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The possibility of a combined application of coal and biomass using two different co-combustion technologies has been investigated. A blending of pulverized biomass with coal showed a high burnout up to 20% thermal input of biomass for all particle sizes of the biofuels tested. CO emissions were generally lower than 150 mg/m 3 (6% O 2 ) and remain below 100 mg/m 3 in the most cases. Reburn investigations with three pulverized biomasses resulted in NO x emissions of approximately 300 mg/m 3 (6% O 2 ). With pyrolysis gas as reburn fuel, minimum NO x emissions of 200 mg/m 3 (100 ppm) at 6% O 2 in the flue gas are possible. The main parameters are pyrolysis gas composition, stoichiometry, and residence time in the reduction zone. Best minimizing results have been achieved with pyrolysis gas produced at about 800 °C using coal as raw material; using biomass as feedstock, the influence of the pyrolysis temperature is only small. The nitrogen concentration, especially in the tar components of the pyrolysis gas, appears to have a positive effect on NO x reduction in the reburn zone of the combustion reactor.

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