CA1141308A - Oxides of nitrogen for improving electrostatic precipitation of dust particles - Google Patents
Oxides of nitrogen for improving electrostatic precipitation of dust particlesInfo
- Publication number
- CA1141308A CA1141308A CA000354976A CA354976A CA1141308A CA 1141308 A CA1141308 A CA 1141308A CA 000354976 A CA000354976 A CA 000354976A CA 354976 A CA354976 A CA 354976A CA 1141308 A CA1141308 A CA 1141308A
- Authority
- CA
- Canada
- Prior art keywords
- nitrogen
- oxide
- stream
- gas
- space charge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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- Treating Waste Gases (AREA)
- Electrostatic Separation (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method is disclosed of increasing the space charge in a stream of particle-laden gas formed by the burning of coal, which particles are collected by an electrostatic precipitator. The method comprises treating the gas-containing particles prior to contact with the electrostatic pre-cipitator at a temperature not greater than about 1800°F with a space charge increasing amount of an oxide of nitrogen and thereafter passing the gas to the electrostatic precipitator.
A method is disclosed of increasing the space charge in a stream of particle-laden gas formed by the burning of coal, which particles are collected by an electrostatic precipitator. The method comprises treating the gas-containing particles prior to contact with the electrostatic pre-cipitator at a temperature not greater than about 1800°F with a space charge increasing amount of an oxide of nitrogen and thereafter passing the gas to the electrostatic precipitator.
Description
~14i308 This invention relates to a method of increasing the space charge in a stream of particle-laden gas.
A conventional way of separating dust particles from a gas stream in which the particles are entrained is by the use of an electrostatic pre-cipitator. This apparatus utilizes the corona discharge effect, i.e., the ionization of the particles by passing them through an ionization field es-tablished by a plurality of discharge electrode wires suspended in a parallel plane with a grounded collecting electrode plate. The ionized particles are attracted to the collector plate from which they may be removed by vibrating or rapping the plate. Examples of this type precipitator are found in Cummings United States Patent ~o. 3,109,720 and Pennington United States Patent No. 3,030,753.
Efficient capture of dust particles by a precipitator depends chiefly upon precipitator size and the precipitation rate parameter. The precipitation rate parameter (otherwise known as "migration velocity") is defined by:
_ k ~ E ~:1 d ~, .., where k = constant ~ = permittivity ~c = charging field = collecting field = particle diameter ~ gas viscosity The migration velocity is seen to depend linearly on both the charging and collecting field. The collecting field is most affected by space charge since i3~)8 its polarity (+) attracts the negative (space) charges. This change in space charge density (an increase at the collection plate) causes a larger E2 and thus a larger precipitation rate parameter.
These effects are illustrated graphically in the attached Figures wherein:
Figure 1 represents the magnitude of the electric field between the corona wire and the collection plate without a space charge increase; and Figure 2 represents the magnitude of the electric field between the corona wire and the collection plate with a space charge increase.
The change in space charge is manifested by an increase in secondary voltage, lower current, and higher collection rates for a given power input.
This is routinely observed in full size and pilot precipitators. We have demonstrated in a pilot precipitator that the introduction of an oxide of nitrogen does increase space charge and manifest these results.
It has now been found that the electrostatic removal of particles entrained in a gas stream can be improved by the addition to such gas stream of preselected amounts of an oxide of nitrogen. Accordingly the invention provides a method of increasing the space charge in a stream of particle-laden gas formed by the burning of coal, which particles are collected by an electro-static precipitator, which method comprises treating the stream of particle-laden gas prior to contact with the electrostatic precipitator at a temperature not greater than about 1800F with a space charge increasing amount of an oxide of nitrogen or a nitrogen compound which decomposes under the conditions of use to provide a space charge increasing amount of an oxide of nitrogen, and then passing the gas to the electrostatic precipitator.
