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

CONTENTS

• Project Purpose

• Treatment Plant Overview

• Data Capturing and Analysis

• Design Analysis

• Conclusion and Recommendation

PROJECT PURPOSE

• Investigate the 70 year old turbine installation

• Evaluate existing turbine performance

• Identify maintenance costs

• Evaluate new design options

• Optimise any underutilised flow

TREATMENT PLANT OVERVIEW

Design Treatment Capacity 150 ML/day

Average Treatment Rate 90 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

ELECTRICAL SUPPLY LAYOUT

• No Eskom backup supply

Total Installed Capacity 320 kW

Turbine no. 1 160 kW

Turbine no. 2 160 kW

Installation Date 1948

Manufacturer Gilkes (London)

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 (safety guard)

Deflector Plate Control

HISTORICAL FLOW DATA - 8 YEARS

0

20

40

60

80

100

120

140

160

28-Sep-04 28-Sep-05 28-Sep-06 28-Sep-07 28-Sep-08 28-Sep-09 28-Sep-10 28-Sep-11

Flo

w R

ate

(M

l/d

)

Year

Ml/d m3/s

Max 148.4 1.72

Avg 90.2 1.04

MEASUREMENTS – TURBINE 2

Readings Taken Data

Net pressure reading 3.11 bar

Total Flow Rate 81.9 Ml/d

Turbine Flow Rate 54 Ml/d

Power Factor - 0.69

Power Reading 89 kW

Frequency 50,2 Hz

Variables

H 31.1 m

P 89 kW

Q 0.625

= 47 % Plant utilisation of energy

DESIGN ANALYSIS

=

= Select Design Capacity Factor @ 95 %

ρ = 1000 kg/m3 g = 9.81 m/s2

Prated = Determine

Case 1 Plant Layout Analysis

Case 2 Refurbishment of Equipment Controls

DESIGN CAPACITY FACTOR

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 10 20 30 40 50 60 70 80 90 100

Flo

w r

ate

(m

^3/s

)

Exceedance Probability (%)

Hstat

TRANSFER CHAMBER

POWER HOUSE

HYDROPOWER CHARACTERSITICS

• Penstock length = 185 m

• Penstock Ø = 800 mm

• Hstat = 36.58 m

• Turbine Power out = 160kW

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

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

Rated Power = 160 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

0.500 0.550 0.600 0.650 0.700

Net

He

ad (

m)

Q (m3/s)

RATED POWER GENERATION

Pr = 160 kW

POWER AND HEAD DURATION CURVES

0

25

50

75

100

125

150

175

200

225

0

5

10

15

20

25

30

35

40

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%

Po

we

r (k

W)

He

ad (

m)

Assurance

Head (m) Actual Power (kW)

160 kW @ 31.2m

TURBINE SELECTION

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

REFURBISHMENT OF CONTROL EQUIPMENT

Item Quantity Estimate Total Price

Electric Governor Package 2 R2 million

Step-up Gearbox and Generator 1 R800 000

Existing mechanical governor Step-up gearbox

CONCLUSION AND RECOMMENDATION

Case 1: Plant Analysis

Original plant turbines still match the existing water treatment plant flow supply and operating pressures.

Power station is under utilised (an excess power of ± 30 % is not utilised)

More hydropower site locations have been explored and this power can be utilised elsewhere in the plant

Provision (e.g. workshop) to utilise full rated power in the plant will be useful

Case 2: Refurbishment of Control Equipment

Step-up Gear Box

Governor Control can be refurbished to modern designs.

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 the Bulk Water Department.