Some Aspects of the Combustion of Heavy Fuel Oil Containing High Asphaltene Levels F.A. Atiku A.R. Lea-Langton, K.D Bartle, P.Biller, J.M. Jones, A.B Ross and A. Williams Energy Research Institute, University of Leeds, LS2 9JT, UK.  1st Chemistry in Energy Conference 20th-22nd July, 2015. Edinburgh, UK

Introduction Emissions from the stacks of furnaces burning heavy oils e.g. Bunker C fuel in both marine and stationary sources pose significant threats to the environment in a number of ways, mainly: Smoke formed during the combustion of asphaltene-rich fuel oils consists of both cenospheres and fine particulate soot-both increased by increasing the asphaltene content of the oil Among the seven  EPA PAH specified as carcinogenic, two - chrysene and benz[a]anthracene- were identified in the mixture of 2-  to 4- ring PAH  detected in the asphaltene pyrolysis experiments described here. Carcinogens derived from these such as methylchrysenes  can also be important;

General mechanism for the thermal decomposition of asphaltene. Objective- is to improve the knowledge of the structure and its thermal decomposition mechanism

Effect of Asphaltene Content Reduces Ignition Delay Increases Stack Solids From single drop studies From drop tube experiments Ignition delay measurements (s) plotted against asphaltene content (wt.%) in the fuel oil: □, suspended droplets; O, falling droplet. Plot of the square root of the concentration of the stack solids produced as a function of asphaltene content of heavy fuel oils K.D. Bartle et al. / Fuel 103 (2013) 835–842

The experimental work consists of: Experimental Methods The experimental work consists of: (i) Separation of asphaltenes from heavy fuel oil (ii) Pyrolysis in a reactor followed by analysis

Microflow Cell Reactor –schematic diagram of reactor interface and AED Py-GC was carried out in a microflow cell reactor with MS AED

Py-GC-MS of asphaltene at different temperatures Experimental Results Py-GC-MS of asphaltene at different temperatures 4000C 5000C 6000C ‘A’ denotes alkane/alkene pairs and also data interrogation shows aromatic hydrocarbons such as substituted benzenes, naphthalenes, phenanthrenes and complex PAH fractions

Results-expanded chromatogram SIM chromatogram showing the blown up dimethyl naphthalenes peaks at 600C with selected  peak  identifications The observed pattern of methyl subsitution in the naphthalenes and phenanthrenes resulting from asphaltene pyrolysis is similar to that of petroleum oil fractions The predominance of 1–subsituted dimethylnaphthalenes resembles that of crude oil and geochemical sediments

Discussion of Py-GC-MS results At 300°C the chromatograms contained peaks from volatile aliphatic and monocyclic aromatic hydrocarbons occluded in the asphaltene particle. Between 400°C and 500°C the compounds evolved were alkane/alkene pairs (from beta-bond scission of long-chain alkyl groups), alkanoic acids, and alkyl aromatics (especially benzenes, naphthalenes, dihydroindenes and tetrahydronaphthalenes), and sulphur heterocycles. Alkyl aromatics detected in the pyrolysis products are the asphaltene building blocks, and also pyrenes, fluoranthenes,  chrysenes and benz[a]anthracenes. Pyrolysis at 600°C gave similar products but also evidence of secondary reactions paths.

Aromatic Hydrocarbons Identified in Asphaltene Pyrolysis Products

Py-GC-AED of Bunker C ashphaltene Intensity Retention time (min) Identified numerous alkylated, mainly methyl, benzothiophens and dibenzothiophens, suggesting an important contribution of sulphur heterocyclic groups to the asphaltene structure. Evidently PASH are also asphaltene ‘building blocks’ in an ‘archipelago’ structure

Results-burn-out of soots Intrinsic oxidation rate of soot, HFO cenospheres and cokes :The intrinsic reaction rate, ρ, for soot and for cenosphere is given by ρ = 1.05 exp(-143.5/RTp)

Conclusions This work shows that the thermal decomposition of the asphaltene follows the route outlined earlier. The evidence points to an archipelago structure of 1-4 aromatic and sulphur aromatic ring units linked by aliphatic structures and with a high degree of alkyl (some long chain) substitution. Pyrolysis produces gas phase PAH and PASH which are health hazards as carcinogens and soot precursors. The primary reactions result in large radical fragments which cross link to yield solid residue namely cenospheres. The burn-out rates of the soot and the cenospheres determine the amount of stack solids emitted and these can be calculated using intrinsic reaction rates for their oxidation

Thank you Any questions? Email address: pmfaa@leeds.ac.uk