Safety Evaluation of Hydrogen Pipeline Transport: an Approach Based on Machine Learning

The issue of global warming imposes a change of paradigm in the energy sector to mitigate the human impact on the environment. In this perspective, hydrogen can be produced through water electrolysis and used in fuel-cell systems with near-zero pollutant emissions. Nevertheless, the distribution system represents one of the main bottlenecks for a future transition to a hydrogen economy. The possibility of transporting hydrogen through the existing pipeline network is economically attractive. Nevertheless, most pipeline steels are prone to hydrogen-induced damage, and their mechanical properties are degraded by hydrogen gas to an extent that could result in sudden component failures. Hydrogen embrittlement can be responsible for undesired releases with potentially catastrophic consequences. This study evaluates the safety of existing European natural gas pipelines for hydrogen transport through machine learning tools. The material susceptibility to hydrogen embrittlement is predicted under different working conditions in order to prevent loss of material integrity and eventual releases. This study aims at bridging the gap between safety and material science, as it can optimize predictive maintenance of hydrogen pipelines, thus promoting the widespread utilization of hydrogen in the forthcoming years

Effects of sediment erosion in guide vanes of Francis turbines

Erosive wear of turbine components has been a major operational challenge for the runoff-river hydropower plants across the basins of Himalaya in Asia. The hard mineral particles, which are carried by rivers reach the turbines and erode the surface in contact. In Francis turbines, guide vanes, cover plates, hub at runner inlet and blades at runner outlet are the most affected areas due to the sediment erosion. Several attempts have been made in the past to minimize the losses due to the sediment erosion in the hydraulic turbines. However, the problem has not been solved satisfactorily. A dry clearance gap between the guide vanes and the cover plates usually exists in the Francis turbines, fromthe design. The deflection of cover plates and the erosion of the components causes the clearance gap to increase by multiple times of its design value. Inherit pressure difference between guide vane surfaces forces a leakage flow from the increased clearance gap. A systematic study of the characteristics of the leakage flow, and its effects on the flow conditions inside the Francis turbine distributor has not been reported yet. Such studies are necessary for the design optimization of the turbine components and to plan the effective maintenance schedules for repairing the eroded turbine parts. The main objective of this work is to study the effects of sediment erosion in hydro turbines, with the focus on the flow around the guide vanes of a low specific speed Francis turbine. Experimental investigations of the characteristics of leakage flow from the increased clearance gap between eroded guide vanes and cover plates, has been the focus of this study. A one-guide vane cascade has been developed to represent the flow inside a low specific speed Francis turbine distributor. Cases with five different sizes of clearance gap are investigated for the guide vane shaped with a symmetric profile. Particle Image Velocimetry techniques are applied for the flow measurement. All experiments have been carried out at the Waterpower Laboratory of Norwegian University of Science and Technology. Flow velocity exceeding 35 m/s, at the runner inlet of Francis turbine, is reported for the first time from such experimental studies. The results show that, that the clearance gap up to 0.5 mm does not have significant effects on the flow parameters and hence can be accepted as the maximum limit. The leakage flow, with clearance gap more than 1 mm, is found to change the velocity components at the runner inlet significantly. The case with the clearance gap of 2 mm is found to have the highest effects on the flow velocities and is considered as the critical size. The total crosswise leakage flow, from the critical clearance gap, is measured to be more than 1% of the main flow. As the consequence of the leakage flow, the relative velocity at the runner inlet is found to increase locally up to three times from its design value. This local increase in relative velocity is identified as the cause to have severe erosion at the runner hub in the sediment-laden projects. The leakage flow also changes the pressure distribution around guide vane, causing the torque on the guide vane shaft to increase up to 28%. Further investigation of the propagation of the leakage flow into the turbine runner, and its effects on the runner’s performance is necessary. Alternative designs of guide vane geometry, to minimize the differential pressure across is recommended as the future works

Velocity and pressure measurements in guide vane clearance gap of a low specific speed Francis turbine

In Francis turbine, a small clearance gap between the guide vanes and the cover plates is usually required to pivot guide vanes as a part of governing system. Deflection of cover plates and erosion of mating surfaces causes this gap to increase from its design value. The clearance gap induces the secondary flow in the distributor system. This effects the main flow at the runner inlet, which causes losses in efficiency and instability. A guide vane cascade of a low specific speed Francis turbine has been developed for experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. The setup is designed for particle image velocimetry (PIV) measurements from the position of stay vane outlet to the position of runner inlet. In this study, velocity and pressure measurements are conducted with 2 mm clearance gap on one side of guide vane. Leakage flow is observed and measured together with pressure measurements. It is concluded that the leakage flow behaves as a jet and mixes with the main flow in cross-wise direction and forms a vortex filament. This causes non-uniform inlet flow conditions at runner blades

Alternative Design of Double-Suction Centrifugal Pump to Reduce the Effects of Silt Erosion

Large amounts of sediment in the Himalayan rivers causes severe silt erosion to the hydraulic machinery operating along these rivers. In this study, the effects of silt characteristics on the silt-erosion characteristics of a double-suction centrifugal pump was studied and the anti-erosion property of bionic convex domes on silt erosion under these conditions was explored by using computational-fluid-dynamics methods, partly supported by a painted-blade erosion experiment. The results show that the silt size affects the erosion position and erosion strength, whereas the silt concentration mainly affects the erosion strength for the studied range. The bionic convex domes provide an effective solution to improve the silt erosion for most of the investigated silt-laden conditions by decreasing the erosion rate and the erosion area of the blade. The anti-erosion mechanism was studied combined with large eddy simulation. The analysis shows that the relative velocity of water around the blade surface is changed and the mass flow rate of silt particles hitting the blade is reduced by inducing swirling flows around the bionic convex domes

Current research in hydraulic turbines against sediment erosion: International partnership and collaborations

The problem of material erosion in hydraulic machineries has been under the investigation since a century ago. However, the proper solutions to the erosion of hydro turbine due to sediment-laden flows has not been found yet. The new and future hydropower development is shifting towards Asia region, which holds the highest capacity of undeveloped hydropower potential worldwide, and is also the largest contributor of the sediment intake to the ocean through its river systems. At present the various academic and research institutions are making advancements in R&D of hydraulic turbines against sediment erosion. This article highlights some major achievements made by Kathmandu University and its consortium partner intuitions in the advancement of the turbine technology for the future market