Process Equipment Design and Heuristics - Pumps

Types of Process Pumps Pumps are designed to handle liquids and do not behave well with vapor Link to Additional Classifications of Positive Displacement and Centrifugal Pumps

Centrifugal Pumps The most common type of pump. Include radial, axial and mixed flow units. They use one or more impellers which attach to and rotate with the shaft Usually the best choice for lower viscosity (thin) liquids and high flow rates Produces head and flow by increasing the velocity of the liquid Has varying flow depending on the system pressure or head They generally work within the following ranges: Flow rate ranges between 5 and 200,000 gpm Total head (pressure) ranges between 10 and 7,500 ft Horsepower ranges between 0.125 and 5,000 hp

Centrifugal Pumps Axial Flow Radial Flow

Positive Displacement Pumps Second only to centrifugal pumps in terms of their popularity. Operates by alternating of filling a cavity and then displacing a given volume of liquid Generally used for special applications such as viscous liquids or liquids containing fragile solids No impellers. Use rotating or reciprocating parts to directly push the liquid in an enclosed movable volume, until enough pressure is built up to move the liquid into the discharge system. Pump delivers a constant volume of liquid for each cycle against varying discharge. PD’s give a relatively constant flow regardless of the system pressure or head PD pumps generally work within the following ranges: Flow rate ranges between .1 and 15,000 gpm Total head (pressure) ranges between 10 and 100,000 psi Horsepower ranges between 0.5 and 5,000 hp Some types can handle millions of SSU viscosity

Positive Displacement Pumps Reciprocating PD Rotary PD

Pump Capacity Heuristics

Pump and System Curves pump supplies pressure increase to increase fluid pressure and to overcome all of these pressure losses

NPSH – Net Positive Suction Head If fluid is too close to vapor pressure at pump inlet, it could flash upon entering pump NPSH Required (NPSHR): The minimum pressure required at the suction port of the pump to keep the pump from cavitating. NPSHA is a function of your system and must be calculated, whereas NPSHR is a function of the pump and must be provided by the pump manufacturer.

Pump Sizing The size and costing of a pump is based on its power consumption. Horsepower = Pressure (psi) x Flow (GPM) / 1714.3 Note: 1714 is units conversion factor: 1 HP = 33,000 (ft-lbf / min) = 396,000 (in - lbf / min) 231 = 123/7.48 in3 - min/ gal 1714.3 = 396,000/231 psi – gpm /HP The power needs to be adjusted by dividing by the pump efficiency (see Table 9.9 above for typical efficiencies)

Pump Design Heuristics

Aspen Plus Pump Input Aspen uses a default efficiency if not specified.