proper relationship to the distance, D, between the wire segment and the adjacent collector electrode surface. (see FIG.  2 ). Too small a spacing, S, will cause the closely spaced wire segments to interfere with each other, thereby reducing the maximum current that can be obtained from each wire. Too large a spacing will cause some empty spots on the collector electrode surface to appear. Within these empty spots, there are no corona current flow. Particles flowing over these empty spots will not encounter corona ions and thus remain uncharged. From experience, it has been found that the ratio, S/D, must be kept between the limits of 0.1 and 10, preferably between 0.3 and 3, for the electrode assembly to function properly and avoid degradation in performance. 
   For application in a Diesel blowby gas recirculation system, the inlet housing  24  is connected to an opening in the crankcase, which is represented at  23 , and the collected oil film is also returned directly to the crankcase. The outlet  42  can be open to the atmosphere to allow the cleaned blowby gas to be discharged to the atmosphere, or the outlet  42  can be connected to the intake of the Diesel engine for exhaust gas recirculation. 
   The total discharge electrode length is greatly increased from that of the conventional precipitator with a single discharge electrode in the center of a tube. The corona current that can be maintained between the discharge electrode and the collecting tube is generally proportional to the total electrode length. The approach described here makes it possible to greatly increase the electrode length and hence the total corona current, thereby increasing the efficiency for both droplet particle charging and precipitation of the charged droplets or particles. A laboratory prototype device has demonstrated the practicality of this approach. As many as sixteen discharge electrodes have been used leading to approximately a factor of sixteen increase in total corona current in laboratory prototypes. 
   Another purpose of the electrode design shown is to allow the discharge electrode to be circumferentially supported on a circle. A large diameter circle of the electrode length mounting will bring the discharge electrodes (the wires) closer to the porous medium  40  collecting surface, thereby reducing the voltage needed to maintain the corona discharge between the electrode and the grounded porous collecting surface. A lower operating voltage from existing precipitators is desirable for the applications described above, to reduce the need for very high voltage insulation. When using a lower voltage, the leakage current through the insulator bushing  18  can be reduced. Using a lower voltage also reduces the cost and complexity of the power supply  16 , thus making the device more economical to produce. In the present device, voltages of between 5,000 to 10,000 volts are most preferred, but voltages up to 20,000, volts DC can be used. 
   Using a circle of electrode lengths spaced from the center rod also forces the gas flowing radially outward toward the porous collecting surface to be exposed to the very high electric field surrounding each discharge electrode. Generally, the electric field strength according to Gauss&#39;s law tends to decrease with increasing distance from the discharge electrode. The closely spaced wires forming the discharge electrodes forces the gas to pass through the high field region between the electrodes and to be exposed to the high electric field around the wires. Each droplet or particle can thus be charged to a higher level than is possible with the conventional single length electrode design, thereby gaining a higher electrical charge and allowing droplets to be more easily removed by electrostatic precipitation. 
   Although a porous collector electrode  40  is shown in  FIG. 1  as the collector electrode, the basic design of the discharge electrode assembly  14  works well also when the collector electrode is made of a solid conducting material, in which case the housing  12  itself can be the collector. The oil droplets will be collected on the interior surface of the housing walls. The collected oil droplets will then flow down the walls and be returned to the oil sump or the crankcase of the diesel engine, eliminating the porous collector electrode will make the device less efficient, but the overall size, the complexity, and the cost of the device will also be reduced. 
   The high-voltage insulator bushing  18 , if unprotected, will be exposed to the suspended droplets or particles in the gas, as well as any condensable vapor which may be present. Over time, the accumulation of deposited and condensed material on the insulator will render it ineffective. The insulator is heated by contact with the electrical heating element  22  to a high enough temperature to prevent vapor condensation on the insulator bushing. 
   To prevent the precipitation of droplets or particles on the insulator bushing surface, a conductive shroud or shield  20  surrounds the insulator. This conductive shroud  20  is connected to the same high voltage source as the discharge electrodes  36  so that a high electric field is created in the region between the shroud and the nearby grounded surfaces of the porous medium  40  or housing  12 . The charged droplets or particles present in the gas will thus be precipitated onto the grounded surfaces and not on the high voltage insulation bushing. 
   Design variations of conductive shroud  20  are shown in  FIGS. 3A and 3B . By using a small gap spacing between the bottom plate of the shield or shroud and the nearby grounded surface, a high electric field can be created in this gap space to also precipitate droplets or particles in the gas. 
