DYNAMICS OF IN-FURNACE PROCESSES IN A CFB BOILER

Paper i proceeding, 2005

With the aim of understanding the dynamics of combustion, this work examines simultaneous fluctuations in fluid dynamic parameters and gas composition in a CFB furnace operated with coal as a fuel. Fluid dynamic parameters are pressure and air flow to the furnace. Gas composition was obtained by a zirconia-cell probe and a gas suction probe connected to a mass spectrometer having a high time resolution (10 Hz). The fluctuations of interest are around 1 Hz and below 0.3 Hz. The fluctuations below 0.3 Hz, which have not been investigated previously, are found to originate from irregularities in the fuel feed. These irregularities give rise to periods of reducing conditions because high inputs of fuel yield an increased pressure in the furnace and a decreased air feed to the furnace, which then occurs concurrent with the release of a high amount of volatiles. There is also a correlation between reducing conditions and the concentration of hydrocarbons.