ANALYSIS OF ETHANOL-FUELLED SOLID OXIDE FUEL CELL SYSTEMS FOR COMBINED COOLING, HEAT AND POWER GENERATION

Abstract

A solid oxide fuel cell (SOFC) fuelled by ethanol, an attractive green fuel that can be renewably produced from agricultural products, is regarded as a promising clean process to generate electricity with high efficiency. Therefore, this research concentrates on the analysis of ethanol-fuelled solid oxide fuel cell systems. Firstly, the thermodynamic analysis of three different ethanol reforming processes (i.e., steam reforming, partial oxidation and autothermal reforming) is investigated in term of product compositions and compared on the basis of energy and exergy analyses to find the most suitable process for solid oxide fuel cell applications. The simulation results show that although the steam reforming process provides the highest hydrogen yield, it is the highest energy requiring process. The exergy analysis shows that the lowest exergy destruction is found in the steam reforming. The integration of ethanol steam reformer operated at temperature of 980 K and steam-to-ethanol ratio of 1.8 and solid oxide fuel cell provides the best energetic and exergetic performances. Secondly, the improvement of the ethanol steam reforming is further investigated by considering the reforming reaction mechanism. To avoid a carbon formation, the steam reforming of ethanol should be carried out into two steps via a reaction intermediate which has a lower coking activity. Ethanol is firstly dehydrogenated to be acetaldehyde and then steam reform into hydrogen rich gas. However, this method faces a limitation of chemical equilibrium reactions which typically produce more dilute products such as CO2 and water. For this reason, the removal of CO2 and excess steam in the reforming environment and its effect on SOFC performance are studied. Thirdly, an economic analysis of improved reforming processes (two-step steam reforming and two-step steam reforming with CO2 capture) is presented and compared with a conventional steam reforming. The study illustrates the feasibility of the two-step steam reforming and CO2 capture integrated processes in the economic aspect. Finally, a heat recovery of the SOFC system is considered to improve the efficiency of the system energy usage. The ethanol-fuelled solid oxide fuel cell system integrated with an absorption chiller is proposed in this study for combined cooling, heat and power generation. The energy and exergy analyses of such system is performed to determine an energy demand and to describe how efficiently the energy usage. The exergoenvironmental analysis is also performed providing useful insights in terms of heat recovery and environmental aspects and the results indicate the benefit of this system.