PUMPS for Process Industries Ranjeet Kumar M.Tech - Chemical
Aug 11, 2014
PUMPSfor
Process Industries
Ranjeet KumarM.Tech - Chemical
08-Jun-08 Ranjeet Kumar 2
Equation of Energy
A pump converts Electrical energy to Pressure Energy via Kinetic Energy.
Electric energy K.E. K.E Pressure Energy
ImpellerRotating Part
VoluteStatic Part
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Types of Pumps
Centrifugal - Impeller & Volute Reciprocating - Piston / Plunger Rotary - Screw, Gear, Lobe, Progressive
Cavity, Sliding Vane Vertical - Peristaltic - Series of rollers to push through
tubing
08-Jun-08 Ranjeet Kumar 4
Basis for selection of Pump
Capacity – No. of pumps in parallel Total Head – No. of stages Physical, Chemical properties of Liquids Viscosity @ Frictional Loss @ Power Required Corrosive Fluid @ MOC
Site conditions Source of Power
>>>Capacity & Head required are most important selection criteria and define size of the pump.
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Capacity
Volume of liquid to be pumped in unit time May vary as per Max, Min & Normal requirement – design should be for Max capacity. Its function of Impeller size and rotational speed
for Centrifugal pump Q = V * A : V = ω * r
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Centrifugal Pump Design Problem
Inability to deliver the desired flow & head Seal problems (leakages, loss of flushing, cooling,
quenching system, etc) Pump & Motor bearings related problems (loss of
lubrication, cooling, contamination of oil, abnormal noise, etc) Leakages from pump casing, very high noise &
vibration levels.
Benefits of Centrifugal Pumps – low cost, easy maintenance, wide selection,& simple design.
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Head of Pump
Total Head = P discharge – P suction Normal head test by vendor was done
for water at 20°C. Advantages of using Head--
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Physical Properties Consideration
Specific Gravity 1) Increases Power consumed directly. 2) Max suction lift inversely.
Viscosity Pump efficiency decrease directly so Power required directly
Open or semi open impeller are better for highly viscose liquid.
Volatile liquid at boiling points require high NPSH. Abrasive property of liquid or solid entrainment
causes erosion and need specific MOC. Corrosive liquid require specific MOC.
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Solid content Centrifugal pump operation is most difficult
when liquid handled contains solid particles. Special attention required for selecting a
centrifugal pump a) Open Impeller for solids > 2%b) Large cross section in Impeller & Volutec) Min No. of Vanesd) Inspection holes in tha casing & suction passagee) Abrasion resistant MOCf) Smooth corners & edges in linesg) Stuffing boxes sealed with clear fluid
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Fig – Types of Impeller
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Temperature of liquid Direct Impact on physical properties of liquid & Vapor Pressure and MOC.
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Site Conditions
Altitude – P atm decreases with altitude & P atm has direct effect on NPSHa
Gas Dust Hazard – if the surrounding atmosphere is hazardous/inflammable Flame proof & Dust proof MOC of Motor.
Stand by unit for vital application.
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Selection of Pump – Capacity & Head
Type Capacity Head Viscosity
Solid % Gas
Centrifugal Upto 7500 m3/h
Upto 105 m
< 200 cSt
Upto 20%
< 2%
Rotary < 350 m3/h
1050 m
Max < 5% > 2%
Positive Displacement
< 300 m3/h
10500 m
< 600 cSt
< 25% > 2%
Peristaltic Upto 1 m3/h
< 25 m < 200 cSt
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Flow Rate DesignMargins for rated/maximum capacity
Service MarginContinuous process pumps
10%
Reflux pumps 20-25%Intermittent pumps 0%Transfer pumps 0-5%Large cooling water pump
3-5%
Recirculation pump 0%Boiler Feed water pump 25%Waste Heat Boiler pump 30%
PFD indicates normal flow rate without any margin & the Maximum flow is Considered for sizing of the pump with margin
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Minimum flow rate ????
Under development………….
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Static Head
Pump centre line as datum for Hydraulic calculation
Pump centre Line from ground (estimated)
Minimum level in Suction & Maximum level in Discharge tank.
Flow Rate (m3/h)
Pump centre line above
ground0 – 100 0.7
100 – 200 0.9Above 200 1.0
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Line Pressure Drop ?
Under development
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Pressure Drop for Control Valve
The following criteria can be used for sizing the control valve
15~25% of the variable system drop is typically allowed.
On recycle and reflux pumps allow 1/3 of the variable system pressure with minimum of 0.7 bar.
For liquid system 0.7 bar For system with large variable pressure drop
( >10 bar) ~15% of the variable pressure drop exclusive of control valve
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Pressure Drop for DevicesDevices in Flow Line Press Drop (in bar)
Shell & Tube type Heat Exchanger
0.7 bar per pass in tube side0.35 – 0.5 bar per shell
Air cooler 1.0 barY, T or Bucket type Strainer 0.07 bar (continuous
strainer)Orifice Flow meter 0.25Venturi Flow Meter 0.02 – 0.05Vortex 0.2 – 0.4Corilolis Flow Meter 0.2 – 0.4Ultrasonic & electromagnetic Flow Meter
0
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NPSH
NPSHA = Suction Pressure – Vapor Pressure NPSHA should be 2 – 3 ft more than NPSHR. It is the pressure enough to prevent formation
of vapor bubbles due to vaporization or release of dissolved gases in the Impeller.
Pressure increases along the impeller on collapse of vapors – Cavitation.
Cavitation – Noise, Vibration, Drop in performance curve, high wear & tear loss.
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NPSHA optimization NPSHA can be increased by – 1) Raise the liquid level2) Lower the pump3) Reduce the friction losses in the suction line4) Use a booster pump5) Sub cool the liquid
NPSHR can be reduced by – 1) Slower speed2) Double-suction impeller3) Large impeller area4) Oversize pump5) Inducers ahead of conventional pump at suction side6) Several smaller pumps
NPSHR Rotary < NPSHR Centrifuge < NPSHR Reciprocating
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Efficiency
Efficiency = WHP/BHPOverall efficiency reflects hydraulic, leakage &
mechanical losses of pump.
ηcentrifugal < ηreciprocating < ηrotary
(50 – 80%) (50 – 90%) (70 – 90%)
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Seals, pumps curvesUnder Development……..