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Nazaruddin Sinaga
Efficiency and Energy Conservation Laboratory
Diponegoro University
International Workshop on Energy Audits
Diponegoro University,
Semarang, August 2 –3, 2010
Pumps and Pumping System
2.1 Introduction
2.2 Type of pumps
2.3 Assessment of pumps
2.4 Energy efficiency opportunities
Introduction
•20% of world’s electrical energy demand
•25-50% of energy usage in some
industries
•Used for
•Domestic, commercial, industrial and
agricultural services
•Municipal water and wastewater
services
Objective of Pumping System
•Transfer liquid from source to
destination
•Circulate liquid around a system
•Main pump components
•Pumps
•Prime movers: electric motors, diesel engines,
air system
•Piping to carry fluid
•Valves to control flow in system
•Other fittings, control, instrumentation
•End-use equipment
•Heat exchangers, tanks, hydraulic machines
What Are Pumping Systems
Pumping Head
•Head
•Resistance of the system
•Two types: static and friction
•Static head
•Difference in height between
source and destination
•Independent of flow
destination
source
Static
head
Static
head
Flow
9
•Static head consists of
•Static suction head (hS): lifting liquid relative to
pump center line
•Static discharge head (hD) vertical distance
between centerline and liquid surface in
destination tank
•Static head at certain pressure
Pumping System Characteristics
Head (in feet) = Pressure (psi) X 2.31
Specific gravity
10
•Resistance to flow in pipe and
fittings
•Depends on size, pipes, pipe
fittings, flow rate, nature of liquid
•Proportional to square of flow rate
•Closed loop system
only has friction head
(no static head)
Friction
head
Flow
Friction Head
11
In most cases:
Total head = Static head + friction head
System
head
Flow
Static head
Friction
head
System
curve
System head
Flow
Static head
Friction
head
System
curve
•Relationship between
head and flow
•Flow increase
•System resistance increases
•Head increases
•Flow decreases to zero
•Zero flow rate: risk of
pump burnout
Pump Performance Curve
Head
Flow
Performance curve for
centrifugal pump
Pump Operating Point
•Duty point: rate of
flow at certain head
•Pump operating
point: intersection
of pump curve and
system curve
Flow
Head
Static
head
Pump performance
curve
System
curve
Pump
operating
point
•Cavitation or vaporization: bubbles inside pump
•If vapor bubbles collapse
•Erosion of vane surfaces
•Increased noise and vibration
•Choking of impeller passages
•Net Positive Suction Head
•NPSH Available: how much pump suction
exceeds liquid vapor pressure
•NPSH Required: pump suction needed to avoid
cavitation
Pump Suction Performance (NPSH)
Type of Pumps
Classified by operating principle
Pump Classification
Dynamic Positive
Displacement
Centrifugal Special effect Rotary Reciprocating
Internal
gear External
gear Lobe Slide
vane
Others (e.g.
Impulse, Buoyancy)
Pumps
Dynamic Positive
Displacement
Centrifugal Special effect Rotary Reciprocating
Internal
gear External
gear Lobe Slide
vane
Others (e.g.
Impulse, Buoyancy)
Pumps
Positive Displacement Pumps
•For each pump revolution
•Fixed amount of liquid taken from one end
•Positively discharged at other end
•If pipe blocked
•Pressure rises
•Can damage pump
•Used for pumping fluids other than
water
Positive Displacement Pumps
•Reciprocating pump
•Displacement by reciprocation of piston plunger
•Used only for viscous fluids and oil wells
•Rotary pump
•Displacement by rotary action of gear, cam or
vanes
•Several sub-types
•Used for special services in industry
Dynamic Pumps
•Mode of operation
•Rotating impeller converts kinetic energy into
pressure or velocity to pump the fluid
•Two types
•Centrifugal pumps: pumping water in industry –
75% of pumps installed
•Special effect pumps: specialized conditions
Centrifugal Pumps
How do they work?
