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What is Condensate? What is the Purpose of a Steam Trap? Condensate Calculation
- Mar 14
- 6 min read
What Is a Steam Trap?
A steam trap is a device that automatically separates steam from condensate and removes condensate, air, and non-condensable gases from the system. While continuing to retain live steam under varying load and pressure conditions, it discharges condensate together with air and other non-condensable gases. The main purpose of a steam trap is to prevent energy loss and increase system efficiency.
What Does a Steam Trap Do?
Steam traps are important components used especially in boilers and steam lines. Their basic function is to discharge condensate and gases such as air from the system without negatively affecting operating efficiency.
Steam produced in boilers is used for heating and energy transfer. After the steam energy is used, it condenses and forms condensate. In addition, steam is exposed to radiation and heat losses through components such as pipes and fittings. Because of these losses, part of the steam turns back into condensate. If condensate is not removed from the system, overall efficiency decreases.
Condensate and air collect in the lower part of the pipes, while steam flows above them. If the amount of condensate increases rapidly, water masses moving with the steam can cause sudden impacts and damage in the system. For this reason, condensate and air must be removed, and the system must be kept continuously clean.
Importance of Air and Non-Condensable Gases
Air entering the system during initial startup
A mixture of air and steam being at a lower temperature than steam itself, which slows heat transfer
Air acting like an insulation layer and reducing heat transfer
Air and other non-condensable gases causing corrosion and shortening system life
Types of Steam Traps
There are various types of steam traps suitable for different applications. Their main characteristic is the ability to separate steam from condensate and air or other gases. When classified by operating principle, each type has its own advantages and disadvantages.
1) Steam Traps Operating by Density Principle
Density-type or mechanical steam traps are based on the density difference between steam and condensate. Since steam has a lower density, it is always lighter. Steam traps working on this principle can discharge large amounts of condensate while retaining steam.
Most common types:
Float steam trap: The float responds to the condensate level and allows condensate to be discharged.
Inverted bucket steam trap: A mechanism with a moving bucket that controls the movement of condensate and gases.
2) Steam Traps Operating by Detecting Temperature Difference
These steam traps operate by sensing the temperature difference between steam and condensate. Their main principles include:
Balanced pressure thermostatic traps
Bimetallic thermostatic traps
By separating condensate and air based on temperature difference, they discharge unnecessary air and condensate from the system.
3) Steam Traps Operating by Thermodynamic Principle
These are based on thermodynamic principles. They separate steam and condensate by controlling liquid and gas flow. They are generally known for high efficiency and reliability.
Steam Trap Selection Table and Calculation Methods
Selecting the correct steam trap is critical for system efficiency and safety. Below are the basic data and calculation steps that should be considered when selecting a steam trap.
Key Information to Consider When Selecting a Steam Trap
1) Steam Trap Type
The type of steam trap is determined according to the characteristics of the system and equipment. A steam trap suitable for the intended use of the system directly affects performance and durability. The correct type should be selected according to the appropriate selection table.
2) Condensate Load (kg/h)
The amount of condensate formed in the system per hour must be determined. This amount is calculated by considering heat loss and the point of use. After applying a safety factor to the calculated condensate load, the required steam trap capacity is determined.
Safety factor:
For temperature-controlled systems such as main steam lines, heat exchangers, and air heating systems: 3
For other systems: 2
Example:For a system producing 250 kg/h of condensate, required capacity is:250 kg/h × 3 = 750 kg/h
3) Differential Pressure (ΔP)
The pressure difference between the inlet and outlet of the steam trap affects selection.
P1: Inlet pressure (barg or bar)
P2: Outlet pressure (back pressure or system pressure, including elevation and friction losses)
Example:If P1 = 4 barg and P2 = 1 barg, then:ΔP = P1 - P2 = 3 barg
If the condensate is connected to a return line, this back pressure must also be included.
Calculating the Condensate Load
Correctly calculating condensate load is important in determining steam trap capacity. In this calculation, heat loss and pipe characteristics must be considered.
Required parameters:
W: Total weight of pipes and fittings (kg)
L: Pipe length (m)
T1: Steam temperature (°C)
T2: Ambient temperature (°C)
c: Specific heat of steel pipe (0.48 kJ/kg°C)
e: Latent heat of evaporation (kJ/kg)
t: Heating time (min)
Formula for heat loss:
Q = W × c × (T1 − T2)
Condensate formation can also be estimated according to heat loss.
