Exergy, energy and environmental evaluation of a biomass-assisted integrated plant for multigeneration fed by various biomass sources

Abstract

It is expected that fossil fuels will be replaced by renewable energy sources to reduce environmental pollution. Multigenerational integrated plants which generate various useful outputs from the same input are required to utilize these sources more efficiently. An innovative multigeneration system based on biomass for useful outputs including district cooling and heating, bioethanol, biogas, and electricity is proposed in this study. The system includes a biomass combustion unit, Rankine cycle, biofuel production unit, and absorption cooling cycle. 15 types of biomass sources are considered for the combined system and a thermodynamic and environmental analyses are carried out to assess the effects of biomass sources on the multigeneration system. According to the modeling results, using cotton stem leads to the highest CO2 emission (195.3 kg/MWh) while switchgrass produces the lowest (147.0 kg/MWh). The thermodynamic analysis reveals that, for all considered cases, the burner has the maximum exergy destruction rate among all the stages. Moreover, the exergy and energy efficiencies of the plant for different fuels were assessed, and show that the use of rice straw and rice husk exhibit the highest (68.30%) and lowest (62.72%) overall energy efficiencies, respectively. It is also observed that the system using rice straw and larch wood has the highest (45.29%) and lowest (42.86%) overall exergy efficiencies, respectively. The effects of significant input factors are examined on the system performance and emission indicants.