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This paper presents experimental results of NO_x emission measurements for combustion of two kinds of coal in a bubbling fluidized bed combustor. The tested fuels were Czech brown coal (CBC) and German young brown coal (GYC). These fuels have different nitrogen contents. The experiments were performed in the pilot scale BFB experimental unit with power output of 500 kW. The influence of several parameters on NO_x formation are investigated in this paper. The parameters studied here include the effect of the nitrogen content in the fuel, the effect of the oxygen concentration in the bed, the effect of bed temperature, the effect of air staging, and the effect of fluidization velocity. Significantly different behaviour of the fuels was found. Although GYC has a lower nitrogen content than CBC, it is more reactive and produces higher NO_x emissions. The biggest dependence of NO_x production for CBC was found for the effects of air staging and fluidization velocity. As the fluidization velocity increases and the amount of secondary air decreases, there is an increase in NOx emissions. The oxygen concentration in the bed has the strongest effect on the NO_x production of GYCs. With increasing oxygen concentration, the production of NO_x also increases. On the basis of the NO_x measurements, the N-NO conversion factor was calculated and the effect of the operating parameters on this conversion factor was investigated.

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Oxyfuel combustion is a promising approach for capturing CO₂ from power plants. This technology produces a flue gas with a high concentration of CO₂. Our paper presents a verification of the oxyfuel combustion conditions in a bubbling fluidized bed combustor. It presents a theoretical analysis of oxyfuel combustion and makes a comparison with combustion using air. It is important to establish a proper methodology for stoichiometric calculations and for computing the basic characteristic fluidization properties. The methodology presented here has been developed for general purposes, and can be applied to calculations for combustion with air and with oxygen-enriched air, and also for full oxyfuel conditions. With this methodology, we can include any water vapour condensation during recirculation of the flue gas when dry flue gas recirculation is used. The paper contains calculations for a lignite coal, which is taken as a reference fuel for future research and for the experiments.