Thermodynamic and Environmental Analysis of Scaling up Cogeneration Units Driven by Sugarcane Biomass to Enhance Power Exports

João Guerra,Alex Nogueira,Luiz Kulay,Fernando Cardoso

doi:10.3390/en11010073

Abstract

When manual harvesting of sugarcane was discontinued in many regions of Brazil, interest in power generation by burning the bagasse and straw in cogeneration units rose. Exergy analysis is often applied to increase the thermodynamic yield of these plants by identifying irreversibility and work availability. Conversely, pressure for adopting clean energy requires these systems to be evaluated for suitable environmental performance. This study identified and discussed the thermodynamic and environmental effects of scaling up systems that operate according Rankine cycle with reheating. Ten scenarios have been designed considering different levels of steam pressure and addition rates of straw remaining in the sugarcane cultivation. The thermodynamic analysis revealed a 37% improvement in the exergy efficiency and 63% of increasing in power generation to raise the steam pressure from 20 to 100 bar. Moreover, the use of 50% of residual straw into units operating at 100 bar can more than double the amount of electricity exported. If addressed considering a life cycle perspective, the use of straw improves the environmental performance of the cogeneration for Climate Change and Particle Matter Formation but provides additional impacts in terms of Water and Fossil resources depletions.

Highlights

Sugar and alcohol production stands out as one of Brazil’s main productive activities
An expressive trend of expansion in this field is expected in the few years. This is because: (i) Brazil still falls short of fully exploring its energy potential in sugarcane biomass [1,4,5]; (ii) the installed capacity for cogeneration from biomass is 143 GW, representing 9.3% of the domestic energy supply in 2014, and the national commitment is to increase this contribution to 23%
The methodology established to fulfill the objectives of this study takes into account five steps: (i) formulation of scenarios that represent different operational scales of cogeneration from sugarcane biomass; (ii) verification of the thermodynamic performance profile of each scenario from exergy analysis; (iii) use of the Life Cycle Assessment (LCA) technique to examine the performance of scenarios from an environmental perspective; (iv) performing an investigation of the obtained results in order to identify agents causing impacts in both dimensions of the analysis; and (v) verification of the effects stemming from the synergy of thermodynamic and environmental indicators when applied in the scale up analysis of the cogeneration process

Summary

Introduction

Sugar and alcohol production stands out as one of Brazil’s main productive activities. The companies of the internal sugar-alcohol sector have been seeking to raise competitiveness by improving agricultural productivity and industrial income, and by reducing losses along the production chain. In this second branch of actions, the reuse of agricultural wastes mostly in the form of bagasse and straw, is noteworthy. An expressive trend of expansion in this field is expected in the few years This is because: (i) Brazil still falls short of fully exploring its energy potential in sugarcane biomass [1,4,5]; (ii) the installed capacity for cogeneration from biomass is 143 GW, representing 9.3% of the domestic energy supply in 2014, and the national commitment is to increase this contribution to 23%

Methods

Results

Conclusion