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DBFZ Deutsches Biomasseforschungszentrum
gemeinnützige GmbH
DBFZ
The 3rd International Cooperation Conference on Biogas
Industrialization in China (Organizers: CAAA, DLG, CBS)
19.05.2012 Nanjing, China
The administration and performance
evaluation of biogas plants in Germany
Jan Postel, Dr. Britt Schumacher, Dr. Jan Liebetrau
DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Torgauer Str. 116, D-04347 Leipzig, www.dbfz.de
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Performance evaluation of
biogas plants
Efficiency: Ratio of actual power output and power input
What is required to evaluate a biogas plant?
1.
Mass balance of in- and output
2.
Energy balance of the biogas plant, including in- and output
3.
Data of the reliability of the equipment (hours/year)
What is needed for the mass/energy balances and the reliability data?
1.
Characterization of substrates
2.
Main state of the art technologies (data acquisition)
3.
Losses/Emissions
4.
Evaluation of the overall biogas plant concept
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Performance evaluation of
biogas plants (process chain)
Excrements
Preliminary
tank
What is required to evaluate a biogas
plant?
• Mass balance of in- and output
• Energy balance of the biogas plant,
including in- and output
• Data of the reliability of the
equipment (hours/year)
Biogas
Energy crops
Digester
Silo
Substratestorage
SubstrateFeed in
Digestate
Gasstorage
Biogasutilization
e.g. combined
heat and power
plant (CHP)
Distribution/Application digestate
Storage tank (digestate)
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Requirements for energy balances
as basis for efficiency evaluation
 Efficiency: Ratio of actual power output and power input
 What is necessary for a qualified evaluation?
1. Definition of theoretical energy output
2. Evaluation, documentation, quantification of mass and energy streams,
Evaluation of operational hours, (documentation of down times, flaring
events, maintenance periods etc. )
3. Calculation of capacity utilization
4. Actual – theoretical comparison
5. Identification of bottlenecks
6. Optimization
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Mass balance
Grass silage
Digester
Cattle Manure
Digestate
Inorganic matter
Organic matter
Water
Water vapour
Carbondioxid
Documentation and
quantification of all
relevant mass streams
Methane
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Mass balances
evaluation
 Does the quality and amount of input masses realized in practice meet the
design assumptions?
 Is the Biogas production according to the theoretical value?
(consider the conversion efficiency within the CHP as important factor if
no direct quantification of the biogas mass flow is available!!)
• If not check:
- Substrate quality (is the assumed biogas potential correct?)
- Infeed amount correct?
- Quantification of degree of degradation by means of a gas
potential test of the digestate
- Stability of biological process (acid concentration?)
- Temperature
- Inhibition effects
- Leackage of biogas within the gas collection system
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Energy
balance
A high degree
of utilization of
waste heat
from the CHP
is of enormous
relevance for
the overall
efficiency
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Energy balance evaluation
 Is the energy output as expected?
 Electrical:
 If not check:
• Biogas production as assumed?
• CHP unit – conversion efficiency as assumed?
• Consumption of devices on site to large?
• Downtime - what are bottlenecks of the process?
 Thermal:
 If not check:
• Losses due to poor insulation?
• Are there other options for heat utilization?
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1. CHARACTERIZATION OF
SUBSTRATES
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Biomass / Substrates
Energy crops
By-products & Residues
Organic waste
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Substrate characteristics
 Gas potential (maximum biogas yield obtainable) measured or
calculated (digestion tests, animal nutrition test, elementary analysis)
 Degradation rate (reduction of the concentration of organic substance)
 Content of micro (trace) and macro elements
 Content of potential inhibitory substances as nitrogen, sulphur,
antibiotics etc.
 Material handling: pumpability, content of disturbing material (e.g.
sand, stones)
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Characterization of Substrates Composition
 Dry matter content (DM): waterless (anhydrous) share of a mixture after
drying at 105 °C.
 Organic dry matter content (oDM): Mixture free of water (anhydrous) and
free of inorganic substances generally per drying at 105 °C and annealing
at 550 °C
 Fractions of fat, protein and carbohydrate analyzed by “Weender” – Animal
nutrition analysis
Representative samples of the biomass are essential for meaningful results!
