Automatic Boiler Surface Blowdown System for TDS Control

The efficient and safe operation of a steam boiler depends directly on the quality of its water. As steam is generated, the dissolved solids that enter with the feedwater stay behind in the boiler and their concentration keeps rising. An automatic boiler surface blowdown system continuously measures this concentration and discharges a controlled amount of boiler water, keeping total dissolved solids (TDS) within safe limits.

This article explains why TDS control matters, how an automatic surface blowdown system works and the benefits it brings.

Why Water Quality Matters in Steam Boilers

Dissolved salts in the feedwater do not leave the boiler with the steam; the steam leaves pure and these substances accumulate in the boiler water. When TDS rises too high:

• Foam forms on the water surface and water and dissolved solids are carried over into the steam lines (carryover).
• Carried-over water and salts foul heat exchangers, valves and steam traps, and steam quality falls.
• The risk of deposits and corrosion on heating surfaces increases, heat transfer deteriorates and equipment life is shortened.

On the other hand, blowing down more than necessary throws away treated, heated water. The aim is to blow down just enough to keep TDS close to, but below, the limit recommended by the boiler manufacturer.

Surface Blowdown vs Bottom Blowdown

How Does an Automatic Surface Blowdown System Work?

1. TDS measurement: Because the electrical conductivity of boiler water is proportional to TDS, it is measured continuously by a conductivity probe installed in the boiler.
2. Signal processing: The probe signal is processed by a transmitter and sent to a digital controller.
3. Control and discharge: The controller compares the measured value with the set limit. When the limit is exceeded, it opens the blowdown valve to discharge some of the surface water; when the value falls, it closes the valve.
4. Heat recovery (optional): Blowdown water leaves at the boiler’s saturation temperature. By adding a plate heat exchanger and a circulation pump, part of this heat can be used, for example, to preheat boiler feedwater or make-up water.

Benefits

• Optimum TDS level: Boiler water is kept within the target range at all times, reducing the risk of foaming, carryover and deposits and extending equipment life.
• Energy and water savings: Blowdown takes place only when needed, reducing hot water and energy losses.
• Chemical savings: Avoiding unnecessary blowdown also reduces the amount of treatment chemicals discharged with the water.
• Lower operating costs: Energy and chemical costs for preparing and heating water fall.
• Less operator intervention: Compared with manual blowdown, control is continuous, consistent and can be logged.

Safety and Installation

The blowdown line carries water at boiler pressure and saturation temperature. The system is designed only for its intended use, and the manufacturer’s safety instructions must be strictly followed during installation and operation. Blowdown water must be cooled to a safe temperature, for example in a blowdown vessel or cooling arrangement, before it is discharged to drain.

Frequently Asked Questions

Conclusion

An automatic boiler surface blowdown system keeps boiler water quality under constant control, improving efficiency, reducing energy and water losses and extending equipment life. The ORFA Endüstriyel Mamüller San. ve Tic. A.Ş. team can help you choose the right blowdown solution for your plant. For surface and bottom blowdown products, explore our Boiler Surface and Bottom Blowdown Systems product group.