   In  FIG. 3A , the modified high voltage shield as indicated at  50 , and as shown has a base plate  50 A, and the surrounding wall  50 B that surrounds the insulator bushing  18 . The grounded housing  12  has a cap portion  52  that comes up from a top wall  54  and defines an opening near the upper end of the insulator  18 , as shown. The surrounding wall  50 B is spaced from the wall over cap  52 , and terminates short of the upper end wall of the cap. Thus there is a gap shown at  56  between the shield wall  50 B and the housing wall  52  around the insulator. The support shown at  56  supports a top plate  32  of the electrode assembly. The central support and the lower electrode plate  34  can be provided as before. 
   In  FIG. 3B , the high voltage shield comprises a flat disc  60  that is fixed to the lower end of the insulator bushing  18 , and the insulator bushing  18  in this case is also surrounded by a sleeve or cap  62  of the housing, which is grounded. 
   The top wall  64  of the housing is spaced from the plate  60 , to form a gap  66  between the housing wall  64 , which is a top wall, and the plate  60  which is a shielding disc. The support  68  can be used for supporting a top plate  32  of the electrode assembly as before. 
   Each of these forms of conductive shroud shows a gap between the high voltage shield or shroud and a portion of the grounded housing. The gap is relatively narrow, and will provide for precipitation of charged particles that come near the high voltage shield, to the walls of the grounded housing. 
   Creating a long pathway in the gap space as shown in  FIGS. 3A and 3B , the charged droplets or particles in the gas can be efficiency precipitated in the regions surrounding the insulator bushing  18  to provide improved protection of the high voltage insulator from particulate contamination. 
   In spite of the efficient high voltage insulator shield design of this invention, there is the possibility that some droplets or particles in the gas may remain uncharged. These uncharged particles will be capable of penetrating through the gap space  56  or  66  between the shroud and the nearby grounded surface to deposit on the insulator. The precipitation of these uncharged particles on the insulator can be prevented by utilizing the phenomena of thermophoresis. Thermophoresis refers to the movement of aerosol particles in the direction of a decreasing temperature gradient due to the radiometric force acting on the particles. For effective thermophoretic motion of the particles to prevent particle precipitation on the insulator the insulator must he held at a sufficiently high temperature. The insulator temperature must be 10° C. or more than the surrounding gas temperature. In contrast, to prevent vapor condensation, the insulator only needs to be held above the dew point of the condensable species in the gas. Usually at least a few degree C above the gas temperature would be sufficient 
   To be effective, the porous medium  40  must be made of a conductive material, usually metal. It can be made of a perforated metal, a porous, sintered metal, one or more layers of wire mesh material rolled into the desired cylindrical shape, a pad of metal fiber or wires formed into a cylinder, and similar configurations. As the gas flows into the porous medium, particles are brought to close proximity to the surface of the conducting elements in the medium, thus allowing the charged particles to be effectively deposited onto the surface of the conducting elements of the porous medium. In comparison, in the conventional electrostatic precipitator using solid collecting electrodes, such as a solid tube surrounding the center electrodes, the charged particles must be precipitated by electrical force through the fluid boundary layer adjacent to the inner surface of the surrounding tube. 
   Depending on the gas flow velocity, the relatively stagnant boundary layers adjacent to the solid collecting surfaces may be a centimeter or more in thickness. The particles must be precipitated through this centimeter thick stagnant gas layer to be deposited on the surface. In comparison, using a porous collecting electrode, as shown here, the gas is forced to flow between the closely spaced conducting elements in the porous medium, thereby greatly reducing the distance the particles must travel to reach the collecting surface. This will increase the efficiency of the precipitator and reduce the overall physical size of the device. 
   Not all electrically conducting porous material can be used with the compact electrostatic precipitator described in this invention. In order to handle the high gas flow rate per unit of collecting surface intended for this application, the porous material must not produce excessive pressure drop at the required high gas flow. In addition, the collected oil drops must drained off easily by gravity and not be collected in the porous medium to clog the medium or produce excessive high pressure drops. Depending on the structure of the porous medium, and the surface tension and viscosity of the liquid droplets being collected, the distance between the conducting elements of the porous medium must be kept above a critical limit. Too small a distance will allow the collected droplets to form surface films bridging neighboring elements and block the flow. For the usual liquid such as lubricating oils, the mean distance between the conductive elements in the medium must be larger than about 5 microns, and preferably larger than 10 μm. The mean distance between the elements in a porous medium is also referred to as the mean pore diameter which can be measured by a commercial poremeter. A mean pore diameter greater than 5 μm, preferably greater than 10 μm, is generally necessary for the medium to work successfully as the porous collecting electrode of the droplet collecting precipitator described herein. 
