Biofuel production via thermal gasification of biomass By Lasse Røngaard Clausen Assistant professor Section of Thermal Energy Technical University of Denmark (DTU)
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Who am I? • Assistant Professor at the Section of Thermal Energy • Expertise in thermodynamic modeling and energy/exergy optimization of
complex energy systems – Focus on biofuel production via thermal gasification
• Other research interests:
– Exergy analysis of energy systems – Thermoeconomics – Integration of agriculture in the energy system – nutrient recycling
• Recent projects at the Section of Thermal Energy
– High temperature heat pumps – Low temperature heat to power (ORC, Kalina, other mixtures of
working fluids, solar thermal power)
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Biofuel production via thermal gasification An overview
Biomass Gasifier
Liquid fuel Synthesis reactor
Biomass
Syngas (synthesis gas)
• Consist of CO and H2 (the building blocks for chemical synthesis)
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Agenda
• Gasification of biomass
– Gasifiers developed at DTU
• Biofuel production plants – Proposed designs
• Biofuel plants based on entrained flow gasification of torrefied biomass
• Biofuel plants plants based on the Two-Stage Gasifier • Biofuel plants integrating electrolysis of water
– Future work • Biofuel plants based on an oxygen-blown Two-Stage Gasifier • Biofuel plants based on an entrained flow gasifier with
integrated torrefaction of biomass
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Gasifiers developed at DTU: The Two-Stage Gasifier
• Downdraft fixed bed
• High energy efficiency (~93%)
• No tar and low CH4 in gas
• Temperature out: 730°C
• Small-scale plant (max 5 MWth)
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Gasifiers developed at DTU: The Two-Stage Gasifier (The Viking Gasifier)
• The Viking gasifier (picture) is 15-20 kWe
• It has been successfully upscaled to 100 kWe
• A 500 kWe plant is being built at the moment.
• The Technology is now owned by the Danish company Weiss.
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Gasifiers developed at DTU: The Pyroneer gasifier
• 2 fluidized beds
• High tar and CH4 in gas
• Temperature out: ~650°C • Can convert almost any kind of
biomass – Straw – Biogas residue
• The ash can be used as
fertilizer because temperatures are below 730°C
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Gasifiers developed at DTU: The Pyroneer gasifier
• The Technology is now owned by the Danish power company DONG Energy
• A 6 MWth demonstration plant is under operation at the moment (picture).
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Straw
Manure
Biogas residue
Sewage sludge
Other agricult. waste Meat-and-bone meal
Wood
Etc.
Cofiring with coal, oil or gas into
existing powerplant boilers
Indirectly fired gasturbines
Large Stirling engines
Production of liquid fuels or more
valuable chemicals
Directly fired gasturbines,
combustion engines or fuel cells (with gas
cleaning)
Industrial waste
Household waste
LT-CFB plant Pyroneer gasifier, or
Suitable plant sizes : ~5-150 MWth (depending on the fuel and the application)
Reforming of the tar and CH4 in the gas is required
Gasifiers developed at DTU: The Pyroneer gasifier
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Agenda • Who am I?
• Gasification of biomass
– Gasifiers developed at DTU
• Biofuel production plants – Proposed designs
• Biofuel plants based on entrained flow gasification of torrefied biomass
• Biofuel plants plants based on the Two-Stage Gasifier • Biofuel plants integrating electrolysis of water
– Future work • Biofuel plants based on an oxygen-blown Two-Stage Gasifier • Biofuel plants based on an entrained flow gasifier with
integrated torrefaction of biomass
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Biofuel production via thermal gasification An overview
Biomass Gasifier
Liquid fuel Synthesis reactor
Biomass
Syngas (synthesis gas)
• Consist of CO and H2 (the building blocks for chemical synthesis)
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1. Biofuel plants based on entrained flow gasification of torrefied biomass
- Shows the potential of state of the art within biofuel plants
2. Biofuel plants based on the Two-Stage Gasifier
- Shows the potential of small-scale biofuel plants
- Economy at this scale is a great challenge – this must be outweighed by the advantages of small-scale (high-efficiency gasifier, co-production of heat).
