Pumps & Fans-Types and How they function

7/27/2019 Pumps & Fans-Types and How they function

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What is a Pump ?

A pump is a device that moves fluids or

sometimes slurries, by mechanical action.

Pumps can be classified into three major groups

according to the method they use to move the

fluid:-

direct lift, displacement, andgravity pumps.

Pumps operate by some mechanism (typically

reciprocating or rotary), and consume energy to

perform mechanical work by moving the fluid.

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Gravity pumps

Gravity pumps include thesyphon and

Heron's fountain

and there also important qanatorfoggara

systems that simply use downhill flow to

take water from far-underground aquifers in

high areas to consumers at lower elevations.

The hydraulic ram is also sometimes called

a gravity pump.

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Pumps

Centrifugal- Single StageMultistage AxialMixed Flow

Positive Displacement-

Gear Type

Screw Type

Reciprocating Type.

Jet Pump


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Basic

A pump transfers liquids from a region of LOWpressure to a region of HIGH pressure.

A pump is a device that moves fluids , orsometimes slurries, by mechanical action.

Pumps can be classified into three major groups

according to the method they use to move thefluid: direct lift, displacement, andgravity pumps.

Pumps operate by some mechanism (typicallyreciprocating or rotary), and consume energy toperform mechanical work by moving the fluid.

Pumps operate via many energy sources,including manual operation, electricity, an engineof some type, or wind power.


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Positive displacement pump

A positive displacement pump makes a fluid

move by trapping a fixed amount, and forcing (displacing) that trapped volume into

the discharge pipe.

Some positive displacement pumps use an

expanding cavity on the suction side and adecreasing cavity on the discharge side.

Liquid flows into the pump as the cavity on thesuction side expands and the liquid flows out of

the discharge as the cavity collapses. The volume is constant through each cycle of

operation.


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Positive displacement pump behaviour and safety

Positive displacement pumps, can produce the same flow at a

given speed (RPM) no matter what the discharge pressure.

Thus, positive displacement pumps are constant f low

machines.

A positive displacement pump must not operate against a

closed valve on the discharge side.

A positive displacement pump operating against a closed

discharge valve continues to produce flow and the raise the

pressure in the discharge line increases until the line bursts.

A safety valve on the discharge side of the positive

displacement pump is therefore necessary. The internal valve

is usually only used as a safety precaution. An external relief

valve in the discharge line, with a return line back to the

suction line or supply tank provides increased safety.


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Positive displacement types

A positive displacement pump can be further

classified according to the mechanism used to

move the fluid:

Rotary-type positive displacement:

internal gear, screw, flexible vane or sliding

vane, helical twisted roots or liquid ring

vacuum pumps

Reciprocating-type positive displacement:

piston or diaphragm pumps


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Rotary positive displacement pumps

Rotary pumps move fluid using a rotating mechanism that

creates a vacuum that captures and draws in the liquid.

Advantages: Rotary pumps are very efficientbecause they

naturally remove air from the lines, eliminating the need to

bleed the air from the lines manually.

Drawbacks: The pump demands very close clearances

between the rotating pump and the outer edge, making it

rotate at a slow, steady speed.

If rotary pumps are operated at high speeds, the fluidscause erosion, which eventually causes enlarged

clearances that liquid can pass through, which reduces

efficiency.


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Piston and Plunger Pump


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Positive Displacement Lobe Pump

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Scroll Pump

The red casing is stationary. The black spiral

revolves in the casing to draw fluid andcompress it.


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Twin Screw Pump


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Gear Pump


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Sliding Vanes Eccentric Rotation

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Centrifugal Pump with backward vanes.(The

vanes can be Radial or Forward also)


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Velocity DiagramsRadial, Backward & Forward curved vanes

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RADIAL

FORWARDBACKWARD

RELATIVE VELOCITY

TIP VELOCITY

RESULTANT

VELOCITY

FORWARD BLADES GIVE HIGHEST VELOCITY


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Closed impellar


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Open Impeller - Non Clogging (For slurry)


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Centrifugal Pump Note the expanding Volute

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Axial Pump (Generally they are mixed flow)In pure axial pump the Motor has to be in the pipe.


