Local measurements of concentrations of O2, CO2, CO, NO and SO2 were carried out inside the 235 MWe circulating fluidized bed boiler no. 3 Turow power plant. The combustion chamber had a cross-sectional area of 21.1 × 9.9 m2 and a height of 43 m. Water-cooled probes with a length of 4.7 m were used to take samples from inside the boiler. 20 ports in 5 different heights were used to introduce the probes. The penetration depth inside the boiler was up to 3 m. The sampled gas was led to online analyzers. Even though the number of ports and the penetration length was not sufficient to get a full 3-D mapping of the concentrations the measured horizontal and vertical gas concentration profiles of NO, CO, CO2, O2 and SO2 clearly indicate a core/annulus structure with a wall layer thickness of about 0.5–1 m. Significant differences are observed between gas concentrations near the front wall and those near the rear wall which indicate an uneven distribution of fuel. One consequence is the formation of plumes with high concentrations of CO, NO, CO2 and SO2 near the front wall which extend up to the exit region. The fact that nevertheless the stack emissions are still below the legal limits may be attributed to the excellent performance of the cyclones as gas mixers and post combustion reactors.

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