Discharge electrode arrangement for disc electrostatic precipitator (DEP) and scrapers for both disc and discharge electrodes

Methods and electrostatic precipitators achieve efficient separation. Scrapers are specifically designed to clean the electrodes in the electrostatic precipitators. Particulates are collected from an entrained air stream by keeping both the discharge and collection electrode surfaces clean during the precipitation process so that the electrical corona discharge remains constant and the electrical field flux lines are maintained. This is accomplished using a plurality of vertical disc electrodes and a plurality of horizontal discharge electrodes preferably combined with the ability to keep the electrodes clean during the exhaust process.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention pertains to the field of electrostatic precipitators. More particularly, the invention pertains to disc electrode precipitators with horizontal discharge electrodes.

Description of Related Art

While regulations currently exist for diesel engine exhaust, at the present time the government is not enforcing emission requirements for coal stoves. Ceramic or metallic filters plus urea treatment are the dominating prior art methods used to process diesel exhaust.

There are a number of problems associated with diesel filters. The primary problem is an increase in back pressure due to porosity changes in the filter. Diesel filter failures are also related to “wet-stacking” (“wet” unburned fuel accumulating in the “stack”). Wet filters would be subject to immediate back pressure conditions.

Similarly, there is a need in the art to reduce the back pressure in electrostatic precipitators that are used by the coal and oil electric power industry.

Prior art patents show the use of circular disc electrodes with vertical discharge electrodes. Prior art patents also show vertical discharge electrodes with attracting electrodes that function independently in front of the disc electrodes.

SUMMARY OF THE INVENTION

Methods used in novel disc electrostatic precipitators achieve efficient particle collection from the entrained air stream by using scrapers that are specifically designed to scrape and clean both the discharge and collection electrode surfaces during the precipitation process so that the electrical corona discharge remains constant and the electrical field flux lines are maintained. This is accomplished using a plurality of vertical disc electrodes and a plurality of horizontal discharge electrodes preferably combined with the ability to keep the electrodes clean during the exhaust process.

In one embodiment, a method removes particles from a single main air stream in a disc electrostatic precipitator. The disc electrostatic precipitator includes a plurality of vertical rotatable circular disc collecting electrodes and a plurality of horizontal discharge electrodes located along an outer circumference of the vertical rotatable circular disc collecting electrodes. The method includes the step of passing entrained air through the plurality of horizontal discharge electrodes and the plurality of vertical rotatable circular disc collecting electrodes. A polarity of the vertical rotatable circular disc collecting electrodes is located at ground potential and high voltage direct current is applied to the discharge electrodes such that an electrical field is established between the horizontal discharge electrodes and the vertical rotatable circular disc collecting electrodes.

In another embodiment, a disc electrostatic precipitator for removing particles from a single main air stream includes a plurality of vertical rotatable circular disc collecting electrodes and a plurality of horizontal discharge electrodes located along an outer circumference of the vertical rotatable circular disc collecting electrodes. A polarity of the vertical rotatable circular disc collecting electrodes is located at ground potential and high voltage direct current is applied to the discharge electrodes such that there is an electrical field established between the horizontal discharge electrodes and the vertical rotatable circular disc collecting electrodes.

In another embodiment, a method for keeping a plurality of horizontal discharge wire electrodes in a disc electrostatic precipitator clean during a precipitating process includes the step of cleaning the horizontal discharge wire electrodes using a plurality of concentric tubular scrapers that traverse over the horizontal discharge wire electrodes to remove material deposited on the horizontal discharge wire electrodes.

In another embodiment, a method for keeping a plurality of disc electrodes in a disc electrostatic precipitator clean includes the step of cleaning the disc electrodes with a plurality of disc scrapers supported by scraper shaft spacer blocks at a first, lower end and supported at a second end on a disc support shaft spacer. A position of the disc scrapers relative to the disc electrodes is controlled by an offset in the scraper shaft spacer blocks and the disc support shaft spacer.

In another embodiment, a method for removing particles from a single main air stream in a disc electrostatic precipitator includes the steps of passing entrained air through a plurality of horizontal discharge electrodes and through a plurality of vertical circular disc collecting electrodes and cleaning the horizontal discharge electrodes and the vertical circular disc collecting electrodes with a plurality of scrapers. The plurality of scrapers are located out of the single main air stream.

DETAILED DESCRIPTION OF THE INVENTION

The disc electrostatic precipitators described herein have a continuous strong electrical discharge and a strong electric field. They also preferably include a mechanism to efficiently and continuously keep the electrodes clean and have very low or no particle re-entrainment. Unlike the prior art, the electrostatic precipitators described herein preferably include horizontal discharge electrodes and/or cleaning methods using scrapers. The horizontal discharge electrodes are preferably wire electrodes or rod electrodes. Although wire electrodes are predominantly described in the figures, the discharge electrodes may alternatively be rod electrodes in the embodiments described herein.

