Ash Forming Matter in Peat - The Role of Iron- Mikko Hupa, Maria Zevenhoven, Jaakko Lehtovaara, Stefan Storholm,

Ash Forming Matter in Peat - The Role of Iron- Mikko Hupa, Maria Zevenhoven, Jaakko Lehtovaara, Stefan Storholm,

Peat in Europe One-third of the peat and peat-topped soils in Europe found in Finland, MKore than a quarter found in Sweden. The remainder found in Poland, the UK, Norway, Germany, Ireland, Estonia, Latvia, The Netherlands and France. Small areas of peat and peat-topped soils also in Lithuania, Hungary, Denmark and the Czech Republic. The distribution of peatland in Europe L. Montanarella1, R.J.A. Jones1,3 and R. Hiederer2 Mires and Peat, Volume 1 (2006), Article 01, http://www.mires-andpeat.net, ISSN 1819-754X

Peat in Finland Peat energy today 6 % of total energy in Finland. Sphagnum peat account for 54 % Carex peat for 45 % of recoverable peat reserves. The remainder, 1 %, is composed of Bryales peat, the bulk of which are encountered in the North- Finland area. The highest values of humification degree are located in Finnish Lake area, in Central Finland.

Peat production Sod peat ridger Sod peat harrow Pneumatic harvester Mechanical harvester www.vapo.fi

Composition of peat 60 50 40 % d.s. 30 irish finnish 20 10 0 Ash C H N O Data taken from ÅA database, min and max values indicated, #16 finnish peat, irish peat #1

Finnish peat (sample10) 18000 16000 14000 12000 Rest fraction, analysed Leached in HCl Leached in Acetate Leached in H2O Untreated Fuel mg/kg 10000 8000 6000 4000 2000 0 Si Al Fe Ti Mn Ca Mg P Na K S Cl

Data taken from ÅA database, min and max values indicated, #16 finnish peat, irish peat #1 60000 50000 Composition of peat irish finnish 40000 mg/kg d.s. 30000 20000 10000 0 Si Al Ca Fe K Mg Na Mn P Ti S Cl

Slagging caused by peat ash

Iron in Peat Wall tube Iron initiator of furnace wall slagging Start by an iron oxide layer on wall tube surfaces. When this layer has grown thick enough, also the bulk fly ash starts sticking 2 cm Flue gas

Background

Iron initiates Flue gas Wall tube slagging Initial iron oxide layer on wall tube surfaces. On this layer silicate fly ash starts sticking Further transormation to glassy slag

Elemental analysis of inner surface of slag

60000 Fe in Finnish peat 50000 40000 mg/kg ds 30000 20000 10000 0 12 1 11 13 2 14 9 4 3 10 5 7 8 6 15

Analysis of Fe in Finnish peat Standard fuel analysis SEM/EDX (samples 1-8, peat and peat ash) XRD (1,3,6,8, peat ash) TOF-SIMS (1,3,6,8, peat) ESCA (1,3,6,8, peat) Sequential leaching in aqueous solutions: water, ammonium acetate and hydrochloric acid (peat 1-8) Sequential leaching with oxidative and reducing agents (peat 9-15)

Selective leaching in aqueous solutions Total ash - all major ash elements H2O Water leachable - alkali sulfates NH4Ac Buffer solution leachable - organically associated /carbonates/chlorides HCl Acid leachable - carbonates/ sulfates Non-soluble rest - silicates

70000 60000 50000 Finnish peat (sample 16) Rest fraction, analysed Leached in HCl Leached in Acetate Leached in H2O Untreated Fuel mg/kg 40000 30000 20000 10000 0 Si Al Fe Ti Mn Ca Mg P Na K S Cl

Irish peat 10000 9000 8000 7000 Rest fraction, analysed Leached in HCl Leached in Acetate Leached in H2O Untreated Fuel 6000 mg/kg 5000 4000 3000 2000 1000 0 Si Al Fe Ti Mn Ca Mg P Na K S Cl

Summary Analytical methods Standard fuel analyses Shows total concentration of Fe in fuel Always needed SEM (fuel, ash) Shows distribution of Fe in fuel - Sensitive for Si particles Ashing often needed to reveal ash forming matter hidden in fuel matrix Gives sometimes valuable extra information, semi-quantitative method XRD (ash) Showed possible presence of reduced iron: FeO, Fe Showed non crystalline Fe, probably organically associated Concentration of Fe too low, fuel needs to be ashed. ESCA (fuel) Could not distinguish between Fe 2+ and Fe 3+ During sample preparation surface oxidises, destroying information on reduced species TOF-SIMS (fuel) Similar to SEM Shows association of Fe, but Fe seems not be on the surface TOF-SIMS is a surface analytical tool only

