Biogas upgrading technologies
Swedish Gas Centre
IEA Bioenergy Task 37 Energy from biogas and landfill gas
Anaerobic digestion 1000 800 kg 600 400 H2O CH4 CO2 VS Ash 200 0 Before AD After AD
Biogas cleaning and upgrading
Gas Composition Biogas Landfill gas Natural gas Methane (vol-%) 60-70 35-65 89 Other hydro carbons (vol-%) 0 0 9.4 Hydrogen (vol-%) 0 0-3 0 Compounds Carbon dioxide (vol-%) 30-40 15-50 0.67 Nitrogen (vol-%) ~0.2 5-40 0.28 Oxygen (vol-%) 0 0-5 0 Hydrogen sulphide (ppm) 0-4000 0-100 2.9 Ammonia (ppm) ~100 ~5 0 Lower heating value (kwh/nm 3 ) 6.5 4.4 11.0
Cleaning of biogas Water Hydrogen sulphide Oxygen Precipitation in digester Adsorption Absorption Biological treatment Nitrogen Ammonia Siloxanes Particles
A bag contains 3 white and 5 black balls. One ball is drawn at random then the probability that it is black or white is: A) 3/8 B) 5/8 C) 1/5 D) 1
Methane Carbon dioxide Formula CH 4 CO 2 Molecular weight 16.043 g/mole 44.010 g/mole Molecular diameter 4 Å 5.1-3.5 Å Density (S.T.P.) 0.7174 kg/m 3 1.977 kg/m 3 Boiling/sublimation point -161.52 C -78.5 C Water solubility 20 C 0.035 Bunsen coeff. 0.8704 Bunsen coeff.
Biogas upgrading technologies Upgrading, i.e. increasing the energy content by removing carbon dioxide from the energy rich metane gas. Different characteristics are used: Size PSA, membrane Solubility Water scrubber, organic physical scrubber Boiling/sublimation point Cryogenic Chemical characteristics Chemical absorption
Pressure Swing Adsorption (PSA) Adsorption on a surface under elevated pressure Absorbing material usually activated carbon or zeolites Regeneration by sequential decrease in pressure Several vessels working in parallell
Water scrubber Biogas meets a counter flow of water in a column filled with plastic packing Carbon dioxide dissolves in the water Methane dissolves to a much lower extent Dissolved methane is recovered in flash tank Water is regenerated in a desorption column where it meets a counter flow of air
Organic physical scrubbing Biogas meets a counter flow of an organic solvent (e.g. polyethylene glycol) in a column filled with plastic packing Carbon dioxide dissolves in the liquid Methane dissolves to a much lower extent
Chemical absorption Biogas meets a counter flow of an amine solution Carbon dioxide is bound chemically to amine It is a very selective reaction Low methane losses MEA (mono ethanol amine) or DMEA (di-methyl ethanol amine) in the liquid Regeneration by heating
Cryogenic Seperation by cooling The biogas is cooled down to a temperature where carbon dioxide condenses or sublimates and can be removed as liquid or solid Methane accumulates in the gas phase If cooled further liquid methane gas is formed
Membranes permeable to carbon dioxide, water and ammonia Hydrogen sulphide and oxygen permeate through the membrane to some extent, while nitrogen and methane only pass to a very low extent Often two stages are used Operated around 8 bars Membrane
Swedish Standard for biogas as fuel for otto engines Particles < 1 μm Methane 97+/- 2 % Water < 32 mg/nm 3 CO 2, O 2, N 2 < 5% Oxygen < 1 vol % Sulphur < 23 mg/nm 3 N (except for N 2 ) expressed as NH 3 <20 mg/nm 3 Odorised Compressed to 200 bar For grid injection: Addition of propane (around 7-9 vol%)
A bag contains 10 red balls, 10 green balls and 6 white balls. Two balls are drawn at random from the bag. What is the probability that they are of different colors?
Upgrading of landfill gas The worlds largest plant for upgrading of landfill gas and biogas to liquid biogas will be built at NSR in Helsingborg, Sweden. Liquid biogas will be produced for heavy vehicles Production of 15 million litres of liquid biogas per year Source: www.nsr.se
Biogas upgrading in Sweden In Sweden today: Water scrubber (33) PSA (8) Chemical absorption (6) Cryogenic (1)
The Swedish gas grid Source: Swedish Gas Association
Utilization of biogas in Sweden (2008) Electricity 4 % Data missing 2 % Flaring 14 % Heat 53 % Vehicle gas 26 %
Thank you for your attention! anneli.petersson@sgc.se www.iea-biogas.net