Biogas production from sugar beet silage

Jin Mi Triolo

University of Southern Denmark

Why sugar beet silage?

• Dedicate energy crop for biogas production: prohibited until 2011

• New regulation since 2012: up to 25% of dedicate energy crop allowed as co-

feedstock (at least 75% must be animal manure)

• Sugar beet : Highest dry matter yield per. ha

: Easily degradable, high methane potential

: Ensilaging produce alcohols and organic acids

(quick biogas production)

Influence of ensilage

Be-fore silo

Silo 1 Silo 2 Silo 3 Silo 4 Silo 5250

280

310

340

370

400

430

460

490

BMP

(CH4

NL

kg V

S-1)

Ensilage effect of beets pulps

DM DM loss VS VS loss VS Total

VFATotal

Alcohol pH BMP BMP

g kg-1 % g kg -1 % (%) % of VS % of VS NL CH4 kg VS-1) CH4 NL kg -1

Fresh silage 194,6 153,4 78,8 0,46 0,00 4,5 342,1 52,5

Silage 1 146,7 24,6 109,8 28,41 74,9 8,48 4,60 3,6 490,3 53,8

Silage 2 157,6 19,0 116,8 23,84 74,1 8,63 4,50 3,6 499,8 58,4

Silage 3 163,5 16,0 121,1 21,05 74,1 6,01 4,66 3,6 456,3 55,3

Silage 4 173,7 10,8 114,2 25,52 65,8 6,78 4,95 3,6 478,0 54,6

Silage 5 135,5 30,4 106,0 30,90 78,2 8,77 4,84 3,7 493,9 52,3

Further Study 1• Grøngas A/S (Hjørring)

• Long term monitering of beet ensilage (Harvested in Nov. 2013- Ensilaging until December 2014) (6 silos with different scenarios)

o GHG emission o Biogas potentialso Optimising high rate biogas production o Organic composition

Further study 2• 1 Spring barley straw • 2 Spring barley straw in the swath, 21/10 • 3 Spring barley straw + aftermath, fresh • 4 Spring barley straw + aftermath, ensiled • 5 Grass seed straw, fresh • 6 Grass seed straw, silage • 7 Grass seed straw, silage grass juice • 8 Grass seed aftermath, fresh • 9 Grass seed after forage ensiled • 10 Maise silage

Further study 3

Beet topStraw with 30% waterRoerod knust

Beet top and straw with different mixing ratiosBeet top + Straw 0 100Beet top + Straw 75 25Beet top + Straw 80 20Beet top + Straw 85 15Beet top + Straw 90 10Beet top + Straw 100 0

Grøngas A/S (Hjørring)

Examples of concept model work Biogas production of sugar beet in Energy production and Greenhouse Gas Reduction

Field

Post -storage

Biogas production

Ensilage

Cleaning

Harvest Harvest in Octobero Beet top for animal feedo Beet root for bigas production

Dry Cleaning in the fieldo Removing soil, sand, stones, etc.

Ensilage for 8 monthso Whole beet root, fermentationo Covered

Co-digestion with cattle manure1200m3, 6ton/day, 37°C, HRT 20days

Cattle manure

PVC roof (avoid dilution), until field application

Applied in October or April

Unit 1. Harvest

Sugar beet in field

Topharvested m2g

x3root g

x2 DM g Root harvested m3g

x2 H2O g

x3soil g

Unit 2.Cleaning

Washed root m5g

Soil m4g

x8 H2O g x8 DM g x8 VS g x8 ash g

Unit 3.Storage

Unit 4.Mixing

Emission m6g

x6 CO2 g x6 CH4 g

Silage m7g

x7 H2O g x7 DM g x7VS g x7 ash g

Unit 7Field

x1root g x1 soil g

x1top g m1g

Cattle slurry m8 gUnit 6.

After-storage

Gas m13g

x13 CO2 g x13 CH4 g

x13 NH3 g

Unit 5.Anaerobic digestion

Biogas(obtained) m10g

x10 CO2 g

x10 CH4 g

x10 NH3 g

Digestate m12 g

x12 H2O g

x12 ash g x12VS g

x12 DM g x9 H2O g

x9 ash g x9VS g

x9 DM g

Mixed substrate m9g

Biogas (emitted) m11g

x11 CO2 g x11 CH4 g

x11NH3 g

Fertilizer m14 g

x14 H2O g

x14 ash g x14VS g

x14 DM g

Gas m15g

m15 CO2 g m15 N2O g

m15 NH3 g

x10 H2O g

x10 H2O g

x5 H2O g

x5 ash g x5VS g

x5DM g

Flow chart of Reference Scenario 7 process units and sub-systems with a total of 15 process streams

Model 1 (Basis unit :1000g beet)Model 2 (Basis unit : ton/ha)

Process unit 1. Harvest

Unit 1. Harvest

Sugar beet in field

TopRemoved

706.9root g

34.2 DM g 221.4 H2O g

37.5soil g

706.9root g 37.5 soil g

744.4g 1000g

Root harvested

255.6g

Total 744.4g

Dry matter192.0g

VS152.7g

VSND14.4g

VSED138.3g

VSED Carbohydrate

129.8 g

VSED Lipid0.8g

VSED Protein

7.8g

Ash39.3g

Water552.4g

Composition of root +soil (stream 3)

• Top for animal feed• Root for biogas production• Soil : 22% of beet’s dry matter

1

2

3

Process unit 2. Cleaning

Unit 2.