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Axial Flow Pump Twisted blades

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Jet Pump

Works on Bernoullis Principle.

As velocity increases, the pressure falls.

Total energy remains constant.


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Boiler Feed Pump


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Centrifugal Pump

Centrifugal pumps are used to transport fluids by the

conversion of rotational kinetic energy to thehydrodynamic energy of the fluid flow.

The rotational energy typically comes from an engine

or electric motor.

The fluid enters the pump impeller along or near to the

rotating axis and is accelerated by the impeller,

flowing radially outward into a diffuser or volute

chamber (casing), from where it exits.

The reverse function of the centrifugal pump is a water

turbine converting potential energy of water pressure

into mechanical rotational energy. 25


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Multistage centrifugal pumps

A centrifugal pump containing two or more impellers is

called a multistage centrifugal pump. The impellers may be

mounted on the same shaft or on different shafts.

For higher pressures at the outlet, impellers can be connected

in series.

For higher flow output impellers can be connected in

parallel.

A common application of the multistage centrifugal pump is

the boiler feed water pump.

All energy transferred to the fluid is derived from the

mechanical energy driving the impeller.

This can be measured at isentropic compression, resulting in

a slight temperature increase (in addition to the pressure

increase).26


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Power Input to a PUMP

Pi = Q H/

where: (SI Units )

Pi is the input power required (W)

is the fluid density (kg/m3)

is the standard acceleration of gravity (9.8 m/s2)

H is the Head added to the flow (m)

Q is the flow rate (m3/s)

is the efficiency of the pump plant as a decimal.

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Illustration

If we consider water as the fluid,

= 1000 Kg/M3; g = 9.81 M/Sec 2; Q = 1 M3 / Second ; H = 10 Meters.

= 0.85 (Motor + Pump)

Then Power required in watts =1000 x 9.81 x 1 x 10 / 0.85

= 115411.76 Watts or

= 115.41 KW

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BFP - 210 MW (200 KHI)

p 1000 Kg/M3

g 9.81Q 430 m3/Hr

Q 0.119 m3/sec

H 1836 Metersn-Motor 0.75

n-Pump 0.75

n-Composit 0.5625

Watts 3824592

KW 3825

Actual Motor Rating = 4000 KW


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The head added by the pump (H) is a sum

of

the static lift,

the head loss due to friction and

any losses due to valves or pipe bends all

expressed in metres of fluid.

The value for the pump efficiency, , may be

stated for the pump itself or as a combined

efficiency of the pump and motor system.

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Difficulties faced in centrifugal pumps:

Cavitationthe net positive suction head (NPSH) of

the system is too low for the selected pump Wear of the Impellercan be worsened by

suspended solids

Corrosion inside the pump caused by the fluid

properties

Overheating due to low flow.(Churning)

Leakage along rotating shaft

Lack of primecentrifugal pumps must be filled

(with the fluid to be pumped) in order to operate

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Note how neck rings prevent recirculation 32


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Centrifugal pumps contain rotating impellers

within stationary pump casings.

To allow the impeller to rotate freely withinthe pump casing, a small clearance is designed

to be maintained between the impeller and the

pump casing. To maximize the efficiency of a centrifugal

pump, it is necessary to minimize the amount of

liquid leaking through this clearance from thehigh pressure or discharge side of the pump

back to the low pressure or suction side.


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Some wear or erosion will occur at the

point,

where the impeller and the pump casing

nearly come into contact.

This wear is due to the erosion causedby liquid leaking through this tight

clearance and other causes.

As wear occurs,

the clearances become larger and the

rate of leakage increases.


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To minimize the cost of pump maintenance, centrifugal

pumps are designed with wearing rings.

Wearing rings are replaceable rings that are attached to

the impeller and/or the pump casing to allow a small

running clearance between the impeller and the pump

casing

without causing wear of the actual impeller or pumpcasing material.

