EM - Escola de Minas

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Analysis of a hybrid molten carbonate fuel cell and gas turbine cycle.
(2020) Leal, Elisângela Martins; Silva, Barbara Emanuelle Sanches; Leal Júnior, Amauri Menezes
Background: Hybrid systems with fuel cells and thermal engines are studied with promising results. Molten carbonate fuel cells (MCFC) show many advantages compatible with the current demands for energy production in a sustainable competitive way. Materials and Methods: This paper focuses on the computational investigation of an indirect internal reforming MCFC coupled to a gas turbine (GT) system. The technical analysis comprises of energy analysis of the hybrid cycle, using the Gibbs function minimization technique for the methane steam reforming process. The assessment is performed to determine the influence of the hybrid cycle operating temperature and pressure, steam-to-carbon ratio, and fuel and oxidant usage in the fuel cell. Results: Results show that the increase in temperature and in operating pressure of the fuel cell and the fuel reform rate improves the hybrid system performance. Variation in the utilization factor, however, did not determine an expressive increase in system efficiency. For the same fuel mass flow rate, it is possible to see that the variation in the operating temperature of the fuel cell resulted in an increase in the total power of the hybrid system when compared to the results of the pressure increase. The increase in temperature resulted in a maximum increase of 12% in delivered power and corresponding to about 7% system efficiency increase. Instead, an increase in pressure of about 4% corresponding to an increase of about 2% system efficiency. Conclusion: Although an increase in the fuel cell's power density was observed for the same mass flow rate in the system, the pressure negatively influenced the total delivered power by the fuel cell.
Technical analysis of a hybrid solid oxide fuel cell/gas turbine cycle.
(2019) Leal, Elisângela Martins; Bortolaia, Luis Antônio; Leal Júnior, Amauri Menezes
The relatively high operating temperature of the solid oxide fuel cell allows for a highly efficient conversion to power, internal reforming, and high-quality by-product heat for cogeneration or a bottoming cycle. Besides, high-temperature fuel cells offer a good opportunity for coupling to a gas turbine. Fuel cell systems have demonstrated minimal air pollutant emissions and low greenhouse gas emissions. This paper focuses on the investigation and technical analysis of a direct internal reforming solid oxide fuel cell (DIR-SOFC) and a gas turbine (GT) system. The technical analysis comprises of an energy and exergy analysis of the hybrid cycle, using the Gibbs function minimization technique for the methane steam reforming process. The assessment is performed to determine the influence of the hybrid cycle operating temperature and pressure, steam-to-carbon ratio and fuel and oxidant usage in the fuel cell. Equilibrium calculations are made to find the ranges of inlet steam-to-carbon ratio and the operating current density of the fuel cell. After that, a hybrid system consists of a DIR-SOFC and a GT is evaluated using computer simulation. The results showed that the fuel cell is the main power producer system at the design point. The high-energy efficiency (around 62%) and exergy efficiency (around 58%) are achieved by the hybrid cycle compared to fuel cell efficiency (about 40%) and the GT (around 38%). The power ratio (SOFC/GT) found was 1.50. An analysis varying the fuel cell current density and the GT pressure ratio was performed showing that the fuel cell power production decreases about 7% with increasing current density when the GT becomes the main power-producing equipment. However, the system energy efficiency decreases with the reduction of power produced by the fuel cell.
Analysis of the energy efficiency of diesel oil consumption in the Brazilian Iron Ore Mining Company.
(2018) Fernandes, Eunírio Zanetti; Leal, Elisângela Martins; Figueiredo, Robson Lage; Reis, Gemírson de Paula dos
This paper aims to evaluate the diesel oil consumption between 2008 and 2015 in the production of iron ore in Brazil, creating correlations between energy intensity (production), economy and checking the impact of fuel prices on the commodity. During the analyzed period, the years 2008-2009 indicated economic crises, which interfered in the price and the commercialization of iron ore products. The physical intensity was 0.2% higher than the economic intensity. In the period from 2010 to 2014, economic activity remained more stable, with a decreasing trend, mainly due to the increase of iron ore prices. The physical intensity is much higher than the economic intensity influenced by the expansion of the Chinese economy. The year of 2014 indicated the end of the high iron ore price cycle and the beginning of supply and demand stabilization with consequent reduction in prices. In 2015, the market entered the stabilization phase, with a continuous reduction in unit production costs and transportation logistics. There was an abrupt change due to the strong increase of the economic intensity due to the fall of the international prices of iron ore. The diesel oil consumption plays a vital role in the scenario of cost reduction in iron ore production and a deeper analysis must be done in order to discover some options to change the energy matrix.

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