DETAILED MEASUREMENTS IN A HEAVY FUEL OIL-FIRED LARGE-SCALE FURNACE

Detailed measurements have been performed for heavy fuel oil (HFO) sprays, generated by a twin-fluid atomiser, in a large-scale laboratory cylindrical furnace. Data are reported for mean gas temperature, major species concentrations (O2, CO2, CO and unburnt hydrocarbons), incident wall radiation flux, flue-gas NOx and solid particulates. Together they allow for an assessment of the effect of the secondary air swirl and excess air levels on the combustion characteristics. The main conclusions drawn are: (i) an increase in secondary air swirl (0.9 to 1.3) leads to improvements in mixing, droplet vaporisation and chemical reaction in the near burner region (NBR). The implications of the changes are manifest in the pollutant emissions wherein the higher swirled flame presents lower exit NOx level due to less “fuel NOx” formation but higher solids emissions due to lower cenospheres residence times in the NBR; (ii) an increase in combustion excess air (l5% to 25%) leads to more combustion in the NBR due to extra O2 and thus more droplet heating and faster vaporisation rates there. The consequences of this increase, apart from reducing the thermal efficiency, are an increase in the exit NOx level due to increased “fuel NOx“formation while the solids emissions are unchanged due to similar cenospheres residence times in the NBR; (iii) NO2 emissions are negligible and solid emissions are essentially cenospheres. There has been scant validation of mathematical models for HFO in the NBR due to the lack of data. Since the NBR plays the dominant role in pollution formation little success in forecasting pollutant emissions can be expected unless the combustion/aerodynamics of it are reasonably well predicted. The data presented herein will help redress this problem. © 1991, Taylor & Francis Group, LLC. All rights reserved.