   There are a number of devices using a porous medium to collect charged particles. One such device is the electrically augmented bag filter described by Penney in U.S. Pat. No. 3,910,779. In Penney&#39;s device, the particles are charged in a corona charger. The charged particles are then carried by the gas flow through a fabric medium and deposited on the surface of the fabric. The particles to be deposited must be a dry solid material, so that the deposited particles on the fabric will form a porous cake. Since a cake will also form on the fabric in the absence of an electrical charge, electrostatics charges are used by Penney to modify the property of this cake namely to increase the pore size of the cake and reduce the pressure drop. The textile fabric used in a fabric filter is usually not electrically conductive, so that it is not possible to maintain a corona discharge directly between the corona electrode and the fabric. A separate corona charger is used upstream of the fabric filter to charge the particles for subsequent filtration by the fabric. 
   Another device using a porous filter media is what is usually referred to as electrostatically enhanced fibrous filter such as that described by Carr in U.S. Pat. No. 3,999,964. A conventional fibrous filter media made of glass, polymeric and other non-conducting fibers is sandwiched between two sets of electrical grids. A potential difference is established between the grids to create an electric field in the medium to enhance the efficiency of the medium for particle collection by electrostatic attraction. The device is most effective when the particles are electrically charged. If the particles are not charged, a corona ionizer can be used upstream of the filter to charge the particles to increase the efficiency of the filter for particle collection. 
   A further version of the electrostatically enhanced fibrous filter is that of Argo et al in U.S. Pat. No. 4,222,748. In Argo&#39;s device, a corona charger is used upstream to charge the particles. As the charged particles are collected in the fiber bed, which is made of a non-conductive material, charge will build up in the bed to raise its electrical potential. To prevent the continuous buildup of charge in the bed, the bed is continuously irrigated by water to make the bed conductive. Particles collected in the bed are also carried away by the flowing water. 
   The electrostatic precipitator of the &#39;136 patent is very efficient and can be made into a small compact size. For many applications, such as diesel blowby filtration, the cylindrical geometry with a circular cross section is the most convenient. However, it is not necessary that the cross section shape be a circle to take advantage of many of the features of this invention. Rectangular, elliptical, and other cross sectional shapes can be easily adapted to the design of an electrostatic precipitator described by the method described in the present invention. 
     FIG. 4  represents a transverse sectional view through a rectangular precipitator. The electrode assembly  72  including a pair of spaced corona wire supports  74  (only one is shown) would be made as before with the two supports  74  spaced along a support rod  76  with wire  77  forming electrodes extending between the supports. The wires  77  are shown in the cross over portions for threading through the holes. A conductive porous medium collecting electrode  78 , surrounds the high voltage electrode assembly  72 , and the porous medium, and the grounded outer housing  79  have a generally rectangular cross-sectional shape. 
   In designing such a rectangular precipitator, it is important to keep the individual corona wire lengths between the support  74  at approximately the same distance from the porous collecting electrode  78 . This will insure that the corona discharge between the high voltage corona wire  76  and the collecting electrode  78  will be uniform at the same applied voltage on the wires. As before, the lateral distance between the wire lengths and the porous collecting electrode  78  can be reduced to lower the required operating voltage of the precipitator. 
   Although the precipitator described in the &#39;136 invention is intended for droplet aerosol collection, it can also be used to collect aerosols containing only dry solid particles. To prevent the build up of solid particles in the porous collecting electrode which will cause plugging of the pores, liquid droplets, usually water, can be added to the aerosol before it is introduced into the precipitator.  FIG. 5  shows an ultrasonic droplet generator  80  used in conjunction with an electrostatic precipitator  82  for droplet addition. As aerosol flows from source  84  through the ultrasonic generator  80 , it picks up droplets in the space  86  above an agitated liquid  88  produced by ultrasonic agitation using an ultrasonic transducer  89 . The dry particulate matter will be precipitated along with the added liquid droplets in the precipitator  82  and be carried away by the liquid stream resulting from the collected droplets, thereby preventing the build up of dry solid material on the collecting electrode in the precipitator. Other droplet generating devices, such as compressed air atomizer, bubblers, and the like can also be used. The electrostatic precipitator can be made as shown in any of the forms disclosed 
   Because of the small droplet size and the large surface area of the droplets produced by ultrasonic agitation or a compressed air atomizer, the combined wet electrostatic precipitator and droplet generator described above will have excellent gas absorptive properties, and can be used as a combined gas and particle scrubber. The combined gas and particle scrubber will have a variety of applications in air pollution control. For instance, in the semiconductor industry, the exhaust gas from the vacuum pump downstream of a semiconductor process equipment often contains both toxic gases as well as fine particulate matter. One such gas is fluorine, which is used at the end of a process cycle to clean the process chamber. Fluorine is very reactive to water and will be efficiently scrubbed by water droplets in the combined droplet generator and wet electrostatic precipitator. Similarly, various acidic vapors such as hydrogen fluoride (HF) and hydrogen chloride (HCl) can be absorbed by water droplets or by an aqueous solution of KOH and other basic solutions. By combining a droplet generator with appropriate chemical scrubbing solutions and the wet electrostatic precipitator, a highly efficient combined gas and particle scrubber can be obtained. 
