Integrated flue gas processing method

• US 4,364,910 A
• Filed: 06/08/1981
• Issued: 12/21/1982
• Est. Priority Date: 03/13/1980
• Status: Expired due to Term

• Current Assignee: Peabody Process Systems Incorporated
• Original Assignee: Peabody Process Systems Incorporated
• Inventors: Bakke, Even, Willett, Howard P.
• Primary Examiner(s): Thomas, Earl C.
• Assistant Examiner(s): Heller, Gregory A.
• Application Number:
  US06/271,512
• Time in Patent Office: 561 Days
• Field of Search: 423/242 A, 423/242 R, 423/244 A, 423/244 R, 55/8, 55/9, 55/10, 55/11
• US Class Current: 423/243.01
• CPC Class Codes: B01D 47/06 Spray cleaning
• CPC Class Codes: B01D 53/48 Sulfur compounds
• CPC Class Codes: B01D 53/50 Sulfur oxides B01D53/60 takes precedence
• CPC Class Codes: B01D 53/501 by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
• CPC Class Codes: B03C 3/017 Combinations of electrostatic separation with other processes, not otherwise provided for
• CPC Class Codes: B03C 3/16 wet type
• CPC Class Codes: B03C 3/41 Ionising-electrodes
• CPC Class Codes: B03C 3/53 Liquid, or liquid-film, electrodes

Abstract

A system and process for flue gas processing to remove both gaseous contaminants such as sulfur dioxide and particulate matter such as flyash integrates spray scrubbing apparatus and wet electrostatic precipitation apparatus and provides for the advantageous extraction and utilization of heat present in the flue gas which is being processed. The integrated system and process utilizes a spray scrubbing tower into which the flue gas is introduced and into which aqueous alkali slurry is introduced as spray for sulfur dioxide removal therein. The flue gas leaves the tower moisture laden and enters a wet electrostatic precipitator which includes a heat exchanger where flyash and entrained droplets in the flue gas are removed by electrostatic precipitation and heat is removed from the flue gas. The cleaned flue gas exits from the precipitator and discharges into a stack. The heat removed from the flue gas finds use in the system or otherwise in the steam generation plant. The wet electrostatic precipitator of the integrated system and process includes a portion constructed as a cross flow heat exchanger with flue gas saturated with water vapor moving vertically upwards inside tubes arranged in a staggered pattern and ambient air being pulled horizontally across the outside of those tubes to cool the tube walls and thereby remove heat from the flue gas and cause condensation of water vapor on the inside wall surfaces. The condensate washes the electrostatically collected flyash particles down from the inside tube walls. The heat that is extracted from the saturated flue gas in the wet electrostatic precipitator heat exchanger may be utilized in several different ways, including: (1) for flue gas reheat after the wet electrostatic precipitator; (2) for preheating of combustion air to the steam generator boiler; and, (3) for heating of buildings. The integrated flue gas processing system and process of this invention provides many advantages resulting in increased efficiency and improved economy of flue gas cleaning and wide application of use.

Claims

1. An integrated process for removing sulfur dioxide and flyash from flue gas comprising feeding flue gas to a scrubber-quencher, introducing aqueous slurry to the scrubber-quencher, saturating the flue gas with water vapor, removing coarse flyash particles from the flue gas in the scrubber-quencher, conducting the flue gas to a spray tower for upward flow therein, spraying alkali slurry into the flue gas within the tower to absorb and react with the sulfur dioxide therein, recirculating slurry containing absorbed sulfur dioxide to increase the residence time for the reaction of alkali and sulfur dioxide, removing slurry containing reaction products of alkali and sulfur dioxide and precipitated flyash from the tower, dewatering the slurry so removed to obtain a waste product, passing the flue gas through an interface tray located in the tower downstream of the alkali slurry spray, spraying the interface tray with an unreactive aqueous solution to substantially saturate the flue gas, passing the flue gas through a wet electrostatic precipitator located downstream of the spray tower, electrostatically precipitating flyash and entrained slurry droplets from the flue gas, removing heat from the saturated flue gas passing through the wet electrostatic precipitator by causing ambient air to flow across the outside of precipitation tubes through which the flue gas passes, heating the flowing ambient air, cooling the precipitation tube walls, causing condensation of water vapor in the flue gas on the tube walls, conducting the heated flowing ambient air away from the precipitator and utilizing the heat therein.

2. An integrated process for removing sulfur dioxide and flyash from flue gas as claimed in claim 1 wherein the utilization of the heat in the heated ambient air comprises mixing the air with the flue gas leaving the wet electrostatic precipitator and heating the flue gas.