Methods and precipitator designs are described that can be used to keep the discharge electrodes and the rotatable disc electrodes clean. A method for achieving the desired and efficient operating performance of an electrostatic precipitator keeps both the discharge and collection electrodes surfaces clean during the precipitation process so that the electrical corona discharge remains constant and that electrical field flux lines can be maintained.

The method combines the use of a plurality of rotatable vertical disc electrodes with fixed scrapers on each side and a plurality of horizontal discharge electrodes with tube scrapers that slide over the discharge wire electrodes to remove deposited material. The scrapers are preferably used during the precipitating process.

The different scrapers described herein may be made of materials including, but not limited to, conductive or nonconductive material. In some preferred embodiments, the scrapers are made from nonconductive dielectric refractory tubular material. This method also includes a major reduction in particle re-entrainment by removing the collected material from the disc electrode out of the main air flow stream, while the material collected on the discharge electrodes agglomerates into larger particles that fall by gravity, or are collected on the disc electrode and removed during the disc cleaning process.

The discharge electrode arrangement used in prior art electrostatic precipitators is vertical and located either in front or between the collecting plates. In the electrostatic precipitators described herein, the discharge electrodes are preferably located horizontally across and in front of the collecting disc electrodes with each horizontal discharge wire electrode positioned to follow the circular periphery of the collecting discs electrode at a common specified distance from the disc electrodes. A polarity of the collecting disc electrodes is located at ground potential and high voltage direct current is applied to the discharge electrodes such that an electrical field is established between the horizontal discharge electrodes and the vertical rotatable circular disc collecting electrodes.

The process uses a plurality of circular discs and a plurality of horizontal discharge electrodes with scrapers that keep the electrodes clean during the precipitating process. This combination results in achieving an efficient, continuously, cost effective and improved method of collecting particulates from entrained gases.

The scrapers preferably are located and operate outside of the main air stream. The circular disc electrodes preferably have two scrapers: one for the sides and another for the leading edge of the disc electrodes. The horizontal discharge electrodes follow the circumference of the circular disc electrodes. The discharge wire or rod electrodes are kept clean by scraper tubes that slide over the surface of the discharge electrodes. The electrostatic precipitators are able to maintain a strong charge and electric field. They also have extremely low particle re-entrainment.

In some embodiments, the discharge wire or rod electrodes are preferably kept clean by heating the discharge electrodes before scraping.

Depending on the application, some auxiliary equipment that might be needed includes a HVDC power supply, one or more electric motors (for disc rotation, the discharge wire scraper, and/or the blower), a disposal collection container, one or more sensors, and/or AC for heating the discharge electrodes.

The DEPs described herein address a number of the problems associated with diesel filters, including the increase in back pressure due to porosity changes in the filter. The DEPs also address the need to reduce the back pressure in electrostatic precipitators that are used by the coal and oil electric power industry. While the consequences of wet filters have not yet been tested, it is anticipated that, unlike in the prior art, wet filters will cause only a minor interruption in the precipitation process.

Some advantages of the DEPs described herein include low back pressure, low particle re-entrainment, low pressure drop, the ability to clean discharge and disc electrodes during operation, the scrapers being located out of the main air stream, the main air stream being located in the upper half of the disc electrodes, the ability to work during a cold start, and at all operating temperatures, particulate collection of greater than 95%, and being able to scale up to meet high CFM (cubic feet per minute) requirements.

The disc electrostatic precipitators (DEPs) described herein could be used in many different applications that require electrostatic precipitators for particle collection and removal. One example is the capture of particulates from coal stove exhaust. Another example is for removal of particles from diesel exhaust, mainly for off-road applications. Additional examples include cleaning exhaust from plasma gasification scrubbers, and the scrubbers used in the syngas (synthesis gas) process of burning garbage.

FIGS. 1-11illustrate electrostatic precipitators with discharge electrodes131that are located horizontally across and in front of collecting disc electrodes132, with each horizontal discharge wire electrode131positioned to follow the circular periphery of the collecting discs electrode132at a common specified distance from the collecting disc electrode132.

Both the diameter and number of discharge electrodes131, as well as the spacing blocks136(shown inFIG. 2) can be varied based on the electrical and application requirements. For the electrical limits, the distance between the horizontal discharge wire electrodes131must be greater than the distance between the discharge wire electrodes and the leading edge166(shown inFIG. 7) of the disc electrode132, illustrated inFIG. 8.

