Reducing Off-Gassing of wood pellets Nordic Pellets 2018 Conference

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2 Reducing Off-Gassing of wood pellets Nordic Pellets 2018 Conference DI Wilfried Pichler

3 Content Wood pellets: a chemically reactive system Strategies to avoid emission problems Reducing the reactivity of wood pellets: selected results 3

4 Wood pellets: a reactive system Cellulose Cell-Lumen Hemicellulose Extractives Lignin Extractives: o Fatty acids o Resins o Tannins o Sugars o Starch o Proteins o Salts Adapted from: Sticklen MB (2008) Plant genetic engineering for biofuel production: towards affordable cellulosic ethanol. Nat Rev Genet 9:

5 Wood pellets: a reactive system Pellet production: Wood modification due to high pressure and temperature o Large specific surface: 430 m²/m³ for 6 mm softwood pellets 67 m²/m³ for standard timber products o Mobilization of extractives towards the surface Intense contact of extractives and oxygen o Thermal modification of Lignin Carbohydrates Extractives Spruce pellet surface Spruce tangential cut pelletising Spruce cross cut 100 µm Pictures: Holzforschung Austria Reactions: adsorption, desorption, emission, (de)-polymerization, oxidation, radical reactions 5

6 Oxidation and radical reactions Autooxidation of unsaturated fatty acids and monoterpenes aldehydes, inorganic products and hydroxyl radicals Hopke (2016) showed, by mass balances, that the amount of fatty acids present in wood cannot explain the amounts of CO and CO 2 formed Formation of hydroxyl radicals leads to radical reactions o Formation of large amounts of CO and CO 2 by radical reactions not only on fatty acids but also on Hemicellulose (Hopke 2016: Mechanistic Patway of Carbon Monoxide Off-Gassing from Wood Pellets) It was shown, that that antioxidants and radical scavengers can reduce the formation of carbon monoxide significantly o DEPV 2011: Tannins (Verbundprojekt Umweltgerechte Herstellung und Lagerung von Holzpellets) o Hopke 2016: 1-butanol o HFA, BE2020+, TI-Graz 2017: Synthetic and Natural Antioxidants (Project Smell Process) 6

7 Strategies to reduce emission hazard Deactivation of Feedstock by anticipated reactions/withdrawal of reactive precursors o Increased storage time of feedstock or pellets ( maturing ) o Implementation of reactive conditions during pellet production o Extraction of reactive precursors Stabilization of the Product o Use of additives (antioxidants, radical scavengers) o Coatings limitation of oxygen access and reduced evaporation rate o Blending's use of natural antioxidants o Implementation of low-reactive process conditions (temperature, water, pressure, cooling) Online Feedstock Monitoring /scanning o combined with other measures pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr pr 7

8 Selected results methods Storage and fungal pre-treatment Wet-Milling Drying 2, 3 or 4 weeks, blue stain fungus 4-Shaft- Shredder Pangrinder Mill Hammermill Belt-Dryer 80 C, 100 C Dry-Milling Conditioning- Blending Pelletising VOC Analysis Pangrinder Mill Hammermill 5, 7 or 10 mm Blendings and additives Flat-Die- Press Ring-Die- Press FLEC /GCMS 8

9 Selected results: involved factors Pelletizing technology Variations in particle size Storage and Fungal treatment Monitoring measurements with NIR Spectroscopy Results not open source due to industrial funding: Variations of moisture regime in the production process Use of additives Blending with antioxidative wood species Cooling and storage conditions~ 100 Pilot scale and Industrial scale experiments 9

10 mg/(m³kg) mg/(m³kg) Selected results: influence of pelletising technology dryed sawdust native pine: ring die TVOC terpenes tot. aldehydes fresh pellets pellets pellets pellets after 2 wafter 4 wafter 6 w dryed sawdust native pine: flat die TVOC terpenes tot. aldehydes fresh pellets pellets pellets pellets after 2 wafter 4 wafter 6 w o Same pattern for ring die press and flat die press 10

11 mg/(m³kg) mg/(m³kg) mg/(m³kg) Selected results: influence of hammermilling native spruce 10 mm milling TVOC Terpene total aldehyde s native spruce 7 mm milling 0 TVOC terpenes total aldehydes 1400 native spruce 5 mm milling TVOC 800 Terpene 600 total aldehydes o Slightly Increasing VOC emissions for finer particles o Similar results found by DEPV 2011 o Results from ongoing projects support this finding 11

12 TVOC concentration [mg/(m³kg)] Selected Results: storage, fungal treatment, drying o Storage for 3 weeks shows significant reduction in TVOC pine reaches emission level of spruce o Treatment with blue stain fungus ceratocystis coerulescens shows minor effect compared to untreated storage o Drying at 80 C instead of 100 C leads to higher TVOC emission o Reaction takes place in 4 to 6 weeks after pelletising Cerat.Coeru. 2 weeks Cerat.Coeru. 3 weeks Cerat.Coeru. 3 weeks, drying at 80 C Cerat.Coeru. 4 weeks fresh untreated pine 3 weeks stored, untreated pine fresh untreated spruce 12

13 Selected results: NIR-Monitoring of CO-Emission rates 78 grinded pellet samples o Heterogeneus set (different feedstock, productions sites, additives) o CO-Emisission rates o NIR-Spectra (Bühler MYRG) PLS-Regression o After removal of 5 outliers Promising Beginning for online Emissions monitoring 13

14 Selected results: not open source General findings: Cooling time and temperature show no significant effect o Not to be confound with storage conditions Some natural additives work Some wood blends can reduce emission rate of fresh pine feedstock o 40% Blend -> 60% CO reduction Moisture regimen showed significant effects on pilot plant scale Overall conclusion: measures within factory gates are possible but: no single solution is available at the moment 14

15 Summary Wood Pellets are a reactive system due to hydrothermal modification, high pressure, high temperature, high surface Strategies: Feedstock / Pellet deactivation Feedstock / Pellet stabilization Online Monitoring Systems Reduction of chemical reactivity by measures within factory gate: o positive effects (high) drying temperature Conditions of milling/(coarse) particle size (long) Storage time Additives Blending o no (major) effects Ring die vs. flat die Microbiological treatment Moisture regimen Cooling conditions 15

16 Outlook Further work needed, focus on blending, additives and feedstock deactivation More emphasis in online NIR-Monitoring Invitation to associations and industry to join research Acknowledgments: 16

17 Standort Stetten Standort Arsenal DI Wilfried Pichler Tel. +43/1/