Pumps Senator .Libya

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Training Agenda: PumpsTraining Agenda: Pumps

Introduction

Type of pumps

Assessment of pumps

Energy efficiency opportunities

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IntroductionIntroduction

20% of worlds electrical energy

demand 25-50% of energy usage in some

industries

Used for Domestic, commercial, industrial and

agricultural services

Municipal water and wastewater services

What are Pumping SystemsE l e

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Objective of pumping system


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(US DOE, 2001)

Transfer liquidfrom source todestination

Circulate liquidaround a system


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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


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Head Resistance of the system

Two types: static and friction

Static head

Difference in height betweensource and destination

Independent of flow

Pumping System CharacteristicsE l e

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destination

source

Stati

chead

Statichead

Flow


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Static head consists of

Static suction head (hS): lifting liquid relative topump center line

Static discharge head (hD) vertical distancebetween centerline and liquid surface indestination tank

Static head at certain pressure


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Head (in feet) = Pressure (psi) X 2.31Specific gravity


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Friction head

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 systemonly has friction head(no static head)


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Frictionhead

Flow


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In most cases:

Total head = Static head + friction head


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Systemhead

Flow

Static head

Frictionhead

Systemcurve

Systemhead

Flow

Static head

Frictionhead

Systemcurve


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Pump performance curve

Relationship betweenhead and flow Flow increase

System resistance increases

Head increases Flow decreases to zero

Zero flow rate : risk of pump burnout


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Head

Flow

Performance curve for centrifugal pump


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Pump operating point


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Duty point: rate of flow at certainhead

Pump operatingpoint:intersection of pump curve andsystem curve

Flow

Head

Statichead

Pump performancecurve

System

curve

Pumpoperatingpoint


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Pump suction performance (NPSH) 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 suctionexceeds liquid vapor pressure

NPSH Required: pump suction needed to avoidcavitation


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Introduction

Type of pumps

Assessment of pumps


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Type of PumpsType of Pumps

Classified by operating principle

Pump ClassificationE l e

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DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internal

gear

External

gear Lobe

Slide

vane

Others (e.g.Impulse, Buoyancy)

Pumps

DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internal

gear

External

gear Lobe

Slide

vane

Others (e.g.Impulse, Buoyancy)

Pumps


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Positive Displacement PumpsE l e

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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


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Positive Displacement PumpsE l e

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Reciprocating pump

Displacement by reciprocation of pistonplunger

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


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Dynamic pumpsE l e

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Mode of operation

Rotating impeller converts kinetic energy intopressure or velocity to pump the fluid

Two types Centrifugal pumps: pumping water in

industry 75% of pumps installed

Special effect pumps: specialized conditions


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Centrifugal PumpsE l e

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How do they work?

(Sahdev M)

Liquid forced intoimpeller

Vanes pass kineticenergy to liquid: liquidrotates and leavesimpeller

Volute casing convertskinetic energy intopressure energy


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Rotating and stationary components

(Sahdev)


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Impeller Sahdev)

Main rotating part that provides centrifugalacceleration to the fluid

Number of impellers = number of pump stages

Impeller classification: direction of flow, suction typeand shape/mechanical construction

Shaft Transfers torque from motor to impeller during pump

start up and operation


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Casings

Volute Casing (Sahdev) 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


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Introduction

Type of pumps

Assessment of pumps


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Assessment of pumpsAssessment of pumps

Pump shaft power (Ps) is actual horsepower delivered to the pump shaft

Pump output/Hydraulic/Water horsepower (Hp) isthe liquid horsepower delivered by the pump

How to Calculate Pump PerformanceE l e

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Hydraulic power (Hp):Hp = Q (m3/s) x Total head, hd - hs (m) x (kg/m3) x g (m/s2) / 1000

Pump shaft power (Ps):Ps = Hydraulic power Hp / pump efficiency Pump

Pump Efficiency (Pump):Pump = Hydraulic Power / Pump Shaft Power

UNEP 2006UNEP 2006hd - discharge head hs suction head, - density of the fluid g acceleration due to gravity


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Assessment of pumpsAssessment of pumps

Absence of pump specification data

to assess pump performance Difficulties in flow measurement and

flows are often estimated

Improper calibration of pressuregauges & measuring instruments Calibration not always carried out

Correction factors used

Difficulties in Pump AssessmentE l e

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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities

Selecting the right pump

Controlling the flow rate by speedvariation

Pumps in parallel to meet varyingdemand

Eliminating flow control valve

Eliminating by-pass control

Start/stop control of pump

Impeller trimming

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1. Selecting the Right PumpE l e

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Pump performance curve for centrifugalpump

BEE India,2004


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1. Selecting the Right PumpE l e

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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


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2. Controlling Flow: speedvariationE l e

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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. ) = largepower reduction (e.g. 1/8)


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Variable Speed Drives (VSD)

Speed adjustment over continuousrange

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: speedvariation


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Benefits of VSDs

Energy savings (not just reduced flow!) Improved process control

Improved system reliability

Reduced capital and maintenancecosts

Soft starter capability

2. Controlling Flow: speedvariation


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3. Parallel Pumps for VaryingDemandE l e

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Multiple pumps: some turned off during lowdemand

Used when static head is >50% of total head

System curvedoes not change

Flow rate lower than sum of individualflow rates

(BPMA)


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4. Eliminating Flow Control ValveE l e

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Closing/opening discharge valve (throttling)to reduce flow

Head increases:does not reducepower use

Vibration andcorrosion: highmaintenancecosts and reducedpump lifetime

(BPMA)


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5. Eliminating By-pass ControlE l e

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Pump discharge divided into two

flows One pipeline delivers fluid to destination

Second pipeline returns fluid to the source

Energy wastage because part of fluidpumped around for no reason


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6. Start / Stop Control of PumpE l e

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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 maximumdemand (pumping at non-peak hours)


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7. Impeller TrimmingE l e

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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 moreexpensive and not always possible


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7. Impeller TrimmingE l e

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Impeller trimming and centrifugal pump performance

(BEE India,2004)


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Comparing Energy EfficiencyOptions

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11.6 kW14 kW23.1 kWPower consumed

80 m 3/hr 80 m 3/hr 80 m 3/hr Rate of flow

77%72.1%75.1%Pump efficiency

34.5 m42 m71.7 mPump head

430 mm375 mm430 mmImpeller diameter

VFDTrim impeller Changecontrol valve

Parameter


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Training Session on EnergyTraining Session on EnergyEquipmentEquipment

Pumps & PumpingPumps & PumpingSystemsSystems

THANK YOUTHANK YOU

FOR YOUR ATTENTIONFOR YOUR ATTENTION

UNEP 2006UNEP 2006

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Pumps Senator .Libya

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