1. Suitability of semi-natural grassland biomass for combustion and the effect of quality optimization strategies Bettina Tonn1, Ulrich Thumm2, Wilhelm Claupein University of Göttingen, 2 University of Hohenheim
24th General Meeting of the EGF 3-7 June 2012 Lublin

2. Benefits of bioenergy generation from grassland biomass
Introduction
Benefits of bioenergy generation from grassland biomass
Production function
renewable energy
Non-production
functions
biodiversity
landscape …
Semi-natural
grassland
Fibre concentrations high
Combustion
small-scale   technological development 

3. Biomass quality challenges for combustion
Environmentally harmful emissions
high biomass ash concentrations  dust emissions
high biomass N concentrations  NOx emissions
 environmental issues / legal restrictions
Ash high-temperature behaviour
high biomass K and Cl concentrations  corrosion, fouling
high proportion of K / low proportion of Ca and Mg in biomass ash  slagging
 risk of damages / decreased lifespan of combustor

4. Questions
1) High variability of biomass quality of semi-natural grasslands  relative importance of:
botanical composition
cutting date
site effects
2) Quality optimization strategies from other herbaceous biofuels  effect on semi-natural grassland biomass of:
a) Delayed harvest in winter / early spring
b) Leaching of unwanted substances through rain after cutting ? ?

5. Materials and methods Natural variability 6 sites 5 harvest dates June
July
August
September
October
2 biomass
fractions
Grasses
Forbs
Winter harvest
2 additional harvests
December
February
Leaching
Control
10 min leaching
≈ mm rain
120 min leaching
≈ > 70 mm rain
3 treatmens

6. Materials and methods Sample analysis
ash, N, Cl, K, Ca, Mg concentrations
ash high-temperature behaviour: visual examination after 2 h at 1000 °C
Statistical analysis
linear contrasts of log-transformed chemical composition parameters for:
June harvest – October harvest
forbs – grasses
site maximum – site minimum
October harvest – winter harvest dates
unleached control – leaching treatments
(expressed as proportion of first contrast variable)

7. Influence of natural variabilityK Cl Ca Mg N
ash
Harvest date
June – Oct
June K Cl Ca Mg N
ash
Biomass fraction
forbs – grasses
forbs K Cl Ca Mg N
ash
Site
max – min
max
-0.4
-0.2
0.2
0.4
0.6
0.8
1.0
linear contrast (fraction of first contrast variable)
error bars: 95 % confidence interval
-0.4
-0.2
0.2
0.4
0.6
0.8 1

8. Influence of winter harvestK Cl Ca Mg N
ash
December harvest
Dec – Oct
Dec K Cl Ca Mg N
ash
February harvest
Feb – Oct
Feb
-0.4
-0.2
0.2
0.4
0.6
0.8
1.0
linear contrast (fraction of first contrast variable)
error bars: 95 % confidence interval
-0.4
-0.2
0.2
0.4
0.6
0.8 1

9. Influence of leaching 10 min leaching control – leaching controlK Cl Ca Mg N
ash
10 min leaching
control – leaching
control K Cl Ca Mg N
ash
120 min leaching
control – leaching
control
-0.4
-0.2
0.2
0.4
0.6
0.8
1.0
linear contrast (fraction of first contrast variable)
error bars: 95 % confidence interval

10. Ash melting behaviour (1000 °C)
Wet hay meadow
Intermediate hay meadow
June
September
September
July
loose
slightly sintered
strongly sintered
molten
K/(Ca+Mg): 0.3
K/(Ca+Mg): 1.1
K/(Ca+Mg): 1.9
K/(Ca+Mg): 2.6

11. Conclusions Ash, N ( emissions) relatively low natural variability
little influence of winter harvest / leaching
 technical solutions necessary
K, Cl, K/(Ca+Mg) ratio ( ash high-temperature behaviour)
strong effects of site and botanical composition
 opportunity for selection of high-quality low-quality biomass
strong positive effect of winter harvest / leaching
 further quality improvement possible

12. Thank you!
Bettina Tonn

14. Ash melting behaviour (1000 °C)
Winter harvest
Leaching
(Ca+Mg)n (%) 80 60 40 20
Kn (%)
Sin (%)
100
(Ca+Mg)n (%) 80 60 40 20
Kn (%)
Sin (%)
100
grasses June-Oct
forbs June-Oct
whole plot Dec, Feb
control
10 min leaching
120 min leaching
Ash melting classes: loose slightly sintered strongly sintered molten

15. Natural variability of Ash and N concentrations
Teil 1
Grasses
Forbs
Sites
120
dry calcerous
grassland I
Ash
120 90 90
dry calcerous
grassland II
Aschegehalt (mg g-1) 60
Aschegehalt (mg g-1) 60
dry hay meadow 30 30
Iintermediate
hay meadow
wet
hay meadow
June
July
Aug
Sep
Oct
June
July
Aug
Sep
Oct N 30 30
tall sedge swamp 20 20
N-Gehalt (mg g-1)
N-Gehalt (mg g-1) 10 10
June
July
Aug
Sep
Oct
June
July
Aug
Sep
Oct

16. Natural variability of K and Cl concentrations
Grasses
Forbs
Sites K 30 30
dry calcerous
grassland I
dry calcerous
grassland II 20 20
K conc. (mg g-1)
K conc.(mg g-1)
dry hay meadow 10 10
Iintermediate
hay meadow
wet
hay meadow
June
July
Aug
Sep
Oct
June
July
Aug
Sep
Oct 16 Cl 16
tall sedge swamp 12 12
Cl conc. (mg g-1) 8
Cl conc. (mg g-1) 8 4 4
June
July
Aug
Sep
Oct
June
July
Aug
Sep
Oct

17. Leaching efficiency (July harvest)
Ash
Nitrogen
Sites
100 16
dry calcerous
grassland I 80 12 60
dry calcerous
grassland II
ash conc. (mg g-1)
N conc. (mg g-1) 8 40
***
all
*** 4 20 *
dry hay meadow 10
120 10
120
Iintermediate
hay meadow
leaching (min)
wet
hay meadow
Potassium
Chlorine 24
all
***
alle
*** 6
all
***
all
*** 18 4
***
/ : *
K conc. (mg g-1) 12
Cl conc. (mg g-1)
significantly different
from control (0 min). 2 6 10
120 10
120
leaching (min)

18. Winter harvest Ash Nitrogen ** ** Potassium Chlorine *** *** *** ***
Sites
120 20
dry calcerous
grassland I 90 15
dry calcerous
grassland II
Aschegehalt (mg g-1) 60
N-Gehalt (mg g-1) 10 ** ** 30 5
dry hay meadow
Iintermediate
hay meadow
Oct
Dec
Feb
Oct
Dec
Feb
wet
hay meadow
Potassium
Chlorine 15
all
***
all
*** 12
all
***
all
***
tall sedge swamp 10 8
K-Gehalt (mg g-1)
Cl-Gehalt (mg g-1)
***
/ : ** 5 4
significantly different
from October values
Oct
Dec
Feb
Oct
Dec
Feb

19. Leaching methods simulated rain Standardized laboratory method
30-40 mm irrigation
10 min leaching
> 70 mm irrigation
120 min leaching

20. Leaching method comparison
Tonn et al. (2011) Grass Forage Sci 66:

21. Effect of leaching on ash melting behaviour (1000 °C)
Control
10 min leachiching
120 min leaching
1 mm