EU research project looks at feeding biogas into the main natural gas grid

The biogas sector is undergoing a rapid transformation in Europe. Whereas green gas production used to be an activity associated with individual farms and community waste management programs, it has been scaled up to become an industry that produces quantities large enough to be fed into the main natural gas grid. More and more, dedicated biogas crops (such as specially bred biogas maize, exotic grass species such as Sudan grass and sorghum, or new hybrid grass types) are being utilized as single substrate feedstocks for large digester complexes, and biogas upgrading to natural gas standards is becoming more common.

Research indicates that the potential for biogas to replace natural gas is very large in Europe. Some studies in fact estimate that by 2020 the EU could replace all gas imports from Russia and produce some 500 billion cubic meters (17.6 trillion cubic feet) of gas equivalent biogas per year. The idea is to build 'biogas corridors': energy farms, biogas plants and purification installations would be established close to Europe's central gas pipelines (map, click to enlarge) so that the energy crops can be digested locally and injected into the grid without going through complex logistical chains (earlier post). Because biogas made from energy crops is a highly efficient biofuel (it yields far more energy per hectare than liquid biofuels) and has very low lifecycle CO2 emissions it is receiving substantial political support.

In this context the natural gas industry in Europe knows it must prepare for the advent of an era in which it will have to partner with many different biogas producers. After all, there is already a European legal framework (Directive 2003/55/EC *.pdf) which aims to open the existing grid for gas from sources other than natural gas, including biogas. It states:

"Member states should ensure that, taking into account the necessary quality requirements, biogas and gas from biomass or other types of gas are granted non-discriminatory access to the gas-system, provided that such access is permanently compatible with the relevant technical rules and safety standards. These rules and standards should ensure, that these gases can technically and safely be injected into, and transported through the natural gas system and should also address the chemical characteristics of these gases" - European Directive 2003/55/EC

A European research project led by the European Gas Research Group (GREG), a pan-European consortium of major natural gas organisations and universities (see below), and GasUnie Engineering & Research, a division of the Nederlandse Gasunie, one of Europe's leading gas infrastructure companies, is now examining this future and aims to assess the challenges ahead. 'BONGO' as the project is called ('Biogas and Others in Natural Gas Operations') is a proposition filed under the 7th European Framework Program (FP7) and will run for 5 years. The motivation behind the project can be summarised as follows:

As the initial composition, and consequently the physical and chemical properties, of biogas differ significantly from those of natural gas, the organizations involved in the chain of transmission-distribution-end user should be prepared to cope with biogas. In order to be able to use biogas widely in domestic, residential and industrial applications, the technical consequences and, in particular, the safety and pipeline integrity aspects related with the addition of biogas to natural gas need to be addressed. As biogas will be an increasingly important fact of life in Europe in the near future, and as the potential problems associated with it are very complex and broad, it is in the interest of the European natural gas industry that this issue be tackled jointly and in strong collaboration with all stakeholders.

With networks becoming increasingly interconnected, a pan-European approach and a common position on the definition of technical rules and safety standards for biogas injection is required.

Upgrading biogas to NG quality
A key technology for injection of biogas into the natural gas grid is upgrading of the biogas to natural gas quality after which it can be compressed to transport grid pressure. Biogas consists of around 50 to 65% of methane, small fractions of other compounds and 50 to 35% of carbon dioxide, which has to be removed before injection. (Earlier we pointed out why this large CO2 fraction makes pre-combustion carbon capture from biogas an interesting option in the context of carbon capture and storage, which results in the concept of a radical carbon negative energy system - previous post).

Four main technologies are currently in use to separate the methane from the CO2:
bioenergy :: biofuels :: energy :: sustainability :: biogas :: biomethane :: carbon dioxide :: natural gas :: pipelines :: European Union ::

Membrane separation technology: commonly used in the petrochemical industry, membranes can separate methane and carbon dioxide because of the different sizes of the molecules of both compounds. However, because the difference is rather small, the separation is not absolute and part of the methane contained in the raw biogas is lost.

Pressure Swing Adsorption (PSA): this technique makes use of the different adsorption capacity of methane and carbon dioxide in fluids. Under pressure raw biogas is pushed through an adsorber which captures the carbon dioxide but allows the methane to pass through. Once the adsorber is saturated, carbon dioxide begins to pass through, a moment at which the adsorber's operation is halted and the carbon dioxide removed under a vacuum. This vacuum pushes the methane simultaneously through another adsorber (hence the 'swing'), after which the cycle starts again. PSA is very effective at separating both compounds completely.

