Biogas from Energy Crops Biogas from Energy Crops and and BiowastesBiowastes

Charles Banks Charles Banks

University of SouthamptonUniversity of Southampton

Acknowledgements - Current project

Acronym: CROPGEN

Title: Renewable energy from crops and agrowastes

Contract: SES6-CT-2004-502824

Duration: 1 March 2004 – 28 February 2007

Total cost: 2.5 M€EC funding: 2.1 M€

website: www.cropgen.soton.ac.uk

Old technology - new application

• The technology of biochemical methane generation is well established

• Traditionally it has been used for waste stabilization

• Current focus is on energy production

• To be cost-effective in this role may require

– engineering and technical improvements to increase conversion efficiencies

– Selection and production of biomass feedstocks from a variety of sources

• including novel and multi-use crops and agro-wastes from integrated farming systems, commercial and industrial wastes and by-products.

BIODEGRADABLE ORGANIC MATERIAL

(CARBOHYDRATES, FATS, PROTEINS)

HYDROLYSIS SIMPLE SOLUBLE ORGANICS

ACID FERMENTATIONPROPIONIC ACID

BUTYRIC ACID

LONG CHAIN VFA

ACETIC ACID

ACETOGENESIS H2 + CO2ACETIC ACID

ACETOCLASTIC

METHANOGENIC

BACTERIA

HYDROGEN-USING

METHANOGENIC

BACTERIA

CH4 + CO2

METHANOGENESIS

Anaerobic digestion in its simplest form

• Closed reactor

• System of gas collection

• Production of biogas

• Production of digestate

Anaerobic

reactor

Gas storage

Energy

Heat

Energy use

excess

Product

Product use

Fibre compost

Product and Energy use

Storage and pretreatment

DIGESTER

Digestate

separator

Liquor

Fibre (straight to land)

Vehicle engine

Transport

CHP

Electricity

Process heat Space heat

Hot water

Gas engine turbine

Gas burner

or boiler

Biogas storage

Biogas cleaning

BIOMASS and AGRO-WASTE

Hydrogen reformation for fuel cell applications

Process types

Wet

Thermophilic

One stage Multi-stage

Dry

Mesophilic

Process differences

Wet Process Dry Process

• less than 15 % feedstock solids concentration

• one or several stages

• usually operate at 35oC

• requires water addition or recycle

• larger reactor

• proven technology for sewage sludge digestion

• more applicable to co-digestion with other waste

• more than 15% feedstock

solids concentration

• usually one stage

• can operate at 35oC or

55oC

• minimal water addition

• smaller reactor

• becoming most popular

choice for MSW

• more data and reference

plants needed

Wet digesterDry digester

mesophilic

thermophilic

Instantly recognisable!

Dry digester

Biogas as a renewable energy source

Local and

national

analysis

boundary

energy crops and crop residues

digestate

gas

FYM & slurry

residues

Anaerobic

digester

Crop and

animal

production

Processing plantproduct

Heat and power

Transport fuel

Local

housing,

industry, commercetransport

transport

Fuel, fertilizers, equipment CO2

CO2

CO2

waste

CO2

transport

analysis

boundary

analysis

boundary

Results: storage and pretreatment

• Some potential to increase methane production by alkaline and water-based pre-treatments, and certain spoilage organisms.

• More important, poor treatment or storage conditions reduce

biogas yields.

Digestion trials

• Single phase digestion trials on a wide range of substrates at laboratory and large scale providing valuable design data

Pilot plant trials for crops and agro-wastes

Results: single phase digestion trials• Single phase digestion trials on a wide range of substrates at

laboratory and large scale providing valuable design data

Volumetric and specific gas yields per kgVS. Trend lines based on 50-day average.

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

01.0

1.20

0529

.01.

2005

26.0

2.20

0526

.03.

2005

23.0

4.20

0521

.05.

2005

18.0

6.20

0516

.07.

2005

13.0

8.20

0510

.09.

2005

08.1

0.200

505

.11.

