Oscillating Combustion for NOₓ-Reduction in Pulverized Fuel Boilers

Thermal power plants in various fields of application are regularly adapted to the latest emission standards, applying the "Best Available Techniques Reference".
In recent years, new, stricter limit values have been in force in the power plant sector for power plant units with a thermal output of more than 300 MW that are operated with hard coal. In order to achieve the new limits, e.g. for NOX emissions, downstream reduction processes (Selective Non-Catalytic Reduction, SNCR or Selective Catalytic Reduction) are usually used, which causes an increase of operating fluids (essentially ammonia water).
With an experimentally validated and patented process in which pulverized fuel is fed by oscillation via a swirl burner into a pilot combustion chamber, nitrogen oxides can be reduced without further measures, for example from 450 mg/mN³ in non-oscillation mode (0 Hz) to 280 mg/ mN³ in oscillation mode (3.5 Hz), normalized to an O2 content of 6 % in each case.
Particularly promising are the experiments that use the oscillation of part of the burnt-out air (combustion gas) instead of the fuel in order to minimize, e.g., the wear of the oscillator.
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The present results show that fuel oscillation alone is not sufficient to achieve nitrogen oxide concentrations below the values specified by the legislator. Therefore, a combination of different primary (and secondary) measures is required.
This paper presents experimental results on oscillating coal-dust firing based on a novel expert model. Detailed information on flame stability determination is presented in the accepted paper for INFUB 2022 "A camera-based flame stability controller for non-oscillating and oscillating combustion".