Designing sustainable bioenergy from residual biomass: Site allocation criteria and energy/exergy performance indicators

This work aims at developing a comprehensive methodology defining the influence of the proper feedstock management, number and location of gasification-power plants, and process configuration based on the thermodynamic performances of the proposed system under different scenarios. The feedstock was citrus peel from local citrus processing factories. A three-step model was adopted: best site criteria decision tool, location-allocation analysis by minimising energetic transport costs, energy/exergy and emissions analysis. This model was applied to three process scenarios. In the first, we considered a wet biomass (65% water content) dried at a local plant using cogenerated heat; in the second, the biomass dried prior to transportation (15% water content) used to power the combined heat and power plant. The cogenerated heat fed an Organic Rankine Cycle (ORC) unit. In the third, the cogenerated heat is used for district heating. The scenario analysis showed that the regional potential for producing renewable electricity from citrus peel gasification is 66.7–74.6 GWh. Results showed that the Energy Return on Investment (EROI) is <1 only when the feedstock is transported dry (15% water content), and the cogenerated heat is used for additional power production in an ORC unit. The highest EROI values (24–47) are obtained when the feedstock is transported wet and dried using the cogenerated heat. A sensitivity analysis reveals that the optimal number of plants is three with a reduction of the energetic transport cost of 46% compared to a single plant. The maximum global energy and exergy efficiencies were 39% and 16%, respectively. The exergy-based renewability indicator showed that the proposed bioenergy system could be considered renewable in only one of the three process scenarios.