Graville, Stephen Rhys; (1993) Pollutant formation during the combustion of heavy liquid fuels. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In this work, emphasis has been placed on the combustion of heavy fuel oils and their water- continuous emulsions. Current knowledge of pollutant formation from heavy fuel oil is most limited on the formation of NOx and its interaction with other combustion products. A literature review was carried out to establish the interaction of NOx with SOx and particulates in various combustion systems. Investigators have found sulphur both to enhance and reduce NOx formation depending on the fuel, equivalence ratio and the sampling position. A kinetic model was used to predict a reduction in fuel NOx under low temperature turbulent conditions and a reduction in thermal NOx on addition of sulphur. Experimental work was carried out on British Petroleum's (BP) Drop tube furnaces, combustion rigs which correlate well with full-sized plant. Measurements have been made of the evolution and interaction of NOx, and particulates as a function of temperature, residence time, fuel type, equivalence ratio, nitrogen and sulphur level in the fuel and the presence of nitrogen in the combustion air. The spray characteristics from the twin-fluid atomiser used in this work were measured to investigate the effect of spray size distribution on NOx and particulate emissions. The NOx and particulate emissions were much lower for water-continuous emulsion than heavy fuel oil. This has been attributed to the pre-atomised nature of emulsions. The fuel from heavy fuel oil decreases with increase in sulphur content. Fuel NOx also decreases with decreasing temperature, droplet distribution and mixing. Therefore NOx emissions from the combustion of heavy liquid fuels are a function of the design of the complete combustion system, rather than the fuel alone. Some outstanding issues which have been identified are the evolution of N2O and NO2 from heavy fuel oil and the importance of atomisation in the formation of fuel NOx.

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