The amount of the oxide of nitrogen that is effective in decreasing the resistivity of the dust particles may vary. Generally it is used in an
A conventional way of separating dust particles from a gas stream in which the particles are entrained is by the use of an electrostatic pre-cipitator. This apparatus utilizes the corona discharge effect, i.e., the ionization of the particles by passing them through an ionization field es-tablished by a plurality of discharge electrode wires suspended in a parallel plane with a grounded collecting electrode plate. The ionized particles are attracted to the collector plate from which they may be removed by vibrating or rapping the plate. Examples of this type precipitator are found in Cummings United States Patent ~o. 3,109,720 and Pennington United States Patent No. 3,030,753.
Efficient capture of dust particles by a precipitator depends chiefly upon precipitator size and the precipitation rate parameter. The precipitation rate parameter (otherwise known as "migration velocity") is defined by:
_ k ~ E ~:1 d ~, .., where k = constant ~ = permittivity ~c = charging field = collecting field = particle diameter ~ gas viscosity The migration velocity is seen to depend linearly on both the charging and collecting field. The collecting field is most affected by space charge since i3~)8 its polarity (+) attracts the negative (space) charges. This change in space charge density (an increase at the collection plate) causes a larger E2 and thus a larger precipitation rate parameter.
These effects are illustrated graphically in the attached Figures wherein:
Figure 1 represents the magnitude of the electric field between the corona wire and the collection plate without a space charge increase; and Figure 2 represents the magnitude of the electric field between the corona wire and the collection plate with a space charge increase.
The change in space charge is manifested by an increase in secondary voltage, lower current, and higher collection rates for a given power input.
This is routinely observed in full size and pilot precipitators. We have demonstrated in a pilot precipitator that the introduction of an oxide of nitrogen does increase space charge and manifest these results.
It has now been found that the electrostatic removal of particles entrained in a gas stream can be improved by the addition to such gas stream of preselected amounts of an oxide of nitrogen. Accordingly the invention provides a method of increasing the space charge in a stream of particle-laden gas formed by the burning of coal, which particles are collected by an electro-static precipitator, which method comprises treating the stream of particle-laden gas prior to contact with the electrostatic precipitator at a temperature not greater than about 1800F with a space charge increasing amount of an oxide of nitrogen or a nitrogen compound which decomposes under the conditions of use to provide a space charge increasing amount of an oxide of nitrogen, and then passing the gas to the electrostatic precipitator.
The amount of the oxide of nitrogen that is effective in decreasing the resistivity of the dust particles may vary. Generally it is used in an
- 2 -~1413~
amount ranging from 0.1 up to about 6 weight percent based on the weight of the particles presen~ in the gas stream. In a preferred embodiment, the dosage ranges between 0.5 - 3% by weight.
Most large coal-fired boilers are composed of a number of regions These regions, starting with the combustion flame and ending with the t. - 2a -11413~8 electrostatic precipitator which, in most instances, is located prior to the exhaust gas stac~, form a series of progressively cooler gas temperature zones. For purpose of simplification, these zones and their respective tem-peratures are set forth below in a simplified manner:
Location Temperature In the flame 2500 - 3500F.
In the furnace-radiant section 2000 - 2500F.
After super heater 1000 - 1600F.
After economizer 500 - 750F.
After air heater 250 - 350F.
Up the stack 250 - 350F.
The oxide of nitrogen is added to the gas stream at a temperature in excess of about 250F., but, preferably, at a temperature greater than 600F. In certain instances, they can be employed at temperatures as high as 1800F.
The oxides of nitrogen that may be used in the practice of the invention may be selected from the following oxides: N20, N0 or (N0)2, N203, N02 or (N02)2, or N205. Of these oxides, N02 is preferred. While the oxides may be used as such, the invention also contemplates using com-pounds which, under conditions of use, decompose to 1 or more of the oxidesof nitrogen mentioned above. Specifically it is possible to use nitric acid or nitrate salts such as manganese nitrate which decomposes to form N02.
