3. arthur williams - the performance of centrifugal pumps as turbines and influence of pump geometry
DESCRIPTION
3. Arthur Williams - The Performance of Centrifugal Pumps as Turbines and Influence of Pump GeometryTRANSCRIPT
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