Eficiência energética em estações elevatórias: Diagnóstico hidroenergético de uma instalação fornecedora de água bruta para posterior tratamento e distribuição de água tratada para dois municípios

Abstract

This work aims to evaluate the operational/financial current situation of a raw water lift station, wich is part of an integrated treated water supply system for two big cities in south of Brazil – hydropower diagnosis. The facility is composed of five motor-pump sets, 560 kW rated power each, wich are triggered according to the operational seasonality. In the project setup, two motor-pump sets were operational reserves and, therefore, even three machines were actionated in parallel, connected to the same output pipe. Since January 2016, because of a higher flow operational need available to the supply system, one of the two standby equipment was put into operation thus totaling up to four jointly operated equipment. With the increase of raw water captured volume, in which the forth equipment was put in operation without a detailed analysis of this activity impact facing to the head losses and, according to the relatively high electric power bills values, it was decided to carry out a multidisciplinary (hydraulic, mechanics, electric, operation and simulation) study aiming the decrease of the electric power bills. The hydropower analysis was focused, basically, looking for cadastre informations (project and field) of the equipment and facilities; in the performance tests and in the motor-pump sets sequencing tests; and in the compilation and in the operational annual data analysis. The study has made it possible to find distinct results, such as: performance determinations of each motor-pump sets and the facility as a whole, as well as the most effective sequencing according to the applicable operational configurations; operational data collection during a period of one year that resulted in the determination of the facility performance indicators; valuation of head losses and the system operational speed; the construction of a hydraulic simulation model in software, calibrated in field, wich allowed the taxes framework analysis as provided by the normative resolution nº 414, from september, the ninth, 2010, according to ANEEL and the operational scenario simulations to establish possible operational/financial gains with and/or without investments. As examples of easily reachable results, only administrative/contractual ones, among others, can be highlighted: 52.327,00 R$ year-1 (-0,96 % of the total energy consumption) – just switching off the fourth equipment at the high peak period; 201.312,00 R$ year-1 (-18,60 % of the contracted demand) – when the contracted demand is changed at the high peak period from 2.150 kW for 1.750 kW; and, 156.728,52 R$ year-1 (-2,89 % of the total energy consumption) – by the optimized selection of the motor-pump sets for the more efficient combinations. Talking about the significant investments, it was diagnosed that the facility has a considerable portion of wasted power, caused by head losses in the pipes, that go much beyond what is considered inevitable/economic. This is explained because the equivalent diameter of the system adductors has a value of 931,2 mm facing an optimal/economic, probable, obtained through the Bresse equation, of 1.350 mm. Moreover, the roughness inadequate values of the pipes, after years of usage, has significant impact in the head losses values too. Therefore, with R$ 289.036,23 (substitution of the five motor-pump sets suctions, four pump rotors machining and the adductor roughness repairs, using pigs), 449.685,45 R$ year-1, or 8,28% of the total facility consumption are estimated to be saved, maintaining the current system flow rates and with a return on investment less than one year. Regarding to the electromechanical devices, the performances occurred as expected. However, the pump types currently installed never reach the maximum sustainable yield conditions at any operational points. Proposing the replacement of the motor-pump sets for another models, the performances, in the manometric heights average values established through hydropower diagnosis would be, in different operational conditions, always closer to the maximum viable. For those alterations, the expected return has been estimated in, approximately, five years considering the replacement of three pumps and three electrical motors, wich is economically viable.