CLEAN TECHNOLOGY FOR ELECTRICITY PRODUCTION BASED ON BIOETHANOL
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies-II: Energy Production (T1-5P)
Keywords: Clean technology, bioethanol reforming, SOFC
Nowadays, because of the fossil fuels progressive reserves depletion and the environmental problems produced for its use (combustion), have induced to look for new energetic alternatives. In this sense, the hydrogen is considered as the new “energetic vector” because of its advantages related to its production from renewable and no renewable energy sources and its mass energetic density. Hydrogen can be obtained from biomass or its products as bioethanol which is produced by fermentation.
In this work, a clean technology for electricity production from renewable sources is proposed. For this aim, an integration of bioethanol steam reforming and a fuel cell system (SOFC) was developed by computer aided design using HYSYS®. For process integration, was taking into account that steam reforming of bioethanol is an endothermic process and this reaction improves its conversion with fed steam excess. Moreover, typical SOFC operational conditions were used. An integrated flowsheet was developed using heat and mass integration of several process streams achieving itself thermal sufficiency. Additionally, a discussion about other integration schemes is presented.
Electricity production from bioethanol and its steam reforming to hydrogen for fuel cells is a clean technology which offers high energy efficiency and zero emissions pollutants like SOx (raw materials does not contain sulphur components), NOx (electrochemical process without combustion) and CO2 which although is produced on reforming it is consumed for the biomass growth. This energetic alternative has high energy efficiency, because the fuel cells are energy conversion devices that produce electricity (and heat) directly from a gaseous fuel by electrochemical reaction between a fuel and an oxidant. Solid oxide fuel cells (SOFCs) are one of the most attracting kinds of fuel cells, for its advantages as high efficiency (near to 60%), high rate in reaction kinetics and high quality heat, which can be used as heat source for heat integration applications such as endothermic bioethanol steam reforming.
The system to produce electricity from bioethanol by steam reforming and fuel cells (SOFC) can be described as follow. The bioethanol is vaporized and fed at a packed bed reactor which contains a Ni-based catalyst. Additionally, water is vaporized and fed at reactor too, but the molar ratio between bioethanol and steam fed was 1:6 to improve the reaction conversion near to 99%. The reaction products are fed to SOFC at 400°C, the reformer operational temperature. This stream has a volume composition on hydrogen of 53% and taking into account that a typical fuel stream for SOFC has a 67% of hydrogen, is assumed that the SOFC performance no is affected seriously. Moreover, an air stream is fed to SOFC which is preheated to 465°C to improve the fuel cell performance. Finally, the SOFC stream products are used to heat the steam reformer and next, they are split on four streams to vaporize the bioethanol, the water, to preheat the air and to feed a turbine to produce more energy. The process was designed to produce 1MW on steady state from bioethanol reformed and hydrogen fed to SOFC. As process sources, was used liquid bioethanol, and water to feed the reformer, and air to feed the SOFC as oxidant. This design was computer aided for HYSYS® software.
