Spray evolution and thermal pyrolysis of low sulfur heavy fuel oils under high temperatures

The spray evolution and thermal pyrolysis of the heavy fuel oil (HFO) and its blends with #2 diesel were firstly investigated. First, the gas chromatography was performed to analyze their molecular distributions. The low sulfur HFOs with different viscosities show similar molecular distributions, and the content of light-end C9 - C17 alkanes and polyaromatics is reduced compared with the high sulfur HFOs. Then, the spray experiments were conducted. The increase of ambient temperature has little effects on the HFO sprays. However, the blends spray of HFOs and #2 diesel penetrates faster and produces some opaque products under high-temperature conditions, probably due to the enhanced turbulence intensity, potential thermal pyrolysis and polymerization. Finally, the thermogravimetric analysis coupled with the isothermal gas chromatography and mass spectrometry were conducted, and the apparent activation energy of thermal pyrolysis for various HFOs were obtained. The results revealed that the HFO undergoes four stages in the inert gas, namely the endothermic evaporation, mixed evaporation-pyrolysis, violent exothermic pyrolysis, and high-temperature polymerization, producing large amounts of residues. However, in the oxygen-containing condition, the combustion occurs instead of the hightemperature polymerization, and the residual quality is prominently reduced. The high ambient pressure is proved to have a significant effect on the pyrolysis and polymerization processes for the low sulfur HFO, the residual mass significantly increases under high pressures. For the blended HFO, due to the volatile components trapped inside the viscous shell generated by polymerization or asphaltene fractions, the residual weight of the blended HFOs increases.