Gasunie and bio-methane (green gas)
Gasunie has made promoting the transition towards a more sustainable use of energy into one of its objectives. Activities aiming to facilitate the development of bio-methane form an important aspect of this. Gasunie is thus making an active contribution towards realising government-driven sustainability and environmental objectives.
National grid operator GTS is making every effort to put these objectives into effect. Our activities include working actively with distribution network operators to trace any possible obstructions to the injection of bio-methane into the networks as well as looking for solutions to the issues. To this end, network operators are working together in Projectgroep Groen Gas, a working group of Netbeheer Nederland (Association of Energy Network Operators in the Netherlands).
We are also putting these objectives into effect by developing and participating in pilot projects. Examples of these are Natuurgas Overijssel (ROVA Zwolle), bi-directioneel GOS and buffering by decreasing pressures (SG3= Smart Green Gas Grid).
Consequences for gas transport
Decentralised bio-methane feeding into the natural gas network differs fundamentally to the transport flows that have been customary for the natural gas network up till now. Decentralised feeding, certainly whenever it occurs in the local distribution companies’ (LDC) networks, means that the gas is supplied to the consumer almost immediately. That sets extra high requirements on the quality of the gas supplied. If the demand in the LDC network is insufficient to take up the bio-methane produced, the surplus can be fed back into the GTS network with the help of compression (see bi-directional GOS). This is what we refer to as ‘bottom up’ gas transport (from low pressure to high pressure), while up till now the flow from source to use has always taken place from high pressure to low pressure (‘top down’).
What is bio-methane?
Bio-methane is produced from the fermentation of biomass. In low-oxygen (anaerobic) conditions, methane-producing bacteria supply biogas consisting mainly of methane (55 – 65%) and CO2 (30 – 35%) and smaller quantities of substances such as oxygen, ammonia, hydrogen, H2S and other trace elements. Reprocessing removes a large proportion of the CO2 and other impurities from the biogas. After purification, the bio-methane is of the same quality as natural gas and can be applied safely. Bio-methane is produced in this way from sewage sludge, from kitchen and garden waste (KGW), from animal manure, often in combination with the addition of other organic materials such as maize, grass, glycerine and residual products from the food industry etc. (this is referred to as ‘co-fermentation’), or is collected from landfill sites (landfill gas).
Bio-methane can also be produced by the gasification of biomass. This technique is still under development and is not yet applied on a commercial scale in our country.
Bio-methane is suitable for being feeded into the natural gas network. It may be feeded into both the LDC networks and into the national grid managed by GTS.
It is an absolute condition that gas quality and safety requirements are met for the injection of bio-methane into the natural gas network to be permitted. In order to guarantee this, stringent requirements apply which are closely supervised.
Bio-methane quality and safety
GTS takes care to provide gas safely and reliably. Stringent requirements regarding the quality of the gas supplied apply to the feeding of bio-methane just as they do to the feeding of natural gas from fossil sources. Only gas that meets the specifications is allowed to enter the network. In this way we can vouch for the safety of humans and animals and guarantee that accommodation of the gas does not cause any damage to installations or the gas network.
The origin of bio-methane is different to natural gas from fossil sources and the quality can vary with the type of biomass used or as a result of the purification method used in the reprocessing plant. That’s why we pay extra attention to a number of aspects relating to the injection of bio-methane in order to be able to guarantee its quality and safety.