چكيده به لاتين
With increasing energy consumption as well as economic and environmental issues in all countries, views have changed towards using clean energy sources even on small and micro-scales power plant despite the higher cost compared to fossil power plants. The development plan for micro-hydropower is expanding with an increasing focus on renewable energy sources. It is very important to adjust the water pressure in the urban water distribution network to provide the desired load as well as to prevent damage to the pipes and connections and reduce water leakage. In order to reduce the pressure in areas where there is an increase in pressure due to the difference in height and topography of the locations, the use of pressure-reducing valves causes the loss of large amounts of energy. The soft pressure regulation system (SPRS) as a potential technology provides the possibility of regulating pressure and energy recovery in pressure-reducing stations. The system consists of various parts where the water turbine is considered as the heart of the system or the main part, and it is possible to use various classic water turbines in this working condition. The low cost of construction and maintenance, short start-up time, small dimensions, and the possibility of generating electricity at the location's consumption are unique features of the SPRS that uses a pump as turbine (PAT).
In this study, the performance of a single-stage centrifugal PAT as the most important part of the soft pressure regulating system in the laboratory has been experimentally investigated by providing hydraulic characteristics similar to the pressure-reducing station. According to the acceptable performance in the investigated work range, the implementation and operation of the power plant in the urban water distribution network have been done in the next stage. Numerical modeling based on the manufacturer's geometric specifications has been used in CFTurbo software, and for meshing the 3D geometry of the Impeller and volute from TurboGrid and AnsysMesh software, as well as simulation in CFX solver by setting the boundary conditions. The results of operation in direct and reverse modes were compared and validated with experimental results. Investigating hourly flow rate variations in WDN shows that the PAT working conditions change frequently and operate for a long time under off-design conditions. Since there are no tools to control and guide the fluid to the impeller, there is no proper conformance between the inlet flow and the blade profile, and loss increases as well as efficiency decreases in this condition. In order to improve the PAT performance in the working range, the effect of modifying the parameters of blade inlet angle, blade warp angle, blade curvature, blade thickness, blade number, blade inlet width, blade inlet angle, blade curvature, and adding splitter blades in the impeller, as well as the effect of the type and diameter of the volute, is numerically investigated. Considering the wide range of flow rate changes in the WDN, changing the blade geometrical parameters doesn't have the same impact on power generation and losses in the whole working range. A statistical analysis has been done based on the daily trend of flow rate to determine the importance of working areas in this case study, and the selection of optimal changes is directly related to working time in the desired ranges. Finally, four geometries were selected as the proposed geometries by simultaneously changing the geometric parameters to improve the PAT performance in the working range, and the simulation results show a greater tendency of the fluid to follow the vane profile and reduce losses due to flow separation and the formation of vortices. The working range with high efficiency of the PAT and also the power generation have been increased due to the geometry modification. The results of investigating the PAT performance with the suggested impellers show that the special impeller (increasing the blade number, reducing the blade thickness, and increasing the blade inlet width) has the greatest effect on increasing the production capacity of the power plant. Using a special impeller instead of the original impeller improves the PAT performance in the range from 100 to 240 m3/h, as well as power generation increases by 5.1% during these four working months. The implementation of this power plant allows the reduction of 16.5 tCO2 emissions compared to a coal power plant with the same capacity over a four-month period. Moreover, using the special impeller has the potential to reduce CO2 emissions by 840 kg more than the original PAT under similar working conditions.