2005

03.1

2.20

05

Inp

ut

oT

S [

t/d

]

0,00

0,20

0,40

0,60

0,80

1,00

1,20

Gas

au

sb

eu

te [

Nm

3/k

g o

TS

]

oTs Input [t oTS/d]

Biogasausbeute [Nm3/kg oTS]

Methanausbeute [Nm3/kg oTS]

Inp

ut

VS

[t/

d]

Ga

s y

ield

[N

m³/

kg

VS

]

Phase separation innovations

Single stage

Two stage

Permeating

bed

UASB

or AF

Plug flow

Uncoupling of solids and liquid retention time

Hydrolysis

and

acidification

reactor

Methanogenic

reactor

Two phase systems(coupled and uncoupled)

Permeating beds

Plug flow reactors

Permeating bed reactors

– Single bed systems using grass

and maize have given poor results even with pH control

– Permeating bed with second stage

high rate methanogenic reactors

gives greater potential for stable operation and biogas production

– May be some potential for certain

crop types but preliminary results

indicate that overall process

efficiency is likely to be poorer

than for single phase mixed reactors

– Potentially an interesting mix of fermentation products

Plug flow systems

– Result from a high initial loading in the reactor

– Plug flow may limit the overall loading that can be achieved

– Give an interesting gas and acid production profile (H2)

– May have potential for certain

waste types and the concept

could be further exploited for

refined fuel production and biorefinery intermediates

– Still to explore very high solids

systems with high recycle rates

R2 VFA profile and gas production

Day 1

0

500

1000

1500

2000

2500

3000

3500

4000

4500

10/0

5/20

06 0

6:00

10/0

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06 0

8:24

10/0

5/20

06 1

0:48

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5/20

06 1

3:12

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06 1

5:36

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8:00

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0:48

mg

l-1

0

5000

10000

15000

20000

25000

30000

35000

ml

Ethanol Methanol C-2 C-3 i-C4 C-4 i-C5 C-5 C-6 C-7 Biogas

R2 VFA profile and gas production

0

500

1000

1500

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5000

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mg

l-1

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10000

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30000

40000

50000

60000

70000

ml

Ethanol Methanol C-2 C-3 i-C4 C-4 i-C5 C-5 C-6 C-7 Biogas

Two phase systems

– Overall performance for the treatment of market wastes at thermophilic temperatures and the loading used shows no advantage in process stability or performance compared to single phase controls

– Uncoupling of solids and liquids retention time in a first phase mixed reactor using maize as a substrate failed to improve rates of hydrolysis and solids destruction

Digester VFA

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140 160 180 200

mg

CO

D/l

SSCSSC

SSC

SSC

start-up I II III

Digester alkalinity

1000

2000

3000

4000

5000

6000

7000

8000

0 20 40 60 80 100 120 140 160 180 200

mg

CaC

O3/l

Alkalinity pH 4

Alkalinity ph 6

SSC

SSC SSC

SSC

start-up I II III

Process modelling• The anaerobic digestion model 1 (ADM1) has been adopted as a

basis for the establishment of:

– Virtual Laboratory

– DSS

European-wide

database on crop

species

Add of a Save option

Simulated results for

anaerobic digestion in

form of Figures and

Data matrices (Print

option)

ADM1

based model

Choice of Substrate

and Mixture of

Substrates

Choice of reactor and

plant type

Input of measured

crop and input data

Choice of reactor

specific data

Input of measured

reactor data

Possibility to change

Parameter

Change of model

Parameter for the

model from project

partners and own

research

European-wide

database on crop

species

Add of a Save option

Simulated results for

anaerobic digestion in

form of Figures and

Data matrices (Print

option)

ADM1

based model

Choice of Substrate

and Mixture of

Substrates

Choice of reactor and

plant type

Input of measured

crop and input data

Choice of reactor

specific data

Input of measured

reactor data

Possibility to change

Parameter

Change of model

Parameter for the

model from project

partners and own

research

Results: process modelling

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

390 400 410 420 430 440 450

Time [days]

Bio

gas p

rod

ucti

on

[m

3d

-1]

0

10

20

30

40

50

60

70

80

90

Meth

an

e c

on

ten

t [V

ol%

]

Biogas production (measured)

Biogas production (model)

Methane content (measured)

Methane content (model)

Preliminary results with original

ADM1. The model follows the

course of the experiment, but

the correlation is too low for

practical application

Adjusted model after first

manual calibration (khyd = 1 d-1)