These wearing rings are designed to be replaced

periodically during the life of a pump and

prevent the more costly replacement of the impeller or

the casing.

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Axial-flow pump

An axial-flow pump, is a pump that essentially

consists of a propeller (an axial impeller) in a pipe.The propeller can be driven directly by a sealed motor

in the pipe or by electric motor or petrol/diesel engines

mounted to the pipe from the outside or by a right-

angle drive shaft that pierces the pipe.

Fluid particles, in course of their flow through the

pump, do not change theirradiallocations since the

change in Diameter at the entry (called 'suction') andthe exit (called 'discharge') of the pump is very small.

Hence the name "axial" pump.

There is no radial movement of the fluid.37


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Pump specific speed

Low-specific speed radial flow impellers develop

hydraulic head through centrifugal force.Pumps of higher specific speeds develop head partly by

centrifugal force and partly by axial force.

An axial flow or propeller pump with a specific speed

of 10,000 or greater generates its head exclusively

through axial forces.

Radial impellers are generally low flow/high head

designs whereas axial flow impellers are high flow/low head

designs.

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Centrifugal pump impellers have specific speed

values ranging from 500 to 10,000 (English units),

Radial flow pumps at 500-4000,Mixed flow at 2000-8000 and

Axial flow pumps at 7000-20,000.

Values of specific speed less than 500 areassociated with positive displacement pumps.

As the specific speed increases, the ratio of the

impeller outlet diameter to the inlet or eye

diameter decreases.

This ratio becomes 1.0 for a true axial flow

impeller.

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Specific Speed-Metric System

Ns = n (Q)1/2 / (g H)3/4

where:

Ns- is specific speed (unitless)

N - is pump rotational speed (radians per

second)

Q - is flow rate (m/s) at the point of best

efficiency.

H - is total head (meters) per stage at the point

of best efficiency

g - is acceleration due to gravity (m/s)40


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Selecting between Centrifugal or Positive

Displacement Pumps

Flow Rate and Pressure Head

The Centrifugal Pump has varying flow depending on the system

pressure or head

The Positive Displacement Pump has a constant flow regardless of the

system pressure or head..

Capacity and Viscosity

In the Centrifugal Pump the flow is reduced when the viscosity is

increased

In the Positive Displacement Pump the flow is increased when

viscosity is increased Liquids with high viscosity fill the clearances of a Positive

Displacement Pump causing a higher volumetric efficiency and a

Positive Displacement Pump is better for high viscosity applications.

A Centrifugal Pump becomes very inefficient at even modest viscosity.41


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Mechanical Efficiency

Changing the system pressure or head has little or no

effect on the flow rate in the Positive DisplacementPump

Changing the system pressure or head has a dramatic

effect on the flow rate in the Centrifugal Pump

Net Positive Suction Head - NPSH

In a Centrifugal Pump, NPSH varies as a function of

flow determined by pressure

In a Positive Displacement Pump, NPSH varies as afunction of flow determined by speed.

Reducing the speed of the Positive Displacement Pump,

reduces the NPSH42


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Losses in Pumps & Efficiency

Internal losses

hydraulic losses - disk friction in the impeller, loss due torapid change in direction an velocities through the pump

volumetric losses - internal recirculation at wear rings and

bushes

External losses

mechanical losses - friction in seals and bearings .

The efficiency of the pump at the designed point is

normally maximum and is called the Best Efficiency Point

- BEP

It is possible to operate the pump at other points than BEP,

but the efficiency of the pump will always be lower than

BEP. 43

B Effi i P i


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Best Efficiency Point

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C t if l P P t


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Centrifugal Pump Parts

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M lti St B F P


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Multi-Stage B.F.P.

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B i M h i l S l


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Basic Mechanical Seal

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WATER PUMPS IN POWER STATION


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WATER PUMPS IN POWER STATION

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Hi h P BFP S l k


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High Pressure BFP Sulzer make

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C d t E t ti P


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Condensate Extraction Pump

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S li f CEP


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Sealing for CEP

The CEP has negative suction.

