Upgrading of biogas for the gas distribution system of Salzburg
Injection of Biogas to the natural gas grid offers a sustainable energy efficient supply of energy, because the power conversion can be managed at locations with permanent heat demand. Actually the most common systems run at decentralised combined heat and power units (CHP) units in rather sparsely populated regions with low heat usage. Additional advanced applications of biogas can be achieved separating the location of the production and the usage of biogas, e.g. production of vehicle fuel or utilisation as fuel for large scale CHP units with gas turbines.
The purification of biogas reaching the required quality is a challenging technical and economic task in the project BioMethan, especially the development of a cost-effective and free of waste-products process. The second main task in BioMethan is the elaboration of all relevant boundary conditions for the building of an industrial demonstration unit injecting biogas to the high pressured natural gas grid of Salzburg.
Evaluating several possible locations the site of Wals was chosen for the planned biogas and composting demonstration plant. A comprehensive list of available substrates shows, that a plant size of approx. 150 m³/h biogas can be reached.
Injection to the grid
Based on the technical directives ÖVGW G 31 "Erdgas in Österreich" and ÖVGW G 177 "thermische Abrechnung" the injection criteria of biogas are defined. Biogas components, which are not listed in the directive G 31 but are harmful for the network and its operation, have to be listed.
Due to economical benefits the current planning sticks to a partial purification of biogas and not to a total cleaning to natural gas quality. Mixing the pre-cleaned biogas with natural gas in a ratio of 1:25 (biogas:natural gas) the required gas quality can be reached.
During summer the high pressure pipeline reaches some flow rate minima, because of the lack of heating demand. The flow rate of the natural gas is on several days too low to reach the desired dilution effect with 100% injection of biogas. During this period a part load operation will be performed, the rest of the biogas produced is used for internal heat production.
Operating the developed test unit of the biological desulphurisation an optimisation of the cleaning capacity could be reached. The realisation of a half-industrial application will be done in nearest future. The investigation of an alternative adsorbent (amine) for the CO2 removal showed positive effects to lower the energy demand in pressure swing adsorptions. The technical application has to be proved.
Following the performed total economic calculation based on the described structure with pre-cleaning and mixing with natural gas and on natural gas prices of 2003 the injection of biogas to the grid is not economical feasible. Besides the investment costs, the operational costs for cleaning and compression to the high pressure grid have main influence. Additionally rather high substrate costs in the region of Flachgau have negative influence on the economic efficiency.
The specific production costs of totally upgraded biogas were calculated by simulation using the biological desulphurisation in combination with the pressure swing adsorption. For plants with less than 150 Nm³/h (~ 1,5 MW energy performance in the upgraded biogas) the specific production costs rise strongly. For bigger plants costs of 50-55 c€/Nm³ (4,3-5,2 c€/kWh) were calculated. In comparison to other cleaning systems like strippers the costs are in the same range and therefore competitive.
A proposal in the programme "Energiesysteme der Zukunft" for support of the planned industrial demonstration plant for biogas injection to the natural gas grid was submitted.
Dipl.-Ing. Johann Bergmair
Profactor Produktionsforschungs GmbH
Im Stadtgut A2
Tel: +43 (0)7252/885-0
Fax: +43 (0)7252/885-101
Profactor Produktionsforschungs GmbH
TU Wien, Institut für Verfahrenstechnik (Werkvertragspartner)
Salzburg AG für Energie, Verkehr und Telekommunikation (Projektpartner)
Integral Umwelt- und Anlagentechnik Gesellschaft m.b.H (Projektpartner)
Thöni Industriebetriebe GmbH (Projektpartner)