Energy models

• Data base of energy inputs into the cultivation of different crop types established

• Factors affecting the energy use in the process have been identified

• Equations developed to account for energy usage in the digestion process

• Energy usage model developed based on typical anaerobic digestion plant configurations and substrates

Energy balance

• Inputs / outputs

• Direct energy

• Indirect energy

• Energy balance

• Energy ratio

Energy inputs

biofuel production

crop

production

biomass feedstock

direct energy

inputs

indirect

energy

inputs

fuel by-products

indirect energy inputs

other agricultural

inputs

Fossil fuels or substitute fuels from

the production process

machinery

labour

Direct and indirect energy

• Direct energy

– consumption of energy directly in the production process -includes:

• fossil fuels

• labour

• Indirect energy

– energy which has been used in producing something then used in the production process - includes:

• fertiliser

• pesticides / herbicides

• machinery

Direct & indirect energy inputs

constructionheat, powerprocessing

transport equipmentfuelproduct distribution

energy input type

production,

application equipmentapplication fuelfertiliser

production and transportfuel

equipmentfuelharvest

indirectdirectoperation/input

equipmentfuelcultivation

Energy inputs in maize crop production

operation

No of

operations equipment time (h/ha)

energy of

equipment

MJ/ha tractor (kW)

fuel used

(l/ha)

CO2 indirect

(kg/ha)

subsoil 1 subsoiler 1.333 120 90 14.6 5.4

plough 1 plough+press 1.333 120 90 17.5 5.4

drill/harrow 1 combined drill and harrow 0.62 158 90 3.9 7.1

fertiliser 1 fertiliser spreader 0.36 45 55 1.2 2.0

spray 2 sprayer 0.54 68 55 2.4 3.1

harvest 1 forage harvester 2 420 17.5 33.6

cart 1 trailer 2 120 55 7.8 5.4

ensile 1 tractor and bucket 1.48 8 55 5.8 0.4

tractor 90 kW 3.286 564 45.1

tractor 55 kW 4.38 297 23.8

fuel used (litres) 2785 MJ/ha 70.7 213.6

total indirect 1920 MJ/ha 131.2

hours

labour 9.7 18.8 MJ/ha

seed kg/ha 16 215 MJ/ha 2.4

chemicals (kg/ha)

N 150 6045 MJ/ha 285.6

P2O5 200 680 MJ/ha 140

K2O 175 1277.5 MJ/ha 79.3

packaging & transport 1362 MJ/ha

sprays 12.8 2432 MJ/ha 63.0

total energy input to crop production and storage 16.7 GJ/ha 915.2 kg/ha

Crop production inputs

0 1 2 3 4 5 6 7 8 9

fuel

machinery

fer tiliser

pesticides

labour

Energy requirement GJ ha-1

sugar beet

maize

wheat

soya

lucerne

Digester energy flows

digester 500m³ digestate

tank

gas collector

heat exchanger

p4

p3

p2

mix1 reception tank mixer 3.0 kJ s-1 0.64 hrs d

-1

mac1 feedstock macerator 2.2 kJ s-1 1.75 hrs d

-1

p1 digester feed pump 3.0 kJ s-1 1.75 hrs d

-1

p2 digester discharge pump 3.0 kJ s-1 1.75 hrs d

-1

p3 digester mixing pump 2.2 kJ s-1 7.25 hrs d

-1

p4 digestate heating pump 0.5 kJ s-1 8.0 hrs d

-1

reception tank

mac1 p1

mix1

air 2°C

dry ground 5°C

cladding steel 0.75mm

structural steel 6mm

insulation 100mm

concrete 300mm

digester contents 35°C

Main energy inputs are heat and electricity

An energy balance

GJ/year49,932energy value

GJ/ha157

m32,331,092biogas produced

m31,398,655methane

GJ/ha30

GJ/year9566total energy requirement

GJ/year259.5digestate disposal energy

GJ/year1350digester embodied energy

GJ/year420parasitic electricity requirement

GJ/year2133parasitic heat requirement

GJ/year93crop transport

GJ/year5310.6crop energy requirement

ha318crop area

t/day34.8daily load

m32000digester capacity

unitvalue

36%

20%1%

22%

4%

14%

3%

crop energy requirement nitrogen fretiliser

crop transport parasitic heat requirement

parasitic electricity requirement digester embodied energy

digestate disposal energy

Digestate

• the digestate is what remains after the biogas has been removed

• it contains most of the nutrients of the original feedstock

• the nutrients are in a form which are more available for crop uptake

• it has a consistency similar to slurry (approx 10% solids)