     FIGS. 6 and 7  show a compact two-stage electrostatic precipitator  98  in which an electrode assembly  100  including a short corona-discharge electrode  102  that is attached to a cylindrical precipitating electrode  104 , and both are held at the same high DC voltage from a voltage or power source  106 . The short corona-discharge electrode  102  has a pair of spaced support discs  108  and  110  held together with a central support  112 . The discs support a fine wire  113  carrying a high voltage to produce a corona-discharge. The cylindrical electrode  104  is a tubular cylinder with a conducting surface. This cylindrical electrode  104  together with the surrounding porous metal media collector  114  form a precipitating region in which the charged particles are precipitated. 
   In this two-stage design, the relatively short corona wire lengths  113 A forming electrodes produce a corona discharge to charge the droplets or particles moving past the corona-discharge electrode  102 . The short length of electrode  102  reduces the corona output from the wires, hence the required current output from the power source  106  is reduced, in turn reducing its physical size, and cost. The design also makes it possible to vary the radius of the circle of the corona wire lengths  113 A independently from that of the radius of the tubular cylinder electrode  104 . By changing these two radii, both the corona discharge electrode  102 , which is an ionizer, and the precipitating cylinder electrode  104  can be independently optimized, leading to improved overall operation of the system. 
   The discs  108  and  110  are held together with a central support  112 . The fine wire  113  is threaded between the discs  108  and  110 , and carries the high voltage from the source  106 . The high voltage again is carried by wire through an insulator bushing  118 , which is surrounded by high voltage carrying shield  120 . An end plate  104 A on tube  104  carries the voltages to the tube  104 . The tube  104  in turn is connected to the disc  108  for powering the corona discharge electrode  102 . The flow of gas is from an inlet  116  of housing  12  to an outlet  117 , which discharges clean gas. 
     FIGS. 8 and 9  show a modified electrode design that can be used with the single-stage and the two-stage precipitators shown in  FIGS. 1 and 6 . In this case, a plurality of support rods  120  are attached to the support discs  122  and  124  to form an assembly. A single corona fine wire  126  is spirally wound around the support rods  120  to extend from one disc to the other, and this forms a plurality of segments of conductive wire carrying current for supporting a corona discharge for charging particle in the droplet aerosol introduced through an inlet  128 . The porous media collector  129  is shown in  FIG. 1  with a coarse filter formed at a bottom panel  130 , and selected porosity on a cylindrical electrically conductive porous side wall media  132 . The cylindrical side wall  132  acts to precipitate charged droplets and particles as previously shown. The cylindrical wall  132  is grounded, as is the housing  12 . An outlet  134  from the housing discharges clean gas. The insulator bushing  18 , heater  22  and voltage source are the same as shown before. 
   The compact electrostatic precipitator described herein can be used to remove suspended particles in the blowby gas from a diesel engine or other internal combustion engines. The blowby gas with the suspended particulate matter removed can be discharged directly into the atmosphere, or can be recirculated into the engine.  FIGS. 10 and 11  described below are both suitable for use for any electrostatic precipitator, including that of the conventional design. 
     FIG. 10  shown one arrangement for blowby gas recirculation using an electrostatic precipitator, preferably one made according to the &#39;136 invention. The diesel engine  135  has a crankcase  136  and blowby gas from the engine crankcase  136  first flows along a passage through an electrostatic precipitator  137  designed as show previously to remove suspended droplets or particles. The clean gas then flows into the inlet section of a T-connector  138  which has a orifice plate  138 A in an outlet section. The gas flows through an orifice  140  in the plate  138 A and into the intake of a turbo charger  142 . The side inlet section  136 B of the T-connector  138  is open to atmosphere. 
