Feed-in and system integration of biogas in existing gas grids
In Austria biogas is used especially in combined heat and power (CHP) generation applications. Therefore a continuous and rather constant heat demand at the plant's location must be available to enable an economic plant operation. Thus biogas production and use are restricted to a rather small number of locations. On the other hand biogas will play a major role in a future energy system based on renewable sources. Biogas supply to public gas grids results in a broader use of this regenerative energy source with a high utilization factor, even without the demand for heat supply.
In this study, the infeed of biogas into public gas grids is analyzed by looking at system integration. Regional and local circumstances are integrated as boundary conditions to incorporate aspects of a sustainable energy supply. The availability of substrate in the region, load characteristics of the gas grid, gas production rate of the biogas plant and quality specifications for infeed-gas have a major impact on design and operation strategies of the biogas plant as well as on the cleaning and conditioning of the gas.
Therefore a method for technical and economic assessment of biogas plants based on key figures is developed. By the use of these key figures, regional and local boundary conditions can be integrated into the assessment process.
Concerning quality specifications for infeed-gas this method is characterized by a high level of flexibility, because the amount of biogas that can be supplied to the public gas grid is calculated based on the desired quality of the resulting gas mixture of biogas and natural gas in combination with the load characteristics of the gas grid.
As a result of the analyses carried out in this study, it was identified that load characteristics of low pressure public gas grids (grid level 3) show a dramatic decrease of the gas demand during summer. The amount of gas distributed in the grids reduces to one tenth of the medium winter gas demand. This has to be taken into consideration when sizing biogas infeed applications. Besides that, prediction of gas demand using standard load profiles is strongly affected by errors during these low-load-periods. Taking this into consideration, biogas infeed to high pressure gas grids (grid level 2) should be promoted for further analysis.
In addition aspects regarding technical security of biogas infeed are documented.
Another task for future research work can be the analysis of the effect of substrate change during operation of the biogas plant. Thus variable load characteristics can be accommodated by changing biogas production.
The availability of data concerning technology and operation of biogas production plants and cleaning and conditioning equipment is rather poor. For that reason standardized biogas plants and efficient monitoring of existing plants should be implemented. Furthermore generally accepted technical rules should be elaborated.
Dipl. Ing. Dr. Matthias Theißing
FH Joanneum Gesellschaft mbH / Infrastrukturwirtschaft
Werk-VI-Straße 46, 8605 Kapfenberg
Tel: +43 3862 33600 - 8382
Fax: +43 3862 33600 - 8381
Institute: FH Joanneum Gesellschaft mbH / Infrastrukturwirtschaft
Technisches Büro für Chemie & Biotechnologie Theißing-Brauhart (Werkvertragspartner)
Steirische Gas-Wärme GmbH (Werkvertragspartner)