• it can be separated into solid and liquid fractions

Effect of digestate use on the energy balance

GJ/ha126.9mineral

GJ/ha22.7total energy requirement

GJ/ha30.1total energy requirement

GJ/ha6.04energy for nitrogen

net energy yield

GJ/ha134.3digestate

GJ/ha157methane energy value

GJ/ha9.3crop energy requirement

digestate fertiliser

GJ/ha16.7crop energy requirement

mineral fertiliser

unitvalue

Example energy comparisons

61.111740.4

energy of fuel produced

(GJ/ha)

13.241.49.2

energy for processing

(GJ/ha)

12.811.912.7

energy for crop production

(GJ/ha)

6.911.53crop yield (t DM/ha)

8563crop yield (fresh yield t/ha)

150147195fertiliser (N kg/ha)

wheat

grain

sugar

beet

OSR

seedcrop

bioethanolbiodieselfuel

Elsayed, M. A., Matthews, R. and Mortimer, N. D. (2003) Carbon and Energy

Balances for a Range of Biofuels Options, School of Environment and

development, Sheffield Hallam University, B/B6/00784/REP

8.346.836.363.795.502.352.201.84energy ratio (output/input)

166157.189124.8

8.38810.8

1616.715.511.9

1512.66.911.5

3840856

160150150147

whole

crop

triticalemaize

wheat

grain

sugar

beet

methane

146.1141.7132.465.5102.135.163.718.5net energy produced (GJ/ha)

166

8.3

11.6

15

38

80

whole crop

triticale

methane

Potential vehicle fuel produced per ha

0 1000 2000 3000 4000 5000

whole crop wheat CH4

silage maize CH4

whole crop OSR CH4

tops

wheat grain bioethanol

OSR biodiesel

wheat grain CH4

sugar beet bioethanol

sugar beet CH4

litres diesel equivalent per hectare (after processing energy deducted)

beet

Potential CHP per hectare

0 2 4 6 8 10 12 14 16 18

wheat grain

wheat whole crop

sugar beet

sugar beet tops

maize whole crop

OSR whole crop

potential output MWh per ha

heat

electricity

Feedstocks for biofuel production

• for biodiesel

– oilseed rape

– sunflower

– linseed

– soya

– peanut

• for bioethanol

– wheat

– sugar beet

– maize

– sugar cane

– lignocellulosicmaterial

• for biogas– barley

– cabbage

– carrot

– cauliflower

– clover

– elephant grass

– flax

– fodder beet

– giant knotweed

– hemp

– horse bean

– jerusalem artichoke

– kale

– lucerne

– lupin

– maize

– marrow kale

– meadow foxtail

– miscanthus

– mustard

– nettle

– oats

– pea

– potato

– rape

– reed canary grass

– rhubarb

– ryegrass

– sorghum

– sugar beet

– triticale

– turnip

– verge cuttings

– fetch

– wheat

Which

crops?

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7Barley

Cabbage

Carrot

Cauliflower

Clover

Comfrey

Cocksfoot

Elephantgrass

Flax

Fodder beet

Giant knotweed

Hemp

Horse bean

Jerusalem artichoke

Kale

Lucerne

Lupine

Maize

Marrow kale

Meadow foxtail

Miscanthus

Mustard

Nettle

Oats

Pea

Potato

Rape

Reed canary grass

Rhubarb

Rye

Ryegrass

Sorghum

Sudangrass

Sugar beet

Sunflower

Sweet sorghum

Triticale

Turnip

Vetch

Wheat

White cabbage

methane potential m³/kg VS added

CO2 and energy cycles

gas scrubbing

transport &

spreading

digestion

vehicle fuel

Sun

biomass

Biogas

digestate

CHP

CO2

vehicle fuel

heat &

electricity

cutting, collection &

transport

energy

material

electricity

biomass