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Methods of substrate´s
characterization
Animal nutrition analysis
Continuous anaerobic digestion
Discontinuous anaerobic digestion
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Methods of substrate´s
characterization
Effort
Informative value
Digestion tests
Medium (approx.
35 days)
High (months)
Medium (general degradability)
High (degradability under real
conditions, inhibition, deficiencies)
Elementary analysis
Medium (approx.
1 week)
Medium (approx.
1 week)
Medium (fat, protein, various
carbohydrates, ash)
Low (all elements, but carbon as
lignin is not degradable)
Data from literature
low
Depended on the quality of source
Batch
Continuous
Tests to calculate the
biogas yield
Animal nutrition
Representative samples of the biomass are essential for meaningful results!
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Biogas potential
Substrate
TS, VS
%, %TS
biogas potential
m3/t substrate
biogas potential
m3/t VS
cow manure
8-11, 75-82
20-30
200-500
pig manure
7, 75-86
20-35
300-700
cow manure
25, 68-76
40-50
210-300
Chicken manure
32, 63-80
70-90
250-450
Corn silage
20-35, 85-95
170-200
450-700
Rye silage
30-35, 92-98
170-220
550-680
molasses
80-90, 85-90
290-340
360-490
Separately collected biowaste
40-75,50-70
80-120
150-600
Lipids from grease separator
2-70, 75-93
11-450
700
Glycerin (SEEG)
47, 70
425
1295
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Characterization of Substrates Conclusion
 Substrates differ in energy density, composition and degradability
 Mostly pre-treatment enhances the degradability of substrates,
except for lignin, which is only aerobic degradable
 High amounts of extreme easy degradable substrates can lead to
process failure, due to a excessive acid production
 Mono-fermentation can lead to an unbalanced nutrient supply,
therefore a suitable mixture of substrates or a supply with lacking
nutrients are recommendable
 High concentrations of ammonia can lead to difficulties in the
biological process
 High concentrations of sulphur can cause damage e.g. CHP
 Sand and stones can lead to technical difficulties
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2. MAIN STATE OF THE ART
TECHNOLOGIES
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General technical requirements
• high reliability/durability and short maintenance interruptions of all plant
components are essential for high operating and full load hours – the
overall process has to be reliable!
• Technology has to match the substrate/biomass, sufficient flexibility for
change in substrate
• Capacity of the plant as a whole and the plant components have to
match the actual substrate and mass flows
• Low energy consumption
• Easy to monitor and control
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Biomass and reactor type
• Digester type is selected according to the substrate characteristics
• Agricultural application TS between 3 – 12 % continuous stirred tank
reactor (CSTR), manure and energy crops
• plug flow digesters mostly for higher total solid concentrations
• Box/garage type digestion only for biomass, which is stackable and
can be easily saturated by percolate (landscape management
material, separately collected biowaste), highly insensitive to sand,
rocks, disturbing material
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Continuously stirred tank reactor (CSTR)
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Plug Flow Tank Reactor (PFTR)
vertical
horizontal
Gas
Intake
Eintrag
Discharge
Austrag
M
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Batch Reactor
Garage type digester
discontinuous
Prozeßschema Boxenfermenter (Abbildung: BEKON GmbH Co. KG); Fotos: Bekon GmbH (oben), DBFZ (unten)
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Process evaluation
Laboratory tests
Online measurement
 Degradation of VS, TS, TOC, COD
 Input
 Content of organic acids (sum
parameter)
 Gas production rate
 Content of organic acids (portion of
each acid)
 Methane content
 pH-value
 Carbondioxid content
 Hydrogen content
 Temperature
not permanent available
Permanent available,
need of sampling
easy integration to automated
process
time consuming,
difficult to automate,
information content???
high information content
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Technologies - Conclusion
 Energy output depended on many factors (substrate qualities,
stability of biological process, efficiencies and availabilities
technical devices)
 Primary target should be: process stability, reliability of
technology
 Secondary target: gas production rate and energy output
 The energy consumption of all devices should be kept by a
minimum
 A high degree of utilization of waste heat from the CHP is of
enormous relevance for the overall efficiency
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3. LOSSES/EMISSIONS
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Losses / Emissions
 Losses reduce the energy output and lead to emissions (gaseous,
liquid, solid)
 Need to minimize losses to
• prevent environmental pollution
• avoid the release of greenhouse gases
• prevent the release of toxic substances
• ensure high energy efficiency
• ensure economical operation
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Sources of emissions
within the process chain
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Elevated N2O und
NH3-Emissions
due to crop growing ?
