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:
The condensate can be reused in different ways:
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
Recirculation
Via feed water vessel
High-temperature feed pumps
Condensate transportation
Condensate pumps
Not required
Steam clouds
Possible (especially with high condensate temperature of consumers)
None
System integration
Straightforward
More complex
Investment costs
Low
Higher
Energy saving
Lower
High
Pipework material
Stainless steel
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
LIC
Level regulator
TI
Temperature indicator
PI
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
LI
Level indicator
PIC
Pressure regulator
M
Motor
High-pressure condensate feed line
Overflow steam discharge line
Make-up water feed line
Heat-up steam pipe
Start-up line
Pressure safeguard blow-off line
Chemical dosing
High-pressure condensate pump module
Drain line