innovative approach to minimize silt erosion in hydro...

Innovative Approach to Innovative Approach to minimize silt erosion in minimize silt erosion in

hydro turbines

By:M k h M lMukesh Mangla

AGM, BHEL BhopalCentre of Excellence – Hydro Turbines

INTRODUCTION

B k d f ilt i th t• Background of silt erosion threat.• Approach to tackle silt erosion problem.• CFD analysis & model testing facility at BHEL.• Silt friendly design through CFD analysis.• Conclusion and scope of further work.

Centre of Excellence – Hydro Machines, BHEL Bhopal

BACKGROUND OF SILT EROSION THREAT

Bh t H El t i l Li it d (BHEL) li d H d t t f • Bharat Heavy Electricals Limited (BHEL) supplied Hydro sets account for 26800 MW (nearly 60%) of the total installed capacity of 44602 MW in the country. y

• In India 80% of available Hydro resources are from Himalayan region.• Silt erosion of hydro turbines is of immense concern.Silt erosion of hydro turbines is of immense concern.• Problem is severe in the Himalayan region because of high silt (>10000

ppm during monsoons) and high quartz content.• Silt erosion causes loss in terms of efficiency & power generation,

enhancement of cavitation damage, vibrations, equipment damage and hi d timachine down time.


SILT EROSION (TYPICAL)

Eroded Guide Vanes of Nathpa Eroded Runner of Dehar HEP Damaged Spear of BhabhaJhakri HEP Eroded Runner of Dehar HEP Hydro Power Station

Damaged Pelton Runner at Malana HEP Damaged Francis Runner Damaged Spear at Malana HEP


MECHANISM OF SILT EROSION:

C ki b ki d di l d i f t t l d t th i t f ilt • Cracking, breaking and dislodging of parent metal due to the impact of silt particles.

• Shearing-off of the metal by hard & sharp silt particles.g y p p• Ductile metals more prone to shearing-off phenomenon.• Damage on the inlet edge of runner, GV is mostly due to impact of silt g g , y p

particles.• Trailing edge of profiled components (like runner, GV) and liner plates,

seals etc are mostly affected by the shearing off seals etc. are mostly affected by the shearing-off.


APPROACH

Fi d h t d l ith Silt P bl Five pronged approach to deal with Silt Problem –• Provision of de-silting chamber to eliminate large size silt particles. • Selection of machine with a lower specific speed, resulting in

comparatively lower velocities & reduced erosion.Design of runner profile to make it silt friendly using advanced CFD • Design of runner profile to make it silt friendly using advanced CFD simulation

• Model testing to ensure almost same efficiency as without Model testing to ensure almost same efficiency as without consideration of silt.

• Application of HVOF coating over the silt prone zones of the profile.pp g p p


PROVISION OF DE-SILTING CHAMBER:

E i t i t l d d t th i f ilt ti l• Erosion rate is a strongly dependent on the size of silt particles.• Large size of silt particles increases the metal removal rate as well as the

area affected therefore restriction is desirablearea affected - therefore restriction is desirable.• Desilting chamber works on the principle of reduction of water velocity and

allows the silt to precipitate or by sharp turning of passage whereby the allows the silt to precipitate or by sharp turning of passage whereby the heavier silt particles get trapped.

• In Himalayan rivers, it is recommended to remove all particles above 75 microns size, from the water before entry to the turbine.


SELECTION OF LOWER SPECIFIC SPEED MACHINE:

E i d d d t l th h d / ifi d f th • Erosion damage depends strongly on the head /specific speed of the machine.

• High and medium head Francis machines have maximum erosion damage g gat exit of guide vanes and inlet of runner blades.

• In low head Francis turbines maximum erosion damage occurs on the runner blades towards the outlet edge near the skirt side runner blades towards the outlet edge near the skirt side.

• For a given hydraulic data, machine with a lower specific speed is selected because it results in lower absolute and relative velocities thereby yreduction in erosion

• For example, for a silt prone project instead of rotational speed of 214.3 rpm (Ns = 145 mkW) to have the minimal effect of silt erosion one step rpm (Ns = 145 mkW), to have the minimal effect of silt erosion, one step lower speed of 200 rpm (Ns = 135 mkW) should be chosen.


HARD COATING: • By elaborate experimental set-up to test the efficacy of coatings for hydro turbine applications, BHEL y p p y g y pp ,

has found that High-velocity-Oxy-Fuel (Tungsten carbide) spraying has been quite successful for hydro turbine components in terms of chemical bonding, chemical stability, erosion and corrosion resistance

• This coating can withstand silt particles with velocities up to 70m/sec with low angle of incidence• This coating can withstand silt particles with velocities up to 70m/sec with low angle of incidence.

