Condensate management

Wherever steam is used for indirect heating in heat exchangers condensate also forms and should whenever possible be returned to the steam boiler circuit or used for some other purpose.

Reusing accumulated condensate is one of the key measures which can be taken to ensure cost-effective energy-efficient operation of a boiler system.

Condensate has two characteristics that make it particularly valuable:

  • High temperatures
    The condensate downstream of the heat exchanger is normally only slightly undercooled, i.e. it is at a high temperature. By recirculating the condensate, this energy content remains in the system and does not have to be expended again.
  • Treated water
    Condensate is already treated hardness-free water with a low conductivity. Returning condensate to the steam circuit therefore saves make-up water. This means that less softening or demineralisation of water is required which reduces the amount of energy and chemicals used and these treatment systems can be sized smaller from the outset.

The condensate can be reused in different ways:

  • As preheated boiler feed water
    by returning it to the feed water vessel via condensate pipes and tanks or by feeding it directly into the boiler.
  • As hot water
    for heating of processes at a low temperature level, e.g. for cleaning.
  • As steam
    by using the expansion steam in a secondary low-pressure steam network for consumers requiring lower temperatures.

Before the condensate can be reused, it must first of all be checked for contamination and collected in a tank. This can be done either in an open or closed condensate collection system.

Info on Water quality monitoring

The differences between the two systems are highlighted in the following table:


Open system
Low-pressure condensate

Closed system
High-pressure condensate

Container type

Low-pressure container (0.5 – 1 bar)
connected to atmosphere via an air vent line

High-pressure container
Pressure in container maintained by heat-up steam or overflow regulator

Oxygen in condensate

Oxygenic condensate
(in contact with atmospheric oxygen, renewed deaeration required)

Oxygen-free condensate

Condensate temperature
when returned

≤ 100 °C

> 100 °C


Via feed water vessel

High-temperature feed pumps

Condensate transportation

Condensate pumps

Not required

Steam clouds

Possible (especially with high condensate temperature of consumers)


System integration


More complex

Investment costs



Energy saving



Pipework material

Stainless steel


Use of condensate

Boiler feed water
(recirculation to feed water vessel for deaeration)

Boiler feed water
(direct recirculation in the boiler)

Hot water

Use of expansion steam

Mainly unused

In exhaust vapour heat exchanger for preheating of make-up or process water

In the low-pressure steam network

For heating of feed water vessel

Comparison of different condensate collection systems

Schematic diagram of condensate tank – low pressure

Schematic diagram of condensate tank – low pressure


Level regulator


Temperature indicator


Pressure indicator

Air vent line

Condensate pipe leading directly to feed water module

Condensate pipe, unpressurised

Drain line and overflow

Pump bypass pipe

Line to boiler

Condensate pump module

Schematic diagram of condensate tank – high-pressure

Schematic diagram of condensate tank – high-pressure














High-pressure condensate feed line

Overflow steam discharge line

Make-up water feed line

Heat-up steam pipe

Start-up line

Air vent line

Pressure safeguard blow-off line

Chemical dosing

Pump bypass pipe

Line to boiler

High-pressure condensate pump module

Drain line