PUMP SIZIN G CALCULATION CALCULATION B y C h e G u i d e ( H t t p s : / / C h e g u i d e . C o m / A u t h o r / A n u k a t / ) | M a y 7 , 2 0 1 7 ( H t t p s : // // C h e g u i de d e . C o m / 2 0 1 7 / 0 5 / P um u m p - S i z i n g - Ca Ca l c u l a t i o n / ) |
Pump is a most common equipment used in a chemical plant to transfer fluid from one location to another. This article shows how to do pump sizing calculation to determine dierential head required to be generated by pump based on suction and discharge conditions.
Suction Pressure Pressure at pump suction is calculated as following
PSuct. = P1 + Pstatic - ΔPEquipment - ΔPfriction
where, P1 is pressure at liquid surface in suction vessel. Pstatic is pressur pressuree due due to height height of liquid level abov abovee pump pump suction suction.. pressur suree drop drop in an equipm equipment ent at pump pump suct suction ion like like str strain ainers ers,, filt filters ers etc. etc. ΔPEquipment is pres pressu sure re dro drop p due due to suc suctio tion n pipe pipe and and fit fitti ting ngs. s. ΔPfriction is pres P static
where, h1 is height of liquid above pump suction, SG is specific gravity of liquid, ρ is liquid density ( kg/m³) and g is gravitational constant constant (9.81). ΔP friction
ΔPfriction = ΔPPipe + ΔPFittings ΔPPipe is pressure drop in a
pipe due to single phase fluid flow (https://cheguide.com/2015/08/single-phase-fluid-flow (https://cheguide.com/2015/08/single-phase-fluid-flow-pressure-drop/). -pressure-drop/). ΔPFittings is pres pressu surre dr drop du due to to pip pipee
fittings, which can be calculated based on 2-K & 3-K method (https://cheguide.com/2015/09/pipe-fitting-losses/).
Discharge Pressure Pressure at pump discharge is calculated as following
PDisch. = P2 + Pstatic + ΔPEquipment + ΔPfriction
9/24/2017
Pump Sizing Calculation – ChE Guide
where, P2 is pressure at liquid surface in discharge vessel. Pstatic is pressure due to height of liquid level above pump suction. ΔPEquipment is pressure drop in equipment at pump discharge like heat exchangers, control valve, flowmeter, valves etc. ΔPfriction is pressure drop due to suction pipe and fittings. P static
where, h2 is height of liquid above pump suction at which liquid is to be discharged. ΔPfriction is calculated in similar way as mentioned above for discharge piping.
Differential Head Dierential head required to be generated by pump is calculated as following.
Head (ft) = (PDisch. - PSuct. )*2.31/SG Head (m) = (PDisch. - PSuct. )*100000/(ρ.g)
Hydraulic Power Hydraulic power is calculated as following.
Power (bhp) = Head(ft) * Flow(gpm) * SG / 3960 Power (kW) = Head(m) * Flow(m³/h) * SG * g / 3600
NPSH Available Net Positive Suction Head (NPSH) available is calculated as following.
where, PVapor is vapor pressure of liquid at suction vessel temperature.
System Head Curve System head curve is a graphical representation of the relationship between flow and hydraulic losses in a given piping system. It is prepared by calculating dierential head as specified above at di erent flow. The intersection of the pump manufacturer’s curve with system curve defines the operating point of the pump.
Pump curve and system curve can be fitted into a second order polynomial. Operating point is calculated by solving these equations for positive roots. Web based calculation available at CheCalc.com (https://checalc.com/calc/pump.html)
Spreadsheet Spreadsheet for Pump Sizing Calculation (https://cheguide.com/wp-content/uploads/2017/05/Pump_Sizing_Calculation.xlsx) Like 89
