3. Arthur Williams - The Performance of Centrifugal Pumps as Turbines and Influence of Pump Geometry

The Performance of Centrifugal

Pumps as Turbines

and Influence of Pump Geometry

Arthur Williams – University of Nottingham(School of Electrical & Electronic Engineering)

Arnaldo Rodrigues – Flowserve Pumps, Newark, UK

Photo: Energy for Sustainable Development

Photo: Border Green Energy Thailand

Pump as Turbine (PaT) range

For Medium head Micro hydro, use either:

Crossflow

or

Pump as Turbine

For Pico size (< 5 kW)

e.g. 22 m head, 22 l/s : –

a pump is much more compact than a crossflow turbine, which needs either belt-drive or 8-pole generator

Typical pump and PaT curves

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40 50 60

Flow (litre/s)

Head

(m

)

0

1000

2000

3000

4000

5000

6000

7000

Tu

rbin

e p

ow

er

(W)

Pump best efficiency: 72%

End-suction centrifugal pump with 4-pole motor

PaT Head

PaT Power

Typical pump and PaT curves

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60

Flow (l/s)

Head (

m)

0

10

20

30

40

50

60

70

80

Eff

icie

ncy (

%)

Pump best efficiency: 72%

PaT best efficiency: 72%

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

10 100 1000

Pump Specific Speed (Nq - metric units - logarithmic scale)

PA

T:P

um

p e

ffic

ien

cy r

atio

>2% lower efficiency

+/- 2% efficiency

>2% higher efficiency

Double suction pumps

Cylindrical volute pump

+/- 5%

PaT efficiencies can be as good as pump mode – but not always

Examples of PaT applications

Kinko, Tanzania (10 kW) ->

^ Thima, Kenya (2.2 kW) ->

Sahyadri Energy Systems

Photo

s: Pico

Energ

y L

td.

Rural Electrification:

Examples of PAT applications

^ PATs for water pumping:

Cave system in Java, Indonesia

(45 kW each set) Diagram adapted from KSB Pumps

PAT GearboxMulti-stage

Pump

To drinking water tank

Water In

Zones for PAT loss study (CFD)

Zone i

Zone ii

Zone iii

Zone iv

Zone vZone vi

Zonevii

Plane v-viPlane vi-vii

Zone vi

Pump Centreline

Volute

Draft Tube

Impeller

“Churning region”

Measure-ment plane for suction head

CFD was checked against tests

Simplification of pump geometry changes CFD predictions

V-shaped interface

- OK for pump mode

- not acceptable for turbine modelling

Full model No leakage

No churning volume

PAT with constricted impeller eye

CFD streamlines: Turbine mode

Modification to impeller

= material removed

Enlarging suction eye –reduces head

0

4

8

12

16

20

24

0.04 0.08 0.12 Q/ND3

gH

/N2D

2

0

10

20

30

40

50

60

70

80

Eff

icie

nc

y (

%)

Non-Modified Modified-Eye

gH/N2D

2

hhyd curves

No

lo

ad

lin

e

En

d o

f p

art

loa

d r

eg

ion

Ov

erl

oa

d r

eg

ion

be

gin

s

0.0

0.4

0.8

1.2

1.6

2.0

0.04 0.08 0.12 Q/ND3

Ph

yd/ρN

3D

5

0

10

20

30

40

50

60

70

80

Eff

icie

ncy (

%)

Phyd/ρN3D

5

hhyd curvesN

o lo

ad

lin

e

En

d o

f p

art

Ov

erl

oa

d r

eg

ion

Non-Modified Modified-Eye

Enlarging suction eye – reduces head, but not power

0

1

2

3

4

8 12 16 20 24 28 32

Discharge (l/s)

Lo

ss

(m

)

No

lo

ad

En

d o

f p

art

lo

ad

Ov

erl

oa

d r

eg

ion

BE

P

Double suction pump with ribs to prevent pre-swirl

End suction pump with Cylindrical Volute

Examples of pumps NOT suitable for turbine application

PaT selection

Estimating PaT match for Thima site

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40 45

Flow (l/s)

He

ad

(m

)

0

10

20

30

40

50

60

70

80

Eff

icie

nc

y (

%)

Pump head

Net site head

Estimated Turbine

Pump eff (%)

Predicted operating point

Correcting PaT match at Thima

A reduction in impeller diameter improved PaT efficiency at this site

0

5

10

15

20

25

30

35

40

15 20 25 30 35

Flow (l/s)

He

ad

(m

)

0

10

20

30

40

50

60

70

80

Eff

icie

nc

y (

%)

Full size impeller

Cut down impeller

Conclusions

Pumps as Turbines (PaTs):

• Are suitable for medium-head micro & pico hydro

• Have acceptable efficiency for fixed flow operation

• May need modification to improve efficiency

Computational Fluid Dynamics (CFD):

• Gives useful insight into hydraulic losses

• Needs to use appropriate geometrical models

• Indicates some pump geometries not suitable for micro-hydro

Acknowledgements

…where most of the research was done

…where much of testing was done

(Prof Franz Nestmann & Dr Punit Singh)

… funded most of Arnaldo’s PhD

… funded research exchange with Karlsruhe

… funded my travel to Hidroenergia 2008