1. 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, Edinburgh, UK

2. 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;

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

4. 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

5. 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

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

7. 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

8. 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

9. 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.

10. Aromatic Hydrocarbons Identified in Asphaltene Pyrolysis Products

11. 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

12. 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)

13. 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

14. Thank you
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