The COSIN project: synthetic natural gas production from biogas in a waste water treatment plant in Barcelona

The CoSin project is an industrial action aiming to demonstrate the technical economic viability of synthetic natural gas production at a sewage treatment plant in Barcelona area. In contrast with current fossil natural gas,... [ view full abstract ]

The CoSin project is an industrial action aiming to demonstrate the technical economic viability of synthetic natural gas production at a sewage treatment plant in Barcelona area. In contrast with current fossil natural gas, the gas obtained is totally renewable when integrated to green electricity. 

The selected sewage plant (EDAR Riu Sec, Sabadell) has now in operation two anaerobic digesters to treat the primary and secondary slurry, only for environmental purposes. After anaerobic digestion, the obtained biogas is now used to maintain the digesters at the mesophilic range. In this project, two routes to upgrade this biogas to synthetic natural gas, with the required quality to be injected to the local gas grid, are evaluated.

The first technology to be validated is biogas upgrading with membranes. The installed capacity is 50 Nm³/h. Prior to upgrading, the biogas will be dried, cleaned and compressed. A renewable biomethane stream will be obtained and it could be injected to the gas grid. The carbon dioxide stream will then be used in the second route, a power-to-gas plant where the catalytic hydrogenation to methane takes place

The catalytic methanation unit with will be able to convert the raw biogas and the carbon dioxide released by the upgrading unit to synthetic natural gas. The conversion is carried out by means of Sabatier reaction and the necessary hydrogen is produced on-line through alkaline electrolysis under pressure at 12 bar (37 kW). Then, hydrogen will be mixed with the carbon dioxide source, preheated and introduced to compact reactors with advanced catalysts to obtain the synthetic natural gas. The integration of renewable energy to the electrolyzer allow the synthetic natural gas to be a renewable gas. The two demonstration units are integrated in the sewage plant together with a biogas cleaning and an analytic unit. 

Cetaqua and Labaqua are the responsible for the membrane biogas unit, IREC and Gas Natural Fenosa for the biogas methanation unit and catalyst development. 

Acknowledgements

Authors are gratefully acknowledge the funding of this work by CoSin project (COMRDI15-1-0037), funded by ACCIÓ.