Example Calculation
At 8 bar pressure, with 120 meters of 100 mm diameter pipe, a total weight of 2200 kg, and a 20-minute heating period, the heat loss is calculated and the condensate load is determined.
Total heat loss:Q = 2200 kg × 0.48 kJ/kg°C × (T1 − T2)
From this, hourly condensate load is calculated as:Condensate load = Q / (20 minutes / 60)
In more advanced calculations, a safety factor is applied to this value.
Example:If the calculated condensate load is 249.3 kg/h and the safety factor is 3, then the required capacity is:
249.3 kg/h × 3 ≈ 750 kg/h
The number and size of steam traps suitable for the pipeline are determined according to this capacity. For example, if one steam trap is installed every 40 meters on a 120-meter steam line, a total of three steam traps will be required.
For main steam lines, the safety factor is taken as 3. In this example:
249.3 × 3 = 747.9 kg/h
If a steam trap is installed every 40 meters along the 120-meter line, three steam traps are required.
According to the selection table for the main steam line, the appropriate trap type is thermodynamic, and the size selected from the capacity chart is DN15 (1/2").
Points to Consider in Steam Trap Selection
Capacity should be determined according to the maximum condensate load formed in the system
The safety factor is important for operating conditions and system safety
Differential pressure and back pressure must be considered during selection
The appropriate steam trap type must be selected according to the application
Steam Leak Control and Air Lock Problems in Steam Traps
Steam Trap Failures and Steam Leakage
If a steam trap fails, or if foreign particles enter between the seat and the valve, the steam trap may remain open. In this case, live steam starts to escape from the system, causing energy loss. These leaks increase operating costs and reduce system efficiency.
Effects of steam leakage:
Increase in energy costs
Increase in fuel consumption
Decrease in system performance
Below are the estimated steam loss values and steam consumption amounts according to the orifice diameter of steam traps.
Steam Trap Orifice Size | Orifice Diameter (mm) |
DN15 | 3 mm |
DN20 | 5 mm |
DN25 | 6.4 mm |
DN40 | 10 mm |
DN50 | 12.5 mm |
Air Locking and Its Effect on System Performance
Air locking is the condition in which condensate cannot be discharged continuously from steam traps. This negatively affects heat transfer, because accumulated condensate blocks efficient heat transfer and reduces overall system performance.
After the system is shut down, air and non-condensable gases build up inside. When the system starts operating again, these gases move together with the steam and accumulate in the steam trap, causing air locking.
Air Venting and Air Locking
If air and gases are not discharged through the air vents of the steam traps, the system can become locked.
In coils, air accumulation can seriously reduce heat transfer.
Air must be discharged effectively by the steam traps; otherwise, air locking will occur and reduce system efficiency.
Inverted bucket steam traps discharge air more slowly, and insufficient air venting can lead to problems. For this reason, it is important that air vents have the right characteristics and, when necessary, that special solutions are developed.
Thermostatic Steam Traps and Air Venting
All thermostatic steam traps fully discharge air during initial startup and also during normal operation.
Float steam traps are equipped with a thermostatic air venting system, allowing them to discharge air effectively and reliably.
Steam Locking and Solution Methods
Steam Locking Problems
One common example of steam locking, especially in industries such as textile and paper, is the following:
In cylinder heating processes, steam enters the steam trap and becomes trapped there.
This prevents proper flow of condensate and steam inside the cylinder.
As a result, thermal efficiency drops significantly and system performance decreases.
How to Prevent and Solve Steam Locking
To prevent and resolve steam locking:
SLR (Steam Lock Release) float steam traps are used. These devices allow incoming steam and condensate to be discharged freely.
After the steam entering the cylinder gives off its heat, the condensate reaches the steam trap through a siphon and is discharged.
However, the returning steam and condensate must also be removed properly from the system to prevent steam locking.
Typical Applications Where Steam Lock Solutions Are Used
Textile jet dyeing systems
Textile drying cylinders
Process tanks
Cooking kettles
Cylinder ironers (calenders)
Multi-cylinder finishing machines
Paper machines
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