Highlights Thermogravimetric analysis of heavy fuel oil samples at different asphaltene concentration is discussed. The influence of high asphaltene concentration on the droplet burning stages is illustrated. The relation between the droplet ignition delay time and droplet size is discussed at different asphaltene concentration. The effect of asphaltene concentration on the droplet evolution with time is measured.
The current study aims to investigate cenosphere formation during single droplet combustion of heavy fuel oil (HFO). A droplet generator was developed to produce freely falling monodisperse droplets uniformly. With the aid of high-speed imaging, droplet diameter was verified to be well controlled within the range of 390~698 μm, and droplets spacing distance was sufficient to avoid the droplet-droplet interactions. Impacts of operation conditions (initial HFO droplet size, temperature, and air co-flow rate) and asphaltene content on cenosphere formation in a drop tube furnace were then investigated. Three types of cenosphere morphology were observed by a field-emission scanning electron microscopy (SEM), namely larger hollow globules, medium porous cenospheres, and smaller cenospheres with a perfectly spherical and smooth structure. The SEM image results show the mean diameter of collected cenospheres increased as initial droplet size and asphaltene content increased, while it decreased as temperature and air co-flow rate increased. The energy dispersive X-ray spectra (EDX) results show these parameters also significantly influenced the evolution of cenosphere surface elemental composition. All parameters show linear effects on the surface content of C, O and S, excluding air co-flow rate. The increase of air co-flow temperature enhanced the droplet combustion, conversely, the larger the initial droplet size and asphaltene content inhibited droplet combustion. The non-linear effect of air co-flow rate indicates that it has an optimum rate for falling droplet combustion, as 90 slpm based on the current experimental setup. Eventually, our study proposed the pathway of cenosphere formation during the HFO droplet combustion.
This work presents a predictive and generally applicable approach to asphaltene pyrolysis modeling. Asphaltenes derived from heavy fuel oil 380 (HFO) were characterized using elemental analysis and FT-ICR MS. The structural information derived from the chemical analysis guided the formulation of five surrogate molecules. The atomic ratios of the surrogate molecules were defined to replicate the elemental composition of each data as their linear combination. This approach makes the model flexible and readily applicable to any asphaltene fraction by only knowing its elemental composition. The formulation of the kinetic model proceeded through chemistry-related considerations on the reactions most likely to take place at a given temperature for each component. The authors also used the experimental data obtained from thermogravimetric analysis (TGA) in an inert atmosphere, either reported in the literature or generated by the authors for the development of the kinetic scheme. The kinetic scheme consists of five first-order reactions. The activation energy (E a) and Arrhenius (A) coefficient were tuned using a subset of the experimental data available and validated with the remaining data. The product distribution of the in-house-produced samples was obtained from a TGA–MS and TGA–FTIR analysis and used to adjust the stoichiometric coefficients together with experimental data reported in the literature. The model presented a satisfactory agreement with the most recent experimental data while showing some discrepancies with older data, which are discussed in the paper. The model reported in this work represents the first step of a more comprehensive project aimed to reconstruct the chemical kinetics of HFOs as a combination of their saturate, aromatic, resin, and asphaltene fractions.
The combustion of hydrocarbons will continue to feed the planet's growing demand for mobility and power generation over the next several decades, shifting to lower value, more difficult-to-burn fuels while at the same time meeting more stringent emissions regulations. These lower-value fuels include heavy fuel oils and vacuum residuals, which are difficult to burn cleanly due to the presence of asphaltenes, the exceptionally high molecular weight insoluble fractions found in high concentrations in crude oils. In particular, heavy fuel oils (HFO) are widely used fuels in marine and power-generation sectors, and International Maritime Organization's (IMO2020) promulgation has redistributed the HFO demand and pushed the world's economy into a new paradigm. We seek solutions for such a complex oil industry paradigm utilizing some state-of-the-art technologies like ultrasonically induced (UIC) cavitation. In the current chapter, we have discussed a roadmap for use of "bottom-of-barrel fuel" with high asphaltene content via UIC-based fuel upgrading, desulfurization, and direct use (emulsions). We expect that a strategy of using UIC for asphaltene modification and water-in-HFO-enabled micro-explosions will significantly impact the combustion of HFO. Furthermore, ultrasonic-assisted oxidative desulfurization (UAOD) can be utilized to remove undesired sulfur to meet marine or power sector requirements. Applications of deasphalting, emulsions, and desulfurization solutions could be for a multiplicity of combustion-driven energy conversion platforms, including compression ignition engines, gas turbines, and boilers.
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