When steam releases its heat in the process, it turns into condensate. This hot water carries, in most cases, a significant portion of the treated feedwater and the energy spent on production. Sending appropriate quality condensate to the channel or releasing the flash steam formed when high pressure condensate passes to low pressure into the atmosphere; It can increase the cost of fuel, water, chemicals and wastewater together.
The purpose of the recovery project is not to return every condensate to the boiler indifferently. First, flow rate, pressure, temperature and contamination risk are measured; Then the safe usage point is determined.
Why is condensate valuable?
Condensate has economic value for three reasons:
- Hotter than make-up water; Reduces the energy required to heat feed water.
- Because it comes from the evaporation-condensation cycle, its dissolved mineral load is lower than most raw water.
- When recycled, it can reduce the need for water preparation, chemical dosing and discharge.
However, if there is a possibility of contamination with product, oil or process chemical, conductivity, pH, oil or application-specific parameters should be monitored; Dirty condensate should be automatically prevented from mixing into the clean system.
How does flash steam occur?
When the hot condensate at high pressure passes to a lower pressure environment, some of the energy that it cannot carry as a liquid at the new pressure evaporates the condensate again. This is called flash steam. The same phenomenon occurs when the high-temperature boiler blowdown pressure is reduced.
The continuous release of steam from the vent of the atmospheric condensate tank is not always a live steam leak; A significant portion may be flash vapor. However, it should be verified by measurement that defective steam traps do not pass live steam.
Difference between open and closed condensate system
In the atmospheric system, condensate returns to an open tank. It is relatively simple to design and operate; However, flash steam may occur due to pressure drop. If the energy in the tank air is not utilized, loss occurs.
In the closed pressurized condensate system, the return line is kept under pressure and the energy of the condensate can be preserved at a higher temperature. This system cannot be directly applied to every facility. Back pressure of traps, process drainage, pump selection, pipe pressure class and safety equipment must be recalculated.
Recovery methods
Returning condensate to the feedwater system
Clean condensate is sent to the deaerator or feed water tank with an appropriate collection and pumping system. The hot return may also affect the steam demand of the deaerator.
Using a flash tank
High pressure condensate is taken into the flash tank in a controlled manner. The separated low-pressure steam can be used in a suitable process, deaerator or hot water application; The remaining hot condensate is sent to the return system.
Blowdown heat recovery
The energy released from continuous surface blowdown can be evaluated as flash steam and hot water. A cooler fluid, such as make-up water, can be preheated with a heat exchanger. Blowdown should not be directly mixed with the use side due to its chemical content.
Heat recovery from vent steam
Steam in the vent of the atmospheric tank can heat process or service water in a heat exchanger. In the design, back pressure should not be created and tank security should not be compromised.
How to make a savings account?
The economic value of condensate recovery is not just the temperature difference. The following items must be calculated together:
- Recovered condensate flow rate,
- Condensate and makeup water temperature difference,
- Boiler efficiency and fuel cost,
- Water and wastewater fee,
- Water preparation and chemical cost,
- Hours when flash steam can be used,
- Pump electricity and system maintenance cost,
- Investment and commissioning expense.
The approximate heat value can be calculated by the difference of condensate flow rate × specific heat × temperature. In flash steam calculation, saturated water enthalpies at high and low pressure are used. Fixed percentage values on the Internet should not be used instead of field measurements.
Most common mistakes
Returning dirty condensate to the system
A single contamination event can disrupt boiler water chemistry. Critical processes require continuous quality measurement and automatic guidance.
Making a project without checking the traps
A steam trap leaking live steam shows the condensate return flow rate and tank ventilation load differently. The condition of the traps should be examined with ultrasonic and temperature measurements.
Not taking into account back pressure
If the pressure in the condensate line increases, the process equipment may not drain. Water hammer and heat transfer loss may occur.
Producing flash steam without point of use
If there is no suitable point to consume the recovered low-pressure steam at the same time, savings will be limited. Production and consumption profiles should be matched.
Field work to start with measurement
- Condensate sources and contamination risks are mapped.
- Flow, pressure and temperature are measured during operation.
- Steam trap performance is checked.
- Current tank, pump and pipe capacities are examined.
- Low pressure consumers where flash steam can be used are determined.
- Energy, water and chemical savings are calculated.
- Security, control and failure scenarios are projected.
Condensate, deaerator and heat recovery components can be evaluated together with the entire boiler room within the scope of Hisarmak’s auxiliary equipment.
Frequently asked questions
Can condensate be fed directly to the boiler?
Flow rate, pressure, temperature and water quality should not be given before they are adjusted. The system is mostly designed with tank, deaerator, pumps and control equipment.
Is the steam coming out of the condensate tank normal?
Some flash steam can be expected; Intense and continuous output may also indicate traps leaking high return pressure or live steam.
Is a closed condensate system always better?
Can save energy better; However, if the process drainage, back pressure and equipment pressure classes are not appropriate, it may cause operating problems.
Is blowdown water sent back to the boiler?
It cannot be returned directly because it contains dense dissolved substances. Its energy can be recovered with a suitable flash/heat exchanger system.
Technical resources
- T.R. Ministry of Energy and Natural Resources, Optimization in Industrial Systems — Steam Condensate Recovery.
- T.R. Ministry of Agriculture and Forestry, Water Efficiency Guide Document.