Cleaning

Root harvested

SoilRemoved

547.9 g H2O

30.8 DM g 4.5 H2O g

161.2 g DM

706.9root g 37.5 soil g

709.1g 744.4g

Root cleaned

35.3g

VS 152.7g

VSD138.3g

VSDCarbohydrate

129.8g

Sucrose101.2g

Cellulose6.5g

Hemicelluloe6.5g

Pectins15.6g

VSD Lipid0.8

VSD protein7.8g

VSND14.4g

VS Composition of cleaned root (Stream 6)

Soil residueo 3.4% (dry cleaning) o 2.1% (wet washing)4

5

68.5 g ash 151.7 g ash

AgroTech (Jørgen Pedersen)

Cleaned root

Process unit 3. Ensilage

VS and BMP loss during ensilage

GHG o CO2 emission through ensilage : 12.7 L /kg beet o CH4 emission during first period ( 2-3 weeks) : 1.24 L/kg beet 2.5% (Agrotech)

VS (g/kg w.w) BMP (L/kg VS) BMP (L /kg w.w) Fresh beet 231 361 83

Ensilage 8 months 212 383 81

VS (g/kg w.w) BMP (L/kg VS) BMP (L /kg w.w) Fresh beet 215 324 70

Ensilage 8 months 187 359 67

o German study (Weißbach et al., 2011)

o Our study

TBMP per kg VS TBMP Before ensilage TBMP After ensilage CH4 NL kg VS-1 CO2 NL kg VS-1 g CH4 NL CO2 NL g CH4 NL CO2 NL

Sucrose 393 (50%) 393(50%) 101 40 40 31 12 12Ethanol 730(75%) 244(25%) 0 0 0 21 15 5

o High BMP of alcohol

Process unit 3. Ensilage

Unit 3. Ensilage

Gas emission

538.9 g H2O

22.6 CO2 g 0.9 CH4 g

136.8 g DM

694.1.g

Silage

23.5g VS loss until the end of March under careful storage

o 16%

7

8

98.5 g ash 128.3 g VS

AgroTech (Jørgen Pedersen)

Root silage

Fraction (%)

In the model (g)

Before ensilage

Up to 6 months

More than 6 months

Beforeensilage

Moren than 6 months

Sucrose 78 60 30 101 31Glucose 0 6 8 0 8.4Ethanol 0 10 20 0 2.1Hexoses 5 7 9 6.5 9.5Pentose 5 7 9 6.5 9.5Pectins 12 10 24 15.6 25.3

Total 100 100 130 105

547.9 g H2O 161.2 g DM

709.1g

Root cleaned

8.5 g ash 151.7 g VS

Changes of Carbohydrate during ensilage

Fraction : Weißbach et al., 2009

Process unit 5. Biogas production

• Methane production rate and cumulative yield

Beet

Cattle manure

3% of total biogas

92% of BMP removed

85% of BMP removed

Sugar beet Cow manure

Input VS g 128 261

Removed VS g 90 66

Remaining VS g 39 196

VS destruction% 70 25

VS destruction

Overview of model 1( 1000 g of beet + cattle manure)

Process unit (g)

Model for beet production per ha (139 ton/ha) (+381 ton cattle manure)

Energy production

Model 1 (1000g) Model 2(ton /ha)

Biogas

• CH4: 60.5g (84.7L)• CO2: 125.1g(63.7L)• Total: 185.6g(148.4L)

Energy

• 3.4MJ

Electricity

• 0.95Kwh

Biogas

• CH4: 8.4.Mg (11780 m3)• CO2: 17.4Mg (8855 m3)• Total: 25.4Mg (20634m3)• 43m3/ton

Energy

• 474588MJul• 941MJ/ton

Electricity

• 131Mwh (261Kwh/ton)

GHG emission using biogas technology ( Model 1)

With Biogas production

• CH4 : 4.177g (0.88g ensilage, 1.87g biogas plant emission, 1.42g after-storage)• CO2 : 28.9g (mainly from ensilage )• GHG as CO2 eq. : 133.3 g

Without biogas production

• CH4 : 4.183g , CO2 : 7.3g , GHG as CO2 eq. : 111.9g

No GHG reduction, may be due to

• GHG emission from beet silage included• High CO2 emission from ensilage• CH4 emission from ensilage • Emission from a biogas plant