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

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

2 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, ISSN X

3 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.

4 Peat production Sod peat ridger Sod peat harrow Pneumatic harvester Mechanical harvester

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

6 Finnish peat (sample10) Rest fraction, analysed Leached in HCl Leached in Acetate Leached in H2O Untreated Fuel mg/kg Si Al Fe Ti Mn Ca Mg P Na K S Cl

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

8 Slagging caused by peat ash

9 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

10 Background

11 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

12 Elemental analysis of inner surface of slag

13 60000 Fe in Finnish peat mg/kg ds

14 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)

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

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

17 Irish peat Rest fraction, analysed Leached in HCl Leached in Acetate Leached in H2O Untreated Fuel 6000 mg/kg Si Al Fe Ti Mn Ca Mg P Na K S Cl

18 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

19 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

20 Example of results: 500 C MgO Al2O SiO P2O SO K2O CaO Fe2O Na2O Cl C MgO Al2O SiO P2O SO K2O CaO Fe2O Na2O Cl

21 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

22 Top Analytica Oy Ab Ruukinkatu 4, Turku Peat 6 Total_Ion [sample4.ims] Cts: ; Max: 214; Scale: 10µm NHú [sample4.ims] 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] Cts: ; Max: 23; Scale: 10µm Fe [sample4.ims] Cts: 7970; Max: 3; Scale: 10µm

23 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 atomic % ( 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 < <0.1

24 Leaching test to better distiguish different forms of iron

25 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

26 Distribution of Fe Fe-silicates Fe2O3, Fe(OH)3 FeS and organic Fe exchangable Fe mg/kg Peat 1 Peat 2 Peat 3 Peat 4 Peat 5 Peat 6 Peat 7 Peat 8

27 Organic/inorganic ratio for Fe 2.2 Organic Fe/Inorganic Fe Peat 1 Peat 2 Peat 3 Peat 4 Peat 5 Peat 6 Peat 7 Peat 8

28 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