The combustion rate of large coal particles in a fluidized bed is to a large extent controlled by the external diffusion. This rate will depend on the particle diameter. There are several processes that affect this diameter: the combustion process itself; attrition; fragmentation; and swelling. The last two processes can cause large diameter changes in a relatively short period, mainly during devolatilization. The experiments reported in this paper are aimed at finding a simple relationship between some properties of the parent coal particles, and the fragmentation and swelling during devolatilization.

The acoustic power of an oscillating flame is measured. A turbulent premixed propane/air flame is situated near a pressure antinode of a standing wave in a laboratory combustion chamber. This standing wave is generated by a piston. The fluctuating heat release of the flame will supply acoustic power to the standing wave as postulated by Rayleigh. This flame acoustic power is obtained by setting up a power balance of the whole combustion chamber.Experiments proved that it is possible to measure quantitatively the acoustic power and the frequency change as a function of relevant parameters. This frequency change is a second phenomenon described by Rayleigh. The acoustic power of the flame as a function of the amplitude of the fluctuating component of the mixture flow velocity at different frequencies can be measured.Measurement techniques are described and results for frequencies ranging from 3 to 120 Hz are given.Address: M. Valk, Technische Hogeschool Twente,

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The 'thermal deN0,' process using urea has been investigated in a 1 MW fluidized bed combustor. NO, reductions of up to 76% were obtainable by using this method. The experimental results show that urea is at least as active as NH,, which is commonly used in this application, but which is far more toxic and corrosive. Emission levels of 200 mg m -3 for NO, could be achieved by injecting the urea at a height of 2 m above the distribution plate in a molar ratio urea:NO,= 1.5. The SO2 emission value also appeared to be reduced when the urea was injected at a urea:NO, molar ratio ~4.