Removal of sulfur and nitrogen oxides from flue gases

#This invention relates to a system for the removal of noxious pollutants, including compounds of sulfur and nitrogen from boiler plant flue gases. It also relates to a system for production of ammonium sulfate by an instantaneous gas phase reaction.

#Boiler plants, particularly those having coal-fired boilers, are well-known sources of pollution. Sulfur emissions from these plants has become a matter of heightened concern in recent years, in light of the perceived effects of "acid rain." Although pollutant emission reduction has long been the object of scientific inquiry, there is still a great demand for methods and apparatus that are effective, easily retrofit onto existing plants, and which convert the collected pollutants into useful and valuable byproducts.

#The prior art recognizes that cooling flue gases that contain sulfur trioxide and water vapor will result in condensation of sulfuric acid. See U.S. Pat. No. 4,526,112 to Warner; U.S. Pat. No. 4,874,585 to Johnson, et al.; U.S. Pat. No. 4,910,011 to Dorr, et al.; and Bovier, Sulfur-Smoke Removal System, 26 Proc. Am. Power Conf. 138 (1964). Other systems of the prior art employ high-volume sprays of water or other liquid agents to scrub particulate matter and pollutants from the flue gas. See U.S. Pat. No. 3,442,232 to White; U.S. Pat. No. 3,456,928 to Selway; and U.S. Pat. No. 3,770,385 to Grey et al.

#FIG. 1 is a flow chart showing the arrangement of the components of the present invention along the flows of flue gas and boiler feedwater in a typical plant application.

#U.S. Pat. Nos. 5,122,352 and 5,198,201 are hereby expressly incorporated by reference herein for their disclosure of a condensing heat exchanger which is the type that can be used to conduct the present process.

#The operation of the preferred embodiment of the present invention may be appreciated by reference to FIG. 1. According to this embodiment, ammonium sulfate or ammonium sulfite, useful as fertilizer, is formed by the introduction of a sufficient amount of an ammoniacal substance such as ammonia or ammonium hydroxide into the flue gas at certain specified locations.

#The flow chart of FIG. 1 shows the basic configuration of a power plant which has been outfitted with the pollution control system of the present invention. In a typical power plant, the coal to be burned is pulverized into dust 50 and is combined with air 60 that has been preheated in conventional air preheaters 70 which heat atmospheric air 80. This forms the fuel which is burned in a boiler furnace 100 which heats the tubes of a heat exchanger 90 to produce steam.