Abstract
A SOFC system with integrated biomass gasification is a promising technology to achieve high
electrical and thermal efficencies for decentralized power generation [20]. This system requires a gas cleaning unit due to impurities in the wood gas to avoid degradation of the Ni-anode. In the case of a hot gas cleaning unit a reformer may be used to convert tars and thus decrease the tar concentration at the anode entry to a very low level. Another possible option would be the direct utilisation or reforming of hydrocarbons at the anode. Wood gas from an allothermal steam gasifier contains sufficient water to allow a complete reforming of the hydrocarbons present in the biogeneous gas. The internal reforming of methane in the SOFC is commonly known [21]. Tests with real woodgas using no pre-reformer in the gas cleaning unit have resulted in no significant degradation of the anode, underlining the apparent insensitivity of the SOFC against tars [3].
Experiments with several synthetic tars at a constant current density identified certain tar species to act as fuel whereas the presence of other tar species significantly decreased the cell voltage due to the inhibition of methane reforming [4]. The electrochemical conversion of methane significantly reduces for naphthalene containing synthetic wood gases [19]. Due to the
temperature dependency of the conversion of hydrocarbons less methane and tars respectively
are being reformed at lower temperatures leading to lower hydrogen partial pressures, higher
hydrogen utilizations and higher degradation rates of the fuel cell. High hydrogen utilizations may cause oxidation of the anode. This paper presents calculations with FactSage of tar laden
syngases present at the anode accounting the individual temperature ranges and H2O contents of tar reforming. The calculated produced amount of H 2 and CO due to reforming which is
electrochemically converted defines the allowable hydrogen utilization for a certain current density.
The calculations are based on gas concentrations as obtained from an allothermal steam gasifier thus using a steam-to-carbon ratio above the critical value for carbon formation. These calculations are expected to enable the predection of a temperature-current density matrix for the maximum tar content allowed in order to reach a maximum hydrogen utilization of 85%. Vice versa it will be possible to predict a maximum possible hydrogen utilization with gas from a certain gasifier type in order to prevent degradation rates of fuel cell stacks operated on biogeneous gas. The calculation model is intended to be a basis for future single cell tests
electrical and thermal efficencies for decentralized power generation [20]. This system requires a gas cleaning unit due to impurities in the wood gas to avoid degradation of the Ni-anode. In the case of a hot gas cleaning unit a reformer may be used to convert tars and thus decrease the tar concentration at the anode entry to a very low level. Another possible option would be the direct utilisation or reforming of hydrocarbons at the anode. Wood gas from an allothermal steam gasifier contains sufficient water to allow a complete reforming of the hydrocarbons present in the biogeneous gas. The internal reforming of methane in the SOFC is commonly known [21]. Tests with real woodgas using no pre-reformer in the gas cleaning unit have resulted in no significant degradation of the anode, underlining the apparent insensitivity of the SOFC against tars [3].
Experiments with several synthetic tars at a constant current density identified certain tar species to act as fuel whereas the presence of other tar species significantly decreased the cell voltage due to the inhibition of methane reforming [4]. The electrochemical conversion of methane significantly reduces for naphthalene containing synthetic wood gases [19]. Due to the
temperature dependency of the conversion of hydrocarbons less methane and tars respectively
are being reformed at lower temperatures leading to lower hydrogen partial pressures, higher
hydrogen utilizations and higher degradation rates of the fuel cell. High hydrogen utilizations may cause oxidation of the anode. This paper presents calculations with FactSage of tar laden
syngases present at the anode accounting the individual temperature ranges and H2O contents of tar reforming. The calculated produced amount of H 2 and CO due to reforming which is
electrochemically converted defines the allowable hydrogen utilization for a certain current density.
The calculations are based on gas concentrations as obtained from an allothermal steam gasifier thus using a steam-to-carbon ratio above the critical value for carbon formation. These calculations are expected to enable the predection of a temperature-current density matrix for the maximum tar content allowed in order to reach a maximum hydrogen utilization of 85%. Vice versa it will be possible to predict a maximum possible hydrogen utilization with gas from a certain gasifier type in order to prevent degradation rates of fuel cell stacks operated on biogeneous gas. The calculation model is intended to be a basis for future single cell tests
| Original language | English |
|---|---|
| Title of host publication | Proceedings - European Fuel Cell Forum 2009 |
| Number of pages | 16 |
| Publication status | Published - 2009 |
| Event | 2009 European Fuel Cell Forum - Luzern, Switzerland Duration: 29 Jun 2009 → 2 Jul 2009 |
Conference
| Conference | 2009 European Fuel Cell Forum |
|---|---|
| Country/Territory | Switzerland |
| City | Luzern |
| Period | 29/06/09 → 2/07/09 |