Search

Abstract This article presents the experimental results of a novel energy storage system that combines CAES (Compressed Air Energy Storage) with PHES (Pumped Hydro Energy Storage) technologies. As a reference, we called this system PH-CAES. In this alternative solution two storage tanks, the first with compressed air and the second with water, are separated by a valve. When electric power is required, the valve is opened and water flows to a Pelton turbine, which is coupled to an electric generator. Water from the Pelton turbine is discharged into a third tank. To store energy and recover the initial state, water is pumped back. We built a prototype to assess the PH-CAES performance, with focus on the power generation system. Experimental conversion efficiency was 45%, whilst the rational efficiency remained close to 30%. We also presented a discussion based on the second law of thermodynamics to show that there is a compromise between tanks exergies that maximizes the system performance. We also provide an operating map of this PH-CAES system to assist authors on new studies about this novel technology. Highlights • We present a novel energy storage system based on CAES and Pumped-Hydro. • We test the performance of the PH-CAES prototype. • The generation efficiency reached 45%, despite the system reduced scale. • Experiments have shown that the PH-CAES can be competitive. [ABSTRACT FROM AUTHOR]

Following new and innovative concepts of energy recovery which use micro-hydro impulse turbines in drinking water systems, more sophisticated turbine designs become essential to improve energy recovery efficiency. In the case of implementing a hydraulic impulse turbine with tailwater depression in such systems, one major challenge to optimising overall efficiency is the reduction of the turbine's air demand. Firstly, a lower air demand would reduce the required dimensions of the ventilation system and therefore increase energy efficiency. Secondly, a minimised air demand would considerably reduce negative effects downstream of the turbine casing, such as a reduced transport capacity and corrosion. To achieve a minimised air demand, detailed experimental investigations are conducted, during which different casing inserts are tested in a micro-hydro Pelton machine. A specially constructed turbine test-bed, featuring two separately installed measuring units, allows for the partitioning and measurement of dissolved and undissolved air. In the case of the used Pelton machine, the results clearly identify different air detrainment processes. The undissolved air demand strongly depends on the particular casing insert and can be reduced by 90 % through optimal flow condition using flow straighteners as insert. In contrast, the amount of dissolved air demand cannot be controlled by additional casing inserts. This can be explained due its different entrainment processes. The analysis of the dependency of the measurement results on scale shows that a direct transfer to a prototype application will underestimate the air demand. Nevertheless, the presented research findings show an effective way, also relevant to turbine manufacturers, to reduce air demand and improve overall efficiency of impulse turbines in counter pressure operation. [ABSTRACT FROM AUTHOR]

Hydraulic turbines are designed for the given values of head, discharge and speed but mostly operate at off designed head and discharge values. Due to variation in head, operating parameters like speed and discharge coefficients are changed affecting the flow and efficiency characteristics of turbine. This makes customary to assess the turbine performance at different operating parameters. Pelton turbine is the most commonly used impulse turbine for high head power plants. The computational fluid dynamics is a cost effective tool to assess the turbine performance in terms of local and global design and operating parameter of turbine. In the present work, multiphase flow analysis in Pelton turbine using water and air as working fluid is carried out to estimate the efficiency, blade loading, velocity and water distribution over the bucket at different operating regimes of the turbine. The effect of mesh size, turbulence model and time step is also studied for transient multiphase flow simulation. [ABSTRACT FROM AUTHOR]

Impulse turbines with tailwater depression are an efficient choice for energy recovery in drinking water systems. To reduce negative effects of detrained air downstream of the turbine casing, such as corrosion and reduced transport capacity, main processes and possible reduction of air detrainment have been investigated in detailed experimental studies on a micro-hydro Pelton machine with tailwater depression. The experimental setup has been designed to distinguish between dissolved and undissolved air detrainment. In case of dissolved air detrainment there is a clear relation between the amount of dissolved air and the counter pressure as well as the flow rate parameter. Experimental results for the amount of undissolved air detrainment show dependencies on geometrical dimensions, velocity coefficient, casing water level and the flow rate of the turbine. To avoid undissolved air detrainment, design equations are deducted for dimensioning the casing height and the casing diameter. Therefore the presented investigations show how air detrainment can be controlled or rather minimized by optimised casing-design of impulse turbines. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the performance of a RO (reverse osmosis) desalination plant at different seawater salinity values. An energy recovery Pelton turbine is integrated with the desalination plant. Thermodynamic analysis, based on the first and second laws of thermodynamics, as well as a thermo-based economic analysis is performed for the proposed system. The effects of the system components irreversibilities on the economics and cost of product water are parametrically studied through the thermoeconomic analysis. The exergy analysis shows that large irreversibilities occur in the high pressure pump and in the RO module. Both thermodynamic and thermoeconomic performances of the overall system are investigated under different operating parameters. For the base case; the system achieves an exergy efficiency of 5.82%. The product cost is estimated to be 2.451 $/m3 and 54.2 $/MJ when source water with salinity of 35,000 ppm is fed to the system. [Copyright &y& Elsevier]

Abstract: In the present study, an experiment was carried out to investigate the mechanism of erosion of a small scale Pelton turbine, under actual flow conditions. Samples of silt were collected from the head work of one of the most silt affected hydro power station in India. Silt parameters (silt particle size and silt concentration) were considered to investigate the mechanism of silt erosion on Pelton turbine buckets for different silt sizes. In the first part of the experimentation, hot spots (spots which are more prone to erosion) were identified under a high silt concentration. Second part of the experimentation was carried out to study the erosion mechanism for small specimens of metal which were fixed at the marked hot spots. Based on the investigation, it has been found that silt size is a strong parameter to produce erosion and the material removal from the surface is due to plastic deformation and ploughing of surface. [Copyright &y& Elsevier]