Condensate Extraction Pumps
Condensate extraction pumps transfer hot process condensate from a condenser hotwell, condensate receiver or collection vessel into the feedwater or condensate recovery system.
Because condensate is often close to its boiling point, even a small pressure reduction at the pump inlet can cause flashing and cavitation. Reliable pump selection therefore depends on condensate temperature, vapour pressure, available NPSH, flow, discharge head and the amount of entrained steam or gas.
AxFlow supplies specialist condensate extraction pumps, hot condensate pumps and condensate recovery pumps for industrial steam systems, power generation, chemical processing and waste-heat recovery.
What Is a Condensate Extraction Pump?
A condensate extraction pump removes condensed steam from a receiver, hotwell or process vessel and transfers it to the next stage of the steam and feedwater system.
In power stations, a condensate extraction pump commonly draws water from the condenser hotwell and sends it through the condensate treatment and low-pressure feedwater system towards the deaerator.
In industrial steam plants, a condensate recovery pump typically transfers collected condensate back to the boiler feed tank or deaerator. The boiler feed pump then raises the final feedwater pressure above boiler pressure.
How Does a Condensate Extraction Pump Work?
Condensate drains from steam-using equipment into a receiver or condenser hotwell. A level controller starts, stops or regulates the pump to maintain the required liquid level.
The pump then raises the condensate pressure sufficiently to overcome:
- Static elevation
- Destination vessel pressure
- Pipe and fitting losses
- Check-valve resistance
- Heat-exchanger or treatment-system pressure losses
- Control-valve pressure drop
Most condensate extraction pumps use centrifugal hydraulics. Depending on the application, the pump may use a low-NPSH first stage, side-channel stages, a vertical submerged inlet or specialist self-regulating hydraulics.
Why Recover Process Condensate?
Returned condensate contains both treated water and useful heat. Recovering it can reduce:
- Boiler fuel consumption
- Cold make-up water demand
- Water-treatment chemical use
- Boiler blowdown losses
- Effluent and disposal costs
Clean condensate can normally be returned to the boiler feed system, while contaminated condensate should be detected and diverted before it reaches the boiler.
Why Is Hot Condensate Difficult to Pump?
Limited NPSH Available
Hot condensate has a relatively high vapour pressure because it is often close to saturation temperature.
If pressure at the pump inlet falls below the liquid’s vapour pressure, some condensate flashes into steam. These vapour bubbles can reduce flow and head, create vibration and cause cavitation damage when they collapse within the pump.
NPSH available—NPSHa—is determined by the system. NPSH required—NPSHr—is a characteristic of the selected pump at a particular flow and speed. NPSHa must exceed NPSHr by a suitable margin throughout the operating range.
Flash Steam and Entrained Vapour
A reduction in condensate pressure can generate flash steam. Vapour entering a conventional centrifugal impeller may interrupt pumping or cause unstable performance.
Side-channel and specialist condensate pump designs can be useful where partial degassing or entrained vapour cannot be avoided.
Variable Condensate Flow
Condensate return can vary with production demand, steam pressure, start-up conditions and the number of operating heat exchangers.
The pump and control system must handle minimum, normal and peak return rates without prolonged deadheading or unstable low-flow operation.
Water Quality and Materials
Condensate is normally a low-viscosity, water-like fluid, but its chemistry depends on the process. Dissolved gases, treatment chemicals or contamination from leaking heat exchangers may affect corrosion and materials selection.
Its limited lubricity must also be considered where the selected pump uses product-lubricated bearings or close-clearance internal components.
Types of Condensate Extraction Pumps
Low-NPSH Centrifugal Pumps
Centrifugal pumps are commonly used where condensate is clean, the flow is continuous and sufficient NPSH is available.
Special suction impellers or low-NPSHr first-stage hydraulics may be required for hotter condensate.
Side-Channel Condensate Pumps
Side-channel pumps are well suited to low-flow, high-head condensate duties and applications involving limited NPSH or partial vapour formation.
Some designs combine a low-NPSH suction impeller with multistage side-channel hydraulics, allowing the pump to maintain flow during partial degassing.
Vertical Condensate Extraction Pumps
Vertical multistage pumps are commonly used for larger condenser-hotwell and power-generation duties.
Positioning the first-stage impeller below the minimum liquid level increases the static pressure at the pump inlet. Special first-stage hydraulics can further reduce NPSHr for critical suction conditions. Vertical API-style condensate extraction pumps are available specifically for high-flow duties with restricted NPSH.