   This T-connector constitutes a crankcase pressure regulating device when an electrostatic precipitator is used to remove particles from the blowby gas for recirculation into the diesel intake. Its operation is as follows. The T-connector  138  inlet  138 B is open to the atmosphere, and thus the outlet of the precipitator  137  is also at atmospheric pressure. The crankcase pressure Pc relative to atmospheric pressure Pa is thus Pc−Pa=ΔP, where ΔP is the pressure drop of the blowby gas through the precipitator  137 . This pressure drop is usually quite low, on the order of a few inches of water or less. The crankcase pressure is thus limited to a few inches of water above atmospheric. In an internal combustion engine, the crankcase pressure must not be allowed to vary by more than a few inches above or below atmospheric to prevent leakage of crankcase oil to the outside, and other operational difficulties. This design makes it possible to achieve crankcase pressure regulation with a simple connection and at low cost. 
   In a diesel engine using a turbo-charger or turbo-compressor to increase the engine power output, as shown in  FIG. 10 , a filter  144  is used at the air intake of the turbo-charger  142  to remove suspended particles in the ambient air. The pressure drop through the filter  144  causes the pressure Pt at the turbo-charger intake to be below atmospheric. The diameter of the orifice  140  in the outlet section of the T-connector  138  is chosen such that the pressure drop across the orifice  140  (ΔP=Pa−Pt) is just sufficient to cause the gas flow through the orifice  140  to be the same as the blowby gas flow Q 1  during normal engine operation, and when the engine intake air filter  144  is new. When the intake filter  144  becomes partially clogged, its pressure drop increases. This increases the gas flow through the orifice Q 2 . The difference, Q 3 =Q 2 −Q 1  is made up by the air flow coming from the ambient through the side inlet section  138 B of the T-connector  138 . 
   Alternatively, as shown in  FIG. 10A , a modified orifice housing  139  can be made as a straight through flow tube with no side inlet for atmospheric air. An atmospheric inlet  139 A can be connected to an opening in the diesel engine crankcase  136 . 
   In both the arrangements shown in  FIGS. 10 and 10A , the blowby gas passing through the electrostatic precipitator  137  is at a relatively high temperature. It also contains oil vapor which is not removed by electrostatic precipitation. This oil vapor will condense on the heat transfer surfaces of an intercooler  146  used at the outlet of the turbo-charger  142 . Over time, the condensed oil will flood the intercooler  146  to cause a drop in the intercooler efficiency and the power output of the diesel engine if not handled or removed. 
   To automatically remove this accumulated oil from the intercooler  146 , an oil sump  148  is provided in the intercooler to allow the condensed oil to flow into the sump by gravity. The airflow from the intercooler  134  is directed through a flow restriction  150 , such as a nozzle or an orifice to create a pressure drop to remove the oil from the intercooler  146  and be carried by the airflow into the engine intake. The oil collected in the oil sump  148  can also be fed to the intake manifold  131  of the engine  135 , by the back pressure created by the flow restriction  150 . 
     FIG. 11  shows a second arrangement for recirculating the blowby gas into a diesel engine  135 . The crankcase  137  is connected to the electrostatic precipitator  137  as before, but the T-connector  138  is removed and the flow from the precipitator  137  is directed to a filter intake plenum  154  and allowed to pass through the filter  144  along with the intake airflow. No crankcase pressure limiting arrangement is needed in this case. Since the precipitator outlet is always at atmospheric pressure, the crankcase pressure will thus be automatically limited to that needed to maintain the blowby gas flow through the precipitator  137 . 
   When the hot blowby gas is directed this way into the filter intake  154 , the oil vapor will be quickly cooled as it comes in contact with the cool collecting filter elements of the filter  144 . The vapor will thus condense and be collected in the filter housing. At the same time, all submicron size particles, which may not be completely removed by the electrostatic precipitator, will also be subjected to the strong thermophoretic forces created by the temperature gradient in the boundary layer of the gas flow around the collecting elements of the filter  144 . This thermophoretic force can be effectively utilized to remove these submicron particles. Normal engine intake air filters are designed to collect particles larger than a few micron in diameter only. Small particles in the submicron size range are usually not collected. By utilizing the thermophoretic force, the fine particles in the blowby gas can also be collected, thus making the incoming air to the turbo-charger cleaner. With proper design, oil and fine particle accumulation in the intercooler can be reduced to very low level. 