3. Biofuel plants integrating electrolysis of water
- Enables full conversion of the carbon in the biomass to biofuel
- Enables conversion of electricity from fluctuating renewables (wind, solar) to biofuel for the transportation sector.
Biofuel plants: Proposed designs
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• Very large scale is possible by using torrefied wood pellets as fuel.
• Torrefied wood has increased energy density (~20 MJ/kg), which increases gasifier energy efficiency.
• Almost all the syngas can be converted to fuel because the syngas contains few inerts (CH4, N2) – oxygen-blown gasification is used.
DME-RC
59%100% 90%
DMEWood
Torrefication
10%
Gasification
73%
WGS
71%
17%
Synthesis
1% Off-gas boiler
11%2%
Chemical energy
Heat
• Modeling shows potential of energy efficiencies up to 59% (LHV) from untreated wood to DME – 64% including net-electricity.
Biofuel plants: Proposed designs (1/3) Biofuel plants based on entrained flow gasification of torrefied biomass
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• Small-scale due to the Two-Stage Gasifier
• High energy efficiency due to high energy efficiency of gasifier
• Modeling shows potential of energy efficiencies up to 58% (LHV) from untreated wood to DME – no net-electricity.
Fly ash
Wet Wood
Methanol reactorGas-liquid separator
Gas engine
Methanol (97 mol%)
Ash
gasifier
750 C1 bar
Water
Steam
200 CDry wood + steam
Pyrolysis reactor
Air
115 C
Air
630 C
730 C
200 C 40 C
100 bar
220 C 40 C
400 C~CO2
Chemical energy
Heat
Biofuel plants: Proposed designs (2/3) Biofuel plants based on the Two-Stage Gasifier
58%100% 93%
DMEWood
7%
GasificationSynthesis
24%Engine11%
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• All the carbon in the biomass ends up in the biofuel – therefore no CO2 emission.
• Potential for storing surplus electricity from renewables (wind, solar, etc.)
• Modeling shows potential of energy efficiencies up to 115% from untreated wood to methanol – with electricity consumption the efficiency drops to 58%.
Water
GasBiomass
O2
Gasifier
Electrolyser
O2 H2
Syngas
Typical gas composition from gasifier (mol%): 29% H2 51% CO 7% CO2 13% H2O.
Chemical energy
Heat
Biofuel plants: Proposed designs (3/3) Biofuel plants integrating electrolysis of water
115%
100% 90%
MeOH
Wood
Torrefaction10%
96%
18%4%
Off-gas boiler
22%
99%
Electrolysis
30%
24%69% 45%
SynthesisGasification
Electricity
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Why integrate electrolysis of H2O/CO2 in a biofuel plant?
• If great amounts of fluctuating renewables (wind, solar, etc.) needs to be integrated
in the electricity grid. This is the case of Denmark: – In 2011 28% of the Danish electricity consumption was provided by wind. – In 2020 the official goal is 50% – In 2050 the official goal is a fossil free energy system.
• If the biomass resource shows to be very limited and expensive.
In a recent Danish Study (CEESA), Biofuel plants with integrated electrolysis supplies 44% of the fuel for the Danish transportation sector in the 2050 Scenario (see next slide).
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The CEESA 2050 renewable energy scenario
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Agenda • Gasification of biomass
– Gasifiers developed at DTU
• Biofuel production plants – Proposed designs
• Biofuel plants based on entrained flow gasification of torrefied biomass
• Biofuel plants plants based on the Two-Stage Gasifier • Biofuel plants integrating electrolysis of water
– Future work • Biofuel plants based on an oxygen-blown Two-Stage Gasifier • Biofuel plants based on an entrained flow gasifier with
integrated torrefaction of biomass
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The planned future work continues to explore the integration of electrolysis in biofuel plants
1. Biofuel plants based on an oxygen-blown Two-Stage Gasifier + SOEC/SOFC
- Can reach unprecedented energy efficiencies (biomass + electricity ⇒ biofuel)
2. Biofuel plants based on an entrained flow gasifier with integrated torrefaction of biomass + electrolysis
- The loss of chemical energy due to torrefaction is eliminated
- High energy efficiency
Biofuel plants: Future work
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Biofuel plants: Future work (1/2) Biofuel plants based on an oxygen-blown Two-Stage Gasifier + SOEC/SOFC
• Work based on the proposed designs: 2 and 3
• Higher energy efficiency due to greater conversion of syngas to biofuel (no N2)
• Integration of a SOEC/SOFC. Used as SOEC when electricity is cheap – used as SOFC when electricity is expensive.