FIG. 1is a cross sectional side view of a DEP where the exhaust entrained gas enters at156and exits at157. The main gas flow is predominately in the upper portion of the disc electrode132because of the position of the input156and exit157ducts and the negative operating pressure that is controlled by an external blower (not shown) located at the exit157.

Cleaning the disc electrode132at specific time intervals is achieved by using stationary disc scrapers142that are located below the disc drive shaft135but not fastened to either the disc rotatable shaft135or the scraper stationary shaft149.FIG. 1also shows the relative position of a disc edge scraper165that is used to remove material deposited on the leading edge166of the disc electrode132.

FIG. 1also shows the direction of rotation158of the disc electrode132. This allows for the collected material to rotate into the edge disc scraper165and the disc scraper142where the discharged material falls by gravity into the collection tray110located in the collection chamber108. Removal of the material from both the disc electrode132and the edge disc scraper165occurs out of the main airstream105, which prevents particle re-entrainment.

FIGS. 2aand 2bshow a front, cross sectional view of an embodiment of a disc electrostatic precipitator with horizontal discharge electrodes131. This horizontal arrangement of the discharge electrodes131is effective not only in charging the particles, but also in allowing the placement of concentric tubular or sleeve scrapers146over and in close proximity to the discharge wire electrode131. The scrapers146slide over the discharge wire electrodes131by moving the scraper tube bar148forward to scrape and remove material that has collected on the discharge wire electrode131during operation.

One end of the discharge wire electrodes131is fastened to electrical terminal connectors114and the other end163is left open-ended. A larger tubular scraper162that allows the smaller diameter tube scraper146to move in for cleaning is located on the bar167. The tubular scraper146is used to clean the discharge wire electrodes131.

Factors to consider when choosing a material for the tubular scrapers162include wear resistance, as well as electrical and dimensional relation to the discharger wire electrode. Both stainless steel tubing and alumina tubing can be used depending on how they are engineered into the structure.

Since the discharge wire electrodes131are connected to the electrical terminal connectors114at a first end and not connected at a second end163, this leaves an open space168between the end163of the stationary discharge wire electrodes131and the larger tube scraper support bar167.FIG. 2bis an expanded view of the area that is not connected. This embodiment allows scraped material to be discharged at the end of the discharge wire electrode131to fall by gravity into the collection tray110. In order to remove material collected on the discharge scraper tubes146, the scraper tube support bar148continues its forward motion and moves the discharge scraper tubes146into another close fitting large inside diameter tube162to be cleaned, detailed inFIG. 3b. For this application, the discharge wire electrode131must be strong enough to resist being attracted towards the disc electrodes132. Several ways to increase the strength of the discharge wire electrodes131are to use larger diameter wire electrodes131or including a harder wire in the discharge wire electrodes131. The wire may be made of a metal including, but not limited to, tungsten, hardened stainless steel or nichrome.

FIG. 2aalso shows how the collection tray110can be removed from the collection chamber108and replaced during operation using a vacuum slide gate169. The vacuum slide gate169is closed and then the collection tray110is removed from the side of the collection chamber108. There are a number of other possible collection tray designs and methods that could be used. The one shown is preferable for a coal stove application.FIGS. 3aand 3bshow a top view of the discharge electrode scraping tubes162in a completed scraping position.

FIGS. 4 and 5illustrate the moveable horizontal discharge wire electrodes131passing through a fixed concentric short length scraper tube172to remove material on the discharge wire electrodes131. Both of the short length scraper tubes172are preferably supported by dielectric panels185.FIG. 4shows the discharge wire or rod electrodes131in operating position andFIG. 5shows the discharge wire electrodes131retracted after being drawn through the scraper tube172. One of the differences betweenFIGS. 2 and 3andFIGS. 4 and 5is that, inFIGS. 4 and 5, the discharge wire electrodes131can be of a smaller diameter, requiring less power to generate an electrical discharge to charge the particulates.FIG. 5also shows that the discharge electrode support bar183does not move in front of the disc electrodes132. Instead, it remains outside the main air stream. This embodiment also preferably includes using higher refractory dielectric materials in any location the horizontal discharge electrodes131pass through. As one example, wear resistant non-conductive refractory tubes172are embededd in the dielectric panels185.

FIG. 6shows an electrode configuration that permits the heating of the horizontal discharge electrodes131prior to scraping and converts the collected material on the horizontal discharge electrode131surface into a powdery state that is relatively easy to remove with the tubular scrapers146. In this embodiment, the horizontal discharge electrodes131are preferably fastened at both ends to electrical terminal connectors114. Also, the wiring of the discharge electrode circuit may be changed from HVDC (high voltage direct current) to the AC power during the cleaning process. A high current AC circuit heats the horizontal discharge electrodes prior to cleaning the horizontal discharge electrodes.

