Pumps for Process Industries

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Published on November 20, 2008

Author: ran_nwd

Source: slideshare.net

Description

This presentation will give a broad idea about selecting pumps in process industies. Design parameters are also discussed.

PUMPS for Process Industries Ranjeet Kumar M.Tech - Chemical

Equation of Energy A pump converts Electrical energy to Pressure Energy via Kinetic Energy. Electric energy K.E. K.E Pressure Energy Impeller Rotating Part Volute Static Part

A pump converts Electrical energy to Pressure Energy via Kinetic Energy.

Electric energy K.E.

K.E Pressure Energy

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

Centrifugal - Impeller & Volute

Reciprocating - Piston / Plunger

Rotary - Screw, Gear, Lobe, Progressive Cavity, Sliding Vane

Vertical -

Peristaltic - Series of rollers to push through tubing

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.

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 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

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

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.

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.

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--

Total Head = P discharge – P suction

Normal head test by vendor was done for water at 20°C.

Advantages of using Head--

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.

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.

Solid content Centrifugal pump operation is most difficult when liquid handled contains solid particles. Special attention required for selecting a centrifugal pump  Open Impeller for solids > 2% Large cross section in Impeller & Volute Min No. of Vanes Inspection holes in tha casing & suction passage Abrasion resistant MOC Smooth corners & edges in lines Stuffing boxes sealed with clear fluid

Centrifugal pump operation is most difficult when liquid handled contains solid particles.

Special attention required for selecting a centrifugal pump 

Open Impeller for solids > 2%

Large cross section in Impeller & Volute

Min No. of Vanes

Inspection holes in tha casing & suction passage

Abrasion resistant MOC

Smooth corners & edges in lines

Stuffing boxes sealed with clear fluid

Fig – Types of Impeller

Temperature of liquid  Direct Impact on physical properties of liquid & Vapor Pressure and MOC.

Temperature of liquid  Direct Impact on physical properties of liquid & Vapor Pressure and MOC.

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.

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.

Selection of Pump – Capacity & Head < 200 cSt < 25 m Upto 1 m 3 /h Peristaltic > 2% < 25% < 600 cSt 10500 m < 300 m 3 /h Positive Displacement > 2% < 5% Max 1050 m < 350 m 3 /h Rotary < 2% Upto 20% < 200 cSt Upto 105 m Upto 7500 m 3 /h Centrifugal % Gas Solid Viscosity Head Capacity Type

Flow Rate Design Margins for rated/maximum capacity PFD indicates normal flow rate without any margin & the Maximum flow is Considered for sizing of the pump with margin 30% Waste Heat Boiler pump 25% Boiler Feed water pump 0% Recirculation pump 3-5% Large cooling water pump 0-5% Transfer pumps 0% Intermittent pumps 20-25% Reflux pumps 10% Continuous process pumps Margin Service

Margins for rated/maximum capacity

Minimum flow rate ???? Under development………….

Minimum flow rate ????

Under development………….

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. 1.0 Above 200 0.9 100 – 200 0.7 0 – 100 Pump centre line above ground Flow Rate (m 3 /h)

Pump centre line as datum for Hydraulic calculation

Pump centre Line from ground (estimated)

Minimum level in Suction & Maximum level in Discharge tank.

Line Pressure Drop ? Under development

Under development

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

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

Pressure Drop for Devices 0 Ultrasonic & electromagnetic Flow Meter 0.2 – 0.4 Corilolis Flow Meter 0.2 – 0.4 Vortex 0.02 – 0.05 Venturi Flow Meter 0.25 Orifice Flow meter 0.07 bar (continuous strainer) Y, T or Bucket type Strainer 1.0 bar Air cooler 0.35 – 0.5 bar per shell 0.7 bar per pass in tube side Shell & Tube type Heat Exchanger Press Drop (in bar) Devices in Flow Line

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.

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.

NPSHA optimization NPSHA can be increased by – Raise the liquid level Lower the pump Reduce the friction losses in the suction line Use a booster pump Sub cool the liquid NPSHR can be reduced by – Slower speed Double-suction impeller Large impeller area Oversize pump Inducers ahead of conventional pump at suction side Several smaller pumps NPSHR Rotary < NPSHR Centrifuge < NPSHR Reciprocating

NPSHA can be increased by –

Raise the liquid level

Lower the pump

Reduce the friction losses in the suction line

Use a booster pump

Sub cool the liquid

NPSHR can be reduced by –

Slower speed

Double-suction impeller

Large impeller area

Oversize pump

Inducers ahead of conventional pump at suction side

Several smaller pumps

Efficiency Efficiency = WHP/BHP Overall efficiency reflects hydraulic, leakage & mechanical losses of pump. η centrifugal < η reciprocating < η rotary (50 – 80%) (50 – 90%) (70 – 90%)

Efficiency = WHP/BHP

Overall efficiency reflects hydraulic, leakage & mechanical losses of pump.

η centrifugal < η reciprocating < η rotary

(50 – 80%) (50 – 90%) (70 – 90%)

Seals, pumps curves Under Development……..

Under Development……..

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