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NIRE Annual Report
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 1999

Pressurized Fluidized Bed Combustion of Coal

Advanced Combustion Systems Division
Thermal Energy and Combustion Engineering Department
Objectives
Pressurized fluidized bed combustion (PFBC) is one of the future coal firing power generation systems with higher thermal efficiency. Advanced countries are developing full scale PFBC system. Details of combustion characteristics, however, are still unknown. NIRE constructed a very unique lab-scale PFBC system, shown in Figs. 1 and 2, to clear the details of combustion in PFBC. This PFBC
system allows visual observation of hot fluidized bed by using a transparent electric furnace. To simulate the emission characteristics of full scale PFBC, volumetric heat release rate and gas residence time through fluidized bed were fixed to the values matching with those of full scale PFBC.
Fig. 1 Photograph and sketch of pressure vessel. Fig. 1 Photograph and sketch of pressure vessel.
Fig. 1 Photograph and sketch of pressure vessel.

Fig. 2 NIRE's lab-scale PFBC system.
Fig. 2 NIRE's lab-scale PFBC system.
Results
Snap shots of motion pictures by video camera are shown in Fig. 3. Motion of bubbles and burning coal particles are recognized. In PFBC condition, volatiles burn within the fluidized bed and very small part of volatiles escaped to free board. Combustion characteristics, such as combustion efficiency or emissions, agreed with those of full scale PFBC. Thus, it is confirmed that design policy explained above is useful to simulate the combustion behaviors in full scale PFBC by a laboratory scale small PFBC.
Fig. 3 Photograph of buring coal particles in PFBC.
Fig. 3 Photograph of buring coal particles in PFBC.
As an example, effect of operating pressure and O2 partial pressure in flue gas (excess air) on NO emission are shown in Fig. 4. Range of conversion of fuel-N to NO was agreed with that of Wakamatsu pilot PFBC. Linear relationship between O2 partial pressure and NO emission was observed. And effect of operating pressure on NO emission was clearly obtained. NO emission was decreased rapidly with increasing in operating pressure at constant O2 partial pressure. This may be caused by enhancement of NO reduction by char particles because of increase in number density of char particle in higher operating pressure.
Fig. 4 Effect of operating presure on NO emission.
Fig. 4 Effect of operating presure on NO emission.
Selected Publication
1) Suzuki, Y. et al., Proc. 5th SCEJ Symp. on Fluidized Beds, pp. 287, Sapporo 1998.
2) Lin, S. et al., to be published in Chem. Eng. Sci., 1999.
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