Performance Analysis of a Solid Oxide Fuel Cell-Gasifier Integrated System in Co-Trigenerative Arrangement

Abstract

The use of renewable sources, such as woody biomass waste, for energy purposes helps to reduce the consumption of fossil fuels and therefore the production of associated pollutants and greenhouse gases. Solid oxide fuel cells (SOFCs) are devices that convert the chemical energy of a product gas produced by a gasifier of biomass waste, before being suitably purified, directly into electric energy, with conversion efficiency, which is higher than that of other conventional energy systems. Since they operate at high temperature, they make available also thermal energy, which can be used for co- and tri-generation purposes. This paper aims at studying the arrangement of a complete trigenerative energy system composed of a gasifier of waste biomass; an energy unit represented by a SOFC system; an absorption cooling section for the conversion into cooling energy of the waste heat. In its layout, the SOFC energy unit considers the anode off gas recirculation, a postcombustor to energize the exhaust stream, and a preheater for the fresh gases entering. The integrated plant is completed by means of batteries for electric energy storage and hot water tanks and thermal energy storage. An ad hoc developed numerical modeling is used to choose the working point of the SOFC energy system at which to operate it and to analyze its energy behavior under syngas feeding. Two biomass-derived syngas are analyzed: one from woody biomass and one from urban solid waste gasification. Hence, the entire integrated plant is analyzed for both feeding types. The energy analysis of the integrated SOFC/gasifier is carried out based on a fixed quantity of biomass waste to be processed in an existing gasifier. Then, the design of the SOFC energy section is carried out. The integrated plant is then applied to a case study to satisfy the energy needs of a user of the tertiary sector. Therefore, based on this, the procedure continues with sizing the cooling section for the cooling power delivery in the warm season, the batteries to store the electric energy to be delivered, and the hot water tanks for the thermal energy storage to be delivered as heat when necessary or to feed the absorption cooling plant. The integrated SOFC/Gasifier defined can be considered as a high-efficiency tri-generator capable of accomplishing an energy valorization of high quality waste biomass.