Steam Boiler Blowdown Procedure, Bottom Blowdown and Surface Blowdown

How to Do Bottom Blowdown and Surface Blowdown Safely, and How to Set Frequency Based on Water Quality

Blowdown is the controlled removal of boiler water to reduce dissolved solids and impurities that build up during steam production. Bottom blowdown removes sludge and settled solids from the lowest point of the boiler. Surface blowdown removes high TDS water from the water surface to control conductivity and prevent foaming and carryover. The safest and most effective blowdown routine is based on measured boiler water conductivity or TDS, stable feedwater quality, and a clear operating procedure that protects people from high temperature discharge.

In field work, Samson Indonesia Boiler often finds that unstable steam pressure, wet steam, and unexpected fuel costs are frequently linked to poor water quality control and inconsistent blowdown, not only to the boiler itself.

1. What is blowdown in a steam boiler

Blowdown is the intentional discharge of a portion of boiler water to remove dissolved solids, suspended solids, and sludge. As a boiler makes steam, pure water leaves as vapor, but most impurities remain in the boiler water. Over time, the concentration rises. Blowdown is how you keep that concentration within safe limits.

Without proper blowdown, the boiler can suffer from

• Foaming and priming

• Carryover that produces wet steam

• Deposits and scaling

• Corrosion and shortened equipment life

• Unstable level control and nuisance trips

2. Why blowdown is necessary

A boiler is like a concentrator. Every hour it evaporates water into steam, the remaining water becomes more concentrated. If you never remove any water, the total dissolved solids keep rising.

High dissolved solids can cause

• Foaming at the water surface

• Water droplets carried into steam lines

• Wet steam that reduces heating performance and damages steam traps and valves

• Increased blowdown later, meaning wasted heat and water

Blowdown is not only about cleanliness. It is about protecting steam quality and reducing long term operating cost.

3. The two main types of blowdown

Bottom blowdown

Bottom blowdown removes sludge and settled solids from the lowest point of the boiler. It is typically done in short bursts. This is a mechanical cleaning action to purge mud, rust particles, and heavier solids.

Surface blowdown

Surface blowdown removes water from near the water surface, where dissolved solids are most concentrated. It is used to control boiler water conductivity and reduce foaming risk. In many modern systems, surface blowdown can be continuous or automatically controlled.

4. Key water quality terms that decide your blowdown

To set blowdown correctly, you need to understand what you are controlling.

• TDS total dissolved solids. A measure of dissolved salts and impurities.

• Conductivity. Often used as a fast operational proxy for TDS.

• pH and alkalinity. Affect corrosion risk and chemical control.

• Hardness as CaCO3. A major driver of scale if water treatment fails.

• Silica. Important for certain pressures and steam purity requirements.

• Dissolved oxygen. A corrosion driver, managed by deaeration and chemicals.

In practice, conductivity or TDS is the primary daily control point for blowdown volume, while the other parameters help diagnose root causes when problems appear.

5. How often should you do blowdown

There is no universal schedule that fits every factory, because it depends on

• Feedwater quality and stability

• Water treatment performance

• Steam load profile and hours of operation

• Boiler pressure and internal design

• Whether condensate return is used and how clean it is

A strong best practice is

• Control surface blowdown based on conductivity or TDS targets

• Do bottom blowdown as short bursts on a routine schedule that fits your operating conditions

If you are designing or upgrading a blowdown setup, Samson Indonesia Boiler can help by aligning the blowdown arrangement, sampling points, and practical operator routines with your site water quality and steam demand profile, so the procedure remains simple and repeatable.

6. Bottom blowdown procedure step by step

Bottom blowdown is high risk if done carelessly because the discharge is hot and can flash into steam. Always follow your boiler manufacturer guidance and site safety rules.

Before you start

1. Confirm the blowdown line is correctly routed to a safe blowdown tank or flash tank.

2. Confirm the discharge destination is rated for temperature and pressure.

3. Wear appropriate PPE, including face shield, heat resistant gloves, and protective clothing.

4. Verify the boiler is operating within normal level range.

5. Verify the blowdown valves move freely and the area is clear of personnel.

Standard two valve bottom blowdown sequence

Many boilers use two valves in series, a quick opening valve and a slow opening valve. The typical safe approach is short, controlled bursts.

