Swirling flame combustion of heavy fuel oil: Effect of fuel sulfur content

In the present work, an experimental investigation on the effect of sulfur content in heavy fuel oil (HFO) on the gaseous emissions under swirling flame conditions was carried out. The sulfur content in HFO was varied by blending with ultra-low sulfur diesel and four fuel samples containing 3.15, 2.80, 1.97, and 0.52% sulfur (by mass) were prepared. Pure asphaltenes were added to the blends to ensure that the asphaltene content in the fuel remained the same. The fuels were then fired in a high-swirl stabilized, turbulent spray flame. The combustion performance of the fuels was evaluated by measuring flame temperature distribution, gaseous emissions (SO_x, NO_x, CO, CO₂, and flue gas pH), and particulate matter (PM) emissions (morphology, composition, and pH). The results showed a significant reduction in the SO₂ emissions and acidity of the flue gas when the sulfur content in the fuel was reduced, as expected. The reduction was more than would be expected based on sulfur content, however. For example, the flue gas SO₂ concentration reduced from 620 ppm to 48 ppm when the sulfur content in the fuel was reduced from 3.15 to 0.52% (by mass). Sulfur balance calculations indicate that nearly 97.5% of the sulfur in the fuel translates into gaseous emissions and the remaining 2.5% appears in PM emissions. Ninety-five percent of the gaseous sulfur emissions are SO₂, whereas the rest appears as SO₃. Varying the sulfur content in the fuel did not have a major impact on the flame temperature distribution or NO_x emissions. The morphologies and the size distribution of the PM also did not change significantly with the sulfur content as the asphaltenes content of the fuels remained the same.