A influência da infestação pelo mexilhão dourado em condutos forçados das centrais geradoras hidrelétricas no Brasil: uma análise das perdas e do transiente hidráulico

Abstract

The golden mussel is a bivalve freshwater mollusc that causes several environmental and economic problems wherever it is found. In Brazil, the first detection of this mollusc took place in the late 1990s. Among all the enterprises that rely on freshwater, the hydroelectric plant is one which suffers greatly from the infestation caused by the golden mussel, as they heavily rely on freshwater to operate. In these enterprises, this infestation causes significant hydraulic losses in the cooling systems, in the water intake grids, amongst others. After the promulgation of Law 13.097/15, the so-called Mini Hydroelectric Plants were able to operate with installed capacity of up to 3,000kW. These enterprises have been widely accepted in the market by companies, mainly by the industries that operate in an isolated system, since no bidding process or license is required for their construction. It is only required to inform the qualified authority of the hydraulic potential used and installed power. The main purpose of this project is to evaluate the influence of infestation by the golden mussel, in hydraulic losses and in the hydraulic transient, in penstocks of the Mini Hydroelectric Plants that operate with individual penstocks, in which they adduct water to the turbines whose nominal powers are of 1,000kW, 1,500kW and 3,000kW. The results show that the values of the hydraulic losses and the higher value of the overpressure during the hydraulic transient in the penstocks are more significant for the smaller diameters with larger extensions and when these machines operate with 100% of the load. In some cases, the value of the average water flow speed exceeds the minimum value for pulling out all the golden mussels, causing the evolution of hydraulic losses to cease. It was also observed that the use of classical methods for the calculation of the maximum overpressure during the hydraulic transient is not recommended in the penstocks of infestation by the golden mussel. In these cases, it is recommended to use the method of characteristics for calculations. In the equations describing this method, the attrition factor (f) is not neglected and, in the penstocks of infestation by this mollusc, this variable presents highly significant value. Lastly, it is necessary to clean from time to time in the penstocks, infested by the golden mussel, so that they can operate ordinarily and produce the nominal power for which they were designed.