1. Open the slow opening valve fully.

2. Quickly open the quick opening valve for a short burst, typically a few seconds, then close it.

3. Repeat short bursts rather than one long opening.

4. Close the quick opening valve fully.

5. Close the slow opening valve fully.

6. Recheck boiler level, feedwater response, and any alarms.

Why short bursts matter

Short bursts create turbulence at the mud drum or bottom zone and remove solids effectively. Long blowdown wastes more energy and can destabilize water level control.

7. Surface blowdown procedure step by step

Surface blowdown is mainly for controlling dissolved solids.

Manual surface blowdown

1. Measure boiler water conductivity or TDS before blowdown.

2. Open the surface blowdown valve gradually and maintain a steady controlled flow.

3. Continue until conductivity drops toward your target range, then close the valve.

4. Record the reading before and after in your log sheet.

Automatic surface blowdown

Many plants use an automatic control valve linked to a conductivity sensor.

Best practice for automatic systems

• Ensure proper sampling and sensor maintenance

• Validate sensor readings with periodic manual tests

• Keep a stable feedwater treatment program so the control loop is not chasing unstable chemistry

8. Safety checklist for blowdown

Blowdown is a routine task, but it must be treated as a controlled hot discharge operation.

Safety essentials

1. Use a proper blowdown tank or flash tank, not an open drain.

2. Keep discharge piping protected and supported to prevent whip and leaks.

3. Prevent people from standing near discharge points.

4. Use clear signage and a defined safe zone.

5. Never blow down if you suspect a blocked line or abnormal valve behavior.

6. Watch boiler level closely, especially right after a bottom blowdown burst.

7. Keep procedures written and consistent across shifts.

For sites building a full steam system operation package, Samson Indonesia Boiler can provide practical operator checklists and commissioning level guidance to ensure blowdown hardware, safety routing, and daily routines work together, not as disconnected pieces.

9. Common blowdown mistakes that increase cost and risk

1. Using a fixed schedule without measuring conductivity. This often leads to either excessive blowdown that wastes heat or insufficient blowdown that causes wet steam.

2. Doing one long bottom blowdown. This wastes energy and can destabilize boiler level.

3. Blowing down into an unsafe drain. This creates major burn risk and can damage piping and flooring.

4. Ignoring condensate return quality. Dirty condensate can drive conductivity up and make blowdown control unstable.

5. Not logging readings and actions. Without records, troubleshooting becomes guesswork.

10. A simple blowdown log sheet structure

A log sheet helps operators stay consistent and helps engineers diagnose issues.

Recommended fields

• Date and time

• Boiler pressure and steam load status

• Boiler water conductivity or TDS before and after

• Bottom blowdown performed yes or no and number of bursts

• Surface blowdown duration or automatic valve status

• Feedwater conductivity

• Notes on foaming, carryover signs, wet steam, abnormal level behavior

11. Short FAQ

Does blowdown reduce fuel efficiency

Blowdown removes hot water, so excessive blowdown wastes energy. However, correct blowdown improves steam quality and prevents deposits that can reduce heat transfer and cause bigger efficiency losses. The goal is optimized blowdown, not maximum blowdown.

How do I know my blowdown is not enough

Common signs include rising boiler water conductivity, foaming, wet steam symptoms, unstable level control, and frequent issues in steam traps and control valves.

What is the best way to set blowdown frequency

Use boiler water conductivity or TDS as your control variable, then adjust surface blowdown to maintain a target range, while scheduling bottom blowdown short bursts to remove sludge.

Summary

A reliable steam system depends on clean boiler water and stable steam quality. Blowdown is the practical control tool that prevents dissolved solids from building up, protects steam dryness, and helps avoid foaming and carryover. The most effective approach is to combine surface blowdown control based on conductivity or TDS with routine short burst bottom blowdown, supported by safe discharge design and consistent operator routines.

If you want help building a blowdown routine that matches your site water source, condensate return quality, and steam load profile, Samson Indonesia Boiler can support system review and practical implementation guidance so your boiler operates safely, efficiently, and consistently.