3. An integrated process for removing sulfur dioxide and flyash from flue gas as claimed in claim 2 wherein the utilization of the heat in the heated ambient air comprises mixing at least part of the air with combustion air for the boiler furnace the flue gas of which is being processed and heating the combustion air.

4. an integrated process for removing sulfur dioxide and flyash from flue gas as claimed in claim 3 wherein the utilization of the heat in the heated ambient air further comprises mixing at least a portion of the air with the flue gas leaving the wet electrostatic precipitator and heating the flue gas.

5. An integrated process for removing sulfur dioxide and flyash from flue gas as claimed in claim 2, 3 or 4 further comprising further heating the heated ambient air prior to utilizing it.

6. An integrated process for removing sulfur dioxide and flyash from flue gas as claimed in claim 1 further comprising producing a totally symmetric electrostatic field when electrostatically precipitating the flyash and entrained slurry droplets from the flue gas.

7. An integrated process for processing hot flue gas in a processing system by removing both particulate material such as flyash and gaseous contaminants such as sulfur dioxide from the hot flue gas comprising feeding hot flue gas to a scrubbing tower for upward flow therein, spraying alkali slurry into the flue gas to react with sulfur dioxide therein, substantially saturating the flue gas passing the scrubbed flue gas to electrostatic precipitation means for precipitating flyash from the scrubbed flue gas, passing the scrubbed flue gas through a channel defined by discharge electrode means and collection electrode means in the electrostatic precipitator means, circulating air in a chamber located in proximity to the collection electrode means to heat the air and to remove heat from the flue gas passing through the channel between the discharge electrode means and collection electrode means to condense water on the collection electrode means, conducting the heated air to mixing means and mixing the heated air with one or more gas streams in the processing system to utilize the heat removed from the saturated flue gas within the processing system to contribute to heating of the gas stream with which the heated air is mixed.

8. The integrated process for processing hot flue gas as claimed in claim 7 wherein the air in the chamber cools the collection electrode means sufficiently to condense water vapor present in the scrubbed flue gas on the surface thereof to flush the collection electrode surface of particles precipitated thereon.

9. The integrated process for processing hot flue gas as claimed in claim 7 wherein the mixing with the heated air comprises mixing the heated air with the cleaned flue gas stream exiting from the wet electrostatic precipitator means for reheating it.

10. The integrated process for processing hot flue gas as claimed in claim 7 wherein the mixing with the heated air comprises mixing the heated air with combustion air fed to a boiler from which the flue gas emanates for preheating it.

11. The integrated process for processing hot flue gas as claimed in claim 10 further comprising further heating the mixed heated air and combustion air and conducting a portion of the thus heated mixed air stream and mixing it with the cleaned flue gas stream exiting from the wet electrostatic precipitator for reheating it.

12. The integrated process for processing hot flue gas as claimed in claim 7, 8, 9, 10 or 11 comprising a high strength electric field between the collection electrode means and the discharge electrode means;

whereby a substantially symmetrical, high density current flow between the discharge electrode and the collection tube is created when high voltage is applied to the discharge electrode.

13. An integrated process for removing sulfur dioxide and flyash from hot flue gas comprising feeding hot flue gas from a boiler furnace to a venturi scrubber quencher, introducing aqueous slurry to the venturi scrubber quencher to saturate the flue gas with water vapor and remove coarse flyash particles from the flue gas, conducting the flue gas from the venturi scrubber quencher to a scrubbing tower for upward flow therein, spraying alkali slurry into the flue gas within the tower to absorb and react with the sulfur dioxide therein, collecting and recirculating slurry containing absorbed sulfur dioxide for use for alkali slurry spraying within the tank to increase the residence time for the reaction of alkali and sulfur dioxide, removing slurry containing reaction products of alkali and sulfur dioxide and precipitated flyash from the tower, dewatering the slurry so removed to obtain a waste product, spraying an interface tray means located downstream of the loation of alkali spraying with an unreactive aqueous solution to saturate the flue gas stream, directing the scrubbed flue gas to a wet electrostatic precipitator comprising a cross flow heat exchanger having collection electrode tubes through which the flue gas passes, the tubes being arranged between tube sheets, causing ambient air to flow across the outside of the tubes to remove heat from the flue gas and heat the flowing ambient air to cool the tube walls to cause condensation on the tube wall surfaces, conducting the heated flowing ambient air to mixing means and mixing at least part of the heated air with combustion air for the boiler furnace to preheat the combustion air, passing the mixed air stream through a preheater means, separating and conducting a portion of the further preheated mixed air stream to further mixing means and mixing it with the cleaned flue gas stream leaving the wet electrostatic precipitator to reheat it.