Experimental setup SEM Fuels (1-8) were ashed in air in a laboratory furnace at 500, 700 and 900 C respectively. Untreated fuel and ashed samples were mounted on carbon tape. SEM/EDS analyses were carried out wit 30, 250 and 5000x magnification At 30x and an area analysis was performed At 250 and 5000x point analyses were performed At 250x elemental maps were scanned for Al, C, Ca, Cl, Fe, K, Mg, Na, O, P, Pb, S, Si, Zn All analyses were calculated on a carbon free basis

Example of results: 500 C 4 5 6 7 MgO 4.62 3.55 4.18 4.78 Al2O3 18.25 16.78 17.75 15.72 SiO2 9.88 19.38 5.65 4.15 P2O5 3.79 3.91 4.03 4.00 SO3 5.03 3.60 4.64 4.94 K2O 7.91 7.12 4.37 4.45 CaO 18.63 14.02 15.99 19.61 Fe2O3 28.65 28.66 41.76 41.04 Na2O 2.52 1.94 0.95 0.63 Cl 0.34 0.39 0.34 0.30 900 C 14 15 16 17 MgO 3.70 7.25 5.59 6.51 Al2O3 13.87 16.56 18.59 22.09 SiO2 46.62 20.80 14.49 4.74 P2O5 3.06 4.19 3.61 4.26 SO3 2.09 3.26 1.66 4.06 K2O 0.25 0.28 0.23 0.21 CaO 10.61 16.74 14.82 16.02 Fe2O3 18.69 29.69 40.56 41.25 Na2O 0.31 0.63 0.36 0.18 Cl 0.00 0.13 0.00 0.03

XRD of peat ash All peats contained amorphous Fe Some also Fe2O3 TOF-SIMS of peat TOF-SIMS showed that Fe could be connected to the organic matrix Not all samples could be analysed since Fe is not always present at the surface

Top Analytica Oy Ab Ruukinkatu 4, 20540 Turku www.topanalytica.com Peat 6 Total_Ion [sample4.ims] - 1501.00 Cts: 4116260; Max: 214; Scale: 10µm NHú [sample4.ims] - 18.03 Cts: 22976; Max: 6; Scale: 10µm distribution of Fe, NH4, C 3 H 7 (mass 43) and total ions (=sum of all ions). Measurement time 50 min, width of the image 100 μm. 43 [sample4.ims] - 43.03 Cts: 293364; Max: 23; Scale: 10µm Fe [sample4.ims] - 55.93 Cts: 7970; Max: 3; Scale: 10µm

ESCA Samples were dried in 110 C 2 hours. For ESCA a large particle with a diameter of few mm was selected and it was fixed to the sample platen with a molybdenum mask plate. The ESCA measurements were done with monochromatized Al Kα X-rays. The diameter of the analysis spot is 100 μm and the analysis depth is 5-10 nm. In Peat 1 the amount of iron was below the detection limit. In the other samples the concentration was 0.3-0.5 atomic % (1.3-2.1 weight-%). For Peat 3,6,8 it was found that that the binding state of iron is Fe 3+ in the analyzed particle. No Fe 2+ was found caused by oxidative drying Sample C O N Fe Si 617785 1 84.0 15.2 0.6 <0.1 0.3 617633 3 78.5 18.4 2.5 0.5 0.1 526108 6 82.2 15.4 1.2 0.3 0.8 617654 8 76.8 20.0 2.7 0.5 <0.1

Leaching test to better distiguish different forms of iron

Determination of forms of Fe all major ash elements HAc Exchangeable + weak acid soluble fraction NH 2 OH HCl Analysis Reducible fraction: Inorganic Fe i.e. oxides and hydroxides H 2 O 2 NH 4 Ac Oxidizable fraction (e,g,, metals associated with organic matter and sulfides) Residual fraction, silicates

Distribution of Fe 45000 40000 35000 Fe-silicates Fe2O3, Fe(OH)3 FeS and organic Fe exchangable Fe 30000 mg/kg 25000 20000 15000 10000 5000 0 Peat 1 Peat 2 Peat 3 Peat 4 Peat 5 Peat 6 Peat 7 Peat 8

Organic/inorganic ratio for Fe 2.2 Organic Fe/Inorganic Fe 2.0 1.8 1.6 1.4 1.2 1.0 Peat 1 Peat 2 Peat 3 Peat 4 Peat 5 Peat 6 Peat 7 Peat 8

Summary Chemical fractionation by Water+NH4+HCl Very good for alkali induced fouling Not suitable for Fe No differentiation between organic and inorganic Fe Fractionation by Redox solutions: Three Fe groups to consider: Organic= Fe 2+ + exchangeable Fe 3+ = oxides/hydroxides Fe-Silicates Important Total amount of organic Fe and inorganic Fe Ratio of organic Fe/inorganic Fe Fe silicate R-Fe....... Fe(OH)x combustion Fines from organic Fe Coarser particles of silicates Iron oxide particles