Boiler Cycles of Concentration

Boiler cycles of concentration (CoC) play a critical role in steam boiler efficiency. Low CoC can result in excessive fuel and water consumption, higher chemical costs, and increased wastewater. Identifying the causes, impacts, and solutions for low CoC is essential to optimize boiler performance and reduce total cost of operation (TCO).

What Are Boiler Cycles of Concentration?

Cycles of concentration measure the ratio of dissolved solids in boiler water to those in feedwater, indicating how much water has been concentrated through evaporation. Higher CoC reduces water usage, while lower CoC requires more fresh feedwater due to increased blowdown. However, excessively high CoC can cause issues such as carryover, reduced steam quality, deposits, and corrosion.

What is Boiler Blowdown?

Cycles of concentration are managed by discharging a controlled amount of concentrated boiler water, which is replaced with less-concentrated feedwater. This process, called blowdown, can be automatic or manual. Surface blowdown controls CoC by removing concentrated water, while bottom blowdown removes sludge, sediment, or drains the boiler.

Causes of Low Boiler Cycles of Concentration

Several factors can lead to low boiler CoC, including:

1. Excessive Blowdown: Excessive blowdown lowers CoC.

2. Condensate Contamination: Poor-quality condensate (such as high iron or process contamination) may require increased blowdown to prevent negative effects.

3. Pretreatment Failures: Failures in water softeners or reverse osmosis units may require lower CoC to prevent scale and corrosion.

4. Carryover: Carryover occurs when liquid water, dissolved solids, or chemicals leave the boiler with steam. Mechanical or chemical causes, such as high solids, excessive alkalinity, grease, or oil, may require lower CoC to prevent downstream issues.

5. Improper Control Settings: Poorly configured automation or control systems can cause unnecessary blowdown, reducing cycle efficiency.

6. Over Sampling: Excessive sampling can lower CoC, particularly in smaller boiler systems.

7. Improper Control Ranges: ASME and ABMA provide boiler water chemistry guidelines. While these are useful starting points, system setup and experience may justify deviations, provided manufacturer recommendations are considered.

8. Low Condensate Return: Returning high-purity condensate supports higher CoC. A sudden decrease in returned condensate can negatively affect CoC.

9. Makeup Water Quality: The pretreatment system may limit achievable CoC without risking scale, corrosion, or carryover. Softeners remove only hardness, while reverse osmosis removes most dissolved solids.

   
   

Impacts of Low Boiler Cycles of Concentration

Operating a boiler with low CoC can result in several negative consequences, including:

• Increased Water Consumption: More blowdown increases water loss and makeup water demand.

• Increased Energy Consumption: Higher makeup water demand requires additional fuel to heat the water.

• Higher Chemical Costs: Increased blowdown results in more treatment chemicals being lost.

• Added Pretreatment Costs: Increased water flow through pretreatment equipment raises salt, energy, chemical, and maintenance requirements.

• Increased Wastewater Generation: More blowdown produces more wastewater.

• Environmental Impact: Increased use of water, energy, and chemicals raises the environmental footprint of boiler operation.

  
  

Solutions to Optimize Boiler Cycles of Concentration

To maintain optimal CoC and improve boiler efficiency, consider these strategies:

1. Optimize Blowdown Control: Use automated controls to monitor conductivity and adjust blowdown rates to maintain CoC and minimize inefficiencies. If automation is not feasible, establish an effective monitoring and manual control plan suited to the system’s needs.

2. Pretreatment Equipment: Use pretreatment systems to reduce impurities and increase CoC. Water softeners remove hardness to prevent scale, while reverse osmosis and deionization systems provide high-quality water, enabling higher CoC.

3. Water Treatment Chemistry: Apply appropriate chemicals to control scale and corrosion while increasing CoC.

4. Reduce Condensate Contamination: Minimize contamination by eliminating sources, discarding affected condensate, or using a condensate polisher before it reaches the boilers.

5. Increase Condensate Return: Returning more high-purity, heated condensate improves CoC and energy efficiency. This may involve repairing pumps, piping, or condensate return systems.

Tracking & Monitoring

Regularly test and monitor makeup, pretreatment, condensate, feedwater, and boiler water to ensure they meet specifications and address issues promptly. Record and graph data to identify trends and problems.

Conclusion

Maintaining optimal cycles of concentration is essential for efficient boiler operation. Addressing low CoC and applying best practices in water treatment, blowdown control, and maintenance can significantly reduce operational costs and environmental impact.

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