Biomass combustion and soot formation mechanism

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1 See discussions, stats, and author profiles for this publication at: Biomass combustion and soot formation mechanism Presentation September 2015 DOI: /RG CITATIONS 0 READS authors, including: Farooq Atiku University of Leeds 46 PUBLICATIONS 182 CITATIONS SEE PROFILE A. R. Lea-Langton The University of Manchester 70 PUBLICATIONS 991 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Future Conventional Power Research Consortium View project Gasification kinetics View project All content following this page was uploaded by Farooq Atiku on 08 January The user has requested enhancement of the downloaded file.

2 Biomass combustion and soot formation mechanism F. A. Atiku, A.R. Lea-Langton, K.D. Bartle, J.M. Jones, and A. Williams. School of Chemical and Process Engineering, University of Leeds, UK

3 Soot from biomass combustion Particulate matter and gaseous emissions produced from biomass combustion are associated with adverse health and climate effects. The nature and composition of bio-derived soot can be different from hydrocarbon soot. Conventional soot mechanisms do not fully describe bio-soot formation because of the oxygenates in bio-fuels. This work concerns an investigation of the formation of soot from the primary pyrolysis products formed during wood combustion. Comparisons are made between the combustion products of model compounds (furfural for cellulose; eugenol and anisole to represent lignin and n-decane for comparison) with the smoke emissions from the combustion of pine wood.

4 Emissions formation Combustion leads to the emission of gases and particulate components including polycyclic aromatic hydrocarbon (PAHs). The mechanism of soot emanating from the burning has been observed to follow the following mechanism: Hydrogen Abstraction Carbon Addition HACA as with decane and heptane Thermolysis of phenols derived from lignin generating a single and most importantly two ring aromatics via CPD i.e. instead of dehydrogenation and demethylation, the instantaneous primary reaction is decarboxylation or elimination of CO 2 to produce cyclopentadiene Eugenol pyrolysis produces mainly benzene, toluene and C-2 benzenes, while anisole and furfural assumes to follow similar route of producing PAH.

5 Experimental methods A high speed soot sampling system for Transmission Electron Microscopy (TEM) grids Rapid and controlled collection at different flame heights. Comprises of a wick burner as a source of flame and TEM grid holder. The grid holder is attached to a compressed air driven piston. Timer to set the TEM grid residence time in the flame -a magnetic control system is used. Soot sampling device set-up

6 Sooting Characterisation Electron microscopy- SEM and TEM to analyse the particle size and structure Py-GC-MS for gas phase analysis at a range of pyrolysis temperatures to investigate soot formation routes PAH analysis to assess adsorbed species on the particulate Thermo-gravimetric analysis to indicate relative amounts of volatile organic species (organic carbon) and elemental carbon (black carbon) Smoke point measurement Smoke point apparatus ASTM D1322.

7 Soot School of something FACULTY characterisation OF OTHER DMS for particle size distributions of soot from eugenol, furfural, anisole, heptane and decane (diffusion flame of a wick burner) Direct and optical filters(430nm,520nm) of soot for CH* and C2* emissions measurements as well as the reaction zone Laser induced incandescence (LII) measurements were made using a pulsed Nd:YAG laser (Surelite Continuum) emitting at 1064 nm for soot volume fraction, and the temporal decay profiles allowed primary particle size to be estimated (work done at Strathclyde University)

8 Results and discussion Combustion properties of the fuels Fuel Smoke point (mm) Emission factor (mg of soot/g of fuel) n-heptane n-decane furfural anisole eugenol

9 Sooting propensities Clear differences are observed between the hydrocarbon fuels and the oxygenated bio-oils, of which eugenol was observed to be highly sooting. The order of sooting propensity is: heptane<decane<anisole=furfural<eugenol

10 C2* detection Images through filters to show an indication of the C* 2 species, a marker of the reaction zone. Flames were photographed using colour optical filter of 520nm, Shows the position of black carbon enveloped within the flame region as indicated in the hydrocarbon flames

11 CH* species A 430nm optical filter was used for an indication of the CH* species, a marker of the reaction zone Differences are observed between the hydrocarbon fuels and the oxygenated bio-oils, of which eugenol was observed to be highly sooting. Eugenol produces the least smoke point value of 6.5 while n-decane has the highest value up to 27, indicating that n-decane produces less soot than the eugenol which was the highest soot producer.

12 Py-GCMS of sampled soot GC-MS of adsorbed hydrocarbons on eugenol flame soot: 1: phenol, 2: guaiacol, 3: naphthalene, 4: 1H-Indenol, 5: 2-methoxy- 4-methylphenol, 6: 4,7dimethyl- 3(2H)-benzofuranone, 7: eugenol, 8:-isoeugenol, 9: phenanthrene.

13 SEM results Analysis using electron microscopy showed particle sizes typically in the range of 10nm- 60nm. These particles had agglomerated to form chains, consistent with the larger particle sizes observed by DMS analysis. As DMS particle size analysis showed peak particle size to be <200nm which will be shown later.

14 TEM results At the base of the flame the particle diameters were about nm in diameter for the eugenol flame, increasing in size with reaction time to the exit particle size stated above of nm. Particles from furfural were similar but soot particles from pine smoke tended to be larger. TEM of eugenol and pine post-flame soots shown in our earlier work showed that they have similar morphology to the in-flame sample shown here The n-decane soot has onion-like concentric rings, the eugenol soots have more disordered regions, and the wood soot is also largely amorphous with only a few pockets of graphitic structure.

15 DMS analysis Samples were taken 5cm above the flame N-decane shows an initial group of about 10-20nm particles, a second group at about 50 nm diameter and a third group up to 400nm but peaking at 200nm (not shown) Eugenol soot is different with extensive agglomeration of particle with sizes above 1000 nm

16 Conclusions Model species of wood pyrolysis products are furfural for cellulose and eugenol for lignin. Smoke from their diffusion flames are initially similar and the initial soot particles grow to larger spherical particles. The particle sizes are approximately 30 nm and the particles agglomerate to form chains. There is a significant difference between the final soot product from furfural and eugenol because of the aromatic nature and concentration of soot particles. This aromatic nature is not seen in biomass soot. Furfural tends to follow HACA because of initial decomposition to suitable molecules to follow the HACA route. Eugenol undergoes side-chain cracking, followed by conventional phenol decomposition reactions, and also decomposition and reaction via cyclopentadiene. Comparison has been made to pine soots which contain both organic carbon and black carbon. The decomposition products suggest an important PAH route via cyclopentadiene, which is derived after cracking of lignin monomer fragments.

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