     FIG. 12  is similar to FIG.  11  and the parts that are identical are identically numbered. In  FIG. 12  a controllable flow restrictor  158  is connected to the outlet of the intercooler  146 . The flow restrictor has a retractable vane or blade  158 A that can be introduced into the interior passage of the restrictor and which is controlled by a solenoid  159 . The solenoid  159  is connected to the vane or blade  158 A and will extend the blade into the flow passage when a signal is received by the solenoid. An oil level sensor  160  is provided on the oil sump  148 , and when the oil level in the sump reaches a set level, the signal is provided to energize the solenoid  159 . The vane or blade  158 A is moved into the flow passage in flow restrictor  158  to restrict flow through the outlet line. 
   This action increases the back pressure in the oil sump and forces the collected oil out a line  161  to the intake manifold  131  of the diesel engine. The solenoid controlled restrictor can be any desired form, such a as a valve that closed partially, or an orifice that is introduced into the flow passageway. 
     FIG. 13  is a sectional view of a modified version of typical electrode support  170 . It can be molded from plastic and has an outer wall  172 , with a plurality of projections or “prongs” shown at  174  which make the outer surface much like a serrated surface. A wire of suitable diameter indicated at  176  can be wound around the support  170  in a helical fashion, much as shown in  FIG. 8 , with the points of the serrations or projections supporting the wire  176  at closely spaced intervals depending on the spacing of the serrations to insure that the wire  176  is maintained in a proper position relative to the collector electrode. 
     FIG. 14  is a vertical cross-sectional view of a modified form of a compact electrostatic precipitator  199 . In this form of the invention, a conductive sleeve  200  forms a passage for fluid, with an inlet connection  202  for receiving an aerosol, and an outlet connection  203 . A flow passageway is defined by a plurality of openings  204  in a housing plate  206  that is supported on sleeve  206 A, which is positioned at the upper end of the conductive sleeve  200 , and is supported on a cap plate  208  on a flange  210  formed on the end of the outer sleeve  200 . 
   The support sleeve  206 A has an open center, and an end insulator portion  215  of a main electrode support  212  is mounted therein. The upper end insulator portion  215  of the support  212  is supported on the cover  208  in a suitable manner. The upper end insulator portion has a receptacle for a heater assembly  216 , which has heaters  218  mounted in a outer jacket  219  that is heat conducting and in contact with the insulator portion  215 . The outer jacket  219  can be made of copper, which is a very good heat conductor, to distribute the heat uniformly to its outer surface and keep the insulator surface  213  hot and clean from contamination by vapor condensation and particle deposition. The top plate  220  is a heat insulator to reduce the heating power required to operate the heater. The electrical power to operate the heater, usually 12 or 24 volts, is carried by the electrical leads  221  passing through the top plate  220 . 
   A power connection line  224  can be passed out through a central opening of a cap  222 . As shown, a power supply  226  to provide the high voltage for the discharge electrode can be potted in the cap  222  and the connector line or rod  225  can be within the precipitator and does not have to extend through the cap. The line  224  can be a relatively low voltage, for example, a 24-volt supply could be provided. The heaters  218  also would be connected generally to a 24-volt supply. 
   The main support  212  includes a hollow center electrode support  214  that can be, for example, injection molded as a single piece with the main support  212 . The electrode support  214  has an interior passageway in which the high voltage connection rod or line electrode  225  extends, and a thin electrode wire  227  can extend for connection directly to the electrode wire shown at  228  that, as shown, is helically wrapped around the insulating support  214 . The electrode wire  228  is shown larger than actual size and is a thin wire as previously explained. The insulating material sleeve  214  may be attached to the main support  212  with suitable screws threaded up into the support  212 . The upper part of the insulating support has a conducting sleeve  217 , which can be made of a metal and connected to the same high voltage electrode wire  226 . The insulating support  214  can have a cross section that is cylindrical, if desired, or as shown in  FIG. 15 , it could be rectangular with the outer collector electrode  200  also being rectangular with care being taken so that at the corners there was a uniform spacing between the wire  228  and the collector electrode. 
   The cross section can take any desired configuration, as long as the spacings are maintained for a corona discharge. 
