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Technical feasibility and economic analysis of the bagasse boiler implementation to operate a reheat regenerative rankine cycle in a sugar and alcohol mill

Abstract

The power generation system of the Brazilian sugar and ethanol industry has been showing a very slow technological growth, compared to high efficiency power generating plants. The maximum values of steam pressure and temperature in Brazilian sugar and alcohol industry are 10MPa and 530oC respectively, with shy regenerator uses (water - steam heat exchanger) and radiators (air - steam heat exchangers). On the other hand, ultra supercritical boilers fueled by heavy oil and / or coal, reach parameters of steam pressure and temperature, in the range of 26MPa and 600oC respectively; up to two steam reheat stages. Considering also that in the power generation system, the boiler has the highest irreversibility, the aim of this work is to contribute to the innovative bagasse boiler project development, provided with regenerators, radiators and steam reheat. For this, it will be held, initially, the bagasse characterization, with the follow analysis: immediate, elementary and higher heating value HHV and lower heating value LHV. Then, the development of three projects will be undertaken: i) Project conventional of bagasse boiler; ii) modified project of the conventional boiler to operate with regenerator and radiator, and iii) bagasse boiler Project with radiator and regenerator plus steam reheater, such as a Reheat Regenerative Rankine Cycle. In all cases the boilers operate at the level of mass flow, pressure and temperature of the steam: 500 t / h; 12MPa and 540oC. The three developed boiler projects will be analyzed via CFD technique (Computational Fluid Dynamics) aiming to optimize the thermal exchange areas of the boiler and reduce the pressure losses of it. The generation cycles: i) Rankine; ii) Regenerative Rankine, and iii) Reheat Regenerative Rankine will be simulated in order to evaluate the system performance in terms of the first and second thermodynamic law. Finally, the economic analysis of the cost of the boiler will be held in the three aforementioned settings. These costs linked to the appropriate turbine costs, deaerators, water treatment, and others will establish an approximate cost of each configuration invested. The revenue obtained by each configuration will be determined using energy standards values (R$/.MW) used in the Brazilian sugar and alcohol industry. The generation of electricity for each configuration will be obtained from the first law of thermodynamics analysis. Thus, based on the generation of electricity each configuration will set the return of investment from each case analyzed. It is expected that from the results obtained from the Reheat Regenerative Rankine cycle setting, it will be offered the best condition for the investment / return of capital and may encourage investors from the Brazilian sugar and alcohol industry on this type of innovative projects. The effect on the sugar and alcohol sector will be an important step in the optimization of the power generation sector, so that it will make the Brazilian sugar and alcohol mills more efficient and competitive in the world market. It also is expected that this development will allow the technical- scientific growth of the Inka's Boiler company with its USP partners (LSCP and FFCLRP) UFABC and ESSS. (AU)

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