US 3581463 A
Description (OCR text may contain errors)
United States Patent  Inventor Lawrence M. Roberts Bound Brook, NJ. 211 Appl. No. 678,300  Filed Oct. 26, 1967  Patented June 1, 1971  Assignee Research-CottrelLlnc. Somerset County, NJ.
[541 ELECTROSTATIC GAS CLEANING 3 Claims, 1 Drawing Fig.
 U.S.Cl. 55/4, 23/2, 23/175, 55/5,55/11, 55/106, 55/128, 55/135, 55/ 136  Int. Cl B03c 3/01  Field oiSearch 55/2, 5,11, 101,122,134,135,4,106,128,136;23/2, 2.2, 174, 175
 References Cited UNlTED STATES PATENTS 334,158 l/1886 Beard 55/220X 1,291,745 l/l9l9 Bradley 55/5 2,180,727 11/1939 Carter 23/175 2,537,558 1/1951 Tigges 55/124X 2,696,892 12/1954 Campbell 55/122X 2,706,533 4/1955 Hedberg et a1. 55/135X 2,740,493 4/ 1956 Wintermute 55/127X 2,746,563 5/1956 Harlow 23/175X 2,758,666 8/ 1956 Prentiss 55/124X 2,795,401 6/1957 Cooper et a1. 55/135X 2,841,242 7/1958 Hall 23/174X 3,054,243 9/ 1962 Howe 55/1 1 3,132,473 S/1964 Hass 60/29 all- OTHER REFERENCES White, Harry J., industrial Electrostatic Precipitation, Addison-Wesley Publishing Company, 1nc., Reading, Massachusetts, 1963, pages 294, 295, and 303- 305 (copy in Technical Library, Call No. TP 156 p7w5i) Primary Examiner-Dennis E. Talbert, Jr. Attorney-Stowell & Stowell 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.
PATENTEU JUN 1 I971 3,581,463
INVENTUR LAWRENCE. M ROBERTS ATTURNHY ELECTROSTATIC GAS CLEANING 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 sub jecting 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 tem' perature, for example, from about 800 to about l,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 is the main flue leading from the combustion chamber ofa coal fired boiler (not shown) through air preheater ll, electrical precipitator l2 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 l5 and catalyst chamber 16 back to the main flue upstream of the main precipitator I2.
In a typical operation, 2 percent of the combustion gases coming from the boiler at about 800 F. and containing about 0.l 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 l2.
l. 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 ortion of the as stream being equivalent to from about 0. 01 percent to a out 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 I 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 l,000 F. and particulate content is removed from the mixed gases by electrical precipitation at a temperature of about 300 F.