‘Green gas’ is fuel gas (containing methane) which has been produced by upgrading biogas.
Green gas can be produced by:
• Chemical processes (bio-SNG: Substitute Natural Gas)
• Biological processes (biogas)
The chemical processes are not yet commercially viable. For the time being, attention must therefore focus on biogas. Biogas is chiefly used for the purposes of electricity generation, although in some cases it is also used to produce heat or is upgraded to natural gas quality (‘green gas’).
Biogas is released from biomass via a natural process and is a viable alternative to natural gas. Biological processes such as the fermentation of animal manure and co products give off biogas that can be upgraded to the same quality as natural gas. When the quality of biogas is enhanced in this way, the end result is termed‘green gas’.
Biogas is a mixture of methane (CH4) and carbon dioxide (CO2). Methane is also the main component of natural gas, which makes biogas suitable as a fuel.
Biogas is produced from various sources or Waste-to-Energy (WtE) applications. In the Netherlands, the gas is primarily produced by wastewater treatment plants and the sediment fermenters operated by water authorities and private sector companies, as well as at landfill sites. Much of this biogas is used to fuel gas turbines which generate ‘green’ electricity. At a number of landfill sites and water treatment plants, the biogas is upgraded to the quality of natural gas and introduced to the mains gas supply. The upgrading raises the energy value to the same level as natural gas, as measured on the Wobbe index. This involves extracting some of the CO2 to increase the concentration of methane.
Cirmac International’s biogas upgrading system
Cirmac International has developed a new and innovative process which results in the best performance in terms of biogas upgrading to date: the LP Cooab system. The process removes CO2 by means of chemical absorption under atmospheric pressure. The absorption fluid is regenerated by heat within a‘stripper column’.
(See Appendix 3, Figure 3 for a representation of the upgrading process from biogas to ‘green gas’.)
Green gas in the national high-pressure mains supply
Natuurgas Overijssel (a partnership of ROVA and the HVC Group) produces green gas. Enexis manages the low-pressure transport connections and Gasunie now injects the green gas into its high-pressure mains supply system, which is the first time that green gas has been injected into system. Natuurgas Overijssel has built a fermentation plant in which waste vegetable matter is converted into biogas. The biogas is then upgraded to natural gas quality and introduced directly into Gasunie’s high-pressure supply system via a dedicated supply pipeline. The plant will produce over two million cubic metres of gas each year, enough to meet the gas requirements of one thousand households. It is also possible to use green gas as a fuel for vehicles.
Heat from biogas
Water treatment plants can also act as suppliers of residual heat. A network can be fed with the heat from biogas produced by fermenting the sediment that remains when wastewater and blackwater (sewage) are purified. This apparently useless sludge therefore becomes a useful source of energy.
(See Appendix 3, Figure 4 for a representation of a biogas/clean water system.)
Unique Selling Points
• Much gas-related knowledge and expertise is available in the Netherlands. Green gas therefore has great potential as an economic motor.
• Dutch companies are often the first to develop purification and upgrading techniques for biogas.
• Upgraded biogas (green gas) can be used as a transport fuel.
• Green gas can be injected into the national gas mains supply.
• Green gas can be injected into the regional gas mains supply.
• The LP Cooab system offers a significant advantage in that the methane loss is less than 0.1%.
The use of biogas as a source of energy does not account for any additional CO2 emissions. Production of gas at a landfill site is extremely beneficial since it serves to contain gas which would otherwise have an adverse environmental impact. Some 60% of this gas is methane, which has a very strong greenhouse effect. Methane emissions are approximately 23 times more harmful than those of CO2. By using the biogas as a source of energy, the use of fossil fuels will also be reduced, thereby reducing emissions of CO2 as well.
Market parties and research institutes
Biothane, BTG, Cirmac International,Energietransitie Platform, Enexis, Gasunie, HVC Group, Microturbine, Omrin, Optimum Environmental & Energy Technologies, Raedthuys Group, ROVA, SenterNovem*, TNO Science& Industry, Technology, Tri O-Gen, Van der Wiel, A. de Jong Group (NB This list is not comprehensive)
Best practice reference projects in the Netherlands
• Zuidbroek residential development, Apeldoorn (2,500 new-build homes)
• De Wierde Ecopark
• ’t Rikkerink landfill site
• Wijster waste processing centre
• Arendal, Gothenborg (a Dutch project in Sweden)
• De Marke demonstration farm project
• ROVA, HVC Group, Enexis and Gasunie: green gas was introduced into the national high-pressure mains supply for the first time in late 2009
Possible obstacles to international business
• Labelling of ‘green gas’: other countries impose different requirements with regard to gas quality.
• A number of countries have a very limited gas infrastructure (or none at all).