"Interferências provocadas pela infestação de mexilhões-dourados (Limnoperna fortunei) sobre bombas centrífugas e seu impacto em sistemas de bombeamento de água"

Abstract

Over the past two decades, water systems in South America have been infected by an invasive specie originating from Southeast Asia, the mollusk Limnoperna fortunei, popularly known as the golden mussel. This is a bivalve mollusk species that has, among other features, high ability to invade environments, clinging easily to substrates along watercourses and infesting hydroelectric systems and water pumping systems. The infestation of pipes by mussel increases its relative roughness and reduces the internal diameter, promoting the occlusion of the duct. As a result, operating costs originally unanticipated are generated, arising from the arrest of systems for the clearing and maintenance, as well as increased consumption of electricity in pumping systems, and the loss of hydraulic efficiency. Research aimed at determining the head losses due the Limnoperna fortunei infestation in hydraulic systems, especially in water pumps, are rare, being necessary to make inferences and interpolations for the estimation of pressure losses. The increased friction provided by the colonization of Limnoperna fortunei in pipelines may refer to situations of hydraulic failure in terms of efficiency hydraulic systems. This research presents an evaluation of the interference caused in the performance curves of centrifugal pumps applied to collection and distribution of water systems. The results obtained show that the infestation of centrifugal pumps by L. fortunei significantly change their performance, both in terms of reduction of the useful energy to the fluid as thrust pumped flow, with consequent reduction of the overall pump efficiency, especially in smaller pumping systems. Alters significantly the operating point of the lift with the advancement of infestation by the suction and discharge, so that it can be considered that a circuit infested with mussel is completely different from the original. Qualitatively, lift systems infested with mussels can be compared to those operating with aggressive water for decades. In other words, the infestation is capable of promoting, possibly in a period of two years or less, the aging effect for the entire predicted life of the system. Alternatively, to avoid infestation of pumps, can be applied larger pumps in smaller pumping systems, adopting the strategy of operating the lift for shorter intervals of time and with higher flow velocities in the pump, thus avoiding infestation of the volute. Another possibility would be the development of anti-mussels pumps , adopting the concept described in this work when designing the pump housing: would modify the geometry of the housing such that obtain speeds, increasing or constant throughout volute, always greater than the upper limit of the speed required for the detachment and release of the golden mussel in the volute (4,1 m/s). It is worth noting that the mussel can develop and adhere to the inner surface of the housing with the flow speeds below 2 m/s, reaching full infestation in a time interval between 1 and 2 years. Since this is a biological phenomenon, in that colonies are being developed within the pump housing, localized speed fluctuations along the volute may occur, which may promote removal of blocks or layers of colonies of mussels. This fluctuation will cause instability in the performance curve, resulting in pulse pressure and flow at the pump and the establishment of new operating concept work for the pump: the operating range, instead of operating point, into which the machine work in different conditions of performance over time. It is recommended further studies to verify the possibility of establishing dimensionless curves to quantify the phenomenon, which will allow economic analysis for each system over different operational conditions and under infestation, both in the pump housing and in the suction and discharge pipelines.