Humus balance?
Nutrition balance?
No data available preliminary tank
Excrements
methane losses of the plant?
Leakages?
Methane losses –
Biogas upgrading?
Coverage?
Silage losses
5-20% ?
Preliminary
tank
Relief pressure valve?
Emissions- from the
Co generation unit ?
Biogas
Energy crops
Digester
Silo
Substratestorage
SubstrateFeed in
Gasstorage
Biogasutilization
Digestate
Distribution/Application digestate
Emissions not extensively investigated yet
dependend on substrates, moisture content of the soil,
climate, time and period of application
Storage tank (digestate)
Large variations in N2O emissions
e.g. Methane emissions from open storage tanks;
Dependend on processing + substrates
Emissions influenced by distribution techniques
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Possible losses I
• Silage storage facilities
 Respiration and decomposition of organic matter
• Hopper/ preliminary tank/ open hydolysis
- Hopper used for mixing of substrate with digestate
 Methane (CH4), Hydrogen (H2)
- Solid material feed in device
 Respiration and decomposition of organic matter
• Digester
- Permeability of rubber membrane, leakages and pressure relief
valves
 Mainly Methane (CH4)
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Possible losses II
• Storage tank (digestate)
 Methane (CH4), nutrients (fertilizer value) (NH3,(N2O))
• Gas utilization
- Co generation unit
 Mainly Methane (CH4) and unburnt hydrocarbon (CnHm)
- Upgrading facilities (Feed in with natural gas quality)
 Methane slip (CH4)
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Gas potential of digestates
Specific biogas yield (l*kgVS-1)
600
500
400
300
200
100
0
0
5
10
15
20
25
30
35
Time (d)
Low retention times lead to incomplete substrate utilization
For comparison: 18-70 m³/t digestate
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3. Losses / Emissions - Conclusion
 due to environmental and economic reasons losses should be
avoided
 Plant design, substrate and operation of the plant affect the
amount of losses
 Frequent check of the plant and operational management should
be self-evident
 Actual – theoretical comparison is needed for precise
identification of losses!
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4. EVALUATION OF THE
OVERALL BIOGAS PLANT
CONCEPT
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Evaluation for Optimization
Aim: Achieving of a defined target state (optimum) by well-directed
modification of current situation


Procedure
Process control
 Greenhouse gas emissions
 Odour emissions
 Noise emissions



Availability
Capacity utilization
Efficiency



Investment costs
Operational costs
Income
No independent optimization of isolated items
possible, due to mutual dependency
Source: Leitfaden Biogas; www.fnr.de
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4. Evaluation of the overall biogas
plant concept - Conclusion
 Are technology and substrates (texture/amount) a good match?
 Which ratio of energy production to energy consumption is achievable?
(electricity and heat)
 Fits the plant to operational needs, infrastructure and consumers - gas,
electricity and/or heat grid?
 Are collection and documentation of data appropriate to avoid malfunction?
 Are the losses reduced to a minimum?
 Which climatic conditions are to consider? Are insulation or cooling
needed?
 Are the distances between biogas plant and substrates source respectively
between biogas plant and residues application short enough? (logistics,
costs)
 Are aspects of environmental protection to consider?
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Thank you very much for your attention!
Research for the Energy of the Future
Deutsches BiomasseForschungsZentrum
German Biomass Research Centre
Torgauer Straße 116
D-04347 Leipzig
www.dbfz.de
Tel./Fax. +49(0)341 – 2434 – 112 / – 133
Contact:
Dr.-Ing. Jan Liebetrau
Jan Postel
Dr. Britt Schumacher