Effect of organic loading rateon biogas yieldfrom animal slurry and biogas crops

Bernd Linke and Pia MähnertLeibniz-Institut für Agrartechnik Bornim (ATB)www.atb-potsdam.de

systems of biogas production in agriculture

basic parameter of CSTR

a simple model of biogas production

results of lab-scale experiments

conclusions

International Energy Agency Task 37 ConferenceUniversity College Cork, September 15, 2011

Systems of biogas production fromgreen biomass and animal waste slurry

Green BiomassSlurry Digested material, liquid

Biogas

Green BiomassSlurry Digested material

liquid

Biogas

Green BiomassFarmyard manure

Biogas

Digested material, solid

Liquor

Plug flow digester

CSTR

Bioleaching

Strom

Wärme

Digestedsludgebiogas crops

1 Animal stables2 slurry pit3 Storage tank4 Biogasreactor5 Gasholder6 CHP7 Storage tank8 Crop land

1

23

4

5

6

7

8

Schematic layout of a typical biogas plant

)( 10

dtmmassinput

VStkgcionconcentratinput )( 1

0

);( 3 tmVfermenterofvolume R

)( 13 dmQbiogasofquantity B

)( 1dtmbiogasofmass B

)( 10

dtmmm

materialdigestedofmass

BA

)( 1tkgc

materialdigestedofionconcentrat

A

Process parameter

)(0

dm

VHRTtimeretentionhydraulic R

dm

kg

t

c

V

cmOLR

mR3

000

Performance parameter

kg

m

cm

Qyyieldbiogas B

B

3

00

dm

mBy

V

Qrratebiogas RB

R

BB 3

3

Basic parameter of dimensioning CSTR

Feed

0

1

2

3

4

5

0 50 100 150 200 250

mittlere hydraulische Verweilzeit tm (d)

oT

S-R

au

mb

ela

stu

ng

BR

(kg

m-3

d-1

)

)( 10

tkgc

50 d 150 d

animalslurry

GreenBiomass

35030025020015010050

Correlation between OLR, HRT und c0

HRT

c

V

cmOLR

R

000

00 cmRV

BQ

AA cm

)(dHRT

)( 13 dkgm

OLR

Effect of OLR on biogas yield y = f(OLR) ?

OLR (kg m-3 d-1)

?

my

y

c

cc

0

0

0)(000

0

crVcmcmdt

dcV RR

overturnoutputinputchange

substrate decay = formed biogas

Zeit t (d)

cc 0

c

y

0c my

ckr

1

1 0

c

c

kHRT

yy

y

kHRT

m

1

HRT

Vm R0

Modeling of biogas productionaccording a 1st order reaction rate

)(

)(1

0

10

tkgc

dtm

)(

)( 1

tV

tkgc

R

)( 13 dmQB

)( 10

dtm

yy

y

c

c

m

m

0

OLR

cHRT 0

OLRck

ckyy m

0

0

yy

y

c

OLRk

max0

yy

y

kHRT

m

1

myy

1

kHRT

kHRT

Efficiency of biogas yield

0,7

0,75

0,8

0,85

0,9

0,95

1

0 50 100 150 200 250 300

tm (d)

An

teil

pv

on

ym

(-)

0.30.4

0.5

0.040.05

0.06

0.150.2

0.125

0.1

0.09

0.08

0.07

0.035

0.03

0.025k=0.02 d-1

h

)(dHRT

)(myof

Schematic layout of lab-scale testing facility (CSTR)

1 thermostat2 effluent3 fermenter4 influent5 stirrer6 gas bag7 magnetic valve8 pressure sensor9 gas meter10 gas analyser11 PC

Substrat pH TS

[% FM]

VS

[% TS]

sugar

[% TS]

XP

[% TS]

XL

[% TS]

XF

[% TS]

Maize silage 3,7 31 (35) 94,6 5,3 (1,5) 14,4 (8,1) 2,6 (3,2) 24,1 (20,1)

Beet silage 3,8 13 (15) 91,8 27 (61) 7,5 (7,7) 0,9 (0,7) 8,2 (6,4)

Rye silage 4,7 23 (21) 86,7 1,1 (-) 9,4 (10,5) 3,3 (3,7) 31,6 (35,1)

