Comparative analysis of electricity cogeneration scenarios in sugarcane production by LCA

Abstract

The decentralization of the Brazilian electricity sector in association with the internal electricity supply crisis has encouraged companies in the sugarcane industry to produce electricity by burning sugarcane bagasse in cogeneration plants. This approach reduces the environmental impact of the sugarcane production and has opened up opportunities for distilleries and annex plants to increase their product portfolios. Potential scenarios for technically and environmentally improving the cogeneration performance were analyzed by using thermodynamic analysis and Life Cycle Assessment (LCA). The method used in this study aimed to provide an understanding and a model of the electrical and thermal energy production and the environmental impacts of conventional vapor power systems which operate with a Rankine cycle that are commonly used by Brazilian distilleries. Vapor power system experts have suggested focusing on the following technical improvement areas: increasing the properties of the steam from 67 bar and 480 °C to 100 bar and 520 °C, regeneration, and reheating. Eight case scenarios were projected based on different combinations of these conditions. A functional unit of “To the delivery of 1.0 MWh of electricity to the power grid from a cogeneration system” was defined. The product system covers the environmental burdens of the industrial stage and the agricultural production of sugarcane. Technical evaluation indicated that the energy efficiency improves as the pressure at which the vapor leaves the boiler increases. Simultaneously, the net power exported to the grid increases and the makeup water consumption in the cooling tower and the makeup water supplied to the boiler reduce. From the LCA, it was noted that the improved energy performance of the system is accompanied by reduced environmental impacts for all evaluated categories. In addition, vapor production at 100 bar and 520 °C results in greater environmental gains, both in absolute and relative terms. Reheating and regeneration concepts were found to be considerably effective in improving the energy and environmental performance of cogeneration systems by burning sugarcane bagasse. For the evaluated categories, the results indicate that the proposed modifications are favorable for increasing the efficiency of the thermodynamic cycle and for decreasing the environmental impacts of the product system.