STEENBRAS WATER TREATMENT PLANT

MICRO HYDROELECTRIC TURBINE INVESTIGATION

Garth Aspeling, Mechatronic Engineer and Mlamli Mabulu, Chief

Mechanical Engineer , Water and Sanitation Department, Utilities

Services Directorate, City of Cape Town, South Africa

MICRO HYDROELECTRIC INVESTIGATION

STEENBRAS WATER TREATMENT PLANT

CONTENTS

• Project Purpose

• Treatment Plant Overview

• Measurement Investigation

• Design and Calculations

• Proposed Solution

• Conclusion

PROJECT PURPOSE

• Investigate the 70 year old turbine installation

• Evaluate existing turbine performance

• Reduce maintenance costs

• Evaluate new design options

• Optimise any underutilised flow

TREATMENT PLANT OVERVIEW

Design Treatment Capacity 150 ML/day

Average Treatment Rate 92 ML/day

Built in 1946

Raw Water Supply Steenbras Lower Dam

Dam Capacity 33 500 Mega Litres

Tunnel Length 752 m through the HH Mountains

Western Cape Clean Water Contribution: ±10%

GORDONS BAY STEENBRAS LOWER DAM

STEENBRAS WTP

INLET TOWER SCREEN CHAMBER

ROCKVIEW DAM

STEENBRAS UPPER DAM

DISTRIBUTION

TREATMENT FLOW DIAGRAM

STEENBRAS TREATMENT PLANT

ELECTRICAL SUPPLY LAYOUT

• No Eskom backup supply

Total Installed Capacity 340 kW

Turbine no. 1 160 kW

Turbine no.2 180 kW

Installation Date 1948

Manufacturer Gilkes

Size and Type 2 x 21” Turgo Impulse

Jet Arrangement Single Jet

Turbine Arrangement Tandem Runners

Normal Speed 428 rpm

Net Head 34.44 m

Flow Rate at full load 0.66 m3 /s (57 Ml/d)

Weight of Runner 285 kg

EXISTING TURBINE SPECIFICATIONS

EXISTING TURBINE LAYOUT

Spear Valve

Spear Valve

Hydraulic Governor

In-Flow

Turgo Runner

Generator

Fly Wheel

Deflector Plate Control

35m

TOP CHAMBER

TURBINE HALL

ELEVATION LEVELS

• 185 m pipe length

• 500 mm Ø pipe

10 YEAR HISTORICAL FLOW DATA

Ml/d m3/s

Max 122.5 1.42

Avg 91.7 1.06

Min 16.4 0.19

CALCULATIONS

Plant Usage Efficiency :

Variables:

Plant efficiency (%)

Q Flow rate in (m3/sec)

P Power (kW)

H Net pressure head (m)

Constants:

= 1000 kg/m3 Density of water (@ 15 ᵒC)

g = 9.81 m/s2 Gravitational acceleration

MEASUREMENTS – TURBINE 2 4 April 2013 – 12:00

Readings Taken Instantaneous SI Units

Net pressure reading 304 kPa 30.4 m

Total Flow Rate 81.9 Ml/d 0.948 m3 s

Turbine Flow Rate 54 Ml/d 0.625m3 s

Power Factor - 0.69 69 %

Power reading 83.8 kW 83.8 kW

Frequency 50,2 Hz 50.2 Hz

Variables

H 30.4 m

P 83.8 kW

Q 0.625 m3 s

𝟖𝟑.𝟖𝒌𝑾

𝟗𝟗𝟗𝒌𝒈

𝒎𝟑𝟗.𝟖𝟏𝒎

𝟐𝒔 𝟑𝟎.𝟒𝒎

𝟎.𝟔𝟐𝟓𝒎𝟑

𝒔 𝑿𝟏𝟎𝟎

= 45 % Plant utilisation of energy

MEASUREMENT RESULTS

• Plant usage efficiency during testing:

• System electrical usage during testing:

• Old inefficient mechanical governors

• Power factor correction needed

45 %

46.8 % average

DESIGN PROPOSAL

Option 1 Replace turbines

Option2 Replace mechanical governors

EVALUATE NEW SYSTEM

𝑷𝒓𝒂𝒕𝒆𝒅 = 𝜼𝝆𝒈𝑯𝑸

Hrated = Hmax − Hmin 0.3 + Mmin

Qrated = Choose Design Capacity Factor @ 80 %

ρ = 999 kg/m3

𝛈rated = Choose

g = 9.81 m/s2

DESIGN CAPACITY FACTOR

Q80% = 0.650m3 s

CALCULATIONS

Q80% = 0.65m3 s

Hr = 31.2 m

For a new modern turbine the hydraulic efficiency can be between 85%

and 95%

Therefore choose : ηℎ𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 = 90%

Calculate hydraulic power: 𝐏r = 𝛈𝛒𝐠𝐇𝐐

Pr = 0.90 1000 9.81 31.2 0.65

= 𝟏𝟕𝟗 𝐤𝐖

TURBINE TYPES

31.2 m

0.65

FRANCIS vs TURGO TURBINE

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Turb

ine

Re

lati

ve E

ffic

en

cy

Percent of Full Flow

Efficiency Comparison

Single Jet Turgo Turbine

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Turb

ine

Re

lati

ve E

ffic

en

cy

Percent of Full Flow

Efficiency Comparison

Francis Turbine

Rated Flow = 0.65 m3/s Rated Head = 31.2 m

Min. Head = 30 m Max. Head = 35 m

Rated Power = 180 kW Load Factor > 20 %

Peak Mechanical Efficiency = 90 %

Turbine Design Parameters

RATED POWER GENERATION

26

27

28

29

30

31

32

33

34

35

36

0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68

Net

He

ad (

m)

Q (m3/s) (1 Turbine)

Pr = 180 kW

0

25

50

75

100

125

150

175

200

225

0

5

10

15

20

25

30

35

40

0 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Po

we

r (k

W)

He

ad (

m)

Assurance (%)

Head (m) Power (m)

180 kW @ 31.2m

POWER AND HEAD DURATION CURVES

EVALUATE GOVERNOR REPLACEMENT

Item Quantity Estimate Unit Price

Electric Governor Package 2 R1 million

Existing mechanical governor

DISCUSSION

Option 1: Replace Complete Turbines

Budget Cost R14 million

Lifespan + 25 years

Option 2: Replace Governors

Budget Cost R2 million

Lifespan ± 10 years

• Therefore preferred short term option

is to replace governors

• Governor can then be reused

CONCLUSION

• Replace the mechanical governors

• Replace old pumps, motors and lighting with energy efficiency

equipment for a 10 % reduction in energy consumption

• Installation of energy efficient devices in residential houses for

a 30% reduction in energy consumption

• Solar water geysers / Heat pump water heaters

• More efficient house-hold heating methods

• Utilise excess power

QUESTIONS

?

This presentation was made possible by the Water and Sanitation section, CoCT.

Thanks for everyone's input and help and a special thanks to Bulk Water.

END