Cow slurry 7,1 9,8 81,2 - - - -

(...) fodder values for ruminants KIRCHGESSNER (1997)XP: raw protein, XL: raw fat, XF: raw fibre

Chemical analysis of biogas substrates

Maize silage, cow slurry and two mixtures

)( 13 dkgmOLR

)( 13

kgm

yieldbiogasVS

Beet silage, cow slurry and two mixtures

)( 13

kgm

yieldbiogasVS

)( 13 dkgmOLR

Cow slurry Pig slurry

Mixture c0

(% FM)

ymax

(m3 kg-1)

k

(d-1)

c0

(% FM)

ymax

(m3 kg-1)

k

(d-1)

100% maize silage 29,2 0,92 0,033 25,3 0,82 0,147

67% maize silage 14,7 0,81 0,052 9,9 0,69 0,301

33% maize silage 9,7 0,74 0,051 6,0 0,62 0,119

100% rye silgae 19,8 0,92 0,040 20,2 1,01 0,028

67% rye silage 12,5 0,82 0,052 9,2 0,88 0,052

33% rye silage 9,2 0,73 0,054 5,9 0,81 0,057

100% beet silage 12,4 0,93 0,316 11,4 1,08 0,162

67% beet silage 10,0 0,80 0,252 7,3 0,89 0,155

33% beet silage 8,4 0,73 0,113 5,5 0,73 0,105

100% slurry 7,2 0,61 0,046 4,4 0,55 0,057

Kinetic parameter for model equation

Biogas potential ym from a batch test

Efficiency of biogas yield

yy

y

c

OLRk

max0

OLRck

yy

y

m

10

OLRck

ckyy m

0

0

1

130

30

087,0

056,5

58

dk

dFMmkgVSck

FMmkgVSc

100/)( EGEGM pyyyy

VS-biogas yield from mixtures of green biomassand animal slurry

Proportion of green biomass in the mixture, VS-basis (%)

Proportion of animal slurry in the mixture, VS-basis (%)

)( 13

kgm

yieldbiogasVS

1

kHRT

kHRT

1

1

kHRT

1FV 2FV

)1(1 FFermenter )2(2 FFermenter

0m

)1(1

1

0

11

11

m

V

kHRT F

F

FF

)2(1

1

0

2121

2121

m

VV

kHRT FF

FF

FFFF

)3(

1

11

1

10

21

210

1

2

1

21

F

F

FF

FF

F

F

F

FF

k

m

k

m

V

V

V

VV

1

1

1

1

2

1

2

121

F

F

F

F

F

FFF

V

V

V

V

1FHRT

1F

21 FF

1

21 FFHRT

k

Two fermenter in line

1

11

121

FFFF

q

q

(1) und (2) solve to VF1 bzw. VF1+VF2 andform ratio:

(3) Solve to h F1+F2 and set VF2/VF1=q :

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

0 1 2 3 4 5

Verhältnis Volumen Nachgärer zum Fermenter q (-)

An

teil

F+

N(-

)

0,60

0,65

0,70

0,75

0,80

0,85

0,90

0,95

1,00

F

0,60

0,65

0,70

0,75

0,80

0,850,90

max

1

y

yF

1

)1(1

121

q

qF

FFF

FBQ ,

00 cmFV

AA cmNV

NBQ ,

Biogas yield from two fermenter in line

)(

21

FF

1F

)(/ 12 qVV FF

0

2

4

6

8

10

12

14

16

18

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0

Raumbelastung BR

Org

an

isch

eS

äu

ren

(gkg

-1)

Pro

pio

nsäu

re(g

kg

-1)

0

1

2

3

4

5

6

7

8

9

pH

-Wert

(-)

NH

4-N

(gkg

-1)

organische Säuren Propionsäure pH NH4-N

Fermenter performance Maize silage (35°C)

)( 13 dkgmOLR

)(

)(

14

gl

NNHpH

)( 1gl

VFA

Conclusion

OLR important parameter for fermenter dimesnioning

value of OLR effects biogas yield and fermenter performance

effect of OLR on biogas yield follows a first order reaction

common treatment of animal waste slurry and green biomass allowshigher values of OLR and better process stability

increase of OLR results in decrease of VS-biogas yield, therefore asecond digester or a gastight storage of digested material isrecommended