Science & Technology in Action

8th Edition

Biomethane

Bord Gáis Networks

As a fuel, biomethane is an attractive option; it is renewable and so reduces our dependence on fossil fuels. It has a similar composition to natural gas and there is already a natural gas distribution network in place.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Biogas and biomethane 
Biogas is produced by the anaerobic breakdown of organic matter in an oxygen free environment. Biogas typically consists of methane (CH4 ≈ 55%) and carbon dioxide (CO2 ≈ 45%) with some water (H2O), hydrogen sulphide (H2S), trace particulates and other compounds. When biogas is injected into the natural gas grid or utilised as a transport fuel, it must be upgraded to biomethane (>97% CH4) by removal of CO2. Its use as a fuel is an attractive option because it is renewable and so reduces our dependence on fossil fuels.

Biomethane is a suitable form of renewable fuel for Ireland as it has a similar composition to natural gas and there is already a natural gas distribution network in place. Therefore, biomethane has the potential to be injected into the network without the requirement to develop significant infrastructure. It is estimated that biomethane could provide 7.5% of Ireland’s natural gas demand by 2020; this would contribute significantly to the Government’s renewable energy commitments. Biomethane offers an environmentally friendly alternative to traditional fossil fuels such as oil, coal, diesel and petrol.

Furthermore, biomethane can be produced from a number of organic resources. This would bring some extra benefits; using agricultural waste to produce biomethane would reduce both air pollution and water pollution. The residue remaining after biomethane production can be used as fertiliser, indirectly reducing energy costs.

Quiz questions

  1. Grass grown for biomethane production will need no management. false
  2. If 10% of Ireland’s grassland was made available for biomethane production, there would be theoretically enough fuel produced to run 1 million cars. true
  3. Methane can be used in CHP (combined heat and power) plants. true
  4. Anaerobic digesters have never been used to produce gas for electricity generation on farms. false
  5. Methane is very reactive chemically. false
  6. Tallow and slaughter waste are potential sources of biomethane. true
  7. Burning of CH4 to CO2 replaces a strong greenhouse gas with a less potent one. true
  8. Biomethane can be produced from spent algae in algal biorefinery systems. true
  9. Wood gas is produced by gasification of biomass. It contains mainly N2, H2, CO but little CH4. true

Glossary of terms

asphyxiation
death by suffocation (lack of oxygen)
bar
initial set-up costs, such as buildings, equipment or other infra-structural cost
Anaerobic
arable
biogas
biomethane
carbon neutral
carbon sequestration
feedstock
fertiliser
fossil fuels
greenhouse effect
H2S
hydrocarbon
kilogram-calorific value
landfill
methane
natural gas
nitrogen oxides
omega oil
renewable
ruminants
siloxanes