   The aerosol flow would come in as shown by the arrow  234 , and flow up and around the passageway  235  between the high-voltage electrode wire  228  and the collector electrode  200 . In this case, the collector electrode  200  is not a porous member, but is a solid member that can either be stainless steel, for example, or could be a conducting plastic. As the flow passes through the space between the electrode wire  228  and the collector  200 , the particles are charged by the corona ions produced by the wire electrode  228 . Some of these particles are precipitated onto the collector  200  in this region. The remaining particles are carried by the gas to the upper part of the assembly between the precipitator electrode  217  and the collector electrode  220 , where they are precipitated onto the collector  220  by virtual of the high voltage on the electrode  217 . The flow then goes up through the openings  204 , and out through the outlet  203  as shown. The main support  212  and the electrode support  214  can be injection molded as a single piece, if desired, with conductors formed as slip-fit jackets, or wrapped wires. The heaters  218  are easily installed to maintain the temperature of the insulator at a desired level. 
   The high temperature at the heaters keeps vapor that enters the space between the sleeve  206 A and the upper high voltage insulator portion  215  from condensing on the surface  213  of the high voltage insulator portion  215  in the region around the center portion  215 . The heaters also provide enough heat to tend to repel contaminant particles by the thermophoretic effect and prevent them from depositing on the surface  213  of the high voltage insulator portion  215 . The heaters  218  are in heat transfer, contacting relation to the insulator portion  215  and will maintain the temperature of the surface  213  sufficiently high to prevent contaminant particles from building up on the surface of the insulator portion. Preferably the temperature of the surface  213  of the insulator portion  215  is 10.degree. or more than the temperature of the gas in the vicinity of the insulating surface  213  inside the precipitator housing. 
     FIG. 16  is a transverse cross sectional view of a modified electrode support  250  taken on the same line as FIG.  15 .  FIG. 17  is a vertical cross sectional view of the modified electrode support  250 . A wire  252  forming the electrode is in contact with the surface  254  of the electrode support  250  and in substantial conformity to it. The wire  252  can be wound around the support  250  as shown, and made to adhere to the surface  254  by using a suitable adhesive material. When adhesives are used the wire  252  can have various patterns. 
   One such pattern for the wire  252  is shown in  FIG. 18  at  258 . In  FIG. 18  a surface  262  of a support  260  has been unrolled to a flat surface to review the wire pattern on the surface  262 . The electrically conductive discharge wire  264  is in contact with the support surface  262 , which is made of an electrically insulating material, such as a plastic or ceramic. The wire electrode  264  is of a substantially uniform diameter and the distance between the wire segments and the adjacent collector electrode is substantially uniform along the length of the wire. With a uniform distance between the wire  264  and the collector electrode, a substantially uniform corona discharge can be maintained. All parts of the wire  267  can thus be utilized effectively to insure a high charging efficiency in a small compact overall physical size for the electrostatic droplet collector. 
   Another way of fabricating the thin wire discharge electrode is to use a flat, thin dielectric, generally plastic, having a thin film clad on the outer surface. The flat thin dielectric with a thin film on the outer surface can be similar to those used in fabricating flexible, electric circuit boards. The electrode wire pattern on the surface can be etched by photolithography. The thin film forming the pattern can then be applied to the surface of the support structure by an adhesive. In such a case, the wire will no longer have a circular cross section. The lateral dimension of the etched electrode, however, must be sufficiently small to sustain a corona discharge at the applied high voltage material. 
   The compact electrostatic precipitators shown are intended primarily for droplet aerosol collection. The high collection efficiency for the compact size also make the precipitators suitable for collecting dry particle aerosols. The collected dry particles will accumulate in the unit and the precipitators must be periodically shut down for cleaning and maintenance. This is usually acceptable for most applications. 
   The compact electrostatic precipitator described herein, though not necessary for the application, is particularly attractive because of its compact physical size and high collection efficiency. 
   Present Invention 
     FIG. 19  shows an electrostatic precipitator  300  in accordance with the present invention. The precipitator includes a canister  302  having a corona discharge electrode assembly  304  having a hollow interior  306 . A power supply  308  is provided in the hollow interior and supplies high voltage to conductor wire  305 , comparable to conductor wire  36 , of the corona discharge electrode assembly. The canister extends axially along axis  310  and has an open axial end  312  closed by a lid  314 . The corona discharge electrode assembly  304  is mounted to lid  314  and extends axially into canister  302 . 