Self-Regulating Process Pumps
Specialist self-regulating pumps can manage fluctuating inflow without conventional level-control throttling.
They are particularly useful for:
- Boiling liquids
- Very low or varying NPSHa
- Vacuum vessels
- Gas-containing condensate
- Evaporators and distillation systems
- Irregular condensate return
Mechanical Condensate Pumps
Steam- or air-powered mechanical condensate pumps may be appropriate where electrical pumps would cavitate, where the receiving equipment operates under vacuum or where steam-system stall prevents normal condensate drainage.
These pumps operate cyclically, so the receiver and discharge line must be sized for the instantaneous pumping rate rather than only the average condensate return.
Condensate Extraction Pump Applications
Industrial Steam Systems
Returning condensate from process heaters, heating coils, dryers and steam distribution systems to the boiler house.
Power Generation
Extracting condensate from steam-turbine condenser hotwells and transferring it through feedwater treatment or low-pressure heater systems.
Heat Exchangers and Process Heating
Removing condensate from shell-and-tube heat exchangers, plate heat exchangers, calorifiers and steam-heated process equipment.
Evaporators, Reboilers and Distillation
Pumping hot condensate from vessels where pressure, vapour content and condensate flow may fluctuate.
Waste-Heat and CHP Systems
Recovering condensate from heat-recovery steam generators, waste-heat boilers and combined heat and power installations.
Food, Beverage and Pharmaceutical Processing
Returning clean condensate from cookers, sterilisers, evaporators, process vessels and hygienic heat-transfer systems.
How to Choose a Condensate Extraction Pump
Define the Condensate Flow
Establish the minimum, normal and maximum condensate return rate.
Also consider:
- Start-up loads
- Simultaneous steam-user operation
- Receiver storage volume
- Desired pump cycling frequency
- Future production demand
The pump should remove peak condensate inflow without being excessively oversized for normal operation.
AxFlow Condensate Pump Ranges
AxFlow’s most relevant ranges include:
- SERO SRZS W: a multistage side-channel pump for hot condensate, low-flow/high-head operation and restricted-NPSH duties. Published limits include flows up to 36 m³/h, pressures up to 40 bar and temperatures up to 220°C.
- Bungartz horizontal and vertical pumps: specialist process pumps for boiling liquids, fluctuating inflow and very low or varying NPSHa. Available configurations include self-regulating and gas-handling designs.
When a Standard Condensate Pump May Not Be Suitable
A conventional centrifugal pump may not be the best choice where:
- NPSHa is below the pump’s required margin.
- Condensate is close to boiling.
- Flash steam or entrained vapour is present.
- The receiver operates under vacuum.
- Condensate inflow varies significantly.
- Long periods of very low flow are expected.
- Process contamination or suspended solids are present.
- The pump cannot be installed with adequate flooded suction.
A side-channel, vertical, self-regulating or mechanical condensate pump may provide a more reliable solution.
Frequently Asked Questions
What is a condensate extraction pump?
A condensate extraction pump removes condensed steam from a condenser hotwell, receiver or collection vessel and transfers it into the condensate recovery or feedwater system.
What is the best pump for hot condensate?
The best pump depends on temperature, flow, pressure, NPSH and vapour content. Low-NPSH centrifugal, side-channel, vertical multistage and self-regulating pumps are commonly used for demanding hot-condensate duties.
Why do condensate pumps cavitate?
Hot condensate is often close to its boiling point. If pressure falls below the liquid’s vapour pressure at the pump inlet, vapour bubbles form and then collapse as pressure rises inside the pump.
How is a condensate extraction pump sized?
Sizing requires the peak condensate return rate, total discharge head, liquid temperature, receiver pressure, NPSHa, vapour content and required control method.
Can a centrifugal pump handle hot condensate?
Yes, provided the pump has suitable materials, adequate NPSH margin and hydraulics matched to the temperature and duty. A specialist low-NPSH or gas-handling design may be required where the condensate is close to boiling.
What is the difference between a condensate pump and a boiler feed pump?
A condensate pump transfers recovered condensate to a feed tank, deaerator or feedwater system. A boiler feed pump then raises the combined feedwater pressure above boiler pressure.
Is process condensate the same as oil and gas condensate?
No. Process or steam condensate is water formed when steam condenses. Oil and gas condensate is a light hydrocarbon liquid recovered from natural-gas production or processing. The two require different pump-selection criteria.