Example Using nitric acid as a source of N02, tests were conducted in a laboratory electrostatic precipitator. These tests showed an approximate 45 reduction in emissions when HN03 was decomposed in flue gas at 400F., at a rate of 0.57% by wt. fly ash. By this application, the applied voltage im-mediately jumped 2Kv while corona current decreased 45~a.
amount ranging from 0.1 up to about 6 weight percent based on the weight of the particles presen~ in the gas stream. In a preferred embodiment, the dosage ranges between 0.5 - 3% by weight.
Most large coal-fired boilers are composed of a number of regions These regions, starting with the combustion flame and ending with the t. - 2a -11413~8 electrostatic precipitator which, in most instances, is located prior to the exhaust gas stac~, form a series of progressively cooler gas temperature zones. For purpose of simplification, these zones and their respective tem-peratures are set forth below in a simplified manner:
Location Temperature In the flame 2500 - 3500F.
In the furnace-radiant section 2000 - 2500F.
After super heater 1000 - 1600F.
After economizer 500 - 750F.
After air heater 250 - 350F.
Up the stack 250 - 350F.
The oxide of nitrogen is added to the gas stream at a temperature in excess of about 250F., but, preferably, at a temperature greater than 600F. In certain instances, they can be employed at temperatures as high as 1800F.
The oxides of nitrogen that may be used in the practice of the invention may be selected from the following oxides: N20, N0 or (N0)2, N203, N02 or (N02)2, or N205. Of these oxides, N02 is preferred. While the oxides may be used as such, the invention also contemplates using com-pounds which, under conditions of use, decompose to 1 or more of the oxidesof nitrogen mentioned above. Specifically it is possible to use nitric acid or nitrate salts such as manganese nitrate which decomposes to form N02.
Example Using nitric acid as a source of N02, tests were conducted in a laboratory electrostatic precipitator. These tests showed an approximate 45 reduction in emissions when HN03 was decomposed in flue gas at 400F., at a rate of 0.57% by wt. fly ash. By this application, the applied voltage im-mediately jumped 2Kv while corona current decreased 45~a.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of increasing the space charge in a stream of particle-laden gas formed by the burning of coal, which particles are collected by an electrostatic precipitator, which method comprises treating the stream of particle-laden gas prior to contact with the electrostatic precipitator at a temperature not greater than about 1800°F with a space charge increasing amount of an oxide of nitrogen or a nitrogen compound which decomposes under the conditions of use to provide a space charge increasing amount of an oxide of nitrogen, and then passing the gas to the electrostatic precipitator.
2. The method of Claim 1 wherein the oxide of nitrogen is NO2.
3. The method of Claim 1 wherein from 0.1 to 6 weight percent of oxide of nitrogen is used, based on the weight of the particles present in the gas stream.
4. The method of Claim 1 wherein from 0.5 to 3 weight percent of oxide of nitrogen is used, based on the weight of the particles present in the gas stream.
5. The method of Claim 1 wherein the stream of particle-laden gas is treated at a temperature of above about 600°F.
6. The method of Claim 1 wherein the stream of particle-laden gas is treated at a temperature of above about 250°F.
7. The method of Claim 1 wherein an oxide of nitrogen is used.
8. The method of Claim 1 wherein a nitrogen compound is used.
9. The method of Claim 8 wherein the nitrogen compound is chosen from nitric acid and nitrate salts.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US5311779A | 1979-06-28 | 1979-06-28 | |
| US53,117 | 1979-06-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1141308A true CA1141308A (en) | 1983-02-15 |
Family
ID=21982029
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000354976A Expired CA1141308A (en) | 1979-06-28 | 1980-06-27 | Oxides of nitrogen for improving electrostatic precipitation of dust particles |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1141308A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6224653B1 (en) * | 1998-12-29 | 2001-05-01 | Pulsatron Technology Corporation | Electrostatic method and means for removing contaminants from gases |
-
1980
- 1980-06-27 CA CA000354976A patent/CA1141308A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6224653B1 (en) * | 1998-12-29 | 2001-05-01 | Pulsatron Technology Corporation | Electrostatic method and means for removing contaminants from gases |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |