Title:
ELECTROSTATIC GAS CLEANING
United States Patent 3581463


Abstract:
Suspended matter is removed from combustion gases containing sulfur dioxide by removing a major portion of the particulate matter from a minor portion of the gases, catalytically converting a major portion of the sulfur dioxide content of said minor portion of the gases to sulfur trioxide, mixing said minor portion of the gases with the main gas stream and subjecting the mixed gases to electrical precipitation.



Inventors:
ROBERTS LAWRENCE M
Application Number:
04/678300
Publication Date:
06/01/1971
Filing Date:
10/26/1967
Assignee:
RESEARCH-COTTRELL INC.
Primary Class:
Other Classes:
95/69, 95/73, 96/57, 96/74, 423/215.5, 423/535
International Classes:
B03C3/013; (IPC1-7): B03C3/01
Field of Search:
55/2,5,11,101,122,134,135,4,106,128,136 23
View Patent Images:
US Patent References:
3221475Wet electrostatic precipitator1965-12-07Wiemer
3162518Lead removal device1964-12-22Thomas et al.
3154389Device for catalytic exhaust treatment with particle separation1964-10-27Hayes III, et al.
3132473Exhaust purifying apparatus and method1964-05-12Hass
3054243High temperature electrostatic precipitator and method of operation1962-09-18Bowie
3022989Hydraulic cement process1962-02-27Pyzel
2841242Method for electrostatically treating gases1958-07-01Hall
2795401Precipitator intermediate series air heaters1957-06-11Cooper et al.
2768062Process and apparatus for increasing the so2 content of converter gases1956-10-23Kartenbeck
2758666Carbon black separation1956-08-14Prentiss
2746563Purification of gases1956-05-22Harlow
2740493Gas cleaning method and apparatus1956-04-03Wintermute
2706533Gas conditioning method and apparatus1955-04-19Hedberg et al.
2696892Gas humidifying and electrical precipitation system1954-12-14Campbell
2537558Removal of solids from gases1951-01-09Tigges
2528103Method of producing sulfuric acid and hydraulic cement from gypsum1950-10-31Willson
2471072Manufacture of sulfuric acid1949-05-24Merriam (G)
2384926Process for producing sulphur1945-09-18Jones
2180727Manufacture of sulphuric acid1939-11-21Carter
1969021Pyritic smelting and recovery of sulphur1934-08-07Lenander
1737320Contact process for manufacturing sulphuric acid1929-11-26Merriam (F)
1291745N/A1919-01-21Bradley
1284167N/A1918-11-05Welch
0334158N/A1886-01-12



Foreign References:
FR1445982A
FR1448415A
GB932895A
GB933286A
GB1003377A
Other References:

White, Harry J., Industrial Electrostatic Precipitation, Addison-Wesley Publishing Company, Inc., Reading, Massachusetts, 1963, pages 294, 295, and 303--305 (copy in Technical Library, Call No. TP 156 p7w5i).
Primary Examiner:
Talbert Jr., Dennis E.
Claims:
I claim

1. A method of removing suspended matter from combustion gases containing sulfur dioxide which comprises removing from a minor portion of the gases a major portion of the particulate content thereof, subjecting said minor portion of the gases to the action of a catalyst to convert a major portion of the sulfur dioxide content thereof to sulfur trioxide, mixing said minor portion of the gases with the main gas stream and subjecting the mixed gases to electrical precipitation, the amount of sulfur dioxide converted to sulfur trioxide in said minor portion of the gas stream being equivalent to from about 0.001 percent to about 0.005 percent by volume of the total gas stream coming from the boiler.

2. A method of removing suspended matter from combustion gases as defined in claim 1 wherein the particulate content is removed from the minor portion of the gas stream at a temperature of from about 800° to about 1,000° F.

3. A method of removing suspended matter from combustion gases as defined in claim 1 wherein the particulate content is removed from the minor portion of the gas stream by electrical precipitation at a temperature of about 800° F. to about 1,000° F. and particulate content is removed from the mixed gases by electrical precipitation at a temperature of about 300° F.

Description:
This invention relates to the removal of suspended particulate matter from combustion gases containing sulfur dioxide by subjecting the gases to electrical precipitation in a high potential electrostatic field.

Difficulty has been encountered in the electrical precipitation of suspended particles or fly ash from combustion gases arising from the phenomenon of "back discharge" due to high resistivity of the particulate material and it has been proposed to overcome this difficulty by catalytically converting sulfur dioxide in the gases to sulfur trioxide to increase the conductivity of the particulate material in the gases. However, the catalyst rapidly loses its efficiency and the catalyst bed rapidly increases its resistance to the flow of gases therethrough due to the accumulation of particulate matter thereon.

Since combustion gases typically contain a much larger amount of sulfur dioxide than is required to produce the amount of sulfur trioxide desired for effective conditioning of the particulate material for efficient electrical precipitation, it has been found that these difficulties may be avoided by subjecting only a minor portion of the gases to catalytic sulfur dioxide conversion after removing from such minor portion of the gases a major portion of their suspended particulate matter preferably by electrical precipitation at a high temperature, for example, from about 800° to about 1,000° F. This minor portion of the gas is then mixed with the main gas stream either before or after it has been cooled, for example, in a combustion air preheater, and the mixed gases are subjected to a conventional electrical precipitation operation.

In a typical powdered coal boiler installation the sulfur dioxide content of the combustion gases coming from the boiler would be about 0.1 percent by volume whereas conversion of from 0.001 percent to 0.005 percent of sulfur dioxide by volume to sulfur trioxide would be effective to adequately condition the gases for efficient electrical precipitation of the fly ash. Thus the auxiliary gas cleaner and catalyst chamber needed for the method of the invention would only have to be large enough, in this case, to handle from 1 percent to 5 percent by volume of the combustion gases.

The invention will be more particularly described with reference to the accompanying drawing showing diagrammatically an illustrative form of apparatus embodying the principles of the invention.

In the drawing 10 is the main flue leading from the combustion chamber of a coal fired boiler (not shown) through air preheater 11, electrical precipitator 12 and fan 13 to a chimney stack (not shown). An auxiliary fan 14 draws a small portion of the gases from the main flue and passes them successively through high temperature electrical precipitator 15 and catalyst chamber 16 back to the main flue upstream of the main precipitator 12.

In a typical operation, 2 percent of the combustion gases coming from the boiler at about 800° F. and containing about 0.1 percent by volume of sulfur dioxide are passed by fan 14 through electrostatic cleaner 15 through catalyst chamber 16, where substantially all of the sulfur dioxide is converted to sulfur trioxide by catalyst 17 which may be, for example, a vanadium pentoxide catalyst on silica gel granules or any of the commercially available sulfur dioxide oxidation catalysts. The sulfur trioxide containing gas is then returned to the main gas stream which has been cooled to about 300° F. in heat exchanger 11 and the mixed gases are passed through electrical precipitator 12.