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Condensate Pumping

Reference data and engineering information about condensate pumping for pumps applications.

condensatepumping

Overview

Engineering reference data for Condensate Pumping in pumps.

Key Formulas

Pump Power

P=Q⋅H⋅ρ⋅gηP = \frac{Q \cdot H \cdot \rho \cdot g}{\eta}

Hydraulic power / efficiency.

NPSH Available

NPSHa=Psρg+vs22g−PvρgNPSH_a = \frac{P_s}{\rho g} + \frac{v_s^2}{2g} - \frac{P_v}{\rho g}

Net Positive Suction Head available.

Affinity Laws

Q∝n,H∝n2,P∝n3Q \propto n, \quad H \propto n^2, \quad P \propto n^3

Flow, head, power vs speed.

Variables

SymbolDescriptionUnit
PPPowerW
QQFlow ratem³/s
HHHeadm
η\etaEfficiency—
nnRotational speedRPM

Cavitation Prevention Methods

Hot condensate near 211°F (100°C) presents a significant challenge: cavitation. Centrifugal pumps generate lower pressure behind the impeller vanes, causing hot condensate to temporarily evaporate and expand before imploding. Over time, this erosion destroys the pump impeller.

Two primary solutions exist to prevent cavitation:

Option 1: Increase Suction-Side Pressure

If the absolute pressure exceeds the vapor pressure at the fluid temperature, the Net Positive Suction Head (NPSH) remains positive and cavitation is avoided.

Methods to increase NPSH:

  • Increase the pressure differential between the receiver and condensate vapor pressure
  • Extend static head hsh_s by elevating the receiver or lowering the pump
  • Increase pipe diameter to minimize friction loss hfh_f in the suction line
  • Install a cooling heat exchanger in the suction pipe to reduce pvpp_{vp}

Option 2: Use a Pressure Powered Pump

Pressure powered pumps use steam or air pressure to push condensate from the receiver back to the boiler room. Key advantages:

  • No external power required — uses available steam or pressurized air
  • No cavitation risk — mechanical displacement rather than centrifugal force
  • Simple intermittent operation — receiver fills with condensate, then steam/air pushes it out in cycles

Pumping Boiling Liquids (LPG)

The principles for condensate pumping apply to other boiling liquids like LPG (boiling point: −43°C at atmospheric pressure).

Key challenges with LPG:

  • LPG is stored at its boiling point for the tank pressure
  • Any temperature increase or pressure decrease causes vapor formation
  • Suction friction head often equals or exceeds static suction head
  • Flow restrictions (excess flow valves, control valves, fittings, strainers) induce vapor formation at the pump suction port

In many LPG installations, available NPSH is negative, making cavitation prevention measures critical for reliable operation.

References

Source: engineeringtoolbox.com