Pyrolysis of heavy fuel oil (HFO) - A review on physicochemical properties and pyrolytic decomposition characteristics for application in novel, industrial-scale HFO pyrolysis technology

Heavy Fuel Oil (HFO) undoubtedly represents the structurally most complex petroleum fraction. Composed from a wide range of refinery resdiua after yielding the more valuable light and middle distillate fractions, it has historically been used as a cheap fuel. This has led to the unfolding of detrimental effects for global warming and prevented opportunities to derive valuable products from the residua as both a potentially cost-effective and environmentally sound alternative to combustion. Driven by stricter emissions regulations, a novel pyrolysis technology for high-contaminant HFO derived from Waste Lubricating Oil (WLO) has been developed and proven on a small industrial-scale. Such pyrolysis of HFO, and especially its scalable application, is very rarely reported in literature. As a basis for pyrolytic processing in the novel HFO pyrolysis application, this study systematically reviews the physicochemical characteristics as well as the behavior of various HFO during pyrolytic decomposition. The article provides a comprehensive overview of various HFO types and how their structural complexity is determined by the underlying crude oil type and the refining techniques applied. Results of the study show that the molecular structure of HFO is extremely complex and its assessment requires a combination of several analysis methods as well as modeling approaches. DTG analysis of HFO pyrolysis yields a varying number of observed peaks between one and three, depending on selective compounding and the connected introduction of more volatile components. Moreover, this review finds that the pyrolysis of HFO can undergo several stages depending on the structural composition while the major mass loss stage mostly occurs between 400 and 500°C. These stages are characterized by a pattern of devolatilized gases, with predominantly alkanes and alkenes evolving from HFO pyrolysis. Asphaltenes contained in HFO are concluded to be the main contributor to coke formation during pyrolysis between 350°C and 500°C. This review concludes the general suitability of crude-derived HFO for pyrolysis applications and shall serve as a basis and guideline for further exploration of industrial-scale HFO pyrolysis as a path away from historically prevailing incineration.