Hence any opening will result in air ingress fromthe atmosphere.

So, the glands of the pump and suction side valves

are provided with sealing water tapped from the

pump discharge.

Even the glands of condenser level indicator

isolating valves must be made leakproof.

If there is air ingress in level indicator, correctlevel indication is not possible.

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P t f CEP


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Parts of CEP

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Balancing Scheme


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Balancing Scheme

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Balancing Disc


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Balancing Disc

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Gland packing Stuffing Box


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Gland packing Stuffing Box

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Mechanical Seal


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Mechanical Seal

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BOILER FEED WATER PUMP


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BOILER FEED WATER PUMP

Boiler feed pump is the major power consumer

among all power consuming equipment in the

power plant. BFP may constitute about 25% of the

total auxiliary power consumption. (4% of Power

Generated)

BFP Main Parameters for 210 MW unit

Model Speed

RPM

Disch. head

mWC

Capacity

TPH

Motor

Power kW

200 KHI 4320 1834.6 430 4000

FK 6D 30 5050 2104 398 350059

BFP LAYOUT


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BFP LAYOUT

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B F P Protections


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B.F.P.- Protections

NPSH (Minimum pressure at suction to

avoid flashing) Minimum Flow Valve (Churning)

Balancing Leak-off

T between Inlet & Outlet Feed WaterTemperature.

Lubricating oil Pressure

Bearing Temperature & Vibrations.

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Condensate Cycle


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Condensate Cycle

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Feed water cycle


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Feed water cycle

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PUMP CURVES


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PUMP CURVES

Pump Operating Point

System head curve Pump Head Flow curve

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C W Pumps


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C.W.Pumps.

Flowwise , this is the largest pump in a TPS.

The Cooling Water Flow is approximately 100 timesthe steam flow condensing in the condenser.

The make up water rate is equal to the rate of steam

flow to the condenser + Drift loss + Blow down loss.

C.W. Pumps may be located close to the condenser or

Located in a separate pump house between the main

plant and the cooling towers.

These are generally vertical mixed flow pumps.

But horizontal, centrifugal pumps are also used.

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Louvres & Drift Eliminators


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Louvres & Drift Eliminators

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ENERGY CONSERVATION OPPORTUNITIES


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Avoiding over sizing of pump


Head

Head

Partially

closed valve

Const. Speed

A

B

C

Meters

Pump Efficiency 77%

82%

Pump Curve at

Full open valve

System Curves

Operating Points

500300

50 m

70 m

Static

42 m

Flow (m3/hr)

Oversize Pump

Required Pump

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[email protected]



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28.6 kW

14.8 kW

Avoiding Over sizing of Pump by

impeller trimming


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Provision of variable speed drive


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Energy Conservation Possibilities- Summary


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Energy Conservation Possibilities Summary Improvement of systems and drives.

Use of energy efficient pumps

Replacement of inefficient pumps

Trimming of impellers

Correcting inaccuracies of the Pump sizing

Use of high efficiency motors

Integration of variable speed drives into pumps: The integration of

adjustable speed drives (ASD) into compressors could lead to energy

efficiency improvements, depending on load characteristics.

High Performance Lubricants: The low temperature fluidity and high

temperature stability of high performance lubricants can increase energyefficiency by reducing frictional losses.

Booster pump application

Centralisation/ decentralisation

Categorising according to the pressure requirement71

ESP duct modification


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or ig inal arrangement . LHS half on ly is shown in the plan

ESP path#1

ESP path# 2

1.8 METER FROM APH 2-inlets

4 METER

BUS

DUCT4 OUTLETS to E.S.P.

2 x 2.5 mtr.

1.8 mtr x 6 mtr duct from APH

2.5 mtr x 4 mtr

BUS DUCT

Suggest

modification

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MODIFICATION


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MODIFICATION

ESP path#1

ESP path# 2

2.5x2.5

2.5x2.5

ETER FROM APH 2-inlets4 OUTLETS to E.S.P.

2 x 2.5 mtr.

Pumps & Fans-Types and How they function

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