Cryogenic separation: a promising technology that is based on the different boiling points of methane and carbon dioxide. By cooling raw biogas, its carbon dioxide becomes solid (through sublimation) and methane of a high purity is obtained. The byproduct of the cryogenic operation - solid carbon dioxide, also called 'dry ice' - has useful applications in industry and a value as a commodity. However, the cryogenic separation technique is currently in a demonstration phase and not applied to biogas on a large scale yet.

Gas scrubbing systems or absorption: based on the way gas compounds phase change into a liquid, which is dependent on their solubility in the fluid. By adding chemical compounds to the washing fluid, the solubility of the gases to be separated can be enhanced. Carbon dioxide can be scrubbed by water, while methane can be washed by methanol or monoethanolamine (MEA).

Upgrading on digestion gas has been practiced since 1935 and, in Germany, there was large scale injection into the gas grid between 1982 and 1999. Since 1992 there has also been injection into the gas grid in Sweden, Switzerland and the Netherlands. Injection currently only occurs in local distribution gas grids, though. In these cases, relatively small volumes are added, at low pressures, mostly for domestic end-users. As far as is known, no major problems have been reported related to the addition of biogas to natural gas.

However, biogas has never been injected in the main transmission grid. Since working pressures are much higher, the types of pipeline materials are different and the variety of end-users is much bigger; consequently the requirements on the composition of the biogas must be much more stringent.

BONGO will therefor address questions that are of major importance for industrial end-users, such as:

• what happens with the microbiological components in the biogas when the gas is not burned?
• how do these components affect the pipeline integrity?
• how are flame temperature and combustion influenced by different components?

The further goals of the BONGO project are to define quality specifications for biogas access to the gas transport system. This is done by performing risk assessments in order to fill the gaps in knowledge concerning the addition of large volumes of biogas in the existing natural gas system, in order to ensure that:
- the system entry;
- the storage;
- the transmission and distribution;
- the utilization; can be performed safely and with acceptable consequences for:
- the integrity of the existing natural gas grid;
- operational, safety, health and technical consequences for the end user (systems);
- the value of the product as a feedstock;

Meanwhile, since the FP7 program will not start until 2007, preliminary ‘short-term’ studies will support activities. In particular, gas distribution companies find themselves faced with solving urgent problems regarding the injection of biogas. These studies will be performed under the name of BINGO, 'Biogas In Natural Gas Operations'. The focus will be on anaerobic digestion gases and end-use applications, not on pipeline integrity. There will be a strong connection with state-of-theart injection sites in distribution grids in Sweden, Switzerland and the Netherlands to learn from their experiences, to perform measurements, study requirements, etc. These actions are to be supported by national grants.

The project will be managed by the Gasunie, which leads a consortium from representatives from the European natural gas industry, research institutes and universities, Marcogaz and GERG. The partners of this consortium include Advantica (UK), European Environmental Consortium (Belgium) North Energy (UK), DEPA S.A. (Estonia), GasNatural (Spain), National Technological University of Athens, DGC (Denmark), Gasunie (Netherlands), SVGW (Switzerland), DVGW (Germany), Gaz de France (France), Synergrid (Belgium), Enagas (Spain) GERG (EU), TAGUS Gas (Portugal), EnergieNed (Netherlands), (Portugal), University of Warwick (UK), E.ON-Ruhrgas (D), Marcogaz (EU).

In the same context, the Dutch research organisation SenterNovem recently published a study on the potential to feed biogas into the natural gas mains of the Netherlands. It indicates that by 2020, the natural gas producing country can replace 10% of its gas consumption by green gas.

Image: freshly harvested energy crops await their entry into the large biogas digesters seen in the background. Credit: Der Standard, Austria.

More information:

Van Burgel, M., O. Florisson, D. Pinchbeck, Biogas and Others in Natural Gas Operations (Bongo), [*.pdf] presented at the 23rd World Gas Conference, Amsterdam.

SenterNovem: Groen Gas: Gas van aardgaskwaliteit uit biomassa ('Green Gas: Gas of Natural Gas Quality From Biomass') [*Dutch, .pdf], January, 2007.