EFFECT OF HYDRAULIC DESIGN OF PELTON TURBINES ON DAMAGE DUE TO SILT EROSION AND ITS REDUCTION
BHEL Bhopal, INDIA AUTHOR: V.K.PANDE Executive Director (TBG)
BHARAT HEAVY ELECTRICALS LTD.,BHOPAL
INTRODUCTION: 他 BHEL is the major power equipment manufacturer in India responsible for establishing nearly two third power projects. 他 In India, 80% of available Hydro resources are from Himalayan region. 他 Silt erosion of Hydro turbines is a widely acknowledged problem. 他 Problem is severe in the Himalayan region because the mountains are young and relatively fragile. BHARAT HEAVY ELECTRICALS LTD.,BHOPAL
Silt and damage • Nature of silt – Quartz rich with quartz content generally 65%-95% – PPM content high: 5000 to 20000 in monsoon – Freshly broken fine conical particles
• Damaged areas – – – – –
Guide vane and Cheek plate Runner inlet at blade skirt and crown Runner outlet on pressure side Pelton Nozzle & Spear Pelton Runner bucket
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Damage due to silt at site
Damage due to silt at site
Damage due to silt at site
3
Strategy to tackle silt erosion: The silt menace can be effectively tackled by a three pronged approach : 他 Effective desilting to prevent silt from reaching the turbine. 他 Applying coating of hard material on various components for withstanding silt. 他 Development of design where silt erosion is inherently minimized.
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Problem in Bhaba HEP • These are 3X40 MW Pelton machines in Himachal Pradesh in Himalayas. Spear and nozzle are facing severe damage due to silt. So much so that they hardly last three monsoon months. • All types of coatings viz plasma nitriding, Boronising, Ceramic coating using D-gun, HVOF, have been tried without success. BHARAT HEAVY ELECTRICALS LTD.,BHOPAL
Examples of erosion:
Eroded spear of Bhabha Hydro Power station after one monsoon.
Examples of erosion:
Eroded spear of Bhabha Hydro Power station after one monsoon.
PRESENT WORK: 他 This paper discusses the approach for combating silt erosion by analyzing the flow dynamics behind it so that it can be avoided by modifying profile of erosion prone areas of Pelton turbines. 他 A systematic attempt to numerically simulate erosion in different nozzle-spear designs and its validation with site feed-back.
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ACTION PLAN: 他 Use of recent advances in the field of numerical simulation of flow to predict performance & silt erosion. 他 Experimental model testing/Data collection from site to validate numerical simulation. 他 Evolving correlation between analytically predicted erosion severity and actual erosion at Site
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Features of Numerical Tool: ¾ Numerical tool used for analysis of flow in turbine components is CFD software CFX-TASCFLOW. ¾ Features of Tascflow CFD software 1. Full 3-Dimensional Navier- Stoke’s solution. 2. κ-ε turbulence model with standard wall functions. 3. Multiple frames of reference for simultaneously solving rotating and stationary components. 4. All calculations have been made assuming smooth walls. BHARAT HEAVY ELECTRICALS LTD.,BHOPAL
CAPABILITIES DEVELOPED IN-HOUSE: 他 Macros for evaluation of performance parameters like efficiency, speed, pressure distribution & cavitation parameters, erosion severity have been developed. 他 Validation of macros by experimental model testing at the state-of-the-art Hydro turbine Model testing Laboratory ,BHEL Bhopal and also with site feedback. 他 To simulate the effect of silt on turbine components, Lagrangian particle tracking module with facility of user defined size and concentration of silt particles is used. BHARAT HEAVY ELECTRICALS LTD.,BHOPAL
APPROACH: ¾ The rate of erosion depends on 1. The size, concentration, shape & hardness of silt particles (Petrographic & Petrofabric data) which are profile independent parameters. For a given site these can be safely assumed to be constant. 2. The velocity of the particles and angle of impact which are profile dependent parameters. 3. To compare silt erosion of different profiles a local erosion rate coefficient (ξ) is defined – Erosion rate coefficient (ξ) α (velocity)n * f (θ) Where f (θ) is a function of impact angle θ. Value of exponent ‘n’ varies with material.
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Physical validation of erosion
Actual damage on Francis runner
Predicted erosion pattern
Application of Numerical Tool: ž Salient features of grid used for numerical analysis. 1. Structured grid with hexahedral elements. 2. Grid domain includes short pen-stock, distributor, nozzle, spear. 3. Number of grid points Distributor– 500,000 nodes. Nozzle assembly (each)- 200,000 nodes 4. To facilitate comparison of results of different variants, similar grids are generated using similar philosophy. BHARAT HEAVY ELECTRICALS LTD.,BHOPAL
RESULTS : NOZZLE WITH EXTERNAL REGULATION
Computational domain for analysis
RESULTS : NOZZLE WITH EXTERNAL REGULATION
Vector plot – Flow velocities
RESULTS : NOZZLE WITH EXTERNAL REGULATION
Particle tracks
RESULTS : NOZZLE WITH EXTERNAL REGULATION
Erosion severity in nozzle
RESULTS : NOZZLE WITH EXTERNAL REGULATION
Erosion severity in Spear
RESULTS : INTERNAL NOZZLE (60-45 design)
Erosion severity in nozzle & spear
RESULTS : INTERNAL NOZZLE (60-45 design)
Particle track in nozzle & spear
RESULTS : INTERNAL NOZZLE (90-50 design)
Flow Velocity vector plot
RESULTS : INTERNAL NOZZLE (90-50 design)
Particle tracks
RESULTS : INTERNAL NOZZLE (90-50 design)
Erosion severity in nozzle & spear
RESULTS : INTERNAL NOZZLE (90-50 design)
Erosion severity in spear
Site Feed-back Project
Reg. Mech.
Material/ Coating
Site feedback
Bhabha
External 60/45
HVOF/Borinising/ Nitriding/Ceramic
Severe erosion damage reported
Malana
Internal 90/50
13/4 St. Steel
Moderate erosion damage reported
Bassi
Internal 60/45
13/4 St. Steel
Negligible damage reported
Baspa
Internal 90/50
St. Steel with Stelliting
Nominal damage reported
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Conclusion : Project
Reg Mech
Erosion Severity Coeff (Numerical)
Site feedback
Bhabha
External 60/45
0.38
Severe erosion damage reported
Malana
Internal 90/50
0.22
Moderate erosion damage reported
Bassi
Internal 60/45
0.16
Negligible damage reported
Baspa
Internal 90/50
Nominal damage reported
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Conclusion : 他 Strong dependence of nozzle design on erosion characteristics. 他 Externally regulated nozzle not conducive from erosion as well as performance point-of-view. 他 Trade-off between performance and erosion characteristics in case of internal nozzles.
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SCOPE FOR FUTURE WORK Project Regulatory Mechanism
Site feedback for damage to runner
Bhabha External 60/45 degrees Malana Internal 90/50 degrees Bassi Internal 90/50 degrees Baspa Internal 90/50 degrees
Very little erosion damage reported Moderate erosion damage reported Negligible damage reported Substantial damage reported
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THANK YOU
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