Doris-Gaseous Fuels Flashcards
Why upgrade biogas to biomethane?
Basic idea:
–> utilization of biogas off-site of biogas plants
–> improved energy efficiency
- Often incomplete utilization of heat during heat & power production by CHPS at-site of biogas plants (no heat customers next to the plant!)
- Use of biogas off-site the biogas plants for generation of electricity and heat or for fuelling natural gas vehicles
- Distribution of the gas via the natural gas pipelines
–> Upgrading of biogas to biomethane to meet the quality standard for feeding into natural gas pipelines!
How to upgrade biogas to biomethane?
- Sulfur removal
- Removal of water and aerosoles
- Removal of CO2
- Conditioning
- -Adoption of lower heating value
- Addition of odorants
- Compression
How is Co2 removed from biogas?
Pressure-swing-adsorption (PSA)
Method
Capture and Seperation of CO2 by molecular sieves
Procedure
- Removal of H2 S and water from biogas
- Adsorption of CO2 at the molecular sieve under pressure
–> purified biomethane
- Regeneration of molecular sieve unit: staged reduction of pressure
(–> vacuum) and degassing –> release of CO2
What are the negative impacts of biogas upgrading?
Hurdles and impacts
high costs of biogas upgrading:
Germany: usually economical feasible for biogas capacities > 500 m3/h
loss of methane at upgrading procedure:
discharge of methane into the atmosphere with CO 2 –off-gas (has to be reduced e.g. by post combustion of the CO2 - off-gas)
Currently mainly corn silage used for energy crop
–> monocultures –> new crop types required
Big biomethane plants (~ 250 – 1000 m3/h biomethane)
–>long distance transports of feedstock and digestate
–>enhanced corn cultivation near the plant
–>big units for silage storage –> odor ! FIIIIIIIT
What are the mono condition, two condition vehicles?
Vehicles for mono-condition and tow-condition operation available
- mono - condition: operation on natural gas/biomethane only
- two - condition: alternating operation on gas or petrol
How do we obtain hydrogen from: ?
- Natural gas/Coal/ crude oil
- Hydropwer/Wind/ SOlar/ Nuclear
- Biomass
- Gasification
- Biogas Fermentation
- Fermentation
Give the steps of the formation of hydrogen from gasification
What is the difference between gaseous hydrogen CH2 and liquifed hydrogen LH2?
Options for hydrogen storage
Compressed („Compressed Hydrogen CH2 “)
- Compression to 200 - 700 bar
- Storage usually in stainless steel tanks ( high weight!)
- On-bord vehicle tanks: Carbon fiber based tanks (low weight!)
–> Compression to 700 bar: densitiy ~ 40 g/L,
energy demand for compression ~ 12%
Liquified ( „Liquid Hydrogen LH2 “)
- Liquefaction at -253°C, 4bar (Bryton-process, Claude-process)
- High energy densitiy: 8,45 MJ/l
- B U T: ~ 1/3 of the H2 energy content required for liquefaction !(0,2-0,3 KWhel / KWh LH2 )
- On-bord-tanks:
- superisolation of tank crucial !
- high losses by evaporatio
Compare a diesel car and a Ch2 fuel cell car travelling a 500 km range
Use of hydrogen for motor fuel:
In combustion engines
similar to natural gas or LPG
In fuel cells
enhanced efficiency compared to combustion engines
but: compared to natural gas or LPG:
- storage and transportation of hydrogen are technically more
demanding
- travelling range per unit of tank volume is shorter
What are the advantages and disadvantages of hydrogen as a fuel for transportation?
Now how can we produce Hydrogen from renewable electricity? is that what we mean by power to gas?
Use of (surplus) electricity, e.g. from wird or solar, to produce H2 , CH4 oder (liquid) hydrocarbons
- > - indirect storage of electricity
- capture and use of CO2
Draw the flow diagram fo power2gas!
Describe the H2 – generation by electrolysis
What are the potentials and drawbacks of power to gas?
