Injection of green gases into natural gas grids

Green gases from biomass digestion processes consist mainly of CH4 and CO2, but also contain a wide variety of chemical and biological components. Some of these components can be corrosive or toxic, or can affect the quality of products made from (natural) gas. The flue gases produced when these gases are burned may have similar unwanted characteristics. Furthermore, the flame properties of green gases can be very different from those of natural gas. Several studies are under way that examine how to facilitate injecting green gases into the natural gas infrastructure, or biogas into biogas networks or hubs.

Objectives
This project was primarily concerned with identifying the risks presented to the integrity of the gas infrastructure by green gas injection, and the effects of those risks on the system.

The following finite objectives were defined:
> To assess possible impacts on the integrity of the natural gas grid and, consequently, possible impacts on maintenance and inspection programs
> To develop a set of general green-gas specifications for biogas-processing facilities

The general conclusion is that injecting purified biogas from digestion processes into the natural-gas grid has no adverse implications either for the integrity of the natural-gas grid or for the safety and health of end users. As long as the composition of green gases is as specified, there is no need to modify inspection programs for natural-gas grids or to carry out special inspections prior to injecting green gas into the grid.

Benefits
The realization of biogas networks or green-gas hubs in the Netherlands is currently under investigation. Most projects are pilot projects. Biogas networks can be economically attractive for biogas producers if they share the costs of the network, refinement, and compression. Biogas networks have great potential in agricultural areas, because of the ready availability of biomass. However, network operators lack experience in biogas transport and with related safety issues. The safety issues for raw biogas networks are different from those for natural-gas networks, into which green gas is injected, because no end users are connected directly to such networks. A raw biogas network is intended only for transporting gas to a central upgrading installation. The transportation of biogas is unregulated. For operators who are in direct contact with raw biogas in the context of maintenance activities, quality specifications need to be researched and defined with the aim of minimizing the safety risks.

Project coordinator
> KEMA, the Netherlands

Project partners
> Gasunie, the Netherlands
> ROVA, the Netherlands
> Enexis, the Netherlands
> Overrijssel Provincial Executive, the Netherlands

Project details
> Duration: 2008-2011