Manual HVOF Coating HVOF Coating by robotic arm


CFD ANALYSIS FACILITY AT BHEL

S f h CFD A l i i ANSYS CFX 15 0 i h i• State‐of‐the‐art CFD Analysis set‐up using ANSYS CFX 15.0 with in‐house developed macros.

• High Performance Cluster (HPC) dedicated for CFD analysis• Hydraulic design & development of all types of turbines & pumps• CFD analysis forms the backbone of Hydraulic Design


NUMERICAL SIMULATION Please Click on the photo below

• Flow in the Reaction Turbines is analyzed as incompressible fluid in closed domain with multiple frames of referencewith multiple frames of reference.

• Through Simulation of flow in reaction turbine, fine tuning of the water passage is carried out to achieve required performance parameters.


MATHEMATICAL FORMULATION:

• First the hydraulic design including runner profile is carried outconventionally to satisfy the hydraulic performance criteriaTh d t il d t d f th ff t f ilt i t i• Then a detailed study of the effect of silt on various components istaken up using CFD tool with petrographic analysis of silt.

• “Finnie’s Model of Erosive Wear” described in next slide is applied, withi d fi d 2 1 d f i i ln is defined as 2.1 and wear function to impact angle as :


MATHEMATICAL FORMULATION:


REASON FOR EROSION:

Silt Particles striking blade at an angle with high velocity is the root cause for erosion.


REASON FOR EROSION:

Comparison between Conventional and Final (Modified) Runner blade profiles Flow vectors almost parallel to blade.


ITERATIVE DESIGN FOR SILT FRIENDLY PROFILE:• Adjustment of blade angle near outlet edge to match flow angle there by j g g g y

reducing erosion.• To compensate the effect on efficiency blade angle at inlet and mid-span is

suitably modified as the velocities are lower compared to outlet edgesuitably modified, as the velocities are lower compared to outlet edge.• To modify the blade angles expertise in CFD and in-depth knowledge of fluid

mechanics is must.

Conventional runner Modified final runner


ITERATIVE DESIGN FOR SILT FRIENDLY PROFILE:• Particle Size

65% particle size below 0.075 mm25% particle size in range of 0.075 mm to 0.15 mm.7% particle size in range of 0 15 mm to 0 20 mm

Conventional runner

7% particle size in range of 0.15 mm to 0.20 mm.3% particle size in range of 0.20 mm to 0.25 mm.

• Silt particle concentration = 2000 PPMP ti l h f t 1 5• Particle shape factor = 1.5

• Hardness of silt particles < 7 moh• Density of silt particles = 2600 kg/m3y p g• Erosion Model : Finnie

Modified final runner


MODEL TESTING

• Numerical simulation alone does not have much acceptance unless until itis backed by experimental results. COE-HM, BHEL, Bhopal is equipped bya sophisticated Test set-up where experiments on a small scale model arep p pconducted to evaluate the various performance parameters of hydraulicturbine. The test bed is accredited by National Accreditation Board forLaboratories as per International standard ISO/IEC17025:2005Laboratories as per International standard ISO/IEC17025:2005.

• All the designs fine-tuned by Numerical simulation are validated byf t i l d d l d if i th i t bmanufacturing a scaled model and verifying the improvements by

experimental model testing.


MODEL TESTING

Major Parameters of Existing Laboratory Major Parameters of New LaboratoryMajor Parameters of Existing LaboratoryMax Head : 100mMax Discharge: 1.8 m3

Dynamometer : 360 KW

Major Parameters of New LaboratoryMax Head : 140mMax Discharge: 1.8 m3

Dynamometer : 360 KWSCADA & segregated data acquisition system Integrated SCADA and data acquisition system


MODEL TESTING

Hill chart of conventional runner Hill chart of final modified runnerHill chart of final modified runner

• CFD analysis predicted efficiency drop of 0.24 % where as by modeltesting it was measured as 0.3 %.testing it was measured as 0.3 %.


CONCLUSION

• BHEL has successfully developed techniques which can be used toreduce the ill-effects of silt by hydraulic redesigning of Francis turbiney y g grunner blades without losing much in efficiency.

• Experimental turbine model testing with silt injected water is not feasiblehowever by model test exact effect on efficiency is capturedhowever by model test exact effect on efficiency is captured.

• Numerical analysis provides a very detailed understanding of thephenomenon of silt erosion and excellent qualitative assessment ofd th th ti l d l d t di t h i l l fdamage, the mathematical model does not predict physical values oferosion. To accurately predict physical quantity of metal removal, themathematical model needs to be closely calibrated with actual erosionydata from site .


innovative approach to minimize silt erosion in hydro...

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