Understanding LOW Boiler Cycles of Concentration: Causes, Impacts, and Solutions

Boiler cycles of concentration (CoC) are a crucial factor in the efficiency of steam boiler systems. When the cycles of concentration are too low, it can lead to excessive fuel and water usage, as well as increased chemical costs and wastewater generation. Understanding the causes, impacts, and solutions to low boiler cycles of concentration is key to optimizing boiler performance and reducing total costs of operation (TCO).

What Are Boiler Cycles of Concentration?

Cycles of concentration refer to the ratio of dissolved solids in the boiler water compared to the feedwater (commonly referred to as “Feedwater Cycles of Concentration”). It is a measure of how much the water has been concentrated through the process of evaporation to make steam. A higher CoC indicates that water usage is being reduced, whereas a lower CoC means that more fresh feedwater is being introduced due to increased blowdown. There are limits, however, to how high CoC can go before problems may begin to occur (e.g., carryover, low steam quality/purity, deposits, corrosion).

What is Boiler Blowdown?

Cycles of concentration are controlled by sending a controlled quantity of concentrated boiler water down the drain, which is replaced with less-concentrated feedwater. This process is called blowdown and can be either an automatic or manual process. Boilers commonly have surface and bottom blowdowns. The surface blowdown removes the concentrated boiler water and is used to control CoC, while the bottom blowdown is typically used to remove sludge and sediment or to drain the boiler.

Causes of Low Boiler Cycles of Concentration

Several factors can contribute to low boiler CoC, including:

1. Excessive Blowdown: If a boiler is blowing down too much, the CoC will be lower.
2. Condensate Contamination: Poor-quality condensate returning to the boiler system (e.g., high iron, process contamination) may require higher blowdown rates to mitigate negative impacts.
3. Pretreatment Failures: Water softeners passing hard water, reverse osmosis units producing low-quality permeate, and other failures may require the boiler to run at lower CoC to prevent scale deposits and corrosion.
4. Carryover: Liquid water, dissolved solids, and/or chemical treatment carried out of the boiler with the steam is called carryover and can have both mechanical and chemical causes. Chemical causes include high solids concentration (dissolved or suspended), excessive alkalinity, grease, oil, or other contaminants, which may require running at lower CoC to prevent them from causing carryover and negatively impacting downstream systems.
5. Improper Control Settings: Automation and control systems that are not properly configured and calibrated may trigger unnecessary blowdowns, lowering the cycle efficiency.
6. Over Sampling: Sampling too frequently and/or too long can also result in low CoC, especially in smaller boiler systems.
7. Improper Control Ranges: The American Society of Mechanical Engineers (ASME) and the American Boiler Manufacturers Association (ABMA) both publish guidelines for boiler water chemistries. These guidelines are good starting points, but system setup and experience may indicate it is safe to deviate from them while taking into account manufacturer recommendations.
8. Low Condensate Return: Condensate should be high-purity water, and returning it to the boiler system may allow running at higher CoC. A sudden drop in the amount of condensate returned may have a negative impact upon the CoC.
9. Makeup Water Quality: The current pretreatment system setup may limit the CoC that can be achieved without risking scale, corrosion, and carryover issues (e.g., softeners remove only hardness while reverse osmosis may remove 99+% of all dissolved solids).

Impacts of Low Boiler Cycles of Concentration

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

• Increased Water Consumption: More blowdown means greater water loss, leading to higher consumption of makeup water.
• Increased Energy Consumption: Greater makeup demand requires fuel to heat this extra water up to boiler temperature.
• Higher Chemical Costs: Increased blowdown means more scale and corrosion treatment chemicals in the boiler water going down the drain.
• Added Pretreatment Costs: Running more water through the pretreatment equipment (e.g, softeners, reverse osmosis) may require additional salt, energy, treatment chemicals, and maintenance.
• Increased Wastewater Generation: Increased blowdown means more wastewater going to the drain.
• Environmental Impact: Increased water, energy, and chemical usage all contribute to a higher environmental footprint required to operate the boiler system.

Solutions to Optimize Boiler Cycles of Concentration

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

1. Optimize Blowdown Control – Implement automated blowdown controls that monitor conductivity and adjust blowdown rates accordingly to control CoC and minimize inefficiencies. When automation isn’t an option, develop an effective monitoring and manual control plan that best fits the dynamic nature of the boiler system.
2. Pretreatment Equipment– Reduce problem-causing impurities by using pretreatment equipment that can increase CoC. Water softeners remove hardness to help prevent dangerous, energy-robbing scale formation in boilers. Reverse osmosis and deionization systems produce high-quality water with low total dissolved solids, possibly allowing boilers to run at much higher CoC.
3. Water Treatment Chemistry – Use optimal chemical products to control scale and corrosion while increasing CoC.
4. Reduce Condensate Contamination –Minimize condensate contamination by eliminating the source, dumping the condensate, or using a condensate polisher to remove the contaminants before they reach the boilers.
5. Increase Condensate Return – Increasing the return of high-purity, heated condensate to the boiler system can improve CoC and energy efficiency. This may require repairing pumps, piping, condensate return systems, etc.

Tracking & Monitoring

Regularly test and monitor makeup, pretreatment, condensate, feedwater, and boiler water qualities to ensure they meet required specifications and any problems can be addressed quickly. Log the data into log sheets. Graph the data to help identify long-term trends and issues.

Conclusion

Maintaining optimal cycles of concentration is critical for efficient boiler operation. By addressing the causes of low CoC and implementing best practices for water treatment, blowdown control, and system maintenance, facilities can significantly influence operational costs and environmental impacts. Chem-Aqua has the experience and expertise to help you manage your boiler water needs. Contact us today.