The feed-in of biomethane to the natural gas grid
The feeding of biogas into the natural gas grid is an efficient energy solution, even if the sites in which the gas is to be applied are far away from the sites at which it is produced. Gas feed-in is facilitated via a compressor, a device raising the pressure level of the biomethane to that of the gas in the closed pressurised lines of the grid. Given European regulatory realities, new gas producers have the opportunity to feed gas into the conventional gas grid. For biogas generators, this multiplication of the possible number of consumers is attractive. For purposes of feeding-in, however, the gas must be up to the quality specifications of the relevant legal provisions and may only deviate within the range of these quality standards. Such standards are realised using technologies for reconditioning gas. Because a non-negligible quantity of energy is necessary for gas compression, the energy balance and the economic feasibility of the compression and feed-in process must be reviewed on a case-by-case basis.
Accessory gas / exchange gas
With regard to feeding biomethane into the natural gas grid, it is necessary to distinguish between exchange gas and accessory gas. The difference lies in the quality of the gases. An exchange gas has the same qualitative standards as conventional natural gas and can be exchanged in the grid as such. Accessory gas possesses a composition that is not equivalent to that of the natural gas, and can therefore only be mixed into the grid beneath a certain threshold.
Regulations distinguish between low-quality natural gas (“Erdgas L”) and high-quality natural gas (“Erdgas H”). Erdgas H possesses a higher methane content, and is used mainly in the GUS federal states and extracted principally in the North Sea.
Erdgas L contains roughly 89% flammable gases (primarily methane, but also small amounts of ethane, propane, butane, and pentane), while Erdgas H contains about 97% flammable gases (the same as those listed for Erdgas L).
The types of natural gas available in Germany vary with geography. Similarly, the degree to which biomethane is upgraded depends on the region from which it comes.