Sediment Management Experiences

- A case from Nepal

PMS Pradhan

BPC, Nepal

November 2017

Content

• Introduction & project background

• Sediment design criteria & operational

problems

• Research initiation with data collection and

analysis

• Operational strategies for improvements

• Conclusion

Introduction

JHIMRUK

KATHMANDU

Jhimruk Project

Type of Power Project : Run of River Project

Installed Capacity : 12 MW

Net Head : 205 m

Discharge : 7.05 m3/s (2.35 m3/s/unit)

Energy : 72 GWh

Catchments area : 645 sq. km

Settling basin : 2 nos 5.5x5x42m

Turbine units and type: 3 nos, Horizontal Francis

Rated unit capacity : 4 MW

Turbine speed : 1000 rpm

Commissioning : 17 August 1994

Sediment design & Operational problems

No sediment data during the design

Settling basin designed by proven technology

Design sediment criteria met

Severe sediment problems during operation

Turbine

wear

Data: Flow & Sediment Concentration

Design discharge

Data: Mineralogical studyQ

uart

z co

nte

nt

[%]

0

10

20

30

40

50

60

70

80

Wes

t S

eti

Jh

imru

k

Ra

pti

Kh

ola

Ma

di

Rev

er

Ga

nah

a

Aru

n K

hola

Mod

i-2

Mod

i -

1

Aa

dh

i K

hola

Tin

au

Ku

lek

han

i

Ch

itla

ng

Palu

ng

Bagm

ati

Ma

na

hara

Dh

ob

i

Gau

r

Rosh

i

Dh

ad

Kh

ola

Kh

imti

Kh

imti

Kh

ola

Ta

ma

kosh

i

Ph

edi

Do

lal

Gh

at

Su

nk

osh

i

Sa

pta

Kosh

i

Ka

rna

li

West Rapti Gandaki

Tin

au Bagmati Bagmati

Kathmandu

Koshi

Source: B. Thapa, PhD Thesis at NTNU, 2004

Sediment/Efficiency Measurements & Analysis

Efficiency measurements at Jhimruk Hydro power plant

60

65

70

75

80

85

90

95

1 1,5 2 2,5 3 3,5 4 4,5

Generator Power [MW]

Hyd

rau

lic E

ffic

ien

cy [

%]

11th November 2003

1st September 200370

75

80

85

90

95

100

0 50 100 150 200 250

Particle Diameter

Pe

rce

nt

fin

er

29.09.2003

15.09.2003

06.09.2003

[mm]

0

4 000

8 000

12 000

16 000

20 000

24 000

27.0

8.03

03.0

9.03

10.0

9.03

17.0

9.03

24.0

9.03

01.1

0.03

08.1

0.03

15.1

0.03

22.1

0.03

29.1

0.03

05.1

1.03

12.1

1.03

Date [dd.mm.yy]

Se

dim

en

t c

on

ce

ntr

ati

on

[P

PM

]

Maximum value :21,594 ppm

13th September

Sediment Load through

one turbine: 6,900 tons

Plant Operation Strategy

Silt Concentration (ppm) Generation (MW)

Below 1500 Full generation

Between 1500 and 3000 Reduced generations

1500 to 2000 – 3 units

2000 to 2500 – 2 units

2500 to 3000 – 1 unit

Above 3000 Complete shutdown

Energy Loss due to Sediment

S.N

.

Months PPM Level Duration of

reduced

operation or

shutdown (Hrs)

Energy Lost due

to high PPM

(MWh)

1 Ashadh

(June-July)

1500 - 3000 6.33 34.54

Above 3000 79.99 959.88

2 Shrawan

(July-Aug)

1500 - 3000 89.32 525.52

Above 3000 105.53 1266.36

3 Bhadra

(Aug-Sept)

1500 - 3000 61.14 426.11

Above 3000 124.92 1499.04

4 Aswin

(Sept-Oct)

1500 - 3000 3.45 25.67

Above 3000 34.02 408.24

Total 504.69 5145.36

Approx. Revenue loss of Rs. 28 million

Turbine Repair Cost

-

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

2064/65 2065/66 2066/67 2067/68 2068/69 2069/70 2070/71 2071/72

Turbine Parts Repair Cost (in million NRs.)

Turbine Parts Repair Cost (mil. NRs.)

Additional Settling Basin Study

Change in Maintenance Period

Month

Pla

nt E

ffic

iency

1 2 3 4 5 6 7 8 9 10 11 12

Sta

rt m

on

so

on

En

d m

on

so

on

Extra generation Maintenance

• Ceramic Spray Coating (R-Type) One runner and one set of side cover were also coated with Ceramic (R-type)

material but was not satisfactory. Guide vanes were not coated, as it tends to

bend while heating for treatment.

• GE Research and DevelopmentGE had used seven (7) type of coating on different guide vanes and

experimented one of the turbine. The results revealed that one of the coating

withstand the silt erosion.

• Spare Runner SetThree sets of turbine parts that are subject to erosion were kept as spare to

reduce the annual maintenance time. Eroded runner can be replaced within few

hours

Initiatives for reducing silt erosion for

Optimizing Generation

Conclusion

• Jhimruk River is one of the high sediment carrying rivers in Nepal containing

high percentage of hard and abrasive mineral.

• Proven sediment design criteria of 90% trapping of 0.2 mm by settling basin is

satisfactorily met. However the excessive war and tear of the turbines induced

by the sediment continued requiring research initiation to address the causes

and consequences.

• So a general knowledge of sediment is not sufficient when it comes to dealing

with sediment management and problems in run-of-river hydropower plants.

• Data collection and analysis indicated hard mineral particles finer than 0.2 mm

are responsible for erosion and damage to turbines

• Experiences over the years have shown that it was necessary to reduce the

power production or completely shut down the plant to avoid the excessive

erosion and losses due to silt (quartz)

• We welcome innovative ideas for operating the plant at full capacity during the

wet season!

28 April 200416

Thank You!