   Lid  314  has first and second distally opposite faces  316  and  318 . Face  316  faces axially outwardly away from canister  302 . Face  318  faces axially inwardly into canister  302 . Corona discharge electrode assembly  304  is mounted to lid  314  by an insulator  320  extending along face  318 . Insulator  320  is axially between face  318  and power supply  308 . Insulator  320  has first and second distally opposite faces  322  and  324 . First face  322  of insulator  320  faces axially toward and engages second face  318  of lid  314 . Second face  324  of insulator  320  faces axially inwardly into canister  302 . Hollow interior  306  of corona discharge electrode assembly  304  extends from second face  324  of insulator  320  axially inwardly into the canister. Power supply  308  faces second face  324  of insulator  320  and extends axially inwardly in hollow interior  306 . Power supply  308  and hollow interior  306  are on the second face side  324  of insulator  320  opposite the first face side  322  of the insulator. The power supply is conventional and includes conventional transformer circuitry for stepping up the voltage, e.g. from a 12 or 24 volt DC input at  326  to a high voltage output at  328 , such as several thousand volts, e.g. 15 kV, connected to corona wire  305 . It is preferred that the power supply include a low voltage circuit board for a 12 or 24 volt DC input, also providing a monitoring circuit, connected by lead  332  to a high voltage circuit board  334 , as is standard. It is further preferred that the circuit boards be potted with electrical potting compound  336  in hollow interior  306  of corona discharge electrode assembly  304 . Low voltage lead  326  extends axially through lid  314  and axially through insulator  320 . The low voltage lead preferably includes a plurality of conductors and respective connection pins therefor, such as a first connection pin  338  for feeding 12 or 24 volts DC from a voltage source, such as the battery or electrical system of the vehicle, a second pin  340  providing the low voltage ground, and a third pin  342  providing a power supply diagnostic. 
   In one embodiment, corona discharge electrode assembly  304  is provided by a plastic insulating bobbin  344  extending axially between first and second axial ends  346  and  348 . Bobbin  344  has an inner surface  350  defining hollow interior  306 , and has an outer surface  352  facing canister  302  and spaced inwardly therefrom. Corona discharge conductor  305  extends along outer surface  352  and is spaced radially outwardly thereof as above. Canister  302  is grounded, as is known, and provides an annular ground plane providing the collector electrode as above. First axial end  346  of bobbin  344  is mounted to second face  318  of lid  314 , in any suitable manner, such as sonic welding, adhesive bonding, etc., and provides the noted insulator. 
   Precipitator  300  is preferably used in a diesel engine electrostatic crankcase ventilation system as above, for blowby gas. Housing  354  has an inlet  356  as above for receiving blowby gas from the diesel engine, and has an outlet  358  as above for discharging the blowby gas after removal of suspended particulate matter including oil droplets from the blowby gas, and returning the blowby gas to diesel engine as above, to the fresh air intake of the diesel engine, for example a turbocharger or compressor, thus providing blowby gas recirculation. Precipitated oil droplets drain from the housing at drain  357  back to the oil pan of the engine, as above. Housing  354  includes axially extending canister  302  having open axial end  312  closed by lid  314 . The lid may include a disc or plate portion  360  having a plurality of apertures  362  providing flow distribution therethrough into the upper plenum space of the canister prior to discharge of the gas at outlet  358 , comparably to above noted disc or plate  206  and apertures  204 . 
   Insulator  320  is axially aligned with hollow interior  306  and axially spaces power supply  308  from lid  314  and is disposed axially inwardly of open axial end  312  of the canister. Low voltage lead  326  extends axially through first and second faces  316  and  318  of lid  314  and axially through first and second faces  322  and  324  of insulator  320 . 
   The invention provides an electrostatic precipitator  300  including a housing  354 , a corona discharge electrode assembly  304  in the housing, an insulator  320  extending along an inner surface  318  of a wall  314  of the housing, a power supply  308  in the housing on the opposite side  324  of the insulator from the housing wall  314  such that insulator  320  is between housing wall  314  and power supply  308 , and a low voltage lead  326  extending through the housing wall  314  and through the insulator  320  to the power supply  308 , the power supply  308  supplying high voltage for the corona discharge electrode assembly  304 . The housing is preferably provided by a canister  302  closed by a lid  314 , with the lid providing the noted housing wall having the noted internal surface  318  along which insulator  320  extends, and with the low voltage lead  326  extending through lid  314  and insulator  320 . Canister  302  has the noted open end  312  closed by lid  314 , and the power supply  308  is recessed in the housing inwardly of open end  312 . Power supply  308  is spaced from lid  314  by insulator  320  therebetween. 
   It is recognized that various equivalents, alternatives and modifications are possible within the scope of the appended claims.