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
Pump as Turbine (PaT) range
For Medium head Micro hydro, use either: Crossflow or
Pump as Turbine Photo: Energy for Sustainable Development
For Pico size (< 5 kW) e.g. 22 m head, 22 l/s : â&#x20AC;&#x201C;
Photo: Border Green Energy Thailand
a pump is much more compact than a crossflow turbine, which needs either belt-drive or 8-pole generator
Typical pump and PaT curves 18
7000
16
6000
PaT Head
12
Head (m)
5000
10
4000
Pump best efficiency: 72%
8
3000
PaT Power
6 2000 4 1000
2 0
0 0
10
20
30
40
50
Flow (litre/s)
End-suction centrifugal pump with 4-pole motor
60
Turbine power (W)
14
16
80
14
70
12
60
10
50
PaT best efficiency: 72%
8
40
Pump best efficiency: 72%
6
30
4
20
2
10
0
0 0
10
20
30 Flow (l/s)
40
50
60
Efficiency (%)
Head (m)
Typical pump and PaT curves
PaT efficiencies can be as good as pump mode â&#x20AC;&#x201C; but not always 1.15 1.1
PAT:Pump efficiency ratio
1.05
+/- 5%
1 0.95
>2% lower efficiency +/- 2% efficiency
0.9
>2% higher efficiency 0.85 Double suction pumps 0.8
Cylindrical volute pump
0.75 10
100 Pump Specific Speed (Nq - metric units - logarithmic scale)
1000
Examples of PaT applications Rural Electrification:
Kinko, Tanzania (10 kW) ->
Sahyadri Energy Systems
Photos: Pico Energy Ltd.
^ Thima, Kenya (2.2 kW) ->
Examples of PAT applications
Water In To drinking water tank
PAT
Multi-stage Pump
Gearbox
^ PATs for water pumping: Cave system in Java, Indonesia (45 kW each set)
Diagram adapted from KSB Pumps
Zones for PAT loss study (CFD)
Plane vi-vii
Plane v-vi
Zone vi
Measurement plane for suction head
Pump Centreline Zone vi
Zone v
Impeller
Zone vii
Draft Tube
Zone iv
Zone iii Zone ii
“Churning region”
Zone i
Volute
CFD was checked against tests
Full model
No leakage Simplification of pump geometry changes CFD predictions
No churning volume
V-shaped interface - OK for pump mode - not acceptable for turbine modelling
PAT with constricted impeller eye
CFD streamlines: Turbine mode
Modification to impeller = material removed
Enlarging suction eye â&#x20AC;&#x201C; reduces head
24
80
4 0 0.04
End of part load region
8
0.08 Non-Modified
2
gH/N D
2
60 50 40 30 20 10 0
0.12 Modified-Eye
Q/ND3
Efficiency (%)
12
Overload region begins
16
No load line
gH/N2D2
70
hhyd curves
20
Enlarging suction eye – reduces head, but not power
2.0
80
3
Phyd/ρN D
0.0 0.04
No load line
0.4
End of part
0.8
0.08 Non-Modified
Overload region
1.2
0.12 Modified-Eye
5
60 50 40 30 20 10 0
Q/ND3
Efficiency (%)
hhyd curves
1.6
Phyd/ρN3D5
70
Loss (m) 3
2
8 12 16 20 24
Discharge (l/s)
Overload region
BEP
End of part load
No load
4
1
0 28 32
PaT selection
Double suction pump with ribs to prevent pre-swirl
End suction pump with Cylindrical Volute
Examples of pumps NOT suitable for turbine application
Estimating PaT match for Thima site
25
80 70
20
50
15
Predicted operating point
40
10
30
5
Pump head Net site head
20
Estimated Turbine Pump eff (%)
10
0
0 0
5
10
15
20
25 Flow (l/s)
30
35
40
45
Efficiency (%)
Head (m)
60
Correcting PaT match at Thima 40
80 70
Cut down impeller
30
60
25
50
Full size impeller
20
40
15
30
10
20
5
10
0
0 15
20
25
30
Flow (l/s)
A reduction in impeller diameter improved PaT efficiency at this site
35
Efficiency (%)
Head (m)
35
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