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.
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.
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.
Both the diameter and number of discharge electrodes 131, as well as the spacing blocks 136 (shown in
Cleaning the disc electrode 132 at specific time intervals is achieved by using stationary disc scrapers 142 that are located below the disc drive shaft 135 but not fastened to either the disc rotatable shaft 135 or the scraper stationary shaft 149.
One end of the discharge wire electrodes 131 is fastened to electrical terminal connectors 114 and the other end 163 is left open-ended. A larger tubular scraper 162 that allows the smaller diameter tube scraper 146 to move in for cleaning is located on the bar 167. The tubular scraper 146 is used to clean the discharge wire electrodes 131.
Factors to consider when choosing a material for the tubular scrapers 162 include 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 electrodes 131 are connected to the electrical terminal connectors 114 at a first end and not connected at a second end 163, this leaves an open space 168 between the end 163 of the stationary discharge wire electrodes 131 and the larger tube scraper support bar 167.
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.
Other benefits derived from using horizontal discharge electrodes 131 are shown in
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
This application claims one or more inventions which were disclosed in Provisional Application No. 62/494,588, filed Aug. 15, 2016, entitled “DISCHARGE ELECTRODE ARRANGEMENT FOR DISC ELECTROSTATIC PRECIPITATOR (DEP) AND SCRAPER CONCEPTS FOR BOTH THE DISC AND DISCHARGE ELECTRODES”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.
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“Collection of diesel exhaust particles using electrostatic charging prior to DPF and regeneration of DPF using sliding discharge”, H. Hayashi et al, Toyohashi University of Technology, IJPEST, vol. 6, No. 2, Sep. 2012. |
Electrostatic air filter (electrostatic precipitator) for pollution free industrial emission, Kelantechnics, Klean Environmental Technology (Foshan) CO., LTD., Cylindrical honeycomb kelantechnics electrostatic precipitator,https://www.alibaba.com/product-detail/Electrostatic-Air-Filter-Electrostatic-precipitator-for—358830959.html, at least as early as Jan. 13, 2017. |
Number | Date | Country | |
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62494588 | Aug 2016 | US |