A heating process may be required because the exhaust from burning coal or wood can produce a creosote soot that is difficult to remove from the discharge electrodes. One solution is to heat the discharge electrodes long enough to break the compounds down until the material can be remove by the scraping tube. The temperature and heating time for coal is higher and longer and generally occurs only at start up.

FIG. 4also shows the use of extra thermal dielectric material119for this embodiment. The enclosure material is preferably made of a combination of conductive and non conductive materials.

Other benefits derived from using horizontal discharge electrodes131are shown inFIGS. 7 and 8.FIG. 7shows a side view of the electrical flux pattern161generated by the emission of ions that follows the periphery or the leading edge166of a circular disc electrode132.

FIG. 8is a front view that shows the electrical flux pattern161extending to the sides of the circular disc electrodes132. The electric field or flux pattern161was derived from viewing the distribution pattern of particles collected.

FIGS. 1 and 5show the relative position of the disc edge scraper165. In each of these embodiments, the disc edge scraper165is located below and out of the main air stream.

FIGS. 9athru9gshow examples of the scrapers and how they are used in the disc electrostatic precipitator.FIG. 9ashows a discharge tube scraper146moving forward and removing material182deposited on a horizontal discharge electrode wire131. In one example, a dimension for the discharge wire electrode is 0.025″ and the discharge tube scraper146has a 0.027 inner diameter with a 0.007″ thick wall. The necessary thickness for the tube walls depends on the difficulty of removing the material from the horizontal discharge electrodes131. While relatively thin walls could be used, in alternative embodiments, tubes with thicker walls could be used.

FIGS. 9bthrough 9fshow different ways the discharge wire electrode131can be operated.

FIG. 9bshows the discharge tube scraper146in an operating position and the horizontal discharge electrode131attached at both ends to electrical terminal connectors114.FIG. 9cshows where the scraper tube bar148moves the discharge tube scraper146over the horizontal discharge electrode131to remove the collected material182(shown inFIG. 9a). This electrode arrangement may be used in standard operation when the horizontal discharge electrode131is heated.

FIG. 9dshows a discharge tube scraper146in operating position over the horizontal discharge electrode131. In this embodiment, the discharge wire electrode131has only one end attached to an electrical terminal connector114. The open end163results in an open space168for material to fall off during scraping.FIG. 9dalso shows a large, stationary tube scraper162that can scrape the discharge tube scraper146.

FIG. 9eshows a design where the horizontal discharge electrode131moves back and forth by moving the discharge electrode support bar183.FIG. 9ealso shows two discharge tube scrapers172. Cleaning the horizontal discharge electrode131takes place at both stationary short tube scraper172locations. The stationary short tube scrapers172may be made from conductive or non-conductive material. Both short tube scrapers172are supported by dielectric panels185.

FIG. 9fshows the movable horizontal discharge electrodes131in the main air stream. Cleaning takes place when the horizontal discharge electrode131are retracted out of the main air stream and passes through the shorter scraper tube172and when the horizontal discharge electrode131returns to its operating position.

FIG. 9gshows a single blade disc edge scraper165, which is preferably a flat, thin plate or blade165, used to clean the leading edge166(shown inFIG. 7) of the disc electrode132. The flat plate165is set at a scraping operating angle such that scraped material falls by gravity into the collection chamber. The flat plate165is located out of the main air flow to prevent re-entrainment of particles back into the main air stream. In order to keep light pressure on the leading edge166of the disc electrode132, a torsion spring (not shown) is mounted in the disc edge scraper support blocks184.

FIGS. 10athrough 10dshow cross sectional views of a thin flat disc scraper142that fits into a groove174machined into the disc spacer block136and into the scraper shaft spacer block176that controls the distance between the disc electrodes132and the disc scraper142.FIG. 10ashows clearance holes177and178, required for both the disc rotating shaft135and the scraper stationary shaft149. This embodiment allows for free movement of the disc electrode132and closer control in the spacing between the disc electrode132and the disc scraper142. The disc scraper blade142shown inFIGS. 10athrough 10dis preferably made from thin gauge spring hardened metal, such as stainless steel.

FIG. 11shows a cross sectional side view of a multi field electrostatic precipitator. This embodiment could be used for higher flow applications. The overall size and the number of fields are based on many factors, including, but not limited to, the solids concentration, type of material to be collected and CFM requirements.

FIG. 11shows the basic location of the disc leading edge scraper165. In this position, material scraped from the disc leading edge will fall by gravity into the collection hopper180and be removed from the precipitator by the auger181. A field divider179is also shown. The field divider179keeps the main air flow105in the upper half of the disc electrode132.