Chemical energy
Heat
• The project will include both theoretical and experimental work.
• Partners: – The Gasification group at DTU – Haldor Topsoe – Danish Gas Technology Centre (DGC)
179%
100% 93%
SNG
Wood
Gasification7%
42%
142%
SOEC Electrolysis
14%
128%
Synthesis
Electricity
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125%
100% 80%
MeOH
Wood
Torrefaction1%
153%
10%
4% Off-gas boiler
24%
91%
Electrolysis
27%
64%
SynthesisGasification
Electricity
19%
Biofuel plants: Future work (2/2) Biofuel plants based on an entrained flow gasifier with integrated torrefaction of biomass + electrolysis
• Work based on the proposed designs: 1 and 3 • The volatiles released during torrefaction is used as a chemical quench in the
gasifier. This increases gasifier efficiency, and ensures that no biomass is lost in the torrefaction.
Chemical energy
Heat
Milling
Oxygen
Wood
900 C
CO2
Feeding & Pressurization
Process heat
Slag
Entrained flow gasifier40 bar
1300 C
Torrefaction
volatiles
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Biofuel production via thermal gasification
Biomass Gasifier
Liquid fuel Synthesis reactor
Biomass Thank you for your attention
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extra slides
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Hurdles to overcome before biofuel plants are commercial
• Cost
– An incentive to use biomass instead of coal is needed • Subsidy on biomass • Tax on coal • Tax on CO2 emission (best option, and also the main hurdle!!)
• Technical
– Up scaling the demonstrated small-scale gasifiers – Using biomass on existing large-scale coal gasifiers
• Environmental
– The biomass used must be sustainable (not replace food/feed production, net greenhouse gas emissions from land use change, etc.)
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Biofuel plants Polygeneration
Biomass Gasifier
Liquid fuel Synthesis reactor
Biomass
• The total energy efficiency of the
biofuel plant can be increased by co-production of:
– Electricity – Heat
Fuel
Electricity
Heat
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Important aspects in the design of BTL plants
Pros Cons
Gasification Air Low cost, simple design N2 in syngas ⇒ lower conversion of syngas to fuel
Oxygen No N2 in syngas ⇒ higher conversion of syngas to fuel
Cost and electricity consumption of oxygen plant
Atmospheric Cost of gasifier, simple design High electricity consumption for pressurization of syngas
Pressurized Low electricity consumption for pressurization of syngas
Cost of gasifier
Synthesis Recycle of unconverted syngas (RC)
Higher conversion of syngas to fuel Lower electricity co-production
Once through synthesis (OT)
Higher electricity co-production
Lower conversion of syngas to fuel
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Oxygen
WGSreactor
Gas cleaning and
conditioning
30 C
DME reactorGas-liquid separator
280 C -40 CDME
methanol
Water
H2S, COS
Unconverted syngas
60 bar
Water
CO2
Slag
Entrained flow gasifier
40 bar1300 C
200 C 300 C
Biomass
Syngas (H2 ,CO)
H2 ,CO, CO2, H2O
~CO2
Adjusting the H2/CO-ratio:
CO + H2O → CO2 + H2
DME: 3CO + 3H2 → CH3OCH3 + CO2
Methanol: CO + 2H2 → CH3OH
The processes in a biofuel plant Generic biofuel plant (DME) showing the important processes
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Gasifier types Fixed bed gasifier Fluidized bed gasifier Entrained flow gasifier
– Updraft – Downdraft
Sand + biomass particles
Updraft