•Liquid forced into impeller
•Vanes pass kinetic energy
to liquid: liquid rotates
and leaves impeller
•Volute casing converts
kinetic energy into
pressure energy
20
CENTRIFUGAL PUMP
Centrifugal Pumps
Rotating and stationary components
23
Centrifugal Pumps
Impeller
•Main rotating part that provides centrifugal
acceleration to the fluid
•Number of impellers = number of pump stages
•Impeller classification: direction of flow, suction type
and shape/mechanical construction
Shaft
•Transfers torque from motor to impeller during pump
start up and operation
Centrifugal Pumps
Casings
•Functions
•Enclose impeller as “pressure vessel”
•Support and bearing for shaft and impeller
•Volute case
•Impellers inside casings
•Balances hydraulic pressure on pump shaft
•Circular casing
•Vanes surrounds impeller
•Used for multi-stage pumps
25
PUMP CALCULATIONS
Hydrolic power, Phx 100
Pump Efficiency = --------------------------------------
Power input to the pump shaft
Where,
Hydraulic power Ph(kW) = Q(m3/s) x Total head,(hd-
hs)(m) x p(kg/m3)xg(m/s2)/1000
Q=Volume flow rate, p=density of the fluid,
g=acceleration due to gravity
hd= Delivery head, hs = Suctionhead
26
POWER CALCULATIONS
Assume that we need to pump 68 m3/hr to a 47
meter head with a pump that is 60% efficient at
that point, motor efficiency 90%.
Calculate motor power.
Liquid Power = 68 * 47 *1000*9.81/ 3600*1000
= 8.7 kW
Shaft Power = 8.7 / 0.60 = 14.5 kW
Motor Power = 14.5 / 0.9 = 16.1 kW
27
Pump Efficiency Example
Illustration of calculation method outlined
A chemical plant operates a cooling water pump for process cooling and refrigeration
applications. During the performance testing the following operating parameters were
measured;
Measured Data
Pump flow, Q 0.40 m3/ s
Power absorbed, P 325 kW
Suction head (Tower basin level), h1 +1 M
Delivery head, h2 55 M
Height of cooling tower 5 M
Motor efficiency 88 %
Type of drive Direct coupled
Density of water 996 kg/ m3
28
Pump Efficiency Example
Flow delivered by the pump : 0.40 m3/s
Total head, h2 -(+h1) : 54 M
Hydraulic power : 0.40 x 54 x 996 x 9.81/1000 = 211 kW
Actual power consumption : 325 kW
Overall system efficiency : (211 x 100) / 325 = 65 %
Pump efficiency : 65/0.88 = 74 %
Assessment of Pumps
•Pump shaft power (Ps) is actual horsepower
delivered to the pump shaft
•Pump output/Hydraulic/Water horsepower (Hp) is
the liquid horsepower delivered by the pump
How to Calculate Pump Performance
Hydraulic power (Hp):
Hp = Q (m3/s) x Total head, hd - hs (m) x ρ (kg/m3) x g (m/s2) / 1000
Pump shaft power (Ps):
Ps = Hydraulic power Hp / pump efficiency ηPump
Pump Efficiency (ηPump):
ηPump = Hydraulic Power / Pump Shaft Power
hd - discharge head hs –suction head,
ρ - density of the fluid g –acceleration due to gravity
•Absence of pump specification data to
assess pump performance
•Difficulties in flow measurement and
flows are often estimated
•Improper calibration of pressure gauges &
measuring instruments
•Calibration not always carried out
•Correction factors used
Difficulties in Pump Assessment
Energy Efficiency Opportunities
1. Selecting the right pump
2. Controlling the flow rate by speed
variation
3. Pumps in parallel to meet varying
demand
4. Eliminating flow control valve
5. Eliminating by-pass control
6. Start/stop control of pump
7. Impeller trimming
1. Selecting the Right Pump
Pump performance curve for centrifugal
pump
33
TYPICAL PUMP CHARACTERISTIC CURVES
•Oversized pump
•Requires flow control (throttle valve or by-pass
line)
•Provides additional head
•System curve shifts to left
•Pump efficiency is reduced
•Solutions if pump already purchased
•VSDs or two-speed drives
•Lower RPM
•Smaller or trimmed impeller
2. Controlling Flow: speed
variation
Explaining the effect of speed
•Affinity laws: relation speed N and
•Flow rate Q N
•Head H N2
•Power P N3
•Small speed reduction (e.g. ½) = large
power reduction (e.g. 1/8)
36
Variable Speed Drives (VSD)
•Speed adjustment over continuous
range
•Power consumption also reduced!
