Simulação off-design de um sistema ORC para recuperação de calor residual de um motor de combustão interna

Abstract

The exhaust gases of an internal combustion engine (MCI) leave the equipment still with sufficient temperature to generate more electrical power, if a system is used for this purpose. Therefore, due to this scenario of the possibility of increasing the efficiency of the energy plant, thus reducing the emission of pollutants and fuel consumption, in this work a study was made on the use of the residual energy existing in the combustion gases of an engine diesel stationary internal combustion. For this, the ORC (Organic Rankine Cycle) was used, a thermodynamic cycle that uses an organic fluid as the working fluid. The analyzes are evaluated in three parts: 1) parametric analysis of an ORC system in permanent on-design regime (within the design conditions) to ascertain the influence of the variation of thermodynamic parameters, both in power and in the flow of working fluid , with the objective of determining the optimum point of operation of the cycle, determined “design point”; 2) parametric analysis of the same cycle, now in a permanent off-design regime (outside the design conditions), to check the influences when they are varied as a characteristic of the heat source (flow and temperature), now without varying the geometric design of the equipment constituents of the cycle, which brings the functioning of the cycle closer to reality; 3) an economic analysis of the feasibility of implantation for such an ORC plant, based on the model based on CEPCI. From the thermodynamic analyzes regarding the cycle efficiency, the system design was determined for a working fluid flow of 0.09 kg / s, evaporation and condensation pressure of 3.870 kPa and 25 kPa, respectively and with the exhaust gas (heat source) at 420 ° C and 0.1697 kg / s. From that point of operation, the geometries of the basic components of the ORC were determined: evaporator, turbine, condenser and pump. For the off-design simulations, performed with the aid of the ASPEN HYSYS® V.11 software, the evaporation pressure, the working fluid flow and the heat source inlet conditions were varied. From such simulations in different conditions, a minimum, average and maximum net power production of 8.56 kW, 15.59 kW and 26.29 kW, respectively, was observed, while in the design condition of 14.72 kW. The informative economic analysis that the initial investment for the implementation of the system is R$ 93,502.22 and the financial return and the rate of return reach an average of 1.5 years and 90%, respectively, depending on the values of interest taken for investment. The study shows that the system does not require large capital investments and can bring return on investment in a short time and with satisfactory gains from then on.