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ABS"rRACT-This paper presents and discusses measurements oflocal flame temperature, local gas species concentrations and incident wall heat fluxes obtained in a 250 MWe residual fuel-oil front fired utility boiler. The work is aimed at improving knowledge of the efficiency of the thermal processes involved in large industrial boilers and covers three different operating conditions, which include load and air-fuel ratio variations.The measurements were made using special design probes through the ports available for inspection of the boiler. Local gas temperatures varied between 1650°C in the centre of the flames attached to the burners to around t tOOtlC close to the boiler nose, with maximum variations in the plane of the burners between the front and rear walls of about 200'C. The levels orco were as high as 2% close to the ash pit and reach I % near the boiler nose, suggesting some limitations in the process of fuel burnout and CO oxidation. Wall incident total heat fluxes varied between 200 kW1m' and 400 kW1m', with the values increased by 30% with the variation from clean to slag wall conditions. This is associated with an increase in the local gas temperatures of at least 100°C, which promotes the deterioration of the boiler. The results are used to assess boiler performance for burning low-quality fuels and are important for validation of mathematical models to be used to interpolate and extrapolate the experimentally acquired information.

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