•Two types
•Mechanical: hydraulic clutches, fluid couplings,
adjustable belts and pulleys
•Electrical: eddy current clutches, wound-rotor
motor controllers, Variable Frequency Drives
(VFDs)
2. Controlling Flow: speed variation
37
Benefits of VSDs
•Energy savings (not just reduced flow!)
•Improved process control
•Improved system reliability
•Reduced capital and maintenance
costs
•Soft starter capability
2. Controlling Flow: speed variation
38
3. Parallel Pumps for Varying Demand
•Multiple pumps: some turned off during low
demand
•Used when static head is > 50% of total head
•System curve
does not change
•Flow rate lower
than sum of
individual
flow rates
(BPMA)
39
PUMPS IN PARALLEL OPERATION
40
CENTRIFUGAL PUMPS IN PARALLEL
•The total head for the combination is the
same as the total head for each pump
hT= h1= h2
•The flowrate or capacity is the sum of the two
pumps
QT= Q1+ Q2
4. Eliminating By-pass Control
•Pump discharge divided into two flows
•One pipeline delivers fluid to destination
•Second pipeline returns fluid to the source
•Energy wastage because part of fluid
pumped around for no reason
42
EFFECT OF THROTTLING
Head
Meters
Pump Efficiency 77%
82%
Pump Curve at
Const. Speed
Partially
closed valve
Full open valve
System Curves
Flow (m3/hr)
Operating Points
A
B
500 m3/hr300 m3/hr
50 m
70 m
Static
Head
C
42 m
43
5. Eliminating By-pass Control
•Pump discharge divided into two
flows
•One pipeline delivers fluid to destination
•Second pipeline returns fluid to the source
•Energy wastage because part of fluid
pumped around for no reason
6. Start/Stop Control of Pump
•Stop the pump when not needed
•Example:
•Filling of storage tank
•Controllers in tank to start/stop
•Suitable if not done too frequently
•Method to lower the maximum demand
(pumping at non-peak hours)
7. Impeller Trimming
•Changing diameter: change in velocity
•Considerations
•Cannot be used with varying flows
•No trimming >25% of impeller size
•Impeller trimming same on all sides
•Changing impeller is better option but more
expensive and not always possible
46
THE AFFINITY LAW FOR A CENTRIFUGAL PUMP
Flow:
Q1 / Q2 = N1 / N2
Example:
100 / Q2 = 1750/3500
Q2 = 200 m3/hr
Head:
H1/H2 = (N12) / (N22)
Example:
100 /H2 = 1750 2/ 3500 2
H2 = 400 m
Power :
P1 / P2 = (N13) / (N23)
Example:
5/P2 = 17503/ 35003
P2 = 40
7. Impeller Trimming
Impeller trimming and centrifugal pump performance
Comparing Energy Efficiency
Options
Parameter Change
control valve Trim impeller VFD
Impeller diameter 430 mm 375 mm 430 mm
Pump head 71.7 m 42 m 34.5 m
Pump efficiency 75.1% 72.1% 77%
Rate of flow 80 m3/hr 80 m3/hr 80 m3/hr
Power consumed 23.1 kW 14 kW 11.6 kW
THANK YOU
for your attention