Thermodynamic modelling of an onsite methanation reactor for upgrading producer gas from small scale biomass gasifiers
MetadataShow full item record
The target for significant reduction of carbon dioxide emissions has led the European Union and its Member States to subsidize renewable energy systems. Small scale biomass gasifiers have the advantage of having higher electrical efficiencies in comparison to other conventional small scale systems. Also their small size not only makes easier the authorization process but also increases the flexibility of the investors in respect to the available areas for installation. As a result the sector of small scale biomass gasification has grown significantly during the last decade. Nonetheless, a major drawback of small scale biomass gasifiers is the relatively poor quality of the producer gas. In addition, several Member States are seeking ways to store the excess energy that is produced from renewables like wind power and hydropower. A recent development is the storage of energy by electrolysis of water and the production of hydrogen in a process that is commonly known as power-to-gas. The present manuscript assesses onsite methanation as an upgrade possibility of producer gas by means of thermodynamic modelling. Methanation primarily converts carbon monoxide and carbon dioxide into methane by reacting with hydrogen. In the framework of this study, producer gases from two representative small scale biomass gasifiers were modelled for their methanation potential and the efficiency of a secondary smaller onsite reactor was assessed. For mixtures of hydrogen and producer gas on a 2:1 ration or above and for temperatures between 450 K and 700 K the heating value and the Wobbe index increase significantly. This is attributed on one hand to the higher concentrations of hydrogen and methane. On the other hand, the quality of the gas is improved due to the partial conversion of molecular nitrogen into ammonia which - after cooling- condenses.