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Air Pollution Control Systems for Boiler and Incinerators Part 12

Tham khảo tài liệu 'air pollution control systems for boiler and incinerators part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TM 5-815-1 AFR 19-6 13-4. Fluidized bed performance a. With the exception of a baghouse or precipitator which is required for particulate removal additional gas cleaning devices are not required for environmental control with fluidized bed systems. b. Fluidized bed boilers are able to remove sulfur dioxide directly in the combustor. This is accomplished by using limestone in the fluid bed. The limestone calcines to form calcium oxide CaO and then reacts with SO2 to form calcium sulfate as follows CaCOg------- CaO co2 CaO S02 1 2 02 ------ - CaS04 The ideal temperature range for desulfurization in a fluidized bed is about 1600 degrees Fahrenheit. c. A bubbling fluidized bed boiler will require a higher calcium to sulfur ratio for control of SO2 while the circulating fluidized bed boiler can achieve similar SO2 removal with the Ca S ratio of 1.5 to 2. See figure 13-8. d. Nitrogen oxide is controlled by distribution of primary air under the bed and secondary air part way up the combustor. The staging of combustion limits the nitrogen oxide to that which is formed only by fuelbound nitrogen. Thermally formed nitrogen oxide is negligible in the fluidized bed. See figure 13-9 for predicted nitrogen oxide emissions. e. Several fluidized bed boiler manufacturers are now offering performance guarantees based upon experience in the bubbling circulating and dual bed designs. 13-5. Materials and construction The materials used for construction of fluidized bed units are similar to those used in conventional boilers depending on the design pressure and temperature of the system. a. In-bed tubes. The fluidized bed boilers that have in-bed tubes have experienced high erosion rates in some cases. Vertically oriented tubes are less prone to erosion than the horizontal ones. Where in-bed tubes are used consideration should be given to use of thicker walls on the tubes and their metallurgy. Wear fins can be installed to reduce erosion. Also some corrosion may be experienced due to .