Investigation On Single Chamber Fuel Cells With Polyalkane Fule And Waste Heat Utilization System

Single chamber solid oxide fuel cell (SC-SOFC) is a novel type fuel cell with only one gas chamber, which is different from other traditional double gas chamber fuel cell. It has many advantages such as free from seal, more simple structure, low operating temperature and various forms of the cell stack, etc. The hydrocarbon fuels mainly used in the previous SOFC research was methane, because methane has the simplest structure among hydrocarbon fuels and the internal reaction is easier to handle. The present thesis mainly researches the characteristic of the cell using polyalkane fuels, such as propane and liquefied petroleum gas (i.e. LPG). Besides, since the by-products from SOFC are high-quality heat, waste heat utilization technologies were also developed, cooperating with a novel unsealed cell stack, to establish a combined heat and power system.Through a series of experiments, cells made of conventional materials were tested in single-chamber conditions under different temperatures and various C3H8 or LPG/O2 gas mixtures. The best working gas ratio of propane to LPG in SC-SOFC was confirmed. When the nitrogen gas flow rate was 100sccm, propane or LPG flow rate was 20sccm, the best performance of a single cell was obtained with propane to oxygen ratio of 0.3, LPG to oxygen ratio of 0.25, respectively. Along with the increase of the oxygen content, the performance of a single cell was improved gradually. This trend was opposite to the cell using methane fuel. Because the fuel cell's anode catalyzing the partial oxidation reactions in fuel-air mixtures are exothermic reactions. The resulting heat release leads to an increase of the cell temperature which thus deviates from the furnace temperature.For the propane and LPG fuel, this study found the temperature effect more apparent than the cell of methane fuel, which is beneficial to the cell operated at intermediate temperatures. According to the measuring result with polyalkane fuel, we found that one of the factors most affecting the stability of the cell is the carbon deposition, but with the increase of oxygen content, the carbon deposition on cell will be relieved. As comparison, the carbon deposition is more serious on the cell using LPG than propane.The study on impedance spectra of LSM cathode show that, in single chamber fuel cell condition with propane or LPG fuel, the LSM cathode has certain catalysis to the fuel. The LSM cathode with impregnated SDC has better performance. For example, the polarization resistances of impregnated LSM cathode are almost 1/35 than the those of pure LSM cathode under the same conditions. At the same time, as the increase of oxygen concentration, the concentration polarization of the cell is the main factors which limited the cell's performance.In order to utilize the waste heat which the cell stack operating needs, heating recycled water flow and thermoelectric module components as the secondary electric power generation were developed. Experiments show that this technology can effectively use the cell stack's waste heat.