Potencial de geração de eletricidade proveniente dos gases efluentes da produção de carvão vegetal em Minas Gerais

Abstract

Minas Gerais is the biggest charcoal producer in Brazil. This production happens in carbonization kilns that emit waste gases to the atmosphere, wasting useful energy and causing an environmental impact. In this work, an evaluation of the electricity generation potential from the effluent gases of the charcoal production in Minas Gerais was carried out using different electricity conversion technologies. A survey of charcoal producers in the State and their production was conducted in order to calculate the energy potential available in 2020 with a projection until 2030. For the electricity generation studies, three technologies were considered, namely: The Steam Rankine Cycle (SRC), the Organic Rankine Cycle (ORC) and the Externally Fired Gas Turbine (EFGT). For each technology, the efficiencies were calculated and applied for each of the previously surveyed producers. Efficiencies ranged from 5% to 24% depending on the type of technology power, ranging from 100kW to 2000kW. Maps of the power generation potentials in Minas Gerais were created, showing a concentration in the North and Northeast regions of the state. The highest power generation potential for the state was 1348 GWh/year using the ORC cycle with regeneration, superheating and n-decane as the working fluid. An economic analysis was also made, taking into account auctions for the energy sale in the energy market, together with a sensitivity analysis for each variable considered: Power, energy sale price, minimum attractiveness rate of return, taxes, plant operation time, and capital expenditure. The results demonstrate that the current technical and economic scenarios are not favorable for the implementation of electricity generation plants based on waste heat recovery from gases in charcoal production plants in the State of Minas Gerais, making feasibility in plants smaller than 10 MW practically impossible over a 10-year horizon. All technologies had energy sales prices above 100 US$/MWh, which is higher than the average of the last 3 years. However, the technological development in the charcoal production kilns and electricity conversion technologies, combined with an economic incentive based on